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Studies of the bivalve, Macoma balthica (L.) on a mudflat receiving sewage effluent and on an unpolluted… McGreer, Eric Rae 1979

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STUDIES OF THE BIVALVE, Macoma balthica  (L.)  ON A MUDFLAT RECEIVING SEWAGE EFFLUENT AND ON AN UNPOLLUTED MUDFLAT, FRASER'RIVER ESTUARY,  BRITISH-COLUMBIA  by  B.Sc,  ERIC RAE McGREER Trent U n i v e r s i t y ,  1971  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  xn THE FACULTY OF GRADUATE STUDIES I n s t i t u t e of 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 s t a n d a r d s  THE,UNIVERSITY OF BRITISH COLUMBIA F e b r u a r y , 1979 • (c) E r i c Rae McGreer,- 1979  In p r e s e n t i n g an  advanced  the I  Library  further  for  this  thesis  degree shall  agree  scholarly  in p a r t i a l  fulfilment  o f the requirements  at the U n i v e r s i t y  of B r i t i s h  Columbia,  make that  by  his representatives.  of  this  written  It  for financial  of  University  OCEANOGRAPHY of British  FF.RKTTAKY  Ifi.  1 Q7Q  Columbia  copying  of this  thesis  by t h e Head o f my D e p a r t m e n t  is understood gain  I agree tha  f o r r e f e r e n c e and s t u d y .  for extensive  may be g r a n t e d  2075 Wesbrook P l a c e Vancouver, Canada V 6 T 1WS  Date  available  permission.  Department The  freely  permission  purposes  thesis  it  shall  f  that  copying  n o t be a l l o w e d  or  or  publication  w i t h o u t my  ii  ABSTRACT' An  investigation  to determine the  factors  responsible for  d i s t r i b u t i o n of a p o p u l a t i o n of Maaoma balthica receiving  sewage e f f l u e n t was  of B r i t i s h Columbia. previous studies invertebrate low  The  t o be  community.  l e v e l s of d i s s o l v e d  t o x i c i t y due  c a r r i e d out  factors  They i n c l u d e d  The  which a f f e c t e d clams.  was  the  the  s e t t l i n g and  s i z e , and  by  macro-  the  n o n - t o x i c to the 7 day  degree of c o n t a m i n a t i o n of  contaminated sediments and  salinity,  in  situ  laboratory bioassays.  distribution  the  substrate  l a r v a l and  were c o n s i d e r e d to be " •-  dissolved  chlorinated  clam i n  r e s p o n s i b l e f o r the  s u r v i v a l of  e f f e c t s of m e t a l  s a t i s f a c t o r i l y explain  Heavy m e t a l s o c c u r r e d i n h i g h c o n c e n t r a t i o n s i n  controlling factor.  estuary  salinity,  Both u n c h l o r i n a t e d and  these r e s u l t s were c o n f i r m e d by  balthica  the  study showed t h a t  s i z e d i d not  balthica.  f a c t o r which appeared to be  of M.  reduced  substrate grain  sewage e f f l u e n t were shown to be t e s t s , and  Fraser River  oxygen, e f f l u e n t t o x i c i t y ,  sediment g r a i n  d i s t r i b u t i o n of M.  a mudflat  examined were those suggested  contaminated sediments. R e s u l t s of the  the  i n the  on  c o n t r o l l i n g the d i s t r i b u t i o n o f  to c h l o r i n a t i o n ,  oxygen l e v e l s and  (L.)  the  juvenile the  the most  likely  iii  S u b l e t h a l e f f e c t s o f e s t u a r i n e sediments c o n t a i n i n g h i g h l e v e l s of heavy m e t a l s were a l s o s t u d i e d u s i n g  <  Maooma bdtthica.  in a l l  contaminated  Burrowing b e h a v i o u r was i n h i b i t e d  sediments as demonstrated  by t h e time r e q u i r e d . .  -i  f o r 50% o f t h e p o p u l a t i o n t o burrow (ET50), which ranged from 0.17 h i n the c o n t r o l to 4.8 h i n the most contaminated comparison  substrate.  A  of l i n e a r r e g r e s s i o n s of t h e c o n c e n t r a t i o n s of i n d i v i d u a l  m e t a l s i n t h e sediments v e r s u s t h e burrowing r e s p o n s e times showed the r e g r e s s i o n s f o r mercury and <0.001 r e s p e c t i v e l y ) . by burrowed M. balthioa significant  and cadmium t o be s i g n i f i c a n t An a c t i v e t h r e s h o l d a v o i d a n c e  was a l s o demonstrated  as clams  (p <0.05) a v o i d a n c e o f the sediment  highest metal l e v e l s .  containing the  Both b e h a v i o u r a l responses were c o n s i d e r e d  The e c o l o g y of Macoma balthica  from an u n p o l l u t e d  m u d f l a t i n " t h e F r a s e r R i v e r e s t u a r y was s t u d i e d (April,  ind i v i d u a l s  1977 - March, 1978). (1830 m" )  throughout the y e a r .  2  response  showed a  u s e f u l s u b l e t h a l t e s t s to a s s e s s t h e impact of p o l l u t e d  year  (p <0.05  sediments. -  f o r one  ~ •  The maximum number of  occurred i n A p r i l ,  then s t e a d i l y  declined  Spawning o c c u r r e d between mid-June and l a t e  J u l y but r e c r u i t m e n t was slow and p r o l o n g e d .  Peak s p a t f a l l (age  0+ i n d i v i d u a l s ) d i d n o t occur u n t i l the f o l l o w i n g March when a maximum d e n s i t y of o n l y 410 m  -2  f o r newly s e t t l e d  spat was o b s e r v e d .  •  The o l d e s t animals found were 5+ y e a r s o f age-.  Maximum growth  took p l a c e from A p r i l through J u l y and had ceased by August.  The  growth r a t e measured was one o f t h e h i g h e s t r e c o r d e d f o r any M. balthica water  population.  A direct  r e l a t i o n s h i p between the h i g h  temperatures, and t h e f a s t growth r a t e as w e l l as reduced  l o n g e v i t y was apparent.  A r e g r e s s i o n o f body weight  h e i g h t was used t o c a l c u l a t e a c o n d i t i o n f a c t o r  on s h e l l  (CF) which  reached  i t s h i g h e s t v a l u e d u r i n g growth and i t s lowest v a l u e immediately a f t e r spawning. wt  m . -2  The mean annual biomass measured was 2.96 g d r y  V  PREFACE The  t h e s i s p r e s e n t a t i o n c o n s i s t s o f t h r e e m a n u s c r i p t s which have been  f o r p u b l i c a t i o n . : The'manuscripts - d e s c r i b e r e s e a r c h c a r r i e d 1  b i v a l v e , Macoma balthica The  first  out on t h e e s t u a r i n e  (L.) i n • t h e ' 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.  and second m a n u s c r i p t s d e s c r i b e t h e r e s u l t s o f f i e l d and  l a b o r a t o r y s t u d i e s of t h e f a c t o r s a f f e c t i n g t h e d i s t r i b u t i o n of •M. balthica The  on Sturgeon Bank, a m u d f l a t  t h i r d manuscript d e s c r i b e s  of M. balthica  r e c e i v i n g sewage e f f l u e n t .  the seasonal  growth and r e p r o d u c t i o n  on Roberts Bank, an u n p o l l u t e d  River estuary.  a r e a of t h e F r a s e r  The r a t i o n a l e f o r t h e approach f o l l o w e d  i n the  r e s e a r c h i s g i v e n below. Previous  e c o l o g i c a l surveys  on Sturgeon Bank i n t h e v i c i n i t y  of t h e Iona I s l a n d sewage treatment p l a n t have shown changes i n t h e d i s t r i b u t i o n p a t t e r n of the b e n t h i c  fauna due t o t h e sewage e f f l u e n t  (Greater Vancouver Sewerage and D r a i n a g e D i s t r i c t , O t t e and L e v i n g s ,  1975).  These surveys  suggested  of d i s s o l v e d oxygen, t h e i n p u t of sewage d e r i v e d effluent  1973, 1975, 1977; t h a t low l e v e l s  organic  matter,  t o x i c i t y , c h l o r i n a t i o n , and e f f l u e n t d e r i v e d heavy m e t a l s  i n t h e sediments, s i n g l y or i n c o m b i n a t i o n , might be 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 of t h e b e n t h i c M. balthica  was c l a s s i f i e d  invertebrates.  as an i n d i c a t o r s p e c i e s , and one f e a t u r e  of i t s d i s t r i b u t i o n was an absence i n t h e a r e a a d j a c e n t sewage o u t f a l l .  F i s h e r i e s & Marine S e r v i c e  t o the  (1976) t e s t e d t h e  J  submitted  t o x i c i t y of the c h l o r i n a t e d  sewage'effluent  organisms i n c l u d i n g M. balthiaa.  in situ  t o a number o f  Organisms were exposed i n a  s e r i e s o f f l o a t i n g cages l o c a t e d a t v a r i o u s s i t e s i n t h e Iona treatment  p l a n t sewage channel  M. balthiaa  (see F i g . 1, p. 3 9 ) .  Survival of  was low r a n g i n g from 100% m o r t a l i t y a t the o u t f a l l ,  to 37% a t s i t e c, mid way a l o n g t h e c h a n n e l , a f t e r  96 h  exposure.  Deaths were a l s o r e c o r d e d as f a r away as s i t e E, a t the seaward end o f t h e Iona j e t t y effluent channel.  ( F i g . 1, p. 3 9 ) .  These d a t a p o i n t e d t o  t o x i c i t y as a major c o n t r o l l i n g f a c t o r w i t h i n t h e sewage T h i s was the o n l y e x p e r i m e n t a l study which had been  undertaken,  and no i n f o r m a t i o n was d e r i v e d f o r t h e m u d f l a t  proper.  C l e a r l y , an e x p e r i m e n t a l study t o a s s e s s more e x t e n s i v e l y which f a c t o r s a s s o c i a t e d w i t h the sewage e f f l u e n t were c o n t r o l l i n g the d i s t r i b u t i o n o f the b e n t h i c fauna was r e q u i r e d . would a l s o p r o v i d e a b e t t e r u n d e r s t a n d i n g of t h i s p o l l u t e d a r e a on Sturgeon as a r e p r e s e n t a t i v e organism species,  Bank.  Such a s t u d y  of t h e b e n t h i c M. balthiaa  ecology  was chosen  because of i t s s t a t u s as an i n d i c a t o r  the a v a i l a b i l i t y o f l i t e r a t u r e on i t s t o l e r a n c e t o  environmental  v a r i a b l e s and i t s s u i t a b i l i t y as an e s t u a r i n e ,  bioassay t e s t animal.  Because o f the r e l a t i v e l y broad  of r e f e r e n c e , the study was designed  :  to be e x p l o r a t o r y i n n a t u r e  w i t h emphasis on the o b s e r v a t i o n o f responses of t e s t c o n d i t i o n s .  frame  t o a wide  The approach combined sampling  variety  i n the f i e l d ,  vii  l a b o r a t o r y and in situ  experiments  l i t e r a t u r e on the p h y s i o l o g y and  and  the use  of a v a i l a b l e  e c o l o g y of the t e s t  s p e c i e s as  w e l l as i n f o r m a t i o n from p r e v i o u s s t u d i e s . The  aim of t h e t h e s i s was  t o a s s e s s a number o f  factors  u s i n g the methods d e s c r i b e d above and  t o i d e n t i f y the f a c t o r  f a c t o r s which were the most important  i n determining  d i s t r i b u t i o n of M. effluent.  The  single factor  balthica  study was  or  the  i n the a r e a a f f e c t e d by the sewage not i n t e n d e d to be d e f i n i t i v e f o r any  (eg. e f f l u e n t  t o x i c i t y ) , but r a t h e r an overview  the r e l a t i o n s h i p of each f a c t o r t o the o t h e r s i n t h e i r  ability  to  two  e x p l a i n the d i s t r i b u t i o n of M. balthica.  manuscripts  i n the t h e s i s a c h i e v e d  The  first  these aims and have  of  identified  areas where f u r t h e r r e s e a r c h i s r e q u i r e d . A twelve month sampling in A p r i l  of 1977  i n an " u n p o l l u t e d " area^Monthly  to determine  the d e n s i t y , biomass, age  depth d i s t r i b u t i o n , growth and  in this thesis.  of M. balthica 1969,  1971;  Bank  Although  i n the t h i r d  D u n n h i l l and  Ellis,  work i s the most comprehensive to d a t e and Fraser River estuary.  composition, balthica.  manuscript  t h e r e have been o t h e r s t u d i e s  on the P a c i f i c Coast of N o r t h America N i c h o l s , 1977;  samples  r e p r o d u c t i v e s t a t u s of M.  The r e s u l t s of t h i s study a r e p r e s e n t e d presented  s t a r t e d on R o b e r t s  t o o b t a i n b a s e l i n e i n f o r m a t i o n on a s p e c t s of the  ecology of M. balthica were c o l l e c t e d  program was  (Vassallo,  1969), the p r e s e n t  the f i r s t  from  the  viii  TABLE OF CONTENTS  Page  ABSTRACT.  i i  PREFACE  v  LIST OF TABLES.  x  LIST OF FIGURES  x i i  ACKNOWLEDGEMENTS  xiv  FACTORS AFFECTING THE DISTRIBUTION OF THE BIVALVE, Macoma balthiaa  (L.) ON A MUDFLAT RECEIVING SEWAGE  EFFLUENT, FRASER.RIVER  ESTUARY, BRITISH COLUMBIA  . . . .  INTRODUCTION Description  1 -2  o f t h e study a r e a  3  METHODS  5  F i e l d Methods  . .  L a b o r a t o r y Procedures  .  5 7  RESULTS  11  Sediments  11  D e n s i t y , Biomass and C o n d i t i o n F a c t o r of M. balthiaa-  •  13  Age S t r u c t u r e of M. balthiaa  15  Bioaccumulation  16  i n M. balthiaa  T o x i c i t y Bioassays DISCUSSION  17 19  ix i  Page SUBLETHAL EFFECTS OF HEAVY METAL  CONTAMINATED  SEDIMENTS ON THE BIVALVE Macoma balthica INTRODUCTION  .•  METHODS  44 .45  .  '.  RESULTS. Burrowing  (L.). . . . . . .  46 . .'  48  Behaviour  48  Avoidance Behaviour  49  DISCUSSION  50  GROWTH AND REPRODUCTION OF Macoma balthica  (L.) ON  A MUDFLAT IN THE FRASER RIVER ESTUARY, BRITISH COLUMBIA.  .  59  INTRODUCTION  60  METHODS  62  RESULTS  .  Density Age  Structure.  63 63  . . . . . . .  64  S i z e Composition and Seasonal Growth  65  Depth D i s t r i b u t i o n  65  Seasonal Changes i n S h e l l Height and Body Weight . . . .  66'  Biomass  66  Spawning C y c l e  67  DISCUSSION  68  REFERENCES  87  :  X i  L I S T OF T A B L E S  • "  „ Page  •FACTORS APFECTING THE DISTRIBUTION OF THE BIVALVE, Macoma balthica  (L.) ON A MUDFLAT RECEIVING SEWAGE  EFFLUENT, FRASER RIVER ESTUARY, BRITISH COLUMBIA TABLE 1.  P h y s i c a l and c h e m i c a l c h a r a c t e r i z a t i o n o f sediments i n study a r e a  30  TABLE 2.  Summary of sediment m e t a l  TABLE 3.  R e l a t i o n s h i p between sediment oxygen uptake and d i s t r i b u t i o n o f M. balthica D e n s i t y and biomass f o r M. balthica from s i t e s on Sturgeon Bank.  TABLE 4.  TABLE 5.  data.  . . .  31  32 33  V a l u e s f o r y i n t e r c e p t (a) and s l o p e (b) of r e g r e s s i o n l o g l O y = a + bx where y = mean dry f l e s h weight i n mg, and x = s h e l l h e i g h t  i n mm f o r M. b a l t h i c a TABLE 6.  TABLE 7.  34  C o n c e n t r a t i o n of heavy m e t a l s i n t i s s u e s of M. balthica (ug/g d r y w e i g h t )  .  35  B i o c o n c e n t r a t i o n r a t i o of m e t a l s i n  M. b a l t h i c a  36  TABLE 8.  R e s u l t s o f t o x i c i t y b i o a s s a y s w i t h M. balthica.  37  TABLE 9.  In situ b i o a s s a y r e s u l t s and water d a t a , May 8, 1978  38  quality  xi  LIST OF TABLES SUBLETHAL EFFECTS OF HEAVY METAL  (cont'd)  CONTAMINATED  SEDIMENTS ON THE BIVALVE Macoma balthica TABLE 1.  TABLE 2.  TABLE 3.  TABLE 4.  Page  (L.)  C h a r a c t e r i z a t i o n of contaminated i n burrowing and a v o i d a n c e t e s t s  sediments  used 54  The median e f f e c t i v e time (ET50) and 95% c o n f i d e n c e l i m i t s f o r burrowing of M. balthica i n sediments w i t h d i f f e r e n t c o n c e n t r a t i o n s of- heavy m e t a l s . . . .  55  V a l u e s f o r y - i n t e r c e p t (a) and s l o p e (b) of r e g r e s s i o n y = a + bx where y = ET50 f o r burrowing response i n hours and x = i n d i v i d u a l m e t a l c o n c e n t r a t i o n (ppm) i n sediments. . . . . . . . . . .  56  R e s u l t s of sediment  57  a v o i d a n c e t e s t s w i t h M. balthica.  GROWTH AND REPRODUCTION OF Macoma balthica  (L.) ON A  MUDFLAT IN THE FRASER RIVER ESTUARY, BRITISH COLUMBIA TABLE 1.  Age c l a s s c o m p o s i t i o n of M. balthica sampling o c c a s i o n (no./m )  f o r each 74  2  TABLE 2.  TABLE 3.  TABLE 4.  Mean s h e l l h e i g h t ( i n mm ± S.E.) and range ( i n b r a c k e t s ) f o r v a r i o u s age c l a s s e s of M. balthica on each sampling o c c a s i o n Depth d i s t r i b u t i o n of M. balthica w i t h i n the substratum f o r each sampling d a t e  TABLE 6.  75  77  V a l u e s f o r y i n t e r c e p t (a) and s l o p e (b) of r e g r e s s i o n l o g l O y = a + bx where y = mean d r y f l e s h weight i n mg, and x = s h e l l h e i g h t i n  mm f o r M. b a l t h i c a TABLE 5.  I.  78  Biomass (g d r y weight/m ) o f M. balthica each sampling o c c a s i o n 2  on  Percentage of immature, mature, s e x u a l l y u n d i f f e r e n t i a t e d and p a r a s i t i z e d M. balthica on each/sampling o c c a s i o n  79  80  xii  L I S T OF  FIGURES  Page  FACTORS AFFECTING THE DISTRIBUTION OF THE BIVALVE, Macoma balthica  (L.) ON A MUDFLAT RECEIVING SEWAGE  EFFLUENT, FRASER RIVER ESTUARY, BRITISH COLUMBIA FIGURE 1.  FIGURE 2.  FIGURE 3.  FIGURE 4.  FIGURE 5.  L o c a t i o n of study area and sampling s i t e s on ,Sturgeon 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 D i s t r i b u t i o n p a t t e r n f o r c o n c e n t r a t i o n of copper (ppm) i n sediments over study a r e a  along t r a n s e c t s across  Biomass of M. balthica study a r e a  along t r a n s e c t s a c r o s s  40  41  42  Age c l a s s frequency d i s t r i b u t i o n o f M. a t s i t e s w i t h i n study a r e a  SUBLETHAL EFFECTS OF HEAVY METAL CONTAMINATED  FIGURE 1.  . . . .  D e n s i t y of M. balthica study a r e a  ON THE BIVALVE Macoma balthica  39  balthica 43  SEDIMENTS  (L.)  Burrowing r a t e s f o r M. balthica i n sediments A (•) , B ( X ) , C(+), D(A) and c o n t r o l (•), c o n t a i n i n g ; d i f f e r e n t l e v e l s o f heavy m e t a l s .  GROWTH AND REPRODUCTION OF Macoma balthica  58  (L.) ON A  MUDFLAT IN THE FRASER RIVER ESTUARY, BRITISH COLUMBIA FIGURE 1.  FIGURE 2.  L o c a t i o n of study a r e a (0) i n the F r a s e r R i v e r e s t u a r y . D o t t l e d l i n e i n d i c a t e s approximate seaward edge of t i d a l f l a t s a t low t i d e . . . . .  81  D e n s i t y o f M. balthica o c c a s i o n (± 1 S.E.)  82  on each  sampling .  xiii  L I S T OF FIGURES  (cont'd) Page  FIGURE 3.  FIGURE 4.  FIGURE 5.  FIGURE 6.  Average growth r a t e on R o b e r t s Bank.  ( l e n g t h i n mm) f o r M.  balthica 83  D e n s i t y o f M. balthica expressed as changes i n d i f f e r e n t s h e l l h e i g h t s i z e ranges  84  Changes i n (a) mean s h e l l h e i g h t i n mm, and (b) mean d r y weight p e r i n d i v i d u a l i n mg f o r each sampling d a t e  85  A i r , water and sediment temperatures, and s a l i n i t y over study a r e a d u r i n g sampling p e r i o d , . . . . . . .  86  xiv  ACKNOWLEDGEMENTS I would l i k e t o thank Dr. A.G. Lewis and Dr. K.J. H a l l o f t h e U n i v e r s i t y of B r i t i s h Columbia,  and Dr. C D . L e v i n g s o f t h e P a c i f i c  I n s t i t u t e f o r r e v i e w i n g the m a n u s c r i p t the c o u r s e o f the study.  Environment  and f o r t h e i r a d v i c e throughout  I a l s o g r a t e f u l l y acknowledge t h e a s s i s t a n c e  of t h e a n a l y s t s of the Water Q u a l i t y Group, B.C. Research  f o r performing  the heavy m e t a l s a n a l y s i s , and t h e c o o p e r a t i o n o f B.C. Research i n p r o v i d i n g l a b o r a t o r y space.  I e s p e c i a l l y w i s h t o extend my a p p r e c i a t i o n  to Dr. T.E. Howard f o r h i s p a t i e n c e and u n d e r s t a n d i n g d u r i n g my tenure at B.C. Research.  S p e c i a l thanks must go t o Ms. J u l i e P a u l f o r  a s s i s t a n c e w i t h the r i g o r o u s f i e l d  sampling program.  The a s s i s t a n c e  of M s s r s . Doug MacKay and Stan Vernon o f t h e G r e a t e r Vancouver Sewerage and Drainage D i s t r i c t  i n p r o v i d i n g a c c e s s t o t h e Iona J e t t y , t h e Iona  sewage treatment p l a n t and t e c h n i c a l d a t a r e g a r d i n g p l a n t o p e r a t i o n i s also appreciated.  FACTORS AFFECTING THE DISTRIBUTION OF THE Macoma balthica EFFLUENT,  (L.)  BIVALVE,  ON A MUDFLAT R E C E I V I N G SEWAGE  FRASER RIVER ESTUARY,  B R I T I S H COLUMBIA  2  INTRODUCTION The  Fraser River estuary i s located i n the southeastern corner of  the S t r a i t mudflats jetties  and i s c h a r a c t e r i z e d by an expanse o f i n t e r t i d a l  ( F i g . 1, i n s e t ) . designed  to d e f l e c t (Fig.  of Georgia  river  I n t e r s e c t i n g the t i d a l  flow.  One o f t h e s e  to d e f l e c t  Iona I s l a n d sewage treatment o f Vancouver.  a r e a on Sturgeon this region 1975,  t h e f l o w o f sewage e f f l u e n t  from t h e  p l a n t northwards, away from t h e beaches  Thus, sewage e f f l u e n t  i s concentrated  Bank south of t h e Iona j e t t y .  1977; O t t e and L e v i n g s ,  Previous  i n an  s t u d i e s of  1975) have documented  the b i o l o g i c a l  due t o t h e sewage d i s c h a r g e , p a r t i c u l a r l y  m a c r o b e n t h i c community.  A wide v a r i e t y o f f a c t o r s  o r g a n i c and heavy m e t a l effluent  s t r u c t u r e s , t h e Iona I s l a n d j e t t y  ( G r e a t e r Vancouver Sewerage & D r a i n a g e D i s t r i c t , 1 9 7 3 ,  effects  and  rock  f o r use as deepwater t e r m i n a l s o r a s b r e a k w a t e r s  1) was b u i l t  the c i t y  f l a t s are five  content,  sediment  low l e v e l s o f d i s s o l v e d oxygen  t o x i c i t y ) have been put forward  t i o n p a t t e r n s observed  (eg.  on t h e  b u t no e x p e r i m e n t a l  i n any o f t h e s e  studies.  sewage e f f l u e n t  on e s t u a r i n e m u d f l a t  to e x p l a i n the d i s t r i b u -  d a t a has been  Other s t u d i e s d e a l i n g w i t h  presented  the e f f e c t s of  macrofauna a r e r a r e ( F r a s e r ,  1932), and t h i s a r e a of t h e F r a s e r R i v e r e s t u a r y p r o v i d e d  an e x c e l l e n t  l o c a t i o n f o r r e s e a r c h on t h e r e l a t i v e importance o f s e l e c t e d v a r i a b l e s i n 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 of b e n t h i c i n v e r t e b r a t e s .  3  This  s e c t i o n o f the t h e s i s d e s c r i b e s  t h e r e s u l t s o f the study  undertaken t o examine mpre c l o s e l y a number o f f a c t o r s w i t h the e f f l u e n t d i s c h a r g e which c o u l d the d e p o s i t - f e e d i n g balthica benthic  e x p l a i n the d i s t r i b u t i o n o f  b i v a l v e Macoma balthica  (=M. inconspicua,  Broderip  (Linnaeus, 1758).  sewage treatment p l a n t  (G.V.S.D.D., 1975, 1977; O t t e and L e v i n g s , 1975).  been shown  discharge  The f a c t o r s  i n the p r e s e n t study were e f f e c t s of reduced s a l i n i t y  dilution,  low l e v e l s of d i s s o l v e d  Macoma  & Sowerby, 1829) was one o f t h e  i n d i c a t o r s p e c i e s whose d i s t r i b u t i o n had p r e v i o u s l y  to be a f f e c t e d by the Iona I s l a n d  sidered  associated  condue t o  oxygen, a c u t e l e t h a l t o x i c i t y of  the sewage e f f l u e n t , t o x i c i t y due to e f f l u e n t c h l o r i n a t i o n ,  substrate  p a r t i c l e s i z e , s u b l e t h a l e f f e c t s of metal-contaminated sediments and the e f f e c t s of m e t a l b i o a c c u m u l a t i o n .  In a d d i t i o n t o d i s t r i b u t i o n ,  the e f f e c t s of the e f f l u e n t on the d e n s i t y , recruitment,  Description The  and c o n d i t i o n  of the study  o f M. balthica  biomass, age s t r u c t u r e ,  were a l s o  investigated.  area  study area south o f the Iona j e t t y on Sturgeon Bank ( F i g . 1 ) ,  receives  sewage e f f l u e n t d i s c h a r g e d  treatment p l a n t  (ISTP).  from t h e Iona I s l a n d  Sewage e f f l u e n t from the p l a n t  sewage f l o w s seawards  along a s h a l l o w (1-3 m deep a t low t i d e ) , dredged c h a n n e l and i s dispersed  a t high  t i d e over the mudflat a r e a .  The ISTP p r o v i d e s  primary treatment y e a r round, and c h l o r i n a t i o n b e f o r e d i s c h a r g e f o r approximately  s i x months of the year from May u n t i l October.  The p l a n t  domestic sewage, as w e l l as i n d u s t r i a l wastewater and stormwater  treats runoff,  4  and m  3  has an average d i s c h a r g e o f a p p r o x i m a t e l y 70 Imp. day  - 1  MGD  (318 X  10  J  ).  Sediments near the shore a r e muddy, becoming sandy at lower elevations.  The  tidal flat  t h e r e i s a marsh of sedges  s l o p e s g e n t l y from the s h o r e l i n e where (Carex sp.) and  seaward to the edge o f S t u r g e o n Bank. above c h a r t datum and about  5.8  km.  The marsh a r e a i s about  the d i s t a n c e from  A major t i d a l c r e e k and  c h a n n e l s f l o w a c r o s s t h e m u d f l a t and  b u l l r u s h e s (Scirpus  sp), 3.5  m  s h o r e t o the edge o f Sturgeon Bank i s s e v e r a l minor d r a i n a g e  empty i n t o the sewage c h a n n e l  about midway a l o n g i t s l e n g t h . S t a t i o n s on the m u d f l a t t r a n s e c t l i n e s determined (a-D, line was  were l o c a t e d  from m a r k e r s p o s i t i o n e d a l o n g the Iona  shown as l a r g e b l a c k c i r c l e s  i n F i g . 1 ) , and  (1-8, shown as s m a l l b l a c k c i r c l e s originally  c o n t r u c t e d by B.C.  s t u d y o f the a r e a  a t the i n t e r s e c t i o n o f  i n F i g . 1).  Research  (G.V.S.D.D., 1973).  The  the a d j a c e n t This grid  f o r the f i r s t sampling  stations  example, the c o o r d i n a t e A5 r e p r e s e n t s a s i t e l o c a t e d at the 5.  w i l l be made throughout  Reference this  to s i t e  paper.  shoresystem  intensive ( F i g . 1)  were p o s i t i o n e d by t a k i n g compass b e a r i n g s from t h e s e markers.  of t r a n s e c t s A and  jetty  For  intersection  c o o r d i n a t e s i n t h i s manner  5  METHODS  Field  Methods  Sampling  f o r M. balthica  was  carried  out a t 23 s i t e s on  Bank ( F i g . 1) d u r i n g low t i d e s i n J u l y , sediment w i t h i n a 0.06 a d e p t h of 10 cm.  m  scooped  At each s i t e ,  the  out w i t h a t r o w e l t o  Samples were r e t u r n e d to the l a b o r a t o r y where they were  washed t h r o u g h a 0.5 mm and  q u a d r a t was  2  1977.  Sturgeon  s i e v e and a l l M. balthica  sorted,  enumerated  frozen. Sediment  samples  f o r a n a l y s i s of p a r t i c l e  o r g a n i c c o n t e n t were c o l l e c t e d w i t h a 4.8 c o r e r pushed  i n t o the mud  s i z e , heavy m e t a l s  cm d i a m e t e r  t o a d e p t h o f 5 cm.  plexiglass  D u p l i c a t e c o r e s were  t a k e n a t each s i t e c o n c u r r e n t w i t h s a m p l i n g f o r M. balthica. were f r o z e n i n the f i e l d analysis. the  field  The  salinity  P o l y e t h y l e n e tubes for  of sediment  s u r f a c e water i n t i d e p o o l s was measured i n Salinity-  meter. (4.8 cm d i a m e t e r ) were used  t h e d e t e r m i n a t i o n of sediment  i n d e p t h were t a k e n a t s i x s i t e s o c c a s s i o n s i n September, 1977.  to take core  oxygen u p t a k e r a t e s . (a3, A3,  a5, A5,  Cores 10  samples cm  b5, B5) on t h r e e  C o r e s were t r a n s p o r t e d  t o the  w i t h i n two hours where oxygen u p t a k e d e t e r m i n a t i o n s were immediately.  Samples  and r e t u r n e d t o t h e l a b o r a t o r y f o r l a t e r  w i t h a Y e l l o w S p r i n g s I n s t r u m e n t , Model 33  Conductivity-Temperature  and  laboratory  started  6  In  situ  b i o a s s a y s w i t h M.  week of May  4 - 11,  1978.  balthica  Plastic  were c a r r i e d  containers  out  during  (7 X 7 X 12 cm)  the  with  l a r g e "windows" c u t i n the s i d e s t o f a c i l i t a t e water f l o w were fastened A,  B,  t o wooden p l a n k s  and  C on the  control site  south  and  placed  w i t h two  surface at s i t e s  ( F i g . 1) and  (A) on the n o r t h s i d e of t h e j e t t y .  each c o n t a i n e r and  concrete blocks.  A fine,  at a  bioassay t e n M.  balthica  p l a s t i c mesh n e t t i n g  was  t h e end  and  of t h e experiment  t h e number of dead  clams  (168  h),  recorded.  S u r f a c e water samples were c o l l e c t e d , u s i n g a p l a s t i c  bucket,  each s i t e a t h i g h t i d e on May  temperature  11,  1978.  were determined w i t h a YSI, Model 33, Conductivity-Temperature w i t h a YSI,  F i s h e r and  meter, and  Model 54 p o l a r o g r a p h i c  of t o t a l r e s i d u a l  c h l o r i n e was  P o r t e r Model 17T  S a l i n i t y and  d i s s o l v e d oxygen was oxygen a n a l y s e r .  a l s o measured on  1010  seawater samples was  from  Salinity-  The  employed.  measured concentration  s i t e with a portable,  amperometric t i t r a t o r .  t i t r a t i o n p r o c e d u r e recommended by C a r p e n t e r chlorinated  a,  the p l a n k s were then w e i g h t e d down  At  t h e c o n t a i n e r s were emptied  The  to a depth of 5 cm and  i n d i v i d u a l s were added t o each. over  the mud  s i d e o f Iona j e t t y  c o n t a i n e r s were f i l l e d , w i t h mud  fitted  on  et al.  The  back  (1977) f o r  7  Laboratory  Procedures  Sediment  p a r t i c l e s i z e a n a l y s i s was  s i e v e method a c c o r d i n g t o Morgans  (1956).  s i e v e s w i t h mesh s i z e s of 2, 1, 0.5, used and  determined  The d r y weight  f o r each sample and  c a l c u l a t e d by d i f f e r e n c e . a c u m u l a t i v e p e r c e n t weight Sediment  samples  4N h y d r o c h l o r i c a c i d 60°C under  0.25,  Sediments  50% n i t r i c  the s i l t / c l a y  and  0.063 mm  c u r v e f o r each  f o r each was  (<0.063  mm)  calculated  from  sample.  then 1 g p o r t i o n s were  A c o r r e c t i o n was  applied  with  treatment.  filtered  and  (5:1).  ( e x c e p t mercury) were f o r 12 h i n a m i x t u r e  The d i g e s t s were d i l u t e d  a n a l y s e d f o r m e t a l c o n t e n t by  flame atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y  (AAS) u s i n g a P e r k i n -  i n s t r u m e n t w i t h d e u t e r i u m background  determined  ignited  t o account f o r the  5 g p o r t i o n s were d i g e s t e d  w i t h d e i o n i z e d water,  was  was  to remove c a r b o n a t e s and b i c a r b o n a t e s , d r i e d  acid/perchloric acid  ELmer Model 306  fraction  The median g r a i n s i z e was  f o r a n a l y s i s o f heavy m e t a l s  a t 105°C and  Mercury  0.125  f o r o r g a n i c c a r b o n c o n t e n t were t r e a t e d  weight change on a c i d  of  A Wentworth s e r i e s o f  o f a w e l l mixed subsample  reduced p r e s s u r e , and  i n a LECO f u r n a c e .  dried  out by the wet  r e s u l t s were e x p r e s s e d as t h e p e r c e n t d r y weight  size fraction.  at  carried  on d u p l i c a t e  w i t h aqua r e g i a f o r two m i n u t e s  (0.5 g) a i r d r i e d  a t 95°C,  and p e r s u l p h a t e f o r 30 min a t 95°C.  correction. samples  then potassium  The d i g e s t was  digested  permanganate  treated  with  8  h y d r o x y l a m i n e / H C l , sparged w i t h a i r f o r 30 seconds to remove c h l o r i n e , and reduced w i t h stannous c h l o r i d e .  Mercury was  measured by the  c o l d vapour t e c h n i q u e u s i n g a Pharmacia UV m o n i t o r . t i s s u e s of M. balthica  M e t a l s i n the  were a n a l y s e d i n a s i m i l a r manner a f t e r the  clams had been a l l o w e d to depurate themselves of sediments f o r 24 h in clean  seawater.  The r a t e o f sediment oxygen undisturbed containing had been  uptake was  Sturgeon Bank sediments were f i l l e d  the seawater  i n each tube was  p o l a r o g r a p h i c oxygen The  The d i s s o l v e d  a n a l y s e r and  The  oxygen  c o n c e n t r a t i o n measured  iduals.  i n each  of 15 -  16°/ o> 0  c o n d i t i o n s n o r t h o f the Iona j e t t y on Sturgeon  was  use"d as a  control.  d e t e r m i n e d by c o u n t i n g a n n u a l  r i n g s u s i n g the methods o f Lammens (1967). y e a r c l a s s e s from age 0+  Brunswick  e x p e r i m e n t was t e r m i n a t e d  A tube c o n t a i n i n g seawater o n l y was  The age of M. balthica  777  t o promote water m i x i n g w i t h o u t  the sediment s u r f a c e .  c o r r e s p o n d i n g t o ambient  to  c o n t e n t of  i n s i d e a New  tube., T e s t s were r u n a t 15 ± 1°C and w i t h a s a l i n i t y  Bank.  which  the tubes s e a l e d w i t h a rubber  tubes were c o n t i n u o u s l y r o t a t e d  3 h and the d i s s o l v e d  oxygen  measured w i t h a Beckman Model  ' G y r o t o r y ' Schaker, Model G-25  after  w i t h seawater  Cores  from the F r a s e r e s t u a r y and p r e v i o u s l y a e r a t e d  saturation with laboratory a i r .  disturbing  from  c o r e samples on the same day t h e y were c o l l e c t e d .  collected  stopper.  determined  (newly s e t t l e d  growth  A n i m a l s were p l a c e d i n  s p a t ) t o 5+ y e a r o l d i n d i v -  9  All and  dried  soft  t i s s u e was removed from  a t 60°C f o r 24 h.  s h e l l s over  1.0 mm  i n height  F o r each sample, t i s s u e s from  shells  of t h e same s i z e were pooled and a mean d r y w e i g h t d e t e r m i n e d f o r each s i z e c a t e g o r y .  The s i z e  (height) of the s h e l l s  to t h e v e n t r a l edge was measured t o the n e a r e s t condition factor  (CF) was then c a l c u l a t e d  regression logjo y x = s h e l l height. expressed  =  a  t o which 2.5 I o f t e s t  o r g a n i s m s were c o l l e c t e d  Fraser River estuary. screen p r i o r and  t o b e i n g used  used  were c o n d u c t e d photo-period  were c a r r i e d  plant.  from Roberts  and t e s t a n i m a l s  to a depth  o f 5 cm  Sediments  Bank, an u n p o l l u t e d a r e a of the a 1 mm  mesh  were h e l d a t 15  °/ o 0  acclimation to laboratory conditions.  i n temperature  o f 16 h l i g h t  out i n  s o l u t i o n was added.  i n the t e s t s were 5-15 mm  was o b t a i n e d p r i o r treatment  (b) i n t h e  equal to zero.  Sediments were s i e v e d t h r o u g h  10°C one week t o permit  M. balthica  and a  S i g n i f i c a n c e f o r t h e r e g r e s s i o n f u n c t i o n was  p o l y e t h y l e n e c o n t a i n e r s (35 X 15 X 14 cm) f i l l e d  test  t h e umbo  + bx, where y = mean d r y t i s s u e weight and  L a b o r a t o r y b i o a s s a y s w i t h M. balthica  and  0.5 mm,  as t h e s l o p e  as t h e p r o b a b i l i t y o f t h e s l o p e b e i n g  w i t h sediment  from  controlled  i n length.  (±1°C) rooms w i t h a s t a n d a r d  and 8 h d a r k n e s s .  t o each t e s t from  Treated  the o u t f a l l  The e f f l u e n t was c o l l e c t e d  p o l y e t h y l e n e drums and s t o r e d a t 2°C.  A l l bioassays  sewage  o f t h e Iona  I s l a n d sewage  i n a c i d - w a s h e d , 45 g a l l o n  A l l b i o a s s a y s were  w i t h i n t h r e e days of e f f l u e n t c o l l e c t i o n .  effluent  Salinity  started -  measurements were made w i t h a YSI Model 33, S a l i n i t y - C o n d u c t i v i t y Temperature meter and pH measurements were t a k e n w i t h L a b o r a t o r y Model 175 p o r t a b l e pH meter.  an I n s t r u m e n t a t i o n  10  C o n d u c t i v i t y of the t r e a t e d l e s s than 400 umhos/cm from 6.6  t o 7.0.  c o n t r o l s was  2  sewage e f f l u e n t was  (<0.1°/ o O  Unfiltered  s a l i n i t y ) and pH v a l u e s ranged  seawater f o r t e s t d i l u t i o n s  o b t a i n e d from the P a c i f i c Environment  Vancouver, B.C.  seawater ranged from 24.8 and 7.8.  t o 26.2  low t i d e .  I n s t i t u t e , West  °/  t r a t i o n of sewage e f f l u e n t was  and pH v a l u e s ' w e r e between  00  (v/v) sewage  On one o c c a s i o n , a 100%  seawater d i l u t e d c o n t a i n e r was  50% w i t h tap water.  A e r a t i o n f o r each  was  test  s u p p l i e d by l a b o r a t o r y a i r through P a s t e u r p i p e t t e s .  by the h i g h BOD  of the e f f l u e n t .  (Beckman, Model  and were found to be >90% Chlorine  i  Inc) , which  The c o n t r o l f o r a l l o t h e r t e s t s  P r e - a e r a t i o n of the sewage e f f l u e n t b e f o r e d i l u t i o n was  checked d a i l y  concen-  t e s t e d a f t e r the s a l i n i t y was  a d j u s t e d by a d d i t i o n of I n s t a n t Ocean (Aquarium System, a l s o used as a c o n t r o l .  from  S a l i n i t y of t h e  D i l u t i o n s of 80, 40, 20, 10 and 5%  e f f l u e n t were used i n a l l t e s t s .  was  and  seawater i n t a k e system which draws seawater  E n g l i s h Bay a t a depth of 19 m below  7.6  consistently  necessitated  D i s s o l v e d oxygen l e v e l s were  777 p o l a r o g r a p h i c oxygen a n a l y s e r )  of a i r s a t u r a t i o n v a l u e s at a l l t i m e s .  (12% s o l u t i o n sodium h y p o c h l o r i t e ) was  added  to sewage  e f f l u e n t on two o c c a s i o n s t o produce l e v e l s f o r t o t a l  residual  chlorine after  i n the 80%  test solution.  2 h r e a c t i o n time of 1.00  and 2.25  ppm  Measurements o f t o t a l r e s i d u a l c h l o r i n e were t a k e n  w i t h a F i s h e r and P o r t e r Model  17 T 1010  amperometric  titrator  using  a back t i t r a t i o n p r o c e d u r e w i t h excess p h e n y l a r s i n e o x i d e s o l u t i o n .  11  The  effect  o f e f f l u e n t c h l o r i n a t i o n - d e c h l o r i n a t i o n was t e s t e d by  d e c h l o r i n a t i n g one sample o f e f f l u e n t w i t h  an e x c e s s o f 1 M sodium  thiosulphate. Test  s o l u t i o n s were r e p l a c e d  which r a n f o r 7 days the  (168 h ) .  e v e r y 24 h d u r i n g  the bioassays  A l l s o l u t i o n s were a d j u s t e d t o  c o r r e c t t e s t temperature b e f o r e  being  added t o t h e c o n t a i n e r s .  RESULTS  Sediments Data on t h e median p a r t i c l e and  heavy m e t a l content  are given  i n Table  1.  size,  interstitial  o f s e d i m e n t s c o l l e c t e d from Sediments w i t h  (<63um)were g e n e r a l l y found a l o n g (Fig.  1 ) , and a l o n g  salinity,  the f i n e s t  organic  Sturgeon Bank  median g r a i n  size  t h e sewage c h a n n e l up t o s i t e B  t r a n s e c t s a, A, b and B on t h e m u d f l a t .  s i t e s a l s o showed h i g h l e v e l s , o f o r g a n i c s  As t h e s e  ( T a b l e 1 ) , i t can be  assumed t h a t most o f the f i n e p a r t i c u l a t e m a t e r i a l was d e r i v e d the  sewage e f f l u e n t .  This conclusion  o f t h e sediments i n these a r e a s , in  i s s u p p o r t e d by t h e appearance  w h i c h was o f a f i n e ,  c o l o u r and o f t e n s m e l l i n g o f hydrogen s u l f i d e .  seaward o f t r a n s e c t C were c o a r s e r discoloured.  i n texture,  They were a l s o lower i n o r g a n i c  c l o s e r t o t h e sewage o u t f a l l .  from  The v a l u e s  s o f t mud,  black  The sediments  sandy and n o t content  than  for interstitial  sediments salinity  12  r e c o r d e d over the study a r e a the p r e s e n c e relatively was  (4.1 - 9.8  of the sewage o u t f a l l .  uniform s a l i n i t y  0  0  The  s a l i n i t y data r e f l e c t  the  of bottom water over the a r e a which  measured by O t t e and L e v i n g s  (4.1 ° / o ) was  ° / o ) were not extreme d e s p i t e  (1975).  The  lowest  salinity  from s i t e b5, a d j a c e n t t o the major t i d a l  recorded  drainage  channel which f l o w s over the a r e a . The  c o n c e n t r a t i o n of heavy m e t a l s  g i v e n i n T a b l e 1.  i n t h e s e d i m e n t s sampled  E l e v a t e d l e v e l s of most m e t a l s  s i t e s a l o n g the sewage c h a n n e l and  adjacent  w i t h t h e h i g h e s t v a l u e s b e i n g found  were r e c o r d e d  to the  at  sewage o u t f a l l ,  a t s i t e s a and  the sediment m e t a l v a l u e s by t r a n s e c t and  are  A.  A summary of  f o r the s t u d y a r e a  (Table  shows t h a t the h i g h e s t l e v e l s measured were a l o n g t r a n s e c t s a and The  g e n e r a l d i s t r i b u t i o n p a t t e r n observed  o r g a n i c s ) i n Sturgeon F i g u r e 2.  Bank s e d i m e n t s i s i l l u s t r a t e d  Cadmium and manganese were found  general pattern.  not a s s o c i a t e d w i t h the e f f l u e n t not  e n t r a t i o n s of m e t a l s  Hall  (and in  e x c e p t i o n s to  this  and  ( T a b l e 1 ) , and  manganese  the  sewage o u t f a l l .  The  w e r e s i m i l a r t o those r e c o r d e d by B.C. w e r e somewhat lower  (1977) f o r t h i s a r e a .  The  was  d i s c h a r g e as sediment c o n c e n t r a t i o n s  change w i t h d i s t a n c e from  (G.V.S.D.D., 1977)  t o be  f o r copper  A.  Cadmium o c c u r r e d i n h i g h c o n c e n t r a t i o n s a t o n l y  f o u r s i t e s a l o n g the sewage c h a n n e l  did  f o r most heavy m e t a l s  2)  concResearch  than those of B i n d r a  highest l e v e l s for  the  metals  and  13  copper  (234 ppm),  lead  (166 ppm)  and  zinc  (264 ppm)  a r e i n t h e range  of c o n c e n t r a t i o n s found i n contaminated s e d i m e n t s f r o m o t h e r a r e a s of t h e w o r l d ( P h i l l i p s ,  1977) , but a r e one to two o r d e r s ' -  of magnitude lower than the h i g h e s t c o n c e n t r a t i o n s (Phillips,  published  1977).  R a t e s o f sediment oxygen uptake a r e shown i n T a b l e 3. ranged f r o m 82 - 141 mg recorded  0 /m /h and a r e s i m i l a r t o t h e r a t e s  The h i g h e s t v a l u e f o r oxygen uptake was on the. bank of the t i d a l  on t h e e a s t  previously  2  2  f o r the sediments near t h e ISTP o u t f a l l  which was  The v a l u e s  of the study a r e a .  (G.V.S.D.D., 1977).  f o r t h e sediment a t s i t e  b5  c h a n n e l d r a i n i n g t h e marsh  The o c c u r r e n c e of M.  ( T a b l e 3) does not appear t o be r e l a t e d  to the l e v e l of  balthica sediment  oxygen u p t a k e and the mean u p t a k e of s e d i m e n t s c o n t a i n i n g Macoma was  a c t u a l l y g r e a t e r than t h o s e where Macoma d i d n o t o c c u r .  Density,  Biomass  and Condition  Factor  of M. b a l t h i c a  To show more c l e a r l y t h e e f f e c t s of the sewage e f f l u e n t M. balthica, factors  i t i s preferable  such as t i d a l h e i g h t .  t o minimize the i n f l u e n c e of n a t u r a l The d a t a f o r Macoma yrlll  be compared by examining each t r a n s e c t , a s i n g l e t r a n s e c t was biomass  of M. balthica  on  therefore  since the e l e v a t i o n  r e l a t i v e l y constant.  4 respectively.  to t h e o u t f a l l i n which t h e r e was  D a t a on t h e d e n s i t y  and transect  Outside the area adjacent  a c o m p l e t e a b s e n c e o f M.  :  across  i s g i v e n i n T a b l e 4 and a c o m p a r i s o n by  i s shown i n F i g u r e s 3 and  .  balthica^  14  the s i t e s w i t h t h e g r e a t e s t d e n s i t y o f M. balthica m ) were s i t e s C5 and C8. 2  The number o f i n d i v i d u a l s a l o n g  t r a n s e c t was c o n s i s t e n t l y lower i n t h e v i c i n i t y (Fig.  (1038 i n d i v i d u a l s / each  o f t h e sewage c h a n n e l  3 ) . A r e d u c t i o n i n t h e number o f i n d i v i d u a l s a t s i t e s  from t h e sewage c h a n n e l was a l s o o b s e r v e d major f a c t o r  farthest  on t r a n s e c t b and A.  i n e x p l a i n i n g t h e i n c r e a s e i n d e n s i t y o f M.  A  balthica  from t r a n s e c t b t o C i s t h e c o r r e s p o n d i n g d e c r e a s e i n t i d a l h e i g h t . A l t h o u g h t r a n s e c t D i s lower i n e l e v a t i o n t h a n C, fewer  individuals  were r e c o r d e d from'D." \ T h i s i s most l i k e l y due t o t h e c o a r s e , wave-swept sediments which C.  characterize  t h e a r e a seawards o f t r a n s e c t  G e n e r a l l y , t h e numbers o f i n d i v i d u a l s o f M. balthica  study were c o n s i d e r a b l y lower than d e n s i t i e s found by O t t e and L e v i n g s (1975) and t h e G.V.S.D.D. maximum o f 3920/m sites.  2  and 3648/m  2  respectively  2  a t s i t e b5.  i n previous studies  i n samples  T h i s enrichment  from the same  was 8.313 g d r y  The o v e r a l l p a t t e r n f o r biomass  shows a maximum a l o n g t r a n s e c t b.  i n the present  (1977), who r e c o r d e d a  The maximum biomass measured f o r M. balthica  weight/m  ( F i g u r e 4)  due t o t h e a d d i t i o n a l  i n p u t o f o r g a n i c m a t e r i a l from t h e sewage e f f l u e n t was f i r s t by L e v i n g s and C o u s t a l i n Increased adjacent  (1975) and l a t e r by O t t e and L e v i n g s  biomass f o r M. balthica to the e f f l u e n t  channel.  sandy,  observed (1975).  was a l s o n o t e d a t s i t e s C and D,  15 . ;  A regression equation was  c a l c u l a t e d f o r each s i t e and  served  as a c o n d i t i o n f a c t o r  i n c r e a s e i n CF w i t h was  ( s h e l l h e i g h t on body weight of M.  at s i t e b5  were low  and  balthica  (CF).  the h i g h e s t  C and  Beukema and  D.  ( T a b l e 5)  a t s i t e D8  de  then  Bruin  of M.  I t was  where. Macoma was s e t t l e d spat  adjacent  found  (age 0+  i n d i v i d u a l s was  for  CF  interpreted with >CF  i n M.  s i z e range of  l a r g e and v e r y  small  the medium s i z e d  d i s t r i b u t i o n f o r M.  evident  12-20 mm  individuals  animals.  individuals).  0+ but  no  D),  changes due  plotted  to  t o the  A lower p r o p o r t i o n of newly  of M.  1+ y e a r  was  the effluent  channel  there~was no s u c c e s s f u l r e c r u i t m e n t  a t s i t e s b5,  to the a r e a d e v o i d  balthica  that f o r s i t e s c l o s e s t  ( c , C, and  a l s o found  p e r c e n t a g e o f age  (0.1309)  progressively increased  S t u r g e o n Bank ( F i g . 5) t o show any  sewage e f f l u e n t .  general  balthica  age-class, frequency  f o r s i t e s on  than  CF  Values  (1977) have shown t h a t  that both very  line  show a  lowest  (0.4629).  i s independent o f l e n g t h o n l y f o r the  Age Structure  The  However, the d a t a must be  show c o n s i s t e n t l y lower v a l u e s  A5,  data  s l o p e of t h e  d i s t a n c e from t h e o u t f a l l .  i n s h e l l l e n g t h , and  The  The  f o r s i t e s a l o n g t r a n s e c t b and  f o r t r a n s e c t s B, caution.  changes i n the  balthica)  b7  and  balthica,  B8  (Fig. 5).  t h e r e was  old individuals.  a  settled  At  site  high  T h i s may  indicate  o f newly  16  a l a c k of s u r v i v a l of newly s e t t l e d A h i g h p r o p o r t i o n of age s i t e s sampled, but numbers.  2+ year  These data  The  in M.  concentration  are g i v e n (6.76  ppm)  of i r o n , and icient  clams  6.  Copper  (313.6 ppm),  zinc  (743.2 ppm)  concentrations  level for iron  balthica  from a l l s i t e s due  (1452.1 ppm)  f o r c o p p e r , z i n c and  was  from s i t e  numbers and  b2.  outfall  concentration  mercury.  Suff-  t i s s u e f o r a n a l y s i s c o u l d not  t o t h e low  mercury  i n clams from  which showed a sharp i n c r e a s e i n t h e  to a l e s s e r extent  balthica and  w i t h d i s t a n c e from t h e  be  s m a l l s i z e of  l e v e l s of heavy m e t a l s i n sediments and M.  compared u s i n g a b i o c o n c e n t r a t i o n r a t i o r a t i o g i v e s an  tissue:sediment the r a t i o s not  (Table 7).  balthica The  the  ratios  l e v e l s found  r a t i o s of l e s s than 1  sediment.  (18.50 - 45.07) was-that-  f o r z i n c (1.27  concentrated  i n the  to the (0.01  - 10.04) and same d e g r e e - 0.07).  The  copper  were  bioconcentration  i n d i c a t i o n o f t h e degree of c o n c e n t r a t i o n  i n -clam t i s s u e over those  was  t i s s u e s of M.  present. The  by  were found.  balthica  q u a n t i t i e s of M.  obtained  t o 5+ y e a r s o f age  g e n e r a l l y decreased  except f o r s i t e D8  i n large  1+ clams at a l l  the h i g h e s t  Bioaccumulation  other  a h i g h p r o p o r t i o n of 0+ and  exhibited their highest  s i t e b5 w h i l e  at a l l the  of R o b e r t s Bank  of heavy m e t a l s i n the s o f t  i n Table  site.  c o n s i d e r a b l y from those  i n d i v i d u a l s up  Bioaccumulation  1+ clams were p r e s e n t  o l d i n d i v i d u a l s were never found  differ  (p. 74) where t h e r e was s i t e s , and  0+ and  l a r v a e or j u v e n i l e s at t h i s  of m e t a l s The  g r e a t e s t range i n  f o r mercury, (1.95  - 7.98).  followed Iron  having wide range o f v a l u e s  for  17  the b i o c o n c e n t r a t i o n r a t i o s observed the t o t a l t r a c e m e t a l  content  regulating t h i s process.  suggests  t h a t other f a c t o r s  o f the sediments a r e important  A v a i l a b i l i t y w i l l depend upon the  in physical-  c h e m i c a l n a t u r e o f the metal-sediment a s s o c i a t i o n (Luoma and 1975)  and  on b i o l o g i c a l f a c t o r s such as the presence  ( P a t r i c k and  L o u t i t , 1976).  Jenne,  of b a c t e r i a  B a c t e r i a l m e t h y l a t i o n of mercury i s  w e l l e s t a b l i s h e d (Woods, 1974), but more r e c e n t l y P a t r i c k and (1976) have shown t h a t low l e v e l s of o t h e r metals Fe, Pb, and  Zn)  i n e f f l u e n t s and  than passed  Hall  to o t h e r organisms i n a food c h a i n .  M e t a l l e v e l s i n M.  balthica  analytical  T h i s d i f f e r e n c e may  techniques  used i n the two  and be  i n the  i n p a r t to d i f f e r e n t  s t u d i e s (K. B i n d r a , p e r s . comm.).  than those r e p o r t e d f o r M. balthica  although  by Bryan  Humerstone (1977) i n the i n d u s t r i a l l y p o l l u t e d Looe e s t u a r y  Toxicity  is  (Newell,  r e p o r t e d to  M e t a l c o n c e n t r a t i o n i n t i s s u e s were i n the same range, s l i g h t l y lower,  balthica  t i s s u e than found  be due  Mn,  by b a c t e r i a  from t h i s a r e a by B i n d r a  t h r e e o r d e r s o f magnitude h i g h e r i n clam study.  M.  Loutit  Cr,  to sediment p a r t i c l e s  (1977) w i t h the e x c e p t i o n of i r o n , which was  present  (eg. Cu,  sediments a r e c o n c e n t r a t e d  known to f e e d on the b a c t e r i a a t t a c h e d 1965).  than  and (Cornwall).  Bioassays  R e s u l t s of the a c u t e , l e t h a l b i o a s s a y s w i t h sewage e f f l u e n t shown i n T a b l e 8.  No m o r t a l i t i e s were observed  i n any  of the  are  bioassays  carried M.  out  i n d i c a t i n g that  balthica.  The  the  problem of  effluent  lowered  was  n o n - t o x i c to  salinity  i n h i g h .. e f f l u e n t  c o n c e n t r a t i o n s - was- overcome by m i x i n g e f f l u e n t w i t h prepared, t o 100% in  I n s t a n t Ocean s a l t s , but  effluent  t e m p e r a t u r e to 18°C  Feb.  6 tests).  tests),  the  also did  in-plant  chlorinated d i d not  b u r r o w i n g and  e f f e c t s were observed r e s u l t s of  water q u a l i t y presented  not  (May  an  result  i n T a b l e 9.  in  of  situ  the  toxic  No the  mortalities  to M.  had  Residual chlorine  18,  Additional balthica  final  (Jan.  Apr.  23,  25  observations during  the  r e s p o n s e s , but  no  tested. balthica  day  of  the  occurred a f t e r  A reduction  outfall.  not  increase  (Apr.  bioassays, that  balthica.  was  An  chlorinated-dechlorinated  sublethal  the  oxygen v a l u e s were r e c o r d e d  '  and  b i o a s s a y s w i t h M.  laboratory  exposure  mortalities  concentrations  dissolved  samples a n a l y s e d  chlorinated  of  parameters measured on  acutely  i n any  deaths.  indication  i n any  from  6 t e s t , Table 8).  3 test)  produce any  the  c o n f i r m e d r e s u l t s of was  not  commercially  deaths resulted  f e e d i n g b e h a v i o u r of M.  b i o a s s a y s were made as  The  (Feb.  Tests with laboratory  sewage e f f l u e n t on  concentration  no  adult  the  and  the  test  are  7 days which sewage  in salinity  from s i t e a c l o s e s t  d e t e c t a b l e i n any  of  to the  effluent and  the water  19  DISCUSSION S e v e r a l f a c t o r s known t o a f f e c t  the d i s t r i b u t i o n of b e n t h i c  e b r a t e s do not appear t o e x p l a i n i n the s t u d y a r e a on S t u r g e o n values for i n t e r s t i t i a l the s a l i n i t y not lowered is  Bank.  salinity  The  relatively  f o r M.  balthica  s m a l l range  over the s t u d y a r e a i n d i c a t e  of  that  o f the bottom water a d j a c e n t t o the sewage o u t f a l l s i g n i f i c a n t l y by d i l u t i o n w i t h t h e e f f l u e n t .  i n agreement w i t h O t t e and  sewage e f f l u e n t the ebb  the p a t t e r n o b s e r v e d  invert-  Levings  (1975) who  observed  was  This  finding  that  the  flowed o v e r the s u r f a c e o f the more s a l i n e incoming  t i d e , flowed  seaward i n s i d e t h e sewage c h a n n e l .  They  was  on the m u d f l a t .  measured a t s i t e a  s p e c i e s and (Clay,  Some d i l u t i o n of t h e i n c o m i n g  (3.6 ° / ) 0 0  i s f r e q u e n t l y found  but M.  balthica  the  seawater  i s a strong euryhaline  i n areas with s a l i n i t i e s  in this  range  1967).  Dissolved be lowered  oxygen v a l u e s i n the water column have been shown t o  (1.5 - 4 mg/1)  by the h i g h BOD  i n a r e a s a d j a c e n t t o the ISTP o u t f a l l 1975).  However, f o r M.  balthica,  of the  t i o n near  w h i c h extends  t h e bottom i s a.more m e a n i n g f u l  available for respiration.  sewage  (G.V.S.D.D., 1975;  d i s t a n c e i n t o the water o v e r l y i n g the sediment,  result  t i d e and  concluded  t h a t s a l i n i t y d i d n o t i n f l u e n c e the q u a l i t a t i v e d i s t r i b u t i o n o f s p e c i e s found  "fresh"  effluent  O t t e and  Levings,  i t s siphons a short the oxygen c o n c e n t r a -  measure o f the oxygen  A h i g h r a t e o f sediment  oxygen demand  may  i n the d e p l e t i o n o f oxygen i n the o v e r l y i n g water w h i c h i n  turn w i l l  affect  the d i s t r i b u t i o n o f many s p e c i e s o f b e n t h i c  ebrates.  H i g h r a t e s o f sediment  invert-  oxygen demand were measured on  Sturgeon  on  20  Bank i n the p r e s e n t r i b u t i o n of M.  study but  balthica  they were not c o r r e l a t e d w i t h the  (Table 3 ) .  The  h i g h e s t v a l u e s f o r sediment  oxygen uptake were a l s o not c o r r e l a t e d w i t h d i s t a n c e from the which i s common i n areas of sewage p o l l u t i o n Continuously  dist-  (Smith et al.,  outfall  1973).  r e c o r d e d v a l u e s of d i s s o l v e d oxygen l e v e l s 1 cm above the  sediment near the sewage channel have shown t h a t the oxygen c o n c e n t r a t i o n does drop to zero f o r s h o r t p e r i o d s of time  (Otte and  Levings,  but o n l y w i t h i n an area v e r y c l o s e to the sewage o u t f a l l the sewage c h a n n e l ) .  (to s i t e A  At s i t e b, f u r t h e r away from the o u t f a l l  w i t h i n the a r e a d e v o i d of Macoma, oxygen v a l u e s of >5 mg/1 to be p r e s e n t  97% of the time i n the same s t u d y .  have shown t h a t M.  balthica  i s extremely  d i s s o l v e d oxygen.  Brafield  (1963) found M.  under c o m p l e t e l y of oxygen (0.15  ml/1)  s u r v i v e f o r over M.  balthica  anaerobic  ( D r i e s and  exposure to low balthica  and m a i n t a i n  1975).  has been shown to  Theede, 1974).  In a d d i t i o n ,  itself  covered  the mantle c a v i t y when the v a l v e s  Thus, i t does not appear t h a t  Bank.  days  concentrations  l e v e l s of d i s s o l v e d oxygen can e x p l a i n the on Sturgeon  studies  l e v e l s of  can take up oxygen from the a i r when i t i s not  a r e agape (De Wilde,  found  s u r v i v e d 2-3  c o n d i t i o n s , and when v e r y low  w i t h water, by d i f f u s i o n through  of M.  balthica  a r e p r e s e n t , M. balthica  20 days  to low  along  but  were  Laboratory  resistant  1975)  The  ability  over l o n g p e r i o d s of time  acute distribution  of Macoma to f u n c t i o n i n c o n d i t i o n s of  fluc-  t u a t i n g oxygen c o n c e n t r a t i o n s however, i s unknown. Acute t o x i c i t y t e s t s c a r r i e d out i n the p r e s e n t  study  indicated  21  that  the  ISTP e f f l u e n t w a s n o t :  However, i n an cages i n the 37%  at  the  e a r l i e r study, the  outfall,  s i t e A and  Marine S e r v i c e ,  i n t o x i c i t y between the e x p l a i n e d by  the  in  on  But  on  the  be  exposure p e r i o d  sewage e f f l u e n t  1976  situ  unpublished).  b i o a s s a y s i n the  t i d e , the mudflat  the  i s also highly  of t o x i c  ISTP the  constituents  t r e a t m e n t systems, and toxicity  of  the  96  studies  As  may  The  sewage  is  forced the  e n t i r e l y with on effluent  toxicity  and  . -  p r e s e n t , t y p e of  treatment,  the  l e v e l of  outfall,  be  mentioned  effluent  the  "Slug"  have been shown t o d r a m a t i c a l l y  C o r r o s i o n of household p i p i n g  exposure  Thus Af. balthica  storm water r u n o f f .  (Stober et  h  difference  quality  chlorination  discharges  such as heavy m e t a l s o c c u r f r e q u e n t l y  effluent  and  h i g h a c o n c e n t r a t i o n of  variable  constituents  e f f e c t of  two  AO  accumulates near  much s h o r t e r .  water, d i l u t i o n a t  at  The  channel i s f i l l e d  exposed t o as would be  100,  c o n d i t i o n s found i n the  i s exposed.  of and  of  in floating  after  relatively "fresh"  toxic  receiving  of  adjacent mudflat.  depends upon the the  in mortalities  i n c o m i n g s a l t water and  a falling  the m u d f l a t would not  of  balthica  site C respectively,  a r i s i n g t i d e the  sewage e f f l u e n t w h i l e the  the  placement o f M.  very d i f f e r e n t set  s u r f a c e by  outfall.  and  balthica.  c h a n n e l compared w i t h the  previously, to the  to a d u l t M.  sewage c h a n n e l r e s u l t e d  ( F i s h e r i e s and  effluent  toxic  i n sewage  increase  the  al^. ,1977). has  been i d e n t i f i e d as  of copper "in wastewaters from the Vancouver a r e a  a majoo-rsource  (Koch et al.,  "1977).  22  In a study of wastewater t o x i c i t y a t the ISTP, Higgs copper l e v e l s f o r t h e e f f l u e n t to be between 0.11 peak c o n c e n t r a t i o n s up t o 0.43 i n sewage e f f l u e n t between 0.05 0.035 mg/1 Mya  and  samples  0.09  f o r copper  avenavia  mg/1.  (1977) r e c o r d e d  - .0.15 mg/1  with  Copper c o n c e n t r a t i o n s measured  f o r b i o a s s a y s i n the p r e s e n t s t u d y were  mg/1.  T h i s i s w e l l above the 168 h LC50 of  (added as C u C l ) 2  ( E i s l e r , 1977a).  found f o r the s o f t s h e l l  I n f o r m a t i o n on the t o x i c i t y  calm,  to marine  b i v a l v e s o f complex m i x t u r e s of m e t a l s s i m i l a r t o t h a t found i n sewage effluent  i s almost n o n - e x i s t e n t .  this subject  ( E i s l e r , 1977b),  One  of the few papers which  has shown t h a t the LC50 f o r Mya  addresses avenaria  of a m i x t u r e of m e t a l s w i t h c o n c e n t r a t i o n s s i m i l a r t o t h a t o f the e f f l u e n t was bivalve  g r e a t e r than 10 days.  Mercenavia  mortalities.  ISTP  However, i n the same s t u d y the  meTcenaria s u r v i v e d 16 weeks of exposure w i t h no  C l e a r l y , more r e s e a r c h on the t o x i c i t y o f complex m e t a l  m i x t u r e s t o marine  i n v e r t e b r a t e s needs to be c a r r i e d o u t .  In  this  r e g a r d , the c h e m i c a l s t a t e or s p e c i e s of t r a c e m e t a l i s an important c o n s i d e r a t i o n when t r y i n g to p r e d i c t  the t o x i c i t y o f  an e f f l u e n t from the r e s u l t s of l a b o r a t o r y e x p e r i m e n t s . l a b o r a t o r y s t u d i e s expose  t e s t organisms  m e t a l s a l t s which a r e n o t comparable environment.  Most  to s i m p l e s o l u t i o n s of  t o the s i t u a t i o n i n the n a t u r a l  In a review o f the b i o l o g i c a l importance o f copper i n  the s e a , Lewis and W h i t f i e l d  (1974) s t a t e t h a t the b i o l o g i c a l  of copper changes w i t h i t s c o n c e n t r a t i o n , form, and a b i l i t y i n t o complexes w i t h o r g a n i c l i g a n d s .  effect  to enter  Sewage e f f l u e n t has been shown  23  to c o n t a i n s e v e r a l o f the c o m p l e x i n g a g e n t s known t o b i n d m e t a l i o n s and t o d e c r e a s e t h e i r  (Bender et  toxicity  The c o m p l e x i n g c a p a c i t y o f sewage e f f l u e n t  showed that a d d i t i o n o f u n c h l o r i n a t e d  enriched  seawater i n c r e a s e d  Euchaeta  japonica.  Venerupis  exposed  i t s e f f e c t on r e d u c i n g m e t a l  ISTP e f f l u e n t  ,(1972) , t o copper  the s u r v i v a l o f t h e c a l a n o i d  High m o r t a l i t i e s have been  deoussata  at-,. ,1970).  f o r copper by Lewis et al,.  t o x i c i t y has been demonstrated who  and  t o 0.1  mg/1  heavy  copepod,  o b s e r v e d i n the clam,  o f copper b u t no  a c u t e or s u b l e t h a l  e f f e c t s were e v i d e n t i n the same c o n c e n t r a t i o n s of copper which' had c h e l a t e d w i t h EDTA (Stephenson and T a y l o r , Chlorination w i l l also significantly sewage e f f l u e n t  ( E s v e l t , 1973).  c h l o r i n e a r e w e l l documented about  eco-systems. effluent  sea u r c h i n  increase  the t o x i c i t y  (1973) showed t h a t  f e r t i l i z a t i o n a t 0.05  i s known  estuarine  chlorinated ppm  total  c h l o r i n e a f t e r o n l y 5 minutes e x p o s u r e . • L a r v a e o f the clam mercenaria et al  of  Although the t o x i c e f f e c t s o f  c h l o r i n e i n m a r i n e and  Muchmore and E p e l  inhibited  1975).  ( B r u n g s , 1973), v e r y l i t t l e  the t o x i c i t y o f combined  been  were shown t o have a 48 h TL50 o f <0.005 mg/1  by  sewage residual Mercenaria  Roberts  (1975) and s i m i l a r l e v e l s have 'been found t o a f f e c t m o l l u s c  l a r v a e i n the James R i v e r e s t u a r y  ( B e l l a n c a , 1977).  The  concentration  of t o t a l r e s i d u a l c h l o r i n e i n t h e r e c e i v i n g w a t e r o f t h e ISTP were below d e t e c t a b l e l i m i t s chlorinated  (0.01 mg/1)  and no a c u t e e f f e c t s ' o f t h e  e f f l u e n t were o b s e r v e d a f t e r  t h e 7 day in situ  bioassay  24  w i t h a d u l t M.  balthica.  Chlorine  can  combine w i t h a l a r g e number of  the o r g a n i c compounds i n sewage e f f l u e n t to form s t a b l e chlorinated  compounds which are  Cohen, 1976)  but  these were not  S u i t a b i l i t y of the  t o x i c to a q u a t i c investigated  substratum has  biota  organo(Katz  i n the p r e s e n t  frequently  and  (Thorson, 1957;  K n i g h t s , 1975).  inorganic  and  Boyden and  Physical,  (eg. g r a i n  o r g a n i c compounds) and  l i v i n g micro-organisms) p r o p e r t i e s the  e s t a b l i s h m e n t and  The  influence  M.  balthica,  of  the  has  1973;  substrate  which c h a r a c t e r i s t i c s of the  metal concentrations, of n i t r o g e n  and  (eg.  of the  sediments a c t  to  regulate  (Gray, 1974).  including  to be p a r t i c u l a r l y important i n (Anger, 1975;  L e p p a k o s k i , 1975).  further  to determine  substratum i n f l u e n c e b e n t h i c  populations  P a r t i c u l a t e o r g a n i c matter a s s o c i a t e d  w i t h sewage  been suggested to be  ( W a t l i n g , 1975), but  Kay  b i o l o g i c a l (eg. presence of  s t u d i e s , however, have i n v e s t i g a t e d  s l u d g e has  chemical  on many bottom s p e c i e s ,  sewage p o l l u t i o n  i n p o l l u t e d areas.  Gray, 1974;  size),  be  benthic  maintenance of b e n t h i c communities  been demonstrated  a r e a s a f f e c t e d by Very few  Little,  study.  been shown to  the most important f a c t o r g o v e r n i n g the d i s t r i b u t i o n of animals  and  smaller  a major s u b s t r a t e  related  factor  sediment p a r t i c l e s i z e s , h i g h e r  greater  numbers of b a c t e r i a , and  o r g a n i c carbon are a l s o a s s o c i a t e d  i n a r e a s r e c e i v i n g sewage e f f l u e n t  (O'Sullivan,  i d e n t i f i c a t i o n of a s p e c i f i c f a c t o r of c a u s a l sewage p o l l u t i o n i s d i f f i c u l t .  rich  w i t h the  1971).  Thus  sediment deposits sediments the  agent r e l a t e d to  the  25  Data from the p r e s e n t  study  ( F i g . 5) s t r o n g l y suggest  s u b s t r a t e p r o p e r t i e s were r e s p o n s i b l e f o r the d i s t r i b u t i o n M.  balthica  (0+ age along  on Sturgeon Bank.  The  i n d i c a t e s t h a t the s u b s t r a t e was  successful recruitment existing populations  of Macoma s p a t .  at the l a t t e r  absence of one  year  of  l a c k of newly s e t t l e d i n d i v i d u a l s  group) i n the a r e a where no Macoma were found and  the j e t t y  that  If t h i s trend  continues, i n about  two  years.  The  s i t e A5  s u g g e s t s t h a t newly s e t t l e d l a r v a e or young j u v e n i l e clams  cannot s u r v i v e at t h i s l o c a t i o n , and w i l l d i e out. result  The  o r i g i n a l settlement)  the M.  M.  was  recent, previous  s i t e may  balthica  populations.  found i n the p r e s e n t study  the a r e a a f f e c t e d by  have been  study w i t h  those  are  of the most  year,  indicating  the sewage p o l l u t i o n i s expanding.  ( i e . a5,  adjacent  having  to the a r e a p r e v i o u s l y i d e n t i f i e d as  I t i s apparent  disthat  This  the i n c r e a s e i n sediment m e t a l  o r g a n i c l e v e l s over the same p e r i o d f o r s i t e s  the h i g h e s t m e t a l c o n c e n t r a t i o n .  of  A comparison of s i t e s where  from s i t e a5 i n one  by  the  Several a d d i t i o n a l  (G.V.S.D.D., 1977), shows the complete  a l s o confirmed  too,  ( i e . t i d a l movement from the a r e a  as d e s c r i b e d by Beukema (1973) .  appearance of M. balthica  expansion was  at t h i s  the c o n c l u s i o n t h a t changes i n the s u b s t r a t e  controlling balthica  group) i n d i v i d u a l s a t  therefore this population  apparent s e t t l e m e n t  of "secondary s p a t f a l l "  f a c t s support  (1+ age  sites  unsuitable for  s i t e s w i l l d i e out  old  at  and  c, C i n F i g .  2)  26  t h a t M.  balthica  i n a t i o n and f o r age  does not o c c u r  t h a t t h i s a r e a i s growing i n s i z e .  Based on  c l a s s d i s t r i b u t i o n d e s c r i b e d above, one  M. balthica  would next be  e l i m i n a t e d from s i t e  p a t t e r n matches t h a t o f the two along  i n the r e g i o n s o f h i g h e s t  the j e t t y  and  the  data  would p r e d i c t t h a t c, and  major c o n t a m i n a t i o n  A5.  This predicted  gradients,  south-west a l o n g the marsh a r e a as shown by  t r i b u t i o n p a t t e r n f o r copper i n d i c a t o r organisms  contam-  ( F i g . 2).  several species  community have shown  can  be  dis-  Changes i n the d i s t r i b u t i o n of  (eg. Etone longa) and  i n d i c e s a p p l i e d t o the b e n t h i c  the  e x p l a i n e d by  other  diversity  t h i s same  p a t t e r n of expansion  which  changes i n  s u b s t r a t e but not by  the d i s p e r s a l p a t t e r n o f the sewage  the  effluent  (G.V.S.D.D., 1977). Which p r o p e r t y  or p r o p e r t i e s of the s u b s t r a t u m  r e s p o n s i b l e f o r the absence of M.  balthica  a r e not  are  directly  as easy t o d e f i n e .  Sediment g r a i n s i z e i s u n l i k e l y  to c o n t r o l t h e d i s t r i b u t i o n  M. balthica  been found  silt  and  as  t h i s s p e c i e s has  to o c c u r  c l a y sediments which a r e as f i n e o r f i n e r  S t u r g e o n Bank (Beanland,  1940;  Kay  and K n i g h t s ,  of  i n unpolluted than  1975).  those  Extremely  h i g h i n p u t s o f o r g a n i c m a t e r i a l from sewage have been shown t o i n the disappearance f a i l u r e o r by non 1975)>  of t h e Macoma p o p u l a t i o n s  through  s e l e c t i v e i n f l u e n c e on a l l age  groups  (p <0.01) w i t h  result  recruitment (Leppakoski,  hcwever, the a r e a w i t h t h e h i g h e s t sediment o r g a n i c  Bank i s s i g n i f i c a n t l y - c o r r e l a t e d  on  the e l e v a t e d  content  on  Sturgeon  concentrations  27.  of heavy m e t a l s  (G.V.S.D.D., 1975).  The heavy m e t a l s i n s e d i m e n t s  are u s u a l l y not i n a form t o be s u f f i c i e n t l y , b i o l o g i c a l l y a v a i l a b l e to be t o x i c  ( B r y a n , 1976), b u t e v i d e n c e i s a v a i l a b l e t o s u g g e s t  t h a t they may  be r e s p o n s i b l e  f o r s u b l e t h a l e f f e c t s observed i n  marine b i v a l v e s  exposed  Stirling  noted, -an impaired burrowing response..-_  (1975)  f o r the b i v a l v e Tellina sediment .  An  f o r M. balthica and mercury  to contaminated s e d i m e n t s  tenuis  when p l a c e d on  i m p a i r e d r a t e o f b u r r o w i n g has a l s o been f o u n d exposed  to contaminated s e d i m e n t s from S t u r g e o n Bank,  and cadmium w e r e . . s t a t i s t i c a l l y s i g n i f i c a n t  . ( t h i s study;  by burrowed sediment  M. balthica  pp. 44-5S). was  ( s i t e b) t e s t e d .  the response  An a c t i v e a v o i d a n c e r e s p o n s e  a l s o demonstrated  f o r the most  No m o r t a l i t i e s o f a d u l t  the s e d i m e n t s t e s t e d were r e c o r d e d .  clams  Macoma l a r v a e  o r on young, j u v e n i l e M. balthica  (Spehar et aZ.,1978),  settled  toxic i n  b u t M. balthicahas  some  i n the form o f a d e t o x i f i c a t i o n system i n v o l v i n g the p r o t e i n  metallothionein of loading  i n any o f  a r e n o t known.  B i o a c c u m u l a t i o n of m e t a l s has a l s o been shown t o be aquatic invertebrates  contaminated  What s u b l e t h a l o r a c u t e e f f e c t s  t h e s e h i g h sediment m e t a l l e v e l s c o u l d have on r e c e n t l y  protection  1975).  copper -contaminated  (p <0.05 and p <0.001 r e s p e c t i v e l y ) i n e x p l a i n i n g observed  (Stirling,  (Brown et al . ,1977).  However, i f t h e l o a d  o f heavy m e t a l s i s s u f f i c i e n t  or r a t e  t o overcome t h e amount o f  28  m e t a l l o t h i o n e i n produced, enzymes w i l l  occur  ' s p i l l o v e r ' of heavy metals to e s s e n t i a l  resulting in pathological effects.  which the m e t a l l o a d i n g becomes too g r e a t  f o r M.  The  toxicity  the sediment.  The  to the l a r v a e by any  post-larvae  at  b a l t h i c a i s unknown.  M o r t a l i t y of s e t t l i n g l a r v a e on a p o l l u t e d s u b s t r a t e from d i r e c t  point  can  result  number of contaminants i n  of the m a j o r i t y  of bottom  dwelling  s p e c i e s , s e t t l i n g on a h e a v i l y p o l l u t e d s u b s t r a t e , d i e out v e r y  quickly  compared to the l a r v a e of p o l l u t i o n i n d i c a t o r s such as Capitetla (Mileikovsky,  1970).  Leppakoski  (1975) noted t h a t i n s p i t e of  aapitata an  immediate improvement i n water q u a l i t y a f t e r p o l l u t i o n abatement i n a Norwegian f j o r d , benthic  the h a r m f u l e f f e c t s of contaminated sediments  r e c o l o n i z a t i o n for several years.  Data on  the n a t u r e  inhibited and  concentrations  of o r g a n i c s , m e t a l s or o t h e r p o l l u t a n t s i n sediments  as they a f f e c t  s e t t l i n g , metamorphosis and  j u v e n i l e s of b e n t h i c a d d i t i o n to t o x i c i t y , may  i n t e r f e r e with  used to p e r c e i v e 1961).  The  s u r v i v a l of the l a r v a e  i n v e r t e b r a t e s are v i r t u a l l y n o n - e x i s t e n t . i n o r g a n i c and  organic  compounds i n the  p r e s e n c e of dead organisms and  induce s e t t l e m e n t  1955).  The  too few"  presence of b a c t e r i a , " i n numbers n e i t h e r  (Wilson,  of b a c t e r i a settlement  (Gray, 1966)  have been c o n s i d e r e d  Sturgeon Bank occur  critical  matter  bieornis  to  c e r t a i n types induce  Bacteria i n  i n extremely  (Wilson,  too many nor  s u r f a c e f i l m produced by  i n many marine i n v e r t e b r a t e l a r v a e .  the sediments on numbers due  1955), or the  larvae'  (Scheltema,  n o n - l i v i n g organic  i s a l s o known to be r e p e l l e n t to the l a r v a e of Ophelia  In substrate  or mask the chemo-reception a b i l i t y of the  a s u i t a b l e s u b s t r a t e and  and  high  to the i n f l u e n c e of the sewage e f f l u e n t (G.V.S.D.D.,  29  1977), b u t t h e e f f e c t o f t h e s e a b n o r m a l l y abundant b a c t e r i a suitability  of the s u b s t r a t e f o r l a r v a l  on t h e  settlement i s a matter f o r  speculation. In appears  conclusion,  the d i s t r i b u t i o n  to be p r i m a r i l y determined  The p o l l u t e d  substrate affected  and j u v e n i l e M. balthica,  o f M. balthica  on S t u r g e o n Bank  by c o n t a m i n a t i o n o f t h e s u b s t r a t e .  t h e s e t t l e m e n t and s u r v i v a l o f l a r v a l  and the g r o s s l y c o n t a m i n a t e d  a r e a was showh t o be ;  moving seawards, p r o g r e s s i v e l y e x c l u d i n g Macoma p o p u l a t i o n s . heavy m e t a l s from t h e nearby  sewage t r e a t m e n t p l a n t  c o n c e n t r a t i o n s i n the sediments, possible controlling factor.  of the  e f f e c t s o f contaminated  occur i n high  they have been i m p l i c a t e d  as a  However, the q u a n t i t y and q u a l i t y o f  o r g a n i c m a t t e r and b a c t e r i a may the  Since  a l s o be i m p o r t a n t .  sediments  Research  into  on t h e s e t t l e m e n t and s u r v i v a l  t h e l a r v a e o f b e n t h i c i n v e r t e b r a t e s i s l a c k i n g and more d a t a on s p e c i f i c nature of these i n t e r a c t i o n s i s r e q u i r e d .  TABLE 1 PHYSICAL AND CHEMICAL CHARACTERIZATION OF SEDIMENTS IN STUDY A R E A * - J U L Y ,  Site  Median . ., Particle  I" 1  T  . . , Interstitial ,. . ^ Salinity 0  Organic ° , Carbon „ co  Heavy metals  «r *«  M  C  ° -  CU  1977  (ug/g d r y wt)  S/KS  ~ HS  -  M B I PT ZN  a a3 a5  <63 <63 <63  8. 1 5. 9 6.1  4. 28 1. 52 1. 13  1. 0 3. 2 2. 6  3. 0 0. 4 <0. 4  14 13 13  124 72 60  234 95. 0 67. 0  33.5 30.0 30.0  0.89 0.27 0.18  322 296 300  46 41 41  166 48 32  264 134 109  A A3 A5  <63 <63 <63  5. 1 5. 9 5. 6.  3. 12 1. 62 0. 87  1. 4 4. 4 2. 0  2. 0 0. 6 <0. 4  15 14 13  108 79 58  180 106 0 • 47.  34.5 33.5 30.0  0.57 0.28 0.16  332 330 310  46 41 40  134 56 26  212 145 93  b b2 b5 b7  <63 110 70 <63  5. 9 4. 2 4:.1 5. 0  3. 09 0. 47 0. 56 0. 83  1. 0 1. 0 1. 4 1. 4  1. 4 <0. 4 <0. 4 <0. 4  15 10 11 13  90 44 55 56  150 27. 2 39. 6 43. 0  36.0 21.0 26.5 29.5  0.46 0.12 0.15 0.16  340 220 274 300  49 32 38 41  74 16 20 22  172 64 74 84.  B B2 B5 B8  <63 127 <63 <63  5. 0 4. 5 5.,8 4.,5  2. 01 0. 41 1.,12 0.,74  1. 2 0. 6 1.,6 1.,0  0. 8 <0. 4 <0.,4 <0.,4  14 10 13 12  78 38 61 48  110 21.,4 64.,0 35..2  33.5 20.5 32.0 27.5  0.32 0.08 0.16 0.11  318 228 316 330  47 31 42 37  62 14 32 20  150 54 104 80  c  135  6,,1  0,.92  1,.4  0.4  11  44  38,.0  21.0  0.15  226  35  20  82  C C2 C5 C8  120 168 168 130  5,.1 9 .8 6 .9 9 .2  0,.23 0 .20 0 .14  1,.0 <0 .4 <0 .4 <0 .4  0,.4 <0 .4 <0 .4 <0 .4  11 11 12 11  40 32 33 33  30,.0 13 .8 13 .4 13 .8  20.0 20.6 21.0 20.0  0.13 0.05 0.04 0.04  214 282 330 342  32 31 32 33  18 6 6 6  73 50 50 54  D D2 D5 D8  172 170 250 168  7 .0 9 .8 9 .0 6 .0  0 .49 0 .17 0 .13 0 .12  <0 .4 <0 .4 <0 .4 <0 .4  <0 .4 <0 .4 <0 .4 <0 .4  10 10 10 10  35 34 28 32  15 .6 12 .4 12 .6 12 .8  19.0 19.6 19.0 19.0  0.08 0.04 0.04 0.03  232 310 340 330  32 30 28 31  6 6 3 4  52 45 41 47  *see F i g u r e 1  -  o, .59  TABLE 2 SUMMARY OF SEDIMENT METAL DATA (Mean  ± S.D.,  yg/g d r y w e i g h t )  Transect Metal  Study Area D  Ag  <1.3 ± 1.0  2.3 ± 1.1  2.6 ± 1.6  1.2 ± 0.2  1.1 ± 0.4  <0.6 ± 0.3  <0.4 ± 0.0  Cd  <0.6 ± 0.6  1.3 ± 1.5  <1.0 ± 0.9  <0.6 ± 0.5  <0.5 ± 0.2  <0.4. ± 0.0  <0.4 ± 0.0  Co  12.0 ± 1.7  13.3 ± 0.6  14.0 ± 1.0  12.2 ± 2.2  12.2 ± 1.7  11.2 ± 0.5  10.0 ± 0.0  Cr  55.7 ± 25.8  85.3 ± 34.0  81.7 ± 25,1  61.2 + 19.9  56.2 ± 17.3  34.5 ± 3.7  32.2 ± 3.1  Cu  60.1 ± 6 0 . 0  132 ± 89.4  111 ± 66.7  65 ± 57  57.6 ± 39.2  17.8 ± 8.2  13.4 ± 1.5  Fe (g/Kg)  26 ± 6.2  Hg  0.20 ± 0.20  31.2 ± 2.0  32.7 ± 2.4  28.2 ± 6.2  28.4 ± 5.8  20.4 ± 4.5  19.2 ± 0.3  0.45 ± 0.39  0.34 ± 0.21  0.22 ± 0.16  0.17 ± 0.11  0.06 ± 0.04  0.05 ± 0.02  Mn  297 ± 43  306 ± 14  324 ± 12  284 ± 50  298 ± 47  292 ± 58  303 ± :49  Ni  37.2 ± 6.2  42.7 ± 2.9  42.3 ± 3.2  40.0 ± 7.1  39.2 + 6.8  32.0 ±'0.8"  30.2 ± 1.7  Pb  35 ± 4 2  Zn  97.0 ± 58.0  82 ± 73 169 ± 83.2  72 ± 5 6 150 ± 59.6  33 ± 27  32 ± 21  9 ± 6  98.5 ± 49.7  97.0 ± 40.8  56.8 ± 11.0  5 ± 2 46.2 ± 4.6  TABLE  32  3  SEDIMENT OXYGEN .UPTAKE RATE AND PRESENCE/ABSENCE OF M. balthica AT SEVERAL S I T E S OVER STUDY AREA - S E P T E M B E R ,  1977  Mean  Site  Oxygen Uptake Rate mg 02/m2/h (±S.E.)  M. balthica Present/Absent  82 ± 9  A  A3  108 ± 4  A  a5  100 ± 13  A  A5  107 ± 16  P  b5  141 ± 19  P  B5  126 ± 4  P  a3 •  (±S.E.) Oxygen Uptake Values f o r A r e a s o f M. balthica Absence and P r e s e n c e  x = 96 ± 8  x = 125 ± 10  TABLE 4 DENSITY AND  BIOMASS  FOR M. balthica  Density (No./m ± S.E.) 2  a a3 a5  FROM S I T E S ON STURGEON BANK  Biomass (g d r y weight/m ) 2  absent n  -  ti  -  II  -  A A3 A5  128  b b2 b5 b7  absent 391 + 51 405 + 54 256 + 54  B B2 B5 B8  absent 697 + 56 476 + 188 384 + 49  c  121  II  + 21  -  1.061 —  4.529 8.313 2.880 —  1.640 3. 615 2.875  + 19  0.388 6.486 1.662 1.855 2.369  C C2 C5 C8  199 1010 1038 1038  + 68 + 82 + 130  D D2 D5 D8  412 544 576 491  + 14 + 140 + 12  + 179  + 54  3.862 1.037 1.415 0.462  34 TABLE 5 VALUES FOR y INTERCEPT ( a ) AND SLOPE ( b ) OF REGRESSION l o g 1 0 y = a + bx WHERE y = MEAN DRY FLESH WEIGHT IN M G , AND x = SHELL HEIGHT  IN MM FOR M. b a l t h i c a  Sample Size  Site  •  a  b  A5  4  -1.2100  0.1855*  b2 b5 b7  15 15 9  -0.5331 -0.4524 -0.6447  0.1511* 0.1309* 0.1536*  B2 B5 B8  4 8 12  -1.5030 -0.6591 -0.7533  0.2877* 0.1702* 0.1637*  5  -1.4600  0.3256*  C C2 C5 C8  9 9 13 13  -0.7364 -1.5470 -1.2280 -1.0790  0.1834* 0.2538* 0.2353* 0.2140*  D D2 D5 D8  4 7 9 6  -0.9281 -1.1210 -1.2100 -2.2640  0.1688* 0.2403* 0.2249* 0.4269*  c  * Significant  at p  <0.05 l e v e l  •  TABLE 6  35  CONCENTRATION OF HEAVY METALS IN T I S S U E S OF M. balthica (ug/g d r y weight)  Site  Cd*  Cu  Fe  Hg  b5  313.6 (27.4)  475.6 (41.6)  6.76 (0.60)  B2  170.7 (15.4)  1452.1 (131.1)  2.43 (0.22)  74.6 (6.6)  699-6 ' (62.3)  0.76 (0.07)  D5  49.1 (4.8)  368.6 (36.2)  0.74 (0.07)  D8  51.4 (4.8)  797.3 (74.5)  0.89 (0.08)  C5  _  Pb**  Zn 743.2 (65.0)  —  -  -  392.2 (35.4) 531.7 (47.3) 399.3 (39.2) 406.4 (40.0)  Numbers i n b r a c k e t s = ug/g wet weij;ht. * **  C o n c e n t r a t i o n i n 25 ml d i g e s t l e s s than d e t e c t a b l e l i m i t C o n c e n t r a t i o n i n 25 ml d i g e s t l e s s than d e t e c t a b l e l i m i t  of 0.02 ug/1. of 0.2 ug/1.  TABLE  7  36  BIOCONCENTRATION RATIO OF METALS I N M.  Tissue/Sediment Site  balthica  Ratio  Cu  Fe  Hg  Zn  b5  7.92  0.02  45.07  10.04  B2  7.98  0.07  30.38  7.26  C5  5.57  0.03  18.50  10.63  D5  1.95  0.01  18.50  4.27  D8  4.02  0.04  29.67  8.64  TABLE 8  T W of Type of sewage e f f l u e n t  Unchlorinated  Chlorinated  RESULTS OF LABORATORY  TOXICITY  n^p  ^est  Date tested  T  t  e  m  p  l  Salinity  s  e  r  a  (  C  )  '  effluent concentration  t  t  ,  u  r  e  U  V  /  V  )  Jan. 23/78 Jan. 23/78 Feb. 6/78 Feb. 6/78 Apr. 18/78 May 3/78  10 18 10 18 10 10  80 80 100 100 80 80  Apr. 18/78  25/78 May 3/78  10 10 10  80 80 80  Apr. 18/78  10  80  Apr.  Dechlorinated  e  BIOASSAYS WITH M.-  adjusted with Instant  Ocean  1 1  2 3 4  " " " S concentration t e s t e d (°/oo) i  .  balthica  n  S  h  a  i  y  h  e  s  t  y highest effluent concentration (168 h) %  i  M  o  r  t  a  l  n  5.2 5.2 12.2 12.2 5.1 5.1  0 0 0 0 0 0  5.1 5.1 5.1  0 0 0  5.1  R  2  Initial  l e v e l of r e s i d u a l c h l o r i n e i n 80% e f f l u e n t  c o n c e n t r a t i o n was 1.00 ppm  3  Initial  l e v e l of r e s i d u a l c h l o r i n e i n 80% e f f l u e n t c o n c e n t r a t i o n was 2.25 ppm  ^Initial  l e v e l o f r e s i d u a l c h l o r i n e i n 100% e f f l u e n t c o n c e n t r a t i o n was 0.5 ppm  i  t  38  TABLE 9 IN SITU BIOASSAY RESULTS AND WATER QUALITY D A T A , MAY 8 , 1 9 7 8  % Mortality (168 h)  Site  Salinity (°/oo)  Temperature (°C)  Dissolved Oxygen (ppm)  Total Residual C h l o r i n e (ppm)  a  0  3-6  17.5  1.9  N.D.*  A  0  14.1  17.0  7.2  N.D.  B  0  15.2  13.0  7.6  N.D.  C  0  15.2  17.5  7.0  N.D.  0  16.8  13.5  7.1  N.D.  -  <0.1  20.0  3.1  0.50  A-control (North Side of J e t t y ) Effluent  *N.D. = none  detected  D  C  c  B  b  A  +  +  +  +  • +  +  on S t u r g e o n  Bank,  a  Iona Jetty  Sewage Effluent  FIGURE 1 .  Location of Fraser  River  study  a r e a and s a m p l i n g s i t e s  estuary,  British  Columbia.  +  „  FIGURE 2 .  Distribution  pattern  in  over  sediments  for  study  concentration area.  of  copper  (ppm)  41  1200i  iona Jetty  2  4  6  Site n u m b e r along FIGURE 3.  Density  o f M. balthica  along  8  transect  transects  across  study  area.  42  Jetty  Site number along FIGURE 4.  B i o m a s s o f M. balthica study  area.  along  transect transects  across  FIGURE 5 .  Age at  class  frequency  sites within  distribution  study  area.  o f M.  balthica  Sublethal  Effects  S e d i m e n t s on t h e  of  Heavy M e t a l  Contaminated  B i v a l v e Macoma balthica  (L).  Introduction I n c r e a s i n g a t t e n t i o n i s b e i n g p a i d to the e f f e c t s o f p o l l u t a n t s on marine organisms. of measuring  changes  sublethal  The  importance  i n b e h a v i o u r , p h y s i o l o g y and  metabolism  has been r e c o g n i z e d as e s s e n t i a l t o the assessment  of chronic  e f f e c t s of low l e v e l s o f contaminants i n the oceans. of such t e s t s as r o u t i n e b i o a s s a y s was (1975) who  reported  the b i v a l v e Tellina  suggested by  The  use  Stirling  e f f e c t s on the burrowing b e h a v i o u r o f tenuis  a f t e r exposure t o s u b l e t h a l  c o n c e n t r a t i o n s o f copper and p h e n o l .  More r e c e n t l y ,  b e h a v i o u r a l s t u d i e s w i t h m o l l u s c s have been used t o measure the s u b l e t h a l e f f e c t s o f copper oil  ( S t a i n k e n , 1976;  1978)  and  (Stephenson and T a y l o r ,  L i n d e n , 1977;  s o l i d wastes  G i l f i l l a n and  from ocean dumping  1975),  Vandermuelen,  (Chang and L e v i n g s ,  1976). The p r e s e n t paper d e s c r i b e s the r e s u l t s of a s e t o f experiments d e s i g n e d t o i n v e s t i g a t e the e f f e c t heavy m e t a l c o n t a m i n a t e d  of  sediments on the burrowing  avoidance b e h a v i o u r o f the b i v a l v e , Macoma balthica  and (L.).  46  The  taxonomy o f Macoma balthica  inconspicua  (Linnaeus,  1758) [= M.  ( B r o d e r i p and Sowerby, -1829)] on t h e west  of N o r t h America i s i n need o f r e v i e w . of i n t e r e s t  The fundamental  i s whether the A t l a n t i c and P a c i f i c  t h i s v a r i a b l e b i v a l v e are separate species or a s i n g l e species.  (although  closely  species.  related)  I n t h e most r e c e n t paper t o d a t e ,  i s undertaken, i t s h o u l d  circum-arctic  question  specimens o f  Coan (1971) has suggested t h a t u n t i l a major p r o j e c t t h i s subject  coast  be c o n s i d e r e d  addressing as one  T h i s recommendation w i l l be f o l l o w e d  here as i t has i n o t h e r  s t u d i e s from t h e P a c i f i c  coast  (eg. Shaw et al. , 1976).  Methods Test  c o n t a i n e r s were p o l y e t h y l e n e  35 x 15 x 14 cm i n s i z e f i l l e d and  covered  Pasteur  A e r a t i o n was t h r o u g h a  i n the c e n t r e o f t h e tank and c a r e  was taken not t o d i s t u r b t h e sediment. out  a t 10 ± 1°C. .M: balthica  t e s t s were c o l l e c t e d the F r a s e r R i v e r  approximately  t o 5 cm d e p t h with, sediment  by 2.5 I o f seawater.  p i p e t t e placed  tubs  (5-10 mm  A l l t e s t s were c a r r i e d s h e l l l e n g t h ) used i n t h e  from an u n p o l l u t e d  estuary,  mudlfat  (Roberts  Bank) i n  B r i t i s h Columbia and a c c l i m a t e d t o  47  l a b o r a t o r y c o n d i t i o n s f o r 48 h . a l s o t a k e n from t h i s a r e a . collected  Sediments used as c o n t r o l s were  Contaminated  test  a t v a r y i n g d i s t a n c e s from a sewage t r e a t m e n t p l a n t  o u t f a l l which d i s c h a r g e s onto a t i d a l f l a t River  sediments were  i n the F r a s e r  estuary. E f f e c t on b u r r o w i n g b e h a v i o u r was  measured by  each o f f i v e c o n t a i n e r s w i t h a d i f f e r e n t t e n M. balthica  sediment,  and  a t i n t e r v a l s of 15, 30, 45,  contaminated  60,  6, 12, 24 and 48 h.  The a v o i d a n c e t e s t s were s e t up w i t h c o n t r o l p o l l u t e d ) mud  placing  on each sediment and o b s e r v i n g the number o f  a n i m a l s which had burrowed 90, 120 min.  filling  (non-  i n one h a l f of each c o n t a i n e r and a d i f f e r e n t sediment  i n the o t h e r h a l f .  Ten M. balthica  were  added w i t h f o u r i n d i v i d u a l s b e i n g p l a c e d on each s i d e and two on t h e boundary  between t h e two  sediment t y p e s .  24 h, the water was  d r a i n e d o f f , and  After  sediments from each  half  of the c o n t a i n e r were, removed.and s i e v e d t o count the number of M. balthica.  The numbers burrowed  i n each p a i r o f  s u b s t r a t e s at the end of the t e s t were compared u s i n g binomial test  f o r n <25 w i t h p = 0.05.  i n favour of the c o n t r o l s u b s t r a t e  the  A n a l y s e s were 1 - t a i l e d  (Larkin,  1976).  Results The n a t u r e of the t e s t and  characterised  content.  sediments used have been d e s c r i b e d  i n T a b l e 1 by t h e i r  o r g a n i c and heavy  The d a t a a r e t h o s e r e p o r t e d by McGreer  Contaminated  sediments  d i s t a n c e s from a major  (A-D) were c o l l e c t e d  at  metal  (1978).  increasing  sewage e f f l u e n t d i s c h a r g e and  the c o n c e n t r a t i o n of contaminants a l o n g a p o l l u t i o n  reflected gradient  which decreased c o n s i s t e n t l y w i t h d i s t a n c e from the s o u r c e . The m e t a l s which showed e l e v a t e d  l e v e l s c l o s e t o the  ( S i t e A, T a b l e 1) were copper, l e a d , z i n c , chromium, cadmium and  Burrowing  Behaviour balthica  were observed  i n a l l sediments when compared t o the c o n t r o l t e n i n d i v i d u a l s burrowed  e f f e c t i v e time f o r burrowing l i m i t s a r e shown i n T a b l e 2. from a l o g - p r o b i t p l o t of L i t c h f i e l d  (Fig. 1).  i n the c o n t r o l , B, and D  sediments compared t o 90% i n C and  from 0.17  mercury,  iron.  Slower burrowing r a t e s f o r M.  All  outfall  only  (ET50) and  60% i n A.  The median  95% c o n f i d e n c e  The v a l u e s were c a l c u l a t e d  ( F i g . 1) a c c o r d i n g t o the methods  and Wilcoxon  (1949).  The ET50 i n c r e a s e d  h f o r the c o n t r o l and D t o i 8  h i n sediment  A,  the  most h e a v i l y c o n t a m i n a t e d .  A l i n e a r r e g r e s s i o n of t h e  c o n c e n t r a t i o n o f each i n d i v i d u a l m e t a l i n the sediments v e r s u s the  burrowing r e s p o n s e time was  g i v e n i n T a b l e 3.  The  calculated  only s i g n i f i c a n t  l i n e s were f o r the m e t a l s mercury and r e g r e s s i o n f o r cadmium was explained  98.5%  Avoidance  and•the  r e s u l t s are  (p <0.05) r e g r e s s i o n  cadmium.  highly significant  Of t h e s e , the (p <0.001) and  of the t o t a l v a r i a n c e i n the model.  Behaviour  D i s t r i b u t i o n of burrowed M. • balthica tanks c o n t a i n i n g c o n t r o l and i n T a b l e 4.  sediment  i s shown  None of the a n i m a l s were found b u r i e d a t the  boundary between the two significant  contaminated  a f t e r 24 h i n t e s t  sediment  types.  A  statistically  (p <0.05) a v o i d a n c e r e s p o n s e was  most contaminated  sediment  (A).  found f o r the  A l t h o u g h 70% of the a n i m a l s  were found i n the c o n t r o l s i d e i n the t e s t w i t h sediment t h i s was  not s t a t i s t i c a l l y  s i z e used.  significant  No a v o i d a n c e was  evident  C, D, or from one c o n t r o l t o a n o t h e r .  a t the s m a l l sample  i n tests with The  sediments  t h r e s h o l d f o r the  a v o i d a n c e response thus o c c u r r e d between sediments B and T h i s response was  B,  C.  c o n s i s t e n t w i t h t h e i n c r e a s e i n heavy m e t a l  concentrations i n these  sediments.  Discussion The  e f f e c t s o f contaminated  r e s p o n s e of M. balthica  sediments  are s i m i l a r  b i v a l v e s i n other studies  (Stirling,  on t h e b u r r o w i n g  t o those observed f o r 1975; L i n d e n ,  1977).  A mechanism t o account f o r t h i s r e s p o n s e has n o t been d e s c r i b e d ; however, i t s h o u l d be n o t e d t h a t more t h a n one explanation i s possible f o r the observations previously recorded. of  Stirling  a n i m a l s exposed  (1975) measured t h e burrowing  response  t o v a r y i n g c o n c e n t r a t i o n s o f copper i n  s t a t i c b i o a s s a y s , then r e c o r d e d t h e i r r e c o v e r y when p l a c e d in  c l e a n seawater  i n the same c o n t a i n e r s .  There was  little  r e c o v e r y o f burrowing a b i l i t y w i t h copper but i t was noted t h a t t h i s c o u l d have been due t o t h e e f f e c t s o f exposure on metabolism, an experiment effects of  or r e s i d u a l copper  In c o n t r a s t ,  u s i n g a f l o w - t h r o u g h system t o t e s t  (Stephenson and T a y l o r , 1975),  burrowing and f u l l  decussata.  i n t h e sand.  Stirling  found  r e c o v e r y i n t h e clam,  copper  inhibition Venevupis  (1975) a l s o found t h a t r e c o v e r y from  phenol was f a s t e r i n f l o w - t h r o u g h t h a n i n s t a t i c I n a d v e r t e n t c o n t a m i n a t i o n o f c l e a n sediments  tests.  f o r use i n  r e c o v e r y t e s t s was not c o n s i d e r e d i n t h e s e e x p e r i m e n t s .  C o n t a m i n a t i o n o f c l e a n sediments  i s more l i k e l y  s t a t i c r a t h e r than f l o w - t h r o u g h c o n d i t i o n s . of oil  test  sediments  Contamination  c o u l d a l s o e x p l a i n t h e l a c k o f r e c o v e r y from  f o r M. balthica  observed  by L i n d e n  (1977).  R e s u l t s o f the p r e s e n t study c o n f i r m e d sediments  that  contaminated  a f f e c t b u r r o w i n g b e h a v i o u r and demonstrated  need t o use c l e a n sediments is  to occur i n  critical  i n behavioural tests.  the  T h i s need  i n s t u d i e s d e s i g n e d t o t e s t whether t h e t o x i c a n t  i n s o l u t i o n or i n a p r e v i o u s l y contaminated c a u s i n g t h e . i n h i b i t e d burrowing out to d a t e suggest  response.  t h a t b o t h t y p e s of  sediment i s Studies carried  exposure may be  important. R e s u l t s of t h e p r e s e n t study a l s o i n d i c a t e d burrowing  behaviour of l a r g e r  than s m a l l e r i n d i v i d u a l s . burrowed f i r s t  i n d i v i d u a l s was a f f e c t e d  more  G e n e r a l l y , the smaller animals  and i n the t e s t w i t h sediment  i n d i v i d u a l which never burrowed size.  that the  C, t h e one  ( F i g . 1) was t h e l a r g e s t i n  These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e b u r r o w i n g  behaviour  for different  (1975) and L i n d e n  s i z e s o f b i v a l v e s r e p o r t e d by  Stirling  (1977), but an e x p l a n a t i o n f o r t h e s e  o b s e r v a t i o n s has not been a p p a r e n t .  These o b s e r v a t i o n s a r e  c o n t r a r y t o t h e e f f e c t s o f t o x i c a n t s on p e l a g i c  s p e c i e s which  g e n e r a l l y show an i n c r e a s i n g  tolerance to p o l l u t a n t s with  i n c r e a s i n g s i z e and age (Sprague Avoidance demonstrated  of m e t a l - c o n t a m i n a t e d  f o r midge l a r v a e  Wentsel et al.  1969, 1970).  (1977).  sediments was  (Chironomus  A different  tentans)  recently by  threshold response  f o r a v o i d a n c e was observed f o r each m e t a l .  level  The t h r e s h o l d  v a l u e s were h i g h (eg. 213-422 ppm cadmium) and a l i n e a r r e l a t i o n s h i p between sediment m e t a l l e v e l and a v o i d a n c e was found f o r two o f the m e t a l s t e s t e d , namely cadmium and z i n c . The a v o i d a n c e d a t a from the p r e s e n t i n v e s t i g a t i o n the h y p o t h e s i s of a c t i v e a v o i d a n c e of m e t a l sediments by b e n t h i c i n v e r t e b r a t e s . study and the one by Wentsel et al.  supports  contaminated  In both t h e p r e s e n t (1977), the c o n c e n t r a t i o n  of cadmium i n the sediment was most s i g n i f i c a n t  i n explaining  the b e h a v i o u r a l r e s p o n s e s o b s e r v e d .  experiments  using c o n t r o l l e d  Laboratory  c o n c e n t r a t i o n s and c o m b i n a t i o n s o f i n d i v i d u a l  metals a r e r e q u i r e d  to test  this hypothesis further.  An e x a m i n a t i o n o f t h e c h e m i c a l forms o f heavy m e t a l s i n t h e sediments used (Shepard c i t e d  i n the c h i r o n o m i d a v o i d a n c e  tests  i n Wentsel et al., 1977), showed t h a t  less  than 1% o f the cadmium and z i n c was i n t h e "adsorbed or exchangeable  form"  (sic.).  The f a c t  t h a t an a v o i d a n c e  53  r e s p o n s e was o b s e r v e d  i s of i n t e r e s t  o b s e r v a t i o n s by Stephenson  i n light  and T a y l o r  •of burrowing response w i t h clams  of the  (1975), who found no i n h i b i t i o n  (Venerup'Ls deaussata)'  exposed  to copper i n s o l u t i o n which had been c h e l a t e d w i t h EDTA. Both t h e b u r r o w i n g and a v o i d a n c e r e s p o n s e s d e s c r i b e d above may be u s e f u l f o r marine b e n t h i c b i o a s s a y s , i n conjunction with standard chemical t e s t s , t o assess the e n v i r o n m e n t a l impact  of contaminated^sediments.  e c o l o g i c a l s i g n i f i c a n c e o f an i n h i b i t e d i s obvious  (eg. exposure  burrowing  response  t o p r e d a t o r s and wave a c t i o n )  but t h e s i g n i f i c a n c e o f t h e a v o i d a n c e r e s p o n s e t o be t e s t e d  The  i n the f i e l d .  remains  B e n t h i c i n v e r t e b r a t e s have  always been c o n s i d e r e d t o be s e d e n t a r y and thus good i n d i c a t o r s of p o l l u t e d  conditions.  by t h e r e s u l t s o f t h i s  s t u d y , t h e s e organisms may  »vr>i_d  However, as suggested  sediments w h i c h become c o n t a m i n a t e d .  actively  This fact  may  cc important i n e x p l a i n i n g t h e d i s t r i b u t i o n o f organisms i n p o l l u t e d a r e a s and a v o i d a n c e t e s t s s h o u l d be c a r r i e d out as p a r t of f u t u r e s t u d i e s a s s e s s i n g impacts  environmental"  as they have, been shown to be a s e n s i t i v e  ;  indicator.  TABLE 1 CHARACTERIZATION  OF CONTAMINATED SEDIMENTS USED IN BURROWING AND AVOIDANCE T E S T S  Organic Sediment Sample  Substrate Type  Metals  (ppm d r y we i g h t )  Content (%)  Cu  Fe Pb  Zn  Cr  Ag  Hg  Cd (g/Kg)  A  mud  3.09  150  74  172  90  1.0  0.46  1.40  36.0  B  mud  1.52  95  48  134  72  3.2  0.27  0.40  30.0  C  mud  1.13  67  32  109  60  2.6  0.18  <0.40  30.0  0.59  30  18  73  40  1.4  0.13  0.40  20.0  0.13  13  3  41  34  0.4  0.04  <0.40  19.0  D Control  muddy-sand mud  55  TABLE 2 THE MEDIAN E F F E C T I V E TIME ( E T 5 0 ) AND 95% CONFIDENCE L I M I T S FOR BURROWING OF M. balthica IN SEDIMENTS WITH D I F F E R E N T CONCENTRATIONS OF HEAVY METALS  95% C o n f i d e n c e Sample  ET50 (h) Intervals  A  4.8  B  0.76  0.46 - 1.27  C  0.28  0.24 - 0.33  D  0.17  0.15 - 0.19  0.17  0.15 - 0.19  Control  2.4 - 9.6  TABLE 3 VALUES FOR y - I N T E R C E P T ( a ) AND SLOPE ( b ) OF REGRESSION y = a + bx WHERE y = ET50 FOR BURROWING RESPONSE IN HOURS AND x = I N D I V I D U A L METAL CONCENTRATION (ppm) IN SEDIMENTS  Metal  a  b  Percent of t o t a l explained  by  regression  Cu  -1.0320  0.0319  75.2  Pb  -0.9475  0.0624  72.7  Zn  -2.035  0.0309  62.0  Cr  -2.966  0.0710  66.1  Ag  1.999  -0.4436  <1.0  Fe  -4.338  0.2065  56.0  Hg  -1.213  Cd  -1.437  *Significant **Significant  11.34* 4.455**  a t p <0.05 a t p <0.001.  variance  81.4 98.5  TABLE 4 RESULTS OF SEDIMENT AVOIDANCE TESTS WITH M.  Sample  No.  Pair  and l o c a t i o n  clams a f t e r  Test Sediment  ontrol vs,  Control  of  24 h  Total  no.  burrowed  balthi  Significant at 95%confidence  Test Sediment  •'9  10  Yes  vs,  B  7  3  10  No  vs.  C  4  6  10  No  vs,  D  4  6  10  No  5  5  10  No  vs,  Control  level  100%  T3 CD  95r  90  D  * D  control  control / &  100  /  100 %  °/o  x B  d  O L_ D  JO  c o ro Z5  a  70 50 20  o  10 5  o  2  a  o  1  J  0.1  FIGURE 1  I  I  i  0.5  i  i  J  1.0  containing  rates  for  different  M. balthica levels  of  1  4  Time Burrowing  1  I  1  L  6  12  24  (h)  in sediments heavy  1  metals.  A  (.),  48 00  „  (X),  C(+),  D(A)  and c o n t r o l  (•),  GROWTH AND REPRODUCTION OF Macoma balthica IN THE FRASER RIVER ESTUARY,  (L.)  ON A MUDFLAT  B R I T I S H COLUMBIA  60  INTRODUCTION The  Fraser R i v e r estuary i s l o c a t e d i n the southeastern  S t r a i t o f Georgia flats  corner  and i s c h a r a c t e r i z e d by an expanse of i n t e r t i d a l mud-  ( F i g . 1 ) . Seaward of the Main Arm of the F r a s e r R i v e r i s R o b e r t s  Bank, an a c t i v e , h i g h energy t i d a l types.  Surface  f l a t with a v a r i e t y  C o u s t a l i n , 1975).  Two r o c k j e t t i e s extend  the Bank f o r u s e as a c o a l p o r t f a c i l i t y terminal  of substrate  ( t o 1 m) s a l i n i t y v a l u e s f o r t h e i n t e r m e d i a t e and upper  i n t e r t i d a l h a b i t a t s range from f r e s h water t o over  (Tswwassen).  The p r e s e n t  26°/  0 0  ( L e v i n g s and  i n t o deep water a t t h e edge o f  (Westshore T e r m i n a l s )  Bank m u d f l a t .  Although  e x t e n s i v e i n Europe  and a f e r r y  study was p r i m a r i l y c o n c e r n e d  s e a s o n a l changes i n growth and r e p r o d u c t i o n of M. balthica  with  on t h e R o b e r t s  b i o l o g i c a l r e s e a r c h on e s t u a r i n e m u d f l a t s  has been  (eg. Anderson, 1972; Beanland, 1940; Chambers and  M i l n e , 1975; Lammens, 1967) and t h e e a s t c o a s t o f N o r t h America 1973;  of the  (Gilbert,  Burke and Mann,-1974; T u n n i c l i f f e and R i s k , 1977), t h e r e have been  r e l a t i v e l y few d e t a i l e d M. balthica  s t u d i e s from t h e P a c i f i c c o a s t .  have i n c l u d e d r e s e a r c h on v e r t i c a l d i s t r i b u t i o n ( V a s s a l l o ,  1969), s t r a t i f i c a t i o n w i t h i n t h e s u b s t r a t e ecology  S t u d i e s on  and d i s t r i b u t i o n  ( V a s s a l o , 1971),  ( D u n n i l l and E l l i s , 1969), biomass and p r o d u c t i o n  ( N i c h o l s , 1977) and t h e e f f e c t s of o i l p o l l u t i o n  (Myren and P e l l a ,  T h i s paper i s the f i r s t p u b l i s h e d r e p o r t o f t h e s e a s o n a l reproduction, age-class p o p u l a t i o n o f M. balthica  general  1977).  changes i n  s t r u c t u r e and depth d i s t r i b u t i o n o f an i n t e r t i d a l from t h e P a c i f i c  coast.  61  The  study a r e a -was l o c a t e d t o the n o r t h o f t h e Westshore  causeway i n t h e upper i n t e r t i d a l  zone  (Fig. 1 ) . Despite  of i n d u s t r i a l development, t h i s a r e a o f the m u d f l a t to be a f f e c t e d by p o l l u t i o n s t r e s s . sloping t i d a l f l a t s ,  access  the proximity  has n o t been shown  Due t o the l a r g e a r e a o f g e n t l y  t o the r e g i o n i s d i f f i c u l t  have been p r e v i o u s l y u n d e r t a k e n .  Terminals  and few s t u d i e s  A p r e l i m i n a r y b a s e l i n e study  of t h e  macrobenthos was c a r r i e d out by Bawden et al. (1973) which d e s c r i b e d the major s p e c i e s c o m p o s i t i o n  of the area.  Tellina  carpenteri  found to be a dominant b i v a l v e i n t h e a r e a h u t a more r e c e n t a t i o n of t h i s m a t e r i a l has shown t h e s e M. balthica  (L.).  species composition,  of t h e F r a s e r  and C o u s t a l i n  (1975).  River  Data on t h e  biomass, d e n s i t y and sediment type were c o l l e c t e d  f o r 116 quadrat s t a t i o n s throughout t h e e s t u a r y . r o l e of t i d a l  examin-  specimens t o be, i n f a c t ,  The most comprehensive study  e s t u a r y benthos has been by L e v i n g s  was  More r e c e n t l y , t h e  f l a t benthos, i n c l u d i n g Macoma balthica,  i n animal-sediment  r e l a t i o n s h i p s has been i n v e s t i g a t e d (Swinbanks and Murray, 1977). The  taxonomy of Macoma balthica  (Linnaeus,  ( B r o d e r i p and Sowerby, 1829)] on t h e west c o a s t i n need of r e v i e w .  The fundamental q u e s t i o n  A t l a n t i c and P a c i f i c  specimens a r e s e p a r a t e  species or a s i n g l e species. has  1758) [= M.  of N o r t h America i s  of i n t e r e s t (although  i s whether t h e  closely  In t h e most r e c e n t paper, Coan  suggested t h a t u n t i l a major p r o j e c t a d d r e s s i n g  undertaken, i t should  be c o n s i d e r e d  inconspicua  related) (1971)  this subject i s  as one c i r c u m - a r c t i c s p e c i e s .  T h i s recommendation w i l l be f o l l o w e d h e r e and as i t has i n o t h e r from the P a c i f i c  coast  (eg. N i c h o l s , 1977; V a s s a l o ,  1969).  studies  62  METHODS Sampling o f M. balthica between A p r i l  was c a r r i e d  out a p p r o x i m a t e l y a t monthly  intervals  7, 1977 and March 16, 1978 on R o b e r t s Bank a t a t i d a l  h e i g h t of a p p r o x i m a t e l y 3 m above c h a r t datum, as e s t i m a t e d from tides.  Monthly  local  samples were t a k e n a t 5 s t a t i o n s marked a t 5 meter  i n t e r v a l s a l o n g a t r a n s e c t p r o j e c t e d p e r p e n d i c u l a r from t h e Westshore T e r m i n a l s causeway. o u t s i d e the immediate  The f i r s t  s t a t i o n was l o c a t e d  v i c i n i t y o f t h e causeway.  200 meters n o r t h ,  On each o c c a s i o n f i v e  random samples were taken w i t h an aluminum box c o r e r x 25 cm deep) from one of t h e s t a t i o n s .  (12.5 cm x 12.5 cm  The c o r e s were s e c t i o n e d a t  5 cm i n t e r v a l s t o d e t e r m i n e depth d i s t r i b u t i o n and s i e v e d 500 um mesh s c r e e n . where a l l M. balthica i n c l e a n seawater The s i z e  S i e v e d samples were r e t u r n e d t o t h e l a b o r a t o r y were s o r t e d , enumerated,  and a l l o w e d t o d e p u r a t e  f o r 24 hours b e f o r e b e i n g f r o z e n f o r l a t e r  analysis.  ( h e i g h t ) of the s h e l l s from t h e umbo t o t h e v e n t r a l  was measured t o t h e n e a r e s t 0.5 mm,  edge  and age was determined by c o u n t i n g  annual growth r i n g s u s i n g t h e methods of Lammens were p l a c e d  through a  (1967).  Animals  i n t o y e a r c l a s s e s from age 0+ (newly s e t t l e d  spat) t o  5+ y e a r o l d i n d i v i d u a l s . All  t i s s u e was removed from s h e l l s over 1.0 mm i n h e i g h t and d r i e d  at 60°C f o r 24 h o u r s .  T i s s u e s from s h e l l s o f t h e same s i z e were p o o l e d  and a mean d r y weight determined f o r each s i z e c a t e g o r y . factor  (CF) was then c a l c u l a t e d as t h e s l o p e  l°8l0 y  =  a  A condition  (b) i n t h e r e g r e s s i o n  + bx, where y = mean d r y t i s s u e weight and x = s h e l l  height.  63  S i g n i f i c a n c e f o r the r e g r e s s i o n f u n c t i o n was and  unexplained  being equal The  v a r i a n c e , and  to z e r o  expressed  c a l c u l a t e d u s i n g the  as the p r o b a b i l i t y of the  spawning c y c l e of the M.  balthica  p o p u l a t i o n was  one o f f o u r c a t e g o r i e s as d e s c r i b e d by Caddy  gonads d e v e l o p i n g  c) u n d i f f e r e n t i a t e d - no gonad t i s s u e ; and  On of  and  s a l i n i t y was Model 33,  and  by  and  a) immature palp  attachment;  palp attachment;  d) p a r a s i t i z e d  - parasites  i n p l a c e of gonads.  each sampling  5 cm),  (1967):  p a s t p o i n t of g i l l  studied  Animals were p l a c e d  but not r e a c h i n g the p o i n t of g i l l  b) mature - gonads developed  developing  slope  (Table 3).  examining the s t a t e of gonad development each month. in  explained  seawater  date,  t e m p e r a t u r e of the a i r , sediment  (1 m d e p t h ) was  measured.  Surface  measured i n the l a b o r a t o r y w i t h a Y e l l o w  S a l i n i t y - C o n d u c t i v i t y - T e m p e r a t u r e Meter.  r a i n w a t e r was  not a f a c t o r on any  o f the sampling  (at a d e p t h  seawater  Springs  Instrument,  D i l u t i o n due  to  occasions.  RESULTS  Density The  number of M.  late April, Settled  spat  1977, (age  l a t e r as these Low  then  balthica  .1+  and  o l d e r reached  a peak (1817/m ) i n 2  s l o w l y d e c l i n e d throughout the year  0+ y e a r s ) were p r e s e n t  i n the A p r i l  (Fig. 2).  samples but  disappeared  i n d i v i d u a l s formed a growth r i n g and became 1+ year  numbers of newly s e t t l e d  spat were p r e s e n t  a g a i n from l a t e J u l y  old.  64  through 410/m  2  the f a l l i n March  and w i n t e r months u n t i l r e a c h i n g t h e i r peak number o f (Table 1 ) .  compared t o the over Milne  6000/m  T h i s d e n s i t y of s p a t f a l l 2  0+ i n d i v i d u a l s r e c o r d e d  (1975) i n t h e Ythan e s t u a r y , u s i n g s i m i l a r  i s e x c e e d i n g l y low by Chambers and  sampling  techniques.  However, the number of 1+ and o l d e r i n d i v i d u a l s f o r t h e R o b e r t s (1817/m ) and Ythan e s t u a r y 2  similar.  Bank  (1940/m ) Macoma p o p u l a t i o n s were v e r y 2  The t o t a l numbers o f i n d i v i d u a l s from a l l age groups i n summer  (1971/m ) was comparable t o t h a t r e c o r d e d 2  by V a s s a l l o (1969) from San  F r a n c i s c o Bay (1380/m ); b u t , much s m a l l e r than t h e maximum d e n s i t y 2  r e c o r d e d by N i c h o l s found  35007m  2  (1977) o f 3900/m  on m u d f l a t s  2  o r T u n n i c l i f f e and R i s k  (1977) who  i n San F r a n c i s c o Bay and t h e Minas B a s i n  respectively.  Age  structure The  T a b l e 1. to  age c l a s s c o m p o s i t i o n  on R o b e r t s  Bank i s shown i n  The o l d e s t i n d i v i d u a l s r e c o v e r e d were 5+ y e a r s o l d which  the l o n g e v i t y r e c o r d e d  elsewhere  o f M. balthica  f o r M. balthica  from s i m i l a r  (Chambers and M i l n e , 1975; Lammens, 1967).  3+ t o 5+ year age groups were p r e s e n t they s l o w l y d i e d out over  tidal  summer but  Thus t h e two main a d u l t  year c l a s s e s were t h e 1-2+ year o l d s which were a l s o found in  areas  I n d i v i d u a l s i n the  i n the s p r i n g and e a r l y  the summer and f a l l .  flat  corresponds  t o be dominant  p o p u l a t i o n s from San F r a n c i s c o Bay ( N i c h o l s , 1975) and Nova S c o t i a  (Burke  and Mann, 1975).  Until  t h e p e r i o d o f maximum r e c r u i t m e n t , t h e most  abundant y e a r c l a s s was t h e 1+ age group which comprised  up t o 73% o f t h e  65  population  (October  14).  Newly s e t t l e d  numbers d u r i n g F e b r u a r y and  spat  March when they  (0+ y r ) o c c u r r e d comprised  in greatest  65-76% of  the  population.  Size  Composition Data on  (Fig.  and Seasonal  Growth  changes i n the s h e l l h e i g h t  3) f o r each age  c l a s s of M.  the growth of the p o p u l a t i o n . stopped by group.  the end  balthica  similar  is  shown i n F i g u r e  Depth  length  Growth f o r a l l ages s t a r t e d i n A p r i l the end  Growth f o r 0+  changing d e n s i t y of d i f f e r e n t  and  of J u l y f o r the  to the t i m i n g shown i n the p o p u l a t i o n  by Lammens (1967) i n the Wadden Sea. The  shell  (Table. 2) were used t o d e t e r m i n e  of June f o r 2+ a n i m a l s and  This i s very  e a r l y September.  (Table 2) and  1+  studied  i n d i v i d u a l s ceased i n s i z e groups of M.  balthica  4".  Distribution The  percent  of the M.  balthica  w i t h i n the s u b s t r a t u m i s g i v e n w i t h i n the top 10  cm  and  p o p u l a t i o n b u r i e d at d i f f e r e n t  i n Table  3.  The  majority  depths  of a n i m a l s r e s i d e d  p a r t i c u l a r l y w i t h i n the top 5 cm  of  sediment.  Some i n d i v i d u a l s burrowed to the maximum depth sampled of 25 cm.  Generally,  n e a r l y a l l s i z e s of a n i m a l s were found a t each depth, except f o r t h e settled  spat which were o n l y encountered near the  surface.  newly  66  Seasonal  changes  -in shell  height  and body  weight  Mean i n d i v i d u a l s h e l l h e i g h t and body weight f o r 1+ and 2+ y e a r i n d i v i d u a l s were p l o t t e d t o show s e a s o n a l relationship imately  (Fig. 5).  4-5 mm d u r i n g  The r a p i d i n c r e a s e i n s h e l l h e i g h t  s p r i n g and e a r l y summer  e q u a l l y r a p i d i n c r e a s e i n body weight constant  loss prior  t o t h a t o f the 1+ year  t h e d r y t i s s u e weight  decreases  o l d s began t h e p e r i o d o f weight By F e b r u a r y o f t h e f o l l o w i n g  ( s h e l l height  on body w e i g h t ) was a l s o c a l c u l a t e d  monthly changes i n the s l o p e of the l i n e served  (CF)  remains  i n c r e a s e i n body weight.  A r e g r e s s i o n equation  (Table 4 ) .  rapid  The c o n d i t i o n f a c t o r was h i g h e s t  growth then d e c l i n e d t o i t s lowest  period. again in  group.  The s h e l l h e i g h t  some growth i n s h e l l h e i g h t was apparent accompanied by a g r e a t l y  accelerated  and  The 2+ year  of a p p r o x -  ( F i g . 5a) c o i n c i d e s w i t h an  ( F i g . 5b).  f o r t h e remainder o f t h e y e a r w h i l e  over the same p e r i o d o f time.  year,  changes i n t h e i r  during  the p e r i o d of  v a l u e a t t h e end o f t h e spawning  CF then f l u c t u a t e d s l i g h t l y u n t i l F e b r u a r y and March when  showed a r a p i d i n c r e a s e c o i n c i d e n t w i t h  i n d i v i d u a l body weight.  similar  as a c o n d i t i o n f a c t o r  t o t h a t observed  The s e a s o n a l  i n other  studies  the accelerated  values  increase  c y c l e o f CF f o l l o w s a p a t t e r n (Chambers and M i l n e , 1975;  Beukema and De B r u i n , 1977) except f o r an e a r l i e r  decline.  Biomass The April  biomass o f M. balthica  t o June  (Table 5 ) .  was h i g h e s t  (6.25 - 7.30 g d r y wt/m ) from 2  T h i s p e r i o d c o r r e s p o n d e d t o t h e time o f h i g h e s t  67  densities  ( F i g . 2) and  CF v a l u e s  d e c l i n e , the biomass a l s o f e l l period.  annual biomass was  2.96  - 10.3  2  study  from the Ythan  lower  g dry wt  per m  than the 4.86  2  ~ f o r M.  g dry wt p e r m ) 2  balthica  from  The mean a n n u a l biomass r e c o r d e d g d r y wt  e s t u a r y (Chambers and M i l n e , 1975)  (1.26  The mean  which i s w i t h i n t h e range d e s c r i b e d  l o c a t i o n s i n San F r a n c i s c o Bay.  from R o b e r t s Bank was  Nova  low throughout most of the  i n c r e a s e i n i n d i v i d u a l body w e i g h t .  g d r y wt per m  by N i c h o l s (1977) of 1.2  the v a l u e  and was  As d e n s i t i e s c o n t i n u e d t o  T o t a l biomass v a l u e s i n c r e a s e d a g a i n i n F e b r u a r y and March i n  response t o the a c c e l e r a t e d  different  (Table 4).  per m  f o r M.  2  but was  balthica  more than  double  measured by Burke and Mann (1974) from  Scotia.  Spawning The  Cycle spawning c y c l e f o r M. balthica  the s e x u a l s t a t e s shown i n T a b l e 6. then underwent a p r o l o n g e d through most o f J u l y . Scotland  i s e v i d e n t from the changes i n The  a n i m a l s matured i n May  spawning p e r i o d which l a s t e d  T h i s was  considerably later  (Chambers and M i l n e , 1975)  spawning p e r i o d ,  lasting  (1967).  of the spawning p e r i o d  end  v a l u e observed  f o r the  than observed  (Lammens, 1967).  f o r s e v e r a l months, was  CF.  from l a t e  The  June,  June in  or i n the Thames e s t u a r y (Caddy,  but s i m i l a r t o c o n d i t i o n s i n the Wadden Sea  The  and  1967)  prolonged  a l s o observed by Lammens .  a l s o c o i n c i d e d w i t h t h e lowest  68  After  spawning, gonad development d i d not commence a g a i n  until  December and by March o n l y 10% o f the p o p u l a t i o n were s e x u a l l y mature. P a r a s i t i s m d i d n o t appear t o p l a y a r o l e i n s u p p r e s s i n g  gonad development  as c y s t s d i d n o t d e v e l o p i n p l a c e of gonads i n any of the a n i m a l s examined  (Table 6 ) .  DISCUSSION F a c t o r s which have been c i t e d have i n c l u d e d t i d a l h e i g h t size  as r e g u l a t i n g t h e d e n s i t y o f Macoma  (Beanland, 1940; V a s s a l l o , 1969), sediment g r a i n  (Anderson, 1972), and carbon and n i t r o g e n c o n t e n t  (Newell,  1965).  populations  The e n v i r o n m e n t a l v a r i a b l e s r e c o r d e d  o f t h e sediment over t h e study  period  on Roberts Bank ( F i g . 6) were w e l l w i t h i n the t o l e r a n c e l i m i t s f o r M. balthica  (McGreer, 1978), and t h e f i n e sandy sediments o f t h i s  area  have been shown t o be r e a d i l y c o l o n i z e d by a d u l t s o f ' . t h i s s p e c i e s i n laboratory experiments Availability  (Chang and L e v i n g s ,  of a s u i t a b l e food  1976).  s u p p l y was s u g g e s t e d a s a p o s s i b l e  e x p l a n a t i o n f o r t h e d i f f e r e n c e s i n abundance o f Macoma by Beanland and N e w e l l  (1965) l a t e r  (1940),  showed t h e i n c r e a s e d d e n s i t i e s o f M. balthica  be a t t r i b u t a b l e t o i n c r e a s e s  i n t h e numbers o f sediment m i c r o o r g a n i s m s .  D e n s i t i e s of M. balthica  were shown t o be p o s i t i v e l y c o r r e l a t e d w i t h  b a c t e r i a but not organic  c a r b o n on m u d f l a t s  and  R i s k , 1977).  i n t h e Minas B a s i n  However, the r o l e p l a y e d by n u t r i t i o n  d e n s i t i e s of M. balthica  to  (Tunnicliffe  i n determining the  was n o t i n v e s t i g a t e d i n t h e p r e s e n t  study.  69  S e l e c t i v e p r e d a t i o n by s h o r e b i r d s on a Macoma p o p u l a t i o n i n Morecambe Bay was  d i s c u s s e d by Anderson  M. balthica  (1972).  t a k e n by most b i r d s  She found  (eg. D u n l i n ) was  f l o c k s of s h o r e b i r d s have been seen to feed t i o n s ) and  this  s i z e of M. balthica  that  the s i z e range of  between 2-13  mm.  on R o b e r t s Bank (own  Large observa-  d i s a p p e a r e d most r a p i d l y d u r i n g the  study  (Fig. 4).  F l a t f i s h a l s o f e e d upon M. balthica  ( R i s k and  Craig,  1976)  but t h e i r r o l e i n r e d u c i n g the p o p u l a t i o n i n t h e F r a s e r R i v e r e s t u a r y  i s unknown. The a n n u a l growth r a t e of 6-8 was  yr  - 1  measured on R o b e r t s Bank ( F i g . 3)  one of the h i g h e s t ever r e c o r d e d when compared t o the d a t a on growth  r a t e s f o r p o p u l a t i o n s of M. balthica comparison, was  mm  faster  (Lammens, 1967). l o n g e v i t y i n M. temperatures  i n Rand Harbour,  than a p o p u l a t i o n i n the Wadden Sea,  Gilbert balthica  Netherlands  (1973) c o n c l u d e d t h a t b o t h t h e growth r a t e  the i n v e r s e r e l a t i o n s h i p between growth r a t e and  (1975) demonstrated  that  and  were a f u n c t i o n of t e m p e r a t u r e , w i t h warmer  p r o d u c i n g a f a s t e r growth r a t e but a s h o r t e r  known f o r c e r t a i n but may  and  By  Massachusetts (Gilbert,1973)  T h i s o b s e r v a t i o n i s borne out by d a t a o b t a i n e d i n t h i s for  (1973).  t h e growth r a t e f o r t h i s a r e a of the F r a s e r R i v e r e s t u a r y  slower than t h a t observed  but s l i g h t l y  summarized by G i l b e r t  be due  life  study.  longevity  t o a change i n energy b a l a n c e .  the b a l a n c e between energy u p t a k e  energy expended becomes n e g a t i v e above 15°C  f o r M.  span. The  i s not De  through  balthica.  reason  Wilde feeding  This  70  resulted  i n e m a c i a t i o n and  specimens.  High temperatures  considered  to be p o t e n t i a l l y  S a l i n i t y was is  increased mortality  i n the l a r g e r  e x p e r i e n c e d over a m u d f l a t l e t h a l t o M.  balthica  r u l e d out as h a v i n g a p r o f o u n d  supported by the r e c e n t e x p e r i m e n t s  found growth d i f f e r e n c e s f o r M.  i n summer were  by N i c h o l s  effect  (1977).  on growth and  o f McLusky and A l l a n  balthica  (older)  this  (1976)  who  c o u l d not be e x p l a i n e d by  differences in salinity. Data  t o e x p l a i n the r e l a t i o n s h i p between s h e l l  f o r Macoma has been c o n t r a d i c t o r y . a n i m a l s burrowed deeper  1978)suggested  d e p t h of burrowing v a r i e d daylengths.  (Reading  t h a t the r e l a t i o n s h i p between s i z e  s e a s o n a l l y as a n i m a l s responded p e r c e n t of t h e i r  to  and  changing  study a n i m a l s were  cm.  R e s u l t s of the p r e s e n t s t u d y  ( T a b l e 3) shows e v i d e n c e of s e a s o n a l  "movement w i t h more a n i m a l s r e s i d i n g near S e a s o n a l m i g r a t i o n w i t h i n the sediment (1969) to the presence of a p a r a s i t i c but  the sediment  was  Ching, 1974),  significant  d i f f e r e n c e between p a r a s i t i z e d  None of the animals i n t h i s o t h e r forms o f p a r a s i t i s m (Ching, 1973).  (Parvatrema  the s t u d y by H u l s c h e r  s t u d y had  s u r f a c e i n summer.  o r i g i n a l l y ascribed  infection  Swennen and  flats  larger  (1973) showed .  A r e c e n t s t u d y from England  However, l e s s t h a n one  found below 7.5  (1971) showed t h a t  than s m a l l e r ones whereas H u l s c h e r  the o p p o s i t e i n the Wadden Sea. and McGrorty,  Vassallo  s i z e and d e p t h b u r i e d  and  (1973) found  no  n o n - p a r a s i t i z e d Macoma.  this infection  (1973) suggested  Swennen  affinis;  (see T a b l e 5 ) , but  a r e known t o i n f e c t Macoma on nearby  Hulscher  by  that  tidal  the l a r g e r Macoma  71  might move t o t h e s u r f a c e a t p e r i o d s oxygen c o n d i t i o n s .  T h i s seems t h e most p r o b a b l e  a l s o e x p l a i n why some p o p u l a t i o n s l i m i t e d depths.  Roberts  t h e area  compares f a v o u r a b l y  of one i n San F r a n c i s c o Bay ( N i c h o l s , 1977).  production  low t i d e  with  that  Both groups-had a predominance  s p a t f a l l , w h i c h l a s t e d s e v e r a l months.  were few specimens over 2+ y e a r s mentioned, o v e r l a p p e d .  observed during  i s n o t known.  Bank Macoma p o p u l a t i o n  of 0+ i n d i v i d u a l s a f t e r  e x p l a n a t i o n as i t would  o f Macoma a r e never found below c e r t a i n  whether the depth d i s t r i b u t i o n  changes when the t i d e c o v e r s The  o f h i g h t e m p e r a t u r e t o meet b e t t e r  There  o l d and t h e range i n biomass, as a l r e a d y  I t i s , therefore, reasonable  t o assume t h a t the  t o biomass r a t i o f o r the F r a s e r R i v e r p o p u l a t i o n would a l s o be  s i m i l a r , t h a t i s , about 4.5, which would y i e l d an e s t i m a t e d p r o d u c t i v i t y for  this population  of 13.3 g m  - 2  yr  _ 1  r a t i o o f 1.53 found by Burke and Mann Atlantic. any  Newly s e t t l e d  T h i s i s i n c o n t r a s t t o the lower  (1974) i n M. balthica  from the  spat o n l y a c c o u n t e d f o r 15% o f the p o p u l a t i o n a t  time and 2+ y e a r o l d i n d i v i d u a l s were always dominant.  biomass  (1.26 g/m ) 2  The a n n u a l  was a l s o much lower t h a n i n t h e p r e s e n t  Temperature i s a l s o an important c,?. spawning i n M. balthica 10°C  .  was t h e c r i t i c a l  study.  f a c t o r i n t h e t i m i n g and d u r a t i o n  and o t h e r b i v a l v e s .  Lammens  (1967) noted  that  temperature r e q u i r e d t o i n i t i a t e spawning i n the  Wadden Sea and t h a t as s p r i n g warming o f water t e m p e r a t u r e v a r i e d from one  year  t o a n o t h e r , so d i d t h e s t a r t  o f spawning.  u s u a l l y d e v e l o p e d over the f a l l and w i n t e r  As gonad t i s s u e  months, a s e v e r e ,  cold  winter  72  was  found  to h a l t  t h i s development and  a g a i n postpone t h e a c t of  In h i s s t u d y o f t h e Thames e s t u a r y , Caddy (1967) o b s e r v e d M.  balthica  i n temperatures  temperatures If  remained  between 7 and  t w i c e i n the p r e s e n t  study;  and  below 14°C  are o t h e r f a c t o r s reviewing  that i f  occur a l l year  i n t e r e s t i n g aspect  i n the f a l l  (1967) found  balthica  ( F i g . 6).  spawning  Obviously,  there  After  a number of d i f f e r e n c e s i n  which i l l u s t r a t e d environmental  of spawning i n t h i s  an a b i l i t y  conditions.  s p e c i e s noted  t o adapt  Another  by Lammens  (1967),  i n c r e a s e d oxygen consumption d u r i n g t h i s p e r i o d .  be an a d d i t i o n a l f a c t o r  round.  once as water temperature r o s e i n the s p r i n g ,  c y c l e to d i f f e r e n t  their  suggested  (eg. food s u p p l y , energy budget) i n v o l v e d .  the spawning h a b i t s of M.  concerned  spawning i n  f a c t o r , one would have expected  t h e l i t e r a t u r e , Caddy  their breeding  and  i n t h i s range, spawning would  t h i s were t h e o n l y c r i t i c a l  a g a i n as i t f e l l  14°C  spawning.  This  i n e x p l a i n i n g the m i g r a t i o n of Macoma towards  may the  sediment s u r f a c e i n summer. The  l e n g t h of time which Macoma l a r v a e remain i n the p l a n k t o n  s e t t l i n g out v a r i e s c o n s i d e r a b l y but IlLele attention.  A range from two  of  f i v e months  (Chambers and  in  the l i t e r a t u r e .  between spawning study  (Table 1 ) .  i s an a s p e c t w h i c h has  before  received very  t o f i v e weeks (Caddy, 1969), t o upwards  M i l n e , 1975)  a r e common v a l u e s  appearing  These a r e i n c o n t r a s t to the e i g h t months p e r i o d  (Junt  and  peak s p a t f a l l  (February)  A major s p a t f a l l i n F e b r u a r y ,  by Chapman (1978) who  1978  e v i d e n t from was  sampled a s u b t i d a l p o p u l a t i o n of M.  also  this  recorded  balthica  in  73  the F r a s e r R i v e r n o r t h arm  (see F i g . .1); but, i n J u l y of the  y e a r , l a r g e r numbers of spat were a l r e a d y p r e s e n t Sturgeon  Bank  over  l a r g e areas  ( t h i s study; p. 43). Which p o p u l a t i o n s .spawned t h e s e  i s not known and,  indeed,  i d e n t i f i c a t i o n and  impossible.  of l a r v a e i n any  year  a r e a w i l l a l s o v a r y from one  changes i n p a r t i c u l a r  recruitment  environmental  abnormally  variables.  h i g h temperatures  of species  t r a c i n g of the l a r v a l  from a s i n g l e p a r e n t p o p u l a t i o n i s a t p r e s e n t  r i v e r flow and  previous  The  to t h e next  stage  settlement with  F o r example, the r a t e of  have been shown to  i n some e s t u a r i n e b i v a l v e p o p u l a t i o n s  (Mitchell,  affect  1974).  74  TABLE 1 AGE C L A S S COMPOSITION OF M. balthica  FOR  EACH SAMPLING OCCASION  Age c l a s s Date 5+  4+  3+  2+  1+  0+  13  64  64  666  410  77  0  38  307  474  998  154  May 19  0  51  166  282  486  0  June 8  0  26  26  358  410  0  June 28  13  13  115  422  371  0  J u l y 23  0  0  38  179  371  26  Aug. 17  0  0  13  179  358  13  Sept. 7  0  0  26  65  192  26  Oct.  0  0  0  51  205  26  Nov. 8  0  0  0  166  154  51  Dec. 5  0  0  0  0  77  51  13  0  0  0  51  115  64  Feb. 10  0  13  0  . 77  77  282  Mar. 16  0  0  0  77  51  410  1977 Apr.  7  Apr.  29  14  1978 Jan.  (No./m2)  75 TABLE 2 MEAN S H E L L HEIGHT  ( i n mm ± S . E . )  FOR VARIOUS AGE C L A S S E S OF M. balthica  Age  AND RANGE  (in  brackets)  ON EACH SAMPLING OCCASION  class  Date 5+  4+  3+  2+  1+  0+  10. 0* (10. 0)  9.5±0.3 : • (8.5-10.0)  8.6±0.2 . (8.0-9.0)  6.310.1 5-7.5)  2.6±0.2 (1.5-4.0)  1.210.1 (1.0-1.5)  -  . 9.8±0.2 (9.5-10.0)  8.6+.0.2 (6.0-10.5)  7. 510.2 (5. 5-9.5)  3.0±0.1 (1.5-6.5)  1.510.0 (1.5)  May '. 19  -  11.1±0.7 (10.0-13.0)  11.5±0.2 (10.0-12.5)  10. 0±0.2 (7. 5-12.0)  4.6±0.3 (2.0-7.5)  -  June 8  -  12.5±0.0 (12.5)  11.8±0.2 (11.5-12.0)  10. 2±0.2 (8. 0-12.0)  5.910.2 (4.0-8.0)  -  12.0* (12.0)  12.0±0.1 (11.5-12.5)  10. 2±0.1 (9. 0-12.0)  5.910.3 (3.0-8.0)  12.0±0.0 (12.0)  11. 1±0.2 (10. 0-12.0)  6.510.2 (3.5-8.5)  1.010.0 (1.0)  11.0* (11.0)  10. 8±0.2 «9. 5-12.0)  6.210.2 (3-0-9.0)  3.5* (3.5)  11.2+0.2 (11.0-11.5)  10. 3±0.6 (9. 0-12.0)  6.210.3 (4.5-8.0)  2.Oil.0 (1.0-3.0)  1977 Apr.  7  Apr.  29  June 28  12. 5* (12. 5)  -  J u l y 23  -  -  Aug. 17  -  -  Sept . 7  -  -  -  - •  -  9.4±0.2 .(9. 0-10.0)  6.210.3 (3.0-7.5)  0.710.2 (0.5-3.0)  Nov. 8  -  -  -  10. 2±0.9 (8. 0-12.0)  5.810.3 (3.0-7.5)  1.910.8 (0.5-3.0)  Dec. 5  -  -  - •  '6.610.4 (5.0-7.5)  1.910.1 (1.5-2.0)  Oct.  t /i  *Data from one i n d i v i d u a l  -  only Cont.  76  TABLE 2 ( c o n t ' d ) MEAN SHELL HEIGHT  ( i n mm ± S . E . )  FOR VARIOUS AGE CLASSES OF M. balthica  Age  AND RANGE  (in  brackets)  ON EACH SAMPLING OCCASION  class  Date 5+  4+  3+  2+  1+  0+  1978 J a n . 13  Feb.  10  13.0* (13.0)  Mar. 16  *Data from one i n d i v i d u a l ^only (Sample s i z e s g i v e n i n T a b l e 3 ) .  10.6±0.2 (10.0-11.0)  6.5±0.4 (5.0-8.5)  1.710.1 (1.5-2.0)  10.110.4 (9.0-11.5)  6.1±0.9 (4.5-8.5)  1.310.2 (1.0-3.5)  10.4±0.5 (9.5-12.5)  6.810.6 (5.0-7.5)  1.510.2 (1.0-4.0)  77  TABLE 3 WITHIN  DEPTH D I S T R I B U T I O N OF M. balthica  THE SUBSTRATUM FOR EACH SAMPLING DATE  Number Date  Examined  % of popu l a t i o n a t each d e p t h 0-5 cm  5-10 cm  1977  -  82.2  11.9  153  64.5  17.4  7.1  May 19  76  70.1  27.2  -  June 8  64  73.5  26.5  June 28  73  93.2  5.4  :T"ly 23  48  87.8  12.2  Aug. 17  45  100.0  Apr. 29  cm  15-20 cm  20-25 cm  •  99  Apr. 7 •  j.  10-15  5.9 7.1  3.9 2.7  -  -  1.4  -  -  -  _  4.0  -  -  Sept. 7  24  96.0  -  Oct. 14  22  90.9  9.1  Nov. 8  29  86.2  Dec. 5  10  100.0  18  83.3  16.7 14.3  3.5  10.3 T  -  -  -  1.978 J a n . 13 Feb. 10  35  85.7  Mar. 16  42  97.6  -  _  -  -  2.4  TABLE 4 VALUES FOR y  1-0910  INTERCEPT  ( a ) AND SLOPE  ( b ) OF REGRESSION  y = a + bx WHERE y = MEAN DRY F L E S H  IN MG, AND x =  Date  1977 Apr.  SHELL  HEIGHT  Number o f data p o i n t s  WEIGHT  IN MM FOR M.  a  b  balthica  7  15  -0.5764  0.1641*  29  19  -1.2680  0.2598*  May 19  21  -0.8744  0.1872  June 8  17  -0.5626  0.1563*  June 28  18  -0.6193  0.1564*  J u l y 23  14  -0.3980  0.1204*  Aug. 17  15  0.4279  Sept. 7  11  -0.2423  0.1182*  Oct.  12  -0.3931  0.1211*  Nov. 8  14  -0.1818  0.0998*  Dec. 5  6  -0.7123  0.1598*  13  11  -0.3241  0.1226*  Feb. 10  15  -0.4859  0.1572*  Mar. 16  10  -0.9388  0.2211*  *Significant  at p  Apr.  14  0.0466  1978 Jan.  <0.05 l e v e l  TABLE 5 BIOMASS  (g d r y w e i g h t / m 2 )  OF M.  balth  ON EACH SAMPLING OCCASION  Biomass Date (g d r y wt/m ) 2  1977 Apr.  7  Apr.  29  6.70  May 19  6.94  June 8  6.25  June 28  7.30  J u l y 23  2.56  Aug. 17  3-03  Sept. 7  1.79  Oct.  0.74  14  Nov. 8  1.25  Dec. 5  0. 22  1978 ' 13  0.86  Feb. 10  1.58  Mar. 16  2.17  Jan.  80  TABLE 6 PERCENTAGE OF IMMATURE, MATURE, SEXUALLY AND P A R A S I T I Z E D M. balthica  Number examined  Date  Immature (%)  UNDIFFERENTIATED  ON EACH SAMPLING OCCASION  Mature (%)  Undifferentiated (%)  Parasitized (%)  1977 Apr.  7  99  65  2  33  0  Apr.  29  153  55  1  44  0  19  76  14  57  29  0  June 8  64  16  54  30  0  June 28  73  10  35  5  0  July  23  48  0  6  94  0  Aug. 17  45  0  2  98  0  Sept. 7  24  0  0  100  0  Oct.  14  22  0  0  100  0  Nov.  8  29  0  0  100  0  Dec. 5  10  0  101  90  0  13  18  0  0  100  0  Feb. 10  35  0  3  97  0  Mar.  42  2  10'  88  0  May  '  5  1978 Jan.  16  81  FIGURE 1 .  Location estuary. edge o f  of  study  Dotted tidal  area line  f l a t s at  (I)  i n the  Fraser  River  i n d i c a t e s approximate low  tide.  seaward  2200 CM CO  r  2000 1800  ©  1600  E  © 1+year and older  © — © 0+ year  1400  6 1200 c +->  1000  IT)  c 800 QCD 600 400 200  A M J 1977 FIGURE 2 .  J A S O N D J Time (months) D e n s i t y o f M. balthiaa  F M 1978  on e a c h s a m p l i n g o c c a s i o n ( ± 1  S.E.)  83  0  2  5  4  Age ( years) FIGURE 3 .  Average  growth  on R o b e r t s  Bank  rate (±1  (length S.E.).  i n mm) f o r M.  balthica  84  1500  r  Shell height o—@ 0.5-5.0 mm o—o 5.5-10.0 mm A - - A 10.0-15.0 mm  1200 h  £ 800 n  E 13  Z  400  h  Time (months) FIGURE 4 .  Density  o f M. balthica  different  shell  height  expressed size  as changes  ranges.  in  12  r  (a)  E E 10 X "C9 JZ  /  8 6  ex.  /  LO C  ,-o-cr  4  /  nj 2 2  9  /  (b) cn  E  25  o—o o—a  20  2+ Year 1 + Year  cn  1  15  Q 10 c  2  5  /  c/  / ^©  —-O  .Q L^i_j  ,  1  j  j  1  1  j  1  1  A M J J A S O N D J Time (months) FIGURE 5 .  Changes (b)  in  (a)  mean s h e l l  mean d r y w e i g h t  each s a m p l i n g  date.  per  height  1  J  F M  i n mm,  individual  i n mg  and for  86  ®—® Air Temperature o—o Sea Water Temperature  A M J J FIGURE 6 .  Air,  A S O N D J Time ( months) w a t e r and s e d i m e n t t e m p e r a t u r e s ,  F M and  over study area during sampling p e r i o d .  salinity  87  REFERENCES Anderson,  S.S.  1972.  The e c o l o g y of Morecambe Bay.  i n v e r t e b r a t e s and Ecol. Anger,  K.  factors affecting their distribution..  1975.  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