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Environmental factors controlling floral zonation and the distribution of burrowing and tube-dwelling… Swinbanks, David Donald 1979

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ENVIRONMENTAL THE  FACTORS CONTROLLING FLORAL ZONATION AND  DISTRIBUTION OF BURROWING AND TUBE-DWELLING ORGANISMS ON FRASER DELTA TIDAL FLATS, BRITISH COLUMBIA  by  DAVID DONALD SWINBANKS B.Sc,  S t . Andrews U n i v e r s i t y , 1975  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE  REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  In THE  FACULTY OF GRADUATE STUDIES  (Department o f G e o l o g i c a l  Sciences  and I n s t i t u t e o f Oceanography)  We accept t h i s t h e s i s as conforming to the r e q u i r e d  THE  standard  UNIVERSITY OF BRITISH COLUMBIA March, 1979  {£) David Donald Swinbanks, 1979  )E-6  In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s  for  an advanced degree a t the U n i v e r s i t y of B r i t i s h C o l u m b i a , I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s  thesis  f o r s c h o l a r l y purposes may be g r a n t e d by the Head of my Department o r by h i s r e p r e s e n t a t i v e s .  I t i s understood t h a t c o p y i n g or  publication  of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my written permission.  Department o f  Geological Sciences  The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5  Date  BP  75-51  1 E  March 19,  1979  ABSTRACT  The  d i s t r i b u t i o n of v a r i o u s burrowing and  t h e i r b i o g e n i c sedimentary s t r u c t u r e s , and  tube-dwelling  the r a t e s at which they  over sediment are I n v e s t i g a t e d on t h r e e d i f f e r e n t of the F r a s e r D e l t a . and  The  organisms,  tidal flat  turn  environments  organisms s t u d i e d i n c l u d e C a l l i a n a s s a c a l i f o r n i e n s i s  Upogebia p u g e t t e n s l s , both t h a l a s s i n l d e a n burrowing shrimps, the burrow-  ing polychaete sp. and  A b a r e n i c o l a sp.,  Spio sp.,  the t u b e - d w e l l i n g  the b i v a l v e Mya  a t t r a m e n t a r i a and N a s s a r i u s i n t e r e s t because they  a r e n a r i a and  mendicus.  polychaetes,  the gastropods  Praxillela Batlllaria  T h a l a s s i n i d e a n shrimps are of most  are widespread over the D e l t a , i n p a r t i c u l a r C a l l i a n a s s a  and because t h e i r d i s t i n c t i v e burrows are w e l l known i n the g e o l o g i c a l record. The  ' m a r i n e ' t i d a l . " . f l a t s of Boundary Bay 5  of the F r a s e r Deltas^ are mantled w i t h s o r t e d sands.  The  on the i n a c t i v e southern  f i n e t o very  i n t e r t i d a l r e g i o n has  saltmarsh,  a l g a l mat,  c h a r a c t e r i z e d by  creates l a t e r a l heterogeneity  distinc-  These are from the s h o r e l i n e seawards, the  upper sand wave, e e l g r a s s and  Topography o f both s m a l l and  well  f i v e f l o r a l / s e d i m e n t o l o g i c a l zones  d e l i m i t e d p r i m a r i l y by e l e v a t i o n and exposure and t i v e m a c r o f a u n a l assemblages.  f i n e , w e l l to very  flank  lower sand wave zones.  l a r g e s c a l e of b i o g e n i c or p h y s i c a l o r i g i n w i t h i n the b i o f a c i e s of each zone.  g An e s t i m a t e d  4.25  6 rework about 10 limiting  A b a r e n i c o l a on Boundary Bay  tidal flats  annually  3 m  the extent  Abarenicola  x 10  of sand.  The  b i o t u r b a t i o n of t h i s worm may  of the a l g a l mat  can s e p a r a t e  head s h a f t i r r i g a t i o n  a sand/clay  zone.  By  mixture by  i r r i g a t i n g i t s burrow, floating  the c l a y out i n the  current.  T h a l a s s i n i d e a n burrowing shrimps are most abundant on the f l a t s of s o u t h e a s t e r n  be a f a c t o r  'marine'  tidal  Roberts Bank on the a c t i v e D e l t a - f r o n t . These . t i d a l f l a t s  iii can  divided- i n t o  mat,  four.' f l o r a i / s e d H . ^ n t o l o ^ i . c a i ^ p n e s :  s a n d f l a t and e e l g r a s s zones.  the s a n d f l a t  zone.  are abundant 2.6  t o 4.0  T h a l a s s i n i d e a n burrowing shrimps  Upogebia d e n s i t i e s are p o s i t i v e l y  t e n t of the sediment.  the saltniarsh",  algal  dominate  c o r r e l a t e d to mud  con-  C a l l i a n a s s a show no c l e a r g r a i n s i z e p r e f e r e n c e and  i n sediments r a n g i n g from 5 to 50% i n mud  0 i n median g r a i n s i z e .  c o n t e n t and from  At t h e i r peak d e n s i t y  (446 burrow  openings  -2 m  ) C a l l i a n a s s a rework the s u b s t r a t e they l i v e i n t o a depth o f 50 cm i n  about f i v e months. On c e n t r a l Roberts Bank a major t r a n s i t i o n from a 'marine' t o a b r a c k i s h environment o c c u r s . levels  A b r a c k i s h marsh zone e x t e n d i n g t o much lower  than the s a l t m a r s h l a t e r a l l y  h a l f of the s a n d f l a t zone.  r e p l a c e s the a l g a l mat  A sandflat/mudflat  intertidal  zone and the upper  zone c r o s s - c u t by channels  d i s p l a c e s the e e l g r a s s zone and lower h a l f o f the s a n d f l a t zone.  The peak  i n C a l l i a n a s s a d i s t r i b u t i o n moves to lower i n t e r t i d a l l e v e l s because of the presence o f low s a l i n i t y water at h i g h e r t i d a l l e v e l s and because o f the absence of e e l g r a s s i n lower i n t e r t i d a l r e g i o n s .  Upogebia a l t h o u g h p h y s i o -  l o g i c a l l y b e t t e r adapted t o cope w i t h reduced s a l i n i t y  demonstrates lower  t o l e r a n c e o f b r a c k i s h water i n i t s d i s t r i b u t i o n than C a l l i a n a s s a , p r o b a b l y because the f u n c t i o n o f i t s mud-lined burrow  as a c o n d u i t f o r s u s p e n s i o n  f e e d i n g and r e s p i r a t i o n exposes Upogebia t o low s a l i n i t y s u r f a c e w a t e r s , w h i l e C a l l i a n a s s a , i n i t s u n l i n e d burrow  used f o r d e p o s i t f e e d i n g , i s p r o -  t e c t e d from s u r f a c e waters by h i g h s a l i n i t y i n t e r s t i t i a l w a t e r s . t i n c t i o n between these two  types o f burrow  The d i s - ..;  i s c o n s i d e r e d to be v e r y ' s i g n i f i -  cant-: for: paleoenvironment'al r e c o n s t r u c t i o n s . 1  A new  system o f s u b d i v i d i n g the i n t e r t i d a l r e g i o n i n t o exposure  zones  (the atmozone, amphizone and aquazone), based on c r i t i c a l t i d a l l e v e l s at which the maximum d u r a t i o n o f continuous exposure or submergence 'jumps,' i s advocated.  I t a l l o w s c r o s s c o r r e l a t i o n between d i f f e r e n t  tidal  regions  iv  experiencing  d i f f e r e n t types of a s t r o n o m i c a l l y c o n t r o l l e d t i d e s and much of  the i n t e r t i d a l to  z o n a t i o n of F r a s e r D e l t a t i d a l  these exposure zones.  [J  f l a t s may  be  causally related  V  TABLE OF CONTENTS Page ABSTRACT  1  TABLE OF CONTENTS  .  1  v  LIST OF TABLES  x  LIST OF FIGURES  x i i  ACKNOWLEDGEMENTS  xxii  INTRODUCTION  1  REFERENCES  8  Part 1 —  Part 2 —  INTERTIDAL EXPOSURE ZONES: THE INTERTIDAL REGION  A NEW SCHEME FOR SUBDIVIDING 9  Abstract  10  Inroduction  11  Critical  12  T i d a l Levels  Exposure Zones  18  I n t e r t i d a l Zonation  22  Acknowledgements  24  References  25  BIOSEDIMENTOLOGICAL ZONATION OF BOUNDARY BAY TIDAL FLATS, FRASER RIVER DELTA, BRITISH COLUMBIA  .27  Abstract  28  Introduction .  '  Methods F l o r a l / S e d i m e n t o l o g i c a l Zonation  o f the T i d a l F l a t s  30 33 39  Description  39  D i s c u s s i o n o f Sand Waves  42  E n v i r o n m e n t a l F a c t o r s and Zonation  44  G r a i n S i z e of S u r f a c e  Sediments  45  S a l i n i t y and T u r b i d i t y  49  Exposure Time  51  vi TABLE OF CONTENTS (Cont'd) Page Part 2 — (Cont'd)  F l o r a Fauna and T h e i r B i o g e n i c  Sedimentary S t r u c t u r e s  Saltmarsh Zone  60  A l g a l Mat Zone  61  B.atillaria  61  Spio  65  Fly  Larvae  70  Abarenicola  70  Mya  74  Callianassa  74  Zone  81  Upogebia  82  Praxillela  85  Nassarius  88  Lower Sand Wave Zone  88  D i s c u s s i o n of Zonation  89  Summary  94 A l g a l Mat Zone  94  Upper Sand Wave Zone  97  E e l g r a s s Zone  97  Conclusions  98  Acknowledgements  99  References 3 —  70  Upper Sand Wave Zone  Eelgrass  Part  60  101  SEDIMENT REWORKING AND THE ^10GENICjFORMATION OF-CLAY ' ''LAMINAE'- BY" ABARENICOLA PACIFIC^ -"  106  Abstract  107  Introduction  108  vii TABLE OF CONTENTS (Cont'd) Page Part 3 — (Cont'd)  Methods  '  111  Results  112  F i e l d Results  112  Sediment Reworking Rates  112  Budget o f Sediment Turnover  _  Laboratory Results  112 117  Discussion  117  Acknowledgements  121  References  122  P a r t 4A - ENVIRONMENTAL. CONTROLS ON THE DISTRIBUTION OF THALASSINIDEAN BURROWING SHRIMPS ON FRASER DELTA TIDAL FLATS, BRITISH COLUMBIA: A Marine T i d a l F l a t Between Two Man-Made Causeways--on-iSoutheastem.'Roberts Bank  124  Abstract  125  Introduction  12 7  Methods  130  The Inter-Causeway T i d a l F l a t  134  F l o r a l / S e d i m e n t o l o g i c a l Zones  134  Grain Size of Surface  144  Salinity  Sediments  and T u r b i d i t y  D i s t r i b u t i o n of T h a l a s s i n i d e a n Influence  Biogenic  146 Shrimps  147  of G r a i n S i z e on T h a l a s s i n i d e a n  Shrimp D i s t r i b u t i o n  152  Thalassinidean  158  Shrimp I n t e r r e l a t i o n s h i p s  Reworking o f Sediment  158  Discussion  163 Upper L i m i t s o f T h a l a s s i n i d e a n Distribution  Shrimp 163  viii  TABLE OF CONTENTS (Cont'd) Page P a r t 4A (Cont'd)  Lower L i m i t s o f T h a l a s s i n i d e a n Distribution  Shrimp 164  F a c t o r s I n f l u e n c i n g T h a l a s s i n i d e a n - Shrimp Density . Acknowledgements  166  '  •p. j—  170  . References P a r t 4B - ENVIRONMENTAL CONTROLS ON THE DISTRIBUTION OF THALASSINIDEAN BURROWING SHRIMPS ON FRASER DELTA TIDAL FLATS, BRITISH COLUMBIA: The Marine t o B r a c k i s h T i d a l F l a t s of C e n t r a l and Northern Roberts Bank .  173  Abstract  174  Introduction  176  Methods  '  179  N o r t h e r n and C e n t r a l Roberts Bank  183  Floral/Sedrmentological  183  Zones  Salinity  191  D i s c u s s i o n o f S a l i n i t y Regime D i s t r i b u t i o n of T h a l a s s i n i d e a n  199  Shrimps  Description  200 .  200  R e l a t i o n s h i p Between Shrimp D e n s i t y and S u b s t r a t e Parameters Discussion of Thalassinidean  203 Shrimp D i s t r i b u t i o n  208  Burrow Geometry  213  Review and C o n c l u s i o n s  221  Acknowledgements  226  References  227  SUMMARY AND CONCLUSION APPENDIX 1 —  SURVEY DATA FOR BOUNDARY BAY (Part 2)  APPENDIX 2 —  FAUNAL DENSITIES AND GRAIN SIZE DATA ON TRANSECTS A AND B, BOUNDARY BAY (Part 2)  230 -235 .  244  ix TABLE OF CONTENTS  (Cont'd) Page  APPENDIX 3 —  APPENDIX 4 —  APPENDIX 5 —  APPENDIX 6 —  APPENDIX 7 —  APPENDIX 8 —  APPENDIX 9 —  SURVEY DATA FOR STATIONS ON THE INTERCAUSEWAY TIDAL FLAT ( P a r t 4A) GRAIN SIZE AND THALASSINIDEAN SHRIMP DENSITY DATA FOR STATIONS ON THE INTER-CAUSEWAY TIDAL FLAT ( P a r t  248'  4A)  254  SUPPLEMENTAL INFORMATION REGARDING SURFACE SUBSTRATE SALINITY AND SUBSTRATE SALINITY PROFILES ON INTERCAUSEWAY TIDAL FLAT, ROBERTS BANK ( P a r t 4A)  257  SUPPLEMENTAL DATA ON CORRELATIONS BETWEEN THALASSINIDEAN SHRIMP DENSITIES AND GRAIN SIZE ON THE INTERCAUSEWAY TIDAL FLAT (Part 4A)  261  CHARACTERISTICS OF THE STATIONS USED TO DETERMINE REWORKING RATES BY THALASSINIDEAN SHRIMPS  •265  SUPPLEMENTAL DATA ON SALINITY FOR NORTHERN AND CENTRAL ROBERTS BANK (Part 4B)  '2661?  SUPPLEMENTAL DATA ON CORRELATIONS BETWEEN CALLIANASSA DENSITY AND SUBSTRATE PARAMETERS FOR NORTHERN AND CENTRAL ROBERTS BANK ( P a r t 4B)  '272,  X  LIST OF TABLES Part 2 Table I. II. III. IV.  Page Dates and L o c a t i o n s o f F i e l d O b s e r v a t i o n s  36  E l e v a t i o n s o f Zone B o u n d a r i e s  40  A e r i a l photographs and s a t e l l i t e imagery i l l u s t r a t i n g the low t u r b i d i t y l e v e l s of Boundary Bay w a t e r s  50  S a l i n i t y of Water i n T i d a l P o o l s a t Low T i d e  52  Part 3 I. II. III.  Rates o f Sediment Turnover by A b a r e n i c o l a  113  Rates of Sediment Turnover by A b a r e n i c o l a (Cont'd)  114  Annual Budget of Sediment Turnover f o r A b a r e n i c o l a i n Boundary Bay  116  Part I.  4A  Rates of b i o g e n i c r e w o r k i n g of sediment by C a l l i a n a s s a and Upogebia, as measured i n p r o t e c t e d m e t a l e n c l o s u r e s on the s u r f a c e of the s u b s t r a t e  160  P a r t 4B I.  II. III. IV.  V.  E l e v a t i o n ranges f o r zone b o u n d a r i e s on the 'marine' t i d a l f l a t s as d e t e r m i n e d from a t o p o g r a p h i c map. The a c c u r a c y o f e l e v a t i o n s o b t a i n e d from the map i s checked by comparing w i t h s u r v e y e d e l e v a t i o n d a t a o b t a i n e d i n the i n t e r - c a u s e w a y a r e a ( P a r t 4A) .  186  E l e v a t i o n of the Lower L i m i t o f the B r a c k i s h Marsh  188  Comparison of T h a l a s s i n i d e a n Shrimp D e n s i t i e s a t S t a t i o n s Sampled i n 1977 and Reoccupied i n 1978  202  Comparison of C o r r e l a t i o n C o e f f i c i e n t s ( r ) Between C a l l i a n a s s a Burrow Opening D e n s i t y and P e r c e n t Mud U s i n g P o o l e d and Unpooled P e r c e n t Mud Data  206  R e l a t i o n s h i p Between S u r f a c e S u b s t r a t e S a l i n i t y and C a l l i a n a s s a Burrow Opening D e n s i t y a t a F i x e d T i d a l L e v e l a t S i x S t a t i o n s Midway Between Canoe Pass and the C o a l p o r t Causeway ( F i g . 2)  207  xi  LIST OF TABLES (Cont'd) SUMMARY AND CONCLUSION Table I. II. III.  Page SUMMARY OF ENVIRONMENTAL FACTORS LIMITING THALASSINIDEAN SHRIMP DISTRIBUTION ON FRASER DELTA TIDAL FLATS  233  SUMMARY OF EFFECTS OF VARIOUS ENVIRONMENTAL FACTORS ON THALASSINIDEAN SHRIMP DENSITY  233  Schematic Summary o f A l l F l o r a l and F a u n a l D i s t r i b u t i o n a l L i m i t s on F r a s e r D e l t a T i d a l F l a t s Which L i e W i t h i n 15 cm Or L e s s o f an Exposure Zone Boundary Or Other Extreme C r i t i c a l T i d a l L e v e l  234  xii LIST OF FIGURES  Part 1 Figure 1.  Page (a) Schematic d a i l y t i d a l curves f o r the t h r e e main types o f tide. Shading i n d i c a t e s submergence. F o r mixed t i d e s t h e r e are f o u r c r i t i c a l t i d a l l e v e l s (dashed l i n e s ) at which the d u r a t i o n o f exposure or submergence 'jumps' - and which d e f i n e f i v e exposure l e v e l s w i t h i n which exposure and submergence changes, c o n t i n u o u s l y w i t h r e s p e c t to e l e v a t i o n . Higher high water d e f i n e s the boundary between Exposure L e v e l s 1 and 2, and i s a c r i t i c a l t i d a l l e v e l above which the d u r a t i o n o f expos u r e doubles from l e s s than one l u n a r day t o at . l e a s t n e a r l y two. Lower h i g h water d e f i n e s the boundary - between Exposure L e v e l s 2 and 3 and i s a l e v e l above which the d u r a t i o n of exposure doubles from l e s s than h a l f a l u n a r day to j u s t under one l u n a r day. E q u i v a l e n t c r i t i c a l t i d a l l e v e l s l i e . a t the h e i g h t s o f h i g h e r low water and lower low water but i n v o l v e s t e p s i n submergence d u r a t i o n . They d e f i n e Exposure L e v e l s 4 and 5. The same c r i t i c a l t i d a l l e v e l s and exposure l e v e l s can be r e c o g n i z e d f o r s e m i - d i u r n a l t i d e s . Exposure L e v e l 3 cannot be d e f i n e d f o r d i u r n a l t i d e s because they l a c k lower h i g h water and h i g h e r low water s t a g e s . (b) The p r e d i c t e d d a i l y h e i g h t s of lower low water at P o i n t A t k i n s o n , B.C. between August and November, 1977 a r e p l o t t e d as d o t s . The low waters are modulated i n t o two neap t i d e s and two s p r i n g t i d e s per month. S u c c e s s i v e s p r i n g t i d e s a r e of d i f f e r e n t ranges. The s p r i n g t i d e of l e s s e r range d e f i n e s a c r i t i c a l t i d a l l e v e l a t which d u r a t i o n of continuous submergence jumps from about 10 t o 20 days, and t h a t o f g r e a t e r range a jump from about 24 to 45 days. (c) Annual c r i t i c a l l e v e l s are d e f i n e d by the s p r i n g h i g h e r h i g h waters o f June and December f o r p r e d i c t e d t i d e s i n 1977/78 at P o i n t A t k i n s o n , B.C. Dots i n d i c a t e h e i g h t s o f s p r i n g and neap t i d e s . The s p r i n g h i g h t i d e s o f June, 1978 and December, 1978 are so s i m i l a r i n h e i g h t t h a t these two c r i t i c a l t i d a l l e v e l s merge i n t o one, i n v o l v i n g a jump from about six.months to a t l e a s t n e a r l y two y e a r s o f continuous exposure. The s p r i n g h i g h t i d e o f December, 1977 was h i g h e r and d e f i n e s a c r i t i c a l t i d a l l e v e l above which the d u r a t i o n o f exposure i s at l e a s t nearly three years. (d) The l e v e l of the lowest lower low water ( i . e . , extreme s p r i n g lower low water) f o r each y e a r from 1967 to 1987 a t Tsawwassen, B.C. i s graphed. T h i s l e v e l has r i s e n g r a d u a l l y from about -3.1 m G e o d e t i c Datum i n 1968 to about -2.6 m G e o d e t i c Datum i n 1978 based on observed t i d a l r e c o r d s . Mean s p r i n g lower low water ( i . e . , the mean of twelve monthly s p r i n g lower low waters f o r each year) h e l p s d e f i n e the t r e n d . The p r e d i c t e d trends over the next n i n e y e a r s are dashed i n . The l e v e l o f the  14  xiii LIST OF FIGURES  (Cont'd)  Figure  ;Page lowest extreme s p r i n g lower low water i n December, 1968.defines a c r i t i c a l t i d a l l e v e l below which the d u r a t i o n o f continuous submergence jumps from about 18 y e a r s t o a t l e a s t n e a r l y 36 years.  2.  (a)y:"• C c o s a a c o f r e l a t - i o n x o f ^ e - x t r e m e ^ c r l t i c a l ^ t l d a l ^ l e v e l s a b e t w e e n the i n t e r t i d a l r e g i o n s o f S t . John,; New Brunswick and Tsawwassen, B.C. Based on p r e d i c t e d t i d e s f o r 1978 f o r S t . John's and o b s e r ved t i d e s between June, 1977 and June, 1978 at Tsawwassen. The numbers above and below c r i t i c a l t i d a l l e v e l s i n d i c a t e the maximum d u r a t i o n of continuous exposure i n days i n the case of nt.i atmozonal c r i t i c a l t i d a l l e v e l s , and the maximum d u r a t i o n of continuous submergence i n days i n the case o f aquazonal c r i t i c a l tidal levels. For example at the upper l i m i t o f the lower atmozone a t S t . John the jump i s from 10 to 20 days.and the a a : . . : . next c r i t i c a l t i d a l l e v e l up i n v o l v e s a jump from 26 t o 72 days. In the case of atmozonal c r i t i c a l t i d a l l e v e l s only the lowest l e v e l a t t a i n e d by a p a r t i c u l a r c r i t i c a l t i d a l l e v e l is indicated. In the case of aquazonal c r i t i c a l t i d a l l e v e l s o n l y the h i g h e s t l e v e l a t t a i n e d by a p a r t i c u l a r c r i t i c a l t i d a l l e v e l i s i n d i c a t e d , i . e . , o n l y extreme c r i t i c a l t i d a l l e v e l s are indicated.  19  (b) L e v e l s o f exposure zone b o u n d a r i e s over the p a s t ten y e a r s at Tsawwassen, B.C. based on observed t i d a l r e c o r d s . In the case of the boundary between the lower atmozone and the upper atmozone the numbers above and below c r i t i c a l t i d a l l e v e l s i n d i c a t e the maximum d u r a t i o n o f exposure i n days. In the case of the boundary between the upper aquazone and the lower aquazone the numbers above and below c r i t i c a l t i d a l l e v e l s i n d i c a t e the maximum d u r a t i o n of submergence i n days. On.the extreme r i g h t hand s i d e of the diagram h o r i z o n t a l b a r s i n d i c a t e the mean l e v e l s of exposure zone b o u n d a r i e s w h i l e the v e r t i c a l b a r s i n d i c a t e the s t a n d a r d d e v i a t i o n from the mean. Mean l e v e l s are not i n d i c a t e d i n the case of the b o u n d a r i e s of the lower aquazone because they undergo s i g n i f i c a n t m o d u l a t i o n by the e f f e c t s o f an 18.6 y e a r s o l i - l u n a r d e c l i n a t i o n a l c y c l e .  Part 2 1.  2.  Map of the F r a s e r D e l t a a r e a , showing the l o c a t i o n of Boundary Bay t i d a l f l a t s (reproduced from K e l l e r h a l s and Murray, 1969).  32  F l o r a l / s e d i m e n t o l o g i c a l z o n a t i o n o f Boundary Bay w i t h the l o c a t i o n s o f t r a n s e c t s A and B i n d i c a t e d . Between the t i d a l channels the w a t e r l i n e approximates to the -2.4 m (-8.0 f t ) contour ( G e o d e t i c Datum). The w a t e r l i n e i n the t i d a l channels does not f o l l o w a s p e c i f i c contour s i n c e these d e p r e s s i o n s remain waterf i l l e d d u r i n g low t i d e , d e s p i t e the f a c t that they are w e l l above sea l e v e l .  34  xiv LIST OF FIGURES (Cont'd) Figure  Page  3.  R e f l e c t i o n i n t e r f e r e n c e p a t t e r n s i n the upper sand wave zone i n the a r e a o f Beach Grove. A l s o i n d i c a t e d are the p r o b a b l e d i r e c t i o n s o f wave i n d u c e d c u r r e n t s .  4.  V a r i a t i o n s i n mean g r a i n s i z e , s o r t i n g and mud content on t r a n ^ s e c t A.  46'  5. sr.-  V a r i a t i o n s i n mean g r a i n s i z e , s o r t i n g and mud content on t r a n s e c t B.  47  6.  Mean d a i l y exposure w i t h r e s p e c t to e l e v a t i o n f o r Boundary Bay tides. T h i s was compiled from 16 r e p r e s e n t a t i v e d a i l y t i d a l curves ( e i g h t mean t i d e s , f o u r s p r i n g t i d e s and f o u r neap t i d e s ) s e l e c t e d from 25 a v a i l a b l e i n the d a t a o f Weir (1963) c o v e r i n g the p e r i o d o f June t o September, 1959. U s i n g more than 16 days of t i d a l r e c o r d s would p r o b a b l y reduce some o f the s t a n d a r d d e v i a t i o n s , b u t i t would i f a n y t h i n g i n c r e a s e the ranges o f possible values.  54  7.  (a) The f i v e tides.  57  'exposure l e v e l s ' p o s s i b l e f o r mixed s e m i - d i u r n a l  43-.  ;  (b) The ranges o f d u r a t i o n o f continuous exposure f o r each of the f i v e exposure l e v e l s . (c) The ranges o f d u r a t i o n of continuous submergence f o r each of the f i v e exposure l e v e l s . (d) The monthly modulation o f the f i v e exposure l e v e l s f o r the p e r i o d June 2 1 - J u l y 31, 1959. T i d a l d a t a from Weir (1963) 8.  9.  The requency o f f o u r o f the f i v e exposure l e v e l s w i t h r e s p e c t to e l e v a t i o n f o r a p e r i o d o f 73 l u n a r days from June 21-September 4, 1959 ( s o u r c e : Weir, 1963). L e f t hand s c a l e i n days, r i g h t hand s c a l e i n p e r c e n t . A l s o p l o t t e d i s the maximum number of c o n s e c u t i v e l u n a r days o f exposure o r submergence f o r those e l e v a t i o n s where exposure o r submergence can exceed one l u n a r day. (a) D e n s i t i e s o f B a t i l l a r i a sp. on t r a n s e c t A;.; d i f f e r e n t i a t i n g between dry s i t e s and under water s i t e s ( s h a l l o w t i d a l p o o l s ) . (b)  10.  59 62  D e n s i t i e s o f B a t i l l a r i a sp. on t r a n s e c t B.  (a) B a t i l l a r i a a t t r a m e n t a r i a p r o d u c i n g a g r a z i n g t r a i l . s h e l l i s about 3 cm l o n g .  Its  (b) B a t i l l a r i a g r a z i n g t r a i l s and r e s t i n g t r a c e s ( p i t s ) . Note the t r a i l s l e a d i n g t o p i t s . Trowel head i s about 5 cm wide. (c) R e s t i n g t r a c e p i t s produced by B a t i l l a r i a sp. Four B a t i l l a r i a sp. can be seen s t i l l o c c u p y i n g p i t s . Trowel head i s about 5 cm wide.  63  XV  LIST OF  FIGURES  (Cont'd)  Figure 11.  Page (a) B a t i l l a r i a sp. h e a d i n g upstream p r o d u c i n g g r a z i n g t r a i l s p a r a l l e l i n g the c u r r e n t d i r e c t i o n ( e e l g r a s s at top of photo indicates current d i r e c t i o n ) . B a l l p o Lnt'pen i s about 15 cm long.  66  (b) Behaviour of B a t i l l a r i a sp. i n weak c u r r e n t s : the g a s t r o pod heads upstream g r a z i n g , and produces a t r a i l p a r a l l e l i n g the c u r r e n t . O c c a s i o n a l l y the c u r r e n t causes the gastropod t o roll. Once s t a b i l i z e d again the gastropod turns i n towards the c u r r e n t and r e v e r t s to g r a z i n g i n an upstream d i r e c t i o n . 12.  (a) Mounds produced by the f e e d i n g a c t i v i t i e s of Spio sp. Pen i s about 15 cm l o n g .  67  (b) P l a n view o f Spio sp. Two t e n t a c l e - l i k e p a l p s draw food i n t o i t s tube and are a l s o used to v o i d sandy p s e u d o - f e c a l strings i n a radial pattern.  13.  14.  (c)  Cross s e c t i o n of S p i o sp. i n i t s d w e l l i n g  (a)  D e n s i t i e s of Spio sp. on  t r a n s e c t A.  (b)  D e n s i t i e s of S p i o sp. on  transect  16.  69  B.  (a) Morphology of an A b a r e n i c o l a burrow ( a f t e r H y l l e b e r g , 1975). Arrows i n d i c a t e d i r e c t i o n of r e s p i r a t i o n c u r r e n t . (b) Patchy d i s t r i b u t i o n of A b a r e n i c o l a h i g h e s t d e n s i t i e s o f c a s t s occur i n and Trowel i s about 25 cm h i g h .  15.  tube.  fecal casts. around t i d a l  The pools.  (a) D e n s i t i e s of A b a r e n i c o l a f e c a l c a s t s on t r a n s e c t A. Upper h i s t o g r a m d i s t i n g u i s h e s between wet and dry s i t e s , and i s based on f o u r wet s i t e readings and f o u r dry s i t e readings at each s t a t i o n w i t h a 0.25 m quadrat. S t a t i o n s A8 and A9 had no wet s i t e s which c o u l d be sampled. S t a t i o n s A11-A17 had no dry sites. S t a t i o n A5 had dry s i t e s , but A b a r e n i c o l a was absent from them. Lower h i s t o g r a m p r e s e n t s the average d e n s i t i e s , based on random q u a d r a t s . (b)  D e n s i t i e s of A b a r e n i c o l a  f e c a l c a s t s on t r a n s e c t  (a)  D e n s i t i e s of My a sp'. on t r a n s e c t A.  71  73  B. 75  (b) S p r e i t e t r a c e s l e f t by Mya sp., and downwarping of l a m i n a t i o n s caused by movement of the clam w i t h i n i t s burrow due t o i t s growth or changes i n the l e v e l o f the sediment water i n t e r f a c e ( a f t e r Reineck, 1958). 17.  (a) D e n s i t i e s of C a l l i a n a s s a and ' t r a n s e c t A.  Upogebia burrow openings on  76  xvi LIST OF  FIGURES (Cont'd)  Figure  Page  17.  (b)  Densities  of C a l l i a n a s s a burrow openings on t r a n s e c t  B.  18.  (a) P l a n view o f a C a l l i a n a s s a burrow c a s t , showing bulbous 'turnarounds.' Cast i s about 60 cm i n p l a n view l e n g t h . M e t r i c r u l e r (1 m) w i t h c e n t i m e t e r s u b d i v i s i o n s p r o v i d e s s c a l e .  76 79  (b) S i d e view o f a C a l l i a n a s s a burrow c a s t showing h o r i z o n t a l m i n e - l i k e n a t u r e o f burrow system. Burrow extends to about 30 cm depth. M e t r i c r u l e r (1 m) w i t h c e n t i m e t e r s u b d i v i s i o n s provides scale. Overflow of r e s i n produced 'heads' on c a s t . (c) P l a n view of a l a r g e C a l l i a n a s s a burrow c a s t which i s j u s t over 1 m l o n g . M e t r i c r u l e r (1 m) p r o v i d e s s c a l e . 19.  (a) Cast of two Upogebia 'Y' shaped burrows j o i n e d by a c o n s t r i c t e d neck. Cast i s j u s t over 50 cm i n depth. Metric r u l e r (1. m) w i t h c e n t i m e t e r s u b d i v i s i o n s p r o v i d e s s c a l e . (b) Side view of c a s t i n (a.) the c a s t . .  20.  83  showing shrimp entombed w i t h i n  (a) A.  Densities  of P r a x i l l e l a sp.  and N a s s a r i u s sp.  on  transect  (b) B.  Densities  of P r a x i l l e l a sp.  and  N a s s a r i u s sp. on  transect  21.  V e r t i c a l agglutinated  22.  Z o n a t i o n of b i o g e n i c sedimentary s t r u c t u r e s i n t h r e e of the f l o r a l / s e d i m e n t o l o g i c a l zones of Boundary Bay t i d a l f l a t s , and the expected s t r a t i g r a p h i c s u c c e s s i o n of b i o g e n i c sedimentary s t r u c t u r e s and g r a i n s i z e parameters, i f the t i d a l f l a t s are p r o g r a d i n g seawards without s u b s i d e n c e .  95  L a t e r a l h e t e r o g e n e i t y w i t h i n z o n a l b i o f a c i e s caused by graphy of s m a l l and l a r g e s c a l e .  topo-  96 '  (a) A l g a l mat zone: a l g a l mat platforms.  upraised  23.  sand tube of P r a x i l l e l a sp.  86  L a t e r a l heterogeneity  (b) Upper sand wave zone: sand waves. (c) E e l g r a s s zone: mounds and burrows.  c r e a t e d by  L a t e r a l heterogeneity  L a t e r a l heterogeneity  87  created  created  by  by  Callianassa  xvii  LIST OF FIGURES (Cont'd) . :•-  Part 3  Figure  P  a g e  1.  L o c a t i o n o f study a r e a . Upper map shows the g e n e r a l l o c a t i o n o f Boundary Bay on the F r a s e r D e l t a and the lower maps the f l o r a l / s e d i m e n t o l o g i c a l zones o f the t i d a l f l a t s . The two t r a n s e c t s A and B were s e t up i n 1976 (Swinbanks, 1979).  109  2.  G r a i n s i z e s o r t i n g by A b a r e n i c o l a :  118  (a) S t a r t of the experiment. An i n d i v i d u a l A b a r e n i c o l a • (-2 g) was p l a c e d i n a homogenized mixture of sand (>63 /'m) and m o n t m o r i l l o n i t e (<63/im). (b) A f t e r 24 hours a t h i c k , b i o g e n i c a l l y formed lamina o f m o n t m o r i l l o n i t e (white) has developed as a r e s u l t o f the i r r i g a t i o n a c t i v i t i e s o f the worm. (c) A f t e r t h r e e days the lamina has been b u r i e d by f e c a l c a s t s and the lamina has been deformed and b i o t u r b a t e d by the f e e d i n g and i r r i g a t i o n a c t i v i t i e s o f the worm. 3.  Sketch o f a comparable s i t u a t i o n to that i l l u s t r a t e d i n F i g u r e 2b. The important f e a t u r e s o f the A b a r e n i c o l a burrow a r e l a b e l l e d and the d i r e c t i o n o f flow o f the r e s p i r a t i o n c u r r e n t which i r r i g a t e s the burrow i s i n d i c a t e d . A c l a y lamina has developed as a r e s u l t o f f i n e g r a i n e d c l a y p a r t i c l e s f l o a t i n g out i n suspension i n the head s h a f t i r r i g a t i o n c u r r e n t and then s e t t l i n g on the s u b s t r a t e .  119  P a r t 4A 1..  2.  3.  L o c a t i o n o f the study a r e a i s i n d i c a t e d by h o r i z o n t a l c r o s s hatching. T i d a l f l a t s are s t i p p l e d , l a n d a r e a o f Recent a l l u v i u m i s blank, and o l d e r d e p o s i t s d i a g o n a l l y c r o s s hatched (adapted from Luternauer,/, and Murray, 1973).  128  The f l o r a l / s e d i m e n t o l o g i c a l zones o f the inter-causeway t i d a l f l a t w i t h the l o c a t i o n s o f t r a n s e c t s , s t a t i o n s and bench marks i n d i c a t e d .  131  The e l e v a t i o n a l l i m i t s o f the f o u r major f l o r a l / s e d i m e n t o V . l o g i c a l zones on the inter-causeway t i d a l f l a t w i t h r e s p e c t to Geodetic Datum and the average exposure zone l i m i t s f o r observed t i d e s between 1968-78 a t the Tsawwassen t i d a l gauge (source: Swinbanks, 1979). The d o t t e d envelopes i n d i c a t e one s t a n d a r d d e v i a t i o n from the mean l e v e l o f the exposure zone boundary. The exposure zone l i m i t s f o r the lower aquazone a r e based on o n l y two y e a r s of r e c o r d s (1976-78) because these b o u n d a r i e s a r e s i g n i f i c a n t l y modulated by. an 18.6 y e a r d e c l i n a t i o n a l c y c l e i n the moon (Swinbanks, 1979).  136  xviii  LIST OF FIGURES (Cont'd) Figure  Page The e l e v a t i o n of the s a l t m a r s h / a l g a l mat zone boundary was determined a t seven p o i n t s between t r a n s e c t s B and C ( F i g . 2)  4.  (a) Laminated s i l t s of the s a l t m a r s h . The stand out i n r e l i e f . Pen i s 15 cm l o n g .  c o a r s e r laminae  138  (b) The weathered s u r f a c e of the s a l t m a r s h r e v e a l s t h a t the s a l t m a r s h d e p o s i t s are r i d d l e d w i t h r o o t l e t s , which have weathered out as h o l e s h e r e . Pen i s 15 cm l o n g . 5.  6.  The mud contents of s u r f a c e sediments. Numbers next to s t a t i o n s i n d i c a t e the p e r c e n t mud at each s t a t i o n . The g e n e r a l trends of the contours between t r a n s e c t s have been determined by q u a l i t a t i v e f i e l d o b s e r v a t i o n s . (a) The a l g a l mat zone. The channel i n the foreground i s about one meter wide. Taken on f l o o d t i d e , j u s t as the channels are b e g i n n i n g to f i l l . Mudcracked p l a t e a u s l i e between the channels, and w a t e r - f i l l e d d e p r e s s i o n s are p r e s e n t on the p l a t e a u s .  140 141  (b) Mudcracked s u r f a c e of the a l g a l mat zone. The a l g a l mats b l i s t e r and c u r l under the e f f e c t s of d e s i c c a t i o n , and c r a c k i n g produces i s o l a t e d ' a l g a l mat cakes.' (c) Undersurface burrows.  o f an  ' a l g a l mat  cake,' r i d d l e d by  crab  (d) Laminated sediments of an a l g a l mat cake, c r o s s - c u t by a crab burrow (Hemigraspus o r e g o r t e n s i s ) . 7.  The median g r a i n s i z e . (0) next  8.  9.  10.  11.  12.  o f , s u r f a c e sediments.'  t o - s t a t i o n s i n d i c a t e median' grain v  size  (0)  The  numbers  at each s t a t i o n .  145  S u r f a c e s u b s t r a t e s a l i n i t i e s as measured on t r a n s e c t s A, B and C August 13, 1977 a t low t i d e between 11:30 and 14:25 i n the o r d e r i n d i c a t e d . Numbers next to s t a t i o n s i n d i c a t e salinity.  148  Typical substrate s a l i n i t y p r o f i l e area.  149  from the  inter-causeway  D i s t r i b u t i o n of C a l l i a n a s s a burrow openings i n contoured map form. G e n e r a l trends of contours between t r a n s e c t s d e t e r mined by q u a l i t a t i v e f i e l d o b s e r v a t i o n .  150  D i s t r i b u t i o n o f Upogebia burrow openings i n contoured form.  151  (a) (0),  map  D e n s i t y o f Upogebia burrow openings vs median g r a i n s i z e r e g a r d l e s s of e l e v a t i o n .  153  xix LIST OF FIGURES (Cont'd)  Figure  Page  12.  (b) D e n s i t y of Upogebia burrow openings vs mud (%), r e g a r d l e s s of e l e v a t i o n . .  13.  R e l a t i o n s h i p between mud content (%) and Upogebia burrow opening d e n s i t y , w i t h data grouped i n t o 0.25 m e l e v a t i o n class intervals; B e s t - f i t l i n e a r r e g r e s s i o n l i n e s are i n d i c a t e d , along w i t h t h e i r c o r r e l a t i o n c o e f f i c i e n t s ( r ) and c o n f i d e n c e l e v e l s (r_ t e s t ) . E l e v a t i o n (Geodetic Datum) i n c r e a s e s from A to J .  155  R e l a t i o n s h i p between mud content (%) and C a l l i a n a s s a burrow opening d e n s i t y , w i t h data c l a s s e d i n t o 0.25 m elevation class intervals. B e s t - f i t linear regression l i n e s are i n d i c a t e d , a l o n g w i t h t h e i r c o r r e l a t i o n c o e f f i c i e n t s (r) and c o n f i d e n c e l e v e l s ( r t e s t ) . Elevation (Geodetic Datum) i n c r e a s e s from A to L.  156  14.  15.  16.  2.  3.  4.  5.  153  R e l a t i o n s h i p between Upogebia burrow opening d e n s i t y and C a l l i a n a s s a burrow opening d e n s i t y w i t h the d a t a c l a s s e d i n t o 0.25 m e l e v a t i o n c l a s s i n t e r v a l s . Best-fit linear r e g r e s s i o n l i n e s are i n d i c a t e along w i t h t h e i r c o r r e l a t i o n c o e f f i c i e n t s (r) and c o n f i d e n c e l e v e l s (r_ t e s t ) . Elevation (Geodetic Datum) i n c r e a s e s from A to J .  159  The n e a r - s u r f a c e s t r a t i g r a p h y of the t i d a l f l a t on t r a n s e c t A. Upogebia burrows extend down i n t o a b l u e - g r e y c l a y e y mud h o r i z o n (the v e r t i c a l dimensions of the burrows are drawn to scale). T h i s b i o t u r b a t i o n may account f o r the anomalously h i g h mud contents of the s u r f a c e sediments.  162  Part 1.  content  4B  L o c a t i o n of study area. T i d a l f l a t s are s t i p p l e d , l a n d a r e a of Recent a l l u v i u m i s b l a n k , and o l d e r d e p o s i t s cross-hatched (adapted from L u t e r n a u e r and Murray, 1973).  177  L o c a t i o n s o f s t a t i o n s sampled by h o v e r c r a f t , ; h e l i c o p t e r on f o o t i n 1977 and 1978.  180  Topographic map of Roberts Bank i n 1967. c o n t o u r s i n t h i s map i s -2.63 m Geodetic meters ( s o u r c e : Swan Wooster, 1967).  and  The datum f o r Datum. Contours i n 181  F l o r a l / s e d i m e n t o l o g i c a l zones of Roberts Bank, p r e p a r e d from a c o l o u r a e r i a l photograph of June, 1978 (A37597-146, N.A.P.L., Ottawa, Canada).  184  High l e v e l a e r i a l photograph of the F r a s e r D e l t a . The waterl i n e l i e s at about -0.12 m Geodetic Datum on a f l o o d i n g t i d e ,  190  XX  LIST OF FIGURES (Cont'd)  and l i e s above the lower l i m i t of the marsh at Westham I s l a n d ( c e n t r e ) i s approaching the a l g a l mat zone i n the inter-causeway a r e a and l i e s a t the upper l i m i t of the e e l g r a s s zone i n Boundary Bay ( r e f e r to F i g . 1 f o r l o c a t i o n ) . Water i s b e g i n n i n g to f l o o d i n t o the d i s t r i b u t a r y channels o f the Brunswick P o i n t marsh from Canoe Pass. P e r c e n t mud i n s u r f a c e sediments o f n o r t h e r n and Roberts Bank. M e c h a n i c a l c o n t o u r i n g employed.  central  D i s c h a r g e curves f o r the F r a s e r R i v e r i n c l u d i n g the f r e s h e t p o r t i o n of the r u n o f f f o r 1948, a severe f l o o d y e a r i n the F r a s e r V a l l e y (adapted from R. Thompson, u n p u b l i s h e d d a t a ) . S u r f a c e s u b s t r a t e s a l i n i t i e s on Roberts Bank at low August 17, 1978. M e c h a n i c a l c o n t o u r i n g employed.  tide  on  (a) Surface-water s a l i n i t i e s a t h i g h t i d e on ebb between Canoe Pass and the f e r r y causeway on June 8, 1978. Stippled area i n d i c a t e s r e g i o n where a h a l o c l i n e i s p r e s e n t i n the water column. M e c h a n i c a l c o n t o u r i n g employed. Three representative salinity/temperature' p r o f i l e s included. (b) S u r f a c e s u b s t r a t e and s h a l l o w water s a l i n i t i e s on approaching low t i d e on June 8, 1978. Mechanical contouri n g employed. P e r c e n t t h i c k n e s s of the s a l t wedge, f o r 17.5%. as the boundary between marine and b r a c k i s h water masses. Mechan i c a l c o n t o u r i n g . Numbers next to s t a t i o n s i n d i c a t e , p e r c e n t t h i c k n e s s of s a l t wedge. D i s t r i b u t i o n of t h a l a s s i n i d e a n shrimp burrow openings on Roberts Bank based on data c o l l e c t e d i n 1977 and 1978. Where s t a t i o n s sampled i n 1977 were r e o c c u p i e d i n 1978 the average d e n s i t y has been used. Data f o r the inter-causeway a r e a are p r e s e n t e d i n P a r t 4A. M e c h a n i c a l c o n t o u r i n g employed. R e l a t i o n s h i p between C a l l i a n a s s a burrow opening d e n s i t y and the s a l i n i t y of s u r f a c e s u b s t r a t e waters. Best-fit linear r e g r e s s i o n l i n e s are drawn a l o n g w i t h t h e i r c o r r e l a t i o n c o e f f i c i e n t s ( r ) and s i g n i f i c a n c e l e v e l ( r t e s t ) . (a) R e l a t i o n s h i p between C a l l i a n a s s a burrow opening d e n s i t y and s u r f a c e s u b s t r a t e s a l i n i t y at a f i x e d t i d a l l e v e l (-1.55 m G e o d e t i c Datum), September 10-11, 1977. (b) S u b s t r a t e s a l i n i t y p r o f i l e s at S t a t i o n s 1-6, 10-11, 1977.  September  xxi  LIST OF FIGURES  (Cont'd)  Figure 14.  15.  Page T y p i c a l geometry o f C a l l i a n a s s a and Upogebia burrows on the F r a s e r D e l t a . Dimensions f o r c r o s s - s e c t i o n of Upogebia burrow l i n i n g o b t a i n e d from Thompson (1972). (a) R e s i n c a s t o f a C a l l i a n a s s a burrow coated i n sand w i t h a knobbly s u r f a c e r e m i n i s c e n t of OphiomOrpha. Note t h a t a t top l e f t the sand l i n i n g has been worn away by the s t r i n g and the i n n e r burrow l i n i n g i s smooth.  214 216  (b) F o s s i l i z e d C a l l i a n a s s a burrow h a v i n g the appearance of Thalassinoides. Sand has i n f i l l e d a burrow i n mud. 16.  Cast of a C a l l i a n a s s a burrow taken from an a r e a of h i g h burrow d e n s i t y (446 burrow openings m ) . Two c o n s t r i c t e d e n t r a n c e s meet as a bulbous chamber at about 10 cm depth, and a v e r t i c a l stem extends from t h i s to about 50 cm depth. Cryptomya c a l i f O r n i c a c l u s t e r around the bulbous chamber at the j u n c t i o n o f the two e x i t s . About t h i r t y of these commensal b i v a l v e s a r e a t t a c h e d t o the c a s t . The burrow i s o c c u p i e d by one shrimp. A burrow system o f s m a l l e r diameter branches o f f from t h i s system. It i s j o i n e d to the main burrow system by a narrow c o n s t r i c t e d neck and i s o c c u p i e d by a s m a l l j u v e n i l e shrimp. Scale i n centimeters.  218  17.  Summary o f the d i s t r i b u t i o n of t h a l a s s i n i d e a n burrow and f l o r a l / s e d i m e n t o l o g i c a l zones on a l l the t i d a l f l a t s o f the F r a s e r D e l t a south o f Main Channel, i n the form a s t r a t i g r a p h i c s u c c e s s i o n , c o n s t r u c t e d by p r o j e c t i n g a l l the d e n s i t y d a t a i n F i g u r e 11 onto a v e r t i c a l p l a n e p a s s i n g through p o i n t s A, B and C i n F i g u r e 11. The data on p e r c e n t t h i c k n e s s o f the s a l t wedge i n F i g u r e 10 have a l s o been i n c l u d e d to demonstrate the r e l a t i o n s h i p between t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n and s a l i n i t y regime. No d a t a on the s a l t wedge a r e a v a i l a b l e NW o f Canoe Pass. Data from Boundary Bay a r e based on T r a n s e c t A a l o n e (Swinbanks, 1979). Exposure zones a l l o w c r o s s c o r r e l a t i o n between Roberts Bank and Boundary Bay. Winter t i d a l d a t a are not a v a i l a b l e f o r Boundary Bay and as a r e s u l t the upper l i m i t o f the atmozone cannot be d e f i n e d , but the :. s p r i n g t i d a l l e v e l s f o r June i n d i c a t e d a l l o w c r o s s c o r r e l a t i o n i n the uppermost i n t e r t i d a l r e g i o n s .  222  xxii  ACKNOWLEDGEMENTS  I  would l i k e  providing me i n t o  to s i n c e r e l y thank Dr.  c o n s t a n t m o r a l and f i n a n c i a l s u p p o r t ,  this  Luternauer,  fascinating line  of  G e o l o g i c a l Survey of  and t r a n s p o r t a t i o n  f o r much o f  s i a s m and i n t e r e s t . ronment  Institute,  I for  Canada f o r  arranging f i n a n c i a l  the  am g r a t e f u l  f i e l d work, to Dr.  and f o r h i s  this  his  I  support  constant  enthu-  facilities  for  Envi-  the  <JX?C:>  criticism  thank Dr. W.C. Barnes  r e a d i n g and r e - r e a d i n g the m a n u s c r i p t .  Environment I n s t i t u t e ,  directing  to Dr. J . L .  a d v i c e and c o n s t r u c t i v e  thesis.  for  C D . Levings,fPacific  making a v a i l a b l e l a b o r a t o r y  of  initially  I  am a l s o g r a t e f u l  the b i o l o g i c a l content  critically  and f o r  research.  e x p e r i m e n t s on A b a r e n i c o l a and f o r of  J . W . M u r r a y , my s u p e r v i s o r ,  for  D r . M. P o m e r o y , P a c i f i c  D r . P . G . H a r r i s o n , U n i v e r s i t y o f B r i t i s h C o l u m b i a and  Dr. T . H . Carefoot, U n i v e r s i t y of B r i t i s h Columbia i d e n t i f i e d  many o f  the  f l o r a and f a u n a . I  am e s p e c i a l l y i n d e b t e d t o  Guard H o v e r c r a f t operating Muhlert, i n the  their  Unit, craft  the o f f i c e r s  Vancouver I n t e r n a t i o n a l for  field  investigations  and crew o f Airport  for  the  Canadian Coast  providing  on R o b e r t s B a n k .  M r . J . P . N a p o l e o n i , M r . G . Hodge a n d D r .  and  M r s . M.  J . P . S y v i t s k i ably a s s i s t e d  field.  G o r d o n H o d g e , E l s p e t h A r m s t r o n g a n d B e r n i e v o n S p i n d l e r d r a f t e d many the diagrams. but not  T h e i r p a t i e n c e a n d e x c e l l e n t w o r k i s much a p p r e c i a t e d .  of  Last  l e a s t I must • thank'#Nof.$ko,tjinyggiM ffriend,u.^holi:hegiped&int<teheff i e l d g o n i  i n n u m e r a b l e o c c a s i o n s , d r a f t e d many o f t y p e d , r e - t y p e d and r e - r e - t y p e d compilation of  this  thesis.  the rough d r a f t v e r s i o n s of  the s c r i p t  a n d who h a d t o l i v e  diagrams,  through  the  1 INTRODUCTION G e o l o g i s t s a r e becoming i n c r e a s i n g l y aware o f t h e p o t e n t i a l o f t r a c e f o s s i l s as p a l e o e n v i r o n m e n t a l i n d i c a t o r s . s t r u c t u r e s and animal-sediment an expanding  Study o f b i o g e n i c . s e d i m e n t a r y  r e l a t i o n s h i p s i n p r e s e n t day environments i s  f i e l d o f r e s e a r c h , which i s a t t r a c t i n g t h e a t t e n t i o n o f sedimen-  t o l o g i s t s , p a l e o n t o l o g i s t s and marine b i o l o g i s t s . g e o l o g i s t s i n modern environments  I n t h e p a s t r e s e a r c h by  has tended t o be l a r g e l y d e s c r i p t i v e .  In-  v e s t i g a t i o n o f t h e f a c t o r s c o n t r o l l i n g t h e d i s t r i b u t i o n o f organisms was the domain o f the marine b i o l o g i s t .  However t h i s s i t u a t i o n i s changing  and geoU ofgI'sitfs a r e becoming i n v o l v e d i n i n c r e a s i n g numbers i n e c o l o g i c a l l y r  o r i e n t a t e d s t u d i e s o f animal-sediment  relationships.  A wealth of e c o l o g i c a l  d a t a ^ a l r e a d y e x i s t s i n the b i o l o g i c a l l i t e r a t u r e , b u t o f t e n i t s r e l e v a n c e t o sedimentology  and p a l e o e n v i r o n m e n t a l s t u d i e s i s n o t i m m e d i a t e l y  apparent.  For example much o f t h e c l a s s i c work on i n t e r t i d a l z o n a t i o n by marine b i o l o g i s t s has been c a r r i e d o u t on r o c k y i n t e r t i d a l s h o r e l i n e s , w h i c h i n themselves are o f no p a r t i c u l a r i n t e r e s t t o s e d i m e n t o l o g i s t s .  However, many o f t h e - p r i n ;  cip-Ies and f i n d i n g s on r o c k y i n t e r t i d a l s h o r e l i n e s can be a p p l i e d t o t i d a l f l a t s , which a r e , o f c o u r s e , o f g r e a t i n t e r e s t t o s e d i m e n t o l o g i s t s . f o s s i l s a r e t o a t t a i n t h e i r f u l l p o t e n t i a l as p a l e o e n v i r o n m e n t a l  I f trace  indicators  f u r t h e r i n f o r m a t i o n on the e f f e c t s o f p e r t i n e n t e n v i r o n m e n t a l f a c t o r s on the d i s t r i b u t i o n o f t r a c e making organisms must be o b t a i n e d . t h i s i n mind t h a t t h e f o l l o w i n g study was c a r r i e d out.  I t was w i t h  This study of the  F r a s e r D e l t a i s o f n e c e s s i t y i n t e r - d i s c i p l i n a r y i n n a t u r e i n v o l v i n g the d i s c i p l i n e s o f s e d i m e n t o l o g y , b i o l o g y , oceanography and even some astronomy! The buzz word I n t e r - d i s c i p l i n a r y may be new, b u t t h e approach science  i s as o l d as  itself.  T h i s t h e s i s a n a l y z e s the d i s t r i b u t i o n o f v a r i o u s t r a c e making organisms  2 on the t i d a l f l a t s o f the F r a s e r D e l t a ?  The organisms i n v e s t i g a t e d i n c l u d e  the t h a l a s s i n i d e a n burrowing shrimps C a l l i a n a s s a c a l i f o r n i e n s i s pugettensis,  the burrowing p o l y c h a e t e  dwelling polychaetes  r  and N a s s a r i u s  As an irit^igXiail-; p a r t o f t h i s r e s e a r c h in  the i n t e r t i d a l r e g i o n  analyzed.  A b a r e n i c o l a p a c i f i c a and t h e tube-  P r a x i l l e l a a f f i n i s p a c i f i c a and S p i o sp.,  B a t i l l a r i a attramentaria  and Upogebia  the gastropods  mendicus and the b i v a l v e Mya a r e n a r i a . the d i s t r i b u t i o n o f v a r i o u s  (e.g., s a l t m a r s h ,  floral  zones  a l g a l mats, e e l g r a s s ) i s a l s o  The burrowing shrimp C a l l i a n a s s a c a l i f O r n i e n s i s i s the organism  of most i n t e r e s t because i t i s u b i q u i t o u s  to a l l Fraser Delta t i d a l  t o l e r a t i n g wide ranges i n s u b s t r a t e type and s a l i n i t y  regime.  flats,  Of almost  e q u a l i n t e r e s t i s Upogebia p u g e t t e n s i s , but t h i s shrimp i s more r e s t r i c t e d in  occurrence.  f o s s i l record  T h a l a s s i n i d e a n shrimp burrows are w e l l known i n the t r a c e ( T h a l a s s i n o i d e s and Ophiomorpha) e x t e n d i n g  as the Cretaceous out  ( B o r r a d a i l e , 1903).  to answer a r e :  the t i d a l  (1)  The q u e s t i o n s  a t l e a s t as f a r back  which t h i s  What i s the d i s t r i b u t i o n o f these  thesis sets  organisms on  f l a t s o f the F r a s e r D e l t a and how do v a r i o u s e n v i r o n m e n t a l f a c t o r s  influence their distribution?  (2)  What i s the n a t u r e  sedimentary s t r u c t u r e s the organisms produce?  (3)  o f the b i o g e n i c  At what r a t e do they  rework the s u b s t r a t e by burrowing i n t o and/or i n g e s t i n g sediment? e n v i r o n m e n t a l f a c t o r s which have been c o n s i d e r e d  include:  a)  which determines the d u r a t i o n o f exposure and submergence b) of the s u b s t r a t e interactions . saltmarsh, and  c)  E n v i r o n m e n t a l energy  d)  Salinity  The  Elevation; Grain  regime  size  e)  Bio-  Bio-rinter..ae.tions£in£ludetfiheiiiffijj.ue.riGeooff f l o r a l c o o v e r ((e«g. ,  e e l g r a s s o r a l g a l mats) on f a u n a l d i s t r i b u t i o n and v i c e v e r s a ,  a l s o any i n t e r - f a u n a l i n t e r a c t i o n s —  e.g., t r o p h i c group ammensalism  (Rhoads and Young, 1970). The  study  area  l i e s on the coast o f . B r i t i s h Columbia i n temperate  tudes and e x p e r i e n c e s  lati-  a west c o a s t maritime c l i m a t e , c h a r a c t e r i z e d by summers  3 which a r e c o o l , sunny and not very humid and by w i n t e r s which are c l o u d y , m i l d and wet.  The F r a s e r R i v e r i s the dominant source  to the S t r a i t o f G e o r g i a  (Pharo and Barnes, 1976).  The S t r a i t o f G e o r g i a  l i e s on the western margin o f the N o r t h American p l a t e . o c c u p i e s began i t s f o r m a t i o n extensive Georgia Depression. years  ago and the S t r a i t  o f t e r r i g e n o u s sediment  The b a s i n which i t  about 150 m i l l i o n years ago as p a r t o f the Mountain b u i l d i n g ceased  took i t s p r e s e n t  about.two m i l l i o n  form about a m i l l i o n y e a r s  later.  S i n c e then, g l a c i a l s c o u r i n g , downwarpirjg and e r o s i o n have c o n t i n u e d t o modify i t . P r e s e n t  evidence  i n d i c a t e s t h a t the F r a s e r D e l t a began to f a n  out from a gap i n the P l e i s t o c e n e uplands a t New Westminster, where the present  F r a s e r R i v e r b i f u r c a t e s i n t o North Arm and Main Channel ( F i g . 1 ) ,  about 8,000 y e a r s ago. have been d e p o s i t e d  S i n c e then an e s t i m a t e d  120-210^m o f d e l t a i c  (Mathews and Shepherd, 1962).  the s e a a l o n g a p e r i m e t e r  about 35 km l o n g .  The p r e s e n t  Of t h i s , a f r o n t  sediments  d e l t a meets approximately  20 km l o n g f a c e s west i n t o the S t r a i t o f G e o r g i a , w h i l e a now i n a c t i v e about 15 km l o n g f a c e s south onto Boundary Bay. lies and  Between these two f r o n t s  a former i s l a n d , now the P o i n t Roberts P e n i n s u l a . tidal flats  front  I n t e r t i d a l marshes  4 t o 8 km wide s l o p e g e n t l y seaward from the edge of the  c u l t i v a t e d lands o f the d e l t a , b e f o r e the d e l t a s u r f a c e d i p s more s t e e p l y i n t o the S t r a i t o f G e o r g i a .  The mean t i d a l range i s about 3iamwi'th extreme  s p r i n g t i d a l ranges o f 5 m and neap t i d a l ranges o f 1.5 m.  T i d e s are o f  mixed s e m i - d i u r n a l type i . e . , t h e r e a r e two h i g h waters and two low waters each day but s u c c e s s i v e h i g h and s u c c e s s i v e low waters a r e o f d i f f e r e n t The  F r a s e r R i v e r reaches  i t s peak d i s c h a r g e d u r i n g l a t e s p r i n g and e a r l y S u m -  merger The l e s s dense r i v e r water spreads Strait  height.  over the s a l i n e waters o f the  of G e o r g i a as a v i s i b l e plume o f muddy f r e s h t o b r a c k i s h water.  C e n t r a l S t r a i t o f G e o r g i a waters a r e thus s t r a t i f i e d i n t o a b r a c k i s h s u r f a c e l a y e r and an u n d e r l y i n g s a l t wedge (Waldichuk, 1957).  The s a l t wedge i n t r u d e s  *  4  F i g u r e 1.  G e n e r a l l o c a t i o n of F r a s e r D e l t a . T i d a l f l a t s a r e s t i p p l e d , l a n d a r e a o f Recent a l l u v i u m i s b l a n k , and o l d e r d e p o s i t s c r o s s - h a t c h e d (adapted from L u t e r n a u e r and Murray, 1973).  5 the F r a s e r R i v e r on f l o o d t i d e s e x t e n d i n g inner t i d a l f l a t s f l a t s during The is split  d u r i n g w i n t e r , but no  as f a r as 20 km  upstream o f  f u r t h e r than the i n n e r edge of  format of t h i s i n t o two  t h e s i s i s a s e r i e s of papers — P a r t s  s e c t i o n s P a r t 4A and  B.  I t i s intended  1 to 4.  that  t h e r e f o r e be  I n e v i t a b l y , as they a l l d e a l  a b l e to stand on i t s own.  the same study a r e a ,  t h e r e i s some r e p e t i t i o n of f a c t s and  as f a r as p o s s i b l e t h i s has  Cross r e f e ^  i t i s not  obvious  Swinbanks  a b a s i s f o r d e s c r i b i n g l o c a t i o n i n the i n t e r t i d a l  which i s a p p l i e d i n the  t i d a l f l a t studies that f o l l o w .  I t i s a new  f o r s u b d i v i d i n g t h e i i n t e r t i d a l r e g i o n based on c r i t i c a l  tidal levels  which the maximum d u r a t i o n o"fjiconti>nuous^exposu-re i n a s t e p - l i k e manner.  or submergence  types of a s t r o n o m i c a l l y mixed t i d e s w i t h  one  c o n t r o l l e d t i d e s , e.g., experiencing  t i c a l t i d a l l e v e l s on which the scheme i s based may i n t e r t i d a l zonation.  be  mean t i d a l l e v e l c a r r i e s w i t h  i t no  fulfills  information  as i n the computation of.mean exposure no discontinuous  organisms s h o u l d  experiencing  (2)  region  the  cri-  c a u s a l l y r e l a t e d to  e i t h e r of these r o l e s . on the d u r a t i o n of  exposure or continuous submergence at t h a t l e v e l , nor  continuous and  it  None of the schemes c u r r e n t l y i n use, based on mean  t i d a l l e v e l s o r mean exposure l e v e l s ,  value,  at  increases  between a  semi-diurnal  region  scheme  T h i s scheme i s advocated because (1)  allows m e a n i n g f u l c r o s s c o r r e l a t i o n between i n t e r t i d a l r e g i o n s  experiencing  the  3).  Part 1 provides  different  with  i d e a s between  P a r t r e f e r r e d to i n which case P a r t number i s i n c l u d e d , e.g.,  abruptly  4  Each P a r t must  been kept to a minimum.  rences are u s u a l l y made as Swinbanks (1979), u n l e s s  Part  shortened  i n the n e a r f u t u r e .  (1979, P a r t  the  the f r e s h e t (Ages and W o o l l a r d , 1976).  v e r s i o n s of each P a r t w i l l be p u b l i s h e d  P a r t s but  the  A  continuous  does a mean exposure  d i s t i n c t i o n i s drawn between  exposure o r submergence.  One  might expect  that  respond to p r e d i c t a b l e r e c u r r e n t extremes i n exposure or  6 submergence, b u t one can h a r d l y  expect them t o have a concept of a b s t r a c t  averages. P a r t 2 i s a study o f the z o n a t i o n  o f Mora:.\, fauna and t h e i r  biogenic  sedimentary structures,, on the t i d a l f l a t s o f Boundary Bay on the i n a c t i v e southern f l a n k o f the D e l t a . g r a i n s i z e o f the s u b s t r a t e  These t i d a l f l a t s  a r e unusual i n t h a t the  over much o f the Bay v a r i e s l i t t l e ,  predominantly o f f i n e t o very  f i n e w e l l t o very w e l l s o r t e d sands.  i n f l u e n c e o f the F r a s e r R i v e r on 'thisgbay i s s l i g h t 'normal marine' f o r the s o u t h e r n S t r a i t o f G e o r g i a . f l o r a l / f a u n a l zonation  and  As a r e s u l t a d i s t i n c t  t o the p r e c i s e e l e v a t i o n a l d e l i m i t a t i o n o f stable  salinity  The scheme of i n t e r t i d a l s u b d i v i s i o n o u t l i n e d i n P a r t 1 i s a p p l i e d  developed f o r the s p e c i f i c case o f Boundary Bay t i d e s , and i t i s demon-  s t r a t e d t h a t much o f the z o n a t i o n r e l a t e d to c r i t i c a l Part  tidal  o f Boundary Bay t i d a l  3 supplements P a r t  2.  I t i s a study o f the sediment reworking and p a c i f i c a a p o l y c h a e t e which i s  abundant on the Boundary Bay t i d a l f l a t s . surface  f l a t s may be c a u s a l l y  levels.  size sorting c a p a b i l i t i e s of Abarenicola  and  and the Bay waters a r e  found on rocky i n t e r t i d a l s h o r e l i n e s e x p e r i e n c i n g  regimes.  The  e x i s t s , d e l i m i t e d p r i m a r i l y by e l e v a t i o n , which i s  comparable i n many r e s p e c t s zonation  consisting  By c o n s t a n t l y  t u r n i n g over the  sediments t h i s organism may w e l l i n f l u e n c e z o n a t i o n  on the t i d a l  flat,  i n p a r t i c u l a r the b i o t u r b a t i o n o f t h i s worm may be a f a c t o r l i m i t i n g the  extent  o f the a l g a l mat zone, one o f the f i v e major f l o r a l / s e d i m e n t o l o g i c a l  zones o f Boundary Bay t i d a l Part  flats.  4 moves onto the a c t i v e t i d a l  f l a t s of the Fraser Delta.  It i sa  study o f the d i s t r i b u t i o n o f the t h a l a s s i n i d e a n burrowing shrimps, C a l l i a n a s s a . californiensis  and Upogebia p u g e t t e n s i s  n a t u r a l l y and a b r u p t l y  on Roberts Bank.  Roberts Bank d i v i d e s  i n t o a 'marine' environment t o the s o u t h e a s t and a  b r a c k i s h environment t o the northwest.  The t r a n s i t i o n o c c u r s between the  7  Coalport to  causeway and Canoe Pass  ( F i g . 1).  I t was t h e r e f o r e f e l t  s p l i t P a r t 4 i n t o two s e c t i o n s , P a r t 4A d e a l i n g w i t h  an e x c l u s i v e l y  'marine' environment between the two man-made causeways on Roberts Bank and P a r t 4B d e a l i n g w i t h northern  and c e n t r a l Roberts Bank.  appropriate  southeastern  the marine t o b r a c k i s h t r a n s i t i o n on  The inter-causeway t i d a l f l a t s t u d i e d  i n P a r t 4A l i e s between the Tsawwassen f e r r y t e r m i n a l causeway and the Coal-; r . p o r t causeway ( F i g . 1). and  I t has many o f the c h a r a c t e r i s t i c s o f Boundary Bay  a s i m i l a r f l o r a l / f a u n a l zonation  which p r o b a b l y  result  i s developed,  .but t h e r e are d i f f e r e n c e s  from d i f f e r e n c e s i n the s t y l e of t i d a l channel  i n the two a r e a s , which i n t u r n i s a f u n c t i o n o f g r a i n s i z e . greater v a r i a b i l i t y i n Boundary Bay. higher  drainage  T h e r e ! i s much  i n the g r a i n s i z e of the s u b s t r a t e on t h i s t i d a l f l a t  Mud contents  than  o f the sediment a r e an o r d e r o f magnitude  and grainfsd-zer p l a y s an important  r o l e i n c o n t r o l l i n g the d i s t r i b u t i o n  of t h a l a s s i n i d e a n shrimps. T h a l a s s i n i d e a n shrimps a t t a i n t h e i r h i g h e s t  d e n s i t i e s on the i n t e r - c a u s e -  causeway t i d a l f l a t and the e f f e c t s o f g r a i n s i z e on shrimp d i s t r i b u t i o n and i n t e r a c t i o n s between the two s p e c i e s o f shrimp can r e a d i l y be analyzed environment where s a l i n i t y i n f o r m a t i o n from t h i s ment of n o r t h e r n  can be c o n s i d e r e d n o n - v a r i a b l e .  Armed w i t h the  t i d a l f l a t i n P a r t 4B the c o m p l e x i t i e s o f the e n v i r o n -  and c e n t r a l Roberts Bank ate' t a c k l e d where s a l i n i t y  an added v a r i a b l e among the f a c t o r s i n f l u e n c i n g shrimp d i s t r i b u t i o n . passing  becomes On  from the 'marine' to b r a c k i s h environment on c e n t r a l Roberts Bank the  f l o r a l / s e d i m e n t o l o g i c a l zones o f the t i d a l f l a t s and  i n an  a r e completely  shrimp d i s t r i b u t i o n responds t o the changes.  regarding  the apparent s a l i n i t y  which have important  t o l e r a n c e o f these  paleoenvironmental  restructured  Some d i s c o v e r i e s are made two s p e c i e s o f shrimp  implications.  8  :  REFERENCES  Ages, A. and W o o l l a r d , A., 1976, The t i d e s i n the F r a s e r E s t u a r y : Mar. S c i . Rept. 76-5, 100 p.  Pac.  B o r r a d a i l e , L.A., 1903, On the c l a s s i f i c a t i o n of the T h a l a s s i n i d e a : Mag. Nat. H i s t . , s e r i e s 7, 12, p. 534-551.  Ann.  L u t e r n a u e r , J.L. and Murray, J.W., 1973, S e d i m e n t a t i o n on the Western D e l t a f r o n t of the F r a s e r R i v e r , B r i t i s h Columbia: Can. J o u r . E a r t h .Sci., -, v. 10, p. 1642-1663. Mathews, W.H. and Shephard, F.P,,,'Yl962, S e d i m e n t a t i o n o f F r a s e r R i v e r D e l t a , B r i t i s h Columbia: B u l l . iAmer . A s s o c . P e t . G e o f C , " " v. 46, p.: 1416-1443. Pharo, C H . and Barnes, W.C., 197.S-', D i s t r i b u t i o n o f s u r f i c i a l sediments o f the c e n t r a l and s o u t h e r n S t r a i t o f G e o r g i a , B r i t i s h Columbia: Can. J o u r . E a r t h Sci"., v. 13, p. 684-696. Rhoads, D.C. and Young, 1970, The i n f l u e n c e o f d e p o s i t - f e e d i n g benthos on bottom s t a b i l i t y and community t r o p h i c s t r u c t u r e : J o u r . Marine Res. v. 28, p. 150-178. Waldichuk, M., 1957, P h y s i c a l oceanography o f the S t r a i t o f G e o r g i a , Columbia: J o u r . F i s h . Res. B r d . Canada, v. 14, p. 321-486.  British  Part 1 INTERTIDAL EXPOSURE ZONES:  A NEW  SCHEME  FOR SUBDIVIDING THE INTERTIDAL REGION  10 ABSTRACT  There are at l e a s t f o u r o r d e r s of c r i t i c a l intertidal  r e g i o n , at which the d u r a t i o n of continuous  gence 'jumps' - d a i l y and  18.6  t i d a l level within  year  (1st o r d e r ) , monthly  (4th o r d e r )  critical  and  the aquazone.  tidal levels.  Daily c r i t i c a l markedly  tidal  amphizone  t i d a l l e v e l s d i v i d e the atmozone  lower subzones.  order)  different  submergence d u r a t i o n - the atmozone, the  Monthly c r i t i c a l  aquazone i n t o upper and  exposure or submer-  (2nd o r d e r ) , annual (3rd  l e v e l s d e l i m i t three exposure zones which e x p e r i e n c e extremes i n exposure and  the  and  S u b d i v i s i o n of the amphizone i s  o n l y p o s s i b l e f o r mixed t i d e s .  T h i s scheme allows  intertidal  regions  different astronomically c o n t r o l l e d tides,  and may  c a u s a l l y r e l a t e d to i n t e r t i d a l  be  experiencing  zonation.  c r o s s c o r r e l a t i o n between  11  Introduction  The  study o f i n t e r t i d a l z o n a t i o n has a t t r a c t e d the a t t e n t i o n o f marine  b i o l o g i s t s s i n c e the b e g i n n i n g  of nineteenth  century  e x i s t s on the t o p i c ( R i c k e t t s and C a l v i n , 1968,). studying  and a v a s t  literature  G e o l o g i s t s have been  the d i s t r i b u t i o n o f organisms, both f l o r a l and f a u n a l , on carbonate  tidal flats  f o r s e v e r a l decades, and more r e c e n t l y the expanding study o f  animal-sediment r e l a t i o n s h i p s has i n c l u d e d study o f organism d i s t r i b u t i o n on clastic  tidal flats.  A r e c o r d o f the presence and d i s t r i b u t i o n o f i n t e r t i d a l  organisms i s p r e s e r v e d structures. accepted  Despite  this extensive  exception  sedimentary  r e s e a r c h over many years no u n i v e r s a l l y  scheme f o r s u b d i v i d i n g the i n t e r t i d a l r e g i o n e x i s t s .  have d i s c u s s e d  Geologists  the problem o f d e f i n i n g i n t e r t i d a l l o c a t i o n l i t t l e , w i t h the  o f Ginsburg e t a l . (1970) who advocate the use o f 'exposure  (mean percent  exposure).  play i n i n t e r t i d a l 1977).  i n a n c i e n t sediments i n the form o f b i o g e n i c  Among, b i o l o g i s t s  z o n a t i o n has been a matter o f much c o n t r o v e r s y  A t one extreme there  r e l a t e d to z o n a t i o n  the extent, of the r o l e  index'  which:tides (Carefoot,  are those who b e l i e v e t h a t t i d e s a r e n o t c a u s a l l y  (Stephenson and Stephenson, 1949) and they advocate a  scheme o f i n t e r t i d a l s u b d i v i s i o n based p u r e l y on b i o l o g i c a l grounds the upper l i m i t o f b a r n a c l e s  or laminarians,  etc.).  (e.g.,  A t the o t h e r extreme a r e  those who b e l i e v e t h a t s p e c i f i c t i d a l l e v e l s can be c a u s a l l y r e l a t e d to zone b o u n d a r i e s (Doty, 1957).  The c u r r e n t  appears to be t h a t the i n t e r t i d a l biology, while  zone should be s u b d i v i d e d  on the b a s i s o f  only l o o s e l y c o r r e l a t i n g t h i s s u b d i v i s i o n to mean t i d a l  or mean exposure l e v e l s adhering  consensus o f o p i n i o n among b i o l o g i s t s  ( R i c k e t t s and C a l v i n , 1968; Chapman, 1974).  to t h i s v i e w p o i n t  levels  While  Chapman and Chapman .believe, t h a t "when more i s known  -abo.ut the c a u s a l . r e l a t i o n s h i p s between t i d a l phenomena and. the major b e l t • nisms jtt would probably :  be more d e s i r a b l e to use t i d a l d a t a " (1973, p. 353).  orgaBut  12 there i s no reason to expect o r mean exposure  causal relationships  between mean t i d a l  l e v e l s and zone b o u n d a r i e s , and the c o n t i n u e d use o f mean  t i d a l v a l u e s to d e s c r i b e l o c a t i o n  i n the i n t e r t i d a l r e g i o n i n h i b i t s  understanding o f causal r e l a t i o n s h i p s  further  between t i d a l phenomena and z o n a t i o n .  F u r t h e r , schemes based on mean t i d a l l e v e l s cannot j u s t i f i a b l y cross c o r r e l a t e  levels  be used t o  areas e x p e r i e n c i n g mixed t i d e s w i t h those e x p e r i e n c i n g semi-  d i u r n a l , because t h e r e i s no reason t o t h i n k t h a t a s e m i - d i u r n a l mean t i d a l level  (.e.g., mean h i g h water) i s c o r r e l a t i v e w i t h the ' e q u i v a l e n t ' mixed  mean t i d a l l e v e l (mean h i g h e r h i g h water) e i t h e r o r d u r a t i o n o f continuous exposure  i n r e s p e c t to the frequency  o r submergence.  schemes be used, because i n the c a l c u l a t i o n  Nor can mean  o f mean exposure  i s made between continuous and d i s c o n t i n u o u s exposure  exposure  no d i s t i n c t i o n  o r submergence.  C r i t i c a l T i d a l Levels  The  concept on which the scheme p r e s e n t e d here i s based - c r i t i c a l  t i d a l l e v e l s - was f i r s t  d e s c r i b e d over t h i r t y years ago by Doty  and b i o l o g i s t s were aware o f the concept  l o n g b e f o r e then (Doty, 1957).  • however, does n o t advocated the use o f c r i t i c a l  tidal levels  the" i n t e r t i d a l r e g i o n , because he c o n s i d e r s " such ~a system • s a t i s f a c t o r y ^(T9'57',' p. 542).'" 1  Critical  i n s u b d i v i s i o n , of  'too complex to be ....'4  o r submergence changes  manner a t the h e i g h t o f a c r e s t o r t r o u g h i n a d a i l y ,  monthly, annual o r l o n g e r term t i d a l confused w i t h the ' c r i t i c a l  tidal  cycle.  T h i s d e f i n i t i o n s h o u l d n o t be  l e v e l s ' d i s c u s s e d by Underwood (1978) and  o t h e r workers in.'.'Britain (Colman, 1933; Evans, 1947a, b, 1957; Lewis, which are d e f i n e d by breaks clumping  Doty,  t i d a l l e v e l s a r e d e f i n e d here,; as  l e v e l s a t which the d u r a t i o n o f continuous exposure abruptly i n a s t e p - l i k e  (1946),  i n s l o p e o f mean exposure  o f the upper and lower l i m i t s of organisms  1964),  curves and/or by the  at p a r t i c u l a r  tidal  levels.  13  I t has n o t , u n t i l now, been p o i n t e d out t h a t there are s e v e r a l o r d e r s o f critical of  t i d a l l e v e l s which can be r e c o g n i z e d , depending on the d u r a t i o n  the l u n a r , s o l a r o r e a r t h l y c y c l e r e s p o n s i b l e ( F i g . 1 ) . D a i l y ( 1 s t o r d e r )  critical  t i d a l l e v e l s are a r e s u l t o f the e a r t h ' s r o t a t i o n on i t s a x i s  combined w i t h daily tidal considered  Of the t h r e e p r i n c i p a l types of  c y c l e - s e m i - d i u r n a l , d i u r n a l and mixed - the mixed t i d e can be to be the g e n e r a l case and s e m i - d i u r n a l and d i u r n a l t i d e s to be  s p e c i a l forms. for  the d e c l i n a t i o n of the moon.  F o r mixed t i d e s t h e r e are two h i g h waters and two low waters  each l u n a r day o f 24 hours and 50 minutes, but s u c c e s s i v e h i g h and low  waters d i f f e r i n h e i g h t due to the e f f e c t s o f the moon's d e c l i n a t i o n .  On  any p a r t i c u l a r day an i n t e r t i d a l r e g i o n e x p e r i e n c i n g mixed t i d e s can be subdivided into f i v e h i g h and low waters  'exposure l e v e l s , ' which a r e d e f i n e d by the h e i g h t s o f (Fig. l a ) .  The d u r a t i o n o f continuous  mergence i s a t l e a s t h a l v e d o r doubled the n e x t .  on p a s s i n g  exposure o r sub-  from one exposure l e v e l t o  F i g u r e l a i s somewhat o v e r - s i m p l i f i e d , as mixed t i d e s have  both  a h e i g h t asymmetry and a time asymmetry, and the times between s u c c e s s i v e h i g h t i d e s and s u c c e s s i v e low t i d e s a r e n o t e q u a l due to l a g e f f e c t s which are dependent on t i d a l range.  For example, the time between h i g h e r  water and lower h i g h water i s l e s s and  the next h i g h e r h i g h water.  continuous  than  the time between lower h i g h water  As a r e s u l t ,  the maximum d u r a t i o n of  exposure or submergence i s not e x a c t l y h a l v e d or doubled on  l e a v i n g Exposure L e v e l 3.  Nevertheless,  t h e r e i s an abrupt  step i n exposure  o r submergence d u r a t i o n o f the o r d e r o f magnitude i n d i c a t e d .  I n areas  e x p e r i e n c i n g s e m i - d i u r n a l t i d e s the moon's d e c l i n a t i o n has l i t t l e on the t i d e s and thus heights.  high  influence  they l a c k a pronounced d i u r n a l i n e q u a l i t y i n t i d a l  As a r e s u l t , Exposure L e v e l s 2 and 4 are suppressed,  a very narrow e l e v a t i o n range.  spanning  only  I n r e g i o n s e x p e r i e n c i n g d i u r n a l t i d e s the  moon's d e c l i n a t i o n has such a pronounced i n f l u e n c e on the t i d e t h a t the lower  14 F i g u r e 1.  (a) Schematic d a i l y t i d a l curves f o r the t h r e e main types o f tide. Shading i n d i c a t e s submergence. F o r mixed t i d e s t h e r e are f o u r c r i t i c a l t i d a l l e v e l s (dashed l i n e s ) a t which the d u r a t i o n of exposure o r submergence ' j.umps' and which d e f i n e f i v e exposure l e v e l s w i t h i n which exposure and submergence changes c o n t i n u o u s l y with respect to e l e v a t i o n . H i g h e r h i g h water d e f i n e s the boundary between Exposure L e v e l s 1 and 2, and i s a c r i t i c a l t i d a l l e v e l above which the d u r a t i o n of exposure doubles from l e s s than one l u n a r day t o at l e a s t n e a r l y two. Lower h i g h water d e f i n e s the boundary between Exposure L e v e l s 2 and 3 and i s a level," above which the. d u r a t i o n ' o f exposure doubles from l e s s than h a l f a l u n a r day to j u s t under one l u n a r day. Equivalent c r i t i c a l t i d a l l e v e l s l i e •• at. the h e i g h t s o f h i g h e r low water and lower low water but i n v o l v e s t e p s i n submergence d u r a t i o n . They d e f i n e Exposure L e v e l s 4 and 5. The same c r i t i c a l t i d a l l e v e l s and expos u r e l e v e l s can be r e c o g n i z e d f o r s e m i - d i u r n a l tides.' Exposure L e v e l 3 cannot be d e f i n e d f o r d i u r n a l t i d e s because they l a c k lower h i g h water and h i g h e r low water s t a g e s . (b) The p r e d i c t e d d a i l y h e i g h t s o f lower low water a t P o i n t A t k i n s o n , B.C. between August and November, 1977 a r e p l o t t e d as dots. The low waters are modulated i n t o two neap t i d e s and two s p r i n g t i d e s p e r month. S u c c e s s i v e s p r i n g t i d e s are of d i f f e r e n t ranges. The s p r i n g t i d e of l e s s e r range d e f i n e s a c r i t i c a l t i d a l l e v e l a t which d u r a t i o n of continuous submergence jumps from about 10 t o 20 days, and t h a t o f g r e a t e r range a jump from about 24 to 45 days. (c) Annual c r i t i c a l l e v e l s are d e f i n e d by the s p r i n g h i g h e r h i g h waters o f June and December f o r p r e d i c t e d t i d e s i n 1977/78 a t P o i n t A t k i n s o n , B.C. Dots i n d i c a t e h e i g h t s o f s p r i n g and neap tides. The s p r i n g h i g h t i d e s o f June, 1978 and December, 1978 are so s i m i l a r i n h e i g h t t h a t these two c r i t i c a l t i d a l l e v e l s merge i n t o one, i n v o l v i n g a jump from about s i x months to at l e a s t n e a r l y two y e a r s o f continuous exposure. The s p r i n g h i g h t i d e of December, 1977 was h i g h e r and d e f i n e s a c r i t i c a l t i d a l l e v e l above which the d u r a t i o n o f exposure i s at l e a s t n e a r l y three years. (d) The l e v e l of the lowest;.low water ( i . e . , extreme s p r i n g lower low water) f o r each y e a r from 1967 t o .198.7-r a t Tsawwassen, B.C. i s graphed. T h i s l e v e l has r i s e n g r a d u a l l y from about -3.1 m G e o d e t i c Datum i n 1968 to about -2.6 m G e o d e t i c Datum i n 1978 based on observed t i d a l r e c o r d s . Mean s p r i n g lower low water ( i . e . , the mean o f twelve monthly s p r i n g lower low waters f o r each y e a r ) h e l p s d e f i n e the t r e n d . The p r e d i c t e d t r e n d s o v e r the next n i n e y e a r s a r e dashed i n . The l e v e l of the lowest extreme s p r i n g lower low water i n December, 1968 d e f i n e s a c r i t i c a l t i d a l l e v e l below which the d u r a t i o n o f continuous submergence jumps from about 18 y e a r s to at l e a s t n e a r l y 36 y e a r s .  15  A. DAILY C R I T I C A L  TIDAL  LEVELS  DIURNAL  SEMI-DIURNAL  --fl— c  2  +  JJj 0  1 Lunar Days  B. MONTHLY  2  0  CRITICAL  TIDAL  '. KftA5  - °H  e  + 2  o«  It  a -  1 Lunar1 Days  ui  2  LEVELS  (\ ft /  h-to  <D > 0 - 2 0 .-:  45  2  "A 1  O **  |  -I.5H  -3.04  I--3.0 Aug.  C. A N N U A L E  _  |  h-2.5  Sept.  CRITICAL  Oct.  TIDAL  Nov.  LEVELS  S 3 y«ars  *2.0n  • 2.0  ——r r ^ i 2 years  2 •i.s-l w HHW  V  • 1.5 U J V *• '•  ;  O  • 1.0-  (-•1.0  T  N  '  D  '  J  '  F  '  M  '  A  '  M  '  D. FOURTH ORDER C R I T I C A L TIDAL £  Masn  -2.25  c o 3 -2.KH  J  '  J  '  A  S  1  LEVEL  Spring  Lower Low Walar • :\  Extreme  • Tl O 0  Spring  O  -2.754  -2.25  E  '2.50  c o (0 > s  -2.75  2  o -3.00H - - 18 years - S 3 6 years • •3.25  1 — i — i — r 1967  ~i—i—i—i—r 1 1972  r- ~ i — i — r  1977  -3.00  -|—r n — r i — r 1982  | o •  o  0  * Lower Low Watar 2  = > 0  -6 months  1987  •o o 0  -3.25  16  h i g h water and h i g h e r  low water stages  i n e q u a l i t y i n the t i d e s .  As a r e s u l t Exposure L e v e l 3 i s absent.  these d i f f e r e n c e s between t i d a l f e a t u r e s i n common.  a r e e l i m i n a t e d due to extreme d i u r n a l  The step  types the three  Despite  types have two important  i n exposure d u r a t i o n  i n going  from Exposure  L e v e l 2 to Exposure L e v e l 1, i n v o l v i n g a jump from l e s s than one l u n a r day of continuous exposure to a t l e a s t n e a r l y t h r e e t i d a l types,  two l u n a r days, i s common to a l l  as i s the jump i n submergence d u r a t i o n i n p a s s i n g  Exposure L e v e l 4 to Exposure L e v e l 5, which s i m i l a r l y  from  i n v o l v e s a jump from  l e s s than one l u n a r day o f continuous submergence to a t l e a s t n e a r l y two l u n a r days o f continuous submergence.  These two c r i t i c a l  tidal levels  defined-by  the fundamental c y c l e o f the l u n a r day form the b a s i s o f the scheme of i n t e r t i d a l s u b d i v i s i o n to be o u t l i n e d h e r e . F i r s t order  critical  t i d a l l e v e l s a r e m o d u l a t e d ' i n t o monthly c y c l e s  o f s p r i n g and neap t i d a l p e r i o d s which d e f i n e 2nd o r d e r t i d a l levels  (Fig. l b ) .  (monthly)  Depending on the t i d a l r e g i o n the monthly c y c l e  can be caused by the phases o f the moon ( p e r i o d 29.5 d a y s ) , c y c l e o f the moon ( p e r i o d 27.2 days), moon s e p a r a t i o n  critical  ( p e r i o d 27.5 days).  the d e c l i n a t i o n a l  o r the apogee/perigee c y c l e i n e a r t h These c y c l e s a r e a l l o f very s i m i l a r  .duration as they a r e a l l governed by the p e r i o d o f . t h e moon's o r b i t the e a r t h . successive  There are two neap and two s p r i n g t i d a l p e r i o d s spring t i d a l periods  p e r i o d d e f i n e s a 2nd order Figure  lb illustrates  Pt. Atkinson,  B.C.  are o f d i f f e r e n t range.  critical  these c r i t i c a l  The f i r s t  around  each month b u t  Each s p r i n g  tidal  t i d a l l e v e l f o r both h i g h and low waters. t i d a l l e v e l s f o r lower low water a t  critical  t i d a l l e v e l i s d e f i n e d by the s p r i n g  t i d e o f l e s s e r range and i n v o l v e s a jump from about 10 to 20 days o f continuous  submergence, w h i l e  the second c r i t i c a l  t i d a l l e v e l i s d e f i n e d by  the s p r i n g t i d e o f g r e a t e r range and i n v o l v e s a step days o f continuous submergence.  from about 24 t o 45  The s i t u a t i o n i s the same f o r h i g h e r  high  17 w a t e r . ( o r h i g h water) except  t h a t i t i n v o l v e s s t e p s i n exposure r a t h e r  than submergence. Second o r d e r c r i t i c a l  tidal  c y c l e s which d e f i n e 3 r d o r d e r  l e v e l s a r e i n t u r n modulated i n t o  (annual)  critical  tidal  levels  annual  (Fig. l c ) .  T i d a l ranges a r e maximized i n June and December at the time o f the s o l s t i c e s when the sun i s over, the t r o p i c s , and minimized i n March and September when the sun i s over  a t the equinoxes  the equator.  T i d a l ranges a r e  g r e a t e r i n December than i n June because the e a r t h i s n e a r p e r i h e l i o n (nearest the sun) i n December w h i l e i t i s n e a r a p h e l i o n i n June. Pt.  Atkinson t i d e s ,  3rd o r d e r c r i t i c a l  tidal  For  l e v e l s a r e d e f i n e d by the s p r i n g  h i g h t i d e s o f June and December ( F i g . l c ) . That o f June i n v o l v e s a jump i n the d u r a t i o n o f continuous year, while nearly  exposure from about s i x months to almost one  t h a t i n December i n v o l v e s a jump from about one y e a r to a t l e a s t  two y e a r s . / I n F i g u r e v i e these .two s t e p s .are .top_.close.-„tp_resol-v.e.  There"are^equivalent  critical  Third order c r i t i c a l  tidal  tidal  levels  f o r lower low water  ( o r low w a t e r ) .  l e v e l s a r e i n t u r n modulated by an 18.6 year  s o l i - l u n a r c y c l e d e f i n i n g 4th order c r i t i c a l  tidal  levels  (Fig. Id).  Every  18.6 y e a r s , when the maximum d e c l i n a t i o n o f the moon c o i n c i d e s w i t h the maximum d e c l i n a t i o n o f the sun, t i d a l  ranges a r e maximized.  This e f f e c t i s  o n l y d e t e c t a b l e f o r s p r i n g lower low waters f o r t i d e s i n the southern of  Georgia  ( F i g . I d ) . The lowest  1968/69 d e f i n e s a c r i t i c a l mergence p r o b a b l y  tidal  l e v e l o f lower low water reached  around  l e v e l a t which the maximum d u r a t i o n o f sub-  jumps from about 18 to 36 y e a r s , although  records are a v a i l a b l e t o ' c o n f i r m  Strait  insufficient  this.  There a r e , no doubt, h i g h e r order c r i t i c a l  tidal  l e v e l s beyond 4 t h o r d e r  d e f i n e d by v e r y l o n g term a s t r o n o m i c a l c y c l e s , but r e c o r d s a r e not a v a i l a b l e to  analyze  them.  A l l o f the c r i t i c a l  tidal  nized f o r a l l astronomically controlled  l e v e l s d e f i n e d above can be r e c o g -  t i d e s the w o r l d o v e r , w i t h the  18  e x c e p t i o n o f the 1 s t o r d e r L e v e l 3, which cannot be  (daily)  critical  t i d a l levels defining  defined for diurnal  tides.  Exposure  Thus, c r i t i c a l  l e v e l s o f f e r a means of c r o s s c o r r e l a t i o n between d i f f e r e n t t i d a l r e g a r d l e s s of the t i d a l correlation. Georgia with  types  involved.  Here the d e c l i n a t i o n a l  coast of Canada ( S t . John'y~T"; New  regions  F i g u r e 2a i l l u s t r a t e s such a  mixed t i d e s of the southern  on the P a c i f i c coast of Canada (Tsawwassen, B.C.)  the a n o m a l i s t i c s e m i - d i u r n a l  tidal  t i d e s of the Bay  S t r a i t of  are c r o s s  o f Fundy on  cross  the  correlated Atlantic  Brunswick) . u s i n g extreme- c r i t i c a l  tidal  l e v e l s . a t which the maximum d u r a t i o n of continuous, exposure or submergence' jumps.:: D e s p i t e critical John.  t i d a l l e v e l s a t Tsawwassen can be  • I n s e v e r a l i n s t a n c e s one  s p l i t into vice  the very d i f f e r e n t types of t i d e in>the. two  two  o r three c l o s e l y  cross correlated  critical  a r e a s , 24 extreme w i t h 18 at S t .  t i d a l l e v e l at S t . JohnV  spaced steps at Tsawwassen, and  is  occasionally  versa.  Exposure Zones  The rotation  fundamental, 1 s t o r d e r c r i t i c a l about i t s a x i s can be  F i g u r e 2a i n t o  those between Exposure L e v e l s 1 and  Exposure L e v e l s 4 and than one  The  critical  extreme c r i t i c a l  earth's  are  2 where the d u r a t i o n of exposure drops l u n a r day,  and  between  5 where the d u r a t i o n of submergence jumps from l e s s  l e v e l , and  l u n a r days.  The  The  former c r i t i c a l  tidal  the l a t t e r i t s h i g h e s t l e v e l , i n March  September at the time of the equinoxes, and r a t e d i n F i g u r e 2a.  the  t i d a l l e v e l s used  l u n a r days to l e s s than one  to at l e a s t n e a r l y two  reaches i t s lowest  caused by  used to s u b d i v i d e b o t h i n t e r t i d a l r e g i o n s i n  three exposure zones.  from at l e a s t n e a r l y two  t i d a l levels  these extreme l e v e l s are  i n t e r t i d a l 'amphizone' l i e s between these  t i d a l l e v e l s and  level  and illust-  two  thus forms the core to the i n t e r t i d a l  19  F i g u r e 2. (a) Cross c o r r e l a t i o n o f extreme c r i t i c a l t i d a l l e v e l s between the i n t e r t i d a l r e g i o n s o f S t . John> \ ..-New Brunswick and Tsawwassen, B.C. Based on p r e d i c t e d t i d e s f o r 1978 f o r S t . John\_ and observed t i d e s between June, 1977 and June, 1978 a t Tsawwassen. The numbers above and below c r i t i c a l t i d a l l e v e l s i n d i c a t e the maximum d u r a t i o n o f continuous exposure i n days i n the case o f atmozonal c r i t i c a l t i d a l l e v e l s , and the maximum d u r a t i o n of continuous submergence i n days i n the case of aquazonal c r i t i c a l t i d a l l e v e l s . F o r example a t the upper l i m i t o f the lower atmozone a t S t . John^ the jump i s from 10 to 20 days and the n e x t c r i t i c a l t i d a l l e v e l up i n v o l v e s a jump from 26 to 72 days. I n the case of atmozonal c r i t i c a l t i d a l l e v e l s o n l y the lowest l e v e l a t t a i n e d by a p a r t i c u l a r c r i t i c a l t i d a l l e v e l i s indicated. I n the case o f aquazonal c r i t i c a l t i d a l l e v e l s o n l y the h i g h e s t l e v e l a t t a i n e d by a p a r t i c u l a r c r i t i c a l t i d a l l e v e l i s i n d i ^ a cated, i . e . , o n l y extreme c r i t i c a l t i d a l l e v e l s are i n d i c a t e d . x  (b)  L e v e l s o f exposure zone boundaries over the p a s t t e n y e a r s a t Tsawwassen, B.C. based on observed t i d a l r e c o r d s . In the case o f the boundary between the lower atmozone and the upper atmozone t h e numbers above and below c r i t i c a l t i d a l l e v e l s i n d i c a t e t h e maximum d u r a t i o n o f exposure i n days. I n the case of the boundary between the upper aquazone and the lower aquazone the numbers above and below c r i t i c a l t i d a l l e v e l s i n d i c a t e the maximum d u r a t i o n o f submer-J gence i n days. On the extreme r i g h t hand s i d e o f the diagram h o r i z o n t a l b a r s i n d i c a t e the mean l e v e l s o f exposure zone b o u n d a r i e s w h i l e the v e r t i c a l b a r s i n d i c a t e the s t a n d a r d d e v i a t i o n from the mean. Mean l e v e l s are n o t i n d i c a t e d i n the case o f the b o u n d a r i e s o f the lower aquazone because they undergo s i g n i f i c a n t modulation by the e f f e c t s o f an 18.6 y e a r s o l i - l u n a r d e c l i n a t i o n a l c y c l e .  20  ST. J O H N  , NEW  Predicted  BRUNSWICK  Tides  (1978)  TSAWWASSEN, Observed  B. C .  Tides  1977-June,1978)  Mean  Levels  with S t d . Dev.  24 Upper  h2  Atmozone  19 23 _? 2 0 0 2 2 T7 24 . 28 _..i:=-.** Q ^ 7 " - : i T > « - - ' < i : : , . • =«... ..-.v. 14-. 2  2  3  2  2  0  2  !  3 19  -  :  10  10  9  - - '  9  9  8  8  1 1  — Lower  UJ _i UJ  Atmozone  1  Upper  1  2  4  9  20  22 22 2 3 . . -  -  v - ' 8 " ?  :  4  : : :  :  :  «  1  -1-|  — I  10 13 21  2  «> „  T8  1 7  „  J  1968  0  Upper  Aquazone  '22'«---..,. V« 21 ''•=' ,  1 1  28  0  Amphizone  J  1969  D  J  1970  1 9  * 1  Lower  6  8  2  D  4  2  ,  J  D  1971  J  D  1972  14  J  D  1973 (b)  J  o  o  10.;4->8  •2  1  '  tUJ  22  22 31 24  2  Aquazone  ' I ' "  ho  r• > UJ -I ' —1 U l  6.^.13...^  '•-•••:- - -"' 21 19  E  Amphizone  Lower  13..?.  h 1 +  5  8  0  o  UJ a O UJ O  —  7  z O  12-ro*"  1*4«  1 2  22  D  1974  J  D  J  D  h-3  I,,  ,11111,11, ,111,111111111.  J  1 9 7 5 " 1 9 7 6 " 1977  0  o o  UJ O  21 r e g i o n , e x p e r i e n c i n g b o t h exposure and submergence every l u n a r day (hence amphizone  from the Greek  "amphi' meaning b o t h ) .  Above the amphizone  lies  the 'atmozone' where the maximum d u r a t i o n o f exposure exceeds n e a r l y two l u n a r days.  The atmozone can be s u b d i v i d e d a t the l e v e l o f the lowest 2nd  order c r i t i c a l  t i d a l l e v e l which i n v o l v e s a jump i n exposure d u r a t i o n from  about 10 to 20 days.  Above t h i s l e v e l are a whole  2nd and 3rd order c r i t i c a l t i d a l l e v e l s .  s e r i e s o f c l o s e l y spaced  The upper l i m i t o f the atmozone  l i e s a t the l e v e l o f the h i g h e s t h i g h t i d e o f the y e a r . lies  Below the 'amphizone'  the 'aquazone' w i t h i n which the maximum d u r a t i o n o f submergence exceeds  nearly  two l u n a r days.  As i n the case o f the atmozone the 'aquazone' can  be s u b d i v i d e d i n t o an upper and lower p a r t a t the l e v e l o f the h i g h e s t 2nd order c r i t i c a l  tidal level.  The lower l i m i t o f the aquazone  of the lowest t i d e of the y e a r .  F o r mixed t i d e s  d i v i d e d a t the lowest l e v e l o f the c r i t i c a l  lower f r i n g e s .  the amphizone  can be sub-  t i d a l l e v e l between Exposure  L e v e l s 2 and 3 ( F i g . 2 a ) . For s e m i - d i u r n a l t i d e s s u b d i v i d e d because c r i t i c a l  l i e s a t the l e v e l  the amphizone  cannot be  t i d a l l e v e l s o n l y o c c u r w i t h i n i t s upper and  The i n t e r t i d a l  r e g i o n s h o u l d be c o n s i d e r e d  'open-ended' i n  the sense t h a t c r i t i c a l t i d a l l e v e l s of i n f i n i t e o r d e r and i n f i n i t e or submergence d u r a t i o n d e f i n e i t s upper and lower l i m i t s .  exposure  But f o r most  p r a c t i c a l purposes t h i s can p r o b a b l y be taken to l i e a t the l e v e l s o f the h i g h e s t and lowest 4 t h o r d e r c r i t i c a l 18 y e a r p e r i o d . s u p r a t i d a l zone.  t i d a l l e v e l s o c c u r r i n g w i t h i n an  Under t h i s system there would be no such t h i n g as the F o r those g e o l o g i s t s who d e f i n e s u p r a t i d a l as l y i n g  above  mean h i g h water, s u p r a t i d a l i s r o u g h l y e q u i v a l e n t to upper atmozonal. For t h i s scheme to be f e a s i b l e the l e v e l s o f the exposure zone and sub zone b o u n d a r i e s based on o b s e r v e d t i d a l r e c o r d s must l i e c l o s e to the same l e v e l each y e a r , o r , i f n o t , must f o l l o w a p r e d i c t a b l e t r e n d . illustrates  F i g u r e 2b  the l e v e l o f exposure zone and sub zone b o u n d a r i e s o v e r the p a s t  22 ten years  at Tsawwassen, B.C.  based on observed  t i d a l records.  e x c e p t i o n of the l i m i t s of the lower aquazone a l l boundaries the same l e v e l and less  (range  8-14  the s t a n d a r d  cm)  With  s t a y c l o s e to  d e v i a t i o n s from mean l e v e l s are 14  i n a t i d a l range of 5 m.  the  cm  O c c a s i o n a l l y , boundaries  e r r a t i c d e v i a t i o n s (e.g., the l i m i t s of the lower amphizone i n 1970, but  t h i s i s o n l y to be expected  extreme t i d a l l e v e l s and  as exposure zone boundaries  these may  or  o c c a s i o n a l l y be  show  Fig.  are d e f i n e d  the r e s u l t of  2b)  by  unusual,  u n p r e d i c t a b l e m e t e o r o l o g i c a l c o n d i t i o n s r a t h e r than p r e d i c t a b l e a s t r o n o m i c a l events.  Thus, t h i s system p r o b a b l y  c o u l d not be  r o l o g i c a l e f f e c t s dominate over a s t r o n o m i c a l are p r e d i c t a b l e (e.g., s e a s o n a l ) .  The  a p p l i e d to areas where meteo-  unless  upper and  the m e t e o r o l o g i c a l  lower l i m i t s of the  aquazone at Tsawwassen are s i g n i f i c a n t l y modulated by l u n a r c y c l e mentioned above and r i s e n about 30 cm over  i t s 1968/70 l e v e l by  m Geodetic  the mid  year  Q u i t e apart from t h e i r use  from a l e v e l of -1.8  Datum i n 1976/78.  I t s h o u l d r e t u r n to  Zonation  i n c r o s s c o r r e l a t i o n between d i f f e r e n t  t i d a l l e v e l s d e s c r i b e d above may  z o n a t i o n of f l o r a and  fauna.  be  tidal  and  c a u s a l l y r e l a t e d to the  inter-  Doty (1946), and Widdowson (1965) have  attempted to t e s t the t i d e f a c t o r h y p o t h e s i s zone l i m i t s w i t h c r i t i c a l  has  m, Geodetic  r e g i o n s t h e r e i s j u s t i f i c a t i o n f o r t h i n k i n g t h a t the exposure zones  tidal  soli-  to l a t e 1980's.  Intertidal  critical  lower  the upper l i m i t of the lower aquazone  the p a s t n i n e years  Datum i n 1968/70 to -1.5  the 18.6  effects  by comparing f l o r a l  and  faunal  t i d a l l e v e l s , b u t , i n the case of mixed t i d e s  t i d e f a c t o r h y p o t h e s i s w i l l never be proven o r d i s p r o v e n u s i n g t h i s  the  approach,  because, f o r areas e x p e r i e n c i n g mixed t i d e s , any p o i n t w i t h i n the  intertidal  r e g i o n w i l l at some time i n the year l i e w i t h i n a few  of a 1 s t  centimeters  o r d e r c r i t i c a l t i d a l l e v e l , s i n c e h i g h and low water s t a g e s span the whole i n t e r t i d a l region.  In a d d i t i o n , w i t h i n the upper atmozone and lower  there i s a very h i g h p r o b a b i l i t y  t h a t one or more 2nd o r 3rd o r d e r  aquazone  critical  t i d a l l e v e l s w i l l c o i n c i d e w i t h a zone boundary a t any e l e v a t i o n one chooses to s e l e c t .  The q u e s t i o n should not be "does the zone boundary  a c r i t i c a l t i d a l l e v e l ? , " but "which c r i t i c a l boundary  coincide with  t i d a l l e v e l ( s ) does the zone  c o i n c i d e w i t h and i s t h e r e any j u s t i f i c a t i o n f o r t h i n k i n g they a r e  causally related?."  Swinbanks  (1979) has demonstrated t h a t  Callianassa  c a l i f o r n i e n s i s , a t h a l a s s i n i d e a n burrowing shrimp, extends up to lower atmozonal e l e v a t i o n s on the F r a s e r D e l t a t i d a l f l a t s , but does not extend beyond an e l e v a t i o n at'which the-maximum d u r a t i o n of continuous exposure'(rises a b r u p ^ l y f ^ r o m 14^-to^'9^Jl'ays;,; H because p h y s i o l o g i c a l s t u d i e s (Thompson and :  P r i t c h a r d , 1969)  i n d i c a t e t h a t Caboye.) t h i s p o i n t a n o x i a due to exposure would  be l e t h a l to C a l l i a n a s s a .  Upogebia p u g e t t e n s i s , another t h a l a s s i n i d e a n  burrowing shrimp extends up to but not beyond amphizone.  W i t h i n the upper amphizone  the lower l i m i t o f the upper  the d u r a t i o n of a n o x i a d u r i n g p e r i o d s  of Exposure L e v e l 2 i s p r o b a b l y l e t h a l to p o s t m o l t Upogebia  (Swinbanks,  1979).  The s a l t m a r s h e s of the F r a s e r D e l t a are r e s t r i c t e d to upper atmozonal e l e v a tions.  T h i s may be because s a l t m a r s h p l a n t s'eedlangs r e q u i r e the p e r i o d s o f  exposure i n excess o f 10 days which occur i n the upper atmozone i n the s p r i n g , i n o r d e r to germinate and r o o t s u c c e s s f u l l y  (Swinbanks, 1979).  to mixed t i d e s , f o r s e m i - d i u r n a l t i d e s c r i t i c a l w i t h i n the amphizone  except near i t s l i m i t s  t i d a l l e v e l s do not o c c u r  ( F i g . 2a).  Significantly biolo-  g i s t s have found t h a t f o r s e m i - d i u r n a l t i d e s the m i d - i n t e r t i d a l littoral)  In c o n t r a s t  ;  (or mid-  r e g i o n s are d e v o i d o f f l o r a l or f a u n a l zone b o u n d a r i e s (Stephenson  and Stephenson, 1949), whereas f o r mixed t i d a l r e g i o n s a major zone o c c u r s c l o s e to mean sea l e v e l and c r i t i c a l  ( R i c k e t t s and C a l v i n , 1968).  boundary  I f exposure zones  t i d a l l e v e l s are c a u s a l i n i n t e r t i d a l z o n a t i o n , t h i s  observation  might be a n t i c i p a t e d _a p r i o r i .  ACKNOWLEDGEMENTS  I  thank the R e g i o n a l T i d a l S u p e r i n t e n d e n t , W.J. Rapatz,  and F.  Stevenson o f the Canadian Hydrographic S e r v i c e , I n s t i t u t e o f Ocean S c i e n c e s Sidney, B.C. f o r p r o v i d i n g New Brunswick.  t i d a l r e c o r d s f o r Tsawwassen, B.C. and S t . John}  Dr. J.W. Murray, Dr. W.C  Barnes, Dr. C D . L e v i n g s and  Dr. L.F.„Giovando c r i t i c a l l y read the m a n u s c r i p t .  25 REFERENCES  C a r e f o o t , T . C , ±917, P a c i f i c Seashores: J . J . Douglas L t d . , Vancouver, 208 p.  a guide  to I n t e r t i d a l  Ecology:  Chapman, V . J . ( e d . ) , 1974, Saltmarshes and s a l t d e s e r t s o f the w o r l d e d . ) : Leonard H i l l , London, 392 p. . and Chapman, D.J. (eds.) , 1973, The a l g a e : Co. L t d . , London, U n i v e r s i t y P r e s s , Glasgow, 497 p.  (2nd  MacMillan  and  Colman, J . , 1933, The n a t u r e of the i n t e r t i d a l z o n a t i o n of p l a n t s and J o u r . mar. b i o l . Ass. U.K.", v.- 18, p. 435-476.  animals:  Doty, M.S., 1946, C r i t i c a l t i d e f a c t o r s t h a t are c o r r e l a t e d w i t h the v e r t i c a l d i s t r i b u t i o n of marine algae and o t h e r organisms a l o n g the P a c i f i c Coast: E c o l o g y , v. 27, p. 315-328. , 1957, p. 535-585.  Rocky i n t e r t i d a l s u r f a c e s :  G e o l . Soc. Amer. Mem.  Evans, R.G., 1947a, The i n t e r t i d a l ecology of Cardigan Bay: v. 34, p. 2 7 3 - 3 0 9 . . . ' ; . ' J. ".-~ ' ' ~<' '-•  Jour.  67,-. v.  1,  Ecol.,  :  ; , 1947b, The i n t e r t i d a l ecology o f ( s e l e c t e d l o c a l i t i e s , i n the /Plymouth, neighbourhood: Jour., mar. b i o l . Ass. U.K., v. 27", "p. 173-218. , 1957, The i n t e r t i d a l ecology of some l o c a l i t i e s on the c o a s t of France: J o u r . Ecol.", v. 45, p. 245-271.  Atlantic  Ginsburg, R.N., B r i c k e r , O.P. , Wanless, H.R. and G a r r e t t , P., 1970, Exposure index and sedimentary s t r u c t u r e s of a Bahama t i d a l f l a t ( a b s t r . ) : Geol. Soc. Amer. A b s t r . , v. 2, No. 7, p. 744-745. Lewis, J.R.., 1964, London, 323 p.  The  e c o l o g y of rocky s h o r e s :  English Universities  R i c k e t t s , E.F. and C a l v i n , J . ( e d s . ) , 1968, Between P a c i f i c T i d e s S t a n f o r d U n i v e r s i t y P r e s s , S t a n f o r d , C a l i f o r n i a , 614 p.  Press,  (4th e d . ) :  Stephenson, T.A. and Stephenson, A., 1949, The u n i v e r s a l f e a t u r e s of z o n a t i o n between t i d e marks on rocky c o a s t s : J o u r . E c o l . , v. 37, p. 289-305. Swinbanks, D.D., 1979, Environmental f a c t o r s c o n t r o l l i n g f l o r a l z o n a t i o n and the d i s t r i b u t i o n of burrowing and t u b e - d w e l l i n g organisms on F r a s e r D e l t a t i d a l f l a t s , B r i t i s h Columbia: unpub. Ph.D. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B.C. Thompson, R.K. and P r i t c h a r d , A.W., 1969, R e s p i r a t o r y adaptions o f two burrowing c r u s t a c e a n s , C a l l i a n a s s a c a l i f o r n i e n s i s and Upogebia p u g e t t e n s i s (Decapoda, T h a l a s s i n i d e a ) : B i o l . B u l l . , v. 136, p. 274-287.  26  Underwood, A . J . , 1978, A r e f u t a t i o n of c r i t i c a l t i d a l l e v e l s as determinants of the s t r u c t u r e of i n t e r t i d a l communities on B r i t i s h s h o r e s : J o u r . exp. mar. B i o l . E c o l . , v. 33, p.- 261-276. Widdowson, T.B., 1965, A survey o f the d i s t r i b u t i o n of i n t e r t i d a l algae a l o n g a c o a s t t r a n s i t i o n a l i n r e s p e c t t o s a l i n i t y and t i d a l f a c t o r s : Canada F i s h . Res. Board J o u r . , v. 22, p. 1425-1454.  Part 2 BIOSEDIMENTOLOGICAL ZONATION OF BOUNDARY BAY TIDAL FLATS, FRASER RIVER DELTA, BRITISH COLUMBIA  28 ABSTRACT  Boundary Bay t i d a l Fraser Delta.  f l a t s l i e on the i n a c t i v e s o u t h e r n f l a n k o f the  The Bay waters a r e c l e a r , and have s a l i n i t i e s which are  'normal marine' f o r the S t r a i t o f G e o r g i a . sediments v a r i e s l i t t l e ,  The g r a i n s i z e o f the s u r f a c e  c o n s i s t i n g almost e n t i r e l y of very f i n e t o f i n e ,  w e l l to v e r y w e l l s o r t e d sands, which show a g r a d u a l f i n i n g trend.  shorewards  There are f i v e f l o r a l / s e d i m e n t o l o g i c a l zones on the t i d a l  flats,  which a r e , from the s h o r e l i n e seawards, the s a l t m a r s h zone, the a l g a l mat zone, the upper sand wave zone, the e e l g r a s s zone and the lower sand wave zone.  The zones seaward of the s a l t m a r s h have d i s t i n c t i v e macrofaunal commu-  n i t i e s , p r o d u c i n g assemblages o f b i o g e n i c sedimentary s t r u c t u r e s  diagnostic  o f each zone. The lower l i m i t o f the s a l t m a r s h l i e s a t the lower l i m i t o f the upper atmozone, a l e v e l above which the maximum d u r a t i o n o f exposure r i s e s from about 12 to 40 days.  The lower l i m i t  abruptly  o f the a l g a l mat zone l i e s a t the  lower l i m i t o f the lower atmozone, a l e v e l above which the maximum d u r a t i o n of exposure jumps from l e s s than one t o n e a r l y two l u n a r days.  The  upper l i m i t o f the e e l g r a s s zone l i e s a t the upper l i m i t o f the lower amphizone, a l e v e l above which the maximum d u r a t i o n o f exposure jumps from about 0.5 to ;QT7 l u n a r days. Topography  These " c o r r e l a t i o n s " ' a r e "beTi'eved' to b e c a u s a l . -  o f s m a l l and l a r g e s c a l e c r e a t e s l a t e r a l h e t e r o g e n e i t y  w i t h i n the b i o f a c i e s o f each zone.  The a l g a l mat zone and the e e l g r a s s  zone a r e . f l a t , on the l a r g e s c a l e . - H o w e v e r , i n b o t h zones microtoppgraphy o f b i o g e n i c o r i g i n , o n l y a few c e n t i m e t e r s h i g h , p r o f o u n d l y f a u n a l d i s t r i b u t i o n p a t t e r n s on the l o c a l s c a l e . is  influences  The upper sand wave zone  c h a r a c t e r i z e d by s y m m e t r i c a l sand waves w i t h wavelengths o f the o r d e r  of 30 m and very low amplitudes (<0.1 m), which p r o b a b l y form i n response  29  to  s e a waves d u r i n g s e v e r e w i n t e r  most o f  the  troughs  of  time.  Faunal d e n s i t i e s maximize i n  these sand waves.  are of h i g h e r  amplitude  in outline  Faunal d e n s i t i e s  in  over  The s a n d w a v e s o f  and r e m a i n dormant the s h a l l o w the lower  this  and p r o b a b l y  zone a r e l o w ,  form i n  s a n d wave  response to  ( 6 0 m) ,  tidal  and p h y s i c a l s e d i m e n t a r y  zone  currents.  structures  biogenic.  In winter  the  floral  Bay and s u r f a c e s e d i m e n t The d e n s i t i e s o f biogenic sedimentary  zones r e t r e a t . transport  eight  The e n v i r o n m e n t a l e n e r g y o f  i n c r e a s e due t o w i n t e r  storm  macrofaunal organisms which produce  structures  w e r e d e t e r m i n e d o n two s u r v e y e d  both thalassinidean burrowing  the  v  The o r g a n i s m s i n v e s t i g a t e d w e r e C a l l i a n a s s a c a l i f o r n i e n s i s pugettensis,  for  water-filled  (up t o 0 . 5 m ) , h a v e l o n g e r w a v e l e n g t h s  are o f t e n lunate  dominate  storm a c t i v i t y  shrimps,  three  activity. distinctive transects.  and U p o g e b i a polychaete  worms,  A b a r e n i c o l a s p . , S p i o s p . a n d P r a x i l l e l a s p . , t h e b i v a l v e Mya a r e n a r i a and the  gastropods B a t i l l a r i a  distribution  patterns  sedimentary  structures  are i n t e r p r e t e d  and N a s s a r i u s m e n d i c u s .  o f each o r g a n i s m and the n a t u r e they produce are d e s c r i b e d .  as b e i n g t e m p o r a r y  burrows, which are mud-lined, burrows.  attramentaria  of  the  biogenic  Callianassa  feeding structures  The  burrows  whereas Upogebia  a r e s u g g e s t e d to be permanent  dwelling  30  INTRODUCTION The t o p i c  of  animal-sediment  increasing attention in fossil  sediments.  environments,  In  because of  and Dodge, 1 9 7 4 ) . seaboard of Howard,  sediments  their  in  subtidal  1 9 6 9 ; H o w a r d and D b r j e s ,  Bay o f  Risk et  c a r r i e d out Fundy  (Van S t r a a t e n ,  flats  both i n  although  1952; Reineck,  Aller  structures  eastern  Georgia (Frey 1973),  Canada at  1977; Featherstone  the  studies  has c e n t r e d on the  on t h e e a s t e r n s e a b o a r d o f  and  intertidal  several  1 9 7 2 ; Howard and F r e y ,  in particular  recent  has f o c u s e d on  at Sapelo I s l a n d ,  Biogenic sedimentary  by European w o r k e r s ,  receiving  (Rhoads and Y o u n g , 1 9 7 0 ;  tidal  ( R i s k and M o f f a t ,  a l . , 1976).  literature,  access,  areas  in particular  has been  interest  ease of  Work o n c l a s t i c  the U . S . A . ,  are a l s o being Basin,  sedimentological  recent  have been c a r r i e d out  relationships  for  1958; S e i l a c h e r , 1964; D o r j e s ,  studies  Minas  and R i s k ,  have been  German a n d D u t c h ,  and  and  1977;  studied  many 1970;  years Schafer,  1 9 7 2 ) . 'This study, ern flank carried  of  centred  o n B o u n d a r y Bay t i d a l  the F r a s e r D e l t a ,  out on the  tidal  i s one i n a s e r i e s o f  flats  of  of  the s u r f a c e  floral/faunal and e x p o s u r e flats  sediments  (Swinbanks  can p l a y  the  flats  of  and M u r r a y ,  Bay o f  Fundy  the F r a s e r D e l t a  in  the  studies  being  that variations  flats  are s l i g h t ,  is primarily 1977).  coast  This i s  i n determining  ( R i s k and M o f f a t ,  (Levings  unlike in  in  grain  and a  controlled  where v a r i a t i o n s  an i m p o r t a n t r o l e  s u c h as M i n a s B a s i n , tidal  o v e r most of  literature,  inactive  south-  of  '  are unique,  zonation e x i s t s , which  described in  substrate  ..  flats  on the  t h e F r a s e r D e l t a on the w e s t  C a n a d a ( S w i n b a n k s , 1979). Boundary Bay t i d a l  flats  by  distinct  elevation  most o t h e r  grain  size  s i z e of  tidal the  floral/faunal  zonation,  1977)  active  and C o u s t a l i n ,  and the 1975).  31  Boundary Bay l i e s on the southern The  f l a n k o f the F r a s e r D e l t a ( F i g . 1 ) .  Bay i s p r o t e c t e d from the sediment plume o f the F r a s e r R i v e r by the  P l e i s t o c e n e p e n i n s u l a o f P o i n t Roberts.  As a r e s u l t r a t e s o f  sedimentation  are low (0.42 mm/year, K e l l e r h a l s and Murray, 1969), and the Bay waters a r e !  c l e a r and have s a l i n i t i e s which a r e 'normal marine' (24-29 %•) f o r the southern  S t r a i t of-Georgia.  shore d r i f t along by  Sediment i s t r a n s p o r t e d i n t o the Bay by l o n g -  the western and e a s t e r n margins of the Bay, as  the a c c r e t i o n s p i t s a t Beach Grove and C r e s c e n t  evidenced  Beach, and by the r e l i c t  beaches j u s t south o f Beach Grove, a l l of which i n d i c a t e longshore towards the n o r t h  (Figs. 2 & 3).  at P o i n t Roberts a r e an important Bay  ( K e l l e r h a l s and Murray, 1969).  The u n c o n s o l i d a t e d  Pleistocene  present  o f sediment to the  day source  Two s m a l l r i v e r s d i s c h a r g e  amounts o f sediment i n t o the e a s t e r n end o f the Bay ( F i g . 1 ) . western p a r t o f the Bay the s a l t m a r s h i t has receded  drift  i s prograding,  cliffs  minor I n the  whereas to the e a s t  a t l e a s t . 1 . 2 km s i n c e 4,350 y r s . B.P. ( K e l l e r h a l s and  Murray, 1969). K e l l e r h a l s and Murray having The  i n t o f o u r zones each  d i s t i n c t i v e s e d i m e n t o l o g i c a l and f a u n a l / f l o r a l  f o u r zones d e s c r i b e d by K e l l e r h a l s and Murray  the h i g h The  (1969) d i v i d e d the f l a t s  tidal  f l a t s , the i n t e r m e d i a t e  tidal  flats  characteristics.  (1969) a r e the s a l t m a r s h , and the low t i d a l  fauna and f l o r a of Boundary Bay have been d e s c r i b e d by O'Connell  In t h i s paper the z o n a t i o n d e s c r i b e d by K e l l e r h a l s and Murray r e v i s e d and mapped u s i n g a e r i a l photographs and data c o l l e c t e d transects.  D i s t r i b u t i o n o f fauna on the t i d a l f l a t s  (1975).  (1969) i s from  surveyed  i s given i n q u a n t i t a -  t i v e terms and the b i o g e n i c sedimentary s t r u c t u r e s they produce a r e described..^ \_ _  flats.  32  F i g u r e 1.  Map of the F r a s e r D e l t a a r e a , showing the l o c a t i o n of Boundary Bay t i d a l f l a t s (reproduced from K e l l e r h a l s and Murray, 1969).  33 METHODS Two flats  t r a n s e c t s were e s t a b l i s h e d t r a v e r s i n g the Boundary Bay  ( F i g . 2).  T r a n s e c t A, which c o n t a i n e d 22 s t a t i o n s , was  a n a l y s e d d u r i n g June and e a r l y J u l y , 1976. 38 s t a t i o n s , was  tidal  s e t up  T r a n s e c t B, which c o n t a i n e d  e s t a b l i s h e d and analysed, i n Julyaarid August,J.1976.  F u r t h e r o b s e r v a t i o n s were made on the t r a n s e c t s i n November, 1976, at v a r i o u s times o f the-year i n 1977 The  two  and 1978  and  (Table I ) .  t r a n s e c t s , A and B, were surveyed from bench marks w i t h  the use of a t r a n s i t and an a l i d a d e .  The  t r a n s e c t s run n o r t h / s o u t h  from the edge of the s a l t m a r s h to low water mark w i t h s t a t i o n s  taped  at 91.4  change  m (300  f t ) i n t e r v a l s and marked by wooden s t a k e s .  i n e l e v a t i o n between s u c c e s s i v e s t a t i o n s was of about + 5 mm. a l o n g the  and  High accuracy was  determined  The  to an accuracy  r e q u i r e d because e r r o r s are  cumulative  transect.  Some burrowing at the sediment  organisms  produce  v i s i b l e evidence of t h e i r d e n s i t y  s u r f a c e , e i t h e r d i r e c t l y by t h e i r presence  i n the case  of e p i f a u n a , o r i n d i r e c t l y i n the form o f burrow e x i t s o r f e c a l mounds i n the case o f infauna.. U s i n g t h i s s u r f a c e e v i d e n c e i t was  p o s s i b l e to  determine  sampling:  the d e n s i t y of the f o l l o w i n g organisms  by quadrat  C a l l i a n a s s a c a l i f o r n i e n s i s and Upogebia p u g e t t e n s i s , both burrowing  shrimps,  thalassinidean  three p o l y c h a e t e worms, A b a r e n i c o l a s p . , S p i o sp. r  P r a x i l l e l a sp., the b i v a l v e My a a r e n a r i a and the gastropods a t t r a m e n t a r i a and N a s s a r i u s mendicus.  Batillaria  D i r e c t counts o f organisms  made i n the cases o f B a t i l l a r i a , N a s s a r i u s , S p i o , P r a x i l l e l a and whereas i n d i r e c t  and 4 cm . 2  were Mya,  counts o f f e c a l mounds o r burrow openings were made i n  the cases o f A b a r e n i c o l a , U p o g e b i a Quadrats  and  and  Callianassa.  o f f o u r d i f f e r e n t s i z e s were used —  The quadrat  1 m, 2  0.25  m, 2  100  cm , 2  s i z e s e l e c t e d depended on the s i z e and d e n s i t y o f  F i g u r e 2.  F l o r a l / s e d i m e n t o l o g i c a l z o n a t i o n of Boundary Bay w i t h the l o c a t i o n s of t r a n s e c t s A and B indicated. Between the t i d a l channels the w a t e r l i n e approximates to the -2.4 m (-8.0 ft) contour (Geodetic Datum). The w a t e r l i n e i n the t i d a l channels does not f o l l o w a s p e c i f i c contour s i n c e these d e p r e s s i o n s remain w a t e r - f i l l e d d u r i n g low t i d e , d e s p i t e the f a c t t h a t they are w e l l above sea l e v e l .  2000  1000^  FLORAL/SEDIMENTOLOGICAL AND  LOCATION  ZONES of  3000  of B O U N D A R Y  motors  BAY  TRANSECTS  ( C o m p i l e d from C o l o u r A o r t a l P h o t o g r a p h s of J u l y , 1 9 7 4 ) CANADA  LEGEND  U.S.A.  S o u r c e > Intogratod  Salt  Rosourcss  Photography,  Flight  No. 1 4 2 , J u l y , 1 9 7 4 .  | > |•  :!  M a r s h Zone  | A l g a l M a t Zone | Upper Sand Wave Zone Eelgrass  Zone  Lower Sand Wave Zone  ?  ?  ••«o=:  A r e s Not Covered by Aerial Photo Mosaic Relict Features  Al—'—• Transect Line u  u Dyke  •=3.^' 8end Weve Troughs Send Weve Fixed by Eelgrass .'<J>.-  TABLE f;  Dates and L o c a t i o n s  of F i e l d  Observations  June 5-16, 1976  Transect  June 17-July 5, 1976  Sampling on t r a n s e c t A.  J u l y 6-16, 1976  Transect  Aug.  Sampling on t r a n s e c t  2-22, 1976  A e s t a b l i s h e d and surveyed.  B e s t a b l i s h e d and surveyed. B.  Nov. 8, 1976  S a l i n i t y measurements a t s t a t i o n s A5-A12.  Feb.  O b s e r v a t i o n s o f f l o r a l zone l i m i t s on t r a n s e c t A.  10, 1977  A p r i l 5-7, 1977  O b s e r v a t i o n s o f e e l g r a s s and j u v e n i l e A b a r e n i c o l a on t r a n s e c t A.  Sept. 21,- 1977  S a l i n i t y measurements a t s t a t i o n s A1-A22 and B1-B17.  Sept. 27, 1977  S a l i n i t y measurements a t s t a t i o n s A6-A13.  March 25-26, 1978  Observations of j u v e n i l e Abarenicola at s t a t i o n s A1-A6, and e e l g r a s s at s t a t i o n s A13-A17 and B12-B30.  A p r i l 8-9, 1978  Observations of j u v e n i l e at s t a t i o n s A1-A6.  * May 14, 18-21, 26, J u l y 17, 1978  * Quantitative  Abarenicola  Quantitative observations of j u v e n i l e A b a r e n i c o l a a t s t a t i o n s A1-A6.  r e s u l t s to be p u b l i s h e d  elsewhere (Swinbanks, i n p r e p a r a t i o n ) .  37 the organism b e i n g i n v e s t i g a t e d .  The quadrat was thrown down randomly  w i t h i n 5 m o f the s t a t i o n , and organisms o r burrow numbers w i t h i n t h e quadrat counted. was  When the o r i g i n o f a burrow was i n doubt, the burrow  excavated w i t h a spade o r t r o w e l to determine the organism r e s p o n -  sible.  Sample specimens of each organism s t u d i e d were c o l l e c t e d and  p r e s e r v e d i n 10% formaldehyde f o r l a t e r i d e n t i f i c a t i o n .  L i g h t ' s Manual  (Smith and C a r l t o n , 1975) and the d e s c r i p t i o n s o f Boundary  Bay fauna by  O'Connell (1975) were used i n organism i d e n t i f i c a t i o n s . S e v e r a l o f the organisms s t u d i e d a r e s e n s i t i v e t o d e s i c c a t i o n i n the upper l a y e r s o f sediment.  To d i s t i n g u i s h  'wet' sampling s i t e s  from  'dry,' a d e p r e s s i o n about 1 cm deep was made i n the sand w i t h a f i n g e r a f t e r t e n hours o f exposure.  I f t h e d e p r e s s i o n formed immediately  w i t h water, then the sediment was c o n s i d e r e d e s t a b l i s h e s whether  'wet.'  filled  T h i s procedure simply  or not the water t a b l e l i e s w i t h i n 1 cm o f the s u r f a c e .  For a l l t r a n s e c t s the d e n s i t i e s o f A b a r e n i c o l a , B a t i l l a r i a , Upogebia, C a l l i a n a s s a and Mya were determined by sampling a 2 m each s t a t i o n w i t h e i t h e r a 1 m A1-A22 and B1-B12, 2 x 1 m  2  2  o r 0.25 m  2  quadrat (8 x 0.25 m  f o r s t a t i o n s B12-B38).  2  2  Nassarius, area at for stations  P r a x i l l e l a densities , —2  were s i m i l a r l y  determined, except where d e n s i t i e s became e x c e s s i v e  (>10O m  i n which case d e n s i t i e s were determined by t a k i n g e i g h t r e a d i n g s w i t h a 100 cm  2  quadrat.  The d e n s i t y o f S p i o , a s m a l l t u b e - d w e l l i n g p o l y c h a e t e  worm, was determined by t a k i n g f o u r r e a d i n g s a t each s t a t i o n w i t h a 4 cm quadrat. To determine the r e l a t i o n s h i p between burrow  d e n s i t y and organism  d e n s i t y , i n the case o f C a l l i a n a s s a , a l l the sediment w i t h i n a 0.25 m  2  open ended metal box was excavated to a depth o f 50 cm, and the sediment examined  f o r shrimps w i t h the a i d o f a c o a r s e s i e v e  (2 mm mesh). S i x  r e s u l t s were o b t a i n e d by sampling twice a t s t a t i o n s A12, A13 and A14.  2  ),  For A b a r e n i c o l a  the r e l a t i o n s h i p between f e c a l c a s t d e n s i t y  d e n s i t y was determined u s i n g a box core can, which g i v e s a core o f r e c t a n g u l a r deep.  T h i r t y cores were taken.  each core  constructed  and worm  from a two g a l l o n  c r o s s s e c t i o n (15 x 20 cm), 30 .cm  Only two c a s t s were e n c l o s e d  to ensure t h a t the worms r e s p o n s i b l e  within  f o r the c a s t s were  enclosed  w i t h i n the c o r e . Burrow morphologies were examined u s i n g a core  30 cm deep and the other  1 m.  two box c o r e s ,  one g i v i n g  The burrow morphologies o f the  shrimps C a l l i a n a s s a and Upogebia were i n v e s t i g a t e d by t a k i n g r e s i n c a s t s using  the method developed by Shinn (1968).  were v i s i b l e , entombed i n the r e s i n c a s t .  In s e v e r a l casts  shrimps  T h i s gave a means o f c h e c k i n g  the shrimp to burrow r a t i o determined as d e s c r i b e d  above.  G r a i n s i z e samples o f the s u r f a c e sediment were c o l l e c t e d a t a l l s t a t i o n s using  a 2 cm deep r e c t a n g u l a r  waters a t low t i d e were recorded  can. The s a l i n i t y o f s u r f a c e  at s t a t i o n s with a refractometer.  the l a b , g r a i n s i z e samples were washed f r e e of s a l t , 30%  H2O2,  In  treated with  wet s i e v e d through a 63 pm s i e v e f o r e x t r a c t i o n o f the s i l t / c l a y  f r a c t i o n , and then dry s i e v e d a t 0.5 0 i n t e r v a l s .  Between 10 and 30 g  of sample was used. Colour a e r i a l photographs o f Boundary Bay taken i n J u l y , 1974 (Integrated  Resources Photography, F l i g h t No. 142) were used t o map the  d i s t i n c t i v e f l o r a l / s e d i m e n t o l o g i c a l zones o f the exposed t i d a l A t o p o g r a p h i c base map w i t h a 0.3 m contour i n t e r v a l  flats.  ( K e l l e r h a l s and  Murray, 1969), was used to determine the e l e v a t i o n o f zone b o u n d a r i e s between the surveyed  transects.  FLORAL/SEDIMENTOLOGICAL ZONATION OF THE TIDAL FLATS Description A e r i a l photographs  taken i n J u l y , 1974 of Boundary Bay r e v e a l  f l o r a l / s e d i m e n t o l o g i c a l zones on the exposed t i d a l f l a t s  five  ( F i g . 2 ) , which  can be r e c o g n i z e d on the b a s i s o f t h e i r d i s t i n c t i v e f l o r a l cover o r by the presence o f l a r g e s c a l e bedforms.  The zones v i s i b l e i n t h e photo-  graphs a r e , from the s h o r e l i n e seawards,  the s a l t m a r s h zone, the a l g a l  mat zone, the upper sand wave zone, the e e l g r a s s zone and t h e lower sand wave zone.  Dense e e l g r a s s growth a l s o o c c u r s i n the t i d a l channels and  extends down the channels i n t o the s u b t i d a l zone below the l o w e r sand wave zone. The f i v e zones a r e p r e s e n t throughout t h e Bay, e x c e p t a t t h e e a s t e r n and w e s t e r n e x t r e m i t i e s i m m e d i a t e l y s o u t h o f Beach Grove and C r e s c e n t Beach ( F i g . 2 ) , where sand waves cover t h e e n t i r e i n t e r t i d a l zone, and no e e l g r a s s beds, a l g a l mats o r s a l t m a r s h have d e v e l o p e d , because o f the coarseness and p r o b a b l e i n s t a b i l i t y o f the sands i n b o t h these a r e a s . I n these two areas the e n t i r e . i n t e r t i d a l zone has the c h a r a c t e r i s t i c s o f the l o w e r sand wave zone.  The f i v e - f o l d z o n a t i o n i s a l s o absent i n t h e  f i n e r g r a i n e d sediments o f Mud Bay. Table I I t a b u l a t e s the e l e v a t i o n s o f the v a r i o u s zone b o u n d a r i e s w i t h r e s p e c t t o Canadian G e o d e t i c Datum, on b o t h t r a n s e c t s , as determined by s u r v e y i n g i n summer.  The boundary between the a l g a l mat zone and the  upper sand wave zone i s d e f i n e d t o be a t t h e lower l i m i t o f c o n t i n u o u s a l g a l mat growth.  I s o l a t e d a l g a l mat hummocks a r e p r e s e n t below t h i s  l e v e l on b o t h t r a n s e c t s .  A l l boundaries are e l e v a t i o n d e l i m i t e d except  t h a t between the e e l g r a s s and l o w e r sand wave zones, w h i c h i n p l a c e s extends down t o low water l i n e (- 2.4 m. G e o d e t i c Datum, F i g . 2 ) . I n w i n t e r the f l o r a l zones r e t r e a t .  The a l g a l mats d i e back and  TABLE i l l  Elevations  o f Zone Boundaries  Transect A  Transect B  Boundary Station  :  Elevation  (m)  Station  E l e v a t i o n (m)  Lower L i m i t o f Saltmarsh Zone  T6  + LIS:  0.05  2  + 1.10 + 0.01  Upper L i m i t , o f A l g a l Mat Zone  Al  + 0.98 + 0.06  BI  + 1.04 + 0.01  A l g a l Mat Zone/Upper Sand Wave Zone  A5/A6  Upper Sand Wave Zone/Eelgrass Zone  A13  Eelgrass  —  N.B.  Zone/Lower Sand Wave Zone  A l l elevations with respect Tsawwassen, add 2.95 m).  T h i s boundary i s d e f i n e d  to Canadian  + 0.75 + 0.08 -•  0.10  + 0.12  B4/B5 B12  + 0.76 + 0.07 0.00 + 0.05,  Approximately - 1.2 m  Geodetic Datum ( t o convert to 1978 Chart Datum a t  to he a t the lower l i m i t o f continuous a l g a l mat growth.  41 only a few i s o l a t e d hummocks remain. O b s e r v a t i o n s i n mid-February  The e e l g r a s s r e t r e a t s  seawards.  on t r a n s e c t A r e v e a l e d t h a t the e e l g r a s s had  r e t r e a t e d 350 m seawards from i t s summer p o s i t i o n , to an e l e v a t i o n of - 0.5  m ( G e o d e t i c Datum).  On t r a n s e c t B o n l y i s o l a t e d patches o f e e l g r a s s  remain d u r i n g w i n t e r . The e e l g r a s s which d i e s back i n w i n t e r c o n s i s t s l a r g e l y o f the s m a l l e r s p e c i e s Z o s t e r a americana, w h i l e a permanent growth i s m a i n t a i n e d by the l a r g e r s p e c i e s Z o s t e r a marina. i n the s p r i n g .  Z o s t e r a americana reappears from s e e d l i n g s  C o n s i d e r a b l e q u a n t i t i e s o f both s p e c i e s o f e e l g r a s s are  uprooted by w i n t e r storms and r a f t e d i n t o the edge of the s a l t m a r s h zone, forming an o r g a n i c r i c h mat  on which s a l t m a r s h p l a n t s e e d l i n g s s p r o u t i n  the s p r i n g . F i g u r e 2 d e p i c t s sand wave troughs i n p o s i t i o n as t r a c e d from a e r i a l photographs. different  The sand waves o f the upper sand wave zone are d i s t i n c t l y  from those of the lower sand wave zone.  sand wave zone have wavelengths tudes of <0.1  m,  Those of the upper  a v e r a g i n g 30 m (range 20-70 m) and a m p l i -  g i v i n g a wavelength:amplitude  r a t i o g r e a t e r than 300:1.  From q u a l i t a t i v e o b s e r v a t i o n s the waves appear to be symmetrical i n p r o f i l e . The sand waves o f the lower sand wave zone have wavelengths (range 40-80 m),  and, a c c o r d i n g to K e l l e r h a l s and Murray  from 0.3 m to 0.5  m.  At f a i r l y  (1969), amplitudes  In p l a n view these sand waves have both  c r e s t e d and l u n a t e o u t l i n e s . seawards.  a v e r a g i n g 60 m  straight-  The l u n a t e forms are predominantly  concave  r e g u l a r i n t e r v a l s a l o n g the lower l i m i t o f the upper  sand wave zone, sand waves s i m i l a r to those of the lower sand wave zone occur.  They are l u n a t e i n o u t l i n e and concave seawards ( F i g . 2 & 3).  The a l g a l mat  zone i s d e v o i d of sand waves.  T h i s may  due to the sediment b i n d i n g e f f e c t s of the a l g a l mats. o c c u r i n the e e l g r a s s zone. d u r i n g summer ( F i g . 2 ) .  i n part  be  A few sand waves  Some are completely overgrown by  eelgrass  42 D i s c u s s i o n o f Sand Waves The j u s t i f i c a t i o n f o r c a l l i n g the l a r g e scale'bedforms o f the upper sand wave zone  'sand waves' l i e s i n the f a c t t h a t they meet the l o o s e  s p e c i f i c a t i o n s of sand waves g i v e n by Harms e t a l . (1975) — between 5-100  m, s t r a i g h t .to sinuous c r e s t e d and h a v i n g a . r e l a t i v e l y  small height/spacing r a t i o —  and .they .exhibit a c h a r a c t e r i s t i c . p r o p e r t y  of waves, namely i n t e r f e r e n c e p a t t e r n s .  The bedforms  produced i n response to s u r f a c e s e a waves. bedforms  v i z . spacing  are thought to be  The wave p r o p e r t i e s of these  and t h e i r response to s u r f a c e s e a wave a c t i v i t y  r a t e d i n the western p a r t o f the Bay next to Beach i n t e r f e r e n c e patterns are v i s i b l e  ( F i g . 3).  i s best  illust-  Grove, where r e f l e c t i o n  A c o n c r e t e breakwater i s  p r e s e n t a l o n g the w a t e r f r o n t , of Beach Grove, and the beach p r o f i l e i n t h i s a r e a o f the Bay i s s t e e p e r than elsewhere.  S u r f a c e s e a waves are  r e f l e c t e d by the c o n c r e t e breakwater, whereas i n the r e s t of the Bay wave energy i s d i s s i p a t e d i n the s a l t m a r s h zone w i t h o u t r e f l e c t i o n .  The  sand  waves m i r r o r the r e f l e c t i o n i n t e r f e r e n c e p a t t e r n s of the s u r f a c e s e a waves. The l u n a t e sand waves near the lower edge of the upper sand wave zone c o u l d perhaps be produced by r i p c u r r e n t s s e t up i n response to wave a c t i o n ( F i g . 3). Between the p e r i o d o f June, 1976,  to J u l y , 1978, t h e sand waves of  the upper sand wave zone on t r a n s e c t A have not moved or changed  shape  n o t i c e a b l y w i t h r e s p e c t to the p o s i t i o n s of s t a k e s p l a c e d along the t r a n - ' sect.  The sand waves o f the upper sand wave zone are p r o b a b l y o n l y  d u r i n g w i n t e r storms, and when a c t i v e may brium.  active  be i n a s t a t e of dynamic e q u i l i -  The sand waves i n d i c a t e storm wave p r o p a g a t i o n from the south.  Twenty-two p e r c e n t of winds i n excess of 48 km/hour (30 m.p.h.) d u r i n g winter  (October - March) are from the s o u t h , and on average occur f o r  5.5 hours per month (Swan Wooster, 1968).  S o u t h e r l y winds have a g r e a t e r  f e t c h than any o t h e r s , and s h o u l d produce the most s e v e r e storm waves.  43  Hwy.  499  LEGEND Longshore Rip  Drift  Currents  Dyke  0"  S a l t m a r s h Zone A l g a l Mat Zone Upper Sand Wave Zone  o •  N  E e l g r a s s Zone  i  Lower Sand Wave Zone Sand wave  troughs  Area not covered by a e r i a l p h o t o mosaic X  Transect  line A  Beach Grove  reflection  interference patterns  accretion  spit  relict  1000  1000  beaches  2000  meters  Source-.  Integrated  Resources  Photography, N o . 142,  F i g u r e 3.  July,  Flight 1974  R e f l e c t i o n i n t e r f e r e n c e p a t t e r n s i n the upper sand wave zone i n the a r e a o f Beach Grove. A l s o i n d i c a t e d a r e the p r o b a b l e d i r e c t i o n s o f wave induced c u r r e n t s .  The o r i e n t a t i o n of t i d a l channels i n the lower sand wave and  eelgrass  zones g i v e a good i n d i c a t i o n of t i d a l c u r r e n t d i r e c t i o n s , i n p a r t i c u l a r of  ebb  currents  ( K e l l e r h a l s and Murray,  1969; Weir, 1963).  In the lower  sand wave zone i t can be seen that sand waves are a l i g n e d a p p r o x i m a t e l y p e r p e n d i c u l a r to the a x i s o f the t i d a l c h a n n e l s , i n d i c a t i n g t h a t the sand waves may the  be produced by t i d a l c u r r e n t a c t i o n .  summer of 1959,  r e c o r d e d maximum f l o o d and ebb  s p r i n g and mean t i d e s , r a n g i n g from 24 cm s e c "  1  Weir  (1963), d u r i n g  t i d a l currents,  to 49 cm s e c  of s e v e r a l r e a d i n g s through water column) i n the f o u r major west o f the "Great Channel" (beside C r e s c e n t Beach). readings f o r both f l o o d and ebb  c u r r e n t s exceeded  - 1  during  (average  t i d a l channels  S e v e r a l o f the  35 cm s e c  - 1  .  The water  depths i n the lower sand wave zone at the time of these measurements ranged between 0.0 m and 1.7 m. 35 cm s e c  - 1  C u r r e n t v e l o c i t i e s i n excess o f about  i n these water depths are capable of forming sand waves  (Harms e t a l . , 1975).  However, to determine c o n c l u s i v e l y whether the  sand waves are of t i d a l o r i g i n ,  c u r r e n t v e l o c i t y d a t a would have to be  c o l l e c t e d from the lower sand wave zone i t s e l f ,  r a t h e r than e x t r a p o l a t i n g  from data c o l l e c t e d i n the a d j a c e n t t i d a l c h a n n e l s . be the r e s u l t of c u r r e n t s i n d u c e d by the combined  The sand waves c o u l d  a c t i o n of t i d e s  and  storm waves.  ENVIRONMENTAL FACTORS AND  Z0NATI0N  There are t h r e e f a c t o r s i n the p h y s i c a l environment which have the p o t e n t i a l o f b e i n g primary agents i n c a u s i n g f l o r a l / f a u n a l z o n a t i o n on tidal the  flats.  These are the g r a i n s i z e c h a r a c t e r i s t i c s o f the s u b s t r a t e ,  p r o p e r t i e s o f the c o v e r i n g waters at. h i g h arid.vlow'.tides,;Lin-ip.articular  t h e i r s a l i n i t y and t u r b i d i t y l e v e l s , i s a f u n c t i o n o f t i d e s , e l e v a t i o n and  and the d u r a t i o n of exposure, which topography.  45 G r a i n S i z e o f Surface Figures  4 and 5 p r e s e n t  the g r a i n s i z e c h a r a c t e r i s t i c s o f s u r f a c e  sediments on t r a n s e c t s A and B.  In a d d i t i o n to these r e s u l t s , one s u r f a c e  sample (upper 2 cm) from the s a l t m a r s h 100 It  Sediments  zone, c o l l e c t e d on t r a n s e c t A  m landward from the seaward p e r i m e t e r of the marsh, was proved t o be a moderately w e l l s o r t e d very  3.6 0) , c o n t a i n i n g  25% s i l t  analysed.  f i n e sand (Graphic  Mean  and c l a y , and 8% o r g a n i c matter h a l f o f which  c o n s i s t e d of f i b r o u s peat. On both t r a n s e c t s A and B the s u r f a c e sediments g r a d u a l l y seawards from very  f i n e sands to f i n e sands i n going from the s a l t m a r s h  zone to the lower e e l g r a s s  zone, g i v i n g a very  range o f l e s s than 1 0 ( F i g s . 4 & 5 ) . s i z e i s best  coarsen  This  l i m i t e d mean g r a i n s i z e  coarsening  i n mean g r a i n  i l l u s t r a t e d on t r a n s e c t B ( F i g . 5 ) . Towards the lower end  of t r a n s e c t A there  i s a s l i g h t r e v e r s a l i n the t r e n d , b u t t h i s i s due  to an i n c r e a s e i n the mud content o f the sediment r a t h e r than b e i n g due to a f i n i n g i n the g r a i n s i z e o f the sand f r a c t i o n . A and B a r e predominantly w e l l t o very w e l l s o r t e d Dev.  <0.5 0 ) .  F l u c t u a t i o n s i n the s o r t i n g values  The sands on t r a n s e c t s (Incl.  Graphic S t d .  are l a r g e l y a function  of mud c o n t e n t , as i n d i c a t e d by the f a c t t h a t s o r t i n g and mud content values  f l u c t u a t e i n harmony ( F i g s . 4 & 5 ) .  With the e x c e p t i o n  o f the  saltmarsh  zone, mud contents a r e low, amounting to only a few p e r c e n t .  Box  from both t r a n s e c t s r e v e a l monotonous sequences o f sand w i t h  cores  l i t t l e v a r i a b i l i t y i n grain s i z e with  depth.  A f i n i n g i n g r a i n s i z e shorewards i s t y p i c a l o f t i d a l f l a t s ( K l e i n , 1971), b u t the v a r i a t i o n i s u s u a l l y much more extreme, r a n g i n g in  the upper i n t e r t i d a l zone to sand i n the lower i n t e r t i d a l zone  19 39; 'Ey'anf^l90 The  from mud  processes responsible  (Linke,  Risk^and'Moffat /l9,77).V ' f o r t h i s t e x t u r a l t r e n d have been e x t e n s i v e l y  46  3.30 3.20  N  3.10-1 2  ~  3.00  O  2.80  <  ac  2.70  a  2.60  o  I  £ ° »  — i —  — i —  — i —  15  10  20  0.60  11  °- ° 5  °* 0.40 o» c 0.30  I—  I—  10  —I—  20  15  10  a i  _  !-  =s  z in o  8  n  6  (0  v  E  4  |l  ~  UJ  -  a.  2  I  I  1  J  I  I  I I  10  1  I  I  15  l 20  1.50 r  ;  I.OOH  *  0.50  5" * * \ >- - • >  IM  0.50  -J  6  A,  ALGAL ZONE  MAT  UPPER  SANO  WAVE EELGRASS  ZONE  IU  ZONE  1.00  M.L.L.W. 1.50  F i g u r e 4.  1500  1000 DISTANCE,  mate  2000  rs  V a r i a t i o n s i n mean g r a i n s i z e , s o r t i n g and mud A.  content on t r a n s e c t  47  o z  SO  CC  a > • •  0.50 i  5 ° 0.40U CO 0.30-  e —  1  a  8-  S — h- a» < • > Z co u u V K ~  6 ' . 4-  IU  a.  2  I i l  0-  i i . ! . f . •. . 10  •  15  T  |  20  25  1.00  —f30  35  M.H.H.W.  • o.so  6•  «_  ALGAL  °  2  0.50 -  <  1.00 -  "  1.50-  MAT ZONE  UPPER WAVE  SAND ZONE  B25 EELGRASS 1000  1500  2000  3000  DISTANCE,maters  F i g u r e 5.  V a r i a t i o n s i n mean g r a i n s i z e , s o r t i n g and mud content on t r a n s e c t B.  d i s c u s s e d i n the l i t e r a t u r e . Kuenen, 1958)  They i n c l u d e "scour  energy regime (Reineck,  a potent  sheet  1967).  To  this l i s t  flow of water onto the dry  waters any  the f i n i n g shorewards t r e n d .  the advancing w a t e r l i n e . The  On  Dry  c a r r i e d by  the i n i t i a l  foam, p a r t i c u l a r l y The  the advancing w a t e r l i n e i s d e p o s i t e d  h i g h water mark.  l a t e stages  of ebb  This flood  t i d e process  t i d e , because, on ebb,  seeps o f f the w a t e r l o g g e d t i d a l f l a t , no  role  i n f l u x of  flood flat  s t r o n g c u r r e n t a c t i o n due  their  an a b i l i t y  to  f i n e r sediment because  f i l m of foam and along with  i s not  float.  sediment  organic  r e c i p r o c a t e d by  debris the  s u b s u r f a c e water c o n t i n u a l l y foam or pronounced w a t e r l i n e  to l a t e stage  runoff i s l o c a l i s e d  channels. The tidal  although mud  that  on f l o o d t i d e i s  p l a y an important  sediment a l s o has  of i t s l a r g e r s u r f a c e area to volume r a t i o .  forms, and  would add  f i n e r g r a i n s t r a v e l f u r t h e r i n s h o r e because  buoyed up by s u r f a c e t e n s i o n and  Bay  tidal flat  current  T h i s sediment g r a d u a l l y s e t t l e s back onto  s e t t l i n g v e l o c i t i e s are lower.  in  (Postma,  p r o t r u d i n g sediment mounds (e.g. f e c a l c a s t s ) are swept  the s u b s t r a t e .  at  the authors  sediment t r a n s p o r t i n g agent, which may  i n producing  by  to t i d a l v e l o c i t y asymmetry  Groen, 1967), under the i n f l u e n c e of a d e c r e a s i n g wave and  the i n i t i a l  and  and . " s e t t l i n g l a g " (Postma, 1961) , combined w i t h a net  t r a n s p o r t of sediment shorewards due 1961;  l a g " (Van S t r a a t e n  l a c k of mud  and h i g h degree of s o r t i n g i n the sands of Boundary  f l a t s i s probably i t i s a l s o due  due  to the l a c k of a s i g n i f i c a n t source  s i z e sediment i n the Bay.  D e l t a , which experience mud  contents  due  to the i n f l u x of mud  i n p a r t to reworking by w i n t e r  On  storm waves,  of suspended  the a c t i v e t i d a l f l a t s o f the  Fraser  t i d e s and wave a c t i o n s i m i l a r to Boundary  Bay,  of the s u r f a c e sediments are an o r d e r of magnitude h i g h e r , from the F r a s e r R i v e r  (Swinbanks, ,1979")..  - - .  49 Superimposed on the g r a d a t i o n i n mean g r a i n s i z e , which i s c o n t r o l l e d by p h y s i c a l p r o c e s s e s , percentage o f s i l t vegetation  i s a biologically  c o n t r o l l e d f l u c t u a t i o n i n the  and c l a y ( m a t e r i a l <63 ym), due to the a b i l i t y o f  to entrap  f i n e g r a i n e d m a t e r i a l , much as d e s c r i b e d by  and Lowenstam,(1958).  Mud contents  about 25% t o 5% t o 1%, i n p a s s i n g  Ginsburg  decrease i n a s t e p l i k e f a s h i o n from  from the s a l t m a r s h  zone through the  a l g a l mat zone t o the upper sand wave zone, as the e x t e n t o f f l o r a l decreases a b r u p t l y .  I n the lower e e l g r a s s zone on t r a n s e c t A ( S t a t i o n s  A17-A22, F i g . 4 ) , where a continuous present  cover  throughout the y e a r ,  and e x t e n s i v e mat o f e e l g r a s s i s  the percentage o f mud r i s e s a b r u p t l y to '  between 2.5 and 7%. In c o n c l u s i o n , because v a r i a t i o n s i n the g r a i n s i z e o f the s u b s t r a t e are s l i g h t and g r a d u a l , g r a i n s i z e o f the sediments i s n o t c o n s i d e r e d t o p l a y a primary r o l e i n d e t e r m i n i n g The  f l o r a l / f a u n a l z o n a t i o n i n Boundary Bay.  s t e p l i k e v a r i a t i o n i n mud contents  being  o f the sediments, r a t h e r than  a cause of z o n a t i o n , i s c o n s i d e r e d  to be an e f f e c t o f f l o r a l  zonation.  S a l i n i t y and T u r b i d i t y The  plume o f t u r b i d , b r a c k i s h water from the F r a s e r R i v e r seldom i f  ever e n t e r s Boundary Bay.  The plume i s o n l y d i r e c t e d south-eastwards  towards the Boundary Bay a r e a when n o r t h - w e s t e r l y  winds blow i n c o n j u n c t i o n  w i t h an ebbing t i d e  North-westerly  only occur on  (Giovando and Tabata, 1970).  about 13% o f :the .time (Luternauer  these o c c a s i o n s  and Murray, 1973).  the P o i n t Roberts p e n i n s u l a prevents  winds Even  the plume from  e n t e r i n g the Bay, and on the subsequent f l o o d the plume i s n o t f l u s h e d i n t o the Bay, because i n i t i a l are  from the s o u t h - e a s t  f l o o d c u r r e n t s a t the entrance  (Weir, 1963).  to the Bay  A n a l y s i s o f s a t e l l i t e imagery and  a e r i a l photographs r e v e a l s t h a t the plume o f the F r a s e r does n o t e n t e r the Bay and the Bay waters a r e c l e a r (Table III);. A number o f s a l i n i t y  TABLE L L I A e r i a l photographs and s a t e l l i t e  )Film R o l l No.  Frame No,  **IRP  142  . .A 30339  ERTS EMG-1283-A  **  Flight  Altitude (m)  Date  Remarks  nat.  colour  10976  38 & 39  nat.  colour  9451  June 11, 1975  Frame 38 shows c l e a r demarcat i o n between muddy F r a s e r plume and b l u e Bay waters i n v i c i n i t y of P o i n t Roberts. Taken at low t i d e .  19 - 27  nat.  colour  3810  July,  Taken at low t i d e .  nat.  colour  12195  113, 114 & 116  mosaic  ERTS-1  *  Emulsion  the low t u r b i d i t y l e v e l s of Boundary Bay waters  132  >' <*A 37597  :A 37170  imagery i l l u s t r a t i n g  June 20,  1974  J u l y 16,  1971  Contrast frame 132 w i t h the muddy plumes i n frame 146. Taken at low t i d e .  C o n t r a s t frames 113 & 114 w i t h frame 116. Taken a t m i d - t i d e .  infrared  satellite  1973 - 1974  Mosaic w i t h F r a s e r plume clearly visible.  infrared  satellite  11:36 a.m. J u l y 30, 1972  Taken a t m i d - t i d e on ebb, three hours a f t e r lower h i g h water..  Film'»rolls p r e f i x e d (A) a r e f e d e r a l government photographs, a v a i l a b l e L i b r a r y , Ottawa, O n t a r i o , Canada. The r o l l p r e f i x e d  1978  IRP i s a v a i l a b l e  through the N a t i o n a l A i r Photo  through I n t e g r a t e d Resources Photography L t d . , Vancouver, B.C., Canada. s  Note: A l l of these photographs except ERTS EMG-1283-A were taken i n June or J u l y when the F r a s e r R i v e r reaches i t s peak d i s c h a r g e .  51  measurements taken i n t i d a l p o o l s a t low  t i d e c o n f i r m t h a t b r a c k i s h water  from the F r a s e r does n o t e n t e r Boundary Bay, i s i n f r e s h e t (Table IV)V, line  The  even i n June when the F r a s e r  s a l i n i t i e s measured n e a r e s t to low  are p r o b a b l y most i n d i c a t i v e of the s a l i n i t i e s of water e n t e r i n g  the Bay,  s i n c e these are l e a s t a f f e c t e d by exposure o r f r e s h water  from the marsh (Table IVy,Stations A12,  *A9,  t h a t the Bay water s a l i n i t i e s p r o b a b l y  l i e i n the range of 24  which can be  considered  mixed' water mass o f the southern as opposed to the Georgia  next due  A22,  B17 &'A13).  to  Strait  of s u r f a c e waters of the  Strait  of G e o r g i a  drainage  They  3  'normal marine' f o r the southern  as they a r e t y p i c a l of the s a l i n i t i e s  of  tide  indicate 29% , 0  of  Georgia  'vertically  (Waldichuk, 1957),  ' b r a c k i s h s t r a t i f i e d ' water mass of the c e n t r a l  (Waldichuk, 1957).  to the s a l t m a r s h  The  ( S t a t i o n *A1)  to e v a p o r a t i o n d u r i n g prolonged  Strait  e x c e p t i o n a l l y h i g h v a l u e of 39%» by 0 ' C o n n e l l  (1975), was  exposure on a warm day  recorded  probably ( A i r Temp.  20-24° C ) . S a l i n i t y does not vary a p p r e c i a b l y ' o y e r the exposed t i d a l (Table IV.)) and contrast  thus does not i n f l u e n c e z o n a t i o n .  flats  T h i s i s i n complete  to the t i d a l f l a t s on the a c t i v e F r a s e r D e l t a f r o n t , where s u r f a c e  water s a l i n i t i e s ence faunal-and  at low  t i d e range between 1 and  f l o r a l di'stributipn;.patterns  33%« , and markedly  (Swinbanks , 1 9 7 9 )  influ-  .  Exposure Time Exposure time on a t i d a l f l a t i s an important f l o r a l / f a u n a l z o n a t i o n , although  parameter  influencing  i t s e f f e c t s can be masked o r even o v e r r i d d e n  by o t h e r f a c t o r s , such as v a r i a t i o n s i n the g r a i n s i z e of the s u b s t r a t e and/or v a r i a t i o n s i n s a l i n i t y  o r t u r b i d i t y l e v e l s of the c o v e r i n g  waters.  However, as a l r e a d y s t a t e d , these parameters do not vary a p p r e c i a b l y most of Boundary Bay  tidal flats.  As a r e s u l t on these t i d a l f l a t s  over exposure  52 TABLE IV Salinity..-of Water i n T i d a l Pools" at,Low "Tide -  Date  8/11/76  10/6/75  11/6/75  21/9/77  Station  D i s t a n c e from s a l t m a r s h (meters)  Salinity (%o)  A5 A6 A7 A8 A9 AlO All A12  366 457 549 640 732 823 915 1006  26.0 26.5 26.0 26.5 27.0 27.5 28.5 29.0  50 200 350 500 650 975 1275 1575  39.0 33.0 32.0 33.0 32.0 33.0 30.0 28.0  *A1 *A2 *A3 *A4 ' *A5 ' *A7 *A8 *A9 Al A2 A3 A4 A5 A6 A7-A14  (8  23.0 23.0 25.5 26.0 26.5 25.5 24.5 readings)  (8  24.0 readings)  0 91 183 274 366 457 549-1189  Remarks  Cool and  Cloudy  ( A i r Temp. 4-11° C)  Warm  ( A i r Temp. 20-24° C)  Cool and Cloudy A15-A22  1280-1921  21/9/77  BI B2 B3 B4 B5 B6-B17  0 .91 183 274 366 457-1463  27/9/77  A6-A13  457-1098  20.0 21.0 22.0 22.0 23.0 24.0 (12 r e a d i n g s )  (8  *  S t a t i o n l o c a t i o n s and data from O'Connell  28.0 readings)  (1975)  C  o  o  l  a  n  d  c  53 can be seen to p l a y a. major r o l e i n d e t e r m i n i n g f l o r a l / f a u n a l z o n a t i o n , and a d e t a i l e d a n a l y s i s of the r e l a t i o n s h i p between exposure  time and  e l e v a t i o n i s warranted. At  t h i s p o i n t i t s h o u l d be s t r e s s e d t h a t i t i s the e f f e c t s o f  exposure  r a t h e r than exposure i t s e l f which p r o b a b l y most i n f l u e n c e the d i s t r i b u t i o n of  f l o r a and fauna.  The e f f e c t s i n c l u d e such t h i n g s as d e h y d r a t i o n , and  i n s t a b i l i t y o f oxygen l e v e l s , pH,  temperature  and s a l i n i t y , which  may  directly k i l l  f l o r a or f a u n a l o f f s p r i n g o r , a l t e r n a t i v e l y , c r i t i c a l l y  their ability  to cope w i t h competing,  It  p r e d a t o r y or non-compatible  impair  organisms.  s h o u l d be borne i n mind t h a t o t h e r parameters, i n p a r t i c u l a r s m a l l and  l a r g e s c a l e topography and d r a i n a g e , can d r a s t i c a l l y a l t e r the e f f e c t s o f exposure, and t h a t the i n t e r a c t i o n of t i d e s and e l e v a t i o n do not alone determine exposure  effects.  G i n s b u r g e t a l . (1970) suggested t h a t f o r any t i d a l f l a t an vs.  e l e v a t i o n curve s h o u l d be computed, and then at any g i v e n e l e v a t i o n  on the t i d a l f l a t an 'exposure the  index' can be a s s i g n e d , which  mean exposure e x p r e s s e d as a p e r c e n t a g e .  attempted  Ginsburg e t a l . (1970)  to r e l a t e the o c c u r r e n c e o f mudcracks, a l g a l s t r o m a t o l i t e s  o t h e r b i o g e n i c sedimentary s t r u c t u r e s  to t h e i r  'exposure  index.,'  'exposure index' curve has a number o f d e f i c i e n c i e s which  l i m i t i t s usefulness i n interpreting The  i s equal to  Such a c u r v e , w i t h some  a d d i t i o n s , i s p r e s e n t e d i n F i g u r e 6 f o r Boundary Bay.  the  exposure  and  However,  severely  the d i s t r i b u t i o n o f f l o r a and  fauna.  curve's major d e f i c i e n c y i s that i t i s an average, and as such can  p r o v i d e no i n f o r m a t i o n r e g a r d i n g the range of p o s s i b l e exposures at any given e l e v a t i o n .  From the p o i n t o f view o f f l o r a u a n d fauna the most  extreme exposures a r e p r o b a b l y o f more concern than the average. for  Even  some p h y s i c a l sedimentary s t r u c t u r e s , such as mudcracks, i t i s the  l o n g e s t p e r i o d s o f exposure which  determine whether o r not  they form,not t  54  KEY  Mean Daily Exposure Bars indicate one Standard Deviation from Mean \ \^ S N  i — I — I  .50  1.00  1—I  Dotted envelope encloses the complete range of values obtained at any given elevation.  r  +0.50 E L E V ATI O N ,  meters  (Geodetic Datum) Figure  6.  Mean d a i l y exposure w i t h r e s p e c t to e l e v a t i o n f o r Boundary Bay • tides. T h i s was compiled from 16 r e p r e s e n t a t i v e d a i l y t i d a l curves ( e i g h t mean t i d e s , f o u r s p r i n g t i d e s and f o u r neap t i d e s ) s e l e c t e d from 25 a v a i l a b l e i n the data o f Weir (1963) c o v e r i n g the p e r i o d of June t o September, 1959. U s i n g more than 16 days o f t i d a l . r e c o r d s would p r o b a b l y reduce some o f the s t a n d a r d d e v i a t i o n s , b u t i t would i f a n y t h i n g i n c r e a s e the ranges o f p o s s i b l e v a l u e s .  55  the  average. In  F i g u r e 6 an attempt has been made t o overcome these d e f i c i e n c i e s by  d e l i m i t i n g the range o f d a i l y exposure v a l u e s which a r e p o s s i b l e a t any e l e v a tion.  A measure of the n a t u r a l day-liojday v a r i a b i l i t y  i n exposure i s a l s o  g i v e n by i n c l u d i n g the s t a n d a r d d e v i a t i o n from each mean. t h a t a t most l e v e l s , and i n p a r t i c u l a r i n the uppermost  I t can be seen t  and lowermost  inter-  t i d a l r e g i o n s , exposure v a r i e s tremendously from day t o day and 'exposure index' i s a m i s l e a d i n g i n d i c a t i o n o f exposure.  Even w i t h the a d d i t i o n o f  range and s t a n d a r d d e v i a t i o n F i g u r e 6 can g i v e no i n d i c a t i o n o f the maximum d u r a t i o n o f continuous exposure p o s s i b l e at any e l e v a t i o n , because i n i t s computation no d i s t i n c t i o n i s made between continuous and d i s c o n t i n u o u s  ex®©sur  exposure. Swinbanks (1979) has r e c e n t l y e l a b o r a t e d on the concepts o f c r i t i c a l tidal levels  (Doty, 1946),.and  has advocated t h e i r use i n the d e s c r i p t i o n o f  i n t e r t i d a l exposure and i n the s u b d i v i s i o n o f , t h e i n t e r t i d a l  zone.  A  critical  t i d a l l e v e l i s a p a r t i c u l a r t i d a l e l e v a t i o n a t which the d u r a t i o n of c o n t i nuous exposure or continuous submergence changes fashion.  abruptly i n a s t e p - l i k e  There a r e d a i l y , monthly, annual and l o n g e r term c r i t i c a l  l e v e l s , which can be d e f i n e d depending on the time s c a l e c o n s i d e r e d 1979).  As the concepts o f c r i t i c a l  tidal (Swinbanks,  t i d a l l e v e l s are p r o b a b l y u n f a m i l i a r t o  most g e o l o g i s t s , they w i l l be o u t l i n e d below as they apply i n the s p e c i f i c case o f Boundary  Bay t i d e s , a l t h o u g h much o f what i s s a i d a p p l i e s to a l l  astronomically controlled The t i d e s i n Boundary  tides. Bay a r e o f m i x e d - s e m i - d i u r n a l type.  that t h e r e a r e two h i g h t i d e s and two low t i d e s a day, but t h a t h i g h t i d e s and s u c c e s s i v e low t i d e s a r e o f d i f f e r e n t h e i g h t  T h i s means successive  ( F i g . 7 a ) . As  a r e s u l t on any g i v e n day t h e r e are f i v e d i f f e r e n t l e v e l s o f exposure which can be e x p e r i e n c e d , depending on the e l e v a t i o n c o n s i d e r e d .  The d u r a t i o n o f  56  continuous exposure o r submergence jumps on p a s s i n g from one l e v e l to the next.  The f i v e 'exposure l e v e l s ' (Swinbanks, 1979)  as i n d i c a t e d i n  F i g u r e 7a a r e : L e v e l 1.  At an e l e v a t i o n above h i g h e r h i g h water continuous exposure i s at l e a s t n e a r l y two l u n a r days.  L e v e l 2.  At a l e v e l i n t e r m e d i a t e between h i g h e r h i g h water and lower h i g h water, exposure occurs once and i s g r e a t e r than h a l f a l u n a r day, but l e s s  L e v e l 3.  than one.  At a l e v e l between lower h i g h water and h i g h e r low water, exposure i s s p l i t  i n t o two p e r i o d s by lower h i g h water,  each p e r i o d of exposure or submergence b e i n g l e s s than h a l f a l u n a r day.  The t o t a l d a i l y exposure may  o r may  not  exceed h a l f a l u n a r day, but the l e n g t h o f each p e r i o d o f continuous exposure does n o t . L e v e l 4.  Below h i g h e r low water exposure occurs once i n the l u n a r day, and exposure i s l e s s than h a l f a l u n a r day.  Submergence  i s g r e a t e r than h a l f a l u n a r day, but l e s s than one. L e v e l 5.  Below lower low water the t i d a l f l a t merged f o r at l e a s t n e a r l y two  i s continuously  sub-  l u n a r days.  The above f i v e statements are based on the assumption that the time between s u c c e s s i v e h i g h o r low t i d e s i s h a l f a l u n a r day. strictly  t r u e , because there i s a«time asymmetry to mixed  T h i s i s not tides  caused by a  l a g between the p o s i t i o n o f the moon and the response of the t i d e , which i s dependent  on t i d a l range.  However, examination of t w e n t y - f i v e  tidal  curves of a l l ranges r e v e a l s t h a t d e s p i t e t h i s f a c t the f i v e statements still  always h o l d t r u e , f o r Boundary  Bay t i d e s , except f o r L e v e l 3 expo-  sures f o r which continuous exposure can on o c c a s i o n m a r g i n a l l y h a l f a l u n a r day  (Figs.  7b & 7 c ) .  exceed  57  -2.0  2.0 Lunar  Day-" 3  •  r-u  1.5M  o  re  e o  11  u  Is  -1.0  -> 1.0  c o  5S  «• o  -0.5  £  •- K 0.5  •• Key  —I  H.H.W. - H i g h e r  High  L.H.W. - L o w e r  High  H.L.W. - H i g h e r  Water Water  r—  2  1  3  4  1  5  2  Exposure  4 * Exposure  Level 4  (a)  Key  Kay  Low W a t e r  •  m Range I  - Absolute  Limit  a  - Average  •  m Extreme L i m i t  Llmlt  A  - Unlimited  • Rang* i  • Absolute Limit  •  B Average Limit  •  • Extreme Limit  *  • Unlimited  (b)  (c)  l 22 23 2'. 25'26 27 28 29 3o! 1 ' 2 ' 3 '.4 ' 5 ' 6 ' 7 ' 8 ' 9 ' l o ' l l ' 1 2 ' u ' t - M S ' l f i / w ' ,  ,  l  l  June,  : 2.0 •-  l  l  l  4  Level  Level  Low W a t e r  L.L.W. - L o w e r  3  Exposure  l  July.  1959  IS'w'lo'u'llZl'zk'v'lblTia'29V31"  1959  EXPOSED  E  o *i.oH  Level 1 Level  2  Level  a o  3  * \  •  N  z  o  LO H  "  2.0  Level  4  SUBMERGED  (d) F i g u r e 7. (a) The f i v e 'exposure l e v e l s ' p o s s i b l e f o r mixed s e m i - d i u r n a l t i d e s . (b) The ranges o f d u r a t i o n o f continuous exposure f o r each o f the f i v e exposure l e v e l s . (c) The ranges o f d u r a t i o n o f continuous submergence f o r each o f the f i v e exposure l e v e l s . (d) The monthly modulation o f the f i v e exposure l e v e l s f o r t h e p e r i o d June 2 1 - J u l y 31, 1959. T i d a l data from Weir (1963).  58 The f o u r b o u n d a r i e s between exposure l e v e l s a r e 1 s t o r d e r  (daily)  t i d a l l e v e l s , as they a r e d e f i n e d by the d a i l y t i d a l c y c l e . critical  Higher order  t i d a l l e v e l s , d e f i n e d by monthly, annual and l o n g e r term  c y c l e s , a r e common t o a l l a s t r o n o m i c a l l y c o n t r o l l e d t i d e s  critical  tidal  (Swinbanks,  1979).  Over a p e r i o d o f months exposure at any e l e v a t i o n i s a combination of the f i v e exposure l e v e l s  ( F i g . 7d). F i g u r e 8 graphs the frequency o f each  sure l e v e l at 6.1 cm (0.2 f t ) e l e v a t i o n i n t e r v a l s .  expo-  The lowest e l e v a t i o n  a t t a i n e d by L e v e l 1 exposures d e f i n e s the 'atmozone'; the i n t e r t i d a l  exposure  zone i n which t h e maximum d u r a t i o n o f . c o n t i n u o u s exposure exceeds a t l e a s t nearly  two l u n a r days  (Swinbanks, 1979).  Similarly  the h i g h e s t l e v e l  by L e v e l 5 exposures d e f i n e s the upper l i m i t o f the 'aquazone' 1979)  attained  (Swinbanks,  i n which the maximum d u r a t i o n o f continuous submergence exceeds a t  l e a s t n e a r l y two l u n a r days. the 'amphizone'  Between l i e s t h e core t o the i n t e r t i d a l  region,  (Swinbanks, 1979), i n which the maximum d u r a t i o n o f continuous  exposure o r submergence i s always l e s s than one l u n a r day.  The lowest l e v e l  reached by L e v e l 2 exposures d e f i n e s t h e boundary between upper and lower amphizones.  Monthly  (2nd o r d e r ) c r i t i c a l  t i d a l l e v e l s , a t which the maximum  d u r a t i o n o f continuous exposure o r submergence b e g i n s t o r i s e a b r u p t l y about 10 t o 20 days s u b d i v i d e the atmozone and aquazone parts  (Fig.  i n t o upper and lower  8).  Superimposed described.  from  on F i g u r e 8 a r e t h e f l o r a l / s e d i m e n t o l o g i c a l zones p r e v i o u s l y  Some c o r r e l a t i o n s between these zones and t h e exposure zones a r e  immediately apparent, but d i s c u s s i o n o f any c a u s a l r e l a t i o n s h i p s between exposure and z o n a t i o n must await t h e p r e s e n t a t i o n o f f a u n a l d i s t r i b u t i o n data i n the f o l l o w i n g s e c t i o n .  Although F i g u r e 8 p r o v i d e s an extremely u s e f u l  frame-  work f o r d e s c r i b i n g f l o r a l / f a u n a l z o n a t i o n w i t h r e s p e c t t o t i d a l exposure i t s h o u l d be r e a l i z e d t h a t computation o f F i g u r e 8 assumes a p e r f e c t l y t i d a l f l a t which d r a i n s f r e e of water a t each low t i d e . case.  flat  T h i s i s n o t the  Topographic d e p r e s s i o n s o f s m a l l and l a r g e s c a l e cause water cover  Upper  Sand Zona  Wave Lower  0.50 +0.25  0  -0.25  0.50  E l e v a t i o n in M e t e r s  Figure 8 .  The*  f  0.75  (Geodetic  n  hand s c a l e i n p e r c e n t  1.00  J"source.  Wave  Zor  T"  1.25 Datum)  1.50  1.75 .  Also „ i ^ ^  Sand  Weir, 1963).  2.00  2.25  2.50  Data f o r Doundary Bay, B.C., 21 June "- 1k SS eepptt..,, 19";9 1959 J  t  m  e  L e f t hand s c a l e i n days  right Ln  to be "maintained ~during.;16w,:tide i n i t i d a l ' p o o l s within:', the:: d e p r e s s i o n s . /. T h i s has a p r o f o u n d i n f l u e n c e on the d i s t r i b u t i o n o f f l o r a and fauna on the l o c a l s c a l e , p a r t i c u l a r l y o f the s m a l l e r macrofauna. be found growing i n the w a t e r - f i l l e d sand wave zone, and i s o l a t e d  E e l g r a s s can  troughs o f sand waves i n the upper  a l g a l mats may be found growing on the sand  wave c r e s t s , d e f y i n g t h e i r r e s p e c t i v e zone limits.'..  FLORA FAUNA AND THEIR BIOGENIC SEDIMENTARY  STRUCTURES  Saltmarsh Zone The s a l t m a r s h l i e s exposure  ( F i g . 8).  a t an e l e v a t i o n which  i s upper  atmozonal i n  A t r i p l e x p a t u l a , G r i n d e l i a i n t e g r i f o l i a , Rumex c r i s p u s ,  A c h i l l e a m i l l e f o l i u m , and A s t e r s p . dominate on the landward p o r t i o n o f the marsh, whereas on the seaward s i d e h a l o p h y t e s f t h a t a r e more s a l t t o l e r a n t predominate,  such as S a l i c o r n i a s p . , T r i g l o c h i n m a r i t i m a and  S p e r g u l a r i a m a r i t i m a , ( K e l l e r h a l s and Murray, 1969; O ' C o n n e l l , 1975; P a r s o n s , 19:75) .. :• D i s t i c h l i s ;  .  The sediments  stratified  spicata':is, ab undarit a t ~ a l l l e v e l s l X P a r s o h s , 19.75) . , A  accumulating i n t h i s r e g i o n c o n s i s t o f i r r e g u l a r l y .  sand, p e a t , s i l t  and c l a y .  Sand and o r g a n i c d e b r i s  (eelgrass  and d r i f t w o o d ) a r e t r a n s p o r t e d onto the s a l t m a r s h by w i n t e r storms, whereas peat and f i n e r g r a i n e d sediment  accumulate  d u r i n g the summer.  However, due t o d i s r u p t i o n of b e d d i n g by v i g o r o u s r o o t l e t stratification within  i s f a i r l y p o o r l y developed.  growth,  I t i s noteworthy  that,  t h i s d e n s e l y v e g e t a t e d zone o f the uppermost i n t e r t i d a l  sand i s s t i l l  even  region,  the dominant sediment component.  None o f the organisms saltmarsh  seasonal  zone.  investigated  i n t h i s study o c c u r w i t h i n t h e  The s m a l l shore crab Hemigrapsus.r.Q gg°. ensis<is'  a l o n g the s a l t m a r s h perimeter;'  r  n  abundant ;.-  61 A l g a l Mat Zone The  a l g a l mat zone i s lower atmozonal i n exposure ( F i g 8 ) .  c h a r a c t e r i s e d by an almost summer.  continuous  It is  growth o f cyanophyte a l g a l mats i n  The a l g a l mats c o n s i s t predominantly  o f M i c r o c o l e u s s p . and  Phormidium s p . w i t h minor amounts o f the c h l o r o p h y t e s Enteromorpha s p . . .>! and R h i z o c l o n i u m  s p . ( K e l l e r h a l s and Murray, 1969).  smother the a l g a l mats w i t h sand. o r g a n i c r i c h and sandy laminae The  Thus, an annual  i s produced  s t r a t i f i c a t i o n of  ( K e l l e r h a l s and Murray, 1969).  f o l l o w i n g organisms and b i o g e n i c sedimentary  istic  I n w i n t e r , storms  structures are character-  o f the zone.  Batillaria B a t i l l a r i a a t t r a m e n t a r i a (Sowerby),>is _a h e r b i v o r o u s , d e p o s i t - T f e e d i n g gastropod  ( F i g . 10a). A c c o r d i n g to W h i t l a c h  mainly on diatoms.  B a t i l l a r i a i s found throughout  a r e a i n summer, b u t i t s numbers decrease zone ( F i g s . 9a & 9b). pools mat  (1974),  i t feeds  most o f the i n t e r t i d a l  to zero i n the lower e e l g r a s s  B a t i l l a r i a d e n s i t i e s maximize i n s h a l l o w  ( F i g . 9 a ) . B a t i l l a r i a ' s presence  '  tidal  i s most n o t i c e a b l e i n the a l g a l  zone, where i t s t r a c e s a r e w e l l p r e s e r v e d i n the c o h e s i v e a l g a l mats.  B a t i l l a r i a produces both r e s t i n g t r a c e s and g r a z i n g t r a c e s . R e s t i n g T r a c e s — B a t i l l a r i a produces a r e s t i n g t r a c e by b u r y i n g head f i r s t  i n the sand u s i n g a corkscrew  s p i r a l l i n g action.  the p o i n t e d t i p o f i t s s h e l l remains p r o t r u d i n g . p r o b a b l y a p r o t e c t i v e response  itself  Often only  This behaviour i s  against desiccation.  Resting trace .pitsv  are p r e s e r v e d between t i d a l c y c l e s , w h i l e the g r a z i n g t r a c e s l e a d i n g to them ( F i g . 10b), which a r e much s h a l l o w e r d e p r e s s i o n s , a r e u s u a l l y removed by the incoming  tide.  w i t h l i t t l e evidence  Hence, e x t e n s i v e areas o f dense p i t t i n g of the o r i g i n a t o r remaining  result  ( F i g . 10c). P i t t i n g  by B a t i l l a r i a i s most p r e v a l e n t on the u p r a i s e d a l g a l mats.  62  120  DENSITY (No.  m-2)  1.50-1  '6  C  UNDER W A T E R S I T E S  D  DRY S I T E S  D  AVERAGE  P  = PRESENT  A,  M.H.H.W.  ; i.oo-  I  0.50  . • ^ I  ALGAL  MAT  0  h> Ul  ZONE  0.50H  UPPER  SAND  WAVE  1  -l w  EELGRASS  ZONE  ZONE  1.00  1.50H  2000  1000 DISTANCE,  B  maters  60r Batillaria 40  DENSITY (Nam- ) 4  20  11  «  1.50-1  1  i  1  _i_L  t i l l STATION  25  20  35  _ 1500 DISTANCE,  F i g u r e 9. a) b)  2000  2500  3000  m a t o n  D e n s i t i e s o f B a t i l l a r i a sp. on t r a n s e c t A, d i f f e r e n t i a t i n g between dry s i t e s and under water s i t e s ( s h a l l o w t i d a l p o o l s ) D e n s i t i e s o f ' B a t i l l a r i a ' ' s p . on t r a n s e c t B.  63 F i g u r e 10  (a) B a t i l l a r i a a t t r a m e n t a r i a p r o d u c i n g i s about 3 cm l o n g .  a grazing t r a i l .  Its shell  (b) B a t i l l a r i a g r a z i n g t r a i l s and r e s t i n g t r a c e s ( p i t s ) . Note the t r a i l s leading to p i t s . T r o w e l head i s about 5 cm wide. (c) R e s t i n g t r a c e p i t s produced by B a t i l l a r i a sp. Four B a t i l l a r i a sp. can be seen s t i l l o c c u p y i n g p i t s . Trowel head i s about 5 cm wide.  64  65  G r a z i n g T r a c e s — B a t i l l a r i a , as i t grazes a simple  on the sediment, produces  furrow w i t h u p r a i s e d edges (Figs.I0a,,& 10b) .  Batillaria  does  not e x h i b i t p h o b o t a c t i c b e h a v i o u r — a v o i d a n c e o f p r e v i o u s l y grazed  sediment.  In f a c t , on o c c a s i o n B a t i l l a r i a were observed to f o l l o w p r e c i s e l y  grazing  t r a i l s o n l y minutes o l d , w i t h as many as three B a t i l l a r i a  on one t r a i l .  In the p r e s e n c e o f weak c u r r e n t s , f o r example where water d r a i n s o u t of sand wave troughs,  B a t i l l a r i a heads upstream g r a z i n g on the sediment,  leaving grazing t r a i l s p a r a l l e l i n g abrupt  the c u r r e n t d i r e c t i o n  t e r m i n a t i o n o f t r a i l s due to r o l l i n g  ( F i g . 1 1 a ) . The  o f the gastropod  i n d i c a t e s c u r r e n t sense as w e l l as d i r e c t i o n  by the c u r r e n t  ( F i g . l i b ) . The c u r r e n t s i n  which t h i s b e h a v i o u r was observed were too weak to remove the t r a i l s . stronger currents B a t i l l a r i a pointed  d i v e s head f i r s t  In  i n t o the sediment w i t h i t s  t i p p o i n t i n g downcurrent, and ceases moving.  Alignment o f b i o g e n i c  s t r u c t u r e s w i t h a c u r r e n t has been d e s c r i b e d by Rhoads (1975) f o r b i v a l v e siphon  openings and p o l y c h a e t e  d w e l l i n g tubes.  I t has a l s o been d e s c r i b e d  i n the g e o l o g i c a l r e c o r d by S e i l a c h e r (1964) f o r t r i l o b i t e On the r a r e o c c a s i o n s  trails.  i n summer t h a t s t r o n g winds blow from the south  to s o u t h e a s t , waves a r e blown i n t o Boundary Bay from the open S t r a i t o f Georgia,  and f a i r l y c o n s i d e r a b l e movement o f sediment by wave-formed  r i p p l e s occurs.  On these o c c a s i o n s  B a t i l l a r i a burrows i t s e l f out o f s i g h t  about 1 cm below the s u r f a c e to a v o i d b e i n g currents.  Such o c c u r r e d  r o l l e d over by wave  induced  on August 4, 1976, when on f i r s t s i g h t the t i d a l  f l a t s appeared to be almost completely  devoid o f B a t i l l a r i a , b u t on s c r a p i n g  the ;surface w i t h a t r o w e l B a t i l l a r i a was r e v e a l e d i n i t s u s u a l r  densities.  Spio Spio sp. i s a s m a l l t u b e - d w e l l i n g  p o l y c h a e t e worm ( F i g s . 12a, 12b & 1 2 c ) .  I t c o n s t r u c t s an a g g l u t i n a t e d sand tube. and  It.lives  u p r i g h t i n the tube  draws food and sediment i n t o i t s tube w i t h i t s two t e n t a c l e - l i k e  palps  66  F i g u r e 11.  a) B a t i l l a r i a sp. h e a d i n g upstream p r o d u c i n g g r a z i n g t r a i l s p a r a l l e l i n g the c u r r e n t d i r e c t i o n ( e e l g r a s s at top o f photo i n d i c a t e s current d i r e c t i o n ) . B a l l p o i n t pen i s about 15 cm l o n g , b) Behaviour of B a t i l l a r i a sp. i n weak c u r r e n t s : the g a s t r o p o d heads upstream g r a z i n g , and produces a t r a i l p a r a l l e l i n g the current. O c c a s i o n a l l y the c u r r e n t causes the g a s t r o p o d to r o l l . Once s t a b i l i z e d again the gastropod t u r n s i n towards the c u r r e n t and r e v e r t s t o g r a z i n g i n an upstream d i r e c t i o n .  67  2. cm y  *  (b) F i g u r e 12. a) Mounds produced by the f e e d i n g a c t i v i t i e s o f S p i o sp. Pen i s about 15 cm l o n g . b) P l a n view o f S p i o sp. Two t e n t a c l e - l i k e p a l p s draw food i n t o i t s tube and are a l s o used t o v o i d sandy p s e u d o - f e c a l s t r i n g s in a radial pattern. c) Cross s e c t i o n o f S p i o sp. i n i t s d w e l l i n g tube.  68 ( F i g s . 12b  & 12c).  Sediment, p a r t i c u l a r l y l a r g e r sand g r a i n s , tends  to  catch on the t i p of the tube as the worm draws i n i t s food laden p a l p s . As a r e s u l t a mound up to 0.5  cm i n h e i g h t forms around the tube ( F i g . 12a).  The worm a l s o v o i d s f r a g i l e , e l o n g a t e , sandy p s e u d o - f e c a l s t r i n g s . are e x t r u d e d  r a d i a l l y around the tube ( F i g . 12b).  are f l a t t e n e d by  the incoming  The  These  sediment mounds  tide.  Spio i s abundant i n the a l g a l mat i t s maximum d e n s i t y of about 10^ m  zone ( F i g s . 13a  next  -2  & 13b)  to the s a l t m a r s h  attaining  (Al & B l ) .  However, Spio o n l y occurs i n t i d a l p o o l s between the u p r a i s e d a l g a l mats. In the upper sand wave zone Spio decreases  i n d e n s i t y by an o r d e r of  magnitude ( F i g s 13a  p o s s i b l e reasons  & 13b).  There are two  d e n s i t i e s of Spio i n the upper sand wave zone. c r e s t s , although of v e r y low amplitude, ment f o r Spio d u r i n g low troughs  Secondly,  -2  cm of sediment u p r o o t i n g many  but Spio does not  Callianassa californiensis.  Spiophanes w i g l e y i , another and Risk  make an i n h o s p i t a b l e , dry e n v i r o n -  In the e e l g r a s s zone Spio i n c r e a s e s markedly i n  d e n s i t y a t t a i n i n g 5 x 10^ m , mounds formed by  the sand wave  i n w i n t e r , storm waves cause wave-  to d i s t u r b the upper 2-3  Spio i n the p r o c e s s .  lower  t i d e and Spio Is r e s t r i c t e d to the w a t e r - f i l l e d  of the sand waves.  formed r i p p l e s  Firstly,  f o r the  c o l o n i z e the  conical  Comparable d e n s i t i e s  s p i o n i d worm, have been r e p o r t e d by  (1977) i n Minas B a s i n , Bay  of  Featherstone  o f Fundy.  Measurements o f sediment t u r n o v e r by Spio c o u l d not be made d i r e c t l y , however, an e s t i m a t e  can be made.  20 hours i n the a l g a l mat o f sediment.  During exposure at low  (about  zone) Spio produces a mound of about 0.02  At a d e n s i t y o f 10^ m  -2  this  per m .  T h i s i s e q u i v a l e n t to reworking  sand 100  um  2  tide  t h i c k i n t h a t one  square  t u r n o v e r amounts to 200  cm cm  3  3  a monogranular s u r f a c e l a y e r of  meter twice between t i d e s .  69  Spio 40,000 DENSITY (Na  m-*) 20,000  I • • • STATION  20  M.H.H.W.  ; 1.00 I  0 . 0 ,  1  ALGAL  o-l  K  -  >  •  ZONE  0.50  -j  MAT  UPPER  ty  SAND  WAVE  ZONE  EELGRASS ZONE  1.00 1.50  T  500  1000 DISTANCE,  meters  B 20,000  P = PRESENT  DENSITY (No.  RN.D. = P R E S E N T , B U T N O T  m' ) z  DETERMINED  lopoo  '  p  '  •  P  P  ill! JL I l . i I  -P.N.D.-  •  15  20  30  STATION  • 1.00 • 0.50 E  -  0 -  z  0.50 -  Ul -J Ul  1.50 -  VAT  o  1.00 -  ALGAL MAT ZONE  UPPER WAVE  SAND ZONE 6  2  0  B  EELGRASS 500  1— 1500  2000  DISTANCE,motors  F i g u r e 13. a)  D e n s i t i e s o f S p i o sp. on t r a n s e c t A.  b)  D e n s i t i e s o f Spio sp. on t r a n s e c t B.  30  p  p p  70 Fly  Larvae In the upper h a l f of the a l g a l mat  are r i d d l e d w i t h • TO  cm deep and  small 0.25-  ' U' shaped burrows.  to 1.0  mm  the u p r a i s e d a l g a l mats and from .0 to 1 0  m  5  -2  i n . diameter.^  burrows are 1.5  i n general  searching  through numerous box  the burrows c o u l d not be The  of the order  of lO * m . 1  Despite  -2  cm  2  thorough  the a l g a l mats.  h a t c h , burrow downward f e e d i n g on the n u t r i t i o u s a l g a l mat burrow out and  ranging  a 4  The burrows are thought to be  l a y eggs i n or on  . -..•'>  core samples the organism r e s p o n s i b l e  found.  flies  to-  They only, occur, on  ( e x t r a p o l a t i n g from measurements taken w i t h  but  f l y larvae.  The  platforms  t h e i r d e n s i t i e s are h i g h l y v a r i a b l e ,  quadrat),  by  zone the r a i s e d a l g a l mat  for  produced  The  larvae  seams, then  f l y o f f without a t r a c e .  Upper Sand Wave Zone The  upper sand wave zone i s upper amphizonal i n exposure ( F i g . 8).  I t i s c h a r a c t e r i z e d by very f l o r a l mat,  and  low  amplitude sand waves, l a c k s any  i s dominated by  the f o l l o w i n g organisms and  extensive  biogenic  sedimentary s t r u c t u r e s . Abarenicola . A b a r e n i c o l a p a c i f i c a 'Healy and W e l l s i s a d e p o s i t - f e e d i n g polychaete  worm (Hobson, 1967), which c o n s t r u c t s  shaped burrow ( F i g . 14a).  j  The  a v e r t i c a l l y orientated 'J'  t a i l s h a f t reaches the s u r f a c e and  c a s t s are e x c r e t e d here i n the form of sand c o i l s . of a c o l l a p s e cone produced by  ' -  the  The  fecal  head s h a f t c o n s i s t s  f e e d i n g a c t i v i t i e s o f the worm, and  t h i s i s o c c a s i o n a l l y v i s i b l e as a d e p r e s s i o n  at the s u r f a c e .  Abarenicola  p a c i f i c a c i r c u l a t e s water through i t s burrow system ( H y l l e b e r g , 1975). The be  r a t i o of f e c a l c a s t d e n s i t y to worm d e n s i t y was  1.07:1 by  casts  t a k i n g 30 box  cores betweenC5.tatio,nsAA6TAll.  (30 x 2) were found to be  associated with  determined to Sixty.'fecal  56 worms (26 x 2,  4x1).  71  (b) F i g u r e 14.  (a) Morphology of an A b a r e n i c o l a burrow ( a f t e r H y l l e b e r g , 1975). Arrows i n d i c a t e d i r e c t i o n of r e s p i r a t i o n c u r r e n t , (b) Patchy d i s t r i b u t i o n o f A b a r e n i c o l a f e c a l c a s t s . The h i g h e s t d e n s i t i e s o f c a s t s o c c u r i n and around t i d a l p o o l s . Trowel i s about 25 cm h i g h .  72 For a l l i n t e n t s and purposes the r a t i o can be taken as 1:1.  Abarenicola  appears a b r u p t l y near the lower edge o f the a l g a l mat zone.  Densities  r i s e from zero t o about 20 m a = 37 m ) -2  -2  (A5 x = 19 m , -2  a = 12 m ; -2  B5 x = 2015 m~ , 2  i n the d i s t a n c e o f l e s s than 100 m ( F i g s . 15a & 15b).  Sixty-  f o u r quadrat r e a d i n g s between S t a t i o n s A-1-A4 and 31-B4, s a m p l i n g i n t o t a l 16 m , 2  registered  zero A b a r e n i c o l a .  The upper l i m i t o f the worms' o c c u r -  rence on t r a n s e c t A l i e s between A4 a t + 0.87 m e l e v a t i o n  ( G e o d e t i c Datum)  and A5 a t + 0.75 m e l e v a t i o n , and on t r a n s e c t B between B4 (+ 0.83 m) and B5 (+ 0.70 m) .  There i s no change i n g r a i n s i z e over the 100 m i n t e r v a l  i n which the worms appear.  Abundant j u v e n i l e A b a r e n i c o l a have been observed  w e l l above t h i s l i m i t , up to the s a l t m a r s h p e r i m e t e r , i n e a r l y  spring.  However, they d i s a p p e a r from t h i s a r e a by J u l y , p r o b a b l y because  desicca-  t i o n d u r i n g p r o l o n g e d exposure on warm, sunny  periods  days a t neap t i d a l  r e s u l t s i n h i g h m o r t a l i t y amongst j u v e n i l e A b a r e n i c o l a w i t h i n the atmozone ( F i g . 8 ) , whereas m o r t a l i t y w i t h i n the amphizone ( F i g . 8) i s reduced because the t i d a l f l a t everyday  i s i n u n d a t e d w i t h f r e s h s e a water at l e a s t  once  (Swinbanks, i n p r e p a r a t i o n ) .  A b a r e n i c o l a a t t a i n s i t s maximum d e n s i t i e s i n the upper sand wave zone and extends i n t o the e e l g r a s s zone  ( F i g s . 15a & 15b).  I t s densities are  h i g h e r i n wet sediments than dry ( F i g . 1 5 a ) . A b a r e n i c o l a congregates i n the troughs o f sand waves and i n t i d a l p o o l s which are wet o r under water ( F i g . 14b). T h i s i s p r o b a b l y the r e s u l t o f d i f f e r e n t i a l m o r t a l i t y amongst juvenile  Abarenicola.  In the upper sand wave zone A b a r e n i c o l a e x c r e t e s on average about 1-5 wet ml worm ^ day ^ (1 wet ml = 1.5 g dry w e i g h t ) , but r a t e s v a r y depending on the wetness  o f the sediment.  can be as low as 0.02 ml worm ^ day can be as h i g h as 8.4 ml worm  day  I n dry sediment average r a t e s  w h i l e i n t i d a l p o o l s average Tn the eel grass'zone l a r g e  rates Abarenicola  73  Abarenicolo  1  DENSITY (No.  |  m ) -2  WET SITES  Q  111  DRY SITES  P a PRESENT  J_JL  Abarenicola  DENSITY (No. •»-»)  II  1  11 1 Bi 9  • i  P  P.  P  m  P  P  20  Abarenicola  DENSITY (No.  I 11  Ii  I  1500  .  .  .  P  .  , I  . I  I  P  - I  P  -  1  3000  DISTANCE, m o t o r I  Figure  15. a) D e n s i t i e s o f A b a r e n i c o l a f e c a l c a s t s on t r a n s e c t A. Upper h i s t o g r a m d i s t i n g u i s h e s between wet and dry s i t e s , and i s based on f o u r wet s i t e r e a d i n g s and f o u r dry s i t e readings at each s t a t i o n w i t h a 0.25 m quadrat. S t a t i o n s A8 and A9 had no wet s i t e s which c o u l d be sampled. S t a t i o n s A11-A17 had no dry s i t e s . S t a t i o n A5 had dry s i t e s , but A b a r e n i c o l a was absent from them. Lower h i s t o g r a m p r e s e n t s the average d e n s i t i e s , based on random quadrats. . ' j. b) D e n s i t i e s o f A b a r e n i c o l a  f e c a l c a s t s on t r a n s e c t B.  74 e x c r e t e on average 29 wet Abarenicola  ml worm  p a c i f i c a i n the  ( H y l l e b e r g , 1975)  and  day  (Swinbanks, 1979).  course of e a t i n g r e j e c t s coarse  through i r r i g a t i o n of i t s burrow can  the s u r f a c e i n the head s h a f t i r r i g a t i o n c u r r e n t could r e s u l t i n biograded  b e d d i n g as d e s c r i b e d by  However, the f i n e g r a i n s i z e and renders these p r o c e s s e s  low mud  virtually  content  grains  float  c l a y towards  (Swinbanks, 1979). Rhoads and  This  Stanley  of Boundary Bay  (1965).  sands  indetectable.  My a Mya  a r e n a r i a Linna^uV, a";^us"pensioh f e e d i n g bivalve,'Jqccurs f  i n the upper sand wave zone ( F i g . 16a). i n the t i d a l p o o l s  of the a l g a l mat  A few  zone, but  i n d i v i d u a l s also  ' occur  i n d e n s i t i e s l e s s than  -2 0.5 Mya  m  .  Mya  was  not  observed i n the e e l g r a s s zone. The maximum d e n s i t y -2 a t t a i n s i s about 4 m . I t occurs i n the upper sand wave zone on -2  t r a n s e c t B but i n d e n s i t i e s l e s s than 0.5 Mya  constructs  Movement of Mya laminations  i s not Bay  ( F i g . 16b). exhalent  The  to 15  cm i n depth ( F i g .  v e r t i c a l tube c o n s t r u c t e d by Mya  siphons which are  from the e x h a l e n t  considered  through  v e r t i c a l tube up  w i t h i n i t s burrow causes downward warping o f a l g a l  the i n h a l e n t and are v o i d e d  a simple  m  siphon.  fused  together.  Because of i t s low  to c o n t r i b u t e s i g n i f i c a n t l y  16b).  mat  accommodates Fecal pellets  densities  Mya  to the sediments o f Boundary  defecation.  Callianassa C a l l i a n a s s a c a l i f o r n i e n s i s ' Dana.is a burrowing t h a l a s s i n i d e a n , , . ^ L ' ^ j shrimp.  Figures  17a  burrow openings on burrows occur  and  17b  present  t r a n s e c t s A and  i n the a l g a l mat  quadrat r e a d i n g s  on  B.  the d e n s i t y d i s t r i b u t i o n o f C a l l i a n a s s a Isolated individual Callianassa  zone, but  i n very  low  densities.  Eighty  t r a n s e c t s A and B taken w i t h i n the a l g a l mat zone, 2 sampling i n t o t a l 20 m , r e g i s t e r e d zero C a l l i a n a s s a burrow openings.  75  (b)  F i g u r e 16.  (a) (b)  D e n s i t i e s of Mya sp. on t r a n s e c t A. S p r e i t e t r a c e s l e f t by Mya sp., and downwarping o f l a m i n a - , t i o n s caused by movement- o f the clam w i t h i n i t s burrow due to i t s growth o r changes i n the l e v e l o f the sediment water i n t e r f a c e ( a f t e r Reineck, 1958).  76  40  Collianossg / Upoqebio  DENSITY (No. m"*)  Q  CALLIANASSA  H  CALLIANASSA a  |  20  UPOGEBIA  ONLY UPOGEBIA  ONLY  P » PRESENT  p  p  p  p  p  "  -  - n  p  IL  STATION  1.50  ;  J z  .  O  M.H.H.W.  LOO 0.50  H  • ALGAL 0-)  MAT  ZONE  UPPER  < > 0.50ui  -j  SANO  WAVE  ZONE  Ul  EELGRASS  1.00  1.50'  500  1000 DISTANCE,  1500  2000  motors  B Collionasso 10 P=  PRESENT  DENSITY (No. m" ) 2  1 5  20  25  30  35 STATION  1  1.00  •  0.50  M.H.H.W.  ::» 2  0.50  <  LOO  3  1-50  H  ALGAL MAT ZONE  *10 UPPER WAVE  H  SAND ZONE EELGRASS  500  3000 DISTANCE,  F i g u r e 17. a)  b)  motors  D e n s i t i e s o f C a l l i a n a s s a and Upogebia burrow openings on t r a n s e c t A. • D e n s i t i e s o f C a l l i a n a s s a burrow openings on t r a n s e c t  B.  77  Walking seawards along the' t^ans.ect\and scanning. approximately ^2 m'on s i d e o f the t r a n s e c t l i n e the f i r s t at  A2  (+ 0.94 + 0.07  (+ 0.83  + 0.02  m,  either  C a l l i a n a s s a burrow encountered was  m, Geodetic Datum) on t r a n s e c t A, and at B4  G e o d e t i c Datum) on t r a n s e c t B ( F i g s . 17a & 17b).  On  exposure the d i s s o l v e d oxygen content o f Upogebia burrows, which a r e mud-lined, decreases r a p i d l y and a n o x i c c o n d i t i o n s can p r e v a i l one hour  (Thompson and P r i t c h a r d , 1969).  reached more r a p i d l y the  Anoxic conditions are probably  i n the burrows o f C a l l i a n a s s a c a l i f o r n i e n s i s because  l a c k o f a f i r m burrow l i n i n g exposes the burrows to h y p o x i c i n t e r -  s t i t i a l waters (Thompson and P r i t c h a r d , 1969). can  within  s u r v i v e a p p r o x i m a t e l y 5.7  Thompson and P r i t c h a r d , 1969).  days o f a n o x i a At + 0.79  Callianassa  californiensis  , (range 3.2-7:-8 days, N=35,  m ( G e o d e t i c Datum) the maximum  d u r a t i o n of c o n t i n u o u s exposure i s 4 l u n a r days, a t + 0.85  m i t i s 5 l u n a r days  w h i l e a t +>0-.-91 mVarid jff 0v97 m ' i t is-(9 l u n a r days ( F i g . 8).  In Boundary Bay the  upper l i m i t of C a l l i a n a s s a , l y i n g a t about + 0.9 m ( G e o d e t i c Datum), i s , t h e r e f o r e , almost c e r t a i n l y determined by exposure because above t h i s the  maximum d u r a t i o n o f ;anOxia }due to exposure exceeds the l e t h a l  for  Callianassa.  to  limit  C o n c e i v a b l y the o c c a s i o n a l C a l l i a n a s s a i n d i v i d u a l  s u r v i v e above t h i s l e v e l , i f a t i d a l p o o l w i t h oxygenated water  level  could  happened  o v e r l i e i t s burrow e n t r a n c e , because C a l l i a n a s s a c o u l d then draw oxygen-  ated s u r f a c e water i n t o i t s burrow by r a p i d l y f a n n i n g i t s p l e o p o d s , as r e p o r t e d by F a r l e y and Case (1968).  Rare i n d i v i d u a l C a l l i a n a s s a burrows  have been observed o f f t r a n s e c t i n t i d a l p o o l s next to the s a l t m a r s h p e r i m e t e r , and these may  f a l l i n t o the above c a t e g o r y .  However, the  p r e c i s e e l e v a t i o n s of these p o o l s are^unknown"; In  the upper sand wave zone C a l l i a n a s s a burrow openings appear i n  c l u s t e r s c o v e r i n g a r e a s o f about one square meter;. w i t h i n a c l u s t e r may  be 10 m , -2  Burrow opening d e n s i t y  b u t c l u s t e r s are s e p a r a t e d by tens o f  78  meters, and as a r e s u l t average d e n s i t i e s are l e s s than 0.5 m .  Below  -2  about + 0 . 6 m e l e v a t i o n ( G e o d e t i c Datum) C a l l i a n a s s a ' s d i s t r i b u t i o n i s more u n i f o r m and g r e a t e r than 0.5 m the day-to-day  ?  C a l l i a n a s s a probably requires  r e l i a b i l i t y o f t i d a l i n u n d a t i o n found w i t h i n the amphizone  i n o r d e r t o t h r i v e , unhindered by the s t r e s s o f p e r i o d s o f e x c e s s i v e l y prolonged •;anoxia - ( T o r r e s e t al.j,'XL977}> as3mus_t"'"6ccu'r '"in"the" atmozone. r  Average  C a l l i a n a s s a burrow d e n s i t i e s maximize a t about 20 m ^ a r o u n d the edge o f -2  the e e l g r a s s zone. elevation.  C a l l i a n a s s a d e n s i t i e s a r e v e r y low below - 0.6 m  S e v e n t y - e i g h t quadrat r e a d i n g s taken on both t r a n s e c t s below  - 0.6 m e l e v a t i o n , sampling i n t o t a l 54 m , 2  burrow openings.  These  r e g i s t e r e d zero C a l l i a n a s s a  low d e n s i t i e s may be the r e s u l t o f the dense  r o o t l e t s o f ^Zostera 'marina^irihib^itirig- the m i n i n g a c t i v i t i e s o f t h e shrimps, thereby l i m i t i n g t h e i r p o p u l a t i o n . U s i n g an open ended m e t a l box the r a t i o o f burrow openings  to shrimp  d e n s i t y was determined t o be 2.5 ( a r i t h m e t i c mean d e v i a t i o n 0.8, N=6) to 1.  I n s e v e r a l r e s i n c a s t s shrimps were v i s i b l e entombed within-thev.)  casts.  I n v a r i a b l y each burrow system was o c c u p i e d by one shrimp.  are u s u a l l y two openings  to each burrow system, a l t h o u g h o c c a s i o n a l l y  t h e r e may be t h r e e and r a r e l y f o u r openings. opening to shrimp 0  t 1 :  e  t la  There  r a t i o i s 2.5 to 1.  Hence,'the average burrow  T h i s agrees w i t h the f i n d i n g s d f  (1976) and Hertweck (1972) f o r o t h e r t h a l a s s i n i d e a n  Burrow M o r p h o l o g y — S i n c e  the development  shrimps.  of a resin casting  technique  by Shinn (1968) , burrow morphology o f t h a l a s s i n i d e a n shrimps has been studied quite extensively.  Frey and Howard (1975) c i t e numerous r e f e r e n c e s .  F i g u r e s 18a, 18b and 18c i l l u s t r a t e the morphology o f these burrows.  They extend 20-30 cm down i n t o the sediment  horizontally  f o r d i s t a n c e s o f up t o a meter.  callianassid  and then branch  Each system u s u a l l y has two  e x i t s which j o i n as a bulbous chamber a t from 5 cm t o 10 cm depth.  The  7.9  Figure  18.  a)  P l a n view o f a C a l l i a n a s s a burrow c a s t , showing bulbous 'turnarounds.' Cast i s about 60 cm i n p l a n view l e n g t h . M e t r i c r u l e r (lm) w i t h c e n t i m e t e r s u b d i v i s i o n s p r o v i d e s scale.  b)  S i d e view o f a C a l l i a n a s s a m i n e - l i k e n a t u r e of burrow 30 cm depth. M e t r i c r u l e r provides s c a l e . ^Overflow  c)  P l a n view o f a l a r g e C a l l i a n a s s a burrow c a s t which i s j u s t over 1 m l o n g . M e t r i c r u l e r (1 m) p r o v i d e s s c a l e .  burrow c a s t showing h o r i z o n t a l system. Burrow extends to about (1 m) w i t h c e n t i m e t e r s u b d i v i s i o n s o f r e s i n produced 'heads' on c a s t .  81 e x i t s have c o n s t r i c t e d a p e r t u r a l necks.  B r a n c h i n g i s dichotomous.  are bulbous turnarounds w i t h i n the systems and b l i n d a l l e y s . no d i s t i n c t  lining  There  There i s  to the burrow w a l l s except t h a t the sediment i s o x i d i z e d  and l i g h t e r i n c o l o u r . The l a c k o f a f i r m burrow l i n i n g and the h o r i z o n t a l , b r a n c h i n g n a t u r e of the burrows suggest they are temporary f e e d i n g burrows r a t h e r than permanent  d w e l l i n g burrows.  O t t e t a l . (1976) came to a s i m i l a r  r e g a r d i n g the burrows o f C a l l i a n a s s a s t e b b i n g i .  The geometry  conclusion  o f the  burrows o f C a l l i a n a s s a c a l i f o r n i e n s i s have a l l the c h a r a c t e r i s t i c s o f a mine used f o r d e p o s i t f e e d i n g .  However, the presence o f a bulbous chamber  c l o s e to the s u r f a c e does suggest that the shrimps may s u s p e n s i o n feed w h i l e the t i d e i s i n . A l l organisms to some e x t e n t a l t e r t h e i r environment to the b e n e f i t of some and d e t r i m e n t o f o t h e r s . Bay  T h i s i s nowhere more apparent i n Boundary  than i n the case o f C a l l i a n a s s a .  For example  Cryptomya  californica,  a s m a l l b i v a l v e , uses the sediment-water i n t e r f a c e o f the C a l l i a n a s s a burrow as a s u r f a c e f o r s u s p e n s i o n f e e d i n g , c l u s t e r i n g around the bulbous chamber 5-10 cm below the s u r f a c e .  On the other hand, on the s u r f a c e ,  Spio cannot c o l o n i z e the mounds heaped up by C a l l i a n a s s a because they dry o u t d u r i n g low t i d e , and C a l l i a n a s s a ' s e x c a v a t i o n a c t i v i t i e s p r o b a b l y choke s u r f a c e s u s p e n s i o n f e e d e r s l i k e Mya a r e n a r i a .  E e l g r a s s Zone The e e l g r a s s zone i s l a r g e l y lower amphizonal to upper aquazonal i n exposure  ( F i g . 8 ) , and i s , on the l a r g e s c a l e , f l a t , except where the  upper reaches o f t i d a l channels c r o s s the zone p r o d u c i n g b r o a d , s h a l l o w , water-filled  depressions  (e.g., between S t a t i o n s B18 to B25 on t r a n s e c t B ) .  The uppermost p a r t o f t h i s  zone i s dominated by a summer growth o f Z o s t e r a  americana, w h i l e i n the r e s t o f the zone a perennial-growth, o f Z. marina  82 i s present.  The f o l l o w i n g organisms and b i o g e n i c sedimentary s t r u c t u r e s  are t y p i c a l of the Z_. marina subzone. Upogebia Upogebia p u g e t t e n s i s (Dana), l i k e C a l l i a n a s s a , i s a t h a l a s s i n i d e a n burrowing shrimp.  I t has been s t u d i e d i n d e t a i l by Thompson (1972).  Upogebia o n l y o c c u r s on t r a n s e c t A, a p p e a r i n g a b r u p t l y a t the edge of the Z. marina subzone at A16, and a t t a i n i n g a maximum burrow opening d e n s i t y o f 44 m  -2  ( F i g . 17a).  There i s a r e g i o n o f o v e r l a p where C a l l i a n a s s a  and Upogebia burrows occur s i d e by s i d e .  Data c o l l e c t e d from the t i d a l  f l a t s o f the a c t i v e F r a s e r D e l t a f r o n t i n d i c a t e s t h a t Upogebia p r e f e r s muddy s u b s t r a t e s  (Swinbanks, T?79^ 'Part,;4'A)'X.' . . *T -,, ': v  Upogebia i s p r o b a b l y r e s t r i c t e d to the Z. marina beds on t r a n s e c t A i n Boundary Bay because o f t h e i r h i g h e r mud  content.  Upogebia uses mud  to  l i n e i t s burrow, and so i t i s not s u r p r i s i n g t h a t Upogebia's o c c u r r e n c e i s r e s t r i c t e d by the mud  content o f the sediment, p a r t i c u l a r l y i n an  environment such as Boundary Bay where mud  contents are o n l y a few p e r c e n t .  Amongst the organisms s t u d i e d Upogebia i s an e x c e p t i o n to the e a r l i e r c o n t e n t i o n that exposure time, r a t h e r than s u b s t r a t e , i s the prime l i n g agent o f f l o r a l / f a u n a l z o n a t i o n . i n Boundary Burrow M o r p h o l o g y — T h e  control-  Bay.  Upogebia burrow i s a 'Y' shaped  ( F i g . 19a).  The  two branches of the 'Y' system meet 20-30 cm below the s u r f a c e , and the burrow stem continues down to depths o f 50 to 60 cm.  In c o n t r a s t to  C a l l i a n a s s a burrows, Upogebia burrows are predominantly v e r t i c a l l y oriente'd,;"^ do not have c o n s t r i c t e d e n t r a n c e s , and l a c k bulbous turnarounds. i n t e r n a l w a l l s of the burrow are smooth and l i n e d w i t h mud.  The  Upogebia  burrows v e r y seldom have sediment mounds o u t s i d e t h e i r e n t r a n c e s , i n d i c a t i n g t h a t the burrows are p r o b a b l y not used f o r mining purposes. burrows appear to be permanent d w e l l i n g burrows.  Upogebia  Q t t e t al.•(1976) reached  F i g u r e 19.  a)  Cast of two Upogebia 'Y' shaped burrows j o i n e d by a c o n s t r i c t e d neck. Cast i s j u s t 50 cm i n depth. M e t r i c r u l e r (1 m) w i t h centimeter s u b d i v i s i o n s p r o v i d e s s c a l e .  b)  Side view of cast i n (a.) showing shrimp entombed w i t h i n the c a s t .  ,"  '.••<•/  over  r i  oo  84  85  a s i m i l a r c o n c l u s i o n r e g a r d i n g the burrows o f Upogebia l i t o r a l i s . 'Y' burrow much l i k e  Adjacent  systems are o f t e n i n t e r c o n n e c t e d by c o n s t r i c t e d a p e r t i i a l necks those d e s c r i b e d by Frey and Howard (1975) f o r Upogebia  affinis  ( F i g . 19a). The excavated c a s t s are f r e e o f any sand c o a t i n g , because o f the mud lining casts  to the burrows, and shrimps a r e c l e a r l y v i s i b l e entombed w i t h i n the ( F i g . 19b). F i v e  'Y' tube c a s t s were o b t a i n e d and i n v a r i a b l y  'Y' tube c o n t a i n e d one shrimp, g i v i n g a burrow 2 to 1. the  each  opening to shrimp r a t i o o f  The body w i d t h o f the shrimp determines the i n t e r n a l diameter o f  burrow.  Praxillela P r a x i l l e l a af f i n i s p a c i f i c a B e r k e l e y i ^ a tub~e-dwelling mald_ani'V£ p o l y c h a e t e worm, and i s c l o s e l y r e l a t e d t o C l y m e n e l l a t o r q u a t a d e s c r i b e d by Rhoads and S t a n l e y  (1965) and F e a t h e r s t o n e and R i s k (1977).  Praxillela  c o n s t r u c t s an a g g l u t i n a t e d sand tube up t o 15 cm i n l e n g t h and the worm l i v e s . u p s i d e down i n the tube and e x c r e t e s u n c o n s o l i d a t e d sandy the s u r f a c e  feces onto  ( F i g . 2 1 ) . I t o c c u r s i n the same a r e a o f the e e l g r a s s  Upogebia, b u t i s p r e s e n t on b o t h t r a n s e c t s .  zone as  I t a t t a i n s d e n s i t i e s o f 650  m  -2  ( F i g s . 20a & 20b), and extends i n t o the lower sand wave zone. No e v i d e n c e o f b i o g r a d e d bedding as d e s c r i b e d by Rhoads and S t a n l e y (1965) f o r C l y m e n e l l a was found i n the case of P r a x i l l e l a .  However, t h i s  i s n o t s u r p r i s i n g , s i n c e the sands i n which P r a x i l l e l a l i v e s on these t i d a l f l a t s a r e f i n e g r a i n e d and the worm need n o t be s e l e c t i v e about the g r a i n s i z e o f sediment i t e a t s .  The g r a i n s i z e d i s t r i b u t i o n o f the d w e l l i n g tubes  of P r a x i l l e l a were found to have an i d e n t i c a l g r a i n s i z e d i s t r i b u t i o n to t h a t of the s u r r o u n d i n g sediment, w i t h i n the e x p e r i m e n t a l e r r o r s of g r a i n size analysis.  T h i s i s c o n t r a r y to the f i n d i n g s o f F e a t h e r s t o n e and R i s k  (1977) who found t h a t the g r a i n s i z e d i s t r i b u t i o n o f C l y m e n e l l a tubes was  86  Nassarius  DENSITY (No. ru"*)  1  1  I 1 R  II  Z '  s o <  *  1000  ._L=_  1300  DISTANCE,  2000  maters  Nassarius DENSITY (No. P =• P R E S E N T  P  |  P  |  P  Jj  I  P  P |  |  P  i'  P  P  P  III  Pranilleifl DENSITY (No. in-*)  t i l l  1500 DISTANCE,  F i g u r e 20.  a) b)  2000 fliitin  D e n s i t i e s o f P r a x i l l e l a sp. and N a s s a r i u s D e n s i t i e s o f P r a x i l l e l a sp. and N a s s a r i u s  s p . on t r a n s e c t A. s p . on t r a n s e c t B.  87  PRAXILLELA.  -7T  E in  U  *  <r—»  3-4  F i g u r e 21.  mm  ( V e r t i c a l agglutinated.• ~sand;tube' of.,Eraxi 11 e l a  sp.  88 significantly slightly  c o a r s e r than'that  sediment.  c o a r s e r g r a i n s i z e of the sands i n Minas B a s i n  about 2.2  0 as opposed to 2.7  g r a i n s d u r i n g tube b u i l d i n g . those  of the s u r r o u n d i n g  rejected during  0 i n Boundary Bay) The  Perhaps :the  (median g r a i n s i z e  induces  s e l e c t i o n of  coarser grains possibly being  coarser  d e r i v e d from  feeding.  Nassarius Nassarius  mendicus ( G o u l d ) - i s a gastropod  Upogebia and P r a x i l l e l a  ( F i g s . 20a  moving than B a t i l l a r i a but  T h i s i s due  faster  d i s t i n c t i v e t r a c e s , apart  and P r a x i l l e l a are bimodal  to the presence of a t o p o g r a p h i c  d r a i n s o f f t h i s e l e v a t e d r e g i o n from both s i d e s and d u r i n g low  "  trail.  t r a n s e c t B the d i s t r i b u t i o n s of N a s s a r i u s  ( F i g . 20b).  alongside  I t i s more a c t i v e and  i t does not produce any  from a very s u p e r f i c i a l g r a z i n g On  & 20b).  which occurs  t i d e , whereas the d e p r e s s i o n  h i g h at B25.  Water  i t r a p i d l y d r i e s out  c e n t r e d on B20  remains w a t e r - f i l l e d ,  d e s p i t e the f a c t t h a t i t l i e s above sea l e v e l , because water c o n s t a n t l y d r a i n s i n t o i t . As a r e s u l t e l e v a t i o n s on  the r e g i o n near B25  the t i d a l  s p l i t by  the  topographic  has  higher the  Praxillela high.  This  t h a t the method o f s u b d i v i d i n g the i n t e r t i d a l zone i n t o  exposure zones, p r e s e n t e d flat is relatively  around B20  A bimodal d i s t r i b u t i o n of  r e s u l t s , the modes b e i n g  emphasizes the f a c t  the c h a r a c t e r i s t i c s of  f l a t , whereas the d e p r e s s i o n  c h a r a c t e r i s t i c s o f lower e l e v a t i o n s . and N a s s a r i u s  has  e a r l i e r , only holds  c o n s t a n t , w i t h no  abnormal exposure or prolonged  true i f the s l o p e of the  topographic  submergence due  highs  o r lows  to drainage  tidal  producing  effects.  Lower Sand Wave Zone The  lower sand wave zone i s aquazonal i n exposure ( F i g . 8):and i s  c h a r a c t e r i z e d by  l a r g e sand waves - and by  : Some q u a l i t a t i v e o b s e r v a t i o n s a t the end  the l a c k of a f l o r a l  cover.  of t h i s zone have been made, p a r t i c u l a r l y  of t r a n s e c t B which encroaches upon i t ( F i g . 2 ) .  Praxillela  and  89  l a r g e . A b a r e n i c o l a "\ are p r e s e n t i n t h i s  zone, as are sand d o l l a r s  (Kellerhals  and Murray, 1969), but a l l o t h e r organisms c o n s i d e r e d i n t h i s study absent  or p r e s e n t i n very low d e n s i t i e s .  sedimentary  structures.  R i p p l e s and  bedforms o f the r e s t of the zone.  of t h i s  DISCUSSION OF  The  characteristic  (1969) r e p o r t tidal  channels marina),  ( K e l l e r h a l s and Murray, 1969).  ZONATION  cause of i n t e r t i d a l z o n a t i o n has been a t o p i c o f g r e a t debate amongst  biologists  f o r many y e a r s , and  z o n a t i o n has  the e x t e n t o f the r o l e which t i d e s p l a y i n  been a matter of much c o n t r o v e r s y  19"&8^"Chapman and Bay  zone.  .  zone are l i n e d w i t h a dense growth o f e e l g r a s s (Z.  and s h e l l l a g d e p o s i t s are a l s o p r e s e n t  The  sand waves are the  K e l l e r h a l s and Murray  coarse sands a l o n g the lower p e r i m e t e r this  zone i s dominated by p h y s i c a l  Dunes l i n e the s i d e s of the t i d a l channels  ( K e l l e r h a l s and Murray, 1969).  which d i s s e c t  The  are  the evidence  ('Doty, 1957;  R i c k e t t s and'Calvin;,  Chapman, .1973I; Chapman, 1974;"''Carefoot, 1977)'.^ _ I n :  suggests  that tides,and i n p a r t i c u l a r c r i t i c a l  B o u n d a r y  tidal  levels,  are a major cause of z o n a t i o n . There are t h r e e f l o r a l zone l i m i t s which s u r v e y i n g and have r e v e a l e d to be saltmarsh  zone, the lower l i m i t  the e e l g r a s s zone. The  d e l i m i t e d by e l e v a t i o n .  These are the lower l i m i t  of the a l g a l mat  zone and  lower l i m i t  of the s a l t m a r s h m on  transect B  the e r r o r s o f s u r v e y i n g , w i t h  the  the upper l i m i t  lies  a t + 1.15; m  of  ( G e o d e t i c Datum) on  (Table I I ) . T h i s i s c o i n c i d e n t , w i t h i n  the lower l i m i t o f the upper atmozone (+ 1.16  8 ) , which i s a l e v e l a t which the maximum d u r a t i o n o f continuous  begins  of  F i g u r e 8 can o f f e r e x p l a n a t i o n s f o r a l l t h r e e .  t r a n s e c t A and + 1.10  Fig.  t o p o g r a p h i c maps  to r i s e a b r u p t l y from 12  L e v e l 3 exposures and  to 40 days.  r e s u l t sea water o n l y covers  exposure  I t i s a l s o the upper l i m i t  the e l e v a t i o n of the h i g h e s t lower h i g h water.  m,  of  As  t h i s a r e a d u r i n g the l a t e a f t e r n o o n , evening  a or  "\  90 at n i g h t i n summer.  The  saltmarsh  p r o l o n g e d d a y l i g h t exposure.  The  apparently  t h r i v e s under c o n d i t i o n s  of  p e r i o d t h a t a plant, i s c o n t i n u o u s l y "flooded  and  the d u r a t i o n of continuous exposure are b o t h l i m i t i n g f a c t o r s i n t h e i r  own  right  (Chapman, 1974).  Continuous f l o o d i n g l i m i t s p l a n t growth by  logging roots reducing  r e s p i r a t i o n due  s t r e s s and by  light availability.  reducing  physiological stress.  Nutrient  sodium i o n s i n p r e f e r e n c e salt stressed  delivery Waisel,  d e f i c i e n c y ,, s t r e s s i s caused by  r o o t r e s i s t a n c e thereby d e c r e a s i n g  not  apply_to  c o n s i d e r S a l i c o r n i a sp. to be  zone (Parsons,  an o b l i g a t e h a l o p h y t e  a h a l o p h y t e which r e q u i r e s s a l t  f o r optimum growth.  of o b l i g a t e h a l o p h y t e s i s q u e s t i o n a b l e  the s a l t m a r s h  zone i n Boundary Bay,  water than w i t h  1974)—i.e.  However, the  existance  Ungar, 1966).  soils.  s p i c a t a , which i s abundant throughout grows b e t t e r i n s o i l s a t u r a t e d w i t h  d i l u t e seawater or seawater.  at l e a s t i n the  physiological stress.  case of D i s t i c h l i s  Chapman (1974)'stressed' the importance of a l s o con-. . / plant  seedlings  r e q u i r e s e v e r a l days of continuous exposure w i t h o u t f l o o d i n g i n o r d e r  days w h i l e  root s u c c e s s f u l l y .  Aster  Bay  s p i c a t a , because f l o o d i n g imposes  s i d e r i n g the maximum d u r a t i o n of exposure, s i n c e s a l t m a r s h  germinate and  tap  I t i s t h e r e f o r e r e a s o n a b l e to  suggest t h a t f l o o d i n g frequency: i s a l i m i t i n g f a c t o r i n the Boundary saltmarsh,  Ungar,  because they  t e r r e s t i a l plants i n non-saline  (1975) found t h a t D i s t i c h l i s  5'  1975), as some  (1966) suggested t h a t h a l o p h y t e s grow i n s a l i n e s o i l s simply cannot compete e f f e c t i v e l y w i t h  1972;  '  (Chapman,  (Barbour, 1970;  and  water  (Levitt,  S a l i c o r n i a sp. , the p r e -  dominant h a l o p h y t e i n - t h e lower s a l t m a r s h  Parsons  by  i n h i b i t e d i n t r a n s p o r t of hormones to l e a v e s ,  also increases  T h i s may  uptake of  Hormonal s t r e s s i s induced  to l e a v e s , a l l of which r e s u l t s i n growth r e d u c t i o n 1972)~V  salinity  A s a l i n e environment imposes  to p o t a s s i u m i o n s .  roots being  osmotic p r e s s u r e  to l a c k of oxygen, imposing  water-  S a l i c o r n i a s t r i c t a requires  tripolium requires five  (Chapman, 1974).  two  to  to three  Continuous exposure  91 must coincide with germination.  The c r i t i c a l tides which define the boundary  between the upper and lower atmozones occur at the spring and autumn equinoxes (Swinbanks, ;1979)".  Saltmarsh /plant seedlings 'have'beeh^obs'erve'd  "  }  sprouting i n Boundary Bay i n March close to the time of the spring equinox, and so the long periods of continuous exposure which occur i n the upper atmozone at this time have a high probability of coinciding with seedling germination.  Thus there are reasonable physiological grounds for suggesting  that the break i n exposure duration and submergence frequency between the upper and lower atmozones i s a causative factor i n l i m i t i n g the saltmarsh zone rather than a mere coincidence. The lower l i m i t of the a l g a l mat zone coincides within the errors of surveying with the lower l i m i t of the lower atmozone (Fig. 8).  Apparently  the cyanophyte a l g a l mats thrive i n an area subject to the prolonged periods of exposure associated with Level 1 exposures. obligate photoautotrophs light.  Many blue-green algae are  (Fogg,et a l . , 1 9 7 3 ) — i . e . they cannot grow without  Phormidium sp. can grow very slowly i n the dark on a medium of glucose  and yeast autolysate (Allen, 1952), but for any blue-green algae to thrive, sufficient light i s essential.  However, as a l g a l mats can be found growing  on the crests of sand waves, w e l l below the lower l i m i t of the a l g a l mat zone i t would seem unlikely that the a l g a l mat zone i s l i g h t limited, but rather that desiccation for some reason i s necessary for the a l g a l mats to thrive. An a b i l i t y to withstand desiccation i s a c h a r a c t e r i s t i c feature of blue-green algae, and the vegetating c e l l s of O s c i l l a t o r i a c e a e (the family; tol which. Phormidium and Microcoleus belong) which have no perennating c e l l s , survive desiccation better than other families of blue-green algae (Fogg.-et a l . , 1973). Although some species show great resistance to desiccation, growth of these does not occur at r e l a t i v e humidities of less than 80% (Hess, 1962), and therefore desiccation must only be i n d i r e c t l y beneficial.'  92 I t has been demonstrated  t h a t c e r i t h i d g a s t r o p o d s , such as B a t i l l a r i a ,  d e s t r o y b l u e - g r e e n a l g a l mats by t h e i r g r a z i n g a c t i v i t i e s  (Garrett,  1970),  and i t has been suggested t h a t a l g a l mats a r e r e s t r i c t e d t o the uppermost intertidal  t o s u p r a t i d a l r e g i o n s because  g r a z i n g gastropods and burrowing  organisms are absent o r p r e s e n t i n low d e n s i t i e s i n these areas ( G a r r e t t , In Boundary Bay B a t i l l a r i a alone cannot l i m i t  1970).  the e x t e n t o f the a l g a l mat zone,  because B a t i l l a r i a d e n s i t i e s a r e the same o r o f the same o r d e r o f magnitude w i t h i n the a l g a l mat zone as w i t h o u t i t (see average d e n s i t i e s F i g s . 9a & 9 b ) . However, the g r a z i n g a c t i v i t i e s o f B a t i l l a r i a combined  w i t h the i n t e n s e \._  reworking a c t i v i t i e s o f A b a r e n i c o l a and C a l l i a n a s s a might be s u f f i c i e n t to limit  the e x t e n t o f the a l g a l mats.  The d e n s i t i e s o f A b a r e n i c o l a and .:  C a l l i a n a s s a i n c r e a s e a b r u p t l y near the lower l i m i t o f the a l g a l mat zone ( F i g s . 15a & 15b, F i g s . 17a & 17b). to be m u t u a l l y e x c l u s i v e , because  The a l g a l mats and these organisms  tend  the r a i s e d a l g a l mat p l a t f o r m s a r e dry and  i n h o s p i t a b l e t o the organisms, i n p a r t i c u l a r A b a r e n i c o l a , w h i l e the reworking and g r a z i n g a c t i v i t i e s o f the organisms i n h i b i t a l g a l mat f o r m a t i o n . I f burrowing and g r a z i n g organisms were absent from Boundary Bay, a l g a l mats would p r o b a b l y develop a t lower i n t e r t i d a l l e v e l s as demonstrated by G a r r e t t (1970).  I t i s t h e r e f o r e . s u g g e s t e d t h a t the s t e p i n exposure d u r a t i o n between  the amphizone and the atmozone s e t s the l i m i t  t o the a l g a l mat zone  because  d e s i c c a t i o n a s s o c i a t e d w i t h L e v e l 1 exposures d u r i n g neap t i d e s p r e v e n t s e x t e n s i v e p o p u l a t i o n by burrowing organisms, i n p a r t i c u l a r Abarenicola.•': The i n t e r a c t i o n between f l o r a and fauna i s an e s s e n t i a l element i n the r e s t r i c t i o n of the a l g a l mat zone, but the abruptness o f the zone's lower l i m i t i s caused by the s t e p - l i k e n a t u r e o f i n t e r t i d a l The'upper  exposure.  l i m i t o f the e e l g r a s s zone t e r m i n a t e s a t the upper l i m i t o f  the lower amphizone and thus never e x p e r i e n c e s L e v e l 2 exposures K e l l e r and H a r r i s  (1966) found a d i r e c t  (Fig.  8).  c o r r e l a t i o n , between ..the e x t e n t d f  Z. marina coverage and e l e v a t i o n i n Humboldt Bay, C a l i f o r n i a .  The e e l g r a s s  showed a pronounced upper l i m i t a t a l e v e l o f 15% mean exposure 0.3 m above MLLW.  They suggested that the upper l i m i t o f e e l g r a s s  i s c o n t r o l l e d by t i d a l  exposure, because d e s i c c a t i o n d u r i n g exposure decreases the v i g o r and v e g e t a tive reproduction  o f the e e l g r a s s .  The upper l i m i t o f e e l g r a s s i n Boundary  Bay l i e s a t a much h i g h e r t i d a l e l e v a t i o n (mean s e a l e v e l ) and i s exposed almost 50% o f the time ( F i g . 6 ) . However, t h e uppermost p a r t o f the e e l g r a s s zone i n Boundary  Bay c o n s i s t s e n t i r e l y o f the s m a l l e r s p e c i e s Z. americana.  We t h e r e f o r e suggest that the upper l i m i t o f the e e l g r a s s  zone t e r m i n a t e s  at the upper l i m i t o f the lower amphizone because Z_. americana cannot- t o l e r a t e L e v e l 2 exposures, which are always w e l l i n excess o f h a l f a l u n a r day and occur d u r i n g d a y l i g h t hours i n summer, and Z. americana r e q u i r e s the i n f l u x of seawater brought by lower h i g h water i n order t o s u r v i v e .  In Boundary Bay  the upper l i m i t o f Z. marina does n o t appear t o be c o n t r o l l e d by e l e v a t i o n but  r a t h e r seems to be s t r o n g l y i n f l u e n c e d by the d i s t r i b u t i o n o f t i d a l  channels.  T h i s i s w e l l i l l u s t r a t e d i n the map o f Z_. marina  p r e s e n t e d by O'Connell (1975). d u r i n g low t i d e d e s p i t e  The t i d a l  distribution  channels remain w a t e r - f i l l e d  the f a c t that they l i e w e l l above s e a l e v e l because  water c o n s t a n t l y d r a i n s i n t o them.  Z. marina growth extends up the f l o o r s  and f l a n k s o f the channels and has thus a t t a i n e d e l e v a t i o n s which i n theory have as much as 30% exposure ( S t a t i o n A17 a t - 0.5 m G e o d e t i c Datum), b u t i n f a c t u s u a l l y remain under s e v e r a l c e n t i m e t e r s o f water throughout low t i d e , because o f the presence o f a t o p o g r a p h i c low and because the dense mat  o f Z. marina i t s e l f  i n h i b i t s drainage.  The lower l i m i t o f the e e l g r a s s by e l e v a t i o n .  zone on the t i d a l f l a t s i s n o t d e l i m i t e d  I t may be l i m i t e d by the presence o r absence o f sand waves  or by the 'current or'~wave regime^ a s s o c i a t e d , with"-sand-w.aves  (Fig.  2).  94 SUMMARY  Each of  the  three  s a l t m a r s h zone and the assemblage,  floral/sedimentological  l o w e r s a n d wave zone h a s a d i s t i n c t i v e  and as a r e s u l t  (Fig. 22).  cannot be c o r r e l a t e d d i r e c t l y  Although l i v i n g  with trace  the  trace  f o s s i l record.  population  Topography o f  c r e a t e s l a t e r a l h e t e r o g e n e i t y w i t h i n the b i o f a c i e s of  (Fig.  23).  s m a l l and  of  large  e a c h zone  may b e p h y s i c a l o r b i o g e n i c i n o r i g i n .  c h a r a c t e r i s t i c biogenic sedimentary structures  is  living:.organisms •  scale  The t o p o g r a p h y  macrofaunal  fossil densities, it  a s s u m e d t h a t .the. distribution.'patterns:-and '.assemblages o f w i l l be p r e s e r v e d i n  the  e a c h zone h a s a c h a r a c t e r i s t i c a s s e m b l a g e o f  biogenic sedimentary structures densities  zones l y i n g between  The  e a c h zone a r e as  follows.  A l g a l Mat Zone The r a i s e d a l g a l mat p l a t f o r m s this  fication  c o n s i s t i n g of  riddled w i t h ' U ' larval origin. water-filled Batillaria this  ( F i g . 23a).  alternating  shaped burrows Batillaria pits  grazing t r a i l s  limit  have an i n t e r n a l  of  to strati-  sandy and o r g a n i c r i c h l a y e r s , w h i c h  are  (up t o 1 0 0 , 0 0 0 m ) , s u s p e c t e d t o b e o f  fly  - 2  a l s o a b o u n d on t h e r a i s e d p l a t f o r m s .  are abundant.  (10^ m  - 2  In ),  C a l l i a n a s s a a n d Mya b u r r o w s  i n v e r y low d e n s i t i e s .  and occur  A b a r e n i c o l a appears a b r u p t l y  near  t h e a l g a l mat z o n e .  The mean g r a i n s i z e o f 3 . 1 - 3 . 3 0.  The p l a t f o r m s  depressions Spio are present i n high d e n s i t i e s  zone, but  the lower  of  within  z o n e ' s b i o f a c i e s , b e c a u s e t h e y q u i c k l y become d r y a n d i n h o s p i t a b l e  organisms d u r i n g low t i d e  in  create l a t e r a l heterogeneity  the sands of  The s a n d s a r e w e l l  a n d c o n t a i n a b o u t 5% mud ( r a n g e  sorted  this (Incl.  3.6-8.0%).  zone u s u a l l y l i e  in  the  range  Graphic Std. Dev.-0.35-0.50  0)  ALGAL L E G E N D  Alg«I  Hat l a m i n a t i o n *  3at11larla BatH l a r l i  \f  ' U ' shaped burrows  (1  DISTANCE STRATIGRAPHIC S U C C E S S I O N  ALGAL  MAT  *? '  , * ; I I I  5  GRAIN  ,  (& 2  7  i  FROM  SIZE  ) i i_|^ 3  -  1  SALTMARSH, SORTING  (Inclutiv. Graphic Std. Dev.) «  2000  malar.  MUO  CONTENT  ^  grazing  Sp to d w e l l i n g  tubes  burrow;.  Calllanassa  burrows  burrows  Zostera  americana  Z o s t e r a marina  { '/•< S 3 JI |  trails {t F l y l a r v a e )  Abarenicola  Hye  MEAN  pits  *^3fc>  rootlets  rootlets  0 1 2 3 4 5 6 7 8 '  ZONE  "  t v i '  '  '  ALGAL MAT ZONE  PraxllIda  dwelling  tubes  UPPER SAND  UPPER  WAVE  SAND  ZONE Z O  WAVE  Upogebia  burrows  ZONE  u  Z  Nassarius  gracing  trails  EELGRASS EELGRASS  Grain  size  data  b a s e d on T r a n s e c t A  Grain  size  data based on Transect  Break  In e x p e c t e d  ZONE  UPPER  1  0  ZONE  ui  AQUAZONE  p r e s e n c e of Transect  F i g u r e 22.  VERY WELL  WILL  MOO WEIL  SOHTED  SORTED  SOHTCO  preserved  sequence:  a topographic  8 which w i l t  9  due t o t h e h i g h on  not  be  In t h e s u c c e s s i o n .  Z o n a t i o n o f b i o g e n i c sedimentary s t r u c t u r e s i n three o f the f l o r a l / s e d i m e n t o l o g i c a l zones o f Boundary Bay t i d a l f l a t s , and the expected s t r a t i g r a p h i c s u c c e s s i o n o f b i o g e n i c sedimentary s t r u c t u r e s and g r a i n s i z e parameters, i f the t i d a l f l a t s are p r o g r a d i n g seawards without subsidence.  'U' shaped burrows (7 Fly Larva*)  a)  B a t i l l a r i a pits Batl1larla grazing t r a i l s Algal mat laminations Sp lo tubas Ea I g r a s s  x x b)  AbarenI c o l a burrow  A l g a l mat  pla tforn  C a l l i a n a s s a burrow  Cryptomya sp.  c)  F i g u r e 23. L a t e r a l h e t e r o g e n e i t y w i t h i n z o n a l b i o f a c i e s caused by topography o f s m a l l and l a r g e s c a l e , a A l g a l mat zone: L a t e r a l h e t e r o g e n e i t y c r e a t e d by u p r a i s e d a l g a l mat p l a t f o r m s . b) Upper sand wave zone: L a t e r a l h e t e r o g e n e i t y c r e a t e d by sand waves. c) E e l g r a s s zone: L a t e r a l h e t e r o g e n e i t y c r e a t e d by C a l l i a n a s s a mounds and burrows  ON  97 Upper Sand Wave Zone T h i s zone i s c h a r a c t e r i z e d by l a c k o f a f l o r a l cover. of t h i s  zone.  c r e a t e d by  Mya  the presence of A b a r e n i c o l a and by  a t t a i n t h e i r maximum d e n s i t y i n the lower p a r t  L a t e r a l h e t e r o g e n e i t y w i t h i n the b i o f a c i e s of t h i s  the low  amplitude  sand waves ( F i g . 23b).  and Spio congregate i n the w a t e r - f i l l e d  troughs  Batillaria  of the sand waves,  grazing t r a i l s p a r a l l e l i n g  the sand wave c r e s t s , which dry out d u r i n g low  and  Weak c u r r e n t s produced  by water d r a i n i n g a l o n g the a x i s o f the sand wave troughs  On  zone i s  Abarenicola,  patches of Z o s t e r a americana are a l s o p r e s e n t h e r e .  to head upstream, p r o d u c i n g  the  cause  Batillaria  the c u r r e n t  direction.  tide, B a t i l l a r i a  grazing  t r a i l s are s i n u o u s , p i t t i n g by B a t i l l a r i a i s e v i d e n t , A b a r e n i c o l a d e n s i t i e s are low crests.  and  Spio are absent.  The  A l g a l mat  p l a t f o r m s may  be p r e s e n t  on  the  d i s t r i b u t i o n of C a l l i a n a s s a burrows i s not i n f l u e n c e d by  the  sand waves, because C a l l i a n a s s a i s a deeper burrowing organism, and i t s burrow system i s always w a t e r - f i l l e d , whether or not i t occurs wave  i n the sand  troughs.. The  sands o f t h i s zone have a mean g r a i n s i z e i n the range of 311-2.'..7 0.  They are w e l l to very w e l l s o r t e d ( I n c l . Graphic c o n t a i n about 1% mud,  except  S t d . Dev.  0.33-0.39 0 ) ,  at the zones upper l i m i t where v a l u e s  rise  and to  4%.  E e l g r a s s Zone The  e e l g r a s s zone can be s u b d i v i d e d i n t o an upper and  upper e e l g r a s s zone i s c h a r a c t e r i z e d by a ^ Z o s t e r a Abarenicola-Batillaria  lower p a r t .  The  americana-Callianassa-  'community, ) w h i l e the lower e e l g r a s s zone i s charac-  t e r i z e d by a '-Zostera m a r i n a - U p o g e b i a - P r a x i l l e l a - N a s s a r i u s '  community.  C a l l i a n a s s a a t t a i n t h e i r maximum d e n s i t i e s i n the upper e e l g r a s s zone.  Their  sediment mounds and burrows c r e a t e l a t e r a l h e t e r o g e n e i t y w i t h i n the b i o f a c i e s o f t h i s zone ( F i g . 23c). i s present  In the lower e e l g r a s s zone Z o s t e r a marina growth  throughout the y e a r , and,  i f i t forms an e x t e n s i v e and  permanent  98 f l o r a l mat,  mud  accumulates i n t h i s  zone.  The mean g r a i n s i z e i n the e e l g r a s s zone i s i n the range of 2.4-2.8 0 . The  sands are very w e l l to moderately  0.29-0.60 0 ) ,  and i n the upper e e l g r a s s zone c o n t a i n about 1% mud,  i n the lower e e l g r a s s zone mud an e x t e n s i v e f l o r a l mat, The  w e l l s o r t e d ( I n c l . Graphic S t d .  contents  can a t t a i n  s u c c e s s i o n of b i o f a c i e s and Boundary Bay  of the Bay,  zone.  1%.  the expected  stratigraphic  g r a i n s i z e parameters i f the t i d a l f l a t s  are p r o g r a d i n g w i t h o u t  the a l g a l mat  while  7% i f Z. marina forms  i f not, values- drop w e l l below  lower h a l f of F i g u r e 22 i l l u s t r a t e s  subsidence,  and  of  a core were sunk i n  T h i s s u c c e s s i o n might be expected  where there i s evidence  Dev.  i n the w e s t e r n h a l f  t h a t the s a l t m a r s h i s  advancing  ( K e l l e r h a l s and Murray, 1969).  CONCLUSIONS  In Boundary Bay  a distinct  f l o r a l / f a u n a l z o n a t i o n e x i s t s , which i s  c o n t r o l l e d p r i m a r i l y by exposure, although p l a y an important  role.  The  f l o r a l / f a u n a l interactions also  e x t e n t of exposure which a g i v e n l o c a t i o n on  the  t i d a l f l a t experiences-) i s a f u n c t i o n o f the r e l a t i o n s h i p between e l e v a t i o n and  t i d e s , and  i s a l s o a f u n c t i o n o f l o c a l topography, which may  or b i o g e n i c o r i g i n .  be of p h y s i c a l  For t i d a l f l a t s e x p e r i e n c i n g a s t r o n o m i c a l l y c o n t r o l l e d  t i d e s , the i n t e r t i d a l zone can be d i v i d e d i n t o t h r e e d i s t i n c t exposure zones. The  d u r a t i o n of maximum continuous  exposure o r maximum continuous  'jumps' on p a s s i n g from one.zone to the n e x t . zones to a l a r g e e x t e n t d e l i m i t macroscopic  scale.  these exposure  the f l o r a l z o n a t i o n o f the t i d a l f l a t s on  However, on-the more l o c a l s c a l e , topography can be  to p r o f o u n d l y i n f l u e n c e f a u n a l and  the  seen  f l o r a l d i s t r i b u t i o n p a t t e r n s , s i n c e topo-:.:--. :.c  graphic-,highs dry :out r a p i d l y , d u r i n g low water-filled.  In Boundary Bay  submergence  t i d e , while depressions  remain:  .  99  Boundary Bay t i d a l f l a t s previously described over the b u l k  a r e e x c e p t i o n a l , i n comparison w i t h  i n the l i t e r a t u r e , because g r a i n s i z e v a r i e s  o f the t i d a l f l a t s .  to very w e l l s o r t e d f i n e to very continues  The f l a t s f i n e sand.  a r e mantled w i t h  intertidal  t a t i o n of f l o r a l / f a u n a l zonation attempting patterns  clean, well  from box c o r e s .  of t h i s homogeneity i n g r a i n s i z e Boundary Bay t i d a l rocky  flats  s h o r e l i n e s where p r e c i s e e l e v a t i o n a l d e l i m i i s w e l l documented ( C a r e f o o t , 1977).  (e.g. g r a i n s i z e , mud content  to the w a t e r l i n e  Because  a r e t o some e x t e n t  to e l u c i d a t e the e f f e c t s o f o t h e r parameters on f a u n a l  the e l e v a t i o n parameter.  little  The homogeneity i n g r a i n s i z e  to a depth o f a t l e a s t 30 cm, as r e v e a l e d  comparable w i t h  those  or s a l i n i t y ) ,  In  distribution  one must f i r s t  eliminate  T h i s can be done by s e t t i n g up s t a t i o n s p a r a l l e l  a t some chosen t i d a l h e i g h t ,  from t r a n s e c t s s e t up p e r p e n d i c u l a r  r a t h e r than u s i n g d a t a c o l l e c t e d  to the s h o r e l i n e .  I n a d d i t i o n to e l i m i -  n a t i n g the e l e v a t i o n parameter, one must take care to compare s t a t i o n s w i t h comparable topographic s i t u a t i o n s . The  most s t r i k i n g f e a t u r e o f Boundary Bay t i d a l f l a t s i s t h e f a c t  from s h o r e l i n e to low water mark the t i d a l a result  flats  the s t r a t i g r a p h i c s u c c e s s i o n p r e s e r v e d  a r e mantled w i t h by t h i s t i d a l  that  sand.  As  f l a t would  c o n s i s t o f a monotonous sequence o f sand, and the only means by which a d e t a i l e d i n t e r p r e t a t i o n o f the s u c c e s s i o n the study o f b i o g e n i c by  grain size analysis  c o u l d be made, would be through  sedimentary s t r u c t u r e s  (both  f l o r a l and f a u n a l ) , and  techniques.  ACKNOWLEDGEMENTS  Mrs. data. No.  M. Muhlert and Ms. N. Hayakawa ably a s s i s t e d i n c o l l e c t i o n of f i e l d  T h i s p r o j e c t was f i n a n c e d by G e o l o g i c a l Survey o f Canada c o n t r a c t D.S.S.  0SS76-02075 from the Department o f Supply and S e r v i c e s , Ottawa,  Ontario,  100  Canada.  We a r e i n d e b t e d t o W. Weir o f C.B.A. E n g i n e e r i n g L t d . , Vancouver,  f o r p r o v i d i n g t i d a l d a t a from the Boundary Bay a r e a .  Many p r o f i t a b l e  discus-  s i o n s r e s u l t e d from c o n t a c t w i t h Dr. J . L. L u t e r n a u e r , G e o l o g i c a l Survey o f Canada.  We thank Dr. W. C. Barnes, Dr. C. D. L e v i n g s and Dr. J . P. S y v i t s k i '  for c r i t i c a l l y  r e a d i n g the m a n u s c r i p t .  H a r r i s o n , Botany Department, in  E s p e c i a l thanks a r e due t o Dr. P. G.  University of B r i t i s h  Columbia f o r a s s i s t a n c e  the s p e c i e s i d e n t i f i c a t i o n o f e e l g r a s s , and to Dr. T. H. C a r e f o o t , Zoology  Department,  U n i v e r s i t y of B r i t i s h  Columbia, f o r a s s i s t a n c e i n the d i s s e c t i o n  and i d e n t i f i c a t i o n o f A b a r e n i c o l a s p . We thank Mrs. C. M. Armstrong, Mr. B. von S p i n d l e r and Mr. G. D. Hodge f o r d r a f t i n g the diagrams, and Ms. N. Hayakawa f o r t y p i n g the s c r i p t .  L a s t l y , thanks a r e due to Dr. J . D. M i l l i m a n ,  c u r r e n t l y o f Woods Hole Oceanographic I n s t i t u t i o n , Woods H o l e , M a s s a c h u s e t t s , for i n i t i a t i n g  f i n a n c i a l support f o r t h i s  project.  101  REFERENCES A l l e n , M. B., 1952, The v. 17, p. 34-53.  c u l t i v a t i o n of Myxophyceae:  Arch. M i k r o b i o l . , •  A l l e r , R. C. and Dodge, R. E., 1974, Animal-sediment r e l a t i o n s i n a t r o p i c a l lagoon, D i s c o v e r y Bay, Jamaica: Jour. Mar. Res., v. 32, p. 209-232. Barbour, M. G., 1970, Is any angiosperm an o b l i g a t e halophyte? Nat., v. 84(1), p. 105-120.  Amer. Mid.  .•Care f o o t , TT C., 1977 ,-. P a c i f i c "Seashores :•" a guide.• to I n t e r t i d a l " "Ecology : TT J.^Douglas "Ltd'.,"" Vancouver, 20'8~p.' *'y * Chapman," V. J . 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M.Sc. t h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, B. C., 153 p. O ' C o n n e l l , G., 1975, F l o r a and fauna of Boundary Bay t i d a l f l a t s , B r i t i s h Columbia: unpub. r e p o r t to B. C. Government P r o v i n c i a l P a r k Branch, V i c t o r i a , B. C. O t t , J . A., Fuchs, B., Fuchs, R., and Malasek, A., 1976, O b s e r v a t i o n s on the b i o l o g y o f C a l l i a n a s s a s t e b b i n g i B o r r o d a i l e and U p o g e b i a . l i t o r a l i s R i s s o and t h e i r e f f e c t upon sediment: Senckenbergiana m a r i t i m a , v. 8, p. 61-79. Parsons, C. 0., 1975, V e g e t a t i o n p a t t e r n i n a s a l t marsh a t Boundary B. C : Lamda, v. 1 ( 2 ) , p. 45-52.  Bay,  Postma, H., 1961, T r a n s p o r t and a c c u m u l a t i o n o f suspended, matter i n the Dutch Wadden Sea: Neth. J o u r . Sea Research, v. 1, p. 148-190. Reineck, H. E., 1958^."Wuhlbau-Gef'uge i n A b h a n g i g k e i t von SedjLment-Umlagerungen: .Senckenbergiana-Lethaea, B-... 39,..p. 1-23, 54-56. \ 1967, L a y e r e d sediments o f t i d a l f l a t s , .beaches, and s h e l f bottoms o f the North Sea: I n L a u f f , G. H. (ed:) , E s t u a r i e s , Amer. -Assoc. adv. S c i S p e c . Pub.lv 83, p. 191-206. •>-,-,.. Rhoads, D. C , 1975, T h e . p a l e o e c o l o g i c a l and e n v i r o n m e n t a l s i g n i f i c a n c e o f trace f o s s i l s : I n F r e y , R. W. ( e d . ) , The Study o f Trace F o s s i l s , S p r i n g e r V e r l a g , New York, P. 147-160. ))  and S t a n l e y , D. J . , 1965, P e t r o l o g y , v . 35, p. 956-963.  B i o g e n i c graded bedding:  J o u r . Sed.  and Young, D. K., 1970, The i n f l u e n c e of- d e p o s i t - f e e d i n g benthos on bottom s t a b i l i t y and community t r o p h i c s t r u c t u r e : J o u r . Marine Res., v. 28, p. 150-178. CRicketts., . E. F. and C a l v i n , J . ( e d s . ) , 1968, Between P a c i f i c T i d e s (4th e d . ) : S t a n f o r d U n i v e r s i t y P r e s s , S t a n f o r d , C a l i f o r n i a , 614 p.  104  R i s k , M. J . , M o f f a t , J . S., Yeo, R. K., C r a i g , H. D. and T u n n i c l i f f e , V. J . , 1976, Animal-sediment r e l a t i o n s h i p s i n the Minas B a s i n , Bay o f Fundy: Geol. Assoc. Canada Program w i t h A b s t r a c t s , v. 1, p. 84. , 1977, S e d i m e n t o l o g i c a l s i g n i f i c a n c e o f f e c a l p e l l e t s o f Macoma b a l t i c a i n Minas B a s i n , Bay o f Fundy: Jour. Sed. P e t r o l o g y , v. 47, p. 1425-1436. S c h S f e r , W., 1972, Ecology and p a l a e o e c o l o g y o f marine environments: Oliver and Boyd and U n i v e r s i t y Chicago P r e s s , Edinburgh and Chicago, 568 p. S e i l a c h e r , A., 1964, B i o g e n i c sedimentary s t r u c t u r e s : I n Imbrie, J . , and N e w e l l , N. D. ( e d s ) , Approaches t o p a l e o e c o l o g y , John W i l e y , New York, p. 296-316. Shinn, E. A. , 1968, Burrowing i n r e c e n t lime sediments o f F l o r i d a and the Bahamas: J o u r . P a l e o n t o l o g y , v. 42, p. 879-894. Smith, R. I . and C a r l t o n , J . T., ( e d s . ) , 1975, L i g h t ' s Manual: intertidal i n v e r t e b r a t e s o f the c e n t r a l C a l i f o r n i a c o a s t : T h i r d E d i t i o n , U n i v e r s i t y of C a l i f o r n i a P r e s s , B e r k e l e y , Los Angeles, 716 p. Swan Wooster, 1968, Roberts B a n k — S t a g e 1 dredging and r e c l a m a t i o n : wind information: r e p o r t o f Swan Wooster E n g i n n e r i n g L t d . to N a t i o n a l Harbours Board, Vancouver, B. C. Swinbanks, D. D., 1979, Environmental f a c t o r s c o n t r o l l i n g f l o r a l z o n a t i o n and the d i s t r i b u t i o n o f burrowing and t u b e - d w e l l i n g organisms on F r a s e r D e l t a t i d a l f l a t s , B r i t i s h Columbia: unpub. Ph.D. t h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, B. C , 274 p. and Murray, J . W., 1977, Animal-sediment r e l a t i o n s h i p s o f Boundary Bay and Roberts Bank t i d a l f l a t s , F r a s e r R i v e r D e l t a : Geol. Assoc. Canada Program w i t h A b s t r a c t s , v. 2, p. 51. Thompson, R. K., 1972, F u n c t i o n a l morphology o f the h i n d - g u t o f Upogebia p u g e t t e n s i s ( C r u s t a c e a , T h a l a s s i n i d e a ) and i t s r o l e i n burrow c o n s t r u c t i o n : unpub. Ph.D. t h e s i s , U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y , 202 p. and P r i t c h a r d , A. W., 1969, R e s p i r a t o r y adaptions o f two burrowing c r u s t a c e a n s , C a l l i a n a s s a c a l i f o r n i e n s i s and Upogebia p u g e t t e n s i s (Decapoda, T h a l a s s i n i d e a ) : B i o l . B u l l . , v. 136, p. 274-287. T o r r e s , J . J . , Gluck, D. L. and C h i l d r e s s , J . J . , 1977, A c t i v i t y and p h y s i o l o g i c a l s i g n i f i c a n c e o f the pleopods i n the r e s p i r a t i o n o f C a l l i a n a s s a c a l i f o r n i e n s i s (Dana) ( C r u s t a c e a : T h a l a s s i n i d e a ) : B i o l . B u l l . , v. 152, p. 134-146. Ungar, I . A., 1966, S a l t t o l e r a n c e o f p l a n t s growing i n s a l i n e areas o f Kansas and Oklahoma: E c o l o g y , v. 47, p. 154-155. Van  S t r a a t e n , L.M.J.U., 1952, Biogene t e x t u r e s and the f o r m a t i o n o f s h e l l beds i n the Dutch Wadden Sea, I & I I : P r o c . K o n i n k l . Ned. Akad. " Wetenschap., B55, p. 500-516.  105 Van  S t r a a t e n , L.M.J.U., and Kuenen, PH.H., 1958, T i d a l a c t i o n as a cause o f c l a y accumulation: J o u r . Sed. P e t r o l o g y , v. 28, p. 406-413.  W a i s e l , Y. X-ed.), 1972, B i o l o g y o f h a l o p h y t e s : 395 p.  Academic P r e s s , New York,  Waldichuk, M., 1957, P h y s i c a l oceanography o f the S t r a i t o f G e o r g i a , Columbia: J o u r . F i s h . Res. B r d . Canada, v. 14, p. 321-486.  British  Weir, W., 1963, Boundary Bay r e c l a m a t i o n : P a r t I I I — R e p o r t on c u r r e n t measurements and t i d a l a n a l y s i s . P r i v a t e r e p o r t o f C.B.A. E n g i n e e r i n g L t d . , Vancouver, B. C. W h i t l a c h , R. B., 1974, S t u d i e s o f the s a l t - m a r s h gastropod V e l i g e r , v. 17, p. 47-55.  Batillaria  zonalis:  Part 3 SEDIMENT REWORKING AND THE BIOGENIC FORMATION f OF CLAY LAMINAE BY ABARENICOLA PACIFICA  107  ABSTRACT  An e s t i m a t e d Bay  4.25 x 10  on the s o u t h e r n  g  Abarenicola populate  the t i d a l f l a t s o f Boundary  f l a n k o f the F r a s e r D e l t a and a n n u a l l y  m i l l i o n c u b i c meters o f sand.  rework about one  In t i d a l p o o l s , where A b a r e n i c o l a  attain  -2 d e n s i t i e s o f 200 m  , the worms completely  rework the s u b s t r a t e they  live i n  to a depth o f 10 cm i n 100 days. In the l a b o r a t o r y A b a r e n i c o l a  can separate  f l o a t i n g the c l a y o u t i n s u s p e n s i o n  a sand/clay  m i x t u r e , by  i n the head s h a f t i r r i g a t i o n c u r r e n t .  The  c l a y then s e t t l e s as a b i o g e n i c a l l y formed lamina, which i s subsequently b u r i e d and reworked by the worm.  I n the n a t u r a l i n t e r t i d a l environment the  c l a y would be c a r r i e d away by t i d a l c u r r e n t s , and by u s i n g t h i s Abarenicola s o r t e d sand.  could  process  ' c l e a n ' mud out of a mud/sand m i x t u r e c r e a t i n g a b e t t e r  108  INTRODUCTION  The  t o p i c of b i o t u r b a t i o n and b i o d e p o s i t i o n has  i n c r e a s i n g a t t e n t i o n i n the l i t e r a t u r e Young, 1970;  A l l e r and  c l a s s i c work i n t h i s Van  S t r a a t e n , 1952;  sediment and Stanley,  Dodge, 1974;  (Rhoads and  Reineck, 1958;  German and  Schafer,  c r e a t e b i o g e n i c graded b e d d i n g  1965;  Featherstone  and  S t a n l e y , 1965;  Risk and M o f f a t ,  f i e l d has been by  R i s k , 1977).  r e c e n t l y been r e c e i v i n g  1977).  Much of  Organisms can  (Van S t r a a t e n , 1952;  compressibility, etc.).  b i o l o g i c a l consequences. i n g and  nisms from the a r e a During flats one  can produce an u n s t a b l e  c u r r e n t s and which thereby  a study  (Swinbanks, 1979)  on the southern  A l l e r and  T h i s pply^chaete  mounds of l o o s e l y c o i l e d sediment onto the s u r f a c e .  and  filter  feeding  (Fig. 1).  orga-  Dodge, 1974). tidal  limit  interesting  produces the  By c o n s t a n t l y  the e x t e n t  I t i s thus of i n t e r e s t  was }  ;  continually excreting reworking  o f the a l g a l mat  of the f i v e major f l o r a l / s e d i m e n t o l o g i c a l zones of the t i d a l  (Swinbanks, 1979)  and  f l a n k of the F r a s e r D e l t a ( F i g . 1 ) ,  of b i o t u r b a t i o n i n Boundary Bay,  the s u r f a c e sediments A b a r e n i c o l a may  relief,  through t h e i r burrow-  of the organisms s t u d i e d which proved to be e s p e c i a l l y  most v i s i b l e evidence  and  sedi-  (e.g.,  o f b i o s e d i m e n t o l o g i c a l z o n a t i o n on Boundary Bay  A b a r e n i c o l a p a c i f i c a Healy and W e l l s .  one  Rhoads  substrate that i s e a s i l y  tends to exclude  (Rhoads and Young, 1970;  size-sort  both s e d i m e n t o l o g i c a l  For example, d e p o s i t f e e d e r s  feeding a c t i v i t i e s  reworked by  T h i s has  the  c o n s t a n t l y reworking  ments, organisms can d r a s t i c a l l y a l t e r i t s p h y s i c a l p r o p e r t i e s water content,  and  Dutch workers (Schwarz,.1932;  1972).  By  Rhoads  zone -  flats  from both the e c o l o g i c a l  s e d i m e n t o l o g i c a l p o i n t of view to determine the r a t e at which t h i s  orga-  nism reworks sediment. A b a r e n i c o l a p a c i f i c a i s the P a c i f i c coast e q u i v a l e n t of the w e l l known lugworm, A r e n i c o l a marina, which i s found on the A t l a n t i c c o a s t s of North  109  I  F i g u r e 1.  LOWER SAND WAVE ZONE  <;;;"•;;,  SAND W A V E  FIXED  BY E E L G R A S S  L o c a t i o n o f study a r e a . * Upper m a p s n w of Boundary Bay on the F r a s e r D e l t a and the lower maps the f l o r a l / s e d i m e n t o l o g i c a l zones o f the t i d a l f l a t s . The two t r a n s e c t s A and B were s e t up i n 1976 (Swinbanks, 1979).  110  America and Europe, and which i s mentioned i n s e v e r a l i n t e r t i d a l s t u d i e s by sedimentologists  (Van S t r a a t e n , 1952; Reineck, 1958; Evans,  1965).  A b a r e n i c o l a p a c i f i c a i s a d e p o s i t feeder b u t there i s some evidence t h a t , as i n the case o f A r e n i c b l a marina, i t may a l s o s u s p e n s i o n feed by f i l t e r i n g the s e a water t h a t i t c i r c u l a t e s (Hobson, 1967).  through i t s burrow  I t c o n s t r u c t s a ' J ' shaped burrow w i t h a v e r t i c a l  s h a f t , and h o r i z o n t a l g a l l e r y  Hylleberg  micro-organisms  Hylleberg  the percentage o f coarse by Van S t r a a t e n f o r Clymenella selectively  'gardens' the sediment by  c r e a t i n g an o x i d i z i n g micro-environment i n which the  (e.g., c i l i a t e s ,  feeds, f l o u r i s h .  lies  ( H y l l e b e r g , 1975; Swinbanks,  (1975) suggested t h a t A b a r e n i c o l a  i r r i g a t i n g i t s burrow,  tail  t h a t ends i n a f e e d i n g chamber above w h i c h  a cone o f c o l l a p s e d sediment on which i t feeds 1979).  f o r r e s p i r a t i o n purposes  f l a g e l l a t e s and nematodes),  (1975) found t h a t A b a r e n i c o l a  on which i t  locally  increases  g r a i n s around i t s f e e d i n g chamber much as r e p o r t e d  (1952) f o r A r e n i c o l a marina and by Rhoads and S t a n l e y tOrquata.  Hylleberg  f e e d i n g on sediment l e s s  of b i o g e n i c s i z e - s o r t i n g ,  (1965)  (1975) a t t r i b u t e d - t h i s to A b a r e n i c o l a than 80 um i n s i z e .  Another mechanism  caused by A b a r e n i c o l a i r r i g a t i n g i t s b u r r o w ; - i s  reported here. There are f i v e f l o r a l / s e d i m e n t o l o g i c a l zones on the Boundary flats  ( F i g . 1 ) . These a r e , from the s h o r e l i n e seawards,  Bay t i d a l  the s a l t m a r s h  zone,  the a l g a l mat zone, the upper sand wave zone, the e e l g r a s s zone and the lower sand wave zone.  A b a r e n i c o l a i s most abundant! i n the upper sand .wave zone and  appears a b r u p t l y near the lower l i m i t o f the a l g a l mat' zone. -2 rises 100 m.  from much l e s s than 0.5 m  -2 t o about 20 m  i n the d i s t a n c e o f l e s s than  They are no changes i n g r a i n s i z e parameters  mud c o n t e n t ) over t h i s i n t e r v a l  I t s density  (Swinbanks, 1979).  (mean s i z e , s o r t i n g o r Hobson (1967) and Healy  and W e l l s (1959) c o n s i d e r t h a t sediment type r a t h e r than i n t e r t i d a l governs the d i s t r i b u t i o n .of A b a r e n i c o l a p a c i f i c a and A b a r e n i c o l a  exposure  claparedi  Ill vagabunda H e a l y  andJJelXs_ in .False.'.Bay., on  San Juan . I s l a n d ,  p r e f e r r i n g muddy s u b s t r a t e s and A., vagabunda c l e a n sand.  pacifica  I n Boundary Bay  A. p a c i f i c a i s abundant i n pure sands c o n t a i n i n g o n l y about 1% mud, and t h e a b r u p t upper l i m i t t o t h e i r d i s t r i b u t i o n o c c u r s a t a c o n s t a n t e l e v a t i o n t h a t i s p r o b a b l y d e t e r m i n e d by exposure (Swinbanks, 1979).  METHODS  Two t r a n s e c t s r u n n i n g n o r t h / s o u t h from t h e s a l t m a r s h edge t o low w a t e r mark were e s t a b l i s h e d i n the summer o f 1976 (Swinbanks, 1979) ( F i g . 1 ) . S t a t i o n s marked w i t h wooden s t a k e s were p l a c e d a t 91.4 m (300 f t ) i n t e r v a l s and t h e i r e l e v a t i o n s d e t e r m i n e d by s u r v e y i n g .  The r a t e a t w h i c h A b a r e n i c o l a  reworks sediment was d e t e r m i n e d i n June, 1976, November, 1976 and August, 2 1978.  A 1 m  area.was  s t a k e d o u t a t s t a t i o n s A5 t o A14 on t r a n s e c t , A ( F i g . 1)  j u s t as the: w a t e r l i n e r e t r e a t e d from t h e o a r e a . _ A l l A b a r e n i c o l a c a s t s were c a r e f u l l y removed and counted.  The s t a t i o n s were r e o c c u p i e d about 10 hours  l a t e r j u s t b e f o r e t h e t i d e r e t u r n e d and t h e volume o f c a s t s accumulated was measured w i t h a g r a d u a t e d c y l i n d e r .  To d i s t i n g u i s h 'wet' s i t e s from 'dry' a  d e p r e s s i o n about 1 cm deep was made i n the sand w i t h a f i n g e r a f t e r about 10 hours o f e x p o s u r e . was  I f the d e p r e s s i o n i m m e d i a t e l y f i l l e d w i t h w a t e r t h e s i t e  c o n s i d e r e d 'wet;' I n t h e l a b o r a t o r y A b a r e n i c o l a was k e p t and o b s e r v e d i n sandwich tanks  u s i n g t h e r u n n i n g s e a w a t e r f a c i l i t i e s o f the P a c i f i c Environment  Institute,  West Vancouver, d u r i n g t h e w i n t e r o f 1977. Worms were p l a c e d i n wet s i e v e d Boundary Bay sand (>63- ijm) , w h i c h had been homogenized %  w e i g h t ) f i n e l y powdered (<63 um) m o n t m o r i l l o n i t e .  w i t h about 10% (by  Abarenicola's a b i l i t y to  s i z e s o r t sediment was c l e a r l y v i s i b l e u s i n g t h i s t e c h n i q u e as c o n c e n t r a t i o n s of the f i n e grained white montmorillonite stood out i n constrast to the dark grey sand.  112  RESULTS F i e l d Results  Sediment Reworking Rates  The  r a t e a t which A b a r e n i c o l a reworks sediment d u r i n g v a r i o u s  times  of the y e a r i s p r e s e n t e d i n T a b l e s I and I I . .In the upper sand wave zone ( s t a t i o n s A5 to A12),  the f a c t o r which seems to i n f l u e n c e the r a t e o f s e d i -  ment t u r n o v e r most i s the wetness o f the sediment.  The h i g h e s t r a t e s were  r e c o r d e d i n t i d a l p o o l s where the worms remain under water d u r i n g low t i d e . They e x c r e t e 5.1 ± 2.4 wet ml worm ^ day average.  (1 wet ml=1.5 g d r y weight) on  Rates were lower i n sediment which remained wet b u t n o t under water,  the average  r a t e b e i n g 1.8 ± 0.9 wet ml worm ^ day  sediment, a v e r a g i n g 0.5 ± 0.6 wet ml worm ^ day ^. regions  intertidal  The "rates ^of sediment t u r n o v e r a t  ;  s t a t i o n s A5 t o A12 do n o t decrease  it  I n the lower  ( S t a t i o n s A13 and A14) r a t e s were an o r d e r o f magnitude h i g h e r ,  a v e r a g i n g 29 ± 18 wet ,mr worm ^ % a y ,  wet  and lowest i n dry  r a t e i n June averaged  :  g r e a t l y between summer and w i n t e r .  The  2.5 ± 0 . 5 wet ml worm ^ day ^ w h i l e i n November  dropped to 0.9 ± 0.4 wet ml worm ^ day ^, b u t the under water r a t e d i d n o t  decrease  (June, 4.4 ± 2.7 wet ml worm  worm ^ day " S .  day  November, 6.6 + 2.3 wet ml  On the o t h e r hand f o r the worms p r o d u c i n g h i g h r a t e s o f s e d i -  ment t u r n o v e r i n summer a t A13 and A14, there i s such a marked decrease i n r a t e of turnover i n winter  t h a t f e c a l c a s t s are very hard to f i n d . When present"  they o n l y c o n t a i n 1 or 2 ml o f sediment as opposed t o 20 to 50 ml i n summer.  Budget o f Sediment  Turnover  T a k i n g i n t o account  the above v a r i a b l e r a t e s , an annual budget-^of  ment t u r n o v e r by A b a r e n i c o l a can be c a l c u l a t e d u t i l i z i n g d e n s i t y d a t a  sedi-  113  TABLE I  Rates o f Sediment  Turnover by A b a r e n i c o l a  June 28, 1976 Mean A i r Temperature 18.5 °C (range 16-21 °C)_  Station  A5 A6/A7 A8 *A9 1/3 All A13  State of Substrate  Rate_ (wet ml worm  dry dry dry wet dry u.w.  1  day  )  0.02 0.72. 0.08 3.05 ' 0.30 18.00  H  43 102 18 37 10 5  * Between A9 and A10 30.5 m (100 f t ) from A9 •  June 30, 1976 Mean A i r Temperature 17 °C (range 13-20 °C)  Station  A5 A6 A7 A8 A9 A10 All A12 A13 A14  State of Subs t r a t e u.w. u.w. u.w. u.w. dry wet wet wet u.w. u.w.  Rate (wet ml worm  Note:  8.4 2.8 4.0 2.5 1.4 2.6 1.9 2.4 21.8 19.6  -  N = number o f f e c a l c a s t s i n sampled u.w. = under water  1  area  1  day  )  N  63 54 43 19 130 66 96 52 18 23  (1 m")  A i r temperature data based on r e c o r d s d u r i n g the hours o f sampling at . Vancouver I n t e r n a t i o n a l A i r p o r t a p p r o x i m a t e l y 20 km from the study s i t e ( s o u r c e : Monthly m e t e o r o l o g i c a l summary, Atmospheric Environment S e r v i c e , F i s h e r i e s and Environment Canada).  114  • TABLE I I  Rates -of Sediment Turnover by A b a r e n i c o l a  November 8, 1976 Mean A i r Temperature 9.5 C (range 9-10 °C)_  Station  A5 A5/A6 A6 A5 A6  State of Substrate  Rate (wet ml worm  wet wet wet u.w. u.w.  N  1  day  )  30 52 47 28 25  1.4 0.4 1.2 8.2 5.0  August 22, 1978 Mean A i r Temperature 17.5 °C (range 16.5-18.5 °C)  Station  AlO A13  S u b s t r a t e Temperature (°C) cm depth)  State of Substrate  19- 21 20- 22  N = number o f f e c a l c a s t s i n sampled u.w. = under water Note:  R  a  t  e  (wet ml worm  u.w. u.w.  -1  5.1 56.0  -1 day )  N  211 9  a r e a (1 m*")  A i r temperature d a t a based on r e c o r d s d u r i n g the hours o f sampling at Vancouver I n t e r n a t i o n a l A i r p o r t a p p r o x i m a t e l y 20 km from the study s i t e ( s o u r c e : Monthly m e t e o r o l o g i c a l summary, Atmospheric Environment S e r v i c e , F i s h e r i e s and Environment Canada).  115 c o l l e c t e d by Swinbanks  (1979).  The f o l l o w i n g assumptions and e s t i m a t e s a r e  made ( T a b l e I I I ) : (1)  Most A b a r e n i c o l a occupy t h e upper sand wave zone which l i e s b e t 7  ween mean s e a l e v e l and +0.75 m G e o d e t i c Datum and has an a r e a o f 0.8 x 10  2 m .  The a r e a i s exposed on average 70% o f t h e time ( e s t i m a t e d from mean exposure c u r v e p r e s e n t e d by Swinbanks, 1979).  I n summer d u r i n g exposure about one  t h i r d o f t h i s a r e a remains under w a t e r due t o the p r e s e n c e o f t i d a l p o o l s . The r e m a i n i n g two t h i r d s  i s 'wet' d u r i n g e x p o s u r e , e x c e p t d u r i n g d a y l i g h t  summer exposure when one t h i r d i s 'wet' and t h e o t h e r ' d r y . '  T h i s was e s t i -  mated from 77 random q u a d r a t s t a k e n on t r a n s e c t A i n June, 1976, o f w h i c h 24 were under w a t e r , 27 were 'wet' and 26 'dry.' (2)  The average d e n s i t y o f A b a r e n i c o l a a t wet o r under w a t e r  sites, -2 w h i c h c o n s t i t u t e two t h i r d s o f t h e a r e a above mean s e a l e v e l , i s 57 m , w h i l e t h e average d e n s i t y i n d r y a r e a s , w h i c h c o n s t i t u t e one t h i r d o f the —2 8 a r e a i s 10 m . Hence t h e under w a t e r + wet p o p u l a t i o n amounts t o 3 x 10 g  individuals, (3) 5.1 ml worm  w h i l e the d r y p o p u l a t i o n i s 0.25 x 10  individuals.  I n the upper sand wave zone, A b a r e n i c o l a t u r n s o v e r about day  when under w a t e r , throughout the y e a r .  summer they average 2.5 ml worm The summer d r y r a t e i s 0.5 ml worm  day  A t wet s i t e s i n  and i n w i n t e r 0.9 m l worm ^ day" 1.  day g  (4)  There i s an e s t i m a t e d p o p u l a t i o n o f 10  A b a r e n i c o l a i n the e e l -  g r a s s and l o w e r sand wave zones below mean s e a l e v e l , w h i c h t u r n o v e r s e d i ment a t an average under w a t e r r a t e o f 29 ml worm ^ day  d u r i n g summer.  The  r a t e o f sediment t u r n o v e r . i n w i n t e r i s n e g l i g i b l e . (5)  'Summer' c o n d i t i o n s l a s t from A p r i l t o September and ' w i n t e r '  c o n d i t i o n s from October t o March. 6  The t o t a l a n n u a l budget i s about 1 x 10  3  m  (Table I I I ) .  Of t h i s  budget  more than h a l f i s reworked i n the a r e a below mean s e a l e v e l d u r i n g summer.  TABLE I I I  Annual Budget of Sediment Turnover f o r A b a r e n i c o l a i n Boundary Bay  Zone  UPPER  State _ _. , of Tide  , No. of days J  n  L  „ , . Population  Turnover , q. (m )  r  J  IN  H Q  u.w. 5.1  3.25 x 1 0 ( t o t a l pop.)  1.82 x 1 0  5  OUT  255  u.w. 5.1  1.50 x 1 0 ( t i d a l pools)  1.95 x 1 0  5  w i n t e r wet 0.9 summer wet 2.5  1.50 x 1 0 1.50 x 1 0 ('wet pop.)  0.17 x 1 0 0.48 x 1 0  0.25 x 1 0 0.25 x 1 0 ('dry' pop.)  0.03 x 1 0 0.01 x 1 0  5  4.46 x 1 0  5  5.30 x 1 0  5  9.76 x 1 0  5  SAND WAVE  Rate , _ i, _is (ml worm } day )  OUT  255 {  127.5 127.5  8  8  8  8  5  5  1  ZONE  OUT  255 {  127.5 127.5  w i n t e r wet 1.00 summer dry 0.25  8  8  Mean Sea  5  Level EELGRASS IN/OUT  182.5  u.w. 29  10  8  ZONE T o t a l Budget  117 To p l a c e t h i s budget i n p e r s p e c t i v e , i t can be compared w i t h sediment d i s c h a r g e  the annual  o f the F r a s e r R i v e r which amounts to about 20 x 10  6  m  3  (Mathews and Shephard, 1962). On  the s m a l l e r s c a l e , A b a r e n i c o l a  can a t t a i n d e n s i t i e s as h i g h as  _2 200  m  i n t i d a l p o o l s , and t h e worms t u r n over sediment a t the under water  r a t e o f about .5 ml worm t h i c k i s extruded  day ^.  Each day a l a y e r o f sediment about 1 mm  onto the s u r f a c e by A b a r e n i c o l a .  a l a y e r about e i g h t g r a i n s t h i c k .  T h i s i s e q u i v a l e n t to  I n 100 days A b a r e n i c o l a reworks a l l the  sediment i t l i v e s i n t o a depth o f 10 cm.  However, i t s h o u l d be remembered  t h a t t h i s r a t e i s under optimum c o n d i t i o n s . Laboratory  In the l a b o r a t o r y A b a r e n i c o l a s i z e - s o r t sediment.  demonstrates an amazing c a p a c i t y to  When p l a c e d i n a mixture of homogenized sand and c l a y  Abarenicola q u i c k l y segregates (Fig.  Results  the two through i t s i r r i g a t i o n  activities  2 ) . Water i s drawn i n through the t a i l s h a f t and r e t u r n s to the  s u r f a c e through the head s h a f t ( F i g . 3 ) . F i n e g r a i n e d c l a y p a r t i c l e s to  the s u r f a c e c a r r i e d i n s u s p e n s i o n  float  b y the head s h a f t c u r r e n t and i n the low  energy environment o f the l a b o r a t o r y the c l a y s e t t l e s out on the s u b s t r a t e forming lamina  a t h i c k lamina w i t h i n 24 hours ( F i g . 2 b ) . W i t h i n a few days the i s b u r i e d by f e c a l c a s t s e x c r e t e d  through the t a i l  '•  s h a f t , and i s then  deformed by the f e e d i n g and r e s p i r a t i o n a c t i v i t i e s o f the worm ( F i g . 2 c ) .  DISCUSSION  The  r a t e s o f sediment t u r n o v e r  r e p o r t e d here are comparable w i t h  determined by Hobson (1967) and Healy and W e l l s the e x c e p t i o n o f the very h i g h r a t e s recorded  those  (1975) f o r A. p a c i f i c a ,  with  i n the e e l g r a s s zone (Tables I  118  (c) Figure 2. Grain size sorting by Abarenicola: a) Start of the experiment. An i n d i v i d u a l Abarenicola (-2 g) was placed i n a homogenized mixture of sand (>63/«"\) and montmorillonite (<63^). b) After 24 hours a thick, biogenically formed lamina of montmorill o n i t e (white) has developed as a result of the i r r i g a t i o n a c t i v i t i e s of the worm. c) After three days the lamina has been buried by f e c a l casts and the lamina has been deformed and bioturbated by the feeding and i r r i g a t i o n a c t i v i t i e s of the worm.  119  respiration current  respiration current  head shaft tail s h a f t  5cm  pocket sand  F i g u r e 3.  Sketch of a comparable s i t u a t i o n t o t h a t i l l u s t r a t e d i n F i g u r e 2b. The important f e a t u r e s o f the A b a r e n i c o l a burrow are l a b e l l e d and the d i r e c t i o n o f flow of the r e s p i r a t i o n c u r r e n t which i r r i g a t e s the burrow i s i n d i c a t e d . A c l a y lamina has developed as a r e s u l t of f i n e g r a i n e d c l a y p a r t i c l e s f l o a t i n g out i n s u s p e n s i o n i n the head s h a f t i r r i g a t i o n c u r r e n t and then s e t t l i n g on the s u b s t r a t e .  120 and  I I ; s t a t i o n s A13 and A14).  worm  day \  These h i g h r a t e s , r a n g i n g between 18-56 ml  a r e a p u z z l e which remains u n s o l v e d .  zone appear to be l a r g e r and t h i s may account be  t h a t A b a r e n i c o l a migrates  to lower  The worms i n the e e l g r a s s  f o r the h i g h e r r a t e s .  I t may  i n t e r t i d a l l e v e l s as i t gets o l d e r and  l a r g e r as r e p o r t e d f o r A r e n i c o l a marina by Werner (1954a, b ) . But why do reworking  r a t e s decrease so d r a m a t i c a l l y from an average -1  -1  d u r i n g summer to a t most 1 o r 2 ml worm upper sand wave zone r a t e s o n l y decrease II)?  The p o s s i b i l i t y  not be r u l e d out. teen proved  t h a t another  o f 29 ml worm ^ day ^  day  d u r i n g w i n t e r , w h i l e i n the  s l i g h t l y o r n o t a t a l l ( T a b l e s I and  species of A r e n i c o l i d a e i s present should  Of n i n e t e e n specimens c o l l e c t e d i n the v i c i n i t y  o f A13 seven-  to be A b a r e n i c o l a p a c i f i c a upon d i s s e c t i o n ; h a v i n g between 4 to 6  p a i r s o f esophageal of esophageal  caeca each.  However, two specimens had o n l y one l a r g e p a i r  caeca each, which i s d i a g n o s t i c o f the genus A r e n i c o l a (Smith and  C a r l t o n , 19 75).  A r e n i c o l a marina i n the Dutch Wadden Sea demonstrate s e a s o n a l  v a r i a t i o n i n reworking  r a t e s very comparable to those r e p o r t e d above f o r the  e e l g r a s s zone (26-29 ml worm ^ day ^ i n summer, av. a i r temp. 17°C, 2.4 ml worm ^ day ^ i n w i n t e r , av. a i r temp. 3°C, Cadee, 1976). The phenomenal r a t e s a t which A b a r e n i c o l a rework sediment i n Boundary ; Bay p r o b a b l y has a c o n s i d e r a b l e i n f l u e n c e on the sedimentology o f the t i d a l f l a t s .  The r a t e s o f b i o g e n i c reworking  and ecology  o f up to 1mm per day  are f a r i n excess o f e s t i m a t e d r a t e s o f s e d i m e n t a t i o n by p h y s i c a l  processes.  K e l l e r h a l s and Murray  (1969) e s t i m a t e d a l o n g term s e d i m e n t a t i o n r a t e o f  0.41  on r a d i o - c a r b o n d a t i n g , and a s h o r t - t e r m r a t e o f 5 mm  mm y e a r  year \  , based  based  on the t h i c k n e s s o f s e a s o n a l a l g a l mat laminae.  (1979) has suggested  the i n t e n s e reworking  As Swinbanks  a c t i v i t i e s o f A b a r e n i c o l a may a c t  to l i m i t t h e e x t e n t o f t h e a l g a l mat zone - one o f the f i v e major s e d i m e n t o l o g i c a l zones o f the Boundary Bay t i d a l f l a t s may i n h i b i t  floral/  ( F i g . 1 ) . The worms  the f o r m a t i o n o f b l u e - g r e e n a l g a l mats by t h e i r  constant  ••;?.:•.  121  turnover  o f s u r f a c e sediments o r through b u r i a l o f algae by f e c e s .  A b a r e n i c o l a has the p o t e n t i a l o f g e n e r a t i n g biogenically  biogenic  graded b e d d i n g and  formed c l a y laminae through i t s i r r i g a t i o n a c t i v i t i e s .  I n the  i n t e r t i d a l environment where the s u r f a c e i s c o n s t a n t l y reworked by the i n f l o w and  outflow  o f water, the lamina of c l a y seen i n F i g u r e  washed away as f a s t as i t forms, and u s i n g t h i s process conceivably  2 would p r o b a b l y be Abarenicola  could  ' c l e a n ' the mud out o f a l o o s e mud/sand m i x t u r e , c r e a t i n g a  b e t t e r s o r t e d sand.  The h i g h  degree o f s o r t i n g o f sands i n the upper sand  wave zone i n Boundary Bay ( I n c l . G r a p h i c S t d . Dev. 0.30-0.39 0; Swinbanks, 1979)  may a t l e a s t i n p a r t be due to the reworking a c t i v i t i e s o f t h i s worm.  This i s a q u i t e a separate during  from that o f r e j e c t i o n o f coarse  f e e d i n g , r e p o r t e d by H y l l e b e r g  Stanley the  process  (1965) f o r Clymenella  two p r o c e s s e s  (1975) f o r A b a r e n i c o l a ,  and by Van S t r a a t e n  grains  by Rhoads and  (1952) f o r A r e n i c o l a .  s h o u l d produce the same r e s u l t as they both  But  transport  f i n e g r a i n s towards the s u r f a c e e i t h e r i n the head s h a f t i r r i g a t i o n  current  or as f e c e s .  ACKNOWLEDGEMENTS  T h i s work was f i n a n c e d i n p a r t by G e o l o g i c a l Survey o f Canada  Contract  D.S.S. No. 0SS76-02075 from the Department o f Supply and S e r v i c e s , Ottawa, Ontario,  Canada.  Dr. C D . L e v i n g s k i n d l y made a v a i l a b l e the l a b o r a t o r y  f a c i l i t i e s a t the P a c i f i c Environment I n s t i t u t e , West Vancouver, B.C., Canada.  I would l i k e to thank Dr. T.H. C a r e f o o t ,  University of B r i t i s h cation of Abarenicola,  Columbia f o r h e l p i n g i n the d i s s e c t i o n and i d e n t i f i and Dr. J.W. Murray and Dr. W.C. Barnes, U n i v e r s i t y  of B r i t i s h Columbia, Dr. C D . L e v i n g s , Dr.  o f the Zoology Department,  P a c i f i c Environment I n s t i t u t e and  J.L. L u t e r n a u e r , G e o l o g i c a l Survey o f Canada, f o r c r i t i c a l l y  manuscript.  r e a d i n g the  122 REFERENCES  A l l e r , R.C. and Dodge, R.E., 1974, Animal-sediment r e l a t i o n s i n a t r o p i c a l lagoon, D i s c o v e r y Bay, Jamaica: J o u r . Mar. Res., v. 32, p. 209-232. Cadee, G.C, 1976, Sediment reworking by A r e n i c o l a marina on t i d a l f l a t s i n the Dutch Wadden Sea: Neth. J o u r . Sea Res'.,. v. 10, p. 440-460. Evans, C , 1965, I n t e r t i d a l f l a t sediments and t h e i r environments o f d e p o s i t i o n i n the Wash: Quart. J o u r . Geol. Soc. London, v. 121, p. 209-245. F e a t h e r s t o n e , R.P. and R i s k , M.J.,1977, E f f e c t of t u b e - b u i l d i n g p o l y c h a e t e s on i n t e r t i d a l sediments of the Minas B a s i n , Bay o f Fundy: J o u r . Sed. P e t r o l o g y , v. 27, p. 446-450. Healy, E.A. and W e l l s , C P . , 1959, Three new lugworms ( A r e n i c o l i d a e , p o l y chaeta) from the North P a c i f i c a r e a : P r o c . Z o o l . Soc. London, v. 133, p. 315-335. Hobson, K.D., 1967, The f e e d i n g and ecology o f two North P a c i f i c A b a r e n i c o l a s p e c i e s ( A r e n i c o l i d a e , P o l y c h a e t a ) : B i o l . B u l l . , v. 133, p. 343-354. H y l l e b e r g , J . , 1975, S e l e c t i v e f e e d i n g by A b a r e n i c o l a p a c i f i c a w i t h notes on A b a r e n i c o l a vagabunda and a concept of gardening i n lugworms: Ophelia, v. 14, p. 113-137. K e l l e r h a l s , P. and Murray,' J.W., 1969 , T i d a l , f l a t s .at Boundary .Bay, F r a s e r R i v e r D e l t a , B r i t i s h Columbia: B u l l . Can. P e t . G e o l , v. 17, p. 67-91.  ,  Mathews, W.H. and Shephard, F.P., 1962, S e d i m e n t a t i o n of F r a s e r R i v e r D e l t a , B r i t i s h Columbia: B u l l . Amer. Assoc. P e t . Geol., v. 46, p. 1416-1443. Reineck, H.E., 1958, Wlihlbau-Geflige i n A b h a n g i g k e i t Senckenbergiana Lethaea, B. 39, p. 1-23, 54-56. Rhoads, D.C. and S t a n l e y , D.J., P e t . , v. 35, p. 956-963.  1965,  von  Sediment-Umlagerungen:  B i o g e n i c graded bedding:  Jour.  Sed.  and Young, 1970, The i n f l u e n c e o f d e p o s i t - f e e d i n g benthos on bottom s t a b i l i t y and community t r o p h i c s t r u c t u r e : J o u r . Marine Res. v. 28, p. 150-178. R i s k , M.J. and M o f f a t , J.S., 1977, S e d i m e n t o l o g i c a l s i g n i f i c a n c e o f f e c a l p e l l e t s o f Macoma b a l t i c a inc.Mi'nas B a s i n , Bay of Fundy: J o u r . Sed. P e t r o l o g y , "v. 47, p. 1425-1436. S c h a f e r , W. 1972, Ecology and p a l a e o e c o l o g y of marine environments: and Boyd and U n i v e r s i t y Chicago P r e s s , Edinburgh and Chicago, 568  Oliver p.  Schwarz, A., 1932, Der t i e r i s c h e E i n f l u s s auf d i e Meeressedimente (besonders auf d i e Beziehungen zwischen Frachtung, Ablagerung und Zusammen-Setzung von Wattensedimenten): Senckenbergiana, v. 14, p. 118-172.  123 Smith, R.I. and C a r l t o n , J.T., ( e d s . ) , 1975, L i g h t ' s Manual: intertidal i n v e r t e b r a t e s o f the c e n t r a l C a l i f o r n i a c o a s t : Third Edition, University of C a l i f o r n i a P r e s s , B e r k e l e y , Los A n g e l e s , 716 p. Swinbanks, D.D., 1979, Environmental f a c t o r s c o n t r o l l i n g f l o r a l z o n a t i o n and the d i s t r i b u t i o n o f burrowing and t u b e - d w e l l i n g organisms on F r a s e r D e l t a t i d a l f l a t s , B r i t i s h Columbia: unpub. Ph.D. t h e s i s , U n i v e r s i t y o f B r i t i s h Columbia,_Vancouver, B.C., 274 p. Van S t r a a t e n , L.M.J.U., 1952, Biogene t e x t u r e s and the f o r m a t i o n o f s h e l l beds i n the Dutch Wadden Sea, I and I I : P r o c . K o n i n k l . Ned. Akad. Weternschap., B55, p. 500-516. Werner, B., 1954a, E i n e Beobachtung uber d i e Wanderung von A r e n i c o l a marina (Polychaeta s e d e n t a r i a ) : H e l g l . Wiss. Meeresuntersuch, v . 5, p. 93-102. , 1954b, Uber d i e Winterwanderung von A r e n i c o l a marina L . ( P o l y chaeta s e d e n t a r i a ) : H e l g l . Wiss. Meeresuntersuch, v . 5, p. 353-378.  Part 4 A ENVIRONMENTAL CONTROLS ON THE DISTRIBUTION OF THALASSINIDEAN BURROWING SHRIMPS ON FRASER DELTA TIDAL FLATS, BRITISH COLUMBIA  A Marine  T i d a l F l a t Between Two Man-Made Causeways on S o u t h e a s t e r n Roberts Bank  125  ABSTRACT  The t h a l a s s i n i d e a n burrowing shrimps C a l l i a n a s s a c a l i f o f n i e h s i s and Upogebia p u g e t t e n s i s a r e abundant on a sandy t i d a l f l a t , which l i e s between two man-made causeways  on the s o u t h - e a s t e r n t i d a l f l a t s o f the F r a s e r  Delta-  _2 f r o n t , a t t a i n i n g d e n s i t i e s as h i g h as 446 burrow openings m  .  This  f l a t i s 'marine' i n c h a r a c t e r and can be d i v i d e d i n t o f o u r major s e d i m e n t o l o g i c a l zones.  tidal  floral/  These a r e , from the s h o r e l i n e seawards, the s a l t m a r s h  zone, the a l g a l mat zone, the s a n d f l a t zone and the e e l g r a s s zone. nidean burrowing shrimps are most abundant i n the s a n d f l a t  Thalassi-  zone.  At h i g h i n t e r t i d a l l e v e l s C a l l i a n a s s a d i s t r i b u t i o n i s l i m i t e d by the presence o f the s a l t m a r s h , the lower l i m i t o f which l i e s a t the lower l i m i t of the upper atmozone, w h i l e dense e e l g r a s s c o v e r l i m i t s C a l l i a n a s s a b u t i o n a t low i n t e r t i d a l l e v e l s .  distri-  The upper l i m i t o f the e e l g r a s s zone  at the upper l i m i t o f the lower aquazone.  lies  C a l l i a n a s s a a r e abundant (>50  -2 burrow openings m  ) i n sediments which range from 5-50% i n mud content and  from 2.6-4.0 0 i n median g r a i n  size.  Upogebia extend up t o the base o f the upper amphizone  (about mean s e a  l e v e l ) , a l e v e l above which the maximum d u r a t i o n o f a n o x i a due t o exposure p r o b a b l y exceeds the l e t h a l l i m i t  f o r p o s t m o l t Upogebia.  Upogebia show a  d i s t i n c t p r e f e r e n c e f o r muddy s u b s t r a t e s and o n l y a t t a i n h i g h -2 (>20 burrow openings m  densities  ) i n sediments c o n t a i n i n g more than 40% mud.  The  r e l a t i o n s h i p between p e r c e n t mud and Upogebia d e n s i t y can be approximated by a s t r a i g h t l i n e ,  the s l o p e o f which i s dependent on t i d a l  elevation.  There i s some e v i d e n c e t o suggest t h a t C a l l i a n a s s a and Upogebia d e n s i t i e s are n e g a t i v e l y c o r r e l a t e d a t t i d a l e l e v a t i o n s where b o t h Upogebia and C a l l i a n a s s a d e n s i t i e s have the p o t e n t i a l o f b e i n g h i g h .  I t i s speculated  t h a t t h i s may be a consequence o f i n c r e a s e d m o r t a l i t y amongst p o s t l a r v a l  126 s u s p e n s i o n f e e d i n g Upogebia r e s u l t i n g from the s u r f a c e reworking of a d u l t d e p o s i t - f e e d i n g the c a r n i v o r o u s Callianassa.  activities  C a l l i a n a s s a , and/or as a r e s u l t o f p r e d a t i o n by  p l a n k t i c l a r v a e o f Upogebia on the p l a n k t i c l a r v a e o f  I t may be t h a t t h i s n e g a t i v e  i n t e r a c t i o n between Upogebia and  C a l l i a n a s s a o v e r r i d e s and masks a p o s s i b l e p r e f e r e n c e  on the p a r t o f  C a l l i a n a s s a f o r muddy s u b s t r a t e s . C a l l i a n a s s a reworks sediment a t the r a t e o f 18 ± 9 ml/shrimp/day. An  estimated  100 m i l l i o n C a l l i a n a s s a on the i n t e r c a u s e w a y t i d a l f l a t  about 0.2 m i l l i o n c u b i c metres o f sand d u r i n g  rework  the three months o f summer. _2  In the a r e a of t h e i r peak d e n s i t y rework the sediment they l i v e  (446 burrow openings m  ) Callianassa.  i n to a depth o f 50 cm i n about f i v e months.  I t i s suggested t h a t b i o t u r b a t i o n o f a shallow  subsurface  h o r i z o n o f clayey:'  mud by the deep burrowing o f Upogebia has l o c a l l y i n c r e a s e d t h e mud of s u r f a c e sediments on the s o u t h e a s t e r n i n an anomalous p a t c h  content  s i d e of the s a n d f l a t zone, r e s u l t i n g  o f muds w i t h i n t h i s o t h e r w i s e sandy zone.  ,  127  INTRODUCTION  T h a l a s s i n i d e a n burrowing shrimps produce the v e r y d i s t i n c t i v e fossils  Ophiomorpha and T h a l a s s i n o i d e s  Howard, 1975; Pemberton, 1976).  trace  (Weimer and Hoyt, 1964; Frey and  The burrows of these shrimps extend deep  i n t o the s u b s t r a t e and, as a r e s u l t , s t a n d v e r y good chances o f b e i n g preserved  as t r a c e f o s s i l s  paleoenvironmental 1964;  i n the g e o l o g i c a l r e c o r d .  T h e i r p o t e n t i a l as  i n d i c a t o r s has a l r e a d y been p o i n t e d out (Weimer and Hoyt,  Dewindt, 1974), b u t such p o t e n t i a l w i l l remain l i m i t e d as l o n g as d a t a  on t h e i n f l u e n c e o f p e r t i n e n t e n v i r o n m e n t a l f a c t o r s on t h a l a s s i n i d e a n shrimp distribution i s lacking.  The primary aim o f t h i s paper i s t o a s s e s s the  e f f e c t s o f v a r i o u s e n v i r o n m e n t a l f a c t o r s on the d i s t r i b u t i o n o f C a l l i a n a s s a c a l i f o r n i e n s i s ' D a n a and Upogebia p u g e t t e n s i s : lies-between  (Dana) on a marine t i d a l  two man-made causeways on t h e s o u t h e a s t e r n  Tsawwassen f e r r y t e r m i n a l causeway and the C o a l p o r t Coalport  causeway has c u t o f f the supply  that  F r a s e r - D e l t a -. the  causeway ( F i g . 1 ) . The  o f b r a c k i s h s i l t - l a d e n waters from  the F r a s e r R i v e r to t h i s  tidal  'marine' c h a r a c t e r i s t i c s  (Levings and C o u s t a l i n , 1975).  relatively stable s a l i n i t y  flat  f l a t , and has thus p r o b a b l y  enhanced i t s  Because o f the  regime o f the t i d a l f l a t , the combined  effects  of t i d a l e l e v a t i o n , g r a i n s i z e and b i o - i n t e r a c t i o n s on t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n can be s y s t e m a t i c a l l y broken down i n t o t h e i r component B i o - i n t e r a c t i o n s i n c l u d e the e f f e c t s o f f l o r a l cover and  e e l g r a s s ) and any ammensalistic  suspension  negative  a l g a l mats  i n t e r a c t i o n s between Upogebia, a  f e e d e r , and C a l l i a n a s s a , a d e p o s i t f e e d e r .  (1970) i n t r o d u c e d  (saltmarsh,  effects.  Rhoads and Young  the concept o f t r o p h i c group ammensalism t o d e s c r i b e the  i n t e r a c t i o n between d e p o s i t f e e d e r s and s u s p e n s i o n  feeders i n a  s u b t i d a l environment, where the u n s t a b l e bottom c r e a t e d by the reworking activities  o f d e p o s i t f e e d e r s were t e n d i n g  t o exclude  suspension  feeding  128  F i g u r e 1.  L o c a t i o n of the study area.\is i n d i c a t e d .by h p I r U z m t a l c r o s s - h a t c h i n g T i d a l f l a t s are s t i p p l e d , l a n d a r e a of Recent a l l u v i u m i s b l a n k , and o l d e r d e p o s i t s d i a g o n a l l y . cross-hatchecL (adapted from L u t e r n a u e r and Murray, 1973).  129 organisms.  As an e s s e n t i a l part of the study of the interactions between  Callianassa and Upogebia the rates at which these shrimps rework sediment were measured." Armed with the information from this t i d a l f l a t , i n Part £B the comp l e x i t i e s of the environment of central and northern Roberts Bank i s tackled, where s a l i n i t y becomes the overriding factor among the variables influencing thalassinidean shrimp d i s t r i b u t i o n , due to the i n f l u x of freshwater  from the Fraser River.  The environment of Roberts Bank divides  naturally into a brackish environment to the northeast, and a marine environment to the southeast i n this  and i t was  f e l t appropriate to s p l i t Parts 4A.. arid,B i  way.  The presence of Callianassa c a l i f o r n i e n s i s on the active t i d a l of the Fraser Delta was  flats  f i r s t reported by Bawden et a l . (1973) and Luternauer  and Murray (1973) and again by Levings and Coustalin (1975).  The  distribution  of Callianassa and Upogebia i n Boundary Bay on the inactive southern flank of the Fraser Delta (Fig. 1) has been described q u a l i t a t i v e l y (Kellerhals and Murray, 1969;  O'Connell, 1975)  and q u a n t i t a t i v e l y (Swinbanks, '1979).  Thalassinidean burrowing shrimps are f r u s t r a t i n g organisms to study because they prove so d i f f i c u l t to catch, as others have noted (Risk et a l . , 1978). With experience  one i s quickly able to recognize the very c h a r a c t e r i s t i c  burrows, burrow entrances, mounds, f e c a l p e l l e t s and discarded (exuviae) of these shrimps.  Callianassa burrows usually have two entrances  to each system although occasionally they: may T  have three and rarely four  openings, while Upogebia burrows usually have two 1979).  exoskeletons  (Thompson,.1972; Swinbanks,  Thus, one can quantitatively assess the d i s t r i b u t i o n of the shrimps  by counting burrow entrances at the surface rather than catching the shrimps themselves.  It would be more desirable-to-obtain direct shrimp counts and  shrimp biomass data, but to do so would have severely limited the  geographical  130 extent  of this  survey.  A number o f s t u d i e s o f C a l l i a n a s s a c a l i f O r n i e n s i s and Upogebia have been made by b i o l o g i s t s .  MacGinitie  (1930, 1934) r e c o u n t s i n v i v i d  d e t a i l the burrowing, f e e d i n g , r e p r o d u c t i o n both shrimps.  MacGinitie  and M a c G i n i t i e  and day-to-day l i f e s t y l e s o f  (.1968) l i s t n i n e commensal organisms,  i n c l u d i n g pea-crabs, amphipods, b i v a l v e s , goby f i s h and p o l y c h a e t e s , use  pugettensis  which  the burrows o f C a l l i a n a s s a as a p r o t e c t i v e haven o r as a sediment-water  i n t e r f a c e on which to f e e d .  L. Thompson and P r i t c h a r d (1969) have c a r r i e d  out p h y s i o l o g i c a l s t u d i e s on the osmoregulatory c a p a c i t i e s o f b o t h _C. c a l i f o r n i e n s i s and JJ. p u g e t t e n s i s and  as have T o r r e s  e t a l . (1977).  P r i t c h a r d (1969) have s t u d i e d a n o x i a t o l e r a n c e  (1972) has s t u d i e d JJ. p u g e t t e n s i s  R. Thompson  i n b o t h shrimps.  Thompson  i n d e t a i l f o r a doctoral thesis.  METHODS  Three t r a n s e c t s , A, B and C, were e s t a b l i s h e d p e r p e n d i c u l a r s h o r e l i n e on the inter-causeway t i d a l In a d d i t i o n t o these,  p a r a l l e l to the s h o r e l i n e , because q u a l i t a t i v e  i n d i c a t e d t h a t l a t e r a l changes i n g r a i n s i z e were pronounced  i n this region. and  ( F i g . 2) i n June and J u l y , 1977.  two t r a n s e c t s , D and E, were e s t a b l i s h e d between  t r a n s e c t s A and B roughly observations  flat  to the  S t a t i o n s were taped a t 100 m i n t e r v a l s on the t r a n s e c t s  marked by wooden s t a k e s .  The e l e v a t i o n s o f a l l s t a t i o n s on t r a n s e c t s  A, B and C were determined by s u r v e y i n g c l o s e to the ends of each l i n e determined by standard  from three bench marks which l a y  (Fig. 2). Elevations  a t s t a t i o n s were  l e v e l i n g techniques u s i n g a T2 t r a n s i t  (Scientific  Instruments L t d . , Ottawa, O n t a r i o ) , which i s c a p a b l e o f d e t e r m i n i n g e l e v a t i o n differences  to an accuracy o f 5 mm o v e r a d i s t a n c e o f 200 m (the maximum  sighting distance  employed).  A cross  survey between t r a n s e c t s A and B  131  til Ot  1M*M'  ««**  1000  1 I*«T'  0  T))"M •  1000  2000  I  Metere  j  \ ~]  Saltmarsh  Zone  2^  Algal  Zona  fc£>£l  Mat  Sandilai  ~]  .•**t:"*  zone Patchy Stations flaee  Ealgraaa (or  Cover  Cauaaway  fflgH  Drainaga Sand  Rip Rap  Channel!  Sara  Relict  Driftwood Gravel  road  eand bars  of  (dashed)  and  embankment  • BM *  B e n c h Hark  fixed  by  vegetetlon  Imarah and algal  D y k o . with dyka road >•''  elevation  on tower limit  • altmatah  F i g u r e 2.  Zona  colonfilng  E:;;:3 a  Ic'jyj  Zona  Ceueeway  mate)  for T r a n s e c t  A'  landward (hachured)  * A •  Railway Traneect  and station  location  The f l o r a l / s e d i m e n t o l o g i c a l zones o f the i n t e r - c a u s e w a y t i d a l f l a t w i t h the l o c a t i o n s o f t r a n s e c t s , s t a t i o n s and bench marks indicated.  132 was  made a l o n g t r a n s e c t D,  t y i n g bench mark B ( F i g . 2) to bench mark A  by s u r v e y i n g over a d i s t a n c e o f a p p r o x i m a t e l y 2 km.  The d i s c r e p a n c y between  the expected e l e v a t i o n f o r the bench mark A and the observed e l e v a t i o n 6 cm  (observed 6 cm h i g h e r than e x p e c t e d ) .  was  T h i s g i v e s an e s t i m a t e of the  accuracy o f the s u r v e y i n g technique over a t y p i c a l t r a n s e c t l e n g t h , and p r o v i d e d e l e v a t i o n d a t a f o r t r a n s e c t D.  A f u r t h e r check of the survey data  u s i n g observed t i d a l h e i g h t s a t Tsawwassen i n d i c a t e s t t h a t .the .datan.is a c c u r a t e to about ±4 cm was  (range 0.2-9.4 cm,  not surveyed because  N=19,  Appendix  3 ).  Transect E  o b s e r v a t i o n s i n d i c a t e d t h a t i t l a y almost  parallel  to the w a t e r l i n e and the s t a t i o n s on the t r a n s e c t were t h e r e f o r e of v e r y similar elevation.  The survey r e s u l t s c o n f i r m t h i s c o n c l u s i o n as the e l e v a -  t i o n s o f s t a t i o n s B16  and A l l a t e i t h e r end of t r a n s e c t B/A  e l e v a t i o n by 13 ± 2.5  cm.  only d i f f e r i n  In a d d i t i o n to the t r a n s e c t s mentioned  above  s i x s t a t i o n s were e s t a b l i s h e d a d j a c e n t to the causeways 20 m from the edge of the ' r i p r a p , ' ( F i g . 2).  They were not  surveyed.  At a l l s t a t i o n s shrimp burrow opening d e n s i t i e s were determined  by  2 sampling e i g h t times a t each s t a t i o n w i t h a 0.25  m  quadrat.  were e a s i l y d i s t i n g u i s h e d from those o f C a l l i a n a s s a , because mud  Upogebia of t h e i r  burrows firm  l i n i n g , l a c k of c o n s t r i c t e d a p e r t u r a l necks, and d i s t i n c t i v e geometry  (Swinbanks,  1979).  S u r f a c e g r a i n s i z e samples were o b t a i n e d at a l l s t a t i o n s  u s i n g a 2 cm deep r e c t a n g u l a r box,  and s u r f a c e s u b s t r a t e s a l i n i t i e s were  r e c o r d e d at low t i d e u s i n g a r e f r a c t o m e t e r (Endeco  type 102).  Twenty-one  s u b s t r a t e s a l i n i t y • p r o f i l e s were taken on t r a n s e c t s A, B and C sampling at 2.5  cm,  5 cm,  7.5  cm,  10 cm,  15 cm and 45 cm over the p e r i o d J u l y 1-7,  u s i n g a sampler which draws i n t e r s t i t i a l waters F o r t u n a t e l y , because  from these depths  1977,  (Appendix  5;).  of the sandy n a t u r e of the s u b s t r a t e , i n t e r s t i t i a l  waters were c l e a r and s a l i n i t y In o r d e r t o determine  c o u l d be measured d i r e c t l y w i t h a r e f r a c t o m e t e r .  the r a t e a t which the shrimps  turnover  sediment,  133 p r o t e c t e d e n c l o s u r e s were c o n s t r u c t e d and a p l a c e d around a number of burrow openings  ( u s u a l l y about 10) i n o r d e r to p r e v e n t c u r r e n t s from washing away  the mounds which accumulate o u t s i d e the burrow  entrances.  c o n s i s t e d o f open ended m e t a l boxes 50 x 50 x 50 cm. 10 cm i n t o the s u b s t r a t e .  Twelve h o l e s (5 mm  The  enclosures  They were pushed  about  diameter) p l a c e d around the box  a t the l e v e l of the sediment-water i n t e r f a c e a l l o w e d easy i n f l o w and o u t f l o w of water and p r e v e n t e d 'geysers' from forming on f l o o d t i d e . g r a v e l was  used t o mark the i n i t i a l  l e v e l of the sediment-water  P r e l i m i n a r y t e s t s i n d i c a t e d t h a t the boxes c o u l d only be l e f t t i d a l cycle t i d e was  A l a y e r of interface.  i n f o r one  (25 h o u r s ) , because, i f wave a c t i o n a t the b e g i n n i n g o f f l o o d  significant  (>10  cm amplitude) waves b r e a k i n g over the box would  r e d i s t r i b u t e the accumulated mounds to the s i d e s of the e n c l o s u r e and on the subsequent ebb t i d e sand would boxes were emplaced and d a t a was  d r a i n out o f the boxes.  F o r t h i s r e a s o n the  j u s t b e f o r e the f l o o d i n g w a t e r l i n e reached the s t a t i o n  c o l l e c t e d the f o l l o w i n g day, i f u n d i s t u r b e d mounds were found  w i t h i n the box  (i.e.,  t h e r e had been no s i g n i f i c a n t wave a c t i o n at the l a t e  stages of ebb). In the l a b o r a t o r y , g r a i n s i z e samples were washed f r e e o f s a l t ,  wet  s i e v e d through a 63 um s i e v e to e x t r a c t the s i l t / c l a y  f r a c t i o n and dry s i e v e d  at 0.5  used.  0 intervals.  Approximately 10 g of sample was  The d i s t i n c t i v e f l o r a l / s e d i m e n t o l o g i c a l zones of the i n t e r - c a u s e w a y t i d a l f l a t were mapped u s i n g low l e v e l c o l o u r a e r i a l photographs 1:12,000) o f J u l y 29, 1977  (scale  (A31164, N a t i o n a l A i r Photo L i b r a r y , Ottawa,  Canada).  D e t a i l e d d e s c r i p t i o n s o f these zones are i n c l u d e d i n t h i s paper because i t i s e s s e n t i a l to p l a c e the t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n d a t a w i t h i n the o v e r a l l z o n a l framework of the t i d a l f l a t , as the two are i n t i m a t e l y related.  inter-  134  THE  The  f i r s t study o f animal-sediment r e l a t i o n s h i p s c a r r i e d out on the  inter-causeway t i d a l made e x t e n s i v e  on  f l a t was t h a t o f L e v i n g s and C o u s t a l i n  baseline  front, concentrating 2 cm).  INTER-CAUSEWAY TIDAL FLAT  s t u d i e s on a l l the t i d a l f l a t s  on the near s u r f a c e b e n t h i c  They  o f the F r a s e r  organisms  Delta-  (sampling depth  T h e i r r e s u l t s demonstrated t h a t the number o f s p e c i e s o f organisms  this t i d a l  were recorded  f l a t i s the h i g h e s t  f o r the whole d e l t a - f r o n t ; cumaceans  a t almost a l l s t a t i o n s .  are prominent over the e n t i r e t i d a l The  (1975).  Both i n d i c a t e that marine  flat  (Levings  influences  and C o u s t a l i n , 1975).  Canadian N a t i o n a l Harbours Board has r e c e n t l y proposed to expand the  Coalport,  and an e n v i r o n m e n t a l impact study has been c a r r i e d out (Beak-  H i n t o n , 1977).  The r e p o r t i n c l u d e s  e e l g r a s s bed and s a l t m a r s h  d e t a i l e d maps and d e s c r i p t i o n s o f t h e  on t h i s t i d a l  flat.  have a l s o s t u d i e d and mapped the saltmarsh.  H i l l a b y and B a r r e t t  R. Moody (1978) s t u d i e d an  e e l g r a s s b e d on the s o u t h e r n s i d e of the f e r r y causeway. monthly m o n i t o r i n g o f s a l i n i t y  (1976)  H i s study  and t u r b i d i t y l e v e l s adjacent  included  to the e e l g r a s s  bed.  Floral/Sedimentological  F i e l d observations flat  Zones  and a e r i a l photographs o f the inter-causeway  r e v e a l f o u r major f l o r a l / s e d i m e n t o l o g i c a l zones which can be  tidal  recognized  on the b a s i s o f t h e i r d i s t i n c t i v e f l o r a l cover and/or drainage and sediment characteristics  ( F i g . 2 ) . These a r e ,  from the s h o r e l i n e seawards, the s a l t -  marsh zone, the a l g a l mat zone, the s a n d f l a t zone and the e e l g r a s s There are a l s o two d i s t i n c t i v e  zones o f minor a r e a l e x t e n t , which  the two causeways, here c a l l e d  the 'causeway zones'  zone. parallel  ( F i g . 2 ) . The sediments  135 i n the causeway zones are c o a r s e r and c o n t a i n l e s s mud  than the a d j a c e n t  t i d a l f l a t , sand b a r s a r e p r e s e n t , the beach p r o f i l e i s much s t e e p e r than elsewhere, and, a t the seaward end o f the causeways,  these zones l a c k  any  e e l g r a s s c o v e r , d e s p i t e l y i n g a t e l e v a t i o n s which c o u l d be c o l o n i z e d by eelgrass.  The sediments of the causeway zones have i n p a r t been  from sand f i l l  d u r i n g causeway c o n s t r u c t i o n .  derived  Shoreward of the causeway zones  a narrow s t r i p of ' r i p rap' p a r a l l e l s each causeway. F i g u r e 3 p r e s e n t s the e l e v a t i o n a l l i m i t s of the f o u r major  floral/  s e d i m e n t o l o g i c a l zones w i t h r e s p e c t to G e o d e t i c Datum and w i t h r e s p e c t to the average exposure zone l i m i t s the Tsawwassen t i d e gauge.  f o r observed t i d e s between 1968-1978 at  Swinbanks  (1979) advocates the s u b d i v i s i o n o f  the i n t e r t i d a l r e g i o n i n t o exposure zones on the b a s i s o f c r i t i c a l  tidal  l e v e l s a t which the maximum d u r a t i o n of exposure o r submergence changes abruptly i n a step-like fashion. amphizone, 1979).  aquazone) has been i n t r o d u c e d and d e f i n e d elsewhere  The e l e v a t i o n o f the s a l t m a r s h / a l g a l mat  at 7 l o c a t i o n s clumps  Exposure zone t e r m i n o l o g y (atmozone, (Swinbanks,  zone boundary was  ( F i g . 2 ) , where the marsh showed s i g n s o f p r o g r a d i n g  forming seaward of the marsh and no e v i d e n c e of e r o s i o n ) .  l i m i t of the a l g a l mat  zone l i e s a t +0.88 ± 0.04  (i.e.,  The  upper  m (range 0.83-0.92 m,  G e o d e t i c Datum, which i s 13 cm lower than i n Boundary Bay (Fig. 1).  determined  (Swinbanks',  N=7) 1979)  The s a l t m a r s h p l a n t s grow on mounds and p l a t e a u s which are e l e v a t e d  about 20 cm above t h i s l e v e l , and thus the lower l i m i t of the s a l t m a r s h at +1.07  m (range 1.066-1.071 m, N=2)  G e o d e t i c Datum, which i s almost i d e n -  t i c a l i n e l e v a t i o n to the lower l i m i t of the s a l t m a r s h i n Boundary Bay Geodetic Datum, Swinbanks,  lies  (+1.12 m  1979), and as i n Boundary Bay, l i e s v e r y c l o s e to  the lower l i m i t of the upper atmozone ( F i g . 3 ) , which has l a i n a t +1.23  ± 0.08  (range 1.04-1.38 m) G e o d e t i c Datum f o r the p a s t t e n y e a r s a t Tsawwassen (Swinbanks, 1979).  T h i s i s the t i d a l e l e v a t i o n a t which the maximum d u r a t i o n  m  136  EXPOSURE  ZONE  TRANSECT  A  C  B  l  i  I  2H  UPPER ATMOZONE  Saltmarsh Zona Lower limit of LOWER  ' S o l t m o n h surface 1  ATMOZONE  Algal Mat Zono  UPPER AMPHIZONE  Cl  I  OH  LOWER AMPHIZONE  O O O  Sandflat Zona  Sandflat Zona  UPPER AQUAZONE  2H  Eelgrass  Eelgrass  Zona  Zona  LOWER AQUAZONE  3-"  F i g u r e 3.  The e l e v a t i o n a l l i m i t s o f the f o u r major f l o r a l / s e d i m e n t o l o g i c a l zones on the inter-causeway t i d a l f l a t w i t h r e s p e c t to G e o d e t i c Datum and the average exposure zone l i m i t s f o r observed t i d e s between 1968-78 a t the Tsawwassen t i d a l gauge ( s o u r c e : Swinbanks, 1979). The d o t t e d envelopes i n d i c a t e one s t a n d a r d d e v i a t i o n from the mean l e v e l o f the exposure zone boundary. The exposure zone l i m i t s f o r the lower aquazone are based oh o n l y two y e a r s o f r e c o r d s (1976-78) because these boundaries a r e s i g n i f i c a n t l y modulated by an 18.6 y e a r d e c l i n a t i o n a l c y c l e i n the moon (Swinbanks, 1979)• The e l e v a t i o n o f the s a l t m a r s h / a l g a l mat zone boundary was determined at seven p o i n t s between t r a n s e c t s B and C ( F i g . 2 ) .  137  of  exposure jumps from about 10 to 20 days  (Swinbanks, 1979).  The s a l t m a r s h  is  c h a r a c t e r i z e d by a dense growth o f h a l o p h y t i c v e g e t a t i o n w i t h T r i g l o c h i n  m a r i t i m a and S a l i c o r n i a v i r g i n i c a dominating i n the lower r e g i o n s H i n t o n , 1977).  (Beak—  The s a l t m a r s h i s d i s s e c t e d by d e e p l y i n c i s e d t i d a l c h a n n e l s  1-2 m deep, which have remained s t a b l e i n p o s i t i o n f o r decades (Beak-Hinton, 1977).  The sediments o f the s a l t m a r s h c o n s i s t o f l a m i n a t e d s i l t s  with r o o t l e t s  riddled  ( F i g s . 4a, 4 b ) .  The a l g a l mat zone i s lower atmozonal t o upper amphizonal i n exposure and extends down to about +0.30 m G e o d e t i c Datum ( F i g . a to  3 ) , thus a t t a i n i n g  lower e l e v a t i o n than i n Boundary Bay, where the a l g a l mat zone i s r e s t r i c t e d lower atmozonal e l e v a t i o n s  zone are muds o r muddy sands.  (Swinbanks, 1979).  The sediments w i t h i n the  Mud c o n t e n t s decrease r a p i d l y seaward  from  about 90% t o 20% ( F i g . 5 ) . The zone i s d i s s e c t e d by an extremely dense network o f d e n d r i t i c t i d a l channels which d r a i n water from the impermeable muds ( F i g . 6 a ) . The channels t e r m i n a t e a b r u p t l y a t the lower l i m i t o f the zone.  They a r e up t o 1 m i n depth and a r e l i n e d w i t h sand and s h e l l  ( v a l v e s o f Mya a r e n a r i a , many s t i l l  i n growth p o s i t i o n ) .  deposits  Blue-green a l g a l  mats (mainly Phormidium s p . w i t h minor O s c i l l a t o r i a s p . and S p i r u l i n a sp.) bloom i n summer on the p l a t e a u s between the c h a n n e l s .  The a l g a l mats i n the  upper h a l f o f the zone become e x t e n s i v e l y c r a c k e d i n summer and the a l g a l mats b l i s t e r and c u r l cracks and undermine can  ( F i g . 6b) .  Crabs (Hemigrapsus? gregonens.is-) I n f e s t the  the a l g a l mats to such an e x t e n t t h a t a l g a l mat 'cakes'  be p e e l e d from the s u b s t r a t e  a l g a l mat cakes from below  ( F i g . 6 c ) ; Hemigrapsus burrows  ( F i g s . 6c, 6 d ) .  up i n t o the  I n w i n t e r a f i l m o f mud and very  f i n e sand washed i n by w i n t e r storms b u r i e s the a l g a l mats and f i l l s the cracks and crab burrows. of  Thus, the p l a t e a u s between t i d a l channels c o n s i s t  f i n e l y l a m i n a t e d sediments w i t h b l a c k o r g a n i c r i c h laminae and mud laminae  c r o s s - c u t by c a s t s o f cracks and crab burrows  ( F i g . 6d). T i d a l pools are  138  F i g u r e 4.  a)  Laminated s i l t s o f the s a l t m a r s h . The c o a r s e r laminae stand out i n r e l i e f . Pen i s 15 cm l o n g .  b)  The weathered s u r f ace of the s a l t m a r s h r e v e a l s t h a t the s a l t m a r s h d e p o s i t s are r i d d l e d w i t h r o o t l e t s , which have weathered out as h o l e s here. Pen i s 15 cm l o n g .  139  140  F i g u r e 5.  The mud contents o f s u r f a c e sediments. Numbers next to s t a t i o n s i n d i c a t e the p e r c e n t mud a t each s t a t i o n . The g e n e r a l trends o f the contours between t r a n s e c t s have been determined by q u a l i tative f i e l d observations.  F i g u r e 6.  a)  The a l g a l mat zone. The channel i n the f o r e g r o u n d i s about one meter wide. Taken on f l o o d t i d e , j u s t as the channels are b e g i n n i n g t o f i l l . Mudcracked p l a t e a u s l i e between the c h a n n e l s , and w a t e r - f i l l e d d e p r e s s i o n s are p r e s e n t on the p l a t e a u s .  b)  Mudcracked s u r f a c e of the a l g a l mat zone. The a l g a l mats b l i s t e r and c u r l under the of d e s i c c a t i o n , and c r a c k i n g produces i s o l a t e d ' a l g a l mat cakes.'  c)  U n d e r s u r f a c e o f an ' a l g a l mat  d)  Laminated sediments of an a l g a l mat cake, c r o s s - c u t by a crab burrow (HemigrapBus o r e g o n e n s i s ) .  effects  cake,' r i d d l e d by crab burrows.  t-  1  142  143 p r e s e n t i n d e p r e s s i o n s on the p l a t e a u s .  Filamentous  green algae  (mainly  R h i z o c l o n i u m sp. w i t h minor Enteromorpha sp.) bloom around the moist edges of the pools i n summer, w h i l e the p o l y c h a e t e worms A b a r e n i c o l a p a c i f i c a and Spio sp. are abundant i n the p o o l s - Swinbanks (1979) p r o v i d e s d e s c r i p t i o n s of the burrows of these worms. easy  Whereas the a l g a l mats are f i r m  and  to walk on, the t i d a l p o o l s are u n d e r l a i n by s o f t d i l a t a n t muds.  In the lower a l g a l mat b u t i o n , and  zone b l u e - g r e e n a l g a l ' m a t s become patchy  the dominant a l g a l form i s a brown f i l m of diatoms  in distri(Plurosigma  sp., Gyrosigma sp., N a v i c u l a sp. and N i t z s c h i a s p . ) . The  s a n d f l a t zone i s predominantly  i n exposure.(Fig. 3). t i d a l channels  As  lower amphizonal to upper  the name i m p l i e s , the zone i s f l a t ,  and dominated by very f i n e to f i n e sands,  a r e a of muds i s p r e s e n t i n the middle g e n e r a l l y l a c k s any  floral  The  The  zone  cover a l t h o u g h a p a t c h of Z o s t e r a americana a n d C 1 7 and s m a l l e r patches  c h a r a c t e r i s t i c f e a t u r e of t h i s  d e n s i t y of t h a l a s s i n i d e a n burrowing zones o f non-vegetated  lacking in  although a small  of t r a n s e c t A ( F i g . 5 ) .  e e l g r a s s ) i s p r e s e n t between s t a t i o n s C H p r e s e n t elsewhere.  aquazonal  are  zone i s the v e r y h i g h  shrimps which i t s u p p o r t s .  sand i n Boundary Bay  (dwarf  U n l i k e the  (Swinbanks, 1979), t h i s  zone  l a c k s sand wave bedforms. The  e e l g r a s s zone i s e x c l u s i v e l y lower aquazonal  upper l i m i t -1.5  terminates at the upper l i m i t  i n exposure.  Its  of the lower aquazone at about  m G e o d e t i c Datum ( F i g . 3), a l e v e l below which the maximum d u r a t i o n of  submergence begins  to i n c r e a s e a b r u p t l y by a s e r i e s o f s t e p s , the f i r s t  a jump from about 10 to 20 days of continuous  submergence (Swinbanks, 1979).  The e e l g r a s s c o n s i s t s e n t i r e l y of the l a r g e r s p e c i e s Z o s t e r a marina. marina beds a t t a i n h i g h e r e l e v a t i o n s (up to -0.5  Z.  m G e o d e t i c Datum) i n  Boundary Bay by e x t e n d i n g as f i n g e r s up the broad channels which remain w a t e r - f i l l e d d u r i n g low  being  tide  d e p r e s s i o n s of  tidal  (Swinbanks, 1979).  The  144  upper l i m i t o f the e e l g r a s s bed s t u d i e d by Moody (1978) on the southern s i d e o f the f e r r y causeway i s bounded by a 'causex^ay zone.'  Moody  (1978)  r e p o r t e d an anomalously low e l e v a t i o n f o r the upper l i m i t o f the e e l g r a s s bed i n h i s study  area  Moody, 1978).  (-2.10 m Geodetic  Datum; +0.85 m Tsawwassen Chart Datum;  The sediments w i t h i n the e e l g r a s s zone are f i n e sands on  t r a n s e c t s B and C and very On the C o a l p o r t  f i n e sands and muds on t r a n s e c t A ( F i g . 7 ) .  s i d e o f the t i d a l f l a t  eroded by a d e n d r i t i c drainage  the e e l g r a s s zone i s c u r r e n t l y b e i n g  channel system, which extends from the head  of a borrow p i t dredged d u r i n g c o n s t r u c t i o n o f the C o a l p o r t Hinton,  1977).  Since Coalport  c o n s t r u c t i o n , the e e l g r a s s zone has been  advancing shorewards a t the r a t e o f about 25 m y r  (Beak-Hinton, 1977) , b u t  there i s no h i s t o r i c a l data on the d e n s i t y o f e e l g r a s s  Grain Size of Surface  The saltmarsh  general  i n 1969 (Beak-  cover.  Sediments  g r a i n s i z e c h a r a c t e r i s t i c s o f each zone seaward o f the  have a l r e a d y been d e s c r i b e d .  G r a i n s i z e coarsens seawards on  t r a n s e c t s B and C ( F i g . 7 ) , which i s a t y p i c a l c h a r a c t e r i s t i c o f t i d a l ( K l e i n , 1971).  The s t e e p e s t  g r a d i e n t i n g r a i n s i z e occurs  z o n a l e l e v a t i o n s upwards; i . e . , above about mean s e a l e v e l  flats  from upper amphi( j u s t below the  lower l i m i t o f the a l g a l mat zone) much as r e p o r t e d by Swinbanks (1979) f o r Boundary Bay.  Transect  of mud i s p r e s e n t  A does n o t f o l l o w t h i s t r e n d and a p u z z l i n g p a t c h  i n the middle o f the t r a n s e c t .  the two 'causeway zones' i l l u s t r a t e ?  the sediments h a v e - c o a r s e r the immediately a d j a c e n t Box  cores  The s i x samples taken from  the anomalous n a t u r e  of these  zones, as  median g r a i n s i z e s and/or lower mud contents tidal flats  revealed l i t t l e  ( F i g s . 5, 7 ) .  evidence  mentioned i n the a l g a l mat zone.  than  o f s t r a t i f i c a t i o n except t h a t  already  However, on t r a n s e c t C i n the e e l g r a s s  zone,  145  F i g u r e 7.  The median g r a i n s i z e (0) o f s u r f a c e sediments. The numbers next to s t a t i o n s i n d i c a t e median g r a i n s i z e (0) a t each s t a t i o n .  146 b l a c k o r g a n i c r i c h sediments were u n d e r l a i n a t a few c e n t i m e t e r s clean, l i g h t  c o l o u r e d sands p r o b a b l y  ment o f the e e l g r a s s  indicating  zone (Beak-Hinton, 1977).  depth by  the r e c e n t landward encroachOn t r a n s e c t A s t a t i o n s A l  to A4 are u n d e r l a i n a t about 30-40 cm depth by a t h i n peat h o r i z o n which i n t u r n i s u n d e r l a i n by b l u e - g r e y  c l a y e y muds.  Beyond s t a t i o n A4 the peat  h o r i z o n was not d e t e c t e d , b u t i n s t e a d the s u r f i c i a l muddy sands o r muds were d i r e c t l y u n d e r l a i n a t about 40 cm depth by the b l u e - g r e y blue-grey  c l a y e y muds.  This  c l a y e y mud h o r i z o n was t r a c e d as f a r seawards as A7.  S a l i n i t y and T u r b i d i t y  A e r i a l photographs  c l e a r l y i n d i c a t e t h a t the C o a l p o r t  causeway d e f l e c t s  the t u r b i d , s i l t - l a d e n waters o f the F r a s e r plume away from t h i s and  tidal  flat  the inter-causeway waters a r e now c l e a r e r than they were (e.g., A37170-39  N a t i o n a l A i r Photo L i b r a r y , Ottawa, Canada).  R. Moody (1978) has monitored  the s a l i n i t y o f s u r f a c e waters immediately south o f the f e r r y t e r m i n a l causeway on a monthly, b i - m o n t h l y and d i u r n a l b a s i s over a 10-month p e r i o d .  On 18  out o f the 20 days sampled s u r f a c e water s a l i n i t i e s were g r e a t e r than o r equal  to 20%,.% (range 20-28%.).  On two days, one i n August the o t h e r i n  October, s a l i n i t y dropped t o between 14 and 15.5%, (Moody, 19 78).  Moody  (19 78) has demonstrated t h a t the t u r b i d i t y o f s u r f a c e waters i n c r e a s e s  during  the summer months when the F r a s e r i s i n f r e s h e t , as i n d i c a t e d by a decrease i n s e c c h i d i s c depth from about 5 m i n w i n t e r Levings  to 2 m i n summer  (May-September).  and C o u s t a l i n (1975) took three s u r f a c e s u b s t r a t e s a l i n i t y measure-  ments i n the inter-causeway area i n February, 1974.  Their values  ranged  between 26.5%. and 2 7% .„ 0  Surface 1977  s u b s t r a t e s a l i n i t i e s were monitored over the p e r i o d J u l y 1-7,  a t 64 s t a t i o n s on t r a n s e c t s A, B, C and D, and on August 13, 1977 s u r f a c e  147  s u b s t r a t e s a l i n i t i e s were measured a t a l l 67 s t a t i o n s on t r a n s e c t s A, B and C i n a three-hour p e r i o d .  Values ranged between 22 and 32%o (Appendix 5 ) .  R e s u l t s f o r August 13 are t y p i c a l  ( F i g . 8).  v a r i a b i l i t y i n s a l i n i t y over the t i d a l f l a t  The r e s u l t s show l i t t l e apart from a s l i g h t  lateral  increase  i n s a l i n i t y shorewards, p r o b a b l y due to e v a p o r a t i o n (e.g., the s a l i n i t y o f s u r f a c e waters a t C6 i n c r e a s e d (from 30.5%\Tt;o^31i^%o ^overc 'the; three¥hour''samplijig /  ;  interval).  Anomalously low s a l i n i t i e s were r e c o r d e d i n the v i c i n i t y of  s t a t i o n A2.  T h i s i s p o s s i b l y a r e s u l t of groundwater seepage from' the shore  a l o n g the impermeable peat and mud h o r i z o n p r e v i o u s l y mentioned. salinity profile  taken a t s t a t i o n A2 d e t e c t e d low s a l i n i t y water  associated with this horizon  (Appendix 5 ) .  (10%o)  Twenty-two s u b s t r a t e  p r o f i l e s taken on t r a n s e c t s A, B and C were almost a l l i s o h a l i n e F i g u r e 9 shows a t y p i c a l example.  A substrate  salinity (Appendix 5 ).  On June 8, 1978 three s a l i n i t y  profiles  o f the water column, taken i n the inter-causeway a r e a at h i g h t i d e , were v i r t u a l l y i s o h a l i n e w i t h s a l i n i t i e s between 22-24%  0  (Part 4B.).  DISTRIBUTION OF THALASSINIDEAN SHRIMPS  T h a l a s s i n i d e a n shrimp burrows dominate the s a n d f l a t zone ( F i g s . 10, 11). C a l l i a n a s s a are abundant throughout the zone ( F i g . 10) w h i l e Upogebia only a t t a i n high d e n s i t i e s  (>20 burrow openings m  -2  ) i n the muddy sediments on  the f e r r y t e r m i n a l s i d e of the s a n d f l a t zone ( F i g . 11).  Callianassa  attain  -2 a maximum d e n s i t y o f 172 ± 22 burrow openings m  ( e q u i v a l e n t to about 70  -2 shrimps m ) i n the s a n d f l a t zone. However, the h i g h e s t d e n s i t i e s o f C a l l i a n a s s a were r e c o r d e d i n the narrow 'causeway zone' next to the f e r r y -2 t e r m i n a l , where burrow opening d e n s i t i e s a t t a i n 446 i 31 m  .- ...-  ( e q u i v a l e n t to about  180 shrimps'mT )'\. The presence o f the s a l t m a r s h l i m i t s C a l l i a n a s s a 2  at upper i n t e r t i d a l l e v e l s .  -  distribution  C a l l i a n a s s a d e n s i t i e s are low i n the a l g a l  mat  148  Legend Contour of substrate salinity  %o  .2*0  Transect station w i t h  '  measurement indicated  Figure  8.  Sampling  -32-  salinity %o  Co - C29  Times  1130-1200  821 — BI  1225-1305  A12 - A l  1320-  C6-C1  1415-1425  1350  S u r f a c e s u b s t r a t e s a l i n i t i e s as measured on t r a n s e c t s A, B and C August 13, 1977 a t low t i d e between 11:30 and 14:25 i n the o r d e r indicated. Numbers next to s t a t i o n s i n d i c a t e s a l i n i t y .  149  A10  JUL.  5  SALINITY  10 _L_  20 _i  7oo  30 —i  KH  E u Z hO. UJ  2030-  Q  4050  J  Figure 9 .  Typical substrate s a l i n i t y p r o f i l e  from the inter-causeway  area.  150  F i g u r e 10.  D i s t r i b u t i o n o f C a l l i a n a s s a burrow openings i n contoured map form. G e n e r a l trends o f contours between t r a n s e c t s determined by q u a l i t a t i v e f i e l d o b s e r v a t i o n .  151  1000 m  500  Legend »1 "  §11  F i g u r e 11.  Contour of  burrow  density  2  >30m-  Distribution  m~  opening  f o r Upogebia  2  of UpbjeMa burrow openings  i n contoured map  form.  152  zone. on  At low  i n t e r t i d a l levels  t r a n s e c t s B and Upogebia has  C a l l i a n a s s a d e n s i t i e s decrease d r a m a t i c a l l y  C where e e l g r a s s forms a dense and not been o b s e r v e d . i n  the a l g a l mat  i t s h i g h e s t e l e v a t i o n s on  t r a n s e c t A extending  amphizone  level).  (about mean sea  A comparison of F i g u r e 5, showing mud  up  continuous zone.  mat  (.Fig. 10).  Upogebia a t t a i n s  to the base of the upper  d i s t r i b u t i o n , with Figure  11,  showing the d i s t r i b u t i o n of Upogebia, c l e a r l y demonstrates a p r e f e r e n c e the p a r t o f Upogebia f o r mud.  T h i s has been p o i n t e d out q u a l i t a t i v e l y  b i o l o g i s t s many times i n the p a s t and P r i t c h a r d , 1969; f o r JJ- l i t o r a l i s ) .  (Stevens,  Thompson, 1972, In the  on  1928;  M a c G i n i t i e , 1930;  by  L. Thompson  f o r JJ. p u g e t t e n s i s ; Ott e t a l . ,  1976,  f o l l o w i n g s e c t i o n the r e l a t i o n s h i p w i l l be  analyzed  quantitatively.  I n f l u e n c e of G r a i n S i z e on T h a l a s s i n i d e a n Shrimp  The to  study  inter-causeway t i d a l f l a t  forms an almost i d e a l environment i n which  the r e l a t i o n s h i p between g r a i n s i z e and  b u t i o n because:  (1)  Distribution  t h a l a s s i n i d e a n shrimp  L a t e r a l v a r i a t i o n s i n s a l i n i t y and  reduced to a minimum by causeway c o n s t r u c t i o n .  (2)  The  distri-  t u r b i d i t y have been tidal flat  shows  c o n s i d e r a b l e v a r i a t i o n i n g r a i n s i z e parameters i n a d i r e c t i o n p a r a l l e l  to  the s h o r e l i n e , e n a b l i n g comparison of s t a t i o n s o f s i m i l a r e l e v a t i o n but different grain size.  (3)  T h a l a s s i n i d e a n shrimp d e n s i t i e s are h i g h ,  a l l o w i n g easy r e s o l u t i o n o f  U p o g e b i a — F i g u r e 12a w i t h .median g r a i n s i z e and  thus  trends.  compares the d e n s i t y of Upogebia burrow openings F i g u r e 12b w i t h mud  content,  r e g a r d l e s s of  station  -2 elevation.  I t i s apparent t h a t h i g h d e n s i t i e s (:>20  associated with  the f i n e r g r a i n e d sediments  m  (median >3.8  ) of Upogebia are 0)  c o n t a i n i n g more  (b)  (a)  9  •J.  I?  —1»-  25  M i D I A N  F i g u r e 12.,  a) b)  Density Density  (0|  SO M U D  IK)  of Upogebia burrow openings vs median g r a i n s i z e (0) , r e g a r d l e s s of e l e v a t i o n , of Upogebia burrow openings vs mud content (%), r e g a r d l e s s of e l e v a t i o n .  154 than about 40% mud.  However, Upogebia d e n s i t y  i s a l s o a f u n c t i o n o f . .v.i ; ,  e l e v a t i o n , and t h i s obscures the t r e n d s i n F i g u r e problem the s t a t i o n s were c l a s s e d -2.20  size  (Appendix 6 ) .  13.  a straight line,  of the l i n e bution,  The r e s u l t s f o r mud content a r e  .-.r  Very s i m i l a r r e s u l t s were o b t a i n e d f o r median  grain  F o r a l l c l a s s i n t e r v a l s h i g h e r d e n s i t i e s o f Upogebia  o c c u r i n the muddier f i n e r g r a i n e d by  To overcome t h i s  i n t o 0.25 m e l e v a t i o n c l a s s i n t e r v a l s from  m to +0.05 m (Geodetic Datum).  presented i n Figure  12.  the s l o p e  sediments.  The t r e n d  can be approximated  of which i s dependent on e l e v a t i o n .  The s l o p e  i s minimized a t the upper and lower l i m i t s o f Upogebia's  and maximized a t the e l e v a t i o n s  of highest  distri-  Upogebia d e n s i t y .  Corre-  l a t i o n c o e f f i c i e n t s are q u i t e h i g h , many exceeding 0.9 and 13 o u t o f 18 a r e s i g n i f i c a n t a t the 95% c o n f i d e n c e l e v e l  Callianassa—A out.  (jr t e s t ) .  s i m i l a r a n a l y s i s o f the data f o r C a l l i a n a s s a was c a r r i e d  F o r u n c l a s s e d d a t a no trends a r e apparent.  Callianassa  attains high  -2 densities size  (>50 burrow openings m  ) i n sediments which range i n median  grain  from 2.57 0 to 3.94 0 , and' i n mud content from 4.5% to 47% (Appendix 6 )  On b r e a k i n g the d a t a down i n t o 0.25 m e l e v a t i o n c o r r e l a t i o n can be d i s c e r n e d .  Figure  c l a s s i n t e r v a l s no  consistent  14 p r e s e n t s the. r e s u l t s f o r mud content  Very s i m i l a r r e s u l t s were o b t a i n e d f o r median g r a i n s i z e (Appendix 6 ) . At low  elevations  (e.g., F i g . 14D) C a l l i a n a s s a d e n s i t i e s decrease w i t h i n c r e a s i n  mud content and d e c r e a s i n g g r a i n s i z e , but as e l e v a t i o n  increases  the slope  of the r e g r e s s i o n  the t r e n d  i s reversed  line  decreases and a t h i g h e l e v a t i o n s  with high Callianassa densities occurring ments (e.g., F i g . 14H).  i n the muddier f i n e r g r a i n e d  sedi- .  C a l l i a n a s s a d e n s i t i e s are very low (<0.5 burrow  -2 openings m  ) i n the muddiest sediments on the t i d a l f l a t , which o c c u r h i g h  on  C (Stations  transect  However, i t i s d i f f i c u l t  C1-C3), where mud c o n t e n t s range between 65% and 92%. t o know whether the low d e n s i t i e s a r e a f u n c t i o n o f  155  -1.70/-1.45 m  M u d  F i g u r e 13.  %  M u d  %  R e l a t i o n s h i p between mud content (%) and Upogebia burrow opening d e n s i t y , w i t h data grouped i n t o 0.25 m e l e v a t i o n c l a s s i n t e r v a l s . B e s t - f i t l i n e a r r e g r e s s i o n l i n e s are i n d i c a t e d , a l o n g w i t h t h e i r c o r r e l a t i o n c o e f f i c i e n t s (r) and c o n f i d e n c e l e v e l s (£ t e s t ) . E l e v a t i o n ( G e o d e t i c Datum) i n c r e a s e s from A to J .  156  Figure 14.  Relationship between mud content (%) and Callianassa burrow opening density, with data classed into 0.25 m elevation class i n t e r v a l s . B e s t - f i t l i n e a r regression lines are indicated, along with their correlation c o e f f i c i e n t s (r) and confidence levels (r t e s t ) . Elevation (Geodetic Datum) increases from A to L.  157  158 grain size of elevation.  Thalassinidean  Shrimp  Callianassa  Interrelationships  and Upogebia burrows occur s i d e by s i d e  ( F i g . 10, 11).  Upogebia i s a s u s p e n s i o n f e e d e r ( M a c G i n i t i e ,  1930; Thompson, 1972), w h i l e  C a l l i a n a s s a i s a deposit  1934).  niches w i t h i n  feeder (MacGinitie,  the i n t e r t i d a l environment.  They occupy v e r y s i m i l a r  Do the two shrimps  interact?  Is there any evidence of c o m p e t i t i o n o r t r o p h i c group ammensalism and  (Rhoads  Young, 1970)? Linear  density  regression  a n a l y s i s was c a r r i e d out on C a l l i a n a s s a and Upogebia  data which had been c l a s s e d  i n t o 0.25 m e l e v a t i o n  class intervals  ( F i g . 1 5 ) . Three o u t o f n i n e o f the c l a s s i n t e r v a l s have c o r r e l a t i o n c o e f f i c i e n t s wnich a r e s i g n i f i c a n t a t the 95% c o n f i d e n c e l e v e l f o u r t h i s s i g n i f i c a n t a t the 90% c o n f i d e n c e l e v e l . c o r r e l a t i o n c o e f f i c i e n t s are n e g a t i v e . it  i s only  (jr t e s t ) , w h i l e a  In a l l four  Examination o f F i g u r e  cases the  15 r e v e a l s  that  a t e l e v a t i o n s where b o t h Upogebia and C a l l i a n a s s a have the poten-::". ••  t i a l of a t t a i n i n g high densities  t h a t a n e g a t i v e c o r r e l a t i o n between iL.;  C a l l i a n a s s a and Upogebia d e n s i t y  i s apparent.  BIOGENIC REWORKING OF SEDIMENT  Sediment reworking r a t e s were monitored w i t h i n during  the summer o f 1978 (Table  I).  protected  metal e n c l o s u r e s  The r a t e a t which C a l l i a n a s s a  sediment i s q u i t e v a r i a b l e , r a n g i n g between 9 to 33 ml/shrimp/day there a r e 2.5 burrow openings p e r s h r i m p ) . shrimp/day. reported  reworks  (assuming  The average r a t e i s 18 ± 9 ml/  These r a t e s are comparable w i t h the r a t e o f 25 ml/shrimp/day  by O t t e t a l . (19 76)  f o r C a l l i a n a s s a s t e b b i n g i , but i s appreciably  D UO-i  -1.45/-1.20 m  I—  F i g u r e 15~  R e l a t i o n s h i p between Upogebia burrow opening d e n s i t y and C a l l i a n a s s a burrow opening d e n s i t y w i t h the data c l a s s e d i n t o 0.25 m e l e v a t i o n c l a s s i n t e r v a l s . B e s t - f i t l i n e a r regression l i n e s are i n d i c a t e d along w i t h t h e i r c o r r e l a t i o n c o e f f i c i e n t s ( r ) and confidence l e v e l s ( r t e s t ) . Elevat i o n (Geodetic Datum) i n c r e a s e s from A to J .  1  1 6 0  TABLE  I  Rates o f b i o g e n i c reworking o f sediment by C a l l i a n a s s a and Upogebia, as measured i n p r o t e c t e d m e t a l e n c l o s u r e s on the s u r f a c e o f the s u b s t r a t e  Burrow Openings (0.25 m ) *C. *U-  Exposure Duration (hours)  Temperature o f s u b s t r a t e and sea water ( C)  -2  Date  Station  J u l 31/Aug 1 1978  C23  27, 26 (2 cm)** 23, 24 (.10 cm)** 22, 22 (S.W.)***  3.5  C15  27, 28 (2 era) 24, 25 (10 cm) 22, 22 (S.W.)  b.5  C12  27, 29 (2 cm) 25, 26 (10 cm) 22, 22 (S.W.)  7.0  Aug 4/Aug 5 1978  C23  26, 29 (2 cm) 24, 24 (10 cm) 22, 22 (S.W.)  3.3  Aug 30/Aug 31 1978  C17  25, 20 (10 cm) 19, 18 (S.W.)  5.4  A7  25, 19 (10 cm) 19, 18 (S.W.)  4.2  C21  19, 20 (10 cm) 18, 18 (S.W.)  2.0  11  C17  19, 20 (10 cm) 18, 18 (S.W.)  4.0  10  Sept 3/Sept 4 1978  27  17  22  33  11  13  14  15  13  Average  *  C. = C a l l i a n a s s a  ** *** Note:  Rate (.ml/shrimp/day) *C. *U.  18 ± 9  0  U. = Upogebia  2 cm = S u b s t r a t e temperature a t 2 cm. S.W. = F l o o d i n g s e a water-at 50 cm depth. a  l  „ „ . » « . date,-.., o„  "fj^;X \f "r/»/«"; °«i™SeS^; . r  8  f  t  161  l e s s than the e s t i m a t e o f 50 ml/shrimp/day Callianassa c a l i f o r n i e n s i s ; MacGinitie used to determine  made by M a c G i n i t i e  (1934) f o r  (1934) gave no d e t a i l s o f the t e c h n i q u e  rates.  The p o p u l a t i o n o f C a l l i a n a s s a on the inter-causeway t i d a l f l a t was g e s t i m a t e d to be about 100 m i l l i o n  ( a c t u a l e s t i m a t e 1.08 x 10 ) .  by d i v i d i n g F i g u r e 10 i n t o areas o f comparable  T h i s was done  shrimp d e n s i t y and computing  shrimp p o p u l a t i o n s f o r each a r e a , by d e t e r m i n i n g the average burrow density  opening  f o r the a r e a m u l t i p l y i n g t h i s d e n s i t y by the a r e a and assuming a  burrow opening to shrimp r a t i o o f 2.5 to 1.  D u r i n g the summer  (June 21-  September 21), when s u b s t r a t e temperatures a r e p r o b a b l y comparable p r e s e n t e d i n T a b l e 1,-  to those  t h i s p o p u l a t i o n o f C a l l i a n a s s a turns over about 0.2  -2 m i l l i o n c u b i c meters o f sand, and i n areas o f h i g h e s t shrimp d e n s i t y  (178 m  )  C a l l i a n a s s a reworks the sediment i t l i v e s i n to a depth o f 50 cm i n about f i v e months. Upogebia d i d n o t produce any measurable mounds o f sediment w i t h i n 25 hours  ( T a b l e ! ) > s However, t h i s does not mean t h a t Upogebia does n o t rework  sediment.  Both Thompson (1972) and O t t e t a l . (1976) have noted i n the  l a b o r a t o r y t h a t Upogebia c o n s t a n t l y  tends to i t s burrow  and t r a n s p o r t s  sedi-  ment from one p a r t o f the system to another, by e x c a v a t i n g sediment i n one p l a c e and tamping i t i n t o the w a l l s i n a n o t h e r .  Figure 5 i l l u s t r a t e s  that  t h e r e i s an anomalous p a t c h o f muds i n the middle o f t r a n s e c t A, which i s h a r d t o account f o r i n terms o f p h y s i c a l p r o c e s s e s , and i s a s s o c i a t e d w i t h h i g h d e n s i t i e s o f Upogebia  ( F i g . 1 1 ) . As s h a l l be seen i n P a r t B, Upogebia  c o n s t r u c t s a muddy i n n e r l i n i n g  to i t s burrow, which i s 1-4 mm t h i c k .  A  b l u e - g r e y c l a y e y mud h o r i z o n has been d e t e c t e d a t about 40 cm depth on tran--.;.u s e c t A and can be t r a c e d a t l e a s t 600 m seawards  as f a r as A7.  Upogebia  burrows, which extend down to about 60 cm depth, c r o s s i n t o t h i s h o r i z o n ( F i g . 1 6 ) . Perhaps  the anomalously h i g h mud contents o f the sediments on  « 100-,  F i g u r e 16.  The n e a r - s u r f a c e s t r a t i g r a p h y of the t i d a l f l a t on t r a n s e c t A. Upogebia burrows extend down i n t o a b l u e - g r e y c l a y e y mud h o r i z o n (the v e r t i c a l dimensions of the burrows are drawn to s c a l e ) . This b i o t u r b a t i o n may account f o r the anomalously high.mud contents of the s u r f a c e sediments.  , ^ M  163  t r a n s e c t A are the r e s u l t o f i n t e n s e b i o t u r b a t i o n by Upogebia, which a t t a i n d e n s i t i e s of 84 burrow  openings m  -2  i n t h i s a r e a ( F i g . 16).  i n c o n s t r u c t i n g burrows have p o s s i b l y t r a n s p o r t e d mud c l a y e y mud the  can Upogebia  from the b l u e - g r e y  h o r i z o n a t depth and i n c o r p o r a t e d i t i n t o the burrow w a l l s near'  s u r f a c e , thereby i n c r e a s i n g the mud  content of the s u r f a c e sediments.  DISCUSSION  The ranges o f s a l i n i t y encountered w i t h i n the inter-causeway a r e a a r e w i t h i n the t o l e r a n c e l i m i t s o f both C a l l i a n a s s a and Upogebia, the lower l e t h a l l i m i t f o r C a l l i a n a s s a b e i n g 10% and P r i t c h a r d , 19,69).  o  and f o r Upogebia 3.5%  C a l l i a n a s s a i s probably protected  a  (L. Thompson  from any  transient  i n c u r s i o n s o f low s a l i n i t y water by h i g h s a l i n i t y i n t e r s t i t i a l waters a t depth which are f r e e to e n t e r i t s u n l i n e d burrow  (L. Thompson and P r i t c h a r d ,  Thus, i n the inter-causeway area,, s a l i n i t y does not i n f l u e n c e shrimp  1969).  thalassinidean  distribution.  Upper L i m i t s o f T h a l a s s i n i d e a n Shrimp  Distribution  The presence of the s a l t m a r s h l i m i t s C a l l i a n a s s a d i s t r i b u t i o n a t upper intertidal levels.  As i n Boundary  Bay  the lower l i m i t of the s a l t m a r s h l i e s  at the lower l i m i t of the upper atmozone. the  T h i s i s the t i d a l l e v e l at which  maximum d u r a t i o n of exposure jumps from about 10 to 20 days, and  this  p e r i o d o f exposure o c c u r s at the time o f the s p r i n g equinox (.Swinbanks, 1979). As Swinbanks (1979) has suggested, based on the s a l t m a r s h s t u d i e s o f Chapman (1974), t h i s p r o l o n g e d p e r i o d of exposure may seedling germination.  be e s s e n t i a l f o r s u c c e s s f u l  Apart from b e i n g e x c l u d e d by the dense  vegetative  cover of the s a l t m a r s h C a l l i a n a s s a p r o b a b l y cannot s u r v i v e a t the upper atmoz o n a l e l e v a t i o n s o f the marsh because the maximum d u r a t i o n o f exposure exceeds  164" C a l l i a n a s s a ' s t o l e r a n c e o f exposure. l e t h a l to C a l l i a n a s s a  More than about 5 days o f a n o x i a i s  (R. Thompson and P r i t c h a r d ,  1969).  On t r a n s e c t A, Upogebia extends up t o the base o f the upper (about mean s e a l e v e l ) .  amphizone  Upogebia burrow waters can become a n o x i c w i t h i n  one hour o f exposure (R. Thompson and P r i t c h a r d , 1969).  The maximum d u r a t i o n  of exposure within^ the lower amphizone  a l u n a r day  i s l e s s than h a l f  (Swinbanks, 1979), whereas w i t h i n the upper amphizone of exposure l i e s between 0.7 and 1.0 l u n a r days ( i . e . ,  the maximum d u r a t i o n 17-25 h o u r s ,  Swinbanks,  1979), which i s w i t h i n the range o f exposure to a n o x i a l e t h a l t o p o s t m o l t Upogebia  (range 12-42 hours,- R. Thompson and P r i t c h a r d , 1969).  Hence, Upogebia  p r o b a b l y a t t a i n s i t s a b s o l u t e p h y s i o l o g i c a l l i m i t i n e l e v a t i o n on t r a n s e c t A by e x t e n d i n g up to the base o f the upper  Lower L i m i t s o f T h a l a s s i n i d e a n Shrimp  amphizone.  Distribution  Ott e t a l . (19 76) suggest t h a t dense meadows o f s e a g r a s s (Cymodocea) limit  the d i s t r i b u t i o n of Upogebia l i t o r a l i s  and Swinbanks  t h a t C a l l i a n a s s a d i s t r i b u t i o n may be l i m i t e d i n Boundary floral  cover o f Z_. marina i n the lower e e l g r a s s zone.  (1979) suggests  Bay by the dense  Further evidence f o r  Z. marina l i m i t i n g C a l l i a n a s s a d i s t r i b u t i o n i s found i n the inter-causeway a r e a on t r a n s e c t s B and C.  On these t r a n s e c t s C a l l i a n a s s a d e n s i t y d e c r e a s e s -2-  d r a m a t i c a l l y to l e s s than 0.5 m and c o n t i n u o u s . i n t e r t i d a l levels  , were Z. marina coverage becomes dense  In the absence o f e e l g r a s s , C a l l i a n a s s a extend t o lower (Part$B).  The dense r o o t l e t s o f Z. marina may h i n d e r the  m i n i n g a c t i v i t i e s o f C a l l i a n a s s a and/or the dense f l o r a l  cover, b l a c k  organic  r i c h s u r f a c e sediments and dense r o o t l e t s may d i s c o u r a g e s e t t l e m e n t by p o s t l a r v a l C a l l i a n a s s a . .. There i s no e v i d e n c e t h a t Upogebia i s l i m i t e d by Z. marina.  I n Boundary Bay Upogebia i s abundant  i n dense Z. marina beds  165 (Swinbanks,11979). Upper L i m i t o f E e l g r a s s — M o o d y elevation  ( 1 9 7 8 ) a a t t r i b u t e s the anomalously low  (-2.10 m G e o d e t i c Datum, 1% mean exposure) f o r the upper l i m i t o f  e e l g r a s s a d j a c e n t t o the 'causeway zone' s o u t h o f the f e r r y causeway to more r a p i d d e s i c c a t i o n a s s o c i a t e d w i t h the sandy s u b s t r a t e .  However, e e l g r a s s  a t t a i n s much h i g h e r e l e v a t i o n s on sandy s u b s t r a t e s i n the inter-causeway a r e a (-1.43 m G e o d e t i c Datum, 7.8% mean exposure, T r a n s e c t B; -1.56 m G e o d e t i c Datum 6.4% mean exposure, T r a n s e c t C) and a t t a i n s the same e l e v a t i o n on muddy s u b s t r a t e s  (-1.45 m G e o d e t i c Datum, T r a n s e c t A ) , d i s p r o v i n g Moody's  (1978) theory t h a t the upper l i m i t o f e e l g r a s s i s i n f l u e n c e d by g r a i n  size.  D e s i c c a t i o n may be enhanced by the steepened p r o f i l e a s s o c i a t e d w i t h the 'causeway zone,' b u t p r o b a b l y much more important i s the i n c r e a s e d  effects  of wave a c t i o n on the steepened p r o f i l e as e v i d e n c e d by the presence of sand b a r s ( F i g . 2 ) . The ' r i p r a p ' a d j a c e n t t o t h i s a r e a had t o be r e p l a c e d w i t h c o a r s e r m a t e r i a l a f t e r causeway c o n s t r u c t i o n , because i t was b e i n g t r a n s p o r t e d by wave-induced  longshore currents  H y d r a u l i c s , o r a l commun. 1978).  Canada  E e l g r a s s i s absent i n the presence of sand  waves i n Boundary Bay (Swinbanks, 1979). (Beak-Hinton, 1977).  (A. Tamburi, Western  E e l g r a s s cannot t o l e r a t e wave shock  The upper l i m i t o f e e l g r a s s bounded  by the 'causeway  zones' i s p r o b a b l y determined by wave shock, r a t h e r than exposure. The inter-causeway a r e a may be the only a r e a on the F r a s e r D e l t a where the f a c t o r d e t e r m i n i n g the upper l i m i t o f Z. marina may be a s i m p l e f u n c t i o n of t i d e s and e l e v a t i o n , because the area i s n o t s u b j e c t t o s t r o n g wave action  (as e v i d e n c e d by the l a c k o f sand waves), l a c k s t i d a l channels ( i n  which submergence d u r a t i o n i s enhanced), and has a r e l a t i v e l y regime.  The upper l i m i t l i e s  a t the upper l i m i t  o f the lower  stable  salinity  aquazone  t h a t has l a i n a t -1.51 •+ 0.14 m G e o d e t i c Datum f o r the p a s t two y e a r s (Swinbanks, 1979).  T h i s i s the l e v e l below which the maximum  d u r a t i o n o f submergence jumps from about 10 to 20 days, and t h i s p e r i o d o f p r o l o n g e d submergence always o c c u r s a t the time o f the s p r i n g and autumn equinoxes  (Swinbanks, 1979).  upper l i m i t  U n t i l now b i o l o g i s t s have suggested t h a t the  to Z. marina i s .'.determined by d e s i c c a t i o n due to exposure, r a t h e r  than b e i n g any f u n c t i o n o f submergence ( K e l l e r and H a r r i s , 1966; 1970; Moody, 1978). the aquazone  den H a r t o g ,  However, there are no jumps i n exposure d u r a t i o n w i t h i n  and t h e r e f o r e t h e r e i s no way  o f a c c o u n t i n g f o r the abrupt  t e r m i n a t i o n o f the e e l g r a s s zone , i n terms o f exposure.  Perhaps s p r i n g i s  a critical  growth a f t e r w i n t e r  time o f the y e a r when e e l g r a s s p u t s on renewed  dormancy, and s e e d l i n g g e r m i n a t i o n and/or v e g e t a t i v e r e p r o d u c t i o n r e q u i r e s continuous submergence w i t h o u t exposure i n o r d e r to s u c c e e d .  Could the  advance o f the upper l i m i t o f Z_. marina i n the inter-causeway a r e a over the p a s t e i g h t y e a r s (Beak-Hinton, 1977) be a r e s u l t of the f a c t t h a t the upper l i m i t o f the lower aquazone has r i s e n about 30 cm over the p a s t t e n y e a r s from -1.80  m ( G e o d e t i c Datum) i n 1968/70 to -1.51  m (Geodetic Datum) i n  1976/78, due to an 18.6 y e a r c y c l e ..in the moon's d e c l i n a t i o n ' (Swinbanks, . . 1979)?^-These .ideas are designed ;td provoke thought and f u r t h e r study o f the e l e v a t i o n a l l i m i t s o f e e l g r a s s , r a t h e r than to o f f e r  F a c t o r s I n f l u e n c i n g T h a l a s s i n i d e a n Shrimp  C a l l i a n a s s a does not e x h i b i t s i z e o f sediment, and i s abundant pure sands. a l g a l mat  answers.  Density  a clear preference f o r a p a r t i c u l a r  grain  i n sediments r a n g i n g from sandy muds to  C a l l i a n a s s a d e n s i t i e s a r e low i n the muds and muddy sands o f the  zone, but r a t h e r than b e i n g a r e s u l t o f s u b s t r a t e s e l e c t i o n by  C a l l i a n a s s a , t h i s i s p r o b a b l y because drainage enhanced exposure on the p l a t e a u s between t i d a l channels r e s u l t s i n a mudcracked,  inhospitable  ment t h a t can o n l y be c o l o n i z e d by b l u e - g r e e n a l g a e and crabs.  . -.  environ-  Upogebia shows  ,  167  a d i s t i n c t p r e f e r e n c e f o r muddy s u b s t r a t e s igroFab'ly^.e^cause' i t l i n e s " i t s ' burrow with>,mud' (Swinbanks , 19,79 ; Part''4B,);'; A, d u r a b l e "mud-linjid burrow e s s e n t i a l f o r Upogebia's s u s p e n s i o n f e e d i n g  and  respiration  There- i s some evidence to suggest that C a l l i a n a s s a and are n e g a t i v e l y  correlated  are h i g h , s u g g e s t i n g that ficantly,  at t i d a l e l e v a t i o n s they may  the f o u r e l e v a t i o n  be  F) are  activities. Upogebia  where d e n s i t i e s of both shrimps  c l a s s i n t e r v a l s which show h i g h n e g a t i v e and  Upogebia d e n s i t y  and  mud  content  ( F i g . 14C,  n e g a t i v e c o r r e l a t i o n s between C a l l i a n a s s a d e n s i t y  and  D,  (Figure  mud  E and  F).  and  rather  than b e i n g the  C a l l i a n a s s a f o r sandy c o a r s e r  r e s u l t of a p r e f e r e n c e on grained  c o r r e l a t i o n between C a l l i a n a s s a  substrates.  density  and  b e i n g the r e s u l t of any  the p a r t  Upogebia d e n s i t y  w i t h a n e g a t i v e c o r r e l a t i o n between C a l l i a n a s s a and  mud  mud  accept the e x p l a n a t i o n  content, Upogebia  negative  c o u l d be  the ~  content combined content, rather  Upogebia.  o f these four c l a s s i n t e r -  i s completely r e v e r s e d at h i g h e r  e l e v a t i o n s w i t h C a l l i a n a s s a e x h i b i t i n g a p r e f e r e n c e f o r muddier, f i n e r  contradiction  C a l l i a n a s s a and  Such a r e v e r s a l of p r e f e r e n c e i s h a r d to  does not  a r i s e i f we  accept the  grained  explain.  former e x p l a n a t i o n  that  Upogebia e x h i b i t a n e g a t i v e i n t e r a c t i o n where d e n s i t i e s  both shrimps can be  than  that C a l l i a n a s s a shows a p r e f e r e n c e . r f o r ' -.r  must a l s o accept that t h i s trend  sediments ( F i g . 14H).  be  of  n e g a t i v e i n t e r a c t i o n between C a l l i a n a s s a and  sandy-coarser g r a i n e d - s u b s t r a t e s a t the e l e v a t i o n s  This  D,  The  and  C o n v e r s e l y , the  r e s u l t of a p o s i t i v e c o r r e l a t i o n between Upogebia and  v a l s , we  15C,  mud  combined w i t h a n e g a t i v e c o r r e l a t i o n between C a l l i a n a s s a d e n s i t y  i f we  corre-  content c o u l d  the r e s u l t of a p o s i t i v e c o r r e l a t i o n between Upogebia d e n s i t y  But  Signi-  the same f o u r which have h i g h n e g a t i v e c o r r e l a t i o n c o e f f i c i e n t s  between C a l l i a n a s s a d e n s i t y  density,  densities  competing f o r a v a i l a b l e space.  l a t i o n c o e f f i c i e n t s between C a l l i a n a s s a E and  is"~probably  h i g h , because then we  need only  accept that  of  Callianassa  168 may  be p o s i t i v e l y  c o r r e l a t e d to mud  o n l y e x h i b i t e d at h i g h i n t e r t i d a l only p r e s e n t  i n low  densities.  content.  This p o s i t i v e c o r r e l a t i o n i s  e l e v a t i o n s where UpOgebia i s absent or i s  At i n t e r t i d a l  e l e v a t i o n s where Upogebia  C a l l i a n a s s a d e n s i t i e s can be e q u a l l y h i g h , C a l l i a n a s s a ' s p r e f e r e n c e substrates i s overridden C a l l i a n a s s a and  and  suppressed by a n e g a t i v e  and  f o r muddy  i n t e r a c t i o n between  Upogebia combined w i t h a s t r o n g p r e f e r e n c e  on the p a r t of  Upogebia f o r muddy s u b s t r a t e s . Accepting competition  the above e x p l a n a t i o n of the c o r r e l a t i o n s what form does the  between C a l l i a n a s s a and Upogebia take?  I t may  be  a form o f  t r o p h i c group ammensalism (.Rhoads and Young, 1970) , as Upogebia i s a suspens i o n feeder  ( M a c G i n i t i e , 1930;, Thompson, 19 72), w h i l e  d e p o s i t feeder  ( M a c G i n i t i e , 1934).  Perhaps the reworking a c t i v i t i e s  C a l l i a n a s s a are d e t r i m e n t a l to Upogebia. i n mounds on  the s u r f a c e C a l l i a n a s s a may  Upogebia, which c o n s t r u c t s m a l l in  'Y'  I n c o n s t a n t l y p i l i n g up  Aller  shaped burrows a few  lagoon  sediment may  ( L e v i n t o n and  Bambach, 1970), and h i g h  (Loosanoff,  1962).  (Thompson, activities  The  Shifting,  feeding larvae  feeders  and  prevent  p l a n k t i c l a r v a e o f Upogebia are  (Thompson, 1972), and perhaps the l a r v a e of UpOgebia feed  of C a l l i a n a s s a .  Upogebia could be  The  negative  a r e s u l t of one  ii  f l u x e s of resuspended  c l o g f i l t e r i n g mechanisms of s u s p e n s i o n  feeding  carnivorous those  f e e d i n g organisms.  bottoms cause h i g h m o r t a l i t y f o r s e t t l e d suspension  of b i v a l v e s  efficient  feeding  deep  produce an u n s t a b l e bottom which cannot  c o l o n i z e d by most kinds of s u s p e n s i o n  unstable  sediment  centimeters  and Dodge (1974) have suggested t h a t the reworking  of C a l l i a n a s s a i n a t r o p i c a l  of  i n c r e a s e m o r t a l i t y among, p o s t l a r v a l  the s u r f a c e sediments f o r the purposes of suspension  1972).  be  Callianassa i s a  on  c o r r e l a t i o n between C a l l i a n a s s a and  o r both of these  suggested f a c t o r s .  '.16,9 >  ACKNOWLEDGEMENTS  T h i s r e s e a r c h was f i n a n c e d by G e o l o g i c a l Survey o f Canada c o n t r a c t D.S.S. No. 0SS77-08177 from the Department o f Supply and S e r v i c e s , Ottawa, O n t a r i o , Canada.  We a r e i n d e b t e d to Mr. W. J . Rapatz, R e g i o n a l T i d a l  S u p e r i n t e n d e n t i n Sidney, B.C. f o r p r o v i d i n g r e c o r d s from the t i d a l  ten y e a r s o f observed  gauge l o c a t e d a t t h e Tsawwassen f e r r y  terminal.  Mr. E. Medley, Mr. J.P. N a p o l e o n i and Ms. N. Hayakawa a b l y a s s i s t e d field.  tidal  i n the  Dr. M. Pomeroy i d e n t i f i e d the cyanophytes, c h l o r o p h y t e s and diatoms,  and Dr. W.C. Barnes, Dr. C D . L e v i n g s and Dr. J . L . L u t e r n a u e r c r i t i c a l l y read the m a n u s c r i p t .  We thank Mrs. C M . Armstrong and Mr. G.D. Hodge f o r  drafting  and Ms. N. 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M.Sc. thesis, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B.C., 104 p. O ' C o n n e l l , G., 1975, F l o r a and fauna of Boundary Bay t i d a l f l a t s , B r i t i s h Columbia: unpub. r e p o r t t o B.C. Government P r o v i n c i a l P a r t Branch, V i c t o r i a , B.C. 0 t t , . J . S . , Fuchs, B., Fuchs, R., and Malasek, A., 1976, O b s e r v a t i o n s on the b i o l o g y of C a l l i a n a s s a s t e b b i n g i B o r r a d a l l e and Upogebia l i t o r a l i s R i s s o and t h e i r e f f e c t upon sediment: Senckenbergiana m a r i t i m a , v. 8, p. 61-79. Pemberton, S.G., 1976, Deep b i o t u r b a t i o n by Axius s e r r a t u s i n the S t r a i t of Canso, Nova S c o t i a : unpub. M.Sc. t h e s i s , McMaster U n i v e r s i t y , Canada, 225 p. Rhoads, D.C. and Young, D.K. 1970, The i n f l u e n c e of d e p o s i t - f e e d i n g benthos on bottom s t a b i l i t y and community t r o p h i c s t r u c t u r e : J o u r . Marine Res., v. 28, p. 150-178. R i s k , M.J., V e n t e r , R.D., Pemberton, S.G. and B u c k l e y , D.E. 1978, Computer s i m u l a t i o n and s e d i m e n t o l o g i c a l i m p l i c a t i o n s of burrowing by Axius serratus: Can. J o u r . E a r t h S c i e n c e s , v. 15, p. 1370-1374. Stevens, B., 1928, C a l l i a n a s s i d a e from the west coast Pub. Puget Sound B i o l . S t a . , v. 6, p. 315-369.  of N o r t h America:  Swinbanks, D.D. , 1979, /Environmental factors^ c o r i t r o ^ . l i n g _ f l o r a l zonation",and •. JtHe' d i s t r i b u t i o n Tof -burrowing" and t u b e - d w e l l i n g organisms on Fraser. D e l t a t i d a l f l a t s , B r i t i s h Columbia: unpub. Ph.D. t h e s i s , U n i v e r s i t y of B r i t i s h ' Columbia, Vancouver, B.C., 274 p. Thompson, L.C. and C a l l i a n a s s a and p. 114-129.  P r i t c h a r d , A.W., 1969, Osmoregulatory c a p a c i t i e s of Upogebia ( C r u s t a c e a : T h a l a s s i n i d e a ) : B i o l . B u l l . , v.  136,  Thompson, R.K., 1972, F u n c t i o n a l morphology of the h i n d - g u t of Upogebia p u g e t t e n s i s ( C r u s t a c e a , T h a l a s s i n i d e a ) and i t s r o l e i n burrow c o n s t r u c t i o n : unpub. Ph.D. t h e s i s , U n i v e r s i t y of C a l i f o r n i a , B e r k e l e y , 202 p. and P r i t c h a r d , . A.W., 1969, R e s p i r a t o r y a d a p t i o n s of two burrowing c r u s t a c e a n s , C a l l i a n a s s a c a l i f o r n i e n s i s and Upogebia p u g e t t e n s i s (Decapoda, T h a l a s s i n i d e a ) : B i o l . B u l l . , v. 136, p. 274-287.  172  T o r r e s , J . J . , Gluck, D.L. and C h i l d r e s s , J . J . , 1977, A c t i v i t y and p h y s i o l o g i c a l s i g n i f i c a n c e of the pleopods i n the r e s p i r a t i o n of C a l l i a n a s s a c a l i f o r n i e n s i s '/Dana. ( C r u s t a c e a : T h a l a s s i n i d e a ) : B i o l . B u l l . , v. 152, p. 134-146. Weimer, R.J. and Hoyt, J.H., 1964, Burrows of C a l l i a n a s s a major Say as i n d i c a t o r s of l i t t o r a l and s h a l l o w n e r i t i c environments: J o u r . P a l e o n t o logy,- v. 38, p. 761-767.  P a r t 4B ENVIRONMENTAL CONTROLS ON THE DISTRIBUTION OF THALASSINIDEAN BURROWING SHRIMPS ON FRASER DELTA TIDAL FLATS, BRITISH COLUMBIA  The Marine t o B r a c k i s h T i d a l  Flats  o f C e n t r a l and N o r t h e r n Roberts Bank  174-  ABSTRACT  The t h a l a s s i n i d e a n burrowing shrimps C a l l i a n a s s a c a l i f o r n i e n s i s Upogebia p u g e t t e n s i s  are abundant on the 'marine' t i d a l f l a t s o f the s o u t h -  easternmost s e c t i o n o f c e n t r a l and n o r t h e r n front.  Northwestward  an abrupt t r a n s i t i o n  and  Roberts Bank on the F r a s e r  Delta-  toward the d i s t r i b u t a r i e s o f the F r a s e r R i v e r , t h e r e i s from 'marine' to b r a c k i s h c o n d i t i o n s  i n the v i c i n i t y o f  Canoe P a s s , and t h a l a s s i n i d e a n shrimp d e n s i t i e s decrease d r a m a t i c a l l y . technique f o r c o n t o u r i n g  this transition i n s a l i n i t y  cent t h i c k n e s s o f the s a l t wedge, i s o u t l i n e d . is  regime, based on the p e r - .  Accompanying  this  transition  a complete r e s t r u c t u r i n g o f the f l o r a l / s e d i m e n t o l o g i c a l z o n a t i o n o f the  tidal  flats.  mentological  The  'marine' t i d a l f l a t s  zones.  zone, the a l g a l mat  can be d i v i d e d i n t o f o u r  floral/sedi-  These a r e , from the s h o r e l i n e seawards, the zone, the s a n d f l a t zone and the e e l g r a s s  saltmarsh  zone.  n i d e a n burrowing shrimps are most abundant i n the s a n d f l a t zone. brackish mat  A  On the  t i d a l f l a t s a b r a c k i s h marsh zone d i s p l a c e s the s a l t m a r s h  zones and the upper h a l f o f the s a n d f l a t zone, w h i l e a  zone c r o s s c u t by b o t h a c t i v e and r e l i c t  and  lower t i d a l e l e v a t i o n s than the s a l t m a r s h ,  zone  The b r a c k i s h marsh extends to much almost r e a c h i n g  the upper l i m i t of  In response to these changes, the peak i n C a l l i a n a s s a d i s t r i -  b u t i o n moves to lower i n t e r t i d a l l e v e l s , because of the presence of low n i t y water a t h i g h e r  sali-  t i d a l l e v e l s and because of the d i s a p p e a r a n c e o f e e l g r a s s  i n lower i n t e r t i d a l r e g i o n s . the upper l i m i t  algal  sandflat/mudflat  channels d i s p l a c e s the e e l g r a s s  and the lower h a l f o f the s a n d f l a t zone.  the aquazone.  Thalassi-  The lower l i m i t o f the b r a c k i s h marsh forms  to C a l l i a n a s s a d i s t r i b u t i o n .  In close proximity  to the major  channels of the F r a s e r R i v e r , C a l l i a n a s s a are absent. C a l l i a n a s s a burrow opening d e n s i t y i s p o s i t i v e l y c o r r e l a t e d to the s a l i n i t y of surface substrate waters.  Upogebia, a l t h o u g h p h y s i o l o g i c a l l y  ' : •  .- \ b e t t e r adapted t o cope w i t h  because the f u n c t i o n o f i t s mud-lined burrow as a conduit f e e d i n g and r e s p i r a t i o n exposes Upogebia to low s a l i n i t y C a l l i a n a s s a , i n i t s u n l i n e d burrow used f o r d e p o s i t  protected  7  5  f l u c t u a t i n g s a l i n i t i e s , demonstrates lower  t o l e r a n c e o f b r a c k i s h water i n i t s d i s t r i b u t i o n than C a l l i a n a s s a ,  while  1  from s u r f a c e waters by h i g h s a l i n i t y  probably  f o r suspension surface waters, feeding, i s  i n t e r s t i t i a l waters.  The  d i s t i n c t i o n between mud-lined, permanent d w e l l i n g burrows and u n l i n e d , temporary f e e d i n g burrows i s , t h e r e f o r e , c o n s i d e r e d cance from the p a l e o e n v i r o n m e n t a l p o i n t o f view.  to be o f great  signifi-  The aoundance o f each o f  the two types o f burrow i n the g e o l o g i c a l r e c o r d c o u l d be used as a quali-^."-t a t i v e i n d i c a t i o n o f p a l e o s a l i n i t y , burrows o f the former b e i n g more s e n s i t i v e than those of the l a t t e r . capable o f p r o d u c i n g  Both Upogebia and C a l l i a n a s s a a r e probably  t r a c e f o s s i l burrows resembling  e i t h e r Ophiomorpha o r  T h a l a s s i n o i d e s , depending on whether the knobbly o u t e r o r smooth i n n e r burrow w a l l , r e s p e c t i v e l y , i s accentuated  during  fossilization;  d i s t i n c t i o n between Ophiomorpha and T h a l a s s i n o i d e s little  significance.  regime o f n o r t h e r n  t h e r e f o r e , the  i s considered  I n the h i g h energy environment and u n s t a b l e  to be o f salinity  and c e n t r a l Roberts Bank, C a l l i a n a s s a c o n s t r u c t s burrows  w i t h l o n g c o n s t r i c t e d a p e r t u r a l necks which extend about 30 cm down i n t o the substrate.  T h i s i s thought to r e f l e c t  C a l l i a n a s s a abandoning n e a r - s u r f a c e surface  environment.  a change i n f e e d i n g mode, w i t h  f e e d i n g because o f the i n s t a b i l i t y o f the  173 176  INTRODUCTION  The primary aim o f these two papers  ( P a r t 4Ayand B) i s to a s s e s s the  e f f e c t s o f v a r i o u s e n v i r o n m e n t a l f a c t o r s on the d i s t r i b u t i o n o f the t h a l a s s i n i d e a n burrowing pugettensis  shrimps, C a l l i a n a s s a c a l i f o r n i e n s i s fbana and Upogebia  (Dana) , on F r a s e r D e l t a t i d a l f l a t s , , , i n the^,hope-.;-that..their, d i s t i n l e -  , t i v e burrows may-be_used as p a l e o e n v i r o n m e n t a l i n d i c a t o r s i n . a n c i e n t , d e l t a i c sequences. Cretaceous  T h a l a s s i n i d e a n shrimps ( B o r r a d a i l e , 1903).  b u t i o n on the inter-causeway  shrimp  'marine,'  The s t u d i e s o f t h a l a s s i n i d e a n shrimp  tidal flat  and i n Boundary Bay (Swinbanks, stable,  a r e known to o c c u r as f a r back as the distri-  on s o u t h e r n Roberts Bank ( P a r t 4A)  1979) d e a l t w i t h areas e x p e r i e n c i n g r e l a t i v e l y  s a l i n i t y regimes.  The aim o f t h i s paper i s to examine  d i s t r i b u t i o n on the t i d a l f l a t s o f c e n t r a l and n o r t h e r n Roberts Bank,  n o r t h o f the C o a l p o r t causeway ( F i g . 1 ) , where the i n f l u x o f freshwater from the F r a s e r R i v e r system i s an added e n v i r o n m e n t a l f a c t o r shrimp  d i s t r i b u t i o n . . The f o l l o w i n g q u e s t i o n s a r e c o n s i d e r e d to be the p o i n t s  of most i n t e r e s t : regime? affect  influencing  (2)  (1)  Which shrimp  i s most s e n s i t i v e to changes i n s a l i n i t y  To what e x t e n t does the nature and f u n c t i o n o f the burrow  the shrimps'  c a p a c i t y to t o l e r a t e reduced  salinities?  (3)  d i s t i n c t i v e burrows o f these shrimps be used as p a l e o s a l i n i t y To assess the e f f e c t s o f reduced s a l i n i t i e s  system  Could the  indicators?  on t h a l a s s i n i d e a n  shrimp  d i s t r i b u t i o n i t i s n e c e s s a r y to have a sound u n d e r s t a n d i n g o f the e f f e c t s o f o t h e r parameters datahayebeen  (e.g., e l e v a t i o n , g r a i n s i z e and f l o r a l  cover"K  Such  o b t a i n e d i n the s t u d i e s o f Boundary Bay (Swinbanks ,-..1979) and  of the inter-causeway t i d a l f l a t  (Part 4A).  Secondly, i t i s n e c e s s a r y to  have p h y s i o l o g i c a l d a t a on the responses o f Upogebia reduced s a l i n i t i e s ,  and C a l l i a n a s s a t o  and knowledge o f t h e i r e t h o l o g y , p a r t i c u l a r i l y i n r e g a r d  to f e e d i n g and r e s p i r a t i o n .  Such d a t a a r e a v a i l a b l e i n the s t u d i e s o f L.  F i g u r e 1.  L o c a t i o n of study a r e a . T i d a l f l a t s , are s t i p p l e d , l a n d area o f Recent a l l u v i u m i s b l a n k , and o l d e r d e p o s i t s c r o s s - h a t c h e d (adapted from L u t e r n a u e r and Murray, 1973).  178 Thompson and P r i t c h a r d (1969), R. Thompson and P r i t c h a r d (1969), Thompson (1972) and  MacGinitie  (1930, 1934).  osmoregulatory c a p a c i t i e s of three  Felder  (1978) has  1  d e s c r i p t i o n s o f the nor :did  he  the  s p e c i e s o f C a l l i a n a s s i d a e (jC. major, _C.  i s l a g r a n d e and _C. jamaicense)and r e l a t e d t h i s L o u i s i a n a and M i s s i s s i p p i c o a s t .  recently studied  to t h e i r d i s t r i b u t i o n on  Unfortunately  Felder  the  (1978) -'did. not  include  ;  f e e d i n g or r e s p i r a t o r y a c t i v i t i e s o f the  three  i n c l u d e d e s c r i p t i o n s of t h e i r burrows, a l t h o u g h ,  shrimps,  of course,  the  burrows of C. major are w e l l known to g e o l o g i s t s , as they are a modern e q u i v a l e n t o f Ophiomorpha (Weimer and Hoyt, 1964). Previous  s t u d i e s of Roberts Bank have e s t a b l i s h e d t h a t t h e r e i s a change  from b r a c k i s h to more marine c o n d i t i o n s i n going and  C o u s t a l i n (1975) recorded  higher  immediately n o r t h of the C o a l p o r t f u r t h e r to the n o r t h ,  and  from n o r t h  to south.  numbers of b e n t h i c s p e c i e s  causeway ( F i g . 1)  Levings  on a t r a n s e c t  than on any  transects  cumaceans were abundant at many o f the s t a t i o n s  _2 (up  to 15,872 m  , Levings  and  C o u s t a l i n , 1975), both o f which i n d i c a t e s t h a t  the p o r t i o n of Roberts Bank immediately n o r t h o f the C o a l p o r t has  the  'marine' c h a r a c t e r i s t i c s of the inter-causeway a r e a  causeway  (Part  still  4A).  Amphithoc v a l i d a , an amphipod which p r e f e r s more s a l i n e c o n d i t i o n s , i s a l s o abundant i n the a r e a immediately n o r t h of the causeway (Dr. M.  Pomeroy,  P a c i f i c Environment I n s t i t u t e , West Vancouver, o r a l commun. 1978). Moody (1978) has mapped and  s t u d i e d the marsh a t Brunswick P o i n t  south of Canoe Pass ( F i g . 4 ) . marsh i s dominated by S c i r p u s americanus and  T h i s i s a t y p i c a l b r a c k i s h marsh.  Carex l y n g b y e i w h i l e S c i r p u s maritimus .  causeway the a r e a l e x t e n t  upper p a r t s and  The  upper  the lower marsh c o n s i s t s of However, towards the  of the marsh decreases a b r u p t l y and  f r i n g e of marsh i s p r e s e n t , w i t h  immediately  D i s t i c h l i s sp. and  T r i g l o c h i n m a r i t i m a i n the lower  Coalport  o n l y a narrow  S a l i c o r r i i a sp. i n the  (Moody, 1978).  p l a n t s are t y p i c a l o f the s a l t m a r s h e s of the inter-causeway and  These marsh Boundary  Bay  4.79  areas  (Kellerhals:.and:'Murray:,. 19.69.; ,0' Connell;.1975;  Parsons, :1975; i l i l l a b y  and B a r r e t t , 1976; Beak-Hinton, 1977; Swinbanks, 1979). marsh t r a n s i t i o n , s u r f a c e s u b s t r a t e s a l i n i t i e s  Accompanying  this  i n c r e a s e from <3%o i n t h e  b r a c k i s h marsh t o as h i g h as 21%„ i n the s a l t m a r s h  (Moody, 1978).  The h i g h e s t  s a l i n i t i e s were r e c o r d e d on t h e t r a n s e c t s c l o s e s t t o t h e C o a l p o r t causeway (Moody,.. 1978) . .  METHODS  S e v e n t y - f i v e s t a t i o n s were sampled a t low t i d e by h o v e r c r a f t and h e l i c o p t e r on a g r i d o f approximately  1 km e x t e n d i n g from the marsh p e r i m e t e r  down to about 0.6 m Chart Datum on the dates i n d i c a t e d i n F i g u r e 2.  Nineteen  s t a t i o n s l y i n g on the same g r i d system between Canoe Pass and the Tsawwassen ferry  t e r m i n a l were o c c u p i e d by h o v e r c r a f t on June 8, 1978 a t h i g h  tide,  and s a l i n i t y p r o f i l e s were taken w i t h a Beckman RS5-3 p o r t a b l e , i n d u c t i v e s a l i n o m e t e r , sampling  a t 0.25 m i n t e r v a l s .  r e o c c u p i e d on the same day (June d e n s i t y d a t a a t low t i d e .  E l e v e n o f these s t a t i o n s were  8) to o b t a i n s u b s t r a t e s a l i n i t y  H o v e r c r a f t s t a t i o n s were l o c a t e d u s i n g Decca r a d a r  and are a c c u r a t e t o w i t h i n a r a d i u s o f about 50 m. were p l o t t e d on a r e c e n t a e r i a l photograph L i b r a r y , June, 1978).with visually  and shrimp  Helicopter stations^  (A37597-146, N a t i o n a l A i r Photo  a s c a l e o f 1 to 72,000, a f t e r b e i n g l o c a t e d  from the a i r , and a r e a c c u r a t e to w i t h i n a r a d i u s o f about 100 m.  Using a t o p o g r a p h i c map (Swan Wooster, 1967) o f 0.6 m contour  interval  ( F i g . 3) the h o v e r c r a f t and h e l i c o p t e r s t a t i o n s were grouped i n t o 0.6 m elevation class i n t e r v a l s .  Some of the contours on t h i s map may be i n a c c u r a t e ,  p a r t i c u l a r l y i n the v i c i n i t y o f the main channel o f Canoe Pass, as t h i s has  changed d i r e c t i o n s i n c e 1967. However, i t i s the b e s t e l e v a t i o n  available. Datum.  channel  data  The Chart Datum f o r t h e contours on the map i s -2.63 m Geodetic  The t i d a l d a t a used i n t h i s paper was d e r i v e d from the t i d e gauge a t  180  F i g u r e 2.  L o c a t i o n s of s t a t i o n s sampled by h o v e r c r a f t ^ helicopter-"and foot, Ln -1977  and  .19 78.  on  181  U.S.A.  Figurej3.  Topographic map of Roberts Bank i n 1967. The datum f o r contours i n t h i s map i s -2.63 m G e o d e t i c Datum. Contours i n meters , ( s o u r c e : Swan Wooster, 1967).  .  the Tsawwassen f e r r y t e r m i n a l , where present-day G e o d e t i c Datum. of  Chart Datum i s -2.95  To a v o i d c o n f u s i o n as to datum, throughout  t h i s paper e l e v a t i o n s w i l l be  remains f i x e d i n time and  space.  datum r e f e r r e d to i s present-day  the  m  remainder  given w i t h r e s p e c t to Geodetic Datum, which Where r e f e r e n c e i s made to Chart Datum the datum a t Tsawwassen.  At a l l s t a t i o n s , shrimp burrow opening  d e n s i t i e s were determined  by  2 sampling e i g h t times a t each s t a t i o n w i t h a 0.25  m  quadrat.  Surface  grain  s i z e samples were o b t a i n e d at a l l s t a t i o n s u s i n g a 2 cm deep r e c t a n g u l a r box.  U n f o r t u n a t e l y , the t w e n t y - s i x g r a i n s i z e samples c o l l e c t e d on August  1978 low  were l o s t .  S u r f a c e water s a l i n i t i e s were r e c o r d e d a t a l l s t a t i o n s a t  t i d e u s i n g a r e f r a c t o m e t e r (Endeco type 102).  burrows was  s t u d i e d u s i n g a box c o r e  (Shinn, 1968) In  The  geometry of shrimp  (15 x 20 cm by 30 cm deep), r e s i n c a s t s  and simple e x c a v a t i o n w i t h a spade.  a d d i t i o n to the s t a t i o n s mentioned above, s i x s t a t i o n s were l o c a t e d  on f o o t on Roberts specifically  Bank between Canoe Pass and  to monitor  the e f f e c t s of changing  d i s t r i b u t i o n at a f i x e d t i d a l l e v e l . low  17,  tide  (observed t i d a l h e i g h t :  +1.4  the C o a l p o r t causeway ( F i g . 2) substrate s a l i n i t y  On September 10,  1977  on shrimp  a t s l a c k water  m Chart Datum o r -1.55  m  Geodetic  Datum) s u r f a c e s u b s t r a t e s a l i n i t i e s were monitored w i t h a r e f r a c t o m e t e r at approximately from  100 m i n t e r v a l s i n c l o s e p r o x i m i t y to the w a t e r l i n e w a l k i n g  the C o a l p o r t causeway towards Canoe Pass.  salinity  g r a d i e n t was  An a r e a showing a pronounced  l o c a t e d where s a l i n i t i e s dropped from 24.5%. to 12.5%.  over a d i s t a n c e of about 0.75  km.  S i x s t a t i o n s w i t h sandy s u b s t r a t e s showing  a range i n s u r f a c e s a l i n i t i e s were l o c a t e d w i t h i n a few meters o f the water- :: -  line (Fig.  and marked w i t h wooden s t a k e s , and mapped u s i n g a Brunton 2).  The  f o l l o w i n g day s u r f a c e s a l i n i t i e s , s a l i n i t y  compass  profiles,  7  •„ J  grain  s i z e samples and shrimp burrow d e n s i t y d a t a were c o l l e c t e d a t these s t a t i o n s . 2 S i x t e e n quadrat r e a d i n g s were taken a t each s t a t i o n , w i t h a 0.25 m quadrat  183  }  to o b t a i n a c c u r a t e e s t i m a t e s o f shrimp burrow d e n s i t y . I n the l a b o r a t o r y , g r a i n s i z e samples were washed f r e e of s a l t ,  wet  s i e v e d through a 63 um s i e v e to e x t r a c t the s i l t / c l a y f r a c t i o n , d r i e d the p e r c e n t mud  values calculated.  The  and  d a t a from the i n t e r - c a u s e w a y a r e a  ( P a r t 4A) has  demonstrated t h a t p e r c e n t mud  v a l u e s are p e r f e c t l y adequate  for assessing  the r e l a t i o n s h i p s between t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n  and g r a i n s i z e . The  d i s t i n c t i v e f l o r a l / s e d i m e n t o l o g i c a l zones of the R o b e r t s Bank t i d a l  f l a t s were mapped u s i n g a h i g h l e v e l , c o l o u r , a e r i a l photograph t a k e n i n June, 19 78 (A37597-146, N a t i o n a l A i r Photo L i b r a r y , Ottawa, Canada) i n conj u n c t i o n w i t h low l e v e l , c o l o u r , a e r i a l photographs ( S c a l e 1:12,000) taken i n J u l y , 1977  (A31164, N a t i o n a l A i r Photo L i b r a r y ) .  NORTHERN AND I t i s e s s e n t i a l to place  CENTRAL ROBERTS BANK the t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n d a t a  w i t h i n the o v e r a l l framework of f l o r a l / s e d i m e n t o l o g i c a l zones on the f l a t s as the two  are i n t i m a t e l y i n t e r r e l a t e d ' ( P a r t 4A).  these marine to b r a c k i s h  tidal  I n the case of  t i d a l f l a t s , i t i s a l s o n e c e s s a r y to d e s c r i b e  d e t a i l the l a t e r a l changes i n s a l i n i t y regime w h i c h o c c u r on the f l a t s , as t h i s i n f l u e n c e s shrimp d i s t r i b u t i o n . For these reasons  in  tidal extensive  d e s c r i p t i o n s of b o t h f o l l o w .  Floral/Sedimentological Figure  4 i s a map  n o r t h o f the C o a l p o r t to s u b d i v i d e  of the f l o r a l / s e d i m e n t o l o g i c a l zones of R o b e r t s Bank causeway.  Two  zonation  the i n t e r t i d a l r e g i o n ; one  o f the C o a l p o r t  Zones  causeway and  one  schemes have t o be  f o r the  employed  'marine' a r e a i n the  vicinity  f o r the b r a c k i s h a r e a from B r u n s w i c k P o i n t  F i g u r e 4. F l o r a l / s e d i m e n t o l o g i c a l zones of Roberts Bank, p r e p a r e d from a c o l o u r a e r i a l photograph of June, 1978 (A37597-146, N.A.P.L., Ottawa, Canada).  185 northwards. abrupt.  The  t r a n s i t i o n between the two  environments i s not  In the a r e a s o u t h e a s t ; o f Brunswick P o i n t a f o u r - f o l d z o n a t i o n i s  p r e s e n t which i s v e r y s i m i l a r to t h a t o f the inter-causeway The  zone and  (Part  f i l a m e n t o u s green a l g a e  mentous b l u e - g r e e n  algae  a r e a , t h e r . . a l g a t .mat  (mostly R h i z o c l o n i u m  ( . O s c i l l a t o f i a sp.) .  mats are coated w i t h a brown f i l m o f diatoms and P i n n u l a r i a s p . ) .  The  cyanophytes to cope w i t h  the reduced  . mat  zone "are, more deeply.-entrenched  light  linearly  f a v o u r a b l e to b l u e - g r e e n  the surveyed  The  (Table I ) .  cm)  The  lower l i m i t  unstable  salini-:  Institute,  i n P a r t 4A.  Thus the map  algal  The  zones a r e v e r y  ( F i g . 3) on F i g u r e the  technique was  4,  elevational checked  i n the  then t h i s d a t a was  by  inter-causeway compared w i t h  average d i s c r e p a n c y between the  t h a t from the t o p o g r a p h i c map  (Table I ) .  than  These e l e v a t i o n s  to determine  a c c u r a c y of t h i s  C ( P a r t 4 A j , and  data p r e s e n t e d  -16  i s ±11.cm (range +22  cm  to  g i v e s a r e a s o n a b l e e s t i m a t e of e l e v a t i o n .  of the s a l t m a r s h i s , i f a n y t h i n g , s l i g h t l y h i g h e r than i n  the inter-causeway limit  area  a l g a l mat  the e l e v a t i o n a l l i m i t s of zone b o u n d a r i e s  data and  sp.  a l g a l matedeyeOiopment.  i n t e r p o l a t i n g between contours  a r e a on t r a n s e c t s A, B and  lower  a v a i l a b i l i t y and  by o v e r l a y i n g the t o p o g r a p h i c map  o f each boundary.  determining  algal  ( N a v i c u l a sp., N i t z s c h i a  e l e v a t i o n a l l i m i t s o f the s a l t m a r s h and  were determined  f i l a m e n t o u s green  r e s u l t i n g i n d e s i c c a t i o n on p l a t e a u s b e t -  s i m i l a r to those i n the inter-causeway  surveyed  The  fila-  In a d d i t i o n , t i d a r _ " c h a n r i e l s . i n the inter-causeway  commun. 1978).  ranges  sp.) w i t h o n l y minor  Pomeroy, P a c i f i c Environment  oral  The  mat  zone: i s - dominated  green a l g a e are p r o b a b l y b e t t e r , a d a p t e d  t i e s n o r t h o f the causeway (Dr. M.  we eh channels  4A).  the e e l g r a s s zone.  In ..contrast: to the inter-causeway  and  area  zones a r e , from the dyke seawards, the s a l t m a r s h zone, the a l g a l  zone, the s a n d f l a t  by  g r a d u a l but  a r e a , l y i n g a t +1.02  o f the a l g a l mat  to +1.29  m Geodetic Datum, w h i l e  zone i s p o s s i b l y s l i g h t l y  the  lower, l y i n g c l o s e to  TABLE ...I  E l e v a t i o n ranges f o r zone boundaries on the 'marine' t i d a l f l a t s as determined from a t o p o g r a p h i c map. The accuracy o f e l e v a t i o n s o b t a i n e d from the map i s checked by comparing w i t h surveyed e l e v a t i o n data o b t a i n e d i n the inter-causeway a r e a (Part 4A) .  ZONE BOUNDARY  . GEODETIC ELEVATION (m) North o f C o a l p o r t Inter-Causeway Area (Map) (Map) (Surveyed) (Discrepancy)  Saltmarsh Zone/ A l g a l Mat Zone  +1.02 +1.29  A l g a l Mat Zone/ S a n d f l a t Zone  +0.13 -0.13  S a n d f l a t Zone/ E e l g r a s s Zone  -1.74 (highest elevation)  +0.80 +1.00  +0.83 +1.07  -0.03 -0.07  B C  +0.16 +0.15  +0.29 +0.31  -0.13 -0.16  A  -1.34 -1.21 -1.52  -1.45 -1.43 -1.56  +0.11 +0.22 +0.04  B C  Average  Note:  A, B and C ( r e f e r t o t r a n s e c t s A, B and O i n  ±0.11  the inter-causeway a r e a .  : 187 0.0 m G e o d e t i c Datum. i s -1.74  The h i g h e s t l e v e l t h a t the e e l g r a s s zone  attains  m G e o d e t i c Datum, which i s a p p r e c i a b l y lower than i n the i n t e r -  causeway a r e a (Table I ) , and, u n l i k e i t s c o u n t e r p a r t i n the inter-causeway a r e a , the upper l i m i t  i s not d e l i m i t e d by e l e v a t i o n , but v e e r s o f f towards  low water mark i n a w e s t e r l y to south w e s t e r l y d i r e c t i o n as Canoe Pass i s approached.  The e e l g r a s s c o v e r a l s o becomes p a t c h i e r i n t h i s  direction  (Fig. 4). From Brunswick P o i n t northwards, the i n t e r t i d a l r e g i o n can be  divided  i n t o two major zones, the b r a c k i s h marsh zone and the s a n d f l a t / m u d f l a t  zone  (which i s e q u i v a l e n t to the i n t e r t i d a l p o r t i o n o f the 'main p l a t f o r m , ' L u t e r n a u e r and Murray, 1973).  The Brunswick P o i n t marsh can be  i n t o an upper and lower p a r t on the b a s i s o f Moody's (1978) map.  subdivided The  Westham I s l a n d marsh can t e n t a t i v e l y be d i v i d e d i n t o an upper and lower p a r t on the b a s i s o f i n f o r m a t i o n p r o v i d e d by Burgess; :(197.0) ,."who n o t e d an abrupt change i n e l e v a t i o n o f between 0.15  m to 0.45  m over a d i s t a n c e o f 1.5-3.0 m,  which marks the boundary between the upper marsh, dominated by Carex l y n b y e i , and the lower marsh, dominated by S c i r p u s americanus.  T h i s break appears  to be marked i n a e r i a l photographs by a l i n e o f d r i f t w o o d and changes i n drainage channel d i r e c t i o n . at about +0.10  Moody (1978) determined t h a t t h i s break o c c u r s  m G e o d e t i c Datum i n the Brunswick P o i n t marsh, w h i l e Burgess  (19 70) e s t i m a t e d i t to o c c u r at 0.0 m G e o d e t i c Datum.  The boundary between  upper and lower marshes thus l i e s c l o s e to the boundary between the upper and lower amphizones  a t -0.08  ± 0.15  m G e o d e t i c Datum, a l e v e l above which the  maximum d u r a t i o n o f exposure jumps from l e s s than 0.5 than o r e q u a l to 0.7  1 unar days  (Swinbanks, 1979).  lower l i m i t o f the lower marsh was o v e r l a y i n g the t o p o g r a p h i c map  l u n a r days to g r e a t e r  The e l e v a t i o n o f the  determined a t s e v e r a l l o c a l i t i e s by  ( F i g . 3) on F i g u r e 4 (.Table I I ) . At Brunswick  P o i n t the marsh extends down to -0.20  m G e o d e t i c Datum (Table I I ) .  This  TABLE I I E l e v a t i o n o f the Lower L i m i t o f the B r a c k i s h LOCATION  Marsh  ELEVATION RANGES ( G e o d e t i c Da turn,-cm)  Brunswick P o i n t E/W boundary p a r a l l e l to Canoe Pass  -0.08,to -0.20.0  NW/SE boundary  -0.20.to +0..1.0.-  SSW/NNE boundary ( b r a c k i s h m a r s h / a l g a l mat  +0.04.to +1.02. > zone)  Westham I s l a n d Canoe Pass t o Main Channel  -0.20,to -0.52.  ..189/ compares w i t h Moody's (1978) f i g u r e of -0.13 m Geodetic Datum.  However, t h i s  boundary i s n o t d e l i m i t e d by e l e v a t i o n , but r i s e s from Canoe Pass towards the C o a l p o r t saltmarsh +1.02  causeway, and i n the area where the marsh transforms to a  the boundary r i s e s a b r u p t l y towards the NNE  m G e o d e t i c Datum (Table I I ) .  The lower l i m i t  I s l a n d ranges i r r e g u l a r l y between about -0.20 above the upper l i m i t Swinbanks, 1979).  o f the aquazone  from about +0.04 m to  of the marsh a t Westham  to -0.52 m G e o d e t i c Datum j u s t  (-0.74 ± 0.10 m G e o d e t i c Datum, .  Burgess (1970) e s t i m a t e d t h a t the lower l i m i t o f the marsh  extends down to -0.9 m Geodetic Datum.  However, Burgess (1970) d i d n o t  -.:::../  s p e c i f y whether he was r e f e r r i n g to the main body o f the marsh o r to the isolated l i t t l e i n F i g u r e 4.  clumps of marsh p l a n t s which l i e below the boundary mapped  The lower l i m i t of the b r a c k i s h marsh l i e s a t l e a s t 1 to 1.5  below t h a t o f the s a l t m a r s h ,  and the b r a c k i s h marsh l a t e r a l l y  m  r e p l a c e s the  a l g a l mat zone and the upper p a r t of the s a n d f l a t zone of the 'marine' t i d a l flats.  T h i s i s c l e a r l y i l l u s t r a t e d i n a h i g h l e v e l a e r i a l photograph ( F i g . 5)  taken on a f l o o d i n g t i d e , when the w a t e r l i n e l a y a t about -0.12 Datum ( e s t imated from t i d e t a b l e s f o r P t . A t k i n s o n ) .  m Geodetic  The w a t e r l i n e i n t h i s  photo has reached the lower l i m i t of the marsh a t Westham I s l a n d , i s j u s t below the lower l i m i t of the marsh a t Brunswick P o i n t and i s approaching the a l g a l mat zone i n the a r e a south o f Brunswick P o i n t and i n the inter-causeway a r e a , w h i l e i n Boundary Bay i t l i e s a t the upper l i m i t o f the e e l g r a s s  zone  (which c o n s i s t s of _Z. americana i n the upper r e g i o n s ; Swinbanks, 19 79). The Brunswick P o i n t marsh has been undergoing r a p i d e x p a n s i o n s i n c e the l a t e 1940's  (Moody,  1978).  I t has been suggested t h a t t h i s i s a r e s u l t of  the d e p o s i t i o n o f l a r g e q u a n t i t i e s o f sediment i n f r o n t o f the marsh by a major f l o o d i n 1948, forming an e l e v a t e d r e g i o n which marsh p l a n t s colonize  could  (A. Tamburi, Western Canada H y d r a u l i c s , o r a l commun. 1978).  Below the b r a c k i s h marsh zone l i e s the s a n d f l a t / m u d f l a t  zone which can  190  F i g u r e 5.  High l e v e l a e r i a l photograph of the F r a s e r D e l t a . The w a t e r l i n e l i e s a t about -0.12 m G e o d e t i c Datum on a f l o o d i n g t i d e , and l i e s above the lower l i m i t of the marsh a t Westham I s l a n d ( c e n t r e ) i s approaching the a l g a l mat zone i n the inter-causeway a r e a and l i e s at the upper l i m i t o f the e e l g r a s s zone i n Boundary Bay ( r e f e r to F i g . 1 f o r l o c a t i o n ). Water i s b e g i n n i n g t o f l o o d i n t o the d i s t r i b u t a r y channels of the Brunswick P o i n t marsh from Canoe Pass.  j.9r be s u b d i v i d e d i n t o  'muddy domains' and  'sandy domains.'  The muddy domains (.range 2 9 . 4 - 8 6 % ) w h i l e  c o n s i s t of sediments c o n t a i n i n g more than about 30% mud  the sediments o f the sandy domains c o n t a i n l e s s than about 15% mud 0.21-14.3%).  T h i s was  determined  samples from the sampling  grid  values f o r 48  by o v e r l a y i n g p e r c e n t mud  ( F i g . 6 ) , over the a i r photos - a  developed by Medley and L u t e r n a u e r  (1976).  (range  technique  The muddy domains dominate near  the f r i n g e of the marsh, but are a l s o p r e s e n t at lower e l e v a t i o n s a s s o c i a t e d w i t h t o p o g r a p h i c d e p r e s s i o n s and  in p a r t i c u l a r with r e l i c t  i n c r e a s e i n mud  content shorewards i s c l e a r l y apparent  coarse sampling  g r i d i n most cases f a i l s  i n t e r t i d a l regions. the r e c e n t p a s t . t o p o g r a p h i c map graphs ( F i g . 4 ) . which was  ( F i g . 3) w i t h the map The  The  i n F i g u r e 6 but  the  to d e t e c t the muddy•domains i n lower  The main channel of Canoe Pass has  T h i s can be seen by  channels.  changed d i r e c t i o n i n  comparing the Swan Wooster (.1967) compiled  from present-day  aerial  channel on the C o a l p o r t s i d e of the p r e s e n t main  photochannel,  a major channel of Canoe Pass, i s r a p i d l y n e c k i n g o f f i n the upstream  d i r e c t i o n , and w i l l p r o b a b l y be abandoned and i n f i l l e d w i t h mud future.  To the east of t h i s channel l i e s  probably  the r e l i c o f a former  i n the near  an e l o n g a t e d e p r e s s i o n t h a t i s  channel which s u f f e r e d a s i m i l a r  fate.  Salinity  The F r a s e r R i v e r reaches i t s peak d i s c h a r g e i n June and J u l y  (Fig. 7).  A e r i a l photographs i n d i c a t e t h a t the t u r b i d water ^f'thervF'raser plume i s d i s p e r s e d over a l l p a r t s of n o r t h e r n and  c e n t r a l Roberts  Bank (e.g., F±g..<.3^1,.  A30339-116, N a t i o n a l A i r Photo L i b r a r y ) , but i t i s i m p o s s i b l e to t e l l t h i c k n e s s o f the plume o r the s a l i n i t y o f i t s water from the  the  photographs.  S t r a i t of G e o r g i a waters o f f the F r a s e r D e l t a - f r o n t are s t r a t i f i e d b r a c k i s h s u r f a c e l a y e r and an u n d e r l y i n g s a l t wedge (Waldichuk,  into a  195 7 ) .  The  192  F i g u r e 6.  P e r c e n t mud i n s u r f a c e sediments o f n o r t h e r n Bank. M e c h a n i c a l c o n t o u r i n g employed.  and  c e n t r a l Roberts  193  ure 7.  D i s c h a r g e curves f o r the F r a s e r R i v e r i n c l u d i n g the f r e s h e t p o r t i o n o f the r u n o f f f o r 1948, a s e v e r e f l o o d y e a r i n the F r a s e r V a l l e y (adapted from R. Thompson, u n p u b l i s h e d d a t a ) .  194 s a l t wedge i n t r u d e s the d i s t r i b u t a r y  -  channels o f the F r a s e r on f l o o d t i d e s  by under-running r i v e r water, extending  as f a r as 20 km upstream o f the i n n e r  t i d a l f l a t s d u r i n g the w i n t e r , b u t extends no f u r t h e r than the i n n e r edge of the f l a t s d u r i n g the summer f r e s h e t (Ages and W o o l l a r d , Figure 8 presents  a '. t y p i c a l d i s t r i b u t i o n p a t t e r n o f s u r f a c e  s a l i n i t y on c e n t r a l and n o r t h e r n obtained  1976).  Roberts Bank.  S i m i l a r contour  substrate  p a t t e r n s were  f o r data c o l l e c t e d i n August, 1977 (Appendix 8 ) and F e b r u a r y , 1974  (Leyings and C o u s t a l i n , 1975; Appendix 8 ) , although  the a b s o l u t e v a l u e s a t  equivalent s t a t i o n s v a r i e d quite considerably,<probably wind c o n d i t i o n s and r i v e r d i s c h a r g e  due to d i f f e r i n g  d u r i n g the p r e c e d i n g  are two f e a t u r e s which a l l the r e s u l t s have i n common:  high t i d e . (1)  There  there i s a  g e n e r a l i n c r e a s e i n s a l i n i t y seaward as one goes t o lower i n t e r t i d a l (2)  a h i g h e r s a l i n i t y r e g i o n i s always p r e s e n t  Coalport  levels  immediately northwest o f the  causeway.  How do s u b s t r a t e s a l i n i t i e s a t low t i d e r e l a t e t o s a l i n i t i e s i n the water column a t h i g h should  tide?  I t was suspected  that surface substrate  salinities  c l o s e l y r e f l e c t s u r f a c e water s a l i n i t i e s a t h i g h t i d e on ebb, as s u r - ". •  face s u b s t r a t e waters s h o u l d be d e r i v e d from the l a s t water t o d r a i n o f f the t i d a l  flat.  To t e s t t h i s h y p o t h e s i s  and to b e t t e r d e f i n e the t r a n s i t i o n  from marine t o b r a c k i s h c o n d i t i o n s between Tsawwassen and Canoe Pass, p r o f i l e s ' w e r e recorded  at high  t i d e on ebb a t n i n e t e e n  w i t h i n a, 3. 3 hour,, p e r i o d pnC'June^ 8 , . 19.7'8.. files  salinity  s t a t i o n s ,,in t h i s area;;, ZZA  I n the' v i c i n i t y ' o f Canoe- Pass,"" p r o -  were. I s o h a l i n e and almost:, pure .freshwater,,, w h i l e . immediately, n o r t h of. the  ( C o a l p o r t causeway '.profiles were i s o h a l i n e and- 'marine.' i n s a l i n i t y  ( F i g . ,9a) . /  Between these.;two extremes .lay -a r e g i o n ..where a. dis.tin-et h a l o c l i n e .was •, developed ( F i g . 9 a ) . F i g u r e 9a contours w h i l e F i g u r e 9b contours  s u r f a c e water s a l i n i t i e s a t h i g h t i d e on ebb,  s u r f a c e s u b s t r a t e and s u r f a c e shallow water (<0.7 m)  s a l i n i t i e s on approaching low t i d e  ( t h e shallow water s a l i n i t y p r o f i l e s were  195  Figure„8.  S u r f a c e s u b s t r a t e s a l i n i t i e s on Roberts Bank a t low August 17, 1978. M e c h a n i c a l c o n t o u r i n g employed.  tide  on  F i g u r e 9. a) Surface-water s a l i n i t i e s at h i g h t i d e on ebb between Canoe Pass and the f e r r y causeway„on June 8, 1978. S t i p p l e d area i n d i c a t e s r e g i o n where a h a l o c l i n e i s p r e s e n t i n the water column.. Mechan i c a l c o n t o u r i n g employed. Three r e p r e s e n t a t i v e s a l i n i t y / .'tempera-ture~profiles i n c l u d e d . b) S u r f a c e s u b s t r a t e and s h a l l o w water s a l i n i t i e s on approaching low t i d e on June 8, 1978. M e c h a n i c a l c o n t o u r i n g employed.  197; isohaline  (Appendix 8 ) and these waters would almost c e r t a i n l y have the  same s a l i n i t y as the s u r f a c e s u b s t r a t e waters a t low t i d e , had i t been p o s s i b l e to continue  sampling u n t i l low w a t e r ) .  The contours  and b a r e almost c o i n c i d e n t , the o n l y d i f f e r e n c e b e i n g  i n F i g u r e s 9a  t h a t the two lobes  o f low s a l i n i t y water, one from Canoe Pass and the o t h e r from the s m a l l e r d i s t r i b u t a r y channels o f the Brunswick P o i n t marsh, have extended f u r t h e r to the e a s t d u r i n g the l a t e stages case,  surface substrate s a l i n i t i e s  o f s u r f a c e water s a l i n i t i e s a t h i g h  o f ebb.  slightly  Thus, a t l e a s t i n t h i s  a t low t i d e are a v e r y c l o s e r e f l e c t i o n : : t i d e on ebb.  I t i s n o t p o s s i b l e on the b a s i s o f F i g u r e 8 o r 3 to q u a n t i t a t i v e l y d e f i n e o r contour  the t r a n s i t i o n from marine t o b r a c k i s h environments, because  the data does n o t d i v i d e n a t u r a l l y i n t o two groups.  However, i t i s p o s s i b l e  to p r e c i s e l y d e f i n e b r a c k i s h and marine water masses on the b a s i s o f the salinity profiles,  the boundary between them b e i n g d e f i n e d by the h a l o c l i n e .  T h i s l i e s anywhere between 15 and 20%» ( F i g .  Appendix 8 ).  Three  d i f f e r e n t v a l u e s were t e s t e d t o d e f i n e the boundary between the b r a c k i s h and marine water masses, namely 15%o , 17.5%,, and 20% .  As a measure o f 'marines."  0  n e s s ' the p e r c e n t  t h i c k n e s s o f the s a l t wedge a t each s t a t i o n was c a l c u l a t e d  f o r each o f the three boundary d e f i n i t i o n s  (percent  t h i c k n e s s r a t h e r than  a c t u a l t h i c k n e s s was c a l c u l a t e d to e l i m i n a t e v a r i a t i o n due to v a r i a b i l i t y i n water depth a c r o s s contoured.  the i n t e r t i d a l zone).  The t h r e e s e t s o f v a l u e s were  F i g u r e 10 i s the r e s u l t f o r 17.5%„.  Although the v a l u e s  at i n d i -  v i d u a l s t a t i o n s v a r i e d depending on which o f the t h r e e d e f i n i t i o n s was used, the contours it  remained v e r y s i m i l a r i n l o c a t i o n and p a t t e r n (Appendix 8 ) , and  does n o t appear t o be important  to d e f i n e the boundary between marine and  b r a c k i s h water masses to w i t h i n c l o s e r than 5%». represents year.  F i g u r e .10,  o f course,  only  one p a r t o f one t i d a l c y c l e on one day a t one p a r t i c u l a r time of  However, the data are taken from that p a r t o f the t i d a l .cycle which  198  / F i g u r e 10.  P e r c e n t t h i c k n e s s o f the s a l t wedge, f o r 17.5%. as the boundary between marine and b r a c k i s h water masses. Mechanical contouring. Numbers next to s t a t i o n s i n d i c a t e p e r c e n t t h i c k ness o f s a l t wedge.  :-J"99  determines s u r f a c e s u b s t r a t e s a l i n i t i e s a t low t i d e , which a r e p a r t i c u l a r l y important to b e n t h i c organisms dependent is representative of a f a i r l y  critical  on the s u r f a c e environment, and i t  time o f y e a r when the F r a s e r i s a t  i t s peak d i s c h a r g e .  Discussion of S a l i n i t y  Regime  F i g u r e 10 i l l u s t r a t e s the abrupt t r a n s i t i o n from a marine t o b r a c k i s h s a l i n i t y regime between the C o a l p o r t causeway and Canoe P a s s .  The exact  p o i n t o f t r a n s i t i o n between 'marine' and b r a c k i s h environments can a r b i t r a r i l y be d e f i n e d a t the 50% contour i n F i g u r e 10.  The cause o f the abrupt change i s  thought to be due to the presence of a t o p o g r a p h i c h i g h between Canoe Pass and the C o a l p o r t causeway ( F i g . 3) which d i v i d e s the two environments and p r e v e n t s low s a l i n i t y water i n Canoe Pass from f l o o d i n g over towards the causeway a t the b e g i n n i n g o f f l o o d t i d e .  A t the e a r l y s t a g e s o f f l o o d  S t r a i t o f G e o r g i a water, which i s p r o b a b l y o f h i g h s a l i n i t y ,  tide,  f l o o d s i n around  the C o a l p o r t from the s o u t h e a s t (Beak-Hinton, 1977) i n t o the t o p o g r a p h i c d e p r e s s i o n on the immediate  northwest s i d e o f the causeway ( F i g . 3 ) , estabr-. .  l i s h i n g a s a l i n e wedge i n the a r e a b e f o r e low s a l i n i t y water from Canoe P a s s .  can f l o o d over  The s o u t h e a s t e r l y t i d a l c u r r e n t s on f l o o d would  a l s o tend  to p r e v e n t the low s a l i n i t y waters o f Canoe Pass from r e a c h i n g t h i s However, i n the immediate  v i c i n i t y o f the Brunswick P o i n t marsh,  area.  distributary  channels from Canoe Pass c u t through the marsh and d i s c h a r g e low s a l i n i t y water over t h i s t o p o g r a p h i c h i g h e s t a b l i s h i n g a low s a l i n i t y plume i n f r o n t of the Brunswick P o i n t marsh ( F i g . 9, 10). These d i s t r i b u t a r y channels a r e unusual i n t h a t they dry o u t d u r i n g low t i d e , b u t a c t as r i v e r channels d u r i n g high tide stages.  As the t i d e f l o o d s i n t o Canoe Pass r i v e r water i s d i v e r t e d  i n t o these d i s t r i b u t a r i e s and f l o o d s a l o n g them t o meet the incoming s e a .  200-J Strong seaward f l o w i n g c u r r e n t s c o n t i n u e d u r i n g ebb t i d e as evidenced by the seaward o r i e n t a t i o n o f bedforms (dunes and r i p p l e s ) a t the mouth o f the main channel a t low t i d e .  A t low t i d e , s m a l l streams i n the channels  d r a i n water back towards Canoe Pass, i n d i c a t i n g t h a t the seaward mouths o f the channels l i e a t h i g h e r e l e v a t i o n s than t h e i r e n t r a n c e s a t Canoe P a s s . Thus, the dominant seaward flow i n the channels on b o t h f l o o d and ebb t i d e s must be m a i n t a i n e d by a d i f f e r e n c e i n e l e v a t i o n between  the water s u r f a c e  i n Canoe Pass and s e a l e v e l over Roberts Bank, t h a t of Canoe Pass b e i n g s l i g h t l y higher.  T h i s i s a p e r f e c t l y r e a s o n a b l e s u g g e s t i o n to make as there  must be a d i f f e r e n c e i n h y d r a u l i c head between Canoe Pass and the s e a i n o r d e r to m a i n t a i n r i v e r flow.  These d i s t r i b u t a r y channels a r e p r o b a b l y  essential  f o r the development and maintenance o f the b r a c k i s h marsh a t Brunswick P o i n t , as they e s t a b l i s h a b u f f e r zone o f b r a c k i s h water between 'marine' a r e a immediately o f f s h o r e . Brunswick P o i n t  the marsh and the  The r e c e n t advance o f the marsh a t  (Moody, 1978)»is n o t simply a f u n c t i o n o f e l e v a t i o n , because, i f  i t were, marsh would mantle the e n t i r e a l g a l mat zone s o u t h e a s t o f t h i s  area.  The d i v e r s i o n o f f r e s h water flow from Canoe Pass to : t h i s a r e a has p r o b a b l y been e s s e n t i a l f o r b r a c k i s h marsh e x p a n s i o n .  DISTRIBUTION OF THALASSINIDEAN SHRIMPS Description  The d i s t r i b u t i o n of t h a l a s s i n i d e a n burrowing shrimps i s p r e s e n t e d i n F i g u r e 11, based on h o v e r c r a f t and h e l i c o p t e r sampling surveys i n August, 1977, June, 1978, and August, 1978.  S t a t i o n s sampled on f o o t i n September, 1977  and on a t r a n s e c t i n September, 1976 (Swinbanks and Murray, 1977) a r e a l s o i n c l u d e d to maximize coverage.  R e s u l t s from the i n t e r - c a u s e w a y a r e a are  i n c l u d e d to g i v e a complete p i c t u r e o f shrimp d i s t r i b u t i o n on Roberts Bank. T a b l e I I I compares  C a l l i a n a s s a and Upogebia d e n s i t i e s a t t e n s t a t i o n s sampled  201  —3—  1  Contour of Colllonoiwi burrow opening rjemlry m  - 2  U.S.A.  F i g u r e 11.  D i s t r i b u t i o n of t h a l a s s i n i d e a n shrimp burrow openings on Roberts Bank based on d a t a c o l l e c t e d i n 1977 and 1978. ' Where s t a t i o n s sampled i n 19 77 were r e o c c u p i e d i n 1978 the average d e n s i t y has been used. Data f o r the inter-causeway a r e a are p r e s e n t e d i n P a r t 4A. M e c h a n i c a l c o n t o u r i n g employed.  TABLE  III  Comparison o f T h a l a s s i n i d e a n Shrimp D e n s i t i e s at S t a t i o n s Sampled i n 1977 and Reoccupied i n 1978  St.  August, 19 77 C i l l : LaiiasSan 'Upogebia 0  RA1 RA2  0.5  ±  0.6  0  RA3 RA4  0.5  ±  0.7  RA5  35.5  ±  6.4  RA7  60.5  ±  2.1  RA8  1.0  ±  RA9  36.5  ±  RA10  Note:  0  St.  0  RBI  0  RB2  0  RB3  0  RB4  June, 1978 C a l l i a n a s s a . Upogebia  0.5  0.5  0  0  -  -  ± 0.7  0  -  -  0  0  -  -  ± 0.7  0  -  -  12.5 ± 2.1  RC12  0  -  -  0  -  -  -  -  RC9  • 11.0  ±  5.1  0  _  _  RC6  1.0  ±  1.9  0  RB5  20.5 ±  0  RB6  51.5  0.8  0  RB7  24.0 ±  4.9  0  -  3.5  ±  0  3.5  st-.-,.  August, 1978 :'CGall±anas s ay  7.8  ± 2.1 2.8  26.0  ± 10.0  2.0 ±  2.3  S t a t i o n s i n June, 1978 are c o i n c i d e n t w i t h i n 50 m w i t h those occupied i n August, 1977. S t a t i o n s o c c u p i e d i n August, 1978 l i e w i t h i n 100 m o f those occupied i n August, 1977.  203 i n August, 1977  and r e o c c u p i e d i n June, 1978  and/or August, 1978.  ;•  The agree-  ment between the t h r e e s e t s o f d a t a i s r e a s o n a b l y c l o s e , w i t h the e x c e p t i o n o f s t a t i o n s RA8  and RB7, where C a l l i a n a s s a d e n s i t i e s are markedly d i f f e r e n t  -2 (1 m  -2 a t RA8,  24 m  at RB7).  of data suggests t h a t  The g e n e r a l s i m i l a r i t y between the t h r e e  thalassinidean  shrimps m a i n t a i n f a i r l y  stable  l a t i o n s , which might be expected as they a r e p r o b a b l y l o n g - l i v e d (MacGinitie, density  1930  and 1934).  There i s a pronounced  i n the v i c i n i t y o f s t a t i o n RA8  these two r e s u l t s may  and RB7  sets  popurr  :  n.;  organisms  gradient i n Callianassa  and the d i s c r e p a n c y between  be the r e s u l t o f s a m p l i n g i n s l i g h t l y  different loca-S.L„  tions. _2 High d e n s i t i e s  (>50 burrow openings m  ) o f C a l l i a n a s s a are r e s t r i c t e d  to the marine s e c t i o n o f Roberts Bank immediately n o r t h o f the C o a l p o r t causeway and i n the i n t e r - c a u s e w a y a r e a ( F i g . 1 1 ) . distribution shifts  the  to; lower i n t e r t i d a l l e v e l s as one moves northward from -2  C o a l p o r t , and q u i t e h i g h d e n s i t i e s  C a l l i a n a s s a o c c u r down to the -2.4 on August 17 and 18, 1978.  ties  The peak i n C a l l i a n a s s a  (>20 burrow openings m  m level  ) of  . :, i,,-' '.:  ( G e o d e t i c Datum) - low water mark  As Main Channel i s approached C a l l i a n a s s a _2  decrease to l e s s than 0.5  m  densi-  (burrow openings) a t a l l i n t e r t i d a l l e v e l s .  Upogebia were o n l y r e c o r d e d at two s t a t i o n s on the g r i d , and they a r e restricted  to the 'marine' a r e a between the Brunswick P o i n t marsh and the  causeway. Relationship  Between Shrimp  D e n s i t y and S u b s t r a t e Parameters  S t a t i o n s were grouped i n t o 0.6 of  the Swan Wooster  (1967) t o p o g r a p h i c map  between C a l l i a n a s s a d e n s i t y salinity.  m elevation  c l a s s i n t e r v a l s on the b a s i s  ( F i g . 3 ) , to a n a l y z e r e l a t i o n s h i p s  and the s u b s t r a t e parameters of p e r c e n t mud  Data on Upogebia a r e i n s u f f i c i e n t  to c a r r y  out any  statistical  and  204 analysis.  Mud  content d a t a f o r 1977  and  l y 78 were p o o l e d , because the  l a c k of l a m i n a t e d d e p o s i t s  at s t a t i o n s suggests t h a t mud  appreciably  the  w i t h time.  On  d r a s t i c temporal v a r i a t i o n s  o t h e r hand, s u b s t r a t e  ( F i g s . 8,  d a t a f o r August, 1977 were i n i t i a l l y 1978.  Linear  p e r c e n t mud  regression  and  analysis  level  ( r t e s t ) , and  f o u r out  of  treated no  (Table  IV;  f i v e were not  lations  (Table  the o t h e r hand, s u b s t r a t e  correlated  to C a l l i a n a s s a  1978  ( F i g . 12B,  C,  F, H and  J).  are  zone next to the  absent.  Exclusion  coefficient  1977/78 ( F i g . 12L)  the  classed  Five  of e i g h t  out  s i g n i f i c a n t at the  and  class 95%  confi-  class interval  are h i g h but  also  give  (Appendix 9  ( F i g . 12E),  the  Callianassa  1978  (Fig.  significant positive correlations.  12K)  Pooling  i n s i g n i f i c a n t l y reduced c o r r e l a t i o n  ) because s u b s t r a t e  salinities  i n August, 1978  i n August, 1977  were (Fig.  9;  . .  to s a l i n i t y ,  t e s t the h y p o t h e s i s t h a t  Callianassa  s i x s t a t i o n s were l o c a t e d on  (-1.55 m G e o d e t i c Datum) between Canoe Pass and  i n an  a r e a showing a pronounced s a l i n i t y does not  vary appreciably  gradient.  between the  distribution is  f o o t at a f i x e d  level  substrate  corre-  c o n t a i n s a s t a t i o n from  U n c l a s s e d data f o r 1977  In o r d e r to f u r t h e r correlated  improve  is positively  s i g n i f i c a n t l y lower than those at comparable s t a t i o n s Appendix 8. ) .  80%  salinity  where s a l i n i t i e s  d a t a f o r 1977/78 r e s u l t e d  coefficients  confidence  of t h i s s t a t i o n r e s u l t s i n a p o s i t i v e c o r r e l a t i o n  (r=0.383).  and  Coalport,  95%  I n t e r e s t i n g l y , the o n l y  which showed a n e g a t i v e c o r r e l a t i o n ( F i g . 12G) eelgrass  Correlation  groups d i d not  density.  i n t e r v a l s show p o s i t i v e c o r r e l a t i o n s , which are dence l e v e l  the  f o r August,  even s i g n i f i c a n t at the  d a t a i n t o 1977  significantly  from t h a t  Appendix 9 ).  S e g r e g a t i n g the On  does show>iq.uite  f o r t h i s reason  none were s i g n i f i c a n t at the  and  vary  s i g n i f i c a n t c o r r e l a t i o n between  level.  IV).  salinity  separately  general  contents do not  Appendix 8 ) , and  reveals  C a l l i a n a s s a density  c o e f f i c i e n t s were l e s s than 0.6,  9;  '  the  The  stations  Coalport  (Fig.  grain s i z e of (Table  tidal 2)  the  V)., , and  lies  205 1977 - M l to - 0 8 0  - 0 . 8 0 ro - 0 . 2 0 n  6050-  40-  E >.  «•  1  3020-  30H  10-  \04  20-  C  &  0  10  20  Salinity  30  40  0  10  20  30  40  o  • f'•-  r  0  S a l i n i t y "loo  °fco  10  i  1  20  30  1 40  S a l i n i t y %o  -0.20 to —0.41m  a 0  10  20  30  40  S a l i n i t y %o  S a l i n i t y %o  19 7 8  -2.45 to -2.02 m  7  -2J02 to -141 m  5040-  40  E  E  . 30H  X  -1.41 to'-OjBOm  4 Station in Mrcrass  bad  30-  «•  *5 e • a  ioH 0'  10  20  Salinity  30  40  20-  0  10  20  30  10  40  20  30  40  S a l i n i t y %o  S a l i n i t y %o  %°  -0.80 t o - 0 . 2 0  fe  40.  e  a  20 10  10  20 20  Salinity  ure 12.  %o  0  10  20  Salinity  30 %o  40  0  10  20  Salinity  30  40  %o  R e l a t i o n s h i p between C a l l i a n a s s a burrow opening d e n s i t y and the s a l i n i t y of s u r f a c e s u b s t r a t e waters. B e s t - f i t l i n e a r r e g r e s s i o n l i n e s are drawn along w i t h t h e i r c o r r e l a t i o n : . c o e f f i c i e n t s ( r ) and significance l e v e l (r t e s t ) .  TABLE I V  Comparison o f C o r r e l a t i o n C o e f f i c i e n t s (r) Between C a l l i a n a s s a Burrow Opening D e n s i t y and P e r c e n t Mud U s i n g P o o l e d and U n p o o l e d P e r c e n t Mud D a t a  Elevation Interval ( G e o d e t i c D a t u m , m)  P o o l e d P e r c e n t Mud D a t a 1977/78 r r t e s t (%)  r  U n p o o l e d P e r c e n t Mud D a t a 1977 1978 r t e s t (%) r r test  -2.45  to  -2.02  0.575  80  -2.02  to  -1.41  -0.254  <80  -0.169  <30  -1.41  to  -0.80  -0.201  <80  -0.201  <80  -0.80  to  -0.20  -0.199  <80  -0.230  <80  -0.20  to  +0.41  0.053  <80  0.053  <80  Data  -0.172  <80  -0.189  <80  Unclassed  Insufficient (N=2)  Data  0.886  95  -0.481  <80  (%)  No D a t a  Insufficient (N=l)  Data  No D a t a  -0.322  <80  TABLE V R e l a t i o n s h i p Between S u r f a c e Substrate S a l i n i t y and C a l l i a n a s s a Burrow Opening D e n s i t y a t a F i x e d T i d a l L e v e l at S i x S t a t i o n s Midway Between Canoe Pass and the C o a l p o r t Causeway ( F i g . 2)„  Station  Median  Mud  Surface Substrate S a l i n i t y  Content  (%<>)  Density  Cm" )  (0)  (0)  1  2.94  7.39  24.5  21  23.50 ±  4.4  2  2.73  5.41  24.5  21  19.25  ±  2.4  3  2.60  10.48  18.0  19  10.00  ±  1.4  4  2.73  6.09  17.5  19  10.50  ±  4.1  5  2.96  17.94  12.5  9  6.75  ±  1.7  6  3.36  35.93  12.5  9  5.00  ±  0.8  Note:  Burrow opening quadrat.  2  September. 10  d e n s i t y (m ) -2  September  11  -  estimated by t a k i n g 16 readings w i t h a 0.25  m'  20:8 w e l l w i t h i n the range o f median g r a i n s i z e and p e r c e n t mud  known to be  a c c e p t a b l e to C a l l i a n a s s a i n the inter-causeway a r e a ( P a r t 4A).  Although  the  a consistent  salinity  v a l u e s d i f f e r e d on the two days monitored t h e r e was  decrease in.^.alinity.^from^stations'-!;, t o '6... accompanied Callianassa density  ( F i g . 13a).  d e s c r i b e d i n Appendix  Salinity profiles,  by a decrease i n  taken w i t h the apparatus  5 , revealed that h i g h s a l i n i t y  water  (>20% ) i s o  p r e s e n t w i t h i n 15 cm of the s u r f a c e , even at s t a t i o n s 5 and 6, where s u r f a c e salinities  are low  ( F i g . 13b).  Thus, a d u l t C a l l i a n a s s a , which l i v e at depths  g r e a t e r than 30 cm on Roberts Bank, encounter these high s a l i n i t y waters which  interstitial  are f r e e to e n t e r t h e i r u n l i n e d burrows (L. Thompson and  P r i t c h a r d , 196y), and they are not d i r e c t l y  exposed  to the low  * .-'• -.  salinity  surface waters.  D i s c u s s i o n of T h a l a s s i n i d e a n Shrimp  The absence of Upogebia for  i n terms o f the mud  tidal  flats  Distribution  from n o r t h e r n Roberts Bank cannot be  accounted  c o n t e n t s o f the s u b s t r a t e or t i d a l e l e v a t i o n .  The  immediately i n f r o n t of the Westham I s l a n d marsh are upper  z o n a l to lower amphizonal  i n exposure and the sediments  Under the same c o n d i t i o n s r o f exposure and mud  aqua-  c o n t a i n about 50%  content Upogebia  attain  mud.  densities  _2 of  84 burrow openings m  i n the inter-causeway a r e a ( P a r t 4A) , w h i l e not  one  s i n g l e Upogebia burrow has been observed i n f r o n t of the Westham I s l a n d marsh. S i m i l a r l y , C a l l i a n a s s a d i s t r i b u t i o n on the b r a c k i s h t i d a l f l a t s of Roberts Bank cannot be e x p l a i n e d i n terms of t i d a l e l e v a t i o n or g r a i n s i z e .  Underf-  s t a n d a b l y , C a l l i a n a s s a i s absent i n the b r a c k i s h marshes where dense r o o t l e t s p r o b a b l y render d e p o s i t f e e d i n g and burrowing i m p o s s i b l e f o r C a l l i a n a s s a , because  and,  these marshes extend to much lower e l e v a t i o n s than the s a l t m a r s h e s of  Boundary Bay and the inter-causeway a r e a , the upper  limit  to C a l l i a n a s s a  209 (a) 25  Scllnity on September 10, 1977 Selintty on September 11, 1977  —I 26  IS S A L I N I T Y (%,)  STl  (b)  September 11, 1977 Salinity  ST2  September 10, 1977 ST3  %c Salinity  15 20 -1 L  0  25  30  _J  10 15 _1_ _ i _  0  5  °/oo  15-1 ST4  S«pf e m b e r  10, 1977  Salinity  0 51015-  10  $T3  V  > \  10  I  \  15J  September 11. 1977 •allnlty  September 11, 1977  %o Salinity  25 -J  0  5a.  s  a  5  100 !5 1  10  %o  15  20 _J  5-4  1015-  1977 %o  _1  ST6  %©  15 —L  20 25  \  1  /  15-1  Salinity  f  5  !0-  September 11.  I  15-J  F i g u r e 13. a) R e l a t i o n s h i p between C a l l i a n a s s a burrow opening d e n s i t y and . s u r f a c e s u b s t r a t e s a l i n i t y a t a f i x e d t i d a l l e v e l (-1.55 Geodetxc Datum), September 10-11, 1977. b) S u b s t r a t e s a l i n i t y p r o f i l e s a t S t a t i o n s 1-6, September- 10-11, m  210 d i s t r i b u t i o n i s i n e v i t a b l y lowered. p r e s e n t i n v e r y low  d e n s i t i e s on  But  the ranges known to be  causeway area (Part density  and  explained  4A)..  substrate  mud  c o n t e n t s of the  of  sediment l i e  a c c e p t a b l e to C a l l i a n a s s a i n the  p o s i t i v e c o r r e l a t i o n s between  only  inter-  Callianassa  s a l i n i t y suggest t h a t C a l l i a n a s s a d i s t r i b u t i o n can  oy s u b s t r a t e  although i t cannot be  The  a l s o absent or  the unvegetated t i d a l f l a t s i n f r o n t  Westham I s l a n d , were t i d a l e l e v a t i o n and well within  C a l l i a n a s s a are  salinity.  The  be  same i s a l s o p r o b a b l y t r u e of Upogebia,  demonstrated s t a t i s t i c a l l y , because n e a r l y  a l l of  the _2  quadrat r e a d i n g s r e g i s t e r e d  zero Upogebja ( i . e . , <0.5  C a l l i a n a s s a " c a T l f o r n i e n s i s can but  does not  have any  capacity  response to reduced s a l i n i t y lower than about 10%  o  are  t i e s down to about 3.5%»  t o l e r a t e s a l i n i t i e s down to about  lethal.  Pritchard,  Thompson and  Pritchard, 0  c h l o r i d e l e v e l above t h a t of the Upogebia c o n s t r u c t s  surface  (R.:"Thompson'.and P r i t c h a r d , 1969;  P r i t c h a r d , 1969;  thus the  to t h a t i n t i d a l p o o l s at the  f o r the purposes of f e e d i n g  1969), and  In  Thompson and  shows  strong  Pritchard,  feeding  (R.  Upogebia c i r c u l a t e s water  purposes ( M a c G i n i t i e ,  1930;  s a l i n i t y of water w i t h i n  the burrows i s s i m i l a r  surface  P r i t c h a r d , .1969).  CL.  Thompson and  to c i r c u l a t e s u r f a c e as i t i s a d e p o s i t  t o l e r a t e up  P r i t c h a r d , 1969).  the  contrast,  have c o n s t r i c t e d a p e r t u r a l necks  waters through i t s burrow  feeder (MacGinitie,  does C a l l i a n a s s a need to f o r the purposes of r e s p i r a t i o n d u r i n g because C a l l i a n a s s a can  salini^  maintaining i t s blood  Swinbanks, 1977).  Swinbanks,.1979.) .  through i t s burrow f o r r e s p i r a t o r y and  require  tolerate  a mud-lined burrow which opens d i r e c t l y to  C a l l i a n a s s a burrows l a c k a l i n i n g and  C a l l i a n a s s a does not  10%,  salinities  s u r r o u n d i n g medium (R. Thompson and  1969)..  Thompson, 1972), and  1969);  UpOgebia p u g e t t e n s i s can  osmoregulatory c a p a c i t i e s i n s a l i n i t i e s below 26% ,  Thompson and  ).  to osmoregulate i t s b l o o d c h l o r i d e l e v e l i n  (L. Thompson and  CL.  burrow openings m  1934),  exposure,  to f i v e days of continuous a n o x i a  Thus, because of i t s mode of l i f e , i t s  (R.  nor  211 "% t o l e r a n c e of anoxia  and  i t s u n l i n e d burrow, C a l l i a n a s s a can t o l e r a t e low  s a l i n i t y s u r f a c e waters (L. Thompson and P r i t c h a r d , 1969/. Upogebia i s dependent on s u r f a c e waters f o r suspension and  i t s burrow l i n i n g i s p r o b a b l y  In contrast,  f e e d i n g and  respiration,  impermeable to i n t e r s t i t i a l w a t e r s .  d e s p i t e b e i n g p h y s i o l o g i c a l l y b e t t e r adapted to cope w i t h reduced  Thus,  salinity,  Upogebia demonstrates lower t o l e r a n c e of low s a l i n i t y water i n i t s d i s t r i b u t i o n than C a l l i a n a s s a , as can be 8, 9 and Why  seen by  comparing F i g u r e 11 w i t h  10. then do C a l l i a n a s s a d e n s i t i e s decrease i n areas  s u b s t r a t e s a l i n i t y when s a l i n i t i e s at depth remain h i g h ? probably  Figures  l i e s i n reproduction.  ( M a c G i n i t i e , 1934).  Highest  of reduced The  answer to  Callianassa has a planktic larval 3  shrimp m o r t a l i t y probably  surface  occurs  this  stage  i n the  first  few hours a f t e r the l a r v a e s e t t l e onto the s u b s t r a t e as p o s t l a r v a l shrimps and b e f o r e  they manage to burrow deep i n t o the s u b s t r a t e , because they  then at the mercy of p r e d a t o r s one  and  the environment  ( M a c G i n i t i e , 1934/.  If  can assume t h a t p o s t l a r v a l C a l l i a n a s s a , l i k e the a d u l t s , cannot t o l e r a t e  s a l i n i t i e s below 10%o  f o r any  l e n g t h of time, then one might expect  p o s t l a r v a l shrimp m o r t a l i t y i n areas  experiencing  s a l i n i t i e s , and hence reduced a d u l t p o p u l a t i o n s . may  are  not be e n t i r e l y j u s t i f i e d because F e l d e r  low s u r f a c e  substrate  However, t h i s  (.1978) has  higher  assumption  found l i m i t e d  evi-  dence to suggest t h a t j u v e n i l e ' C a l l i a n a s s a i s l a g f a r i d e can t o l e r a t e s a l i n i t i e s as low this,  as 5%o, whereas a d u l t s d i e i n s a l i n i t i e s below about 15%«. the e x p l a n a t i o n o u t l i n e d above may  s t i l l be v a l i d even i f p o s t l a r v a l  C a l l i a n a s s a c a l i f o r n i e n s i s )haye a l e t h a l l i m i t Upogebia form s m a l l feeding  'Y'  below 3.5%o  lower than 10%..  burrows i n the s u r f a c e sediments f o r  (Thompson, 1972).  Despite  Postlarval suspension  In areas where s u r f a c e s u b s t r a t e s a l i n i t y can  m o r t a l i t y among p o s t l a r v a l Upogebia, i s p r o b a b l y  h i g h , as  must be e n t i r e l y dependent on s u r f a c e s u b s t r a t e waters f o r s u s p e n s i o n  drop  they feeding  ' 212and  respiration. The p o s s i b l y must be e n t e r t a i n e d t h a t the c o r r e l a t i o n between t h a l a s s i -  n i d e a n shrimp d i s t r i b u t i o n and s u b s t r a t e s a l i n i t y i s caused by some o t h e r factor closely interrelated  to s a l i n i t y ,  f o r example  turbidity,  the concent-  r a t i o n o f suspended sediments and/or g r o s s s e d i m e n t a t i o n r a t e s . ,  Syvitski  (19 78) has demonstrated t h a t suspended sediment c o n c e n t r a t i o n and sediment a t i o n r a t e s a r e n e g a t i v e l y c o r r e l a t e d w i t h s u r f a c e s a l i n i t y i n Howe Sound, B.C.  The decrease i n C a l l i a n a s s a and Upogebia d e n s i t i e s  accompanying  decreases i n s a l i n i t y c o u l d perhaps be caused by i n c r e a s e s i n any o r a l l t h r e e o f the f a c t o r s mentioned above.  High t u r b i d i t y l e v e l s might r e s u l t i n  low primary p r o d u c t i v i t y due to reduced l i g h t  availability,  resulting  d i r e c t l y o r i n d i r e c t l y i n a reduced food s u p p l y f o r l a r v a l shrimps.  Or l a r v a l  o r p o s t l a r v a l shrimp m o r t a l i t y might be h i g h i n a r e a s where suspended sediment c o n c e n t r a t i o n s a r e e x c e s s i v e l y h i g h , because, f o r example,  high fluxes of  suspended sediments may c l o g the f i l t e r i n g mechanisms o f p o s t l a r v a l Upogebia preventing e f f i c i e n t  feeding.  Or p o s t l a r v a l shrimp m o r t a l i t y may be h i g h  i n areas where h i g h g r o s s s e d i m e n t a t i o n r a t e s may r e s u l t i n j u v e n i l e shrimps b e i n g smothered t o death. C a l l i a n a s s a a r e absent from the Z_. marina bed a d j a c e n t t o the C o a l p o r t , much as r e p o r t e d f o r the Z. marina beds i n Boundary Bay (Swinbanks, 1979) and the inter-causeway a r e a (Part 4A).  T h i s r e s u l t s i n an anomalous n e g a t i v e  c o r r e l a t i o n between C a l l i a n a s s a d e n s i t y and s u b s t r a t e s a l i n i t y On the b r a c k i s h t i d a l f l a t s , to lower i n t e r t i d a l  levels.  i n F i g u r e 12G.  i n the absence o f e e l g r a s s , C a l l i a n a s s a extend  ,213"  BURROW GEOMETRY  Tn: Boundary^BayJ  C a l l i a n a s s a c o n s t r u c t s u n l i n e d f e e d i n g burrows w h i c h  e x t e n d 20 t o 30 cm down i n t o t h e s u b s t r a t e , and then branch h o r i z o n t a l l y f o r d i s t a n c e s o f up t o a meter  (Swinbanks, 1979; Fig.,014)•'.(< Each'system has two, -  t h r e e o r r a r e l y f o u r e x i t s w i t h c o n s t r i c t e d a p e r t u r a l necks w h i c h meet as a bulbous chamber a t 5 cm t o 10 cm d e p t h .  B r a n c h i n g i s dichotomous, and  t h e r e a r e b u l b o u s t u r n a r o u n d s w i t h i n t h e system.  The Upogebia burrow i s a  'Y' tube„extending down t o depths o f 50 t o 60 cm (Swinbanks, 1979;-'Fig. 1 4 ) . Thompson (1972) r e p o r t s burrow depths as g r e a t as 90 cm.  In contrast to  C a l l i a n a s s a b u r r o w s , Upogebia burrows a r e p r e d o m i n a n t l y v e r t i c a l l y  oriented,  do n o t have c o n s t r i c t e d e n t r a n c e s , and l a c k b u l b o u s t u r n a r o u n d s ( F i g . 1 4 ) . The i n t e r n a l w a l l s o f t h e burrow a r e smooth and l i n e d w i t h mud. burrows appear t o be permanent d w e l l i n g burrows 1979).  Upogebia  (Thompsohy.,1972; Swinbanks,  Thompson (1972) has demonstrated t h a t Upogebia s e c r e t e s mucus from  i t s h i n d - g u t g l a n d t o cement the w a l l s o f t h e burrow.  However, Thompson  s u r p r i s i n g l y a s s e r t s t h a t "no p a r t i c u l a r s i z e c l a s s o f sediment p a r t i c l e i s s e l e c t e d by t h e shrimp t o b u i l d t h e burrow,"  (1972,- p . i i i ) d e s p i t e t h e f a c t  t h a t h i s own g r a i n s i z e d a t a demonstrates t h a t Upogebia burrow l i n i n g s  contain  between one and a h a l f t o f i v e times as much mud (>4.0 0) as t h e s u r r o u n d i n g substrate.  I n a d d i t i o n , t h e S.E.M. m i c r o g r a p h s p r e s e n t e d b y Thompson (1972)  c l e a r l y i l l u s t r a t e a high concentration of p l a t y clay minerals i n the inner burrow l i n i n g , and equant sand g r a i n s i n t h e o u t e r l i n i n g . almost c e r t a i n l y a i d s i n w a l l s u p p o r t . e x t e r i o r t o t h e burrows  The c o h e s i v e mud  The sand g r a i n s form a k n o b b l y  ( F i g . 1 4 ) , r e s e m b l i n g t h e t r a c e f o s s i l Ophiomorpha  (Thompson, 1972). The v a l u e o f d i s t i n g u i s h i n g between t h e t r a c e f o s s i l genera Ophiomorpha and T h a l a s s i n o i d e s has r e c e n t l y been q u e s t i o n e d ( F u r s i c h , 1973) because t h e r e  Callianassa  Boundary  F i g u r e 14.  Bay and  Burrow  Intercauseway  Tidal  Uppgfibiq  Flats  Burrow  unconstricted entrance  T y p i c a l geometry o f C a l l i a n a s s a and Upogebia burrows on the F r a s e r D e l t a . c r o s s - s e c t i o n o f Upogebia burrow l i n i n g o b t a i n e d from Thompson (1972).  constricted apertural neck  Dimensions f o r  215  is  t r a c e f o s s i l evidence  t h a t the same organism can produce b o t h  Thalassinoides  and  Ophiomorpha w i t h i n the same burrow (Kennedy and MacDougall, 1969; Kennedy  and  Sellwood, 1970).  can produce both.  We have found evidence  that C a l l i a n a s s a c a l i f o r n i e n s i s  A l l , b u t one, o f the C a l l i a n a s s a c a s t s r e t r i e v e d from the  F r a s e r D e l t a have the c h a r a c t e r i s t i c smooth burrow s u r f a c e s o f T h a l a s s i n o i d e s . However, one c a s t taken x^ith a slower s e t t i n g r e s i n m i x t u r e impregnated the sandy w a l l s o f the burrow w i t h r e s i n , and the r e s u l t i n g c a s t had a t h i c k c o a t i n g o f sand, which has a knobbly s u r f a c e r e m i n i s c e n t (Fig.  of Ophiomorpha  "• ." .  15a). T h i s may be an a r t i f a c t o f r e s i n c a s t i n g o r the r e s i n may have  p i c k e d out s u b t l e d i f f e r e n c e s i n permeability.* i n the burrow w a l l s whieh"could c o n c e i v a b l y be H i g h l i g h t e d by cementation d u r i n g d i a g e n e s i s .  On s c r a p i n g o f f  the sand c o a t i n g the smooth w a l l s , t y p i c a l o f the o t h e r c a s t s , i s r e v e a l e d underneath ( F i g . 16a). I f one o f these burrows were i n f i l l e d w i t h of a d i f f e r e n t g r a i n s i z e from t h a t o f the w a l l s then the r e s u l t i n g f o s s i l would be c l a s s i f i e d as T h a l a s s i n o i d e s .  sediment trace  A f o s s i l example was found i n  a box core from Boundary Bay ( F i g . 15b). Here a c a i l i a n a s s i d burrow e n t e r s a mud l a y e r and has been i n f i l l e d w i t h sand.  However, i f a burrow such as  i n F i g u r e 15a was i n f i l l e d w i t h sand of the same g r a i n s i z e as t h e burrow w a l l s , the sandy burrow w a l l s w i t h knobbly e x t e r i o r might form the o u t l i n e of the t r a c e f o s s i l ,  and i t would be c l a s s i f i e d as Ophiomorpha.  Similarly  the burrows o f Upogebia c o u l d have the appearance o f T h a l a s s i n o i d e s o r Ophiomorpha depending on whether the smooth i n n e r o r knobbly o u t e r burrow w a l l i s accentuated  by d i a g e n e s i s .  As Bromley and F r e y p u t i t " i n s i d e every  Ophiomorpha t h e r e i s a T h a l a s s i n o i d e s i n the g u i s e o f a burrow c a s t " (1974, p.  330). To t h i s we would add t h a t o u t s i d e every T h a l a s s i n o i d e s may l i e the  ghost o f an; Ophiomorpha (Fig..15a).; .Bromley and Frey  (1974), however,  still  advocate d i s t i n g u i s h i n g the two and i n a subsequent paper Frey and Howard (1975) equate Upogebia a f f i n i s  burrows w i t h T h a l a s s i n o i d e s and those o f  216,  Figure  15.  a)  R e s i n c a s t o f a C a l l i a n a s s a burrow coated i n sand w i t h a knobbly s u r f a c e r e m i n i s c e n t o f Ophiomorpha. Note t h a t at: top l e f t the sand l i n i n g has been worn away by the s t r i n g and the i n n e r burrow l i n i n g i s smooth.  b)  F o s s i l i z e d C a l l i a n a s s a burrow h a v i n g the appearance o f Thalassinoides. Sand has i n f i l l e d a burrow i n mud.  217  2 1 8  F i g u r e 16.  Cast of a C a l l i a n a s s a burrow fallen from an a r e a of h i g h burrow d e n s i t y (446 burrow openings m ) . Two c o n s t r i c t e d e n t r a n c e s meet as a bulbous chamber at about 10 cm depth, and a v e r t i c a l stem extends from t h i s to about 50 cm depth. Cryptomya c a l i f o r n i c a c l u s t e r around the bulbous chamber at the j u n c t i o n o f the two e x i t s . About t h i r t y of these commensal b i v a l v e s are a t t a c h e d to the c a s t . The burrow i s o c c u p i e d by one shrimp. A burrow system o f s m a l l e r diameter branches o f f from t h i s system. It is j o i n e d t o the main burrow system by a narrow c o n s t r i c t e d neck and i s o c c u p i e d by a s m a l l j u v e n i l e shrimp. Scale i n centimeters.  219 U.  p u g e t t e n s i s w i t h Ophiomorpha.  these two  species  burrow l i n i n g s .  Apart  from l a c k i n g knobs the burrows of  of Upogebia are v e r y s i m i l a r . We  f e e l that  Both have smooth d u r a b l e  the presence of knobs i s not  significant. . 0  A. f a r more important d i s t i n c t i o n , i s . t h a t between, permanent d w e l l i n g burrows w i t h f i r m impermeable l i n i n g s and used f o r s u s p e n s i o n f e e d i n g and JJ. a f f i n i s , and  and  open or s h o r t  : -  constricted  exits  r e s p i r a t i o n , such as those of JJ. p u g e t t e n s i s  temporary f e e d i n g  burrows w i t h permeable l i n i n g s  c o n s t r i c t e d e n t r a n c e s , used f o r d e p o s i t  feeding,  like  those of  and  Callianassa  c a l i f o r n i e n s i s , because, as has  been demonstrated, burrow f u n c t i o n has  profound b e a r i n g on  s a l i n i t y which the  the  surface  Upogebia, a l t h o u g h p h y s i o l o g i c a l l y b e t t e r t o l e r a t e reduced s a l i n i t i e s , water because of the feeding  and  organism can  a  tolerate.  adapted than C a l l i a n a s s a  i n f a c t demonstrates lower t o l e r a n c e  to of  brackish  f u n c t i o n of i t s burrow as a c o n d u i t f o r s u s p e n s i o n  respiration.  Such d i s t i n c t i o n s form the b a s i s  (1964) e t h o l o g i c a l c l a s s i f i c a t i o n of ichnotaxonomic system f o r t r a c e without regard f o r f u n c t i o n ,  ,  :  trace f o s s i l s .  fossil  The  of  >  .  Seilacher's  c o n t i n u e d use  an  c l a s s i f i c a t i o n , based on morphology  l i m i t s the u s e f u l n e s s of t r a c e  fossils  in  paleoenvironmental i n t e r p r e t a t i o n s . Farrow (.1971) has  demonstrated t h a t  c a l l i a n a s s i d burrows e x h i b i t markedly  d i f f e r e n t geometries i n the d i f f e r e n t sedimentary environments of an C a l l i a n a s s a burrows show s i g n i f i c a n t v a r i a b i l i t y parts  of the F r a s e r  Delta.  horizontally oriented.  i n geometry on d i f f e r e n t  In most areas C a l l i a n a s s a burrows are  flat  Callianassa constructs  oriented  This  i s p r o b a b l y a r e s u l t of p o p u l a t i o n  the  shrimps to mine v e r t i c a l l y .  Callianassa construct  predominantly  However, i n areas of v e r y h i g h burrow d e n s i t y . o n  inter-causeway t i d a l (.Fig. 16).  atoll.  On  c e n t r a l and  burrows which are  cm  vertically  pressure f o r c i n g  n o r t h e r n Roberts Bank  burrows w i t h u n u s u a l l y l o n g ,  necks, which extend about 30  the  constricted  down i n t o the s u b s t r a t e  apertural  ( F i g . 14).  Beyond  -220  t h i s p o i n t box cores have r e v e a l e d geometry  t h a t the burrows appear to have s i m i l a r  to those found i n Boundary Bay.  However, the l o n g c o n s t r i c t e d  a p e r t u r a l necks have proved to be an insurmountable b a r r i e r to r e s i n , c a s t s have not been o b t a i n e d  from t h i s a r e a .  There are a number of p o s s i b l e  reasons f o r the c o n s t r u c t i o n o f l o n g c o n s t r i c t e d a p e r t u r a l necks. may  be a v o i d i n g  the upper 5-10  and  Callianassa  cm o f the s u b s t r a t e , which i s c o n s t a n t l y  reworked by c u r r e n t s and waves i n the r e l a t i v e l y h i g h  energy environment of  t h i s p a r t of Robert's Bank, and/or i t may be burrowing deeper to r e a c h r e g i o n s of s t a b l e s a l i n i t y .  The l o n g c o n s t r i c t e d necks may  i n f e e d i n g b e h a v i o u r on the p a r t of C a l l i a n a s s a .  also r e f l e c t a  I n the Boundary  inter-causeway areas the bulbous chamber c l o s e to the s u r f a c e may used f o r s u s p e n s i o n f e e d i n g , at h i g h deposit  feeding a c t i v i t i e s  t i d e , as a supplement  (Swinbanks, 1979).  On n o r t h e r n  change Bay and perhaps be  to C a l l i a n a s s a ' s and c e n t r a l  Roberts Bank, where the e n v i r o n m e n t a l energy i s h i g h and the s a l i n i t y unstable,  C a l l i a n a s s a p r o b a b l y abandons near s u r f a c e  regime  f e e d i n g , and e s t a b l i s h e s  i t s main burrow complex a t g r e a t e r than 30 cm depth. Upogebia burrows e x h i b i t s i m i l a r geometry on a l l p a r t s of the F r a s e r Delta  ( F i g . 14).  However, i n areas where c u r r e n t s rework the s u r f a c e of the  s u b s t r a t e , Upogebia c o n s t r u c t s h o r t c o n s t r i c t e d a p e r t u r a l necks to t h e i r burrows.  Thompson (1972) r e p o r t s t h a t Upogebia burrows  surface.  The presence or absence of c o n s t r i c t i o n i s p r o b a b l y a f u n c t i o n of  e n v i r o n m e n t a l energy, c o n s t r i c t i o n s b e i n g surface.  taper  towards the  formed when c u r r e n t s rework the  The degree of c o n s t r i c t i o n and the l e n g t h o f c o n s t r i c t e d s e c t i o n s ,  however, never approaches t h a t o f C a l l i a n a s s a burrows, and i t seems t h a t when c o n d i t i o n s a r e f a v o u r a b l e , Upogebia p r e f e r s no c o n s t r i c t i o n s . i n i t s . b u r r o w .  •  22.1;  REVIEW AND CONCLUSIONS  F i g u r e 17 summarizes a l l the a v a i l a b l e data on t h a l a s s i n i d e a n  shrimp  d i s t r i b u t i o n by i l l u s t r a t i n g the s t r a t i g r a p h i c s u c c e s s i o n o f t h a l a s s i n i d e a n burrow d e n s i t y and f l o r a l / s e d i m e n t o l o g i c a l zones  to be expected i f the  F r a s e r D e l t a progrades seawards w i t h o u t s u b s i d e n c e .  The contours o f  t h a l a s s i n i d e a n burrow d e n s i t y i n F i g u r e 17, based on l i v i n g p o p u l a t i o n denr;( \} sity,iar§ i n t e n d e d t o be used as a q u a l i t a t i v e guide t o the d e n s i t y o f thalassinidean trace f o s s i l s  to be expected i n the g e o l o g i c a l  record.  The d i s t r i b u t i o n o f f l o r a l / s e d i m e n t o l o g i c a l zones i s c r i t i c a l t o t h a l a s s i n i d e a n shrimp elevation  distribution.  I n terms o f b o t h G e o d e t i c e l e v a t i o n and t i d a l  (as d e f i n e d by exposure zones) the a l g a l mat and e e l g r a s s  on the 'marine'  tidal  f l a t s o f Roberts Bank l i e a t lower e l e v a t i o n s  t h e i r e q u i v a l e n t s i n Boundary Bay. the n a t u r e o f t i d a l  zones than  T h i s i s p r o b a b l y due to d i f f e r e n c e s i n  channel d r a i n a g e and s u b s t r a t e i n the two a r e a s .  On the  Boundary Bay t i d a l fiatsefehe s u b s t r a t e c o n s i s t s e n t i r e l y o f sand and the main t i d a l channel system i s c o n f i n e d t o the r e g i o n below mean s.ea l e v e l , e x t e n d i n g into s u b t i d a l regions.  The upper reaches o f the channels a r e broad and s h a l -  low, p r o d u c i n g d e p r e s s i o n s i n which submergence d u r a t i o n i s enhanced and i n which  Z. marina beds can a t t a i n h i g h e r t i d a l e l e v a t i o n s than on Roberts Bank  (Swinbanks,  1979) . On Roberts Bank the main t i d a l channel system o c c u r s  above mean s e a l e v e l as a d e n d r i t i c system o f s m a l l channels d r a i n i n g from the muds o f the upper t i d a l f l a t s .  water  P l a t e a u s between the d r a i n a g e channels  e x p e r i e n c e enhanced exposure f a v o u r a b l e t o the development  of blue-green a l g a l  mats and,.probably  t o lower  levels.  as a r e s u l t , the a l g a l mat zone extends  On Roberts Bank the s a l t m a r s h zone s e t s the upper l i m i t  d i s t r i b u t i o n , and dense Z_. marina,, growth appears  intertidal  to Callianassa  to l i m i t t h e i r p o p u l a t i o n  a t low i n t e r t i d a l l e v e l s , w h i l e the h i g h e s t d e n s i t i e s o f C a l l i a n a s s a o c c u r i n the non-yegetated s a n d f l a t and causeway zones.  I n Boundary Bay Upogebia  F i g u r e 17.  Summary o f the d i s t r i b u t i o n o f t h a l a s s i n i d e a n burrows and f l o r a l / s e d i m e n t o l o g i c a l zones on a l l the t i d a l f l a t s o f the F r a s e r D e l t a south o f Main Channel, i n the form a s t r a t i g r a p h i c s u c c e s s i o n , c o n s t r u c t e d by p r o j e c t i n g a l l the d e n s i t y data i n F i g u r e 11 onto a v e r t i c a l plane p a s s i n g through p o i n t s A, B and C i n F i g u r e 11. The data on p e r c e n t t h i c k n e s s o f the s a l t wedge i n F i g u r e 10 have; a l s o been i n c l u d e d t o demonstrate the r e l a t i o n s h i p between t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n and s a l i n i t y regime. No data on the s a l t wedge'are a v a i l a b l e NW o f Canoe Pass. Data from Boundary Bay a r e based on T r a n s e c t A alone (Swinbanks, 1979). Exposure zones allow cross c o r r e l a t i o n between Roberts Bank and Boundary Bay. Winter t i d a l data a r e not a v a i l a b l e f o r Boundary Bay and as a r e s u l t the upper l i m i t of the atmozone cannot be d e f i n e d , but the s p r i n g t i d a l l e v e l s f o r June i n d i c a t e d a l l o w c r o s s c o r r e l a t i o n i n the uppermost i n t e r t i d a l r e g i o n s .  to rO  NORTHERN  U p o a e b l q  p r e s e n t 05-25 b u r r o w  U p o p e b l a  b u r r o w  o p e n i n g  A N D  o p e n i n g s  d e n s i t y > 25 m ~  m 2  CENTRAL  ROBERTS  INTERCAUSEWAY  BANK  TIDAL  • 251-  -  C o n t o u r o fC o l l l o n o s s o o p e n i n g d e n s i t y m ~ 2  b u r r o w  *'  FLAT  P e r c e n t t h i c k n e s s o f t h e s a l t wedge(>17.5%o. Level o f Spring H i g h e r H i g h W a t e r D e c e m b e r a t T s a w w a s s e n  i n  EXPOSURE  BOUNDARY  ZONES  BAY  Level o f S p r i n g H i g h e r at T s a w w a s s e n  H i g h  W a t e r  i n  Level  H i g h  W a t e r  i n J u n e  at  o f S p r i n g H i g h e r  B o u n d a r y  B a y  No w i n t e r Tidal Boundary B a y  D a t a  a v a i l a b l e f o r  Juno  224  are r e s t r i c t e d t o the beds o f dense Z. marina growth where the mud c o n t e n t s of the sediments a r e s u f f i c i e n t l y h i g h  ( g r e a t e r than about 2% mud).  On  Roberts Bank where mud c o n t e n t s o f the sediments a r e an o r d e r o f magnitude h i g h e r Upogebia span a wider e l e v a t i o n range e x t e n d i n g up to the base o f the upper amphizone,  a l e v e l above which the maximum d u r a t i o n o f a n o x i a due  to exposure p r o b a b l y exceeds the l e t h a l l i m i t  f o r p o s t m o l t Upogebia.  In  Boundary nay where the upper l i m i t o f the a l g a l mat zone extends to a s l i g h t l y h i g h e r e l e v a t i o n than on Roberts Bank, C a l l i a n a s s a a t t a i n s i t s p h y s i o l o g i c a l limit  i n e l e v a t i o n by e x t e n d i n g up t o , b u t not beyond, e l e v a t i o n s  experiencing  a maximum o f about f i v e days o f continuous a n o x i a due to exposure. Between the C o a l p o r t and Canoe Pass on Roberts Bank a major  transition  i n f l o r a l / s e d i m e n t o l o g i c a l z o n a t i o n o c c u r s as a r e s u l t o f an abrupt t r a n s i t i o n from a 'marine' t o b r a c k i s h s a l i n i t y regime.  The a l g a l mat zone i s r e p l a c e d  by the lower p a r t o f the upper b r a c k i s h marsh, w h i l e the lower b r a c k i s h marsh, which c o n s i s t s predominantly o f S c i r p u s americanus, becomes the l a t e r a l v a l e n t o f the upper h a l f o f the s a n d f l a t zone.  equi-  The e e l g r a s s zone i s r e p l a c e d  by a s a n d f l a t / m u d f l a t zone, which i s d e v o i d o f f l o r a l cover and c r o s s c u t by r i v e r c h a n n e l s , b o t h a c t i v e and r e l i c t .  I n response t o these changes, t h e  peak i n C a l l i a n a s s a d i s t r i b u t i o n moves t o lower i n t e r t i d a l l e v e l s , because of the presence of low s a l i n i t y water a t h i g h e r t i d a l l e v e l s and because o f the d i s a p p e a r a n c e o f e e l g r a s s i n lower i n t e r t i d a l r e g i o n s . of the b r a c k i s h marsh forms the upper l i m i t  The lower  limit  to C a l l i a n a s s a d i s t r i b u t i o n .  In  c l o s e p r o x i m i t y t o the major channels o f the F r a s e r R i v e r , C a l l i a n a s s a a r e absent. Upogebia i s a p p a r e n t l y more s e n s i t i v e t o the e n v i r o n m e n t a l f a c t o r s of g r a i n s i z e and s a l i n i t y  than C a l l i a n a s s a .  Upogebia shows a d i s t i n c t  rence f o r muddier s u b s t r a t e s and cannot t o l e r a t e low s a l i n i t y , s t r a t e waters.  prefe-  surface  sub-  The presence o f s u f f i c i e n t mud i n the s u b s t r a t e i s p r o b a b l y  225 essential  to Upogebia f o r  circulation  of  the  c o n s t r u c t i o n of  surface waters  through  its  its  mud-lined burrow,  impermeable m u d - l i n e d burrow  s u s p e n s i o n f e e d i n g a n d r e s p i r a t i o n makes U p o g e b i a more s e n s i t i v e C a l l i a n a s s a to  changes i n  physiologically better The p o s i t i v e strate  salinity,  suggest  that  salinity  adapted to  regime,  and t h e  distribution  the d e n s i t y of  types of burrow,  patterns  f o s s i l burrows  used i n  In  burrows) ricted  this  e n t r a n c e s , used p r i m a r i l y  for  little  is  salinity  f o s s i l burrow.  sediment and/or  On n o r t h e r n  burrows w i t h l o n g e r ,  considered  the  occupant shrimp  fresh water interstitial  very dwelling  waters.  trace  The  of  This i s  thought  to  distinction  considered view,  as  the g r a i n  reflect  the  to  both the size  enhancement of  necks than i n  to  whether  f o s s i l s under  reflect  diagenetic  apertural  exposed  i n c u r s i o n , or  other hand, i s  may s i m p l y  is  and c e n t r a l R o b e r t s Bank C a l l i a n a s s a  causeway or Boundary Bay a r e a s .  in  feeding burrows w i t h long c o n s t - -  t h e mode o f  more c o n s t r i c t e d  tool  ( e . g . , UpOgebia  s i g n i f i c a n c e from a p a l e o e n v i r o n m e n t a l p o i n t  filling  The  d e p o s i t - f e e d i n g ( e l g . , CalIiana'ssa~Kurrbws  c i r c u m s t a n c e s , and t h e d i s t i n c t i o n  the burrow  Upogebia  impermeable, permanent  U p o g e b i a and C a l l i a n a s s a c a n p r o b a b l y p r o d u c e b o t h right  geological  Callianassa.  suspension feeding  s u s c e p t i b l e to  exposed to h y p o x i c , h i g h  the  paleosalinity,  regard i t  b e t w e e n T h a l a s s i n o i d e s and O p h i o m o r p h a , on t h e be of  is  salinities.  should form a powerful  and u n l i n e d , p e r m e a b l e , temporary  oxygenated surface waters is  '.  :  that Upogebia  shrimps i n  than those of  F e c a u s e " these'" f a c t o r s i ' ^ d e t e r m i n e r w h e t h e r  it  fact  than i  C a l l i a n a s s a and U p o g e b i a  of both  d i s t i n g u i s h between m u d - l i n e d ,  burrows w i t h open e n t r a n c e s used f o r  of  i n d i c a t i o n of  conjunction,  paleoenvironmental reconstructions. to  the  for  c o r r e l a t i o n b e t w e e n C a l l i a n a s s a d e n s i t y and s u r f a c e s u b ^  b u r r o w s b e i n g a more s e n s i t i v e i n d i c a t o r  significant  despite  cope w i t h f l u c t u a t i n g  r e c o r d c o u l d be used as a q u a l i t a t i v e  two  and:the  of  the  constructs inter-  a change i n  . > .•  f e e d i n g mode, w i t h C a l l i a n a s s a a b a n d o n i n g n e a r s u r f a c e f e e d i n g , b e c a u s e of  226  the i n s t a b i l i t y fluctuating  o f the s u r f a c e , which i s reworked by c u r r e n t s  and exposed t o  salinities.  ACKNOWLEDGEMENT S  T h i s r e s e a r c h was f i n a n c e d  by G e o l o g i c a l Survey o f Canada  Contract  D.S.S. No. 0SS77-08177 from the Department o f Supply and S e r v i c e s , Ottawa, Ontario,  Canada.  We a r e indebted  to Captain  John MacGrath and a l l crew  members a t the Canadian Coastguard H o v e r c r a f t Airport  f o r p r o v i d i n g and o p e r a t i n g  thank Mr. W.J. Rapatz, R e g i o n a l  U n i t a t Vancouver I n t e r n a t i o n a l  the H o v e r c r a f t  f o r f i e l d sampling.  T i d a l Superintendent  We  a t Sidney, B.C. f o r  p r o v i d i n g observed t i d a l d a t a from t h e t i d a l gauge a t the Tsawwassen f e r r y terminal.  Dr. J.P. S y v i t s k i , . M r . G.D. Hodge and Ms. N. Hayakawa a b l y  i n the f i e l d . diatoms.  the c h l o r o p h y t e s ,  Dr. W.C. Barnes and Dr. C D . L e v i n g s  We thank Mrs. for  Dr. M. Pomeroy i d e n t i f i e d  assisted  cyanophytes and  c r i t i c a l l y the m a n u s c r i p t .  C M . Armstrong f o r d r a f t i n g the diagrams and Ms. N. Hayakawa  t y p i n g the s c r i p t .  227  REFERENCES  Ages, A. W o o l l a r d , A., 1976, The t i d e s i n the F r a s e r E s t u a r y : Mar. ^ScT. Rept. 76-5, 100 p.  Pac.  Beak-Hinton, 1977, E n v i r o n m e n t a l impact assessment of Roberts Bank p o r t expansion. V o l . 3, App. A and V o l . 4, App. B. The e x i s t i n g p h y s i c a l and b i o l o g i c a l environments: Beak C o n s u l t a n t s L t d . , Vancouver. B o r r a d a i l e , L.A., 1903, On the c l a s s i f i c a t i o n o f the T h a l a s s i n i d e a : Mag. Nat. H i s t . , s e r i e s 7, 12, p. 534-551.  Ann.  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Kennedy, W.J. and MacDougall, J . , 1969, C r u s t a c e a n burrows i n the Weald C l a y of s o u t h e a s t England and t h e i r e n v i r o n m e n t a l s i g n i f i c a n c e : P a l a e o n t o l o g y , / v . 12,-.p. 459. and Sellwood, B.W., 1970, Ophiomorpha nodosa, a marine i n d i c a t o r from the S p a r n a c i a n o f southwest England: G e o l . A s s o c . P r o c , v . 8-1, p. 99-110. L e v i n g s , C D . and C o u s t a l i n , J.B., 1975, Z o n a t i o n of i n t e r t i d a l biomass and r e l a t e d b e n t h i c d a t a from S t u r g e o n and Roberts Bank, F r a s e r R i v e r e s t u a r y , B r i t i s h Columbia: F i s h e r i e s and Marine S e r v i c e , Environment Canada, Tech. Rept. no. 458, 138 p.  228  L u t e r n a u e r , J.L. and Murray, J.W., 1973, S e d i m e n t a t i o n on the Western D e l t a f r o n t of the F r a s e r R i v e r , B r i t i s h Columbia: Can. J o u r . E a r t h .Sci., v. 10, p. 1642-1663. M a c G i n i t i e , G.E., 1930, p u g e t t e n s i s (Dana):  Dana:  The n a t u r a l h i s t o r y o f the mud shrimp Upogebia Ann. Mag. n a t . H i s t . , v. 6, p. 36-44.  , 1934, The n a t u r a l h i s t o r y o f C a l l i a n a s s a c a l i f o r n i e n s i s Amer. M i d i . N a t u r a l i s t , v. 15, p. 166-177.  Medley, E. and L u t e r n a u e r , J.L., 1976, Use of a e r i a l photographs to map sediment d i s t r i b u t i o n and to i d e n t i f y h i s t o r i c a l changes on a t i d a l f l a t : In Report of A c t i v i t i e s , P a r t C, G e o l . Surv. Can., Paper 76-1C, p. 293304. Moody, A . I . , 1978, Growth and d i s t r i b u t i o n of the v e g e t a t i o n of a southern F r a s e r D e l t a marsh: ..unpub. M.Sc. t h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, B.C., 153 p. O'Connell, G., 1975, F l o r a and fauna of Boundary Bay t i d a l f l a t s , B r i t i s h Columbia: unpub. r e p o r t to B.C. Government P r o v i n c i a l P a r t Branch, V i c t o r i a , B.C. Parsons, CO., 1975, V e g e t a t i o n Lamda, v. 1 ( 2 ) ; p. 45-52.  p a t t e r n i n a s a l t marsh at Boundary Bay,  B.C.:  S e i l a c h e r , A., 1964, B i o g e n i c sedimentary s t r u c t u r e s : In Imbrie, J . , and N e w e l l , N.D. ( e d s ) , Approaches t o p a l e o e c o l o g y , John W i l e y , New York, p. 296-316. Shinn, E.A., Bahamas:  1968, Burrowing i n r e c e n t lime sediments o f F l o r i d a and Jour. P a l e o n t o l o g y , v. 42, p. 879-894.  the  Swan Wooster, 1967, Roberts Bank and Sturgeon Bank harbour study — topog r a p h i c maps. P r e p a r e d f o r Swan Wooster E n g i n e e r i n g Co. L t d . by Lockwood Survey C o r p o r a t i o n , A p r i l , 1967. N a t i o n a l Harbours Board, Vancouver, B.C. Swinbanks, D.D., 1979, E n v i r o n m e n t a l f a c t o r s c o n t r o l l i n g f l o r a l z o n a t i o n and the d i s t r i b u t i o n of burrowing and t u b e - d w e l l i n g organisms on F r a s e r D e l t a t i d a l f l a t s , B r i t i s h Columbia: unpub. Ph.D. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B.C., 274 p. and Murray, J.W., 1977, Animal-sediment r e l a t i o n s h i p s o f Boundary Bay and Roberts Bank t i d a l f l a t s , F r a s e r R i v e r D e l t a , B.C.: unpub. r e p o r t t o Dept. of Supply and S e r v i c e s , Ottawa, O n t a r i o , Canada, 118 p. Thompson, L.C. and P r i t c h a r d , A.W., 1969, Osmoregulatory c a p a c i t i e s of C a l l i a n a s s a and Upogebia ( C r u s t a c e a : T h a l a s s i n i d e a ) : B i o l . B u l l . , v. p. 114-129.  136,  Thompson, R.K., 1972, F u n c t i o n a l morphology of the h i n d - g u t of Upogebia p u g e t t e n s i s ( C r u s t a c e a , T h a l a s s i n i d e a ) and i t s r o l e i n burrow c o n s t r u c tion: unpub. Ph.D. t h e s i s , U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y , 202 p.  229 Thompson, R.K. and P r i t c h a r d , A.W., 1969, R e s p i r a t o r y adaptions of two burrowing c r u s t a c e a n s , C a l l i a n a s s a c a l i f o r n i e n s i s and Upogebia p u g e t t e n s i s (Decapoda, T h a l a s s i n i d e a ) : B i o l . B u l l . , v. 136, p. 274-287. Waldichuk, M., 1957, P h y s i c a l oceanography o f the S t r a i t of G e o r g i a , Columbia: J o u r . F i s h . Res. Brd. Canada, v. 14, p. 321-486.  British  Weimer, R.J. and Hoyt, J.H., 1964, Burrows of C a l l i a n a s s a major Say as i n d i c a t o r s o f l i t t o r a l and s h a l l o w n e r i t i c environments: J o u r . Pa.laont.o. l o g y , v. 38, p. 761-767.  230  SUMMARY AND  CONCLUSION  The s u b d i v i s i o n of the i n t e r t i d a l r e g i o n i n t o exposure zones at extreme c r i t i c a l  t i d a l l e v e l s i s advocated because 1)  c o r r e l a t i o n between d i f f e r e n t  t i d a l r e g i o n s e x p e r i e n c i n g d i f f e r e n t types  of a s t r o n o m i c a l l y c o n t r o l l e d t i d e 2) i s based may Boundary  The c r i t i c a l  be c a u s a l l y r e l a t e d to i n t e r t i d a l Bay t i d a l f l a t s  limited variability  i t allows cross  t i d a l l e v e l s on which i t  zonation.  are unusual .because they demonstrate v e r y  i n substrate grain size.  As a r e s u l t a c l e a r  floral/  f a u n a l z o n a t i o n i s developed, c o n t r o l l e d p r i m a r i l y by e l e v a t i o n and exposure. There are f i v e f l o r a l / s e d i m e n t o l o g i c a l zones on the t i d a l f l a t s by d i s t i n c t i v e macrofaunal assemblages. seaward:  the s a l t m a r s h , a l g a l mat,  wave zones.  characterized  These are from the s h o r e l i n e  upper sand wave, e e l g r a s s and lower sand  Topography o f s m a l l and l a r g e s c a l e of both p h y s i c a l and  b i o g e n i c o r i g i n c r e a t e s l a t e r a l h e t e r o g e n e i t y w i t h i n the b i o f a c i e s o f each zone.  A b a r e n i c o l a p a c i f i c a i s abundant  i n the upper sand wave zone and 6  t h i s p o l y c h a e t e a n n u a l l y reworks about 10  3 m  o f sand.  A b a r e n i c o l a has the  c a p a c i t y t o s i z e - s o r t a s a n d / c l a y mixture by f l o a t i n g the c l a y out i n the head s h a f t i r r i g a t i o n  current.  The marine t i d a l f l a t s of s o u t h e a s t e r n Roberts Bank have f l o r a l zones to those of Boundary l o g i c a l zones are p r e s e n t :  Bay, but o n l y f o u r major  s a l t m a r s h , a l g a l mat,  The lower l i m i t of the s a l t m a r s h l i e s  Bay, the a l g a l mat  floral/sedimento-  s a n d f l a t and e e l g r a s s zones.  at the same e l e v a t i o n as i n Boundary  Bay; j u s t below the lower l i m i t o f the upper atmozone. w i t h Boundary  comparable  However, compared  zone extends to lower i n t e r t i d a l  levels  while the iZoster'ainarina beds do/not a t t a i n ^ u c h ; h i g h elevations.. , _This i s a t t r i b u t e d to d i f f e r e n c e s i n the s t y l e of t i d a l c h a n n e l d r a i n a g e i n the two. areas,. which i n t u r n i s a .function of the g r a i n s i z e of the s u b s t r a t e .  231  On the inter-causeway t i d a l  f l a t l a t e r a l v a r i a t i o n s i n grain s i z e are  pronounced and g r e a t l y i n f l u e n c e t h a l a s s i n i d e a n shrimp Thalassinidean  shrimps a t t a i n t h e i r h i g h e s t  distribution.  d e n s i t i e s on these t i d a l  flats  and t h e r e i s some e v i d e n c e o f a n e g a t i v e i n t e r a c t i o n between C a l l i a n a s s a and Upogebia which may be a form o f t r o p h i c group ammensalism.  In the a r e a  -2 of t h e i r peak density. (446 burrow openings m substrate  ) C a l l i a n a s s a rework the  they l i v e i n to a depth o f 50 cm i n about f i v e months.  On c e n t r a l and n o r t h e r n Roberts Bank the t i d a l  f l a t s o f the F r a s e r  D e l t a undergo.a major t r a n s i t i o n from a marine t o a b r a c k i s h due t o the i n f l u x o f f r e s h w a t e r from the F r a s e r R i v e r .  environment  The f l o r a l / s e d i m e n t o -  l o g i c a l zones o f the t i d a l f l a t s a r e c o m p l e t e l y r e s t r u c t u r e d . marsh zone l a t e r a l l y r e p l a c e s  A brackish  the s a l t m a r s h zone, the a l g a l mat zone and  the upper h a l f o f the s a n d f l a t zone w h i l e a s a n d f l a t / m u d f l a t by both a c t i v e and r e l i c channels d i s p l a c e s the e e l g r a s s h a l f of the s a n d f l a t zone.  •'  zone  cross-cut  zone and the lower  The b r a c k i s h marsh extends w e l l below mean s e a  l e v e l t o about the upper l i m i t o f the aquazone.  I n response t o these  changes the peak i n C a l l i a n a s s a d i s t r i b u t i o n s h i f t s - - t o lower i n t e r t i d a l l e v e l s and Upogebia d i s a p p e a r a l t o g e t h e r . Upogebia c o n s t r u c t s a mud-lined permanent  d w e l l i n g burrow  f o r suspen-  s i o n f e e d i n g and r e s p i r a t i o n purposes, whereas C a l l i a n a s s a b u i l d s an u n l i n e d temporary f e e d i n g burrow  f o r deposit  feeding.  Upogebia i s much more s e n s i t i v e  to the e n v i r o n m e n t a l f a c t o r s o f g r a i n s i z e , exposure and s a l i n i t y C a l l i a n a s s a due l a r g e l y to the .nature and f u n c t i o n o f i t s burrow. shows a d i s t i n c t p r e f e r e n c e f o r muddy s u b s t r a t e s . mud f o r c o n s t r u c t i n g i t s burrow. l i m i t o f the lower amphizone  than Upogebia  I t probably requires  Upogebia does n o t extend above  the upper  because immediately above t h i s l e v e l the maximum  d u r a t i o n o f exposure p r o b a b l y r e s u l t s i n a d u r a t i o n o f a n o x i a l e t h a l t o postmolt Upogebia.  I n c o n t r a s t C a l l i a n a s s a extends up to lower atmozonal  232 e l e v a t i o n s , because o f i t s g r e a t e r t o l e r a n c e i s an a d a p t i o n  probably  c a p a c i t y to t o l e r a t e anoxia. essential for l i f e  i n an u n l i n e d burrow.  Upogebia a l t h o u g h p h y s i o l o g i c a l l y b e t t e r adapted to cope w i t h salinity  Anoxia  reduced  i n f a c t demonstrates lower t o l e r a n c e o f low s a l i n i t y water i n i t s  d i s t r i b u t i o n than C a l l i a n a s s a , probably as a c o n d u i t  because the f u n c t i o n o f i t s burrow  f o r r e s p i r a t i o n and f e e d i n g s u b j e c t s  the shrimp to low s a l i n i t y  s u r f a c e waters, whereas C a l l i a n a s s a i n i t s u n l i n e d burrow used f o r d e p o s i t feeding i s protected  from low s a l i n i t y  s u r f a c e waters by h i g h  i n t e r s t i t i a l waters which a r e f r e e to e n t e r types o f burrow w i t h  salinity  i t s u n l i n e d burrow.  their differring sensitivity  f a c t o r s o f exposure d u r a t i o n and s a l i n i t y should  These two  to the e n v i r o n m e n t a l form a p o w e r f u l t o o l i n  p a l e o e n v i r o n m e n t a l r e c o n s t r u c t i o n s when used i n c o n j u n c t i o n .  Tables  I and  I I summarize the f a c t o r s l i m i t i n g and i n f l u e n c i n g t h a l a s s i n i d e a n shrimp d i s t r i b u t i o n on F r a s e r D e l t a t i d a l Table on  I I I summarizes a l l n i n e  flats. f l o r a l and f a u n a l d i s t r i b u t i o n a l  limits  the F r a s e r D e l t a t i d a l f l a t s which have been found to l i e w i t h i n 15 cm  or l e s s o f an exposure zone boundary o r any o t h e r  extreme c r i t i c a l  level.  argument f o r t h e i r  I t i s only p o s s i b l e to o f f e r a c o n v i n c i n g  tidal  a c a u s a l r e l a t i o n s h i p between these f a u n a l / f l o r a l l i m i t s and extreme  being critical  t i d a l l e v e l s i n the case o f C a l l i a n a s s a and Upogebia because p e r t i n e n t l o g i c a l data a r e o n l y a v a i l a b l e f o r these organisms. so many d i f f e r e n t  f l o r a l and f a u n a l l i m i t s  delta coincide with  extreme c r i t i c a l  r e c o n s i d e r a t i o n o f the t i d e f a c t o r  However, the f a c t  physiothat  i n d i f f e r e n t environments o f the  t i d a l l e v e l s should hypothesis.  a t l e a s t warrant  TABLE I SUMMARY OF ENVIRONMENTAL FACTORS LIMITING THALASSINIDEAN  INTER-CAUSEWAY AREA AND AREA S.E. OF BRUNSWICK PT.  BOUNDARY BAY LIMIT  ELEVATION (Geodetic Datum, m)  LIMITING FACTOR  EXPOSURE ZONE  ELEVATION (Geodetic Datum, m)  Upper l i m i t of C a l l i a n a s s a  +0.9  Near upper l i m i t o f Lower Atmozone  >5 days anoxia due to exposure  Lower l i m i t of C a l l i a n a s s a  -0.6  Lower h a l f of Lower Amphizone  Dense Z. marina  Upper l i m i t of Upogebia  -0.5  Lower Amphizone  Insufficient mud*  0.0  Upper Aquazone  Insufficient mud  <-2.2  Lower l i m i t of Upogebia  -1.3  SHRIMP DISTRIBUTION ON FRASER DELTA TIDAL FLATS  +0.9  -1.8 to  -1.9  EXPOSURE ZONE  LIMITING FACTOR  Lower Atmozone  Presence o f saltmarsh  Near upper l i m i t o f Lower Aquazone  Dense Z. marina  Upper l i m i t of Lower Amphizone  Anoxia due to L e v e l 2 Exposure  Lower Aquazone  Limit • unknown  NORTHERN AND CENTRAL ROBERTS BANK ELEVATION EXPOSURE LIMITING (Geodetic ZONE FACTOR(S) Datum, m) -0.2 to -0.5  <-2A  Lower Amphizone  Brackish marsh and low s a l i n i t y water  Near base of Lower Aquazone  Limit  unknown  NOT PRESENT DUE TO PRESENCE OF LOW SALINITY WATER  Upogebia r e s t r i c t e d to beds o f dense Z. marina where mud contents o f sediment-are higher (>2%) ,  TABLE I I SUMMARY OF EFFECTS OF VARIOUS ENVIRONMENTAL FACTORS ON THALASSINIDEAN  t Callianassa  t Upogebia  t % Mud  t Salinity**  Callianassa Upogebia  ** t  tt  SHRIMP DENSITY  tt  tt  S a l i n i t y i n the range of 0 to 30%„ Positive correlation + Negative Weak p o s i t i v e c o r r e l a t i o n Strong p o s i t i v e c o r r e l a t i o n  correlation  N3  CO OJ  234  TABLE. I l l  Schematic Summary o f A l l F l o r a l and F a u n a l D i s t r i b u t i o n a l L i m i t s on F r a s e r D e l t a T i d a l F l a t s Which L i e W i t h i n .15 cm Or Less o f an Exposure Zone Boundary Or Other Extreme C r i t i c a l T i d a l L e v e l MARINE  TIDAL  FLATS  Boundary Bay  Inter-causeway Area  Lower L i m i t of Saltmarsh Zone  Lower L i m i t o f Saltmarsh Zone  BRACKISH TIDAL  FLATS  Northern & C e n t r a l Roberts Bank  UPPER  ATMOZONE  LOWER ATMOZONE  Upper L i m i t o f C a l l i a n a s s a * * A l g a l Mat Zone Lower L i m i t A b a r e n i c o l a Upper L i m i t  UPPER AMPHIZONE M.S.L.*  Lower L i m i t o f Upper B r a c k i s h Marsh Upper L i m i t o f Z. Americana  Upper L i m i t o f Upogebia  LOWER AMPHIZONE  UPPER  AQUAZONE  Upper L i m i t o f Z. marina LOWER  AQUAZONE  * **  M.S.L = Mean Sea L e v e l Upper l i m i t o f C a l l i a n a s s a l i e s a t l e v e l a t which the maximum d u r a t i o n o f continuous exposure jumps  from 4 to 9 days.  APPENDIX 1 —  SURVEY DATA FOR BOUNDARY BAY (PART 2)  236  Survey Data f o r T r a n s e c t  Location The  s t a r t i n g point dyke.  gate i n t o the  6.49  The  s t a r t i n g p o i n t l i e s on  f i e l d on  the a x i s of the  ( T l ) i s l o c a t e d approximately where 72nd Avenue the  dirt  Its precise  d i t c h , which p a r a l l e l s the west s i d e of a metal s i g n w i t h B.M.  y e l l o w on a red background), which l i e s  at the  location  72nd Avenue, written  corner of the  the  fence  in  facing  dyke.  O r i e n t a t i o n of The  Transect  transect  runs n o r t h / s o u t h  (i.e.,  a continuation  S t a t i o n A l l i e s a t the edge of the s a l t m a r s h and of  t r a c k e n t r a n c e to  the west s i d e of 72nd Avenue.  m from the bench mark (marked by  the  Bay  of S t a r t i n g Point  meets the  i s on  A Boundary  the s t a r t i n g p o i n t  (300  f t ) i n t e r v a l s by  (Tl).  Stations  A l to A22  t a p i n g w i t h a 30.5  m  i s 513.6  (100  85.03 m ± 0.30  m  T2/T4  155.74 m ± 0.43  m  T4/T5  65.55 m ± U.30  m  T5/T6  99.36 m ± 0.30  m  107.89 m ± 0.30  m  T6/A1  m  (± 0.7  m)  were spaced at 91.4 f t ) tape.  s t a t i o n s T l to T6 were determined by s t a d i a s u r v e y i n g T1/T2  of 72nd Avenue).  and  The are  south  m  spacings as  of  follows:  Accuracy E l e v a t i o n d i f f e r e n c e s were measured u s i n g an a l i d a d e which can measure -4 the s i n e of the angle of e l e v a t i o n d i r e c t l y  to ±0.5  a f o r e s i g h t to next the s t a t i o n and b a c k s i g h t  x 10  .  At every s t a t i o n  to the p r e v i o u s - s t a t i o n .were -  o  237 ~> taken.  I f the instrument was p e r f e c t l y l e v e l e d and no e r r o r s were made,  then the f o r e s i g h t a t a g i v e n s t a t i o n would e x a c t l y e q u a l the b a c k s i g h t from the n e x t .  I f the a l i d a d e was n o t i n p e r f e c t adjustment, such  when i t was l e v e l e d i t was i n f a c t t i l t e d ,  that  then t h i s would i n t r o d u c e a  constant s y s t e m a t i c e r r o r between f o r e s i g h t and b a c k s i g h t r e a d i n g s . an e r r o r was d e t e c t e d .  Such  There was a constant d i s c r e p a n c y between f o r e s i g h t > -4  and b a c k s i g h t readings o f about 12 x 10 t i o n i n c r e a s i n g towards observed by  .  P o s i t i v e readings  s t a t i o n ) ' a l w a y s exceeded n e g a t i v e  t h i s c o n s t a n t amount, i n d i c a t i n g t h a t when the instrument  l e v e l i t was i n f a c t t i l t e d  (i.e.,  downwards a t about 0.03°.  eleva-  readings  registered  To overcome t h i s  problem the d i s c r e p a n c y between f o r e s i g h t and b a c k s i g h t r e a d i n g s was h a l v e d to  o b t a i n an e s t i m a t e o f t r u e zero and the f o r e s i g h t r e a d i n g used i n c a l c u -  l a t i o n s of e l e v a t i o n corrected using t h i s estimated the e s t i m a t e d of  By a v e r a g i n g a l l  zeros f o r t r a n s e c t s A and B (67 s t a t i o n s ) a b e t t e r e s t i m a t e  t r u e zero was o b t a i n e d and t h i s was determined  r e g i s t e r e d an e l e v a t i o n w i t h  t o be when -4  s i n e +5.9 ± 0.7 x 10  the t r u e zero o f the instrument of  zero.  d i d not vary w i t h  instrument  .„ T h i s assumes t h a t time and t h a t d e v i a t i o n s  e s t i m a t e d zeros from t h i s v a l u e were due to a c c i d e n t a l e r r o r s .  Carrying  t h i s assumption one s t e p f u r t h e r an e s t i m a t e o f a c c i d e n t a l e r r o r s i n s u r v e y i n g c o u l d be made by d e t e r m i n i n g  the average d e v i a t i o n o f the e s t i m a t e d  zeros from t r u e z e r o , i . e . , : : ' n E I True zero - e s t i m a t e d average e r r o r o f s i n e v a l u e = — N 1  zero I L  where N = 67. -4 T h i s e r r o r was determined to  to be ±0.6 x 10  , which over the s t a t i o n to s t a t i o n  s t a t i o n d i s t a n c e o f 91.4 m i s e q u i v a l e n t t o an e r r o r o f ±5.5 mm. Another p o s s i b l e source o f e r r o r i s i n the measurement o f d i s t a n c e between  stations.  The e f f e c t s o f t h i s e r r o r a r e very s m a l l u n l e s s the e r r o r i s  (238 3 ;  systematic and  (.e.g., tape was  estimating  not  exactly  30.5  a s y s t e m a t i c e r r o r of 0.3  m long).  Assuming the worst  m i n the measurement of  distance  between each s t a t i o n , then t h i s i n t r o d u c e s  an average e l e v a t i o n e r r o r  ±0.35 mm  A.  f o r the average s l o p e  For s t a t i o n s T l to A l s l o p e introducing The  of t r a n s e c t  distances  e r r o r s e s t i m a t e d i n the  accidental errors. i n proportion e r r o r s are  to the  By  the  This e r r o r i s cumulative. •  were determined by  an a c c i d e n t a l e r r o r of ±0.3  m i n slope  t a b l e are  the  sum  distance. of both s y s t e m a t i c  theory of L e a s t Squares a c c i d e n t a l e r r o r s  I n combining s y s t e m a t i c and  a r r i v e at an o v e r a l l e s t i m a t e of e r r o r the worst was the  two  stadia surveying,  square r o o t o f the number of o b s e r v a t i o n s .  cumulative.  sources of e r r o r are  cumulative.  of  and increase  Systematic  accidental errors  to  assumed, namely  that  Table o f Survey Data T r a n s e c t A  _„ „, station  -i4v  Sine of E l e v a t i o n , 1ri Angle (xlO ) H  Estimated Zero f o r „. SSiinnee (xlO *) -1  Corrected Sine f o r . . , _ foresight (xlCT ) k  Elevation Difference , . (m;  B.M.  Geodetic E l e v a t i o n (m)  B.M.  TI  1.524  Tl/B.M.  -266.0  5.25  -271.25  -0.177  TI  T2  T1/T2  120.5* -110.0**  5.25  115.25  0.978  T2  2.679 + 0.011  T4  T2/T4  - 68.0 79.0  5.50  - 73.50  -1.143  T4  1.536 ± 0.020  T5  T4/T5  76.5 - 61.0  7.75  68.75  0.451  T5  1.987 + 0.022  T6  T5/T6  - 80.0 88.5  4.25  - 84.25  -0.838  T6  1.149 + 0.025  Al  T6/A1  -10.0 21.0  5.50  - 15.50  -0.168  Al  0.981 ± 0.026  3.5 11.5  7.50  -  4.00  -0.037  A2  0.945 + 0.028  3.5 17.0  6.75  - 10.25  -0.094  A3  0.850 ± 0.030  8.0 4.0  6.00  2.00  0.018  A4  0.869 ± 0.031  6.5 19.0  6.25  - 12.75  -0.116  A5  0.753 ± 0.031  5.5 5.0  5.25  0.25  0.003  A6  0.756 ± 0.033  8.0 21.0  6.50  - 14.50  -0.131  A7  0.625 + 0.034  -  3.0 14.0  5.50  -  8.50  -0.076  A8  0.549 + 0.035  -  4.0 15.0  5.50  -  9.50  -0.085  A9  0.463 ± 0.037  (6.75; (6.75)  - 24.75 20.25  -0.076 0.125  A9 1/3 A9 1/3  0.387 ± 0.037 0.390 ± 0.037  A1/A2  A2 A3  A2/A3  A4  A3/A4 A4/A5  A5 A6  A5/A6  A7  A6/A7  A8  A7/A8  -  -  -  1.701 ± 0.005  A9  A8/A9  A9 1/3 A9 1/3  A9/A9 1/3 - 18.0 A10/A9 1/3 27.0  A10  A9/A10  14.5 28.0  6.75  - 21.25  -0.195  A10  0.268 + 0.037  All  A10/A11  6.0 19.0  6.50  -12.50  -0.113  All  0.155 + 0.039  * **  foresight backsight  Station  Sine o f E l e v a t i o n Angle ( x l O " ) -  .Estimated Zero f o r Sine (xlO *) -1  A12  A11/A12  A13  A12/A13  A14  A13/A14  A15  A14/A15  A16  A15/A16  A17  A16/A17  A18 A19  -17.0* 31.0** 2.5  10:0  Corrected Sine f o r foresight (xlO *) -1  Elevation Difference (m)  Geodetic E l e v a t i o n (m)  7.00  -24.00  -0.219  A12  -0.064 + 0.040  6.25  -  3.75  -0.034  A13  -0.098 + 0.040  6.00  -0.055  A14  -0.152 + 0.042  -  0.5 11.5  5.50  -  -  4.5 17.5  6.50  -11.00.  -0.101  A15  -0.253 + 0.043  -  7.0 17.5  5.25  -12.25  -0.113  A16  -0.366 + 0.043  -  8.0 18.0  5.00  -13.00  -0.119  A17  -0.485 + 0.045  A17/A18  - 9.5 22.5  6.50  -16.00  -0.146  A18  -0.631 + 0.045  A18/A19  -14.0 25.0  5.25  -19.75  -0.180  A19  -0.811  A20  A19/A20  -14.0 26.0  6.00  -20.00  -0.183  A20  -0.994 + 0.048  A21  A20/A21  2.0 19.5  10.75  -  8.75  -0.079  A21  -1.073 + 0.048  A22  A21/A22  " -°  -19.75  -0.180  A22  -1.253 + 0.049  * **  foresight backsight  9  (10.75)  i  0.046  '24i;Survey Data f o r T r a n s e c t  Location The  B Boundary  Bay  of S t a r t i n g P o i n t s t a r t i n g point  (1) i s l o c a t e d on  96th Avenue meets the dyke.  the south s i d e of the  I t s e x a c t l o c a t i o n i s on  which p a r a l l e l s the western s i d e of 96th Avenue, and w e s t e r n metal dyke gatepost at the end 25.41 end  m  (uncorrected  of 96th Avenue.  The  of 96th Avenue.  The  I t i s on  bench mark i s l o c a t e d j u s t o u t s i d e the western s i d e of the end  runs n o r t h / s o u t h  ( i . e . , a continuation  S t a t i o n B l l i e s at the s o u t h e r n edge of the are spaced at 91.4  m  (300  ft) intervals.  saltmarsh.  the  this  line  the S.E.  the corner  of 96th Avenue.  of 96th Avenue). Stations  B l to  B38  Survey s t a t i o n 2 i s 28.37 m  f o r e l e v a t i o n d i f f e r e n c e ) south of 1,  These d i s t a n c e s  passes through  line  Transect  transect  (uncorrected  the n o r t h / s o u t h  f o r e l e v a t i o n d i f f e r e n c e ) from the bench mark at  of the garden of the house on  O r i e n t a t i o n of  dyke where  and  48.21  m north  of B l .  were taped.  Accuracy The  average a c c i d e n t a l e r r o r i n e l e v a t i o n between s u c c e s s i v e  at 91.-.4 m i n t e r v a l s i s ±5.5 systematic  mm,  as i n the  error'assuming a distance  case of t r a n s e c t A.  e r r o r of 0.3  i s s l i g h t l y lower than t r a n s e c t A at ±0.21 t r a n s e c t B i s l e s s than that of t r a n s e c t A. sum  of s y s t e m a t i c  and  accidental errors.  mm,  average  m between s u c c e s s i v e  because the The  The  stations  stations  average s l o p e  e r r o r s i n the  t a b l e are  of the  . 24 2  Table o f Survey Data T r a n s e c t B  Station  Sine o f E l e v a t i o n Angle (xlO *) -1  Estimated Zero f o r Sine (xlO ") -  Corrected Sine f o r foresight (xlO ) - 4  Elevation Difference (m)  B.M.  Geodetic E l e v a t i o n (m)  B.M.  1.521  2.002  1  3.523 + 0.005  -853.00  -2.420  2  1.103 ± 0.010  4.50  - 12.50  -0.061  Bl  1.042 ± 0.012  2.0 .14.0  6.00  -  8.00  -0.073  B2 .  0.969 + 0.014  0.0 13.0  6.50  -  6.50  -0.058  B3  0.011 ± 0.016  -  2.0 15.5  6.75  -  8.75  -0.079  B4  0.832 ± O.018  -  8.0 22.0  7.00  - 15.00  -U.137  B5  0.695 ± 0.020  -  2.0 13.5  5.74  -  7.75  -0.070  B6  0.625 ± 0.021  -  2.5 15.5  6.50  -  9.00  -0.082  B7  0.543 ± 0.023  -  5.0 17.0  6.00  - 11.00  -0.101  B8  0.442 ± 0.024  -  7.0 20.5  6.75  - 13.75  -0.125  B9  0.317 + 0.025  1  B.M./l  794* -784**  2  1/2  -846 860  Bl  2/B1  B2  B1/B2  B3  B2/B3  B4  B3/B4  B5  B4/B5  B6  B5/B6  B7  B6/B7  B8  B7/B8  B9  B8/B9  BIO  B9/B10  -  1.5 13.5  6.00  -  7.50  -0.070  B10  0.247 ± 0.026  Bll  B10/B11  -  7.0 18.5  5.75  - 12.75  -0.116  Bll  0.131 ± 0.028  B12  B11/B12  -  8.0 20.0  6.00  - 14.00  -0.128  B12  0.0O3 ± 0.029  B13  B12/B13  - 29.0 41.5  6.25  - 35.25  -0.323  B13  -0.320 + 0.030  B14  B13/B14  8.5 4.U  6.25  2.25  0.021  B14  -0.299 ± 0.031  B15 B16 B17  -  8 17  5.00  789.00  7.00  B14/B15  -  4.5 13.5  4.50  -  9.00  -0.082  B15  -0.381 ± 0 . 0 3 2  B15/B16  - 10.0 19.0  4.50  - 14.50  -0.131  B16  -0.512: ± 0.033  B16/B17  -  4.75  - 11.25  -0.104  B17  -0.616 ± 0.033  foresight  6.5 16.0  **  backsight  243  Station  Sine of Elevation Angle (xlO *) -1  Estimated Zero for Sine txlO" )  Corrected Sine for foresight (xlO )  Elevation Difference (m)  5.50  - 6.50  -0.058  B18  -0.674  +  .0.034  5.25  -13.75  -0.125  B19  -0.799  +  U.035  6.50  - 5.00  -0.046  B20  -0.844  u  - 1.0* 12.0**  -4  Geodetic Elevation  B18  B17/B18  Biy  B18/B19  B20  B19/B20  B21  B20/B21  - 7.5 20.0  6.25  -13.75  -0.125  B21  -0.969  +  0.037  B22  B21/B22  11.5 U.5  6.00  5.50  0.049  B22  -0.920  +  0.038  B23  B22/B23  5.5 5.0  5.25  0.25  0.003  B23  -0.017  +  0.039  B24  B23/B24  9.5 3.0  6.25  3.25  0.030  B24.  -0.887  +  0.039  B25  B24/B25  13.0 - 1.5  5.75  7.25  0.067  B25  -0.820  +  u.041  B26  B25/B26  13.5 - 1«5  6.00  7.50  0.067  B26  -0.753  +  0.041  B27  B26/B27  - 3.5 14.5  5.50  - 9.00  -0.082  B27  -0.835  +  0.042  B28  B27/B28  0.0 11.0  5.50  - 5.50  -0.049  B28  -0.884  +  0.042  B29  B28/B29  3.5 11.0  7.25  - 3.75  -0.034  B29  -0.917  +  0.043  B30  B29/B30  1.0 10.0  5.50  - 4.50  -0.040  B30  -0.057  +  0.044  B31  B30/B31  8.U 4.0  6.00  2.00  0.018  B31  -0.939  +  0.045  B32  B31/B32  - 7.5 18.5  5.50  -13.00  -0.119  B32  -1.058  +  0.045  B33  B32/B33  4.5 8.5  6.50  - 2.00  -0.018  B33  -1.076  +  0.046  B34  B33/B34  5.0 6.5  5.75  - 0.75  -U.006  B34  -1.082  B35  B34/B35  0.0 10.0  5.00  - 5.00  -0.046  B35  -1.128  +  0.047  B3b  B35/B36  - 3.0 14.0  5.50  - 8.50  -0.076  B36  -1.204  +  0.048  B37  B36/B37  1.0 10.0  5.50  - 4.50  -0.040  B37  -1.244  +  0.049  B38  B37/B38  - 7.0 19.5  6.25  -13.25  -0.122  B38  -1.365  ±  0.049  foresight  - 8.5 ly.o 1.5 11.5  **  backsight  0.036  0.047  APPENDIX 2 —  FAUNAL DENSITIES AND GRAIN SIZE DATA ON  TRANSECTS A AND B, BOUNDARY BAY (PART 2)  Transect A Station  Batillaria  Nassarius  Al A2 A3 A4 A5 A6 A7 A8 A9 A9 1/3 A10 All A12 A13 A14 A15 A16 A17 A18 A19 A20 A21 A22  P 16 25 31 32 48 40 28 12 51 28 16 18 36 17 6 5 2  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1.5 4.5 1 1 1 1 1  P 0 0 0 0  P = p r e s e n t (<0.5  N.B. :  m~ ) 2  Callianassa &/or Upogebia  0 P P • P P P P 0..5 (C) P P 1 (C) 4 (c) 7 (C) 14 (C) 22 (C) 24 (c; 10 (c/u) 10 (c/u) 44 (c/u) 28 (u) 18 (u, 10 (U) 6 (U)  Mya  Abarenicola  0 P P P P P P P P P 1 0.5 3.5 2.5 0 0 0 0 0 0 0 0 0  0 0 0 0 19 25 134 28 25 133 65 36 20 24 24 9 13 1 P P P P P  Praxillela  0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 40 110 110 260 410 650 320 390  Spio  7000 4400 4400 4400 600 2500 1200 600 600 <600 1900 1900 36000 22000 33000 48000 27000 37000 20000 12000 4000 7000 <600^  CC) = C a l l i a n a s s a o n l y (C/U) = C a l l i a n a s s a and Upogebia (U) = Upogebia only  a l l d e n s i t i e s i n numbers p e r square meter. Spio d e n s i t i e s rounded to n e a r e s t hundred.  (Cont'd  )  Transect B Station  Batillaria  BI B2 B3 B4 B5 B6 B7 B8 B9 BIO Bll B12 B13 B14 B15 B16 B17 B18 B19 B20 B21 B22 B23 B24 B25 B26 B27 B28 B29 B30 B31 B32 B33 B34 B35 B36 B37 B38  1.5 6 7 28 29 57 18 21 13 4.5 7 5 2.5 1.5 1.5 1 0 0 2 4 13 26 32 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0  P = present P.N.D. N.B.:  Nassarius  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 p p  0.5 P 1 2 5 0.5 P P 0.5 1 P P P P P 5 1 0.5 . 0.5 0 0  Callianassa  Abarenicola  0 0 0 P P 3 4 1 7 6 14 15 5 7 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0  (<0.5 m~ )  present but not determined. a l l d e n s i t i e s i n numbers per square meter.  0 0 0 0 20 5 18 15 42 51 61 23 5 31 14 6 3 4.5 0.5 0.5 0.5 P 0.5 0 1 3.5 1.5 5 4.5 P P 1.5 P P 5 P P P  Praxillela,  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0, 3.5 4.5 56 91 73 54 44 12 0 0 0 0 0 0 10 10 10 10 100 100 150 100  Spio  12500 12500 5000 7500 2500 2500 <600 <600 600 600 <600 600 600 <600 <600 1200 P.N.D. P.N.D. P.N.D. P.N.D. P.N.D. P.N.D. P.N.D. 25000 8100 7500 4400 5000 2500 3800 3800 1200 1200 3100 600 <600 <600 <600  247  G r a i n S i z e Data T r a n s e c t s A and B Boundary Station  Graphic Mean  (0)  I n c l . Graphic S t d . Dev. (0)  %  Mud  Al A2: A3: A4 A5 A6 A7 A8 A9 A9 1/3 AlO All A12 A13 A14 A15 A16 A17 A18 A19 A20 A21 A22  3.21 3.15 3.22 3.31 3.26 3.14 2.99 2.90 2.85 2.88 2.78 2.78 2.70 2.75 2.63 2.69 2.69 2.75 2.77 2.88 2.97 2.97 2.77  0.41 0.40 0.43 0.44 0.36 0.36 0.34 0.33 0.32 0.35 0.36 0.38 0.39 0.39 0.40 0.42 0.39 0.43 0.52 0.60 0.55 0.53 0.45  4.20 4.88 5.98 4.70 3.99 4.14 1.97 1.14 1.24 0.92 0.81 2.09 1.32 1.23 0.95 1.49 0.82 2.51 2.65 7.00 6.07 5.70 2.78  BI B2 B3 B4 B5 B6 B7 B8 B9 BIO Bll B12 B13 B14 B15 B16 B17 B18 B19 B20 B21 B22 B23  2.87 3.07 3.20 3.15 3.09 3.10 2.98 2.94 2.87 2.80 2.80 2.67 2.81 2.76 2.71 2.73 2.71 2.71 2.70 2.74 2.73 2.65 2.65  0.50 0.43 0.45 0.40 0.37 0.38 0.33 0.32 0.35 0.34 0.33 0.33 0.37 0.33 0.34 0.34 0.35 0.34 0.33 0.34 0.36 0.36 0.34  3.56 3.86 8.03 4.53 3.84 2.81 1.71 0.87 0.95 0.56 0.78 0.36 1.36 0.45 0.72 0.41 0.46 0.59 0.51 0.79 1.77 0.62 0.37  Station  B24 B25 B26 B27 B28 B29 B30 B31 . B32 B33 B34 B35 B36  G r a  Bay  P * h  c  (0;  ^  e a n  Incl.  Graphic  S t d . Dev.  (0)  X  Mud  2.60 2.59 2.50 2.55 2.53 2.52 2.48 2.43 2.42 2.41 2.38  0.33 0.31 0.31 0.33 0.32 0.32 0.31 0.32 0.33 0.29 0.32  0.25 0.56 0.26 0.63 0.31 0.44 0.26 0.28 0.25 0.21 0.14  2.47  0.32  0.31  —  —  7.48.  APPENDIX 3 ~  SURVEY DATA FOR STATIONS  ON THE INTER-CAUSEWAY  TIDAL FLAT (PART 4A)  249  Survey Data f o r T r a n s e c t s  Transect  A, B, C and D on the Inter-Causeway T i d a l  Flat  A  Transect A p a r a l l e l s  the Tsawwassen f e r r y  150 ± 1 m from the r a i s e d concrete  t e r m i n a l causeway and l i e s  edge o f Highway 17.  the s a n d f l a t about 10 m from the edge of the cobbles were taped  a t 100 m i n t e r v a l s .  S t a t i o n A l l i e s on  on the shore.  Stations  S t a t i o n numbers i n c r e a s e seawards.  M e t h o d s — E l e v a t i o n s were determined by l e v e l i n g from bench mark ( F i g . 2 i n back cover) w i t h fourth station.  a T2 t r a n s i t .  At each set-up  The instrument  'A'  was s e t up a t every  a b a c k s i g h t was taken to the p r e c e d i n g  two  s t a t i o n s and a f o r e s i g h t to the f o l l o w i n g two s t a t i o n s ( i . e . , maximum s i g h t i n g d i s t a n c e 200 m). spike,  and  f l u s h with  The s t a d i a r o d was mounted on a 0.5 m wooden  : pushed i n t o the s u b s t r a t e a t each s t a t i o n u n t i l i t s base was the s u b s t r a t e , a n d  h e l d v e r t i c a l by the rodman.  This eliminated  e r r o r s due to the rod s i n k i n g i n t o the s u b s t r a t e w h i l e b e i n g h e l d , and by simply  r o t a t i n g i t on i t s a x i s the s t a d i a r o d could be t i e d i n to the next  set-up  o f the t r a n s i t , by b a c k s i g h t i n g .  on the s t a d i a rod c o u l d be read s i g h t i n g d i s t a n c e employed. flipping  The i n t e r s e c t i o n o f the c r o s s h a i r  to an a c c u r a c y  o f ±5 mm over the 200 m  Readings were c o n s t a n t l y double checked by  the t e l e s c o p e through 180°.  T h i s e l i m i n a t e s the p o s s i b i l i t y o f  i n t r o d u c i n g an e r r o r due to i n c o r r e c t l e v e l i n g . t h e r e f o r e , i s an a c c i d e n t a l e r r o r of ±5 mm.  The e s t i m a t e d  By the theory  error,  of l e a s t  squares  t h i s e r r o r i n c r e a s e s i n p r o p o r t i o n to the square r o o t of the number o f observ a t i o n s and t h i s i s how the e r r o r s were e s t i m a t e d of data.  The same s u r v e y i n g  techniques  i n the f o l l o w i n g t a b l e s  were used from t r a n s e c t s B, C and D.  •250 Transect B T r a n s e c t B s t a r t s from the promontory immediately breach i n the dyke.  It parallels  s o u t h e a s t of the  t r a n s e c t A at a d i s t a n c e of 1 km  (±3  S t a t i o n B l l i e s 57 m from the edge of the marsh, which forms a c l i f f 70 cm h i g h .  m).  about  S t a t i o n numbers i n c r e a s e seawards.  TransectvC T r a n s e c t C i s l o c a t e d 258 m from the s o u t h e a s t e r n edge of the causeway r o a d , and p a r a l l e l s of  the dyke.  Transect  the causeway.  S t a t i o n C l i s l o c a t e d 100 m from the base  S t a t i o n numbers i n c r e a s e seawards.  D  T r a n s e c t D s t a r t s a t A2 and ends a t B7. i s a d j a c e n t to  DI i s a d j a c e n t to A2 and  D9  B7.  Transect E T r a n s e c t E s t a r t s at A l l and ends a t B16. i s a d j a c e n t to  Zone/Saltmarsh  e l e v a t i o n of the upper l i m i t  Zone Boundary of the a l g a l mat  zone was  determined  at seven p o i n t s a l o n g the p e r i m e t e r of the marsh between t r a n s e c t s C and S t a t i o n 1 l i e s next  to B.M.  going towards t r a n s e c t B. zone was marsh.  determined The  E9  B16.  E l e v a t i o n of A l g a l Mat The  E l i s a d j a c e n t to A l l and  '„C'  B.  and s t a t i o n s were c o n s e c u t i v e l y numbered  The e l e v a t i o n o f the upper l i m i t  on the t i d a l f l a t immediately  e l e v a t i o n o f the lower l i m i t  of the .algal  mat  a d j a c e n t to the edge of the  of the s a l t m a r s h s u r f a c e was  deter-  mined on the tops of s a l t m a r s h clumps a t the edge of the s a l t m a r s h a t s t a t i o n s 1 and  7.  Bench Marks The e l e v a t i o n s and  l o c a t i o n s of bench marks were o b t a i n e d from  the  -251; municipal engineer of D e l t a M u n i c i p a l i t y . f o r d y k i n g purposes.  Bench mark'A'has r e f e r e n c e number 66.  b l o c k w i t h a m e t a l p l a t e s e t on top w i t h stamped on i t . Highway 17 and  'Legal Survey  the g r a v e l road p a r a l l e l l i n g  British  marsh next to a wooden p o s t .  Hydro s t a t i o n .  south-  Bench mark'B'has r e f e r e n c e m from the edge o f the  I t l i e s about 100 m s o u t h e a s t of a major b r e a c h  Bench mark'c'has r e f e r e n c e number 74.  It i s a n a i l driven  h o r i z o n t a l l y i n t o the base of a t e l e g r a p h p o l e about 0.5 I t i s marked w i t h f l a g g i n g tape. encountered  Columbia'  the causeway about 100 m  I t i s an i r o n p i n , and l i e s about 0.3  i n the dyke.  I t i s a concrete  I t marks the c o r n e r o f a D i s t r i c t L o t and l i e s between  west of the fence o f the B.C. number 70.  The bench marks were e s t a b l i s h e d  The  m above ground  level.  t e l e g r a p h p o l e i s the t w e l t h p o l e  w a l k i n g s o u t h e a s t from the dyke gate a t the C o a l p o r t causeway.  The n a i l i s on the seaward s i d e o f the p o l e .  Independent Check of Survey The  survey data was  Data  i n d e p e n d e n t l y checked by comparing observed  h e i g h t s f o r t e n low waters a t the Tsawwassen f e r r y t e r m i n a l t i d a l  gauge w i t h  the observed h e i g h t of the w a t e r l i n e on each t r a n s e c t a t the time of tide.  The  l o c a t i o n of the w a t e r l i n e between surveyed  to the n e a r e s t 10 m and i t s e l e v a t i o n determined between the known e l e v a t i o n s o f the s t a t i o n s . f o l l o w s the t a b l e s o f survey  data.  s t a t i o n s was  by l i n e a r  The  t a b l e of  tidal  low  estimated  interpolation comparisons,  252  Table of Station Elevations on the Inter-Causeway Tidal Flat  Station  B.M. Al A2 A3 A4 A5 A6 A7 A8 A9 A10 All A12 A13 A14 A15 A16  Station  D2 D4 D6 D8  Transect A Elevation (Geodetic Datum, m) 2.728 0.140 ± -0.062 ± -0.277 ± -0.492 ± -0.722 ± -0.902 ± -1.032 ± -1.192 ± -1.322 ± -1.452 ± -1.597 ± -1.732 ± -1.807 ± -1.907 ± -2.047 ± -2.182 ±  0.005 0.005 0.005 0.007 0.008 0.009 0.009 0.010 0.010 0.011 0.011 0.012 0.012 0.013 0.013 0.014  Transect D Elevation (Geodetic Datum, m; -0.266 + -0.376 ± -0.364 i -0.364 i  0.011 0.010 0.009 0.007  Station  B.M. Bl B2 B3 B4 B5 B6 B7 B8 B9 B10 Bll B12 B13 B14 B15 B16 B17 B18 B19 B20 B21  Station  1 2 3 4 5 6 7  Transect B Elevation (Geodetic Datum, m) 1.594 0.433 ± 0.396 ± 0.256 ± 0.081 ± -0.059 ± -0.224 ± -0.389 + -0.519 ± -0.669 ± -0.839 ± -0.954 ± -1.024 ± -1.149 ± -1.264 ± -1.379 + -1.469 ± -1.544 ± -1.719 ± -1.874 ± -1.889 ± -2.004 ±  0.002 0.005 0.005 0.006 0.007 0.008 0.009 0.009 0.010 0.010 0.010 0.011 0.012 0.012 0.013 0.013 0.014 0.014 0.015 0.015 0.016  Upper Limit of Al(*al Mat Zone Elevation (Geodetic Datum, m) 0.916 0.893 0.823 0.893 0.926 0.926 0.826  ± ± ± ± ± ± ±  0.005 0.007 0.007 0.007 0.007 0.009 0.009  Station  B.M. Cl C2 C3 C4 C5 C6 C7 C8 C9 C10 Cll, C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29  Station  1 7  Transect C Elevation (Geodetic Datum, m) 3.266 0.536 ± 0.006 0.416 ±0.007 0.426 ± 0.008 0.376 ± 0.009 0.371 ± 0.009 0.251 ± 0.010 0.096 ± 0.010 -0.009 ± 0.011 -0.089 + 0.011 -0.189 ± 0.012 -0.294 ± 0.012 -0.404 ± 0.013 -0.469 ±0.013 -0.514 ± 0.014 -0.579 ± 0.014 -0.689 ± 0.015 -0.774 + 0.015 -0.889 + 0.016 -0.974 ± 0.016 -1.074 ± 0.017 -1.189 ± 0.017 -1.294 ± 0.017 -1.409 ± 0.017 -1.499 ± 0.018 -1.559 ± 0.018 -1.759 ± 0.019 -1.782 ± 0.019 -1.892 ±0.019 -1.987 ± 0.019 Lower Limit of Saltmarsh Surface Elevation (Geodetic Datum, m) 1.066 ± 0.005 1.071 + 0.009  Comparison o f Survey Data w i t h Observed T i d a l Data at the Tsawwassen F e r r y T e r m i n a l T i d a l Gauge Time Date  (P.S.T.J  Sept. 22/77  0655  Sept. 24/77  0856  II  II  II  II II  Sept. 26/77  1036  Oct. 2/77 Oct. 31/77  1451 1456  Jul.  1413  n  II  24/78 If It  II  II II  J u l . 25/78  1501  Jul.  1800  II II  28/78 II  Aug. Aug.  6/78 7/78  II II  II  1248 1311  Observed Low Water *Chart Datum (m) 1.42 1.42 1.56 1.56 1.56 1.78 1.78 2.90 3.24 1.55 1.55 1.55 2.03 2.03 2.03 3.19 3.19 1.26 1.44  (LLW) ( ( ( (  " ) " ) " ) " )  c " )  ( " ) (HLW) ( " ) (LLW) ( " ) ( " ) ( " ) ( " ) ( " ) (HLW) ( " ) (LLW) ( " )  P o s i t i o n of Waterline  Surveyed E l e v a t i o n '''Chart Datum (m)  Discrepancy (cm)  A11.0 C24.5 A10.0 B16.25 C23.75 A 8.2 C20.9 C 8.0 C 5.3  1.358 1.425 1.503 1.466 1.477 1.737 1.776 2.945 3.289  + + +  6.2 0.5 5.7 9.4 8.3 4.3 0.4 4.5 4.9  A 9.5 B15.25 C23.5 A 6.5 B11.7 C18.6 B 3.0 C 5.5 B17.5 C24.5  1.568 1.552 1.500 1.988 1.951 2.014 3.210 3.265 1.322 1.425  + + + + + -  1.8 0.2 5.0 4.2 7.9 1.6 2.0 7.5 6.2 1.5  Average  Discrepancy  ± 4.3  * Tsawwassen Chart Datum = - 2.954 m Geodetic Datum P.S.T. = P a c i f i c Standard Time Note: The w a t e r l i n e was observed f o r one hour around the time o f low water and i t s lowest p o s i t i o n r e c o r d e d . Wave a c t i o n was n e g l i g i b l e a t the time o f low t i d e .  APPENDIX 4 —  GRAIN SIZE AND THALASSINIDEAN SHRIMP DENSITY DATA  FOR STATIONS ON THE INTER-CAUSEWAY TIDAL FLAT (PART 4 A )  .255"  Grain size and thalassinidean shrimp density data for Stations on Inter-Causeway Tidal Flat _^ ^. Station  Median (0)  „. , Upogebia „ A Mud ,, — -2, (burrow openings m )  Al A2 A3 A4 A5 A6 A7 A8 A9 A10 All A12 A13 A14 A15 A16  3.18 3.61 3.80 3.94 3.81 3.99 4.04 4.02 4.06 4.15 3.85 4.06 3.65 3.36 3.59 3.26  20.43 38.95 43.33 47.17 44.19 49.51 50.95 50.23 51.71 53.53 47.27 51.12 43.33 33.16 44.13 23.74  Bl B2 B3 B4 B5 B6 B7 B8 B9 BIO Bll B12 B13 B14 B15 B16 B17 B18 B19 B20 B21  3.88 3.75 3.45 3.34 3.30 3.30 3.30 3.24 3.24 3.23 3.26 3.08 2.98 3.02 3.17 3.19 3.17 3.07 3.05 3.03 3.02  44.80 38.98 12.31 11.78 9.93 10.53 13.83 10.99 10.58 10.16 12.49 6.64 6.14 9.90 13.81 7.47 17.07 6.96 8.32 12.82 12.10  Cl C2 C3 C4 C5 C6 C7 C8 C9 CIO  »4.00 »4.00 >4.00 3.40 3.38 3.28 3.25 3.17 3.15 3.07  r  91.84 88.09 65.49 19.18 18.27 9.39 11.58 8.83 . 8.79 7.62  g  0 15 28 4 82 29 81 60 114 32 8 9 0 1 10 0 0 0 0 0 0 0 5. ' 4 10 5 0 6 1 0 7 0 4 2 0 2 0 0 0 0 0 0 0 0 0 0 3  Callianassa _ : -2. (burrow openings m ;  0 3 11 29 44 80 67 26 55 34 14 9 14 4 3 2  70 38 95 56 35 59 30 18 15 10 21 24 10 31 7 9  90 36 113 57 76 17 24 30 22 12 15 15 24 51 8 14  0 0 0 0 0 0 0 3 4 8 0 22 6 7 9 8 0 4 1 6 0  1 1 10 20 32 55 49 36 53 45 51 83 82 112 97 12 108 116 67 0 0  0 1 14 30 12 45 53 46 60 42 49 115 128 111 106 18 72 120 74 2 0  0 0 0 0 0 0 0 0 0 0  0 0 0 2 0 2 5 . 5 4 5  0 0 0 0 0 2 7 6 10 6  256  „ Station  Median (V)  Cll C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29  3.02 2.98 2.92 2.90 2.94 2.89 2.92 2.90 2.88 2.90 2.88 2.82 2.85 2.88 2.75 2.76 2.91 2.86 2.93  7.51 7.03 5.90 6.27 11.05 8.22 9.24 8.75 8.65 9.86 8.65 8.90 12.76 10.99 7.32 8.66 20.74 15.78 25.78  8 13 2 10 6 0 4 7 6 7 9 0 1 8 0 0 0 0 0  7 7 3 12 10 4 7 6 4 2 24 5 4 0 0 0 0 0 0  9 8 16 6 23 43 63 68 84 86 123 96 133 95 22 13 2 0 0  12 18 23 14 26 62 70 87 100 101 84 107 125 82 55 11 0 0 0  DI D2 D3 D4 D5 D6 D7 D8 D9  3.46 3.46 3.44 3.41 3.36 3.27 3.32 3.26 3.26  29.74 27.16 25.94 22.16 15.41 10.29 13.34 8.67 8.78  2 16 22 8 0 0 0 0 0  2 4 18 18 0 0 0 0 0  180 142 92 62 104 106 64 62 42  164 144 120 38 94 96 102 50 76  El E2 E3 E4 E5 E6 E7 E8 E9  4.05 3.75 3.37 3.38 3.34 3.30 3.25 3.13 3.10  51.07 46.06 30.41 29.56 25.30 20.40 19.18 11.21 10.64  22 6 18 26 10 2 18 4 4  20 12 12 10 6 10 4 8 0  8 6 20 22 48 44 28 44 32  20 4 22 30 28 44 20 42 46  *CP12 *CP18 *CP24  2.48 2.57 2.82  7.79 4.55 8.40  **FT4 **FT8 **FT11  3.41 2.65 2.92  38.19 10.48 13.13  c >  f J  *  **  L  Mud  Upogebia _ —r— -2. (burrow openings m ) r  p  Callianassa „ -2. (burrow openings tn )  '  0 0 0  10 83 172  0 2.5 3  70 446 354  CP12 i s i n 'causeway zone' next to Coalport causeway adjacent to C12. CP18 i s i n 'causeway zone' next to Coalport causeway adjacent to C18. CP24 i s i n 'causeway zone' next to Coalport causeway adjacent to C24. FT4 i s i n 'causeway zone' next to ferry causeway adjacent to A4. FT8 i s i n 'causeway zone' next to ferry causeway adjacent to A8. FT11 i s - i n .'causeway zone' next to ferry causeway adjacent to A l l .  Note:  There are two thalassinidean burrow density readings for each station. Every 4 of the 8 quadrats (0.25 m ) taken at each station were summed at the time of data collection. 2  APPENDIX 5 —  SUPPLEMENTAL INFORMATION  REGARDING  SURFACE SUBSTRATE SALINITY AND SUBSTRATE SALINITY PROFILES ON INTER-CAUSEWAY  TIDAL FLAT, ROBERTS BANK (PART 4A)  258  L  I  Apparatus-used to take s a l i n i t y p r o f i l e s o f the sediment column. A metal p l u g a t the end o f each tube, h e l d i n p o s i t i o n by n y l o n l i n e under t e n s i o n , prevents"water f r o m ' e h t e r i n g the sampling tubeseas the apparatus i s pushed i n t o "the s u b s t r a t e . "A metal r o d i s then pushed i n t o each l u b e t o r e l e a s e the p l u g and a l l o w i n t e r s t i t i a l waters to flow i n a t the r e q u i r e d sampling depth. Water samples were drawn o f f w i t h a g l a s s tube and s a l i n i t y determined d i r e c t l y w i t h a r e f ractometer. — —  , 259  Sampling  Lagend -28-  Contour of substrate  • Jio  Transact salinity  nical  contouring.  station  salinity  with  indicated  %°  %<  substrate  Dates  A l - All  JULY  A/Bl - A / B 9  JULY . 6 . 1 9 7 7  5. 1 9 7 7  81-614  JULY  6.1977  C1-C17  JULY  7 1977 ;  260  Al  A l l JUL. 1 SALINITY %o  0  o  10 20  _l  B  30  l_  I  50J  50-  A3  A4  5  0  0  J  I  E a  .  40-1 50  Ag  50  50 A?  JUL. 5  0  10 20  10 20  30  30  50  50  50  30  B3  t  10  30 /  10-1  B9  JUL. 6  V  20  20  JUL. 6  SALINITY  SALINITY %o  %o  10 20  30  10-  40-|  0  20  10  0-  40-|  JUL.  °/oo  I  40-1  SALINITY I  SALINITY  %o  20-|  BI  30  30  AlO JUL. S  JUL. 5  SALINITY  %o  I 20H z S 30' a  %o .  40-  0  All JUL. S  I  40-|  I  I  30  -J  30  7oo  20  J  30  0  0-  I  10  30  30  SALINITY  30  10 20  l 20x £ a 30-  20  10 20  .,  30  JUL. 5  SALINITY  I 20-  20-  SALINITY  I  .6  JUL. S  SALINITY % o  20-1  10  0  I  J  10-  10-  I  10 20  %O  K> 20  40  10-  1 50  J  SALINITY  AS 7oo  30  30-,  50  5  10  20  JUL.  0  0  i  AT  JUL.  SALINITY  %o  20  .« 20  50  jyi. 5  30  0  Duplicate.  40  SALINITY %o  10 20  /  | 30-)  10  io H  ii  S 20  30-  30