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The population biology of two intertidal seagrasses, Zostera Japonica and Ruppia Maritima, at Roberts… Bigley, Richard Ernest 1981

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THE POPULATION BIOLOGY OF TWO INTERTIDAL SEAGRASSES, ZOSTERA JAPONICA  AND  RUPPIA MARITIMA, AT ROBERTS BANK, BRITISH COLUMBIA  by  RICHARD ERNEST BIGLEY B.Sc,  Washington S t a t e U n i v e r s i t y , 1979  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY OF GRADUATE STUDIES (Department o f Botany)  We accept  t h i s t h e s i s as conforming  to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA October, 1981  (c). R i c h a r d E r n e s t B i g l e y 1981  In p r e s e n t i n g requirements  this thesis f o r an  of  British  it  freely available  agree for  that  for  that  for reference  and  study.  I  for extensive be  her  copying or shall  Date  DE-6  (2/79)  the  publication  not  be  of  further this  thesis  this  my  It i s thesis  a l l o w e d w i t h o u t my  Columbia  make  head o f  representatives.  (^rO^V'  The U n i v e r s i t y o f B r i t i s h 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  copying of  g r a n t e d by  the  University shall  permission.  Department of ^  the  Library  h i s or  f i n a n c i a l gain  at  the  p u r p o s e s may by  f u l f i l m e n t of  I agree that  permission  department or understood  advanced degree  Columbia,  scholarly  in partial  written  i ABSTRACT Growing ( v e g e t a t i v e ) and seed components o f c o - o c c u r r i n g  intertidal  p o p u l a t i o n s o f Z o s t e r a j a p o n i c a A s c h e r s . and Graebn. and Ruppia m a r i t i m a L. were s t u d i e d i n southwestern B r i t i s h Columbia f a c t o r s a f f e c t t h e i r p o p u l a t i o n maintenance.  t o determine what  R e s u l t s o f r e p e a t e d mapping  and examination o f shoots (ramets) i n permanent p l o t s on a t i d a l showed t h a t shoot f l u x , age s t r u c t u r e , s u r v i v o r s h i p ,  gradient  l e a f and rhizome  growth, and seed p r o d u c t i o n were a l l a f f e c t e d by t h e amount o f exposure of p l a n t s to the a i r .  P l o t s h a v i n g t h e g r e a t e s t exposure had fewer  shoots, a g r e a t e r percentage o f shoots f l o w e r i n g e a r l y i n t h e season, and s u b s t a n t i a l l y lower seed p r o d u c t i o n than p l o t s w i t h l e s s exposure t o the a i r . The l e n g t h o f the R. m a r i t i m a l i f e c y c l e was t h e same r e g a r d l e s s o f d i f f e r e n c e s i n exposure t o the a i r , w h i l e p l a n t s o f Z. j a p o n i c a with h i g h exposure  i n i t i a t e d and ended f l o w e r i n g and e n t e r e d a q u i e s c e n t  o v e r w i n t e r i n g s t a t e e a r l i e r than p l a n t s w i t h l e s s  exposure.  Seed o f both s p e c i e s was shed i n n a t e l y dormant, and through enumeration  o f seed i n t h e sediment  from t h e s i t e o f p r o d u c t i o n .  i t was found t h a t most was e x p o r t e d  E x p e r i m e n t a l seed b u r i a l showed t h a t  remaining seed s u f f e r e d ^50% o v e r w i n t e r m o r t a l i t y .  Simultaneous  g e r m i n a t i o n o f Z_. j a p o n i c a and R. m a r i t i m a seed was t r i g g e r e d by t h e warming o f sediments time.  i n March when low t i d e s o c c u r r e d d u r i n g the day-  Germination was c o n f i n e d t o a e r o b i c sediments; seed b u r i e d i n  anaerobic sediment was m a i n t a i n e d i n an e n f o r c e d dormancy y e a r - r o u n d . O b s e r v a t i o n s t h a t low temperatures  and a n a e r o b i c c o n d i t i o n s r e t a r d  g e r m i n a t i o n were confirmed by l a b o r a t o r y s t u d i e s .  In a d d i t i o n ,  seed  seed  was found to be n o n - p h o t o b l a s t i c and was prevented from g e r m i n a t i n g by local  seawater  s a l i n i t i e s o n l y when emerging  from i n n a t e dormancy.  -ii TABLE OF CONTENTS Page ABSTRACT  i  LIST OF TABLES  -'v  LIST OF FIGURES  vi  ACKNOWLEDGEMENTS  ,"Ix  INTRODUCTION  1  GENERAL DESCRIPTION OF PLANTS  4  STUDY AREA  9  METHODS P h y s i c a l environment  13  Shoot demography  14  Morphology and ovary f a t e s  16  B u r i e d seed enumeration  17  V i a b i l i t y and g e r m i n a t i o n o f seed s t o r e d i n a e r o b i c c o n d i t i o n s  19  The e f f e c t s o f temperature and a n a e r o b i c c o n d i t i o n s on the v i a b i l i t y o f new seed  21  V i a b i l i t y o f e x p e r i m e n t a l l y b u r i e d seed  22  Data a n a l y s e s  23  Sampling i n t e r v a l s  23  SECTION 1.  PHYSICAL ENVIRONMENT  T r a n s e c t topography  26  Tides  26  Sediments  29  Salinity  29  Sediment temperatures  33  Oxidizing potential  35  SECTION 2. THE GROWING COMPONENT OF THE POPULATION Results Shoot r e c r u i t m e n t  39  Shoot l o s s e s  47  T o t a l shoots  48  iii Cohort c o n t r i b u t i o n s  57  Survivorship  71  Leaf length  71  Rhizome i n t e r n o d e l e n g t h  79  Genet growth  84  Flower and i n f l o r e s c e n c e d e n s i t i e s  88  Ovary f a t e s  89  Seed p r o d u c t i o n  93  Discussion Shoot r e c r u i t m e n t and death L e a f and rhizome  95  internode lengths  100  Genet growth  104  Numbers o f f l o w e r s and i n f l o r e s c e n c e s  104  Ovary f a t e s  105  Seed p r o d u c t i o n  107  SECTION 3.  THE SEED COMPONENT OF THE POPULATION  Results B u r i e d seed  109  V i a b i l i t y o f u n t r e a t e d seed c o l l e c t i o n s s t o r e d a t 5 °C.  117  E f f e c t s o f temperature  and a n a e r o b i c c o n d i t i o n s on seed  v i a b i l i t y and g e r m i n a t i o n  119  V i a b i l i t y o f b u r i e d seed  121  New seed g e r m i n a t i o n  121  Old  seed g e r m i n a t i o n  127  G e r m i n a t i o n i n seed bank  141  Recruitment  and death o f s e e d l i n g s and shoots  o v e r w i n t e r i n g rhizomes  from 141  Discussion B u r i e d seed numbers  148  Seed v i a b i l i t y  155  G e r m i n a t i o n and s e e d l i n g r e c r u i t m e n t  159  SUMMARY  164  LITERATURE CITED  167  APPENDICES  iv APPENDICES 1.  Taxonomy o f Z o s t e r a j a p o n i c a  176  2.  O x i d i z i n g p o t e n t i a l s o f Roberts  3.  Shoot demography d a t a .  191  4.  Averages and s t a n d a r d d e v i a t i o n s o f m o r p h o l o g i c a l d a t a .  202  Bank sediment  188  LIST OF TABLES Page I.  Sampling and o b s e r v a t i o n dates and approximate temperature  II.  times o f  r e a d i n g s a t Roberts Bank, 1980 - 1981.  25  P e r c e n t o f days o f exposure p e r month from t i d e s r e a c h i n g low d u r i n g peak h e a t i n g hours o f the day a t o r below 2.5 m CD t i d a l h e i g h t , Roberts Bank.  III.  Percentage o f sediment  28  i n each o f f i v e  size classes  from  t h r e e s t a t i o n s a t Roberts Bank, 1980 - 1981. IV.  30  Mean numbers o f o v a r i e s p e r i n f l o r e s c e n c e and p e r c e n t a g e s i n each o v a r y f a t e :  ovary a b o r t i o n , o v a r y p r e d a t i o n ,  incomplete development,  mature seed; f o r two age c l a s s e s o f  Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a from t h r e e t i d a l h e i g h t s at  Roberts Bank.  92 2  V.  E s t i m a t e d seed p r o d u c t i o n p e r 0.1 m  o f Z o s t e r a j a p o n i c a and  Ruppia m a r i t i m a a t Roberts Bank, showing percent o f t o t a l  a b s o l u t e number and  a t each s t a t i o n by age c l a s s a t t h r e e t i d a l  heights. VI.  . 94  P e r c e n t v i a b i l i t y o f seed s t o r e d a t 5°C and 27 o/oo  salinity  d u r i n g 1980 - 1981. VII.  Percent v i a b i l i t y ,  118  death, and g e r m i n a t i o n o f new seed  m a i n t a i n e d i n c o n t r o l l e d l a b o r a t o r y environments. VIII. IX.  Percent v i a b i l i t i e s o f b u r i e d seed a t f o u r sediment  s e l e c t e d sediment  XI. XII.  depths.  122  Shoot base depths and a b s o l u t e numbers o f Z o s t e r a shoots e s t a b l i s h e d from o v e r w i n t e r i n g rhizomes  X.  120  i n haphazardly  cores near s t a t i o n 2 a t Roberts Bank,  1981.  144  R e l a t i o n s h i p o f seed depth i n v a r i o u s ecosystems.  149  E s t i m a t e s o f b u r i e d seed numbers from v a r i o u s ecosystems.  152  Mean c h a r a c t e r v a l u e s and s t a n d a r d d e v i a t i o n s o f f o u r ' s p e c i e s i n t h e Z o s t e r a subgenus, Z o s t e r e l l a .  179  vi  LIST OF FIGURES Page 1.  Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a showing  growth form o f  plants.  5  2.  D i s t r i b u t i o n o f Z o s t e r a j a p o n i c a i n North America.  6  3.  General l o c a t i o n o f study s i t e .  8  4.  a.  General l o c a t i o n o f s t u d y t r a n s e c t .  b.  S t a t i o n s and p l o t c o n f i g u r a t i o n a t each s t a t i o n .  5.  Flow c h a r t o f b u r i a l ,  10  s t o r a g e , and g e r m i n a t i o n treatments o f o l d  and new seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a . 6.  24  General topography o f study t r a n s e c t showing p o s i t i o n s o f s t a t i o n s a t Roberts Bank.  7.  27  S a l i n i t y o f water near s t a t i o n 2 a t Roberts Bank, 1980 - 1981, measured i n s h a l l o w p o o l s a t low t i d e .  8.  A i r and sediment  32  temperatures near s t a t i o n 2 a t Roberts Bank,  1980 - 1981. 9.  34  S e l e c t e d p r o f i l e s o f o x i d i z i n g p o t e n t i a l s o f the sediment  near  s t a t i o n 2 a t Roberts Bank 1980 - 1981. 10.  Recruitment and l o s s o f shoots between s u c c e s s i v e sampling dates at each o f t h r e e s t a t i o n s a t Roberts Bank 1980 - 1981.  11.  40  Absolute c o n t r i b u t i o n o f cohorts r e c r u i t e d at successive intervals,  and t o t a l  shoot d e n s i t y o f v e g e t a t i v e and r e p r o d u c t i v e  shoots from t h r e e s t a t i o n s a t Roberts Bank, May 1980 - May 1981. 12.  36  Percentage o f t o t a l  49  shoots which were f l o w e r i n g a t each o f t h r e e  s t a t i o n s on s u c c e s s i v e sampling dates a t Roberts Bank, 1980 1981. 13.  55  Age s t r u c t u r e o f v e g e t a t i v e and r e p r o d u c t i v e shoot p o p u l a t i o n s as p e r c e n t c o h o r t c o n t r i b u t i o n t o t h e t o t a l p o p u l a t i o n f o r t h r e e s t a t i o n s a t Roberts Bank, 1980 -, 1981.  14.  58  S u r v i v o r s h i p c u r v e s o f s e l e c t e d c o h o r t s from t h r e e s t a t i o n s a t Roberts Bank, 1980 - 1981.  72  Vll 15.  Mean l e n g t h s o f newest rhizome at  Roberts Bank, 1980 - 1981.  16.  L e a f c r o s s s e c t i o n s showing  17.  Mean l e n g t h s o f newest rhizome at  18.  i n t e r n o d e s from t h r e e s t a t i o n s 76  lacunae.  80  i n t e r n o d e s from t h r e e s t a t i o n s  Roberts Bank, 1980 - 1981.  Schematic  81  drawing o f h o r i z o n t a l and v e r t i c a l b r a n c h i n g o f  v e g e t a t i v e and r e p r o d u c t i v e shoots o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a and e s t i m a t e s o f ramets p e r genet over time. 19.  Mean number o f o v a r i e s p e r i n f l o r e s c e n c e a t t h r e e s t a t i o n s a t Roberts Bank, 1980.  20.  90  Mean number o f i n f l o r e s c e n c e s p e r f l o w e r i n g shoot a t t h r e e s t a t i o n s a t Roberts Bank, 1980.  21.  "  Roberts Bank.  110  P e r c e n t g e r m i n a t i o n r a t e o f c u r r e n t y e a r v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 10 °C d i s t i l l e d water.  23.  91  Cumulative p e r c e n t o f a l l b u r i e d seed from t h r e e s t a t i o n s at  22.  85  123  P e r c e n t g e r m i n a t i o n r a t e o f c u r r e n t y e a r v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 10 "C water a t f o u r • salinities.  24.  124  Percent g e r m i n a t i o n r a t e o f s c o r e d and u n s c o r e d c u r r e n t y e a r v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 10 °C water a t two s a l i n i t i e s .  25.  128  P e r c e n t g e r m i n a t i o n r a t e o f c u r r e n t y e a r v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 20 o/oo  salinity  water a t temperature regimes o f c o n s t a n t 10°C and 18°C, and 12-hour a l t e r n a t i n g 15 - 7°C. 26.  131  P e r c e n t g e r m i n a t i o n r a t e o f c u r r e n t y e a r v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 10 "C water a t two salinities  27.  i n t h e dark and exposed  t o white l i g h t .  134  P e r c e n t g e r m i n a t i o n r a t e o f p r e v i o u s y e a r s ' v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 10 °C d i s t i l l e d water.  137  viii 28.  Percent g e r m i n a t i o n r a t e o f p r e v i o u s y e a r s ' v i a b l e seed o f Z o s t e r a j a p o n i c a and Ruppia maritima and  i n 10°C water a t 10 o/oo  20 o/oo s a l i n i t y exposed to white l i g h t ,  and at 20 o/oo  i n t h e dark. 29.  138  Percent o c c u r r e n c e  o f s e e d l i n g s i n the sediment p r o f i l e  s t a t i o n 2 a t Roberts 30.  Recruitment  near  Bank, 1981.  142  and l o s s , a b s o l u t e and p e r c e n t c o n t r i b u t i o n o f  s e e d l i n g c o h o r t s o f Z o s t e r a j a p o n i c a and Ruppia maritima t h r e e s t a t i o n s a t Roberts  from  Bank, 1981.  145  31.  C h a r a c t e r s used to d i f f e r e n t i a t e Z o s t e r e l l a t a x a .  180  32.  Representative  183  33.  Principal  spathe  cross sections o f Z o s t e r e l l a taxa.  component a n a l y s i s o f Z o s t e r e l l a t a x a ; p r o j e c t i o n s  o f c h a r a c t e r s on components I and I I .  184  ACKNOWLEDGEMENTS I would l i k e to express my s i n c e r e a p p r e c i a t i o n t o Dr. Paul G. H a r r i s o n who p r o v i d e d d i r e c t i o n o f t h i s work. and  and f i n a n c i a l a s s i s t a n c e a t a l l stages  The o t h e r members o f my committee, Drs. Roy t u r k i n g t o n  Peter J o l l i f f e ,  I would l i k e to thank f o r t h e i r a d v i c e and c r i t i c a l  reading o f t h i s t h e s i s .  I am f u r t h e r i n d e b t e d t o those  students and  f a c u l t y who f r e e l y engaged i n t h e exchange o f i d e a s and t h e l e n d i n g o f equipment, and Dr. Ron P h i l l i p s f o r h i s encouragement on t h i s p r o j e c t . A p o r t i o n o f t h i s work c o u l d n o t have been conducted without t h e f i n a n c i a l support o f the North Cascades Audubon S o c i e t y . Finally,  I wish t o thank my w i f e , J e a n n e t t e ,  o f h e a r i n g about s e a g r a s s e s , endless  f o r c o u n t l e s s hours  r e a d i n g and t y p i n g o f m a n u s c r i p t s ,  encouragement and enthusiasm.  and h e r  1 INTRODUCTION The p o p u l a t i o n o f an annual composed o f two  parts:  (Watkinson 1978).  (or s h o r t - l i v e d perennial) p l a n t i s  the growing p l a n t s and  U n t i l now,  the dormant  seed  the approaches to the study o f  seagrass  p o p u l a t i o n growth and maintenance have been l i t t l e more than d e s c r i p t i v e and p r i m a r i l y concerned w i t h the growing ( v e g e t a t i v e ) component. authors  Few  have mentioned the seed component as a means o f p o p u l a t i o n main-  tenance o r e s t a b l i s h m e n t A u s t i n 1976,  ( A r a s a k i 1950b, P h i l l i p s  Greg and M o f f l e r 1978,  1972,  Verhoeven 1979,  Thorhaug  Lewis and  and  Phillips  1980). The p o p u l a t i o n dynamics o f seagrasses  have been s t u d i e d a t v a r i o u s  l e v e l s to answer a wide range o f q u e s t i o n s .  Seagrass bed  biomass have been s t u d i e d e x t e n s i v e l y , mostly productivity  (see Zieman and Wetzel 1980).  area  i n r e l a t i o n to  On  and  seasonal  the o t h e r hand, s t u d i e s  d e a l i n g w i t h the u n d e r l y i n g changes i n p o p u l a t i o n have been few. (1980) counted and measured l e a v e s o f Z o s t e r a marina L. and  Bak  suggested  t h a t because o f the e x i s t e n c e o f f i v e s i z e c l a s s e s , an equal number o f age c l a s s e s might e x i s t s t u d i e d the l i f e  i n the p o p u l a t i o n he  span o f i n d i v i d u a l  t h a t l e a v e s on v e g e t a t i v e shoots  studied.  l e a v e s i n outdoor c u l t u r e , and  o f Z. marina l i v e d  r e p r o d u c t i v e shoots.  Nienhuis  technique  l e a f t u r n o v e r and p r o d u c t i o n .  to e s t i m a t e  however, g i v e l i t t l e  and  i n s i g h t i n t o the " t a c t i c s "  These methods, and Ogden  t h e i r p o p u l a t i o n dynamics.  1972)  population.  i s the t a s k o f a demographer to d e s c r i b e , measure, and  shoots would i n t r o d u c e a new,  on  leaf-marking  (Harper  changes i n the numbers t h a t compose a p o p u l a t i o n . seagrass  found  l o n g e r than l e a v e s  DeBree (1980) used a  employed by the p l a n t s to a c h i e v e the observed It  Mukai et a l . (1979)  The  explain  demography o f  as y e t unexplored,  aspect  of  Sarukhan and Harper (1973) s t a t e t h a t o n l y  2 i n s t u d i e s where v e r y f r e q u e n t and  d e t a i l e d observations  of  individuals  are made can the u n d e r l y i n g changes i n a p o p u l a t i o n be observed. continue,  and  s t a t e t h a t i t i s a l s o e s s e n t i a l to observe the performance  o f the i n d i v i d u a l s i n terms o f s i z e and r e v e a l those  They  r e p r o d u c t i v e output  i n o r d e r to  e f f e c t s o f b i o t i c and p h y s i c a l f a c t o r s which a r e  otherwise  d i s g u i s e d by simply c o n s i d e r i n g numbers. S t u d i e s c o n t r i b u t i n g to our u n d e r s t a n d i n g  o f b u r i e d dormant seed  l a r g e l y d e s c r i p t i v e , and a r e p r i m a r i l y from t e r r e s t r i a l as a g r i c u l t u r a l  fields  (e.g., Brenchley  environments such  and Warington 1930,  1933,  and C h i l c o t e 1970), f o r e s t s (e.g., O o s t i n g and Humphreys 1940, 1975,  Moore and Wein 1977), and n a t u r a l g r a s s l a n d s  1966). 1939,  van  der V a l k and  Davis  1976,  1978,  Leek and G r a v e l i n e  s u b t i d a l b u r i e d seed  banks.  d i s t u r b e d seagrass 1976,  Phillips  without  beds, a v o i d i n g c o s t l y shoot  1980).  Much p r o g r e s s  or  to r e - e s t a b l i s h  t r a n s p l a n t s (Thorhaug  on these e f f o r t s i s u n l i k e l y  more i n f o r m a t i o n on the b i o l o g y o f  seed.  Seagrass communities are w i d e l y d i s t r i b u t e d along c o a s t s temperate and  tropical  f e a t u r e s o f the shore  seas and are regarded (den Hartog  1970).  nothing  as one  The  g r a s s e s as sediment s t a b i l i z e r s and primary the food web  Pyott  1979,  There have been no s t u d i e s o f i n t e r t i d a l  i n u s i n g seed  Johnson  attention (Milton  van der V a l k 1980).  There i s c o n s i d e r a b l e i n t e r e s t  Schafer  (e.g., Major and  B u r i e d seed o f marsh s o i l s has r e c e i v e d l i t t l e  are  important  producers,  i n many a r e a s , i s w e l l r e c o g n i z e d .  i s known about the e s t a b l i s h m e n t  o f the  of  conspicuous  functions of  sea-  the backbone to  However, e s s e n t i a l l y  and maintenance o f  seagrass  p o p u l a t i o n s and what f a c t o r s determine f l u c t u a t i o n s i n t h e i r numbers (Bak  1980,  Lewis and  Phillips  1980,  Nienhuis  and  De Bree 1980).  If, in  3 the f u t u r e we a r e to manage seagrass beds e f f e c t i v e l y ,  the n a t u r e  magnitude o f f a c t o r s which i n f l u e n c e p o p u l a t i o n numbers must be  and  under-  stood . I t was  the o b j e c t i v e o f t h i s study to p r o v i d e b a s i c i n f o r m a t i o n on  the maintenance o f c o - o c c u r r i n g i n t e r t i d a l p o p u l a t i o n s o f Z o s t e r a j a p o n i c a A s c h e r s . and Graebn. and Ruppia m a r i t i m a L. by examining b o t h the dormant and growing Two  p o r t i o n s o f the p o p u l a t i o n .  g e n e r a l q u e s t i o n s were pursued:  (1) How  do the dynamics o f  shoot p o p u l a t i o n s o f Z. j a p o n i c a and R. maritima v a r y on an g r a d i e n t i n terms o f l i f e span, growth, and seed p r o d u c t i o n ?  exposure (2) Where  i s seed l o c a t e d and what a r e the f a c t o r s which i n f l u e n c e the numbers o f seed t h a t f i n a l l y  germinate and  The approaches  establish?  taken to answer these q u e s t i o n s were f i r s t t o  map  shoots r e g u l a r l y and to observe and measure m o r p h o l o g i c a l f e a t u r e s o f p l a n t s on an exposure  g r a d i e n t over a y e a r , and the second, t o examine  the responses o f seed to f i e l d b u r i a l , and to s t o r a g e and g e r m i n a t i o n under v a r i o u s c o n t r o l l e d  laboratory conditions.  The  i n t e r t i d a l seagrass  community lends i t s e l f w e l l to t h i s type o f study because o f the combination o f c l e a r l y d e f i n e d s h o o t s , easy removal p r o f i l e s , and a c c e s s t o l a r g e numbers o f seed.  of undisturbed s o i l  4 GENERAL DESCRIPTION OF PLANTS Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a  ( F i g . 1) are both  monocotyled-  onous marine v a s c u l a r hydrophytes, and members o f the Potamogetonaceae. They belong to a group o f organisms  c o n f i n e d to a s i n g l e s u b c l a s s  ( H e l o b i a e ) , a p o r t i o n o f which are g e n e r a l l y known as the s e a g r a s s e s . All  s e a g r a s s e s share the c h a r a c t e r i s t i c o f b e i n g a b l e to c a r r y out  e n t i r e l i f e c y c l e submerged i n the marine Both Z. j a p o n i c a and R. m a r i t i m a may  environment. behave as e i t h e r  ( o v e r w i n t e r i n g by seed) o r s h o r t - l i v e d p e r e n n i a l s rhizomes).  annuals  ( o v e r w i n t e r i n g through  The main body o f each p l a n t c o n s i s t s o f an  underground  rhizome which branches and a l s o g i v e s r i s e to v e g e t a t i v e s h o o t s . b r a n c h i n g o f shoots takes p l a c e as f l o w e r i n g proceeds The  their  Sympodial  ( F i g . 1).  i n f l o r e s c e n c e o f Z. j a p o n i c a c o n s i s t s o f a o n e - s i d e d s p a d i x  with a l t e r n a t i n g s e s s i l e staminate and p i s t i l l a t e f l o w e r s i n two Seed o f Z. j a p o n i c a i s e l l i p s o i d , about  2 mm  by 1 mm  t e s t a i s smooth, s h i n y and brown w i t h f i n e s t r i a t i o n s . the i n f l o r e s c e n c e c o n s i s t s o f two f l o w e r has two  i n s i z e , and the In R. m a r i t i m a  f l o w e r s born on a peduncle.  s e s s i l e anthers between g e n e r a l l y f o u r p i s t i l s .  o v o i d to p y r i f o r m , from 1.5  to 3 mm  by 1 mm.  rows.  Each Seed i s  The t e s t a i s b l a c k t o brown  with f i n e pores. Much c o n f u s i o n has surrounded the taxonomic i n North America  (see Appendix  1).  s t a t u s o f Z.  japonica  The e c o l o g y and d i s t r i b u t i o n o f  Z. j a p o n i c a has been summarized by den Hartog i s common on s h e l t e r e d , sandy or muddy t i d a l  (1970).  Zostera japonica  f l a t s , but i t a l s o o c c u r s  i n b r a c k i s h c o a s t a l lagoons w i t h a more o r l e s s f i x e d water l e v e l . extends from 12 to 55 degrees n o r t h l a t i t u d e ; thus growing v a r y from t o p i c a l to c o l d - t e m p e r a t e .  It  conditions  It i s widely d i s t r i b u t e d  i n East  Zostera japonica  Ruppia maritima  6 A s i a from t h e c o a s t o f Vietnam t o the t r o p i c o f Cancer.  The known  d i s t r i b u t i o n o f Z. j a p o n i c a i n North America i s shown i n F i g u r e 2. Some c o n f u s i o n has a l s o surrounded t h e taxonomy o f R. m a r i t i m a because o f i t s wide e c o l o g i c a l amplitude and o v e r l a p p i n g w i t h o t h e r Ruppia s p e c i e s  (see Verhoeven  1979).  distribution  There appear t o be two  d i s t i n c t v a r i e t i e s o f Ruppia maritima, t h e common v a r i e t y m a r i t i m a L. w i t h l o n g podogyns (formed by f e r t i l i z e d p i s t i l s ) variety, brevirostris All  and a v e r y r a r e  (Agardh) A s c h e r s . and Graebn., w i t h s h o r t  podogyns.  r e f e r e n c e s made w i t h i n t h i s t h e s i s t o Ruppia m a r i t i m a w i l l be t o t h e  v a r i e t y maritima. Ruppia m a r i t i m a i s found i n c o a s t a l b r a c k i s h waters and i n l a n d temporary and permanent s a l i n e h a b i t a t s .  I t s d i s t r i b u t i o n i n North  America extends from A l a s k a t o Baja C a l i f o r n i a on t h e West Coast and from Newfoundland  to F l o r i d a i n t h e E a s t .  South America and t h e O l d World  I t i s a l s o found throughout  ( H i t c h c o c k e t a l . 1969).  4 5°  F i g . 2.  Distribution  circles  o f Z o s t e r a j a p o n i c a i n North America.  = known c o l l e c t i o n s ;  by the author d u r i n g 1980  open c i r c l e s  - 1981  Solid  = l o c a t i o n s searched  where no Z. j a p o n i c a was  observed.  Fig.  3.  G e n e r a l l o c a t i o n o f study  site.  9 STUDY AREA F i e l d s t u d i e s were conducted i n January 1980 May  1981  composed o f t h r e e s t a t i o n s , was t e r m i n a l and  perpendicular  The  ( F i g . 3).  The  study  seaward from shore along  a tidal  kilosite,  encompasses a p p r o x i m a t e l y 11,300 h e c t a r e s  d e l t a averages 6.5  km  unconsolidated  i n width and  slopes  Underlying  The  gently  c a r r i e s an estimated  (about 8 degrees)  sediments  F r a s e r R i v e r , n o r t h o f the study  (van der  Leeden 1975).  The  Fraser  River  tons o f suspended  Peak r i v e r d i s c h a r g e  to June (Beak H i n t o n C o n s u l t a n t s  site,  the t h i r t y - s e c o n d l a r g e s t  average o f 20 m i l l i o n m e t r i c  sediment i n t o the d e l t a a n n u a l l y .  area.  the 90 to 120 m t h i c k  i s ranked s i x t h l a r g e s t i n North America and on a world s c a l e by d i s c h a r g e  Sturgeon  of i n t e r t i d a l  sediments o f the d e l t a are P l e i s t o c e n e  Shepard 1962).  gradient  s i d e o f the c o a l p o r t causeway ( F i g . 4 ) .  F r a s e r R i v e r d e l t a i s composed o f Roberts Bank and  (Mathews and  to  l o c a t e d between the Tsawwassen f e r r y  km  to the southeast  toward the S t r a i t o f G e o r g i a .  May  1980  the Roberts Bank c o a l p o r t causeways (49°02'N; 123°08'W).  S t a t i o n s were e s t a b l i s h e d 1.3  Bank and  from May  on the southern p o r t i o n o f Roberts Bank, l o c a t e d twenty  meters south o f Vancouver, B r i t i s h Columbia  The  and  occurs  in late  L t d . 1977) .  Because the c o a l p o r t causeway p r e v e n t s most o f the b r a c k i s h waters from the F r a s e r R i v e r mouth from e n t e r i n g the intercauseway r e g i o n , general  area  i n which the study was  conducted had  than the remainder o f the F r a s e r d e l t a ; t h e r e was t u r b i d i t y o f the water d u r i n g peak r i v e r d i s c h a r g e a l t e r e d p h y s i c a l c o n d i t i o n s at the study  the  a more marine i n f l u e n c e however  increased  which may  have  site.  T i d e s a t Roberts Bank are o f the mixed, m a i n l y d i u r n a l type. mean water l e v e l at the Tsawwassen f e r r y t e r m i n a l  i s 2.96  The  m c h a r t datum  1000  0  1000  2000  U.S.A.  me ters  meters  F i g . 4.  a. General  l o c a t i o n o f the study  transect.  b. S t a t i o n s and p l o t c o n f i g u r a t i o n a t . e a c h s t a t i o n .  11 (CD)'. 3.05  T i d a l amplitude has  m f o r mean t i d e s .  i n f l u e n c e w i t h wet, Few  floristic  The  average ranges o f 4.69  c l i m a t e at Roberts Bank has  cool winters  and warm summers.  Marsh v e g e t a t i o n has  been d e s c r i b e d  by Forbes (1972), McLaren (19,72) and H i l l a b y and q u a n t i t a t i v e l y by Yamamaka (1975) and  s i t e have been s t r o n g l y a l t e r e d by d i k i n g .  Grindelia integrifolia  v i r g i n i c a L. and  DC.  stricta  i n the h i g h e r a r e a s ,  The marshes near  ( T o r r . ) Rydb. and  Salicornia  T r i g l o c h i n m a r i t i m a L. i n the lower areas  channels i n the h i g h i n t e r t i d a l .  o f the marsh  i n areas  Other important  and  between  marsh s p e c i e s  nearshore i n c l u d e Carex l y n b g y e i Hornem., S c i r p u s americanus S c i r p u s maritimus L.,  and  Roberts Bank  i n c l u d i n g the patches o f marsh v e g e t a t i o n which occur drainage  qualitatively  B a r r e t t (1976),  A. Moody (1979).  marshes a r e composed p r i m a r i l y o f D i s t i c h l i s and  a heavy m a r i t i m e  s t u d i e s have been conducted on the n e a r s h o r e p l a n t s o f  the F r a s e r R i v e r d e l t a .  the study  m f o r l a r g e t i d e s and  Pers.,  Scirpus validus Vahl.  S t u d i e s o f submerged v e g e t a t i o n on the F r a s e r f o r e s h o r e i n c l u d e o f R. Moody (1979), who  s t u d i e d the f a c t o r s which i n f l u e n c e the  those  standing  crop o f Z o s t e r a marina L. on the e a s t s i d e o f the Tsawwassen f e r r y t e r m i n a l , and  P.G.  Harrison  o f biomass o f Z. j a p o n i c a  ( i n p r e p a r a t i o n ) , who  (= Z. americana) and  b u t i o n o f submerged and marsh v e g e t a t i o n has satellite  imagery (G. Tomlins p e r s o n a l  Much a t t e n t i o n has Bank area Twenty-five  s t u d i e d the  R. m a r i t i m a .  distribution The  a l s o been s t u d i e d  distri-  by  communication 1980).  been g i v e n to the f i s h p o p u l a t i o n s  i n the Roberts  (Dept. o f Environment, F i s h e r i e s and Marine S e r v i c e 1975). s p e c i e s o f f i s h a r e known to occur at Roberts Bank; the  most important  and  abundant s p o r t and  salmon (Oncorhynchus tshawgtscha) and  commercial f i s h e s are the  chinook  the P a c i f i c h e r r i n g (Clupea  harengus  pallasi).  A l s o common i n t h e lower i n t e r t i d a l and s u b t i d a l  i s the  dungeness c r a b (Cancer m a g i s t e r ) . The F r a s e r R i v e r e s t u a r y i s o f major importance as a f e e d i n g s t o p f o r b i r d s m i g r a t i n g on t h e P a c i f i c  flyway; peak numbers o c c u r i n  November (Beak H i n t o n C o n s u l t a n t s L t d . 1977).  B i r d s commonly observed  at t h e study s i t e were, i n o r d e r o f abundance, American  Widgeon  americana), D u n l i n ( A l i d r i s a l p i n a ) , and Great Blue Heron herodius).  (Anas  (Ardea  Large numbers o f ducks were o f t e n found i n t h e intercauseway  area. Human use o f t h e Roberts Bank a r e a can be t r a c e d many thousands o f years  (Goddard  1945).  The t r a d i t i o n a l Tsawwassen (members o f t h e c o a s t  S a l i s h Indians) w i n t e r v i l l a g e s i t e was l o c a t e d between t h e causeways on what i s now t h e Tsawwassen I n d i a n R e s e r v a t i o n .  Many o f t h e abundant  i n t e r t i d a l r e s o u r c e s once h a r v e s t e d by t h e Tsawwassen a r e gone,  likely  as a r e s u l t o f e x t e n s i v e d i k i n g a l o n g t h e marsh and c o n s t r u c t i o n o f t h e f e r r y t e r m i n a l and c o a l p o r t i n 1960 and 1970, r e s p e c t i v e l y . Today t h e r e i s l i m i t e d u s e o f t h e intercauseway a r e a except f o r t h e o c c a s i o n a l c r a b c o l l e c t o r o r b i r d watcher.  The g r a v e l edges o f t h e cause-  ways a r e r e g u l a r l y used f o r beachcombing year-round.  Future developments  at s o u t h e r n Roberts Bank a r e scheduled t o i n c l u d e a m u l t i - f o l d  expansion  o f t h e e x i s t i n g c o a l t e r m i n a l t o f a c i l i t a t e t r a n s p o r t a t i o n and s t o r a g e o f an i n c r e a s e d volume o f m a t e r i a l s , m o s t l y  coal.  13 METHODS Physical  environment  Sediment p a r t i c l e s i z e a n a l y s e s were conducted u s i n g t h e hydrometer method (Day 1965). Department  P a r t i c l e s i z e c a t e g o r i e s were as d e f i n e d by t h e U.S.  of Agriculture  sand, 2.00 - 0.25 mm,  (Day 1965):  g r a v e l , g r e a t e r than 2 mm,  f i n e sand, 0.25 mm - 0.05 min, s i l t ,  and c l a y , below 0.002 mm.  Subsamples  coarse  0.05 - 0.002  mm,  (200 g) o f sediment f o r a n a l y s i s  were o b t a i n e d from c o r e s 8 cm i n diameter by 20 cm, which had been a i r d r i e d and t h o r o u g h l y mixed. Water samples f o r s a l i n i t y measurements were c o l l e c t e d from depress i o n s near s t a t i o n 2. thousand  S a l i n i t y was e s t i m a t e d t o t h e n e a r e s t p a r t p e r  (o/oo) u s i n g a p o r t a b l e Yellow S p r i n g s Instrument Co. 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 model 33. Temperatures  o f t h e a i r and sediment a t the s u r f a c e and a t 5 and  15 cm depths were measured t o t h e n e a r e s t degree c e n t i g r a d e u s i n g a mercury thermometer. Approximate  A l l measurements r e c o r d e d took p l a c e near s t a t i o n 2.  time o f each measurement was a l s o r e c o r d e d .  Oxidizing  (redox) p o t e n t i a l s o f t h e sediment p r o f i l e s a t s t a t i o n 1  were r e c o r d e d i n the f i e l d .  A P l e x i g l a s tube o f 8 cm i n s i d e diameter  ( i . d . ) was used t o remove a c o r e o f t h e sediment p r o f i l e a p p r o x i m a t e l y 25 cm deep.  Upon removal, t h e tube was corked a t both ends u n t i l  measuring began, u s u a l l y l e s s than 5 minutes from r e c o v e r y .  redox  With  sediment temperatures p r e - s e t , the redox p o t e n t i a l was measured as r a p i d l y as p o s s i b l e t o i n s u r e minimal o x i d a t i o n .  The redox  electrode  was i n s e r t e d a minimum o f 1 cm i n t o t h e s i d e o f t h e c o r e a t 2 cm i n t e r v a l s t o t h e depth o f 20 cm as t h e c o r e was extruded i n t o a l o n g i t u d a l l y cut tube o f 8 cm i . d . f o r s u p p o r t .  E f f o r t s were made t o minimize a i r  14 leakage a l o n g t h e s h a f t o f the probe d u r i n g measurements. used was an O r i o n s p e c i f i c  The instrument  i o n meter model 407 A/F with an O r i o n  p l a t i n u m redox e l e c t r o d e model 96-78. S u b s t r a t e e l e v a t i o n s a l o n g t h e t r a n s e c t were o b t a i n e d by a survey on December 22, 1980. meridian  Standard  t r a n s e c t were used.  l e v e l i n g techniques  McElhanney s u r v e y e r s o f Vancouver  datum No. 9628 (11.67 f e e t Geodetic #158 on t h e Roberts  all  survey  e l e v a t i o n ) , l o c a t e d on power p o l e  Readings were c o r r e c t e d t o t h e 1980 t i d e and c h a r t  2.95 m t o t h e Geodetic datum e l e v a t i o n .  The h e i g h t o f  s t a t i o n s measured was checked by o v e r s i g h t t e c h n i q u e s .  are p r e s e n t e d  White  Bank c o a l p o r t causeway served as t h e r e f e r e n c e datum  f o r a l l measurements. datum by adding  with a David  as meters above t i d e  A l l elevations  (and c h a r t ) datum.  T i d a l h e i g h t s and t h e d u r a t i o n o f exposure a t 2.5 m CD were p r e d i c t e d f o r Tsawwassen i n accordance  w i t h Canadian T i d e and Chart T a b l e s Volume 5.  Exposure p e r i o d s o f t i d e s i n which the low o c c u r r e d d u r i n g peak h e a t i n g hours (1130 - 1400 w i n t e r , 1030 - 1600 summer P a c i f i c Standard  Time,  Environment Canada p e r s o n a l communication, 1980) were o b t a i n e d f o r 2.5 m by c a l c u l a t i n g exposure d u r a t i o n f o r s e l e c t e d t i d e s which appeared t o be c l o s e t o the d u r a t i o n c u t - o f f p o i n t s ; i n t e r m e d i a t e t i d e were not g e n e r a l l y p r e d i c t e d . estimated by a v e r a g i n g  Percent  exposures  exposure f o r 2.5 m and 3.1 m was  exposure p r e d i c t i o n s a t new, f u l l ,  and f i r s t and  l a s t q u a r t e r moons f o r the p e r i o d .  Shoot demography At each o f the t h r e e t i d a l h e i g h t s , n i n e p l o t s were e s t a b l i s h e d a t 1 m intervals relief.  (Fig. 4).  Row l e n g t h was d i c t a t e d by l o c a l  topographic  S t a t i o n s were l o c a t e d s u b j e c t i v e l y t o i n s u r e t h a t r e p l i c a t e  15 p l o t s were from the same t i d a l h e i g h t and s l o p e .  This  subjective  s e l e c t i o n o f v i s u a l l y homogeneous p l o t s and r e p e a t e d sampling o f the same i n d i v i d u a l s remove some o f the need f o r the l a r g e r e q u i r e d i n random biomass samples who  have taken t h i s approach  replication  (Harper and White 1974).  (e.g. Mack 1976)  Others  found t h a t r e p l i c a t e  plot  v a r i a t i o n can be v e r y s m a l l and p o p u l a t i o n f l u x p a t t e r n s can be accurately portrayed for s p e c i f i c  environments.  At each p l o t , a 30 cm l e n g t h o f PVC p l a s t i c p i p e was the sediment  inserted  into  to a depth o f 29 cm t o a c t as a permanent p l o t marker.  p l o t frame o f 20 cm X 50 cm  ( i n s i d e dimensions) c o u l d be  A  relocated  a c c u r a t e l y by p l a c i n g one o f the f o u r l e g s o f the p l o t frame i n t o  the  b u r i e d p i p e and a l i g n i n g the edge o f the frame w i t h the r e m a i n i n g p i p e s i n the row.  A p l o t was  d e f i n e d as the a r e a v e r t i c a l l y p r o j e c t e d  the i n s i d e o f the frame when p r o p e r l y a l i g n e d .  through  A sheet o f P l e x i g l a s f i t  onto the frame to form a t a b l e - l i k e s u r f a c e which, when c o r r e c t l y p o s i t i o n e d , was  10 cm above the  sediment.  P l o t s a t each t i d a l h e i g h t were d i v i d e d e v e n l y i n t o t h r e e t r e a t m e n t s . In treatment A, a l l shoots were r e p e a t e d l y mapped throughout t h e i r span.  In treatments B and C, a l l shoots o f Z. j a p o n i c a and R. m a r i t i m a ,  r e s p e c t i v e l y , were removed on June 11; by removal  o f subsequently  a p p e a r i n g shoots the emergence and i d e n t i t y o f s e e d l i n g s was until  life  the f o l l o w i n g To map  Plexiglas.  monitored  May.  the shoots i n each p l o t , an a c e t a t e sheet was Each shoot was  l a i d over the  i d e n t i f i e d to s p e c i e s and then mapped by  v e r t i c a l l y p r o j e c t i n g the l o c a t i o n o f i t s base onto the a c e t a t e s h e e t . V e r t i c a l alignment was  i n s u r e d by the use o f a p a r a l l a x tube  (a 10  P l e x i g l a s tube o f 8 cm  i n s i d e diameter w i t h c r o s s h a i r s a t e i t h e r  cm end)  16 which remained frame.  Shoot  v e r t i c a l by r e s t i n g on t h e P l e x i g l a s s u r f a c e o f t h e p l o t l o c a t i o n s were coded  dates o f shoot appearance,  first  (by symbol and c o l o r ) t o i n d i c a t e  f l o w e r i n g , and death.  A l l shoots t h a t  appeared between any two s u c c e s s i v e sampling dates were t r e a t e d as a cohort.  Morphology  and ovary f a t e s '  Monthly o b s e r v a t i o n s were made on samples  o f Z. j a p o n i c a and  R. m a r i t i m a c o l l e c t e d from each t i d a l h e i g h t .  Samples c o n s i s t e d o f a  minimum o f 15 shoots s e l e c t e d h a p h a z a r d l y from w i t h i n 3 m o f each s t a t i o n and p r e s e r v e d i n 5% (v/v) formaldehyde  i n seawater.  ments were taken a t a l a t e r date on t e n h a p h a z a r d l y s e l e c t e d  Measureshoots  to determine t h e average l e n g t h o f the l o n g e s t l e a f measured from the top o f t h e l e a f sheath, the number o f i n f l o r e s c e n c e s p e r f l o w e r i n g shoot and t h e number o f o v a r i e s p e r i n f l o r e s c e n c e .  The average  length  o f r e c e n t l y produced rhizome i n t e r n o d e s was found by measuring t h e i n t e r n o d e l e n g t h behind each o f t e n t e r m i n a l s h o o t s .  Attempts  were  a l s o made t o determine the e x t e n t o f c l o n a l growth o f i n d i v i d u a l  genets  through c a r e f u l e x c a v a t i o n i n t h e f i e l d and m o n i t o r i n g s e e d l i n g s grown under  laboratory  conditions.  The f a t e s o f i n d i v i d u a l o v a r i e s c o n t a i n e d w i t h i n two age c l a s s e s o f 25 i n f l o r e s c e n c e s each were a s s e s s e d f o r both Z. j a p o n i c a and R. m a r i t i m a a t the t h r e e t i d a l h e i g h t s t a t i o n s . chosen h a p h a z a r d l y w i t h i n treatment A p l o t s  I n f l o r e s c e n c e s were  (no u n n a t u r a l m a n i p u l a t i o n )  and were mapped and r e l o c a t e d u s i n g the p l o t frame p r e v i o u s l y d e s c r i b e d . The p o s i t i o n o f t h e i n f l o r e s c e n c e s observed was always on t h e second formed  l a t e r a l branch and r e q u i r e d no s p e c i a l  tagging f o r r e l o c a t i o n .  The beginning  first  25 i n f l o r e s c e n c e s were chosen on June 11, 1980, t h e  o f the f l o w e r i n g p e r i o d , f o r each s p e c i e s a t each s t a t i o n .  I n f l o r e s c e n c e s o f the second age c l a s s were s e l e c t e d midway through t h e expected f l o w e r i n g p e r i o d , as determined by o b s e r v a t i o n s s i t e the p r e v i o u s  y e a r (P.G. H a r r i s o n u n p u b l i s h e d  data).  made a t t h e F o r Ruppia,  the i n f l o r e s c e n c e s f o r t h e second age c l a s s were chosen on J u l y 10, 1980, and  f o r Z o s t e r a , on J u l y 30, 1980.  O b s e r v a t i o n s were made on o v a r i e s o f  both age c l a s s e s t w i c e monthly u n t i l u l t i m a t e f a t e was c e r t a i n .  Ovaries  t h e i n f l o r e s c e n c e was l o s t o r the were counted and e v a l u a t e d  i n terms  of four possible f a t e s : 1.  Abortion  o f developing  ovary  2.  Damage (by p r e d a t i o n )  3.  Incomplete development o f ovary r e s u l t i n g from death o f parent  r e s u l t i n g i n death w h i l e on i n f l o r e s c e n c e  shoot 4.  Maturation  Seed p r o d u c t i o n t i d a l heights.  complete was estimated  f o r both s p e c i e s a t each o f t h e t h r e e  The number o f f l o w e r i n g shoots r e c r u i t e d was m u l t i p l i e d  by the average number o f i n f l o r e s c e n c e s p e r f l o w e r i n g shoot, t h e number o f female f l o w e r s p e r i n f l o r e s c e n c e , and the p e r c e n t  o f o v a r i e s produc-  i n g mature seed f o r a d e f i n e d age c l a s s .  B u r i e d seed enumeration The winters  number and d i s t r i b u t i o n o f b u r i e d seed was assessed  i n the  o f 1980 and 1981 and t h e summer o f 1981 by examining t e n d u p l i c a t e  samples w i t h i n a 5 m r a d i u s o f t h e t h r e e s t a t i o n s .  Each sample was  taken by p l a c i n g a P l e x i g l a s tube o f 8 cm i n s i d e diameter i n t o t h e sediment t o a t l e a s t  23 cm depth.  Cores were e x t r a c t e d , p l a c e d i n  18 p l a s t i c bags, and f i r m l y wrapped i n paper to support the c o r e shape and minimize v e r t i c a l  displacement o f s t r a t a .  Samples were then s t o r e d a t 10°C i n the dark f o r between one and two weeks b e f o r e examination.  At the time o f i n s p e c t i o n ,  day  samples  were unwrapped and p l a c e d i n a l o n g i t u d i n a l l y d i v i d e d tube o f the same diameter as the c o r i n g tube.  The sediment c y l i n d e r was  then c u t i n t o  one c e n t i m e t e r d i s c s to the depth o f 20 cm by a w i r e guided by h o r i z o n tal slits  i n the d i v i d e d tube.  by washing,  Each d i s c was  w i t h s a l t w a t e r , through a s e r i e s o f s i e v e s .  s c r e e n o f 4 mm  mesh was  through a s i e v e o f 1.9 mm coarse p a r t i c l e s . trapped seed.  individually  F i r s t a coarse  used to remove m o l l u s k s , the l a r g e r  and much o f the r o o t and rhizome network.  detritus,  Then m a t e r i a l was  passed  mesh t o remove remaining r o o t s , d e t r i t u s ,  T i g h t l y matted r o o t s were s e p a r a t e d to r e l e a s e  Slits,  and  any  sand, seed, and f i n e o r g a n i c p a r t i c l e s c o n t i n u e d  i n t o a s i e v e o f .84 mm materials.  then examined  mesh which r e t a i n e d a l l seeds and few  inorganic  S e v e r a l examinations o f the remaining f r a c t i o n r e v e a l e d  seed, so i n s p e c t i o n was  discontinued.  no  The f r a c t i o n c o n t a i n i n g seed  examined by d i s s e c t i n g scope, i l l u m i n a t e d m a g n i f y i n g l e n s or naked  was eye,  and the number and type o f seed were noted. The v i a b i l i t y o f seed was 0 ( s u r f a c e ) - 5 cm,  5-10  cm,  t e s t e d i n f o u r groups per 10 - 15 cm,  station:  and 15 - 20 cm depth.  s p e c i e s , seed from each o f the ten r e p l i c a t e s was  By  combined i n the f o u r  s e c t i o n s , and twenty seeds, i f a v a i l a b l e , were s e l e c t e d h a p h a z a r d l y for v i a b i l i t y  testing.  V i a b i l i t y was tion.  t e s t e d by two methods used s e p a r a t e l y or i n combina-  Non-dormant seed was  simply germinated i n d i s t i l l e d water a t  10°C; a f t e r a p e r i o d o f about one week, seed which had not  germinated  19 was examined of  with the tetrazolium t e s t .  The t e t r a z o l i u m t e s t  consisted  s o a k i n g seed a t a p p r o x i m a t e l y 15°C f o r between 3 and 24 hours i n a  1% (v/v) s o l u t i o n o f 2 , 3 , 5 - t r i p h e n y l 2 H - t e t r a z o l i u m c h l o r i d e i n d i s t i l l e d water  (Moore 1961).  V i a b i l i t y was confirmed i f t h e seed  germinated o r t h e h y p o c o t y l s t a i n e d r e d w i t h t h e t e t r a z o l i u m  test.  Germination has been d e f i n e d f o r t h e s e s t u d i e s as the emergence of  t h e h y p o c o t y l f o r a minimum o f 5 mm.  T h i s d e f i n i t i o n was needed  because on o c c a s i o n dead seed can imbibe water and the s w o l l e n endosperm s p l i t s , g i v i n g t h e appearance o f i n i t i a l  stages o f g e r m i n a t i o n .  The depth o f seed g e r m i n a t i o n was s t u d i e d a t s t a t i o n 2 on f i v e o c c a s i o n s from March 10 t o May 1, 1981.  Cores were c o l l e c t e d , near  s t a t i o n 2, t r a n s p o r t e d t o the l a b o r a t o r y , and c u t i n t o  1 cm d i s c s as'  p r e v i o u s l y d e s c r i b e d f o r s t u d i e s o f b u r i e d seed numbers.  Shoots  arising  from o v e r w i n t e r i n g rhizomes were a l s o noted when encountered.  V i a b i l i t y and g e r m i n a t i o n o f seed s t o r e d i n a e r o b i c  conditions  Seed used i n t h e f o l l o w i n g experiments was o f two age c a t e g o r i e s . Seed r e c o v e r e d from sediments d u r i n g t h e summer and thus a t l e a s t one year o l d , was d e s i g n a t e d " o l d " .  Seed o b t a i n e d from t h e c u r r e n t y e a r ' s  p r o d u c t i o n w i l l be r e f e r r e d t o as "new". New seed o f R. m a r i t i m a and Z. j a p o n i c a was h a r v e s t e d on J u l y 10, and J u l y 30, 1980, r e s p e c t i v e l y , from mature i n f l o r e s c e n c e s on p l a n t s growing 100 m seaward  from s t a t i o n 3.  Seed was p l a c e d i n 27 o/oo  seawater and were s t o r e d a t 5°C i n t h e dark u n t i l Old  used.  seed o f Z. j a p o n i c a and R. maritima was r e c o v e r e d on J u l y 10,  1980 by s i e v i n g sediments from t h e v i c i n i t y o f s t a t i o n 2 w i t h seawater through a .84 mm mesh s c r e e n .  Seed was s e p a r a t e d by s p e c i e s and s t o r e d  20 i n 27 o/oo seawater  i n the dark a t 10°C f o r one week, a f t e r which  a few seeds were observed to be g e r m i n a t i n g . to  dark s t o r a g e a t 5°C where i t remained  period  Seed was then  time  transferred  the d u r a t i o n o f the s t o r a g e  (9 months) w i t h o n l y an i n f r e q u e n t g e r m i n a t i o n .  The v i a b i l i t y o f new and o l d seed was r e g u l a r l y t e s t e d w i t h two o r t h r e e r e p l i c a t e s o f not l e s s than 50 seeds each, w i t h methods p r e v i o u s l y d e s c r i b e d f o r b u r i e d seed. of  seed i n i t i a l l y  A l l v i a b i l i t i e s were expressed as a p e r c e n t  recovered or harvested.  Germination curves a r e  expressed as the p e r c e n t o f v i a b l e seed i n each r e p l i c a t e a t the end of  the g e r m i n a t i o n p e r i o d . To t e s t the e f f e c t s o f s a l i n i t y  on g e r m i n a t i o n , new Z o s t e r a and  Ruppia seed was p l a c e d between f i l t e r  paper d i s c s i n p e t r i d i s h e s  c o n t a i n i n g 15 to 20 ml o f d i s t i l l e d water and/or at for  10°C.  seawater,  and was h e l d  Four p l a t e s c o n t a i n i n g 50 seeds each were p r e p a r e d p e r s p e c i e s  each o f f o u r s a l i n i t i e s :  0, 10, 20, and 27 o/oo.  The e f f e c t o f  s c o r i n g on g e r m i n a t i o n o f new seed was t e s t e d by n i c k i n g seed c o a t s w i t h a razor blade.  F i f t y - s e e d r e p l i c a t e s o f s c o r e d seed o f each s p e c i e s  were p l a c e d i n 1 and 10 o/oo s a l i n i t i e s . of  Two to f o u r 50-seed  o l d seed o f each s p e c i e s were germinated i n 0 and 20 o/oo  A d d i t i o n a l r e p l i c a t e s o f o l d seed were p l a c e d under salinities;  t h e i r exposure to white l i g h t  under a g r e e n - f i l t e r e d  salinities.  10 and 27 o/oo  was p r e v e n t e d by s o r t i n g  25 watt i n c a n d e s c e n t lamp e m i t t i n g l i g h t o f  450 « 560 nm wavelength. sunlight  replicates  Seed exposed  (200 - 1000 m i c r o e i n s t e i n s m"2  to white l i g h t  was p l a c e d i n  s e c l ) f o r t e n minutes. -  21 The e f f e c t s o f temperature of  new  seed  New  seed o f Z. j a p o n i c a and R. maritima was  as p r e v i o u s l y d e s c r i b e d . of  and a n a e r o b i c c o n d i t i o n s on the  On October  1980,  c o l l e c t e d and s t o r e d  n i n e 100-seed  replicates  each s p e c i e s were p l a c e d i n each o f f o u r s t o r a g e c o n d i t i o n s .  a t u r e s were e i t h e r c o n s t a n t 5°C or  14,  viability  a l t e r n a t i n g between 15° and  temperatures)  ( a n t i c i p a t e d w i n t e r sediment 7°C  f o r 12 hours each.  w i t h and without  oxygen.  (anticipated  temperature)  s p r i n g sediment  Both temperature  Seed was  Temper-  regimes had  p l a c e d between two  treatments  f i l t e r paper d i s c s  i n 9 cm p l a s t i c p e t r i d i s h e s which each c o n t a i n e d 15 t o 20 ml o f 27 seawater.  The p e t r i d i s h e s were s t a c k e d i n s i d e 4 - l i t e r p l a s t i c  o/oo  jars  which were then c l o s e d . To a s s u r e j a r s were g a s - t i g h t , the o u t s i d e s u r f a c e s were p a i n t e d with two  coats o f Varathane p l a s t i c enamel and  coated with a t h i n l a y e r o f petroleum produced  jelly.  the i n s i d e s u r f a c e Anaerobic  by p a s s i n g moist n i t r o g e n gas through  to  b u i l d i n s i d e , and  thus encouraging  water p l a c e d i n a n e a r o b i c treatment  7.3  Several  two  times  closed, allowing pressure  exchange under p e t r i l i d s .  p e t r i d i s h e s was  n i t r o g e n gas f o r 30 minutes b e f o r e i t was the seawater was  c o n d i t i o n s were  the j a r by means o f  p o r t s i n the l i d f o r 30 minutes every week to t e n days. d u r i n g the 30-minute p e r i o d the gas o u t l e t was  was  bubbled  with  added to the seed.  b e f o r e b u b b l i n g with n i t r o g e n , and 8.5  Sea-  The pH after,  as  measured w i t h a F i s h e r Model 150 pH meter. A e r o b i c c o n d i t i o n s were m a i n t a i n e d by p u l l i n g m o i s t a i r through w i t h a vacuum pump.  and  the j a r s a t one-week t o 10-day i n t e r v a l s  The a i r was  l e v e l s that could r e s u l t  u s i n g u n t r e a t e d seawater,  exchanged t o a v o i d e x c e s s i v e C O 2  from the decomposition  o f ovary w a l l s  still  of  22 c o v e r i n g many o f the seeds a t t h e time t h e experiment On February 5, and A p r i l 4, 1981, removed from each s t o r a g e treatment.  began.  f o u r 100-seed r e p l i c a t e s were Each r e p l i c a t e was  divided i n  h a l f ; 50 seeds were p l a c e d a t c o n s t a n t 5°C and 50 under a l t e r n a t i n g and 7°C (12 hours  e a c h ) , a l l i n 27 o/oo  s a l i n i t y , aerobic  15  conditions.  S o r t i n g and o b s e r v a t i o n s i n v o l v i n g t h e n i n t h s e t o f 100-seed  replicates  from each s t o r a g e treatment took p l a c e i n February under a green s a f e light.  These seed were germinated i n a e r o b i c , a l t e r n a t i n g 15 and  7°C  conditions.  V i a b i l i t y o f e x p e r i m e n t a l l y b u r i e d seed To t e s t seed o f Z.  the e f f e c t s o f b u r i a l depth on seed v i a b i l i t y , new  j a p o n i c a and R. m a r i t i m a was  100 seeds each.  and o l d  s e p a r a t e d i n t o 16 r e p l i c a t e s o f  Four r e p l i c a t e s o f each s p e c i e s and age c a t e g o r y were  b u r i e d a t each o f f o u r sediment depths: s t a t i o n 2 a t Roberts Bank.  Additional  5, 10, 15, and 20 cm near 100-seed r e p l i c a t e s o f  new  Z. j a p o n i c a and R_. maritima were b u r i e d a t each sediment l e v e l t o t e s t the g e r m i n a t i o n response o f seed not exposed t o l i g h t . J u s t p r i o r to b u r i a l on October 14, 1980, each s p e c i e s were p l a c e d i n i n d i v i d u a l  100-seed r e p l i c a t e s o f  10 x 15 cm p l a s t i c coated  2 f i b e r g l a s s bags o f 1 mm  mesh.  The bags were p a r t i a l l y f i l l e d  with  sediment from t h e l e v e l the bag would be b u r i e d a t ; the f i n a l volume was  about 150 ml.  one l o c a t i o n .  A t t e n t i o n was  g i v e n not t o have seed aggregate i n  Bags were f o l d e d c l o s e d and a t t a c h e d to  wooden s t a k e s w i t h aluminum  2 X 2 X 50  staples.  B u r i e d samples remained u n d i s t u r b e d u n t i l r e c o v e r y , w i t h t h e e x c e p t i o n o f r e b u r i a l o f an o c c a s i o n a l bag from the 5 cm l e v e l  that  cm  would become p a r t i a l l y exposed.  The exposure o f these bags was  r e s u l t o f e r o s i o n i n the immediate Two  a r e a around the s t a k e .  r e p l i c a t e s o f each s p e c i e s and age c a t e g o r y , and a l l o f the  seed which was sediment 1981.  a  not exposed  to white l i g h t were r e c o v e r e d from  each  depth on February 2; a l l o t h e r s were r e c o v e r e d on A p r i l  9,  The s t a k e s and a t t a c h e d bags were kept moist and t r a n s p o r t e d  d i r e c t l y to the l a b o r a t o r y , about a one-hour t r i p .  The bags were  s t o r e d a t 10°C u n t i l they were s i e v e d under seawater w i t h a .84  mm  screen. Each r e p l i c a t e o f 100 was at  divided  i n h a l f ; 50 seeds were p l a c e d  5°C, and 50 were p l a c e d under temperatures a l t e r n a t i n g from 15 t o  7°C every 12 h o u r s .  Seed was  p e t r i dishes inside p l a s t i c laboratory.  Seed was  c o n t a i n e d between f i l t e r paper d i s c s i n  j a r s as d e s c r i b e d f o r new  seed i n the  checked f o r g e r m i n a t i o n i n i t i a l l y  on a d a i l y  b a s i s and then a t r e g u l a r i n t e r v a l s as i n d i c a t e d i n the r e s u l t s . which was  not exposed  t o l i g h t was  v i o u s l y d e s c r i b e d f o r new  handled i n the same way  Seed  as p r e -  seed s t o r e d i n the l a b o r a t o r y .  F i g u r e 5 summarizes s t o r a g e , r e b u r i a l , and g e r m i n a t i o n treatments of  new  and o l d seed o f Z o s t e r a and Ruppia.  experiments have been o m i t t e d .  S a l i n i t y and  scoring  Both s t o r e d and r e b u r i e d seed  was  submitted to the same g e r m i n a t i o n t r e a t m e n t s .  Data a n a l y s e s One way the  a n a l y s i s o f v a r i a n c e f o r unblocked d a t a was  5% s i g n i f i c a n c e  Sampling  performed a t  level.  intervals  T a b l e I summarizes i n t e r v a l s o f samplings throughout the study.  NEW  SEED  BURIAL  I  5 cm  1  10 cm  1  15 cm  STORAGE 20  I  1 cm  GERMINATION  f t 5 cm  10 cm  t 15 cm  Aerobic 5 C ^  TREATMENTS  TREATMENTS  1  I  Anaerobic 5 C \J/  Aerobic 15/7 C ^  1 Anaerobic 15/7 C ^  (AEROBIC)  f 20  cm  BURIAL OLD  SEED  February Dark 15/7 C  V  Light 5 C  t April  5.  Flow c h a r t o f b u r i a l ,  s t o r a g e , and  seed o f Z o s t e r a j a p o n i c a and  Ruppia  germination  maritima.  Recovery Light 15/7 C  t Recovery  treatments  o f o l d and  new  : I.  Sampling and observation dates and approximate times o f temperature  readings at Roberts Bank, 1980 - 1981. as follows:  Codes f o r observations made are  DI, D2, e t c . = shoot demography e s t a b l i s h i n g cohorts 1, 2,  etc.; R l , R2, Z l , and Z2 = Ruppia maritima and Zostera japonica flower fate age c l a s s e s  1 and 2, M = morphological samples, 0 = o x i d i z i n g  p o t e n t i a l , and S = s a l i n i t y .  Date  May June  July  August  September  Time  15  1200  DI  2  1300  D2  11  1100  D3  Rl -  Zl  23  0900  D4  Rl  Zl  10  1100  D5  Rl,2  Zl  21  0800  D6  30  1300  6  D7  15  1400  26  1500  5  0900  12  October  Observations Made  1000  6  1000  14  0200  21  s M  0  s  M  0  S s  Rl,2  Zl,2  Rl,2  Zl,2  s  0 D8  R2  Z2  M  12  M  D10  M  2200  D12  M  January  6  2300  D13  M  23  0100  0  s  0  s s  0100  D14  M  21  May  s  2 6  Apri 1  0 Dll  3  March  0  s  December  February  s  s D9  23  s  M  0  s  0  s  3  2100  D15  10  14 30  D16  24  1300  D17  9  1400  D18  18  1200  D19  0  s  1  1000  D20  0  s  M  s s  M  26 SECTION 1. Transect  PHYSICAL ENVIRONMENT  topography  F i g u r e 6 shows a p r o f i l e o f g e n e r a l sediment topography a l o n g the study t r a n s e c t . 2.60  S t a t i o n s 1, 2, and 3 were l o c a t e d a t +3.17, 2.54,  m, r e s p e c t i v e l y .  l e v e l at s t a t i o n s marking p l o t  There were no n o t i c e a b l e changes  i n sediment  2 and 3 r e l a t i v e t o the h e i g h t o f the p l a s t i c p i p e s  l o c a t i o n s d u r i n g the study p e r i o d .  At s t a t i o n 1, however,  sand waves t r a v e l l e d a c r o s s the s t a t i o n i n A p r i l , p l o t s w i t h an a d d i t i o n a l still  and  temporarily  covering  8 cm o f sandy sediment, 2 cm o f which were  p r e s e n t on the 1st o f  May.  The d i f f e r e n c e o f .06 m between s t a t i o n s 2 and 3 d i d not cause a d i f f e r e n c e i n the amount o f time they were covered by t i d e s . however, was tidal  Station 2  l o c a t e d where water d r a i n i n g from the h i g h e r areas o f the  f l a t was  channeled and p l a n t s were submerged i n about 4 cm o f  water i n excess o f an hour a f t e r the t i d e receded w h i l e water from the upper a r e a s .  Water d i d not p o o l a t any s t a t i o n .  w i t h i n p l o t s v a r i e d w i t h burrowing animal a c t i v i t y . v a r i a t i o n s i n sediment h e i g h t  drained  Microrelief  Most s m a l l - s c a l e  (mostly from f e c a l c a s t s ) were removed  by the incoming t i d e .  Tides T a b l e I I shows e s t i m a t e s o f t h e p e r c e n t o f days w i t h i n each month o f t h e y e a r on which the t i d e exposes +2.5  m sediments a t Roberts  Bank d u r i n g the peak h e a t i n g hours o f the day. sediments a t +3.2  m,  I t was  estimated that  a p p r o x i m a t e l y t h e h e i g h t o f s t a t i o n 1, a r e  exposed a t o t a l o f between 8 t o 10% more o f t e n than a r e sediments a t +2.5  m.  On t h e c o a s t o f B r i t i s h Columbia d u r i n g the summer,  extreme  F i g . 6.  General topography  s t a t i o n s a t Roberts  o f study t r a n s e c t  Bank.  showing p o s i t i o n s  of  28  Table I I .  Percent of days of exposure per month from t i d e s r e a c h i n g  d u r i n g peak h e a t i n g hours of the day a t or below 2.5 h e i g h t , Roberts Bank. Canada, were 11:30 summer.  Peak h e a t i n g hours,  - 14:00  i n w i n t e r , and  A c t u a l t i d a l exposures may  Month  Total %  tidal  determined by Environment 10:30  - 16:00  i n the  v a r y s l i g h t l y from p r e d i c t e d  l e v e l s a c c o r d i n g to m e t e o r o l o g i c a l events wind, r a i n , or b a r o m e t r i c  m CD  low  (e.g. extreme or  prolonged  pressure).  < 3 hrs.  3-6  hrs..  > 6 hrs.  Jan.  0  0  0  0  Feb.  16  16  0  0  Mar.  48  19  28  0  Apr.  60  10  40  10  May  61  0  32  29  Jun.  63  0  23  40  Jul.  64  6  23  35  Aug.  54  9  29  16  Sep.  43  20  23  0  Oct.  32  29  3  0  Nov.  6  6  0  0  Dec.  0  0  0  0  29 lower water i s a s s o c i a t e d w i t h , bimonthly s p r i n g t i d e s and midday, and  i n the w i n t e r near midnight.  sediments may  have prolonged  Thus i n w i n t e r ,  exposures to n i g h t t i m e  at Roberts Bank d u r i n g midwinter.  near  intertidal  temperatures.  F r e e z i n g o f s u r f a c e sediments to 2 - 3 cm depth was occasions  occurs  observed on s e v e r a l  In the summer, the  exposures take p l a c e d u r i n g the h o t t e s t p a r t o f the day.  longest  During  exposure  to  the midday summer sun and  in  c o n t a c t with the a i r can dry to the p o i n t t h a t they become b r i t t l e .  Considerable at  winds, l e a f s u r f a c e s o f Z o s t e r a and  d e s i c c a t i o n occurred  s t a t i o n s 3 and  Ruppia  at s t a t i o n 1, with p r o g r e s s i v e l y l e s s  2.  Sediments Sediment t e x t u r e s were e s s e n t i a l l y i d e n t i c a l at each t i d a l d u r i n g the w i n t e r ,  and  showed a s l i g h t  f r a c t i o n s i n the summer (Table I I I ) . sediments at the study Increases  increase i n s i l t  P a r t i c l e s i z e analyses  clay of  s i t e show w e l l - s o r t e d homogeneous sands.  i n f i n e p a r t i c l e s i n the summer c o u l d be  input o f s i l t  and  height  from the F r a s e r R i v e r f r e s h e t .  e x p l a i n e d by  the  In a d d i t i o n , slowing  water movements by the v e g e t a t i o n would i n c r e a s e the d e p o s i t i o n o f suspended p a r t i c l e s from the water column. reached the same c o n c l u s i o n when they f r a c t i o n o f sediments was with a d j a c e n t  bare  M a r s h a l l and  found t h a t the  of fine  Lukas (1970)  fine-particle  h i g h e r w i t h i n beds o f Z o s t e r a marina compared  areas.  Salinity S a l i n i t y measurements r e c o r d e d 31 and  21 o/oo,  reaching  a low  at the study  s i t e f l u c t u a t e d between  i n August and h i g h s  i n October and  January.  Table I I I .  Percentage of sediment i n each o f f i v e s i z e c l a s s e s from  t h r e e s t a t i o n s (1 = 3.17 m, 2 = 2.54 m, 3 = 2.60 m CD t i d a l h e i g h t ) at  Roberts Bank, 1980 - 1981.  Jan.  Size Class  1980  Aug. 1980  J a n . 1981  (mm)  > 2.0 (Gravel)  0  0  0  0  0  0  0  0  0  .25 - 2.0 (Coarse Sand)  26  24  22  21  23  24  22  24  27  .05 - .25 (Fine Sand)  68  70  73  73  70  70  72  71  68  .002 - .05 (Silt)  6.5  < .002 (Clay)  0  6.0  0  5.0  0  0  6.5  6.5  0.5  6.0  6.0  0  5.0  0  0  5.5  0  31 Salinities  were t y p i c a l l y  between 39 and 25 o/oo most o f t h e year  ( F i g . 7). Seawater s a l i n i t i e s v a r y c o n s i d e r a b l y i n c o a s t a l r e g i o n s under t h e influence o f the Fraser River.  Swinbanks (1979) r e c o r d e d s u r f a c e  s a l i n i t i e s a t low t i d e on t i d a l  f l a t s o f the Fraser Delta that  between 1 and 33 o/oo.  Waldichuck  (1957), found s a l i n i t i e s  ranged  typically l i e  i n the range o f 24 t o 29 o/oo, i n t h e southern s t r a i t o f G e o r g i a . "normal" S t r a i t  o f Georgia s a l i n i t i e s  a r e what a r e u s u a l l y  These  encountered  i n the intercauseway a r e a a t Roberts Bank (Levings and C o u s t a l i n 1975, Swinbanks  1979).  As i n d i c a t e d by measurements from August, the  intercauseway s a l i n i t y  there i s a reduction i n  as a r e s u l t o f t h e F r a s e r R i v e r f r e s h e t .  The p e r i o d d u r i n g which t h e f r e s h e t o c c u r s v a r i e s from m i d - J u l y t o mid-August the  (Waldichuck 1957) .  L o c a t i o n s immediately n o r t h and south o f  intercauseway a r e a a r e i n f l u e n c e d t o a much g r e a t e r extent by t h e  F r a s e r R i v e r plume. Swinbanks conducted an e x t e n s i v e survey o f s u r f a c e s a l i n i t i e s i n e a r l y J u l y , 1977 and found s a l i n i t i e s of  t o be f a i r l y c o n s t a n t over much  the t i d a l f l a t , between 24 and 27 o/oo.  towards  There was a marked  t h e marsh i n t h e n o r t h e r n c o r n e r , where s a l i n i t i e s  30 o/oo.  increase  reached  The i n c r e a s e d s a l i n i t y o f these areas was thought t o be caused  by e v a p o r a t i o n o f p o o l i n g water  i n this region.  Water d r a i n i n g over  s t a t i o n 2 from marsh areas a t low t i d e may have r e s u l t e d i n s l i g h t l y higher s a l i n i t i e s The s a l i n i t y  t h e r e than i n t h e r e s t o f t h e intercauseway a r e a .  o f i n t e r s t i t i a l waters o f sediment p r o f i l e s was not  monitored, but i t has been s t u d i e d i n the intercauseway a r e a , i n t e r t i d a l l y by Swinbanks (1979) and i n t h e s t r a n d l i n e by A. Moody (1978) .  33 They found t h a t s u b s u r f a c e s a l i n i t i e s d i d not d i f f e r u n l e s s t h e r e were dramatic f l u c t u a t i o n s i n s u r f a c e s a l i n i t i e s .  At Roberts Bank, s m a l l -  s c a l e s a l i n i t y changes o c c u r r e d d a i l y as a r e s u l t o f t i d a l  cycles,  drainage p a t t e r n s , amount and p e r i o d o f p r e c i p i t a t i o n , and  temperature.  These changes were l i k e l y ephemeral c e n t i m e t e r s o f the sediment p r o f i l e , the s a l i n i t y o f the t i d a l  Sediment  and a f f e c t e d o n l y the f i r s t  few  the s u b s u r f a c e s a l i n i t i e s remaining  waters.  temperatures  Sediment temperature  temperatures r o u g h l y p a r a l l e l e d s e a s o n a l changes i n a i r  (Fig. 8).  The magnitude o f temperature  w i t h i n c r e a s i n g sediment depth.  f l u c t u a t i o n s decreased  Maximum s u r f a c e sediment  temperatures  which were w e l l above a i r temperatures o c c u r r e d i n l a t e J u l y and August.  The minimum s u r f a c e temperature was  r e c o r d e d i n December, a t  which time the sediment was  f r o z e n h a r d to the depth o f 1 t o 2 cm  was  2 t o 3 cm.  s t i f f e n e d an a d d i t i o n a l  sediment  early  In March, temperatures  and  at a l l  l e v e l s measured showed a marked i n c r e a s e from w i n t e r v a l u e s .  The a m e l i o r a t i o n o f temperature  f l u c t u a t i o n s w i t h depth r e c o r d e d  at Roberts Bank has a l s o been observed i n most s o i l s Levings and C o u s t a l i n  (Russell  (1975) r e c o r d e d s u r f a c e sediment  temperatures  throughout the F r a s e r f o r e s h o r e and a l s o found t h a t sediment temperatures  1973) .  surface  tended t o f o l l o w seasonal t r e n d s ; they a t t r i b u t e d  extreme f l u c t u a t i o n s o f s u r f a c e sediment and a b s o r p t i v e p r o p e r t i e s o f the sediment  temperatures  to the r e f l e c t i v e  ( P e r k i n s 1963) .  C o u s t a l i n a l s o observed t h e w i n t e r f r e e z i n g o f s u r f a c e  Levings and  sediments.  General t r e n d s i n s u b s u r f a c e temperatures were s t r o n g l y by the seawater  temperature.  the  R. Moody (1978) r e c o r d e d water  influenced temperatures  on the east s i d e o f the Tsawwassen f e r r y t e r m i n a l , 1.5 m below the  May  Jun  F i g . 8.  Jul  Aug  A i r and sediment  1980 - 1981. sediment.  Sep  Oct  temperatures near s t a t i o n  = a i r , — = s u r f a c e sediment,  Readings were taken d u r i n g low t i d e ;  Nov  Dec  Jan  Feb  Mar  2 (2.54 m CD t i d a l h e i g h t ) a t Roberts Bank, = 5 cm depth, and approximate  = 15 cm depth o f  times are l i s t e d i n T a b l e I .  Apr  35 s u r f a c e and found w i n t e r temperatures o f about 8°C. A maximum t u r e o f 16°C was reached i n August.  tempera-  These temperatures c o r r e s p o n d with  temperatures measured 15 cm below t h e sediment s u r f a c e ( F i g . 8 ) .  Oxidizing  potential  A p r o g r e s s i v e r e d u c t i o n o f sediments  ( l o w e r i n g o f redox p o t e n t i a l )  took p l a c e from June to August, and r e s u l t e d i n the a n a e r o b i c boundary i n the sediment  ( d e f i n e d as + 100 mv redox p o t e n t i a l , Fenchel  1969)  r i s i n g from 2 cm depth t o o n l y a few m i l l i m e t e r s below t h e sediment surface  ( F i g . 9 ) . The a e r o b i c l a y e r o f sediment deepened  t h i s t r e n d c o n t i n u e d throughout t h e w i n t e r .  i n t h e autumn,  In the s p r i n g , the r e d u c t i o n  o f sediments a g a i n brought the a n a e r o b i c l a y e r n e a r e r t o t h e s u r f a c e . T y p i c a l redox p r o f i l e s  i n marine sediments, as measured a t Roberts  Bank, a r e the r e s u l t o f many b i o t i c and a b i o t i c  factors  (Fenchel  1969).  H e t e r o t r o p h s w i t h i n t h e sediment can b o t h reduce (through m e t a b o l i c a c t i v i t i e s ) and o x i d i z e t h e i r environment sediments by b u r r o w i n g ) .  (through t h e a e r a t i o n o f  P h o t o a u t o t r o p h i c organisms a l s o reduce and  o x i d i z e t h e i r environment depending on t h e i r p h o t o s y n t h e t i c ( T a y l o r 1964) .  activity  Fenchel (1969) found t h a t t h e redox i n f l u e n c e o f photo-  autotrophs extend o n l y a few m i l l i m e t e r s below t h e sediment  surface.  Any marked d i u r n a l f l u c t u a t i o n s i n s u r f a c e redox a t Roberts Bank were not sampled because the e l e c t r o d e t i p was i n s e r t e d a minimum o f 1.5 cm below t h e sediment s u r f a c e t o p r e v e n t a i r c o n t a m i n a t i o n .  Decomposition  o f d e t r i t u s by microorganisms i s a major c o n t r i b u t o r t o t h e r e d u c t i o n o f sediments  (Fenchel 1969).  Temperature  o f t e n d i c t a t e s t h e r a t e a t which  v a r i o u s o x i d a t i v e and r e d u c t i v e p r o c e s s e s proceed (Sorensen et a l . 1979). Wave a c t i o n and sediment t e x t u r e i n f l u e n c e the i n c o r p o r a t i o n o f o r g a n i c  36  F i g . 9. a - c. the  Selected p r o f i l e s o f o x i d i z i n g  (redox) p o t e n t i a l s  of  sediment near s t a t i o n 2 (2.54 m CD t i d a l h e i g h t ) a t Roberts  Bank 1980 - 1981.  A l l redox measurements are i n Appendix  2.  S e d i m e n t O  CD  o  OD  CTi  cn r~  NJ  KJ  D e p t h O  CO  o oo  ( c m ) CT>  f - N J  r-cj  O C D O r» M O C O (7* *•» NJ  38 material  i n the sediment and a l s o the t r a n s p o r t a t i o n o f oxygenated  down through the sediment  profile.  A major problem i n g a i n i n g an a c c u r a t e p i c t u r e o f marine redox p r o f i l e s  water  i s t h e tremendous  intertidal  h e t e r o g e n e i t y caused by i n f a u n a and  pockets o f o r g a n i c m a t e r i a l w i t h i n t h e sediment.  Jorgensen (1977) has  g i v e n a t t e n t i o n to the presences o f reduced m i c r o s i t e s i n o t h e r w i s e o x i d i z e d environments.  He c a l c u l a t e d t h a t a f e c a l  pellet  o f 200 micro-  meters diameter c o u l d p r o v i d e an a n o x i c c o r e , where the pore water oxygen content o f sediment was  o n l y 1% o f a i r s a t u r a t i o n .  39 SECTION 2.  GROWING COMPONENT OF POPULATION  Results Shoot  recruitment The r e c r u i t m e n t o f shoot  ( F i g . 10).  cohorts, showed d e f i n i t e seasonal  trends  Z o s t e r a shoot r e c r u i t m e n t was s i g n i f i c a n t l y h i g h e r than  o f Ruppia a t a l l s t a t i o n s .  Shoot r e c r u i t m e n t  that  to the Zostera population  o c c u r r e d throughout t h e year, with a d e c l i n e d u r i n g t h e w i n t e r , whereas shoot  recruitment  t o t h e Ruppia p o p u l a t i o n l a s t e d o n l y from March through  August. Recruitments o f Z o s t e r a shoots  a t t h e t h r e e s t a t i o n s showed s e v e r a l  r e l a t i o n s h i p s i n t h e i r s i z e and t i m i n g ( F i g . 10 a - c ) . found  Numbers o f shoots  i n May were n o t s i g n i f i c a n t l y d i f f e r e n t between t i d a l  During  heights.  t h e f l o w e r i n g p e r i o d , June through October, c o h o r t s were  s i g n i f i c a n t l y l a r g e r a t s t a t i o n 2 than a t s t a t i o n 1; c o h o r t s i z e a t s t a t i o n 3 was not s i g n i f i c a n t l y d i f f e r e n t  from 1 o r 2.  Z o s t e r a a t each  s t a t i o n e x h i b i t e d a slow i n c r e a s e i n s i z e o f c o h o r t s u n t i l  t h e end o f  J u l y , and then a r e d u c t i o n t o low l e v e l s o f r e c r u i t m e n t by December. A r e d u c t i o n o f c o h o r t s i z e began a t most s t a t i o n s w i t h c o h o r t 7 (August 6 ) .  Low r a t e s o f r e c r u i t m e n t were maintained  through  February  at each s t a t i o n with a s i g n i f i c a n t i n c r e a s e i n c o h o r t s i z e a t a l l s t a t i o n s i n March. Ruppia shoot numbers a t s t a t i o n 1 were s i g n i f i c a n t l y lower than a t s t a t i o n s 2 o r 3.  The average s i z e o f c o h o r t s d u r i n g t h e f l o w e r i n g  p e r i o d a t s t a t i o n 1 was s m a l l e r than a t 2 and 3, b u t t h e r e were no s i g n i f i c a n t d i f f e r e n c e s o v e r a l l between t h e s t a t i o n s .  The p a t t e r n o f  subsequent growth was s i m i l a r to t h a t i n Z o s t e r a , b u t temporal  boundaries  were much t i g h t e r , and no o v e r w i n t e r i n g v e g e t a t i v e p o p u l a t i o n e x i s t e d .  40  10.  a - f.  sampling 1981  Recruitment and  l o s s o f shoots between s u c c e s s i v e  dates a t each o f t h r e e s t a t i o n s a t Roberts Bank 1980  ( a b s o l u t e numbers).  No  shading  = shoots with no  reproductive  r e c o r d , s t i p p l i n g = shoots which became r e p r o d u c t i v e a f t e r r e c o r d , Crosshatch  -  first  = shoots which were r e p r o d u c t i v e a t f i r s t  record.  75'  Recruitment  50  251  E o  0-  -€S  -e-  -r±r-  B=b—[T]p, m  QJ CL  (/)*  25-  •«  O  o  JZ  50-  Losses  75-  rooH  125-1  May  2  3  A  5  6  -H  1  1  1  1  Jun  Jul  7 H  10  — I  Aug  11 1-  Sep  Oct  12 -+Nov  13 —fDec  15 16 -i—1 Jan  Cohort Number and Month of Sampling F i g . 10a.  Zostera  j a p o n i c a at s t a t i o n 1 (3.17  m CD).  Feb  17  1  Mar  18 19 20 1—I 1 Apr  100  75  Recruitment  50 H  CM  25H  E 0-  o  [TTn LT  -a  ,—  1_L  l_l3  18 19  20  i_  CD  C L  CO  25-  •o4 • o  JZ  CO  50-  Losses  75-  iooH 135  125H H  2  May  3 1  4  H  H  Jun  5  6 1  7 -  Jul  8  10  9  —l  1-  /4ug  Sep  11 Oct  Nov  H -+-  13  12  h-  — f —  Dec  Jan  Cohort Number and Month of Sampling F i g . 10b.  Zostera  j a p o n i c a a t s t a t i o n 2 (2.54raCD).  15 16  —I—I  Feb  17 1  Mar  1  —  Apr  I  1  75-  Recruitment  50H  25H  o  -4-U-i—EH—m, i i i h  CD Q .  25O O  CO 50H  Losses  1 j,  2  May  3  1 1  4  1  5  1  Jun  6  1  Jul  7  1  8  1  Aug  9  1  10  1  Sep  11  12  1  Oct  1  Nov  13. •  Dec  H  1 .  Jan  Cohort Number and Month of Sampling Fig.  10c. Z o s t e r a  j a p o n i c a a t s t a t i o n 3 (2.60  m CD).  15 16  1—I  h  Feb  17  :  —I  Mar  18 19 20  1 1 1 Apr  44  15-1  Recruitment  10  0  JP  Eprp.  H  (-  5-  E CD  I  10 -  15-  L _ QJ CL  Losses  15-  U)  "o O  Recruitment  10-  - C  CO  5-  0 -  4-1  H  H  H  5-  I  10 -  15-  Losses  20 -  2 3 —I  May  5  H- — I —  Jun Jun  H  9  6  1— Jul  Aug  10 —I  Sep  11 h-  Oct  Cohort Number and Month of Sampling  F i g . 10d.  Ruppia m a r i t i m a a t s t a t i o n 1 (3.17 m CD).  F i g . lOe.  Ruppia maritima a t s t a t i o n 2 (2.54 m CD).  Recruitment  1 1  t  1 Losses V/,  1  23 4  1  1 — I  May  1  Jun  5 6 1  1  Jul  7  8  1  1  Aug  9 1  Sep  10 1  j  11 —  Oct  Cohort Number and Month of Sampling  Fig. lOf.  Ruppia maritima a t s t a t i o n 3 (2.60 m CD).  46 Ruppia c o h o r t s i z e peaked i n t h e f i r s t Shoot r e c r u i t m e n t shoots  ended e a r l i e s t a t s t a t i o n 1 ( J u l y 21); no new Ruppia  were seen a f t e r August 6 a t any s t a t i o n .  By p a r t i t i o n i n g c o h o r t s  i n t o f l o w e r i n g and v e g e t a t i v e shoots,  l y i n g p a t t e r n s were r e v e a l e d . and  part of July at a l l stations.  The shoots  t h a t never became r e p r o d u c t i v e ,  thus d i e d ( o r were l o s t from t h e p o p u l a t i o n )  had p a t t e r n s o f r e c r u i t m e n t  i n the vegetative  t h a t were r e c o g n i z a b l y d i f f e r e n t from  w i t h a recorded r e p r o d u c t i v e phase.  under-  state, those  F u r t h e r d i s t i n c t i o n s can be made  between shoots which had a r e c o r d e d v e g e t a t i v e phase b e f o r e they became r e p r o d u c t i v e and those which were r e p r o d u c t i v e from f i r s t r e p r o d u c t i v e , a shoot produced f l o w e r s u n t i l The r e c r u i t m e n t o f Z o s t e r a shoots  record.  i t died.  t h a t e v e n t u a l l y became r e p r o d u c t i v e  i n c r e a s e d with c o h o r t s i z e and then d e c l i n e d once peak cohort reached  ( F i g . 10 a - c ) , except  r e p r o d u c t i v e shoots represented shoot  Once  s i z e was  f o r s t a t i o n 1 where t h e m a j o r i t y o f  were r e c r u i t e d b e f o r e t h e peak c o h o r t .  a marked asymmetry i n the temporal boundaries  This  shift  of reproductive  r e c r u i t m e n t between s t a t i o n 1 and the o t h e r two s t a t i o n s .  2 and 3 were s i m i l a r i n t h e i r g e n e r a l p a t t e r n o f r e c r u i t m e n t ,  Stations  except f o r  the h i g h v e g e t a t i v e r e c r u i t m e n t o f c o h o r t 8 a t s t a t i o n 3. I n i t i a l c o h o r t s o f Z o s t e r a shoots were s i m i l a r i n s i z e but n o t i n fate.  About h a l f t h e f i r s t  cohort a t s t a t i o n 1 became r e p r o d u c t i v e ,  along with a s m a l l p r o p o r t i o n a t 2, and none a t s t a t i o n 3. r e p r o d u c t i v e shoot r e c r u i t m e n t  ( e a r l y August a t s t a t i o n 1 v s . l a t e  August o r e a r l y September a t s t a t i o n s temporal s h i f t (Fig.  10 a - c ) .  The end o f  2 and 3) a g a i n emphasized t h e  to e a r l y r e p r o d u c t i v e shoot r e c r u i t m e n t  at station 1  I t i s n o t know i f any o f t h e o v e r w i n t e r i n g shoots  1980 - 1981 became r e p r o d u c t i v e .  from  47 Ruppia showed two partitioning second, 71,  outstanding  ( F i g . 10 d - f ) . 39, and  First,  26 p e r c e n t  features i n i t s pattern of few  shoots  o f shoots  r e s p e c t i v e l y , were r e p r o d u c t i v e a t f i r s t never observed  to happen w i t h Z o s t e r a  remained v e g e t a t i v e ,  at s t a t i o n s 1,  2, and  At s t a t i o n 1, r e c r u i t m e n t  than a t s t a t i o n s 2 and  was  shoots.  o f Ruppia shoots  reproductive.  p r o p o r t i o n s o f r e p r o d u c t i v e shoots season, a f t e r i t s i n i t i a l  was  in early  typically  less 2),  S t a t i o n 3 showed l a r g e r  than s t a t i o n 2 throughout the growing  t o t a l l y vegetative cohort.  ended at s t a t i o n s 1 and  s t a t i o n 3 with cohort  3,  3 i n the e a r l y growing season ( c o h o r t s 1 and  but a h i g h e r p r o p o r t i o n was  shoot r e c r u i t m e n t  and  r e c o r d , a phenomenon which  Ruppia showed g e n e r a l l y h i g h r e p r o d u c t i v e r e c r u i t m e n t cohorts.  shoot  Reproductive  2 w i t h c o h o r t 6, and  at  7.  Shoot l o s s e s No  Z o s t e r a shoots were l o s t from s t a t i o n 1 between May  June 2, whereas t h e r e were l o s s e s at both Losses  at a l l s t a t i o n s were i n i t i a l l y  c o h o r t s , r e a c h i n g a peak one  s t a t i o n s 2 and  15  and  3 ( F i g . 10  low but i n c r e a s e d w i t h  a-c)  successive  to f o u r c o h o r t s a f t e r maximum r e c r u i t m e n t .  Peak l o s s e s were i n August a t s t a t i o n 1, and d u r i n g October at s t a t i o n s 2 and  3.  Losses  balanced  recruitments  at a l l s t a t i o n s from December to  May. Few  or no Ruppia shoots were l o s t through June ( F i g . 10 d - f ) .  same synchrony seen i n Ruppia shoot was  a l s o d i s p l a y e d i n shoot  loss.  August, were at s t a t i o n s 1 and September  12.  3.  r e c r u i t m e n t between t i d a l Peak l o s s e s , r e c o r d e d A l l shoots  The  heights  in early  o f Ruppia were l o s t  by  48 Z o s t e r a shoots  l o s t u n t i l J u l y 21 (cohort 6) were p r i m a r i l y  v e g e t a t i v e ( F i g . 10).  A d d i t i o n a l vegetative losses occurred  the r e p r o d u c t i v e phase, and were g e n e r a l l y most severe rates of recruitment. successive cohorts. v e g e t a t i v e shoots  Reproductive  throughout  following increased  losses usually' increased  Ruppia showed a s i m i l a r p a t t e r n , l o s i n g  with mostly  f i r s t and then i n c r e a s i n g p r o p o r t i o n s o f r e p r o d u c t i v e  shoots.  Total  shoots Throughout the study Ruppia stands were o n l y o n e - f o u r t h  the s i z e o f Z o s t e r a stands  ( F i g . 11).  Peak shoot d e n s i t i e s o f Z o s t e r a  were twice as h i g h a t s t a t i o n 2 as a t 1, although more shoots t a i n e d a t s t a t i o n 1 d u r i n g the l a t e f a l l .  Z o s t e r a shoot  s t a t i o n 3 was g e n e r a l l y i n t e r m e d i a t e year-round. expected shift  from the a n a l y s i s o f shoot  synchronously,  were main-  density at  A l s o , as would be  r e c r u i t m e n t and l o s s , t h e r e was a  i n the t i m i n g between the t h r e e s t a t i o n s .  ended e a r l i e s t a t s t a t i o n 1.  t o one-ninth  F l o w e r i n g began and  P l a n t s a t s t a t i o n s 2 and 3 f l o w e r e d  but almost two weeks l a t e r than a t s t a t i o n 1.  Numbers o f  both v e g e t a t i v e and r e p r o d u c t i v e shoots peaked l a t e s t a t s t a t i o n 3. Ruppia showed some p a t t e r n s i n shoot h e i g h t s i m i l a r to those o f Z o s t e r a . numbers f o r Ruppia. as many shoots similar.  S t a t i o n 1 had the, lowest  At the time o f maximum shoot  shoot  d e n s i t y t h e r e were h a l f  a t s t a t i o n 1 as a t 2, but f l o w e r i n g shoot numbers were  F l o w e r i n g peaked s i m u l t a n e o u s l y  (cohort 6 ) .  d e n s i t y i n r e l a t i o n to t i d a l  at a l l s t a t i o n s on J u l y 21  F i g u r e 12 summarizes the r e l a t i v e t i m i n g and d e n s i t y o f  f l o w e r i n g shoots  at a l l stations.  49  11. a - f . intervals  Absolute  c o n t r i b u t i o n o f cohorts r e c r u i t e d at successive  ( s o l i d and broken l i n e s d i f f e r e n t i a t e odd and even numbered  cohorts f o r c l a r i t y ) ,  and t o t a l  shoot  v e g e t a t i v e and r e p r o d u c t i v e shoots Bank, May 1980 - May 1981. for clarity.  density (bold l i n e ) o f  from t h r e e s t a t i o n s a t Roberts  Z o s t e r a cohorts  11 - 20 a r e not shown  Data f o r a l l c o h o r t s are l o c a t e d i n Appendix 3.  1001  I  2  3  1—|  May  4  j  5 1  Jun  6  7  1  1  Jul  8  1  Aug  9  1 Sep  10  1  11  12  1  Oct  Nov  H  13  1  1  Dec  Jan  Cohort Number and Month of Sampling F i g . 11a.  Zostera  j a p o n i c a a t s t a t i o n 1 ( 3 . 1 7 m CD t i d a l  height).  15 16  1  1—l  Feb  17  1  Mar  18 19 2 0  1—! 1 Apr  on o  Cohort Number and Month of Sampling Fig. l i b .  Z o s t e r a j a p o n i c a a t s t a t i o n 2 (2.54  m CD).  53  Fig. l i d .  Ruppia maritima a t s t a t i o n 1 (3.17 m  CD).  Fig. l i e .  Ruppia maritima a t s t a t i o n 2 (2.54 m  CD).  54  Fig. l l f .  Ruppia m a r i t i m a at s t a t i o n 3 (2.60 m  CD).  55  F i g . 12.  Percentage o f t o t a l shoots which were f l o w e r i n g a t each o f t h r e e  stations  (  = station  1, 3.17 m,  = s t a t i o n 2, 2.54 m,  =  s t a t i o n 3, 2.60 m CD) on s u c c e s s i v e sampling dates a t Roberts Bank, 1980 - 1981.  X  57 Cohort c o n t r i b u t i o n s F o l l o w i n g i n d i v i d u a l c o h o r t s through one year r e v e a l e d t h a t veget a t i v e and r e p r o d u c t i v e shoots ( F i g . 11).  In both  o f the same cohort d i f f e r e d  Z o s t e r a and Ruppia, the t r a n s i t i o n from t h e v e g e t a t i v e  to r e p r o d u c t i v e s t a t e u s u a l l y i n c r e a s e d a shoot's Cohorts  i n longevity  life  span.  which were i n i t i a l l y the same s i z e a t d i f f e r e n t  h e i g h t s had d i f f e r e n t  impacts on t h e i r r e s p e c t i v e stands,  tidal  e.g. Z o s t e r a  i n cohort 5 made a major c o n t r i b u t i o n to r e p r o d u c t i v e shoot numbers a t s t a t i o n s 1 and 2, but was s h o r t - l i v e d a t s t a t i o n 3. cohort  5 t o numbers o f Ruppia r e p r o d u c t i v e shoots  3 than a t s t a t i o n 2. t i v e i n p u t from cohort  The c o n t r i b u t i o n o f  was h i g h e r a t s t a t i o n  S t a t i o n 1 was i n t e r m e d i a t e , r e c e i v i n g low v e g e t a 5, but a r e l a t i v e l y h i g h r e p r o d u c t i v e c o n t r i b u t i o n .  By examining the i n d i v i d u a l cohort c o n t r i b u t i o n t o t h e t o t a l p o p u l a t i o n , a deeper u n d e r s t a n d i n g can be o b t a i n e d .  o f s m a l l - s c a l e p o p u l a t i o n changes  The i n c r e a s e i n v e g e t a t i v e Z o s t e r a shoot numbers a t  s t a t i o n 1 a f t e r the d e c l i n e i n August can now be seen as a r e s u l t o f the r e t e n t i o n o f c o h o r t 8 shoots simultaneous  and t h e a d d i t i o n o f c o h o r t 9.  d e p r e s s i o n o f Ruppia v e g e t a t i v e shoots  June was c l e a r l y not the r e s u l t o f shoot but o f u n i f o r m l y low shoot  The  at a l l stations i n  l o s s , as might be  expected,  recruitment.  To a l l o w a c l e a r examination  o f the c o n t r i b u t i o n o f i n d i v i d u a l  c o h o r t s to the p o p u l a t i o n over time, F i g . 13 shows the p e r c e n t b u t i o n o f each cohort t o t h e shoots  contri-  p r e s e n t a t the time o f sampling.  In the p e r i o d between May and September ( c o h o r t s 1 - 12), when shoot numbers r a p i d l y i n c r e a s e d and f l o w e r i n g took p l a c e , t h e r e were some members o f two t o f o u r , (a mean o f three) any  g i v e n time ( F i g . 13 a - f ) .  Zostera cohorts present at  Overwintering  shoots, between October  58  Fig.  13. a - L.  Age s t r u c t u r e o f v e g e t a t i v e and r e p r o d u c t i v e  p o p u l a t i o n s as percent  c o h o r t c o n t r i b u t i o n to the t o t a l  f o r three s t a t i o n s ( s t a t i o n  population  1 = 3.17 m, 2 = 2.54 m, 3 = 2.60 m CD  t i d a l h e i g h t ) a t Roberts Bank, 1980 - 1981. c o n t a i n e d every c o h o r t .  shoot  Not a l l s t a t i o n s  Gaps between v e g e t a t i v e c o h o r t numbers  (on time a x i s ) and r e p r o d u c t i v e c o h o r t numbers shown i n the r e p r o d u c t i v e shoot  f i g u r e s r e p r e s e n t time l a g s f o r c o h o r t s t o  become r e p r o d u c t i v e .  F i g . 13a.  Vegetative  shoots  of Zostera japonica at s t a t i o n  1.  F i g . 13b.  R e p r o d u c t i v e shoots o f Z o s t e r a j a p o n i c a a t s t a t i o n  1.  o  Cohort Number and Month of Sampling F i g . 13c.  Vegetative  shoots  o f Z o s t e r a j a p o n i c a at s t a t i o n 2.  1  23 4 1—|  May  1  Jun  5 6 1  1  Jul  7 1  8  —1  Aug  9 1  10 11 1  Sep  12  1  Oct  13  1  Nov  U  1  Dec  15 16  1  Jan  1  Feb  —  1  17 18 19 20 1  Mar  1  1  1  Apr  Cohort Number and Month of Sampling F i g . 13d.  R e p r o d u c t i v e shoots o f Z o s t e r a j a p o n i c a at s t a t i o n 2.  ON  Cohort Number and Month of Sampling Fig.  13e.  Vegetative  shoots  o f Z o s t e r a j a p o n i c a a t s t a t i o n 3. a*  ON  Cohort Number and Month of Sampling Fig.  13g.  V e g e t a t i v e shoots o f Ruppia m a r i t i m a a t s t a t i o n 1.  ON  Fig.  13h.  R e p r o d u c t i v e shoots o f Ruppia m a r i t i m a a t s t a t i o n  1.  ON ON  2 -I  3  U  5  6  7 .  8  1  1  1  1  1  H  May  Jun  Jul  Aug  9  10 Sep  11 Oct  12  13 h  \  Nov  Dec  -  Jan  U  15 16 1  1  Feb  —  I  17 1  Mar  18 19 2 0 1  1  1  Apr  Cohort Number and Month of Sampling Fig.  13j.  R e p r o d u c t i v e shoots o f Ruppia m a r i t i m a at s t a t i o n 2.  ON  00  Cohort Number and Month of Sampling F i g . 13k.  V e g e t a t i v e shoots o f Ruppia m a r i t i m a a t s t a t i o n 3.  ON to  100 908M  C  70-  E  60  o  o  c cu o cu  30H  2010 10  9 Jun  May  Jul  Aug  — f -  Sep  12  11 —tOct  13  - 4 —  Nov  Dec  15 16 17  U Jan  — I — I —  Feb  - 4 -  Mar  18 19 20  —  I  —  I  1  Apr  Cohort Number and Month of Sampling Fig.  13£.  R e p r o d u c t i v e shoots o f Ruppia m a r i t i m a a t s t a t i o n 3.  o  71 and March (cohorts 10 - 14), had is  the o p p o s i t e o f what was  g e n e r a l l y an i n c r e a s e d l i f e span.  seen i n shoots t h a t never became reproduc-  t i v e i n the r a p i d l y growing summer p o p u l a t i o n s . had  a s i n g l e c o h o r t , 11 and  This  Both s t a t i o n s 2 and  10 r e s p e c t i v e l y , t h a t c l e a r l y dominated  3 the  w i n t e r shoot numbers; a t s t a t i o n 1, c o h o r t s c o n t r i b u t e d more u n i f o r m l y throughout  the w i n t e r .  When more r a p i d r e c r u i t m e n t o f Z o s t e r a  shoots  resumed i n March (cohort 15), shoots g e n e r a l l y r e t a i n e d the l o n g e v i t y seen d u r i n g the w i n t e r , although heavy m o r t a l i t y o c c u r r e d i n February and  e a r l y March, r e d u c i n g the l i f e s p a n  that period.  Ruppia stands u s u a l l y had  once, although a t a g i v e n sampling greatly  o f some cohorts p r e s e n t two  during  to f o u r c o h o r t s p r e s e n t a t  date the p r o p o r t i o n s o f c o h o r t s v a r i e d  ( F i g . 13 g-1) .  Survivorship The and  life  time.  The  span o f shoots v a r i e d w i t h s p e c i e s , t i d a l s u r v i v o r s h i p curves f o r s e l e c t e d c o h o r t s  illustrate similarities  height ( i n F i g . 14)  i n s u r v i v o r s h i p between Z o s t e r a and  Ruppia  c o h o r t s which appeared e a r l y i n the growing season (cohort 2) and marked departure of  l a t e r i n the year  (cohort 5 ) .  A l s o , the s u r v i v o r s h i p  c o h o r t s from the same t i d a l h e i g h t can be seen a t d i f f e r e n t  The most marked change was  their  times.  i n the s u r v i v o r s h i p o f Z o s t e r a c o h o r t s a t  s t a t i o n 2 from a Deevey (1947) Type I to a Type I I I between c o h o r t s 5 and  8.  Leaf l e n g t h When o b s e r v a t i o n s began, i n May,  mean l e n g t h s o f the l o n g e s t  Z o s t e r a l e a v e s were equal a t a l l s t a t i o n s ( F i g . 15).  Leaf l e n g t h s at  14. a .- £.  S u r v i v o r s h i p curves o f s e l e c t e d  s t a t i o n s .(  :  s t a t i o n 3, 2.60  = s t a t i o n 1, 3.17  m,  c o h o r t s from t h r e e  = s t a t i o n 2, 2.54m,  m CD t i d a l h e i g h t ) a t Roberts Bank, 1980  -  1981.  73  Zostera japonica  2 3 4  l—l  1  Jun  5 6 1 1  7 1  Ruppia maritima  2 3  (—l  4 1  Jun  Jul  5 6 1 1  7 1  Jul  Cohort Numberand Month of Sampling F i g . 14a.  Cohort 2.  Fig.  14b.  Cohort 2.  74  F i g . 14c.  Cohort  5.  F i g . 14d.  Cohort  5.  75  F i g . 14e.  Cohort  8.  F i g . 14f.  Cohort  12.  76  15. a, b. ( 3, 2.60  Mean l e n g t h s of l o n g e s t l e a v e s from t h r e e  = s t a t i o n 1, 3.17 m CD  m,  = s t a t i o n 2, 2.54  t i d a l h e i g h t ) a t Roberts Bank, 1980  d e v i a t i o n s a r e i n Appendix  4.  stations  m, - 1981.  =  station Standard  Leaf cn  _i  LL  •  Length o  l  (cm) ai  l  o 1  ..i  1/1  0 May  F i g . 15b.  Jun  Jul  Ruppia m a r i t i m a  Aug  79 each s t a t i o n i n c r e a s e d t o c l e a r l y d e f i n e d peaks, and then decreased t o r e l a t i v e l y constant growth i n A p r i l  and w i n t e r .  A f t e r l e a v e s resumed  l e a f l e n g t h a t s t a t i o n 1 i n c r e a s e d . r a p i d l y between May  and June, but f e l l initial  l e v e l s over f a l l  drastically i n July.  S t a t i o n s 2 and 3 had slower  i n c r e a s e s i n l e a f l e n g t h and reached peak lengths which were  c o n s i d e r a b l y g r e a t e r than a t s t a t i o n 1, i n J u l y . maintained  S t a t i o n s 2 and 3  s i m i l a r l e a f l e n g t h s between September and A p r i l which were  longer than a t s t a t i o n 1.  Average l e a f l e n g t h s were t h e same a t a l l  s t a t i o n s i n March. Leaves produced a t s t a t i o n 1 between August and February, and a t s t a t i o n s 2 and 3 from September to February, were narrower than  leaves  which i n i t i a t e d growth d u r i n g the summer ( F i g . 16). Ruppia leaves were g e n e r a l l y s h o r t e r than those o f Z o s t e r a , and mean l e n g t h s showed a c o m p a r a t i v e l y stations. 1.  Initial  uniform  p a t t e r n o f growth a t a l l  l e a f l e n g t h s measured i n May were l o n g e s t a t s t a t i o n  Peak l e a f lengths o c c u r r e d  i n August, leaves p r e s e n t  i n J u l y a t each s t a t i o n .  At l a s t  record  a t a l l s t a t i o n s were s h o r t e r than f o r J u l y ,  but were s i m i l a r to each o t h e r .  Rhizome i n t e r n o d e  length  Lengths o f the newest rhizome i n t e r n o d e s not in  significantly different  i n Z o s t e r a were  ( F i g . 17). S t a t i o n 1 showed o n l y d e c l i n e s  l e n g t h from May v a l u e s , a p a t t e r n c l e a r l y d i v e r g e n t  s t a t i o n 2.  initially  A slow i n c r e a s e i n mean i n t e r n o d e  from t h a t o f  l e n g t h was seen a t  s t a t i o n s 2 and 3; 3 peaked i n June and s t a t i o n 2 peaked i n J u l y .  At  s t a t i o n s 2 and 3 t h e r e was a slow d e c l i n e i n the l e n g t h o f rhizome grown between nodes, beginning  i n July.  Newly produced  internodes  I  DOl  a  o  L  Fig.  16 a - c.  .5 _L millimeters  L e a f c r o s s s e c t i o n s showing lacunae..  a. Z o s t e r a j a p o n i c a w i n t e r l e a f . b. Z.  F i b e r bundles  have been o m i t t e d ,  j a p o n i c a summer l e a f . c. Ruppia  maritima  00  o  17. a, b. stations  Mean l e n g t h s o f newest rhizome i n t e r n o d e s from t h r e e (  = s t a t i o n 1, 3.17  = s t a t i o n 3, 2.60 1981.  Standard  m,  = s t a t i o n 2, 2.54  m CD t i d a l h e i g h t ) at Roberts  d e v i a t i o n s are i n Appendix  4.  m,  Bank,  1980  Rhizome Internode Length (cm)  84 were equal i n l e n g t h a t a l l s t a t i o n s i n September. U n i f o r m l y s h o r t rhizome segments were produced a t each s t a t i o n d u r i n g the  fall.  These s h o r t rhizome segments were s l i g h t l y s m a l l e r i n diameter  than summer rhizomes, 1 - 2 mm i n the summer and 1 mm i n the w i n t e r . upper s u r f a c e o f the rhizome e l o n g a t e d i n the f a l l ,  The  r e o r i e n t i n g the  m e r i s t e m a t i c t i p o f t h e rhizome from i t s h o r i z o n t a l p o s i t i o n i n t h e summer to a v e r t i c a l l y downwards d i r e c t i o n a f t e r a p p r o x i m a t e l y s i x i n t e r nodes. of the  Rhizome a p i c e s c o n t i n u e d growing downwards a t a slow r a t e much  the w i n t e r .  T y p i c a l l y , l e s s than 2 cm o f rhizome was added  w i n t e r , b u r y i n g t h e rhizome apex below  during  i t s summer l e v e l o f 5 cm.  Rhizome i n t e r n o d e l e n g t h s showed a marked i n c r e a s e i n March as they resumed h o r i z o n t a l  growth.  Ruppia rhizome i n t e r n o d e s a t each s t a t i o n i n c r e a s e d i n l e n g t h u n i f o r m l y from May t o a peak i n J u l y .  The l e n g t h o f a l l  i n t e r n o d e s a t a l l s t a t i o n s d e c l i n e d to n e a r l y i d e n t i c a l  newly  produced  lengths i n  August.  Genet  growth Schematic r e p r e s e n t a t i o n s o f Z o s t e r a and Ruppia genets over an  annual c y c l e a r e p r e s e n t e d i n F i g u r e 18.  In Z o s t e r a ,  rhizomes emerge from s e e d l i n g s i n e a r l y May. supports a ramet. the to  first  horizontal  Each node u s u a l l y  S e v e r a l s h o r t nodes were t y p i c a l l y produced b e f o r e  rhizome began b r a n c h i n g i n l a t e May.  i d e n t i f y by l a t e June, even w i t h c a r e f u l  Genets were d i f f i c u l t  e x c a v a t i o n , because o f  rhizome f r a g m e n t a t i o n . In  e a r l y J u l y , h o r i z o n t a l rhizomes branched r e g u l a r l y , and  v e r t i c a l b r a n c h i n g o f f l o w e r i n g shoots had begun.  Throughout  July,  85  Fig.  18.  Schematic  drawing o f h o r i z o n t a l and v e r t i c a l b r a n c h i n g o f  v e g e t a t i v e and r e p r o d u c t i v e shoots o f Z o s t e r a  j a p o n i c a and  maritima and e s t i m a t e s o f ramets per genet over time. rhizome,  = decayed  reproductive  shoot =  rhizome, = vertical  O  = v e g e t a t i v e shoot,  branching.  Ruppia = live  • =  86  Zostera japonica  April  E s i i mated ramets per genet  •  1  5-10  November  March  o  1  1-3  87  88 r a p i d h o r i z o n t a l branching continued. brittle,  e s p e c i a l l y a t the nodes.  O l d e r segments o f rhizomes were  N e a r l y a l l shoots except the most  r e c e n t l y produced were v e r t i c a l l y b r a n c h i n g and f l o w e r i n g i n August. Much o f the o l d e r rhizome was  s e v e r e d and/or d e c a y i n g .  An e x c a v a t i o n i n  September r e v e a l e d t h a t genets had fragmented i n t o u n i t s o f f i v e t o t e n ramets. The decomposition and e r o s i o n o f Z o s t e r a rhizomes i n c r e a s e d through October.  By November, o n l y s m a l l segments o f rhizomes c o u l d be found.  A few longer i n t e r n o d e s u s u a l l y remained a t t a c h e d to a downward hooked apex through February.  The resumption o f r a p i d rhizome growth  i n March  was u s u a l l y i n i t i a t e d from more than one l o c a t i o n on an o v e r w i n t e r i n g rhizome. H o r i z o n t a l rhizomes were i n i t i a t e d By May,  from Ruppia s e e d l i n g s i n A p r i l .  h o r i z o n t a l rhizomes were b r a n c h i n g , each node h a v i n g a ramet.  V e r t i c a l b r a n c h i n g and f l o w e r i n g o f n o n - t e r m i n a l shoots began i n June. In J u l y , h o r i z o n t a l b r a n c h i n g slowed but v e r t i c a l p r o l i f e r a t i o n  con-  tinued.  rhizome  was  Genets were u s u a l l y r e c o g n i z a b l e because much o f t h e i r  o n l y p a r t i a l l y b u r i e d by  sediment.  During l a t e J u l y and e a r l y August, Ruppia rhizomes became b r i t t l e and l e a v e s became h e a v i l y c o v e r e d w i t h e p i p h y t e s and r a p i d l y  decayed.  Large p o r t i o n s o f genets were uprooted and c a r r i e d o f f by the t i d e . Some s e c u r e l y anchored shoots or groups o f shoots remained through much o f August w h i l e t h e i r v e r t i c a l branches and l e a v e s decayed.  Flower and i n f l o r e s c e n c e  densities  The mean numbers o f Z o s t e r a o v a r i e s per i n f l o r e s c e n c e showed no s i g n i f i c a n t d i f f e r e n c e s throughout the f l o w e r i n g p e r i o d a t a g i v e n  tidal  height  ( F i g . 19).  S t a t i o n 1 had c o n s i s t e n t l y lower numbers o f flowers  than s t a t i o n s 2 o r 3, which were e q u a l .  There were no s i g n i f i c a n t  d i f f e r e n c e s between s t a t i o n s i n the number o f o v a r i e s p e r i n f l o r e s c e n c e in  Ruppia f o r any sampling date and over 75% o f a l l i n f l o r e s c e n c e s  produced 8 o v a r i e s . The  number o f i n f l o r e s c e n c e s per f l o w e r i n g  two d i s t i n c t p a t t e r n s  ( F i g . 20).  record  through a t f i r s t  i n August.  for  Stations  continuously  until  i t s last  2 and 3 shadowed one another  a shallow and then a r a p i d i n c r e a s e  i n f l o r e s c e n c e s per f l o w e r i n g  showed  Numbers a t s t a t i o n 1 were a t f i r s t  h i g h e r than a t s t a t i o n s 2 and 3, then f e l l flowering  shoot i n Z o s t e r a  i n number o f  shoot to s i m i l a r peaks i n August; the peaks  s t a t i o n s 2 and 3 were not s i g n i f i c a n t l y d i f f e r e n t .  At l a s t  record  i n October, i n f l o r e s c e n c e number a t s t a t i o n s 2 and 3 had f a l l e n t o June l e v e l s . Ruppia showed a c o n s t a n t i n c r e a s e escences per f l o w e r i n g initial  i n the average number o f i n f l o r -  shoot a t each s t a t i o n .  D i f f e r e n c e s between  v a l u e s were s m a l l , but the mean v a l u e f o r s t a t i o n : 1 i n August  was s i g n i f i c a n t l y lower than f o r s t a t i o n 2; s t a t i o n s 2 and 3 were not significantly different.  Ovary f a t e s The  average number o f o v a r i e s per i n f l o r e s c e n c e and the p e r c e n t o f  those o v a r i e s  that f e l l  i n t o each o f t h e ovary f a t e s , by age c l a s s , a r e  shown i n T a b l e IV. Aborted o v a r i e s ,  f a t e 1, remained c o n s i s t e n t  s i g n i f i c a n t changes between s t a t i o n s . however, showed s i g n i f i c a n t i n c r e a s e s  i n Zostera  with no  Ruppia a t s t a t i o n s 1 and 3, of abortion  i n the second age  Zostera japonica  Ruppia maritima  2H  ; Jun  Fig.  Jul  19. (  Aug  Sep  OJ Oct  Jun  Jul  Mean number o f o v a r i e s (female f l o w e r s ) p e r i n f l o r e s c e n c e a t t h r e e = s t a t i o n 1, 3.17 m,  = s t a t i o n 2, 2.54 m,  t i d a l h e i g h t ) a t Roberts Bank, 1980.  Aug  stations  = s t a t i o n 3, 2.60 m CD  Standard d e v i a t i o n s a r e i n Appendix 4.  F i g . 20.  Mean number o f i n f l o r e s c e n c e s p e r f l o w e r i n g  s t a t i o n 1, 3.17 m, a t Roberts Bank, 1980.  = s t a t i o n 2, 2.54 m, Standard d e v i a t i o n s  shoot at three  stations  (  =  = s t a t i o n 3, 2.60 m CD t i d a l h e i g h t ) a r e i n Appendix 4.  T a b l e IV.  Mean numbers o f o v a r i e s per i n f l o r e s c e n c e and p e r c e n t a g e s i n each o v a r y f a t e :  (1), o v a r y p r e d a t i o n japonica  ( 2 ) , i n c o m p l e t e development  (Z) and Ruppia m a r i t i m a  i n f l o r e s c e n c e s i n age c l a s s s e l e c t e d on J u l y  10  Class  1 were s e l e c t e d on June  m)  No.  Zl  4.3 23.8 (1.0)(28.9)  Z2  (Zostera) .  1  2  25  Standard d e v i a t i o n s a r e i n p a r e n t h e s e s . m)  S t a t i o n 3 (2.60  3  m)  % i n Fate Class: <  No,  0.0 79.5 (0.0)(14.4)  6.1 18.8 (1.3) (17.4)  3.8 3.6 73.8 (9.9)(10.1)(15.4)  4.2 35.6 0.0 49.7 14.7 (1.3M39.1) (0.0) (47.2) (28.7)  6.2 27.2 9.2 13.2 50.4 (1.1)(18.8)(15.1)(31.3)(32.5)  5.7 26.4 (1.0)(19.4)  0.0 9.2 64.4 (0.0)(22.8)(20.5)  Rl  7.4 31.9 (1.2)(22.6)  2.6 (7.3)  7.9 22.7 12.9 (0.5)(23.7)(23.8)  0.0 64.4 (0.0)(32.0)  7.9 29.0 11.4 (0.5)(27.2)(19.2)  R2  6.5 62.8 (1.5)(29.0)  1.9 14.6 20.7 (5.4)(18.0)(28.2)  7.4 36.8 (1.0X27.8)  3.5 57.0 (8.5) (28.9)  7.6 55.2 (0.8X17.0)  0.0 65.5 (0.0X23.6)  6.2 15.8 4.7 (1.2)(14.7)(10.2)  F o r each s p e c i e s ,  25 i n f l o r e s c e n c e s i n age c l a s s 2 were  % i n Fate C l a s s : No.  0.7 16.0 59.5 (3.5)(37.4)(37.4)  1980  11, and  S t a t i o n 2 (2.54  % i n Fate C l a s s :  Age  (4); f o r two age c l a s s e s o f Z o s t e r a  (R) from t h r e e t i d a l h e i g h t s a t Roberts" Bank.  (Ruppia) and J u l y 30,  S t a t i o n 1 (3.17  ( 3 ) , mature seed  ovary abortion  2.7 (5.3)  0.0 59.6 (0.0X31.7)  3.4 15.6 (6.5X18.5)  25.8 (9.3)  to  93 c l a s s t o v a l u e s double those i n the f i r s t  age c l a s s .  Loss o f Z o s t e r a  o v a r i e s by p r e d a t i o n , f a t e 2, was r e c o g n i z e d when p o r t i o n s o f the ovary were m i s s i n g ; p r e d a t i o n remained to  low a t a l l s t a t i o n s except f o r i t s r i s e  n e a r l y 10 p e r c e n t o f age c l a s s 2 a t s t a t i o n 2.  P r e d a t i o n on Ruppia  o v a r i e s was t y p i c a l l y h i g h e r than on Z o s t e r a and showed no s i g n i f i c a n t changes over time. Numbers o f d e v e l o p i n g o v a r i e s l o s t b e f o r e m a t u r a t i o n , f a t e 3, were s i g n i f i c a n t l y h i g h e r i n Z o s t e r a a t s t a t i o n 1 than a t s t a t i o n 2 f o r the first  age c l a s s .  No Ruppia o v a r i e s i n age c l a s s 1 were l o s t because o f  premature i n f l o r e s c e n c e l o s s . i c a n t i n c r e a s e s to around  S t a t i o n s 1 and 3, however, showed  signif-  15% f o r f a t e 3 i n the second age c l a s s .  The percentage o f t h e Z o s t e r a o v a r i e s i n age c l a s s 1 r e a c h i n g m a t u r i t y , f a t e 4, was lowest a t s t a t i o n 1. still  lower f o r the second age c l a s s .  The m a t u r a t i o n r a t e  fell  S t a t i o n 2 a l s o showed a s i g n i f -  i c a n t drop i n seed m a t u r a t i o n between age c l a s s e s . Ruppia ovary success was about first  age c l a s s .  equal between s t a t i o n s w i t h i n the  Seed m a t u r a t i o n a t s t a t i o n s 1 and 3 dropped  signif-  i c a n t l y i n the second age c l a s s .  Seed p r o d u c t i o n E s t i m a t e s o f seed p r o d u c t i o n a t each t i d a l h e i g h t s t a t i o n are p r e s e n t e d i n T a b l e V.  Z o s t e r a seed p r o d u c t i o n a t s t a t i o n 1 was c o n s i d e r -  a b l y lower than a t 3, which was i n t u r n lower than a t s t a t i o n 2. s t a t i o n 1, most o f the seeds were produced  d u r i n g the f i r s t  At  age c l a s s ;  the second age c l a s s y i e l d e d more seeds a t s t a t i o n s 2 and 3. Ruppia seed p r o d u c t i o n was lowest a t s t a t i o n 1 and h i g h e s t a t s t a t i o n 2.  There were e s s n e t i a l l y no d i f f e r e n c e s i n the seed p r o d u c t i o n  94  Table V.  Estimated  Ruppia maritima  seed p r o d u c t i o n per 0.1 m  o f Z o s t e r a j a p o n i c a and  a t Roberts Bank, showing a b s o l u t e number and p e r c e n t  of t o t a l a t each s t a t i o n ( i n parentheses) by age c l a s s at  three  t i d a l heights.  Station 1 Species  Zostera japonica  ;e C l a s s  maritima  m CD)  (2.54  m CD)  Station 3 (2.60  m CD)  1  447 (95)  507 (15)  206 (09)  2  26 (05)  2899 (85)  1967 (91)  3406  2173  Total  Ruppia  (3.17  Station 2  473  1  81 (48)  169 (34)  127 (40)  2  87 (52)  322 (66)  188 (60)  491  315  Total  168  95 between age  c l a s s e s a t s t a t i o n 1.  Both s t a t i o n s 2 and  3 were more  s u c c e s s f u l , i n terms o f seed p r o d u c t i o n , d u r i n g the second age  class.  Discussion Shoot r e c r u i t m e n t and  death  In c l o n a l p l a n t s , a s i n g l e genotype (genet  - individual  arising  from a seed) d i s p l a y s i t s f i t n e s s as a more o r l e s s fragmented phenotype  (Noble  et a l . 1979).  These fragments make a p o p u l a t i o n o f d i s c r e t e  modular shoots, a l s o c a l l e d ramets - v e g e t a t i v e l y produced u n i t s (White 1979).  Ruppia and  Z o s t e r a rhizomes become b r i t t l e w i t h age  making i t almost i m p o s s i b l e to i d e n t i f y i n d i v i d u a l Harper and White (1974) s t a t e t h a t the shoot o f p o p u l a t i o n f l u x i n rhizomatous p l a n t s . r e c r u i t m e n t o f new  and  break,  genets. i s the e f f e c t i v e u n i t  Their reasoning  i s that  genets i s o f t e n r a r e among c l o n a l p l a n t s , and  environment i n f l u e n c e s p r i m a r i l y the r e c r u i t m e n t and  the  death r a t e s o f  s u b u n i t s once i n d i v i d u a l s are e s t a b l i s h e d ; t h i s i s a l s o t r u e f o r Z o s t e r a and  Ruppia. Recruitment and death r a t e s o f shoots  a population's behavior;  t o g e t h e r w i t h immigration  i n d i v i d u a l s they d e s c r i b e p o p u l a t i o n f l u x . p a t t e r n s o f shoot and  are the main i n d i c a t o r s o f and  emigration  T i d a l height a f f e c t e d  f l u x i n Z o s t e r a more than i n Ruppia.  Shoot l o s s e s  gains remained synchronous i n Ruppia a t a l l t h r e e s t a t i o n s , whereas  Z o s t e r a at s t a t i o n 1 r e t a i n e d e a r l y shoots  l o n g e r and  declined in  numbers e a r l i e r than a t o t h e r s t a t i o n s ; t h i s b e h a v i o r may due  of  to the g r e a t e r d e s i c c a t i o n t h a t p l a n t s a t s t a t i o n 1 Researchers  s t u d y i n g monocotyledonous (Lamp 1952,  Langer et a l . 1964,  Robson 1968,  Nobele et a l . 1979)  have been experienced.  Langer  and  1956,  dicotyledonous  96 plants  (Sarukhan and Harper  1973)  have found the g r e a t e s t r i s k o f death  o f ramets c o i n c i d e d w i t h the g r e a t e s t r e c r u i t m e n t r a t e .  Noble et a l .  (1979) a t t r i b u t e d the synchrony i n r e c r u i t m e n t and death to e i t h e r the h i g h e r d e n s i t y due to new a l l o w i n g more b i r t h s .  b i r t h s o r reduced d e n s i t i e s caused by  deaths  My d a t a i n d i c a t e t h a t severe shoot l o s s e s  may  f o l l o w l a r g e shoot r e c r u i t m e n t s , s u g g e s t i n g a density-dependent m o r t a l i t y as found by Noble et a l .  However, because  time l a g s are e v i d e n t  between r e c r u i t m e n t s and l o s s e s e s p e c i a l l y a t the s t a t i o n w i t h the densest p o p u l a t i o n the m o r t a l i t y i s l i k e l y more c l o s e l y t i e d with growth phases o f the shoots cues such as water  ( v e g e t a t i v e o r r e p r o d u c t i v e ) and  temperature and d e s i c c a t i o n  r e f e r e n c e to Ruppia) than a b s o l u t e shoot  ecological  (see Verhoeven  1979 i n  density.  A n t o n o v i c s (1972), working w i t h Anthoxanthum odoratum L. found as I have w i t h Z o s t e r a and Ruppia, a d i f f e r e n t i a l death r a t e between veget a t i v e and r e p r o d u c t i v e s h o o t s .  T h i s phenomenon may  represent a  p r e f e r e n t i a l p a r t i t i o n i n g o f r e s o u r c e s to f l o w e r i n g i n d i v i d u a l s reduces the s u r v i v o r s h i p o f n o n - f l o w e r i n g s h o o t s .  that  Support f o r t h i s 14  h y p o t h e s i s comes from H a r r i s o n (1978) who  found t h a t when  C  was  t r a n s l o c a t e d between shoots on the same rhizome o f Z. americana den Hartog .(= Z. j a p o n i c a ) , f l o w e r i n g and young v e g e t a t i v e shoots were the major s i n k s , and t h a t o l d e r v e g e t a t i v e shoots export two  to s i x times more  14 newly-fixed  C than f l o w e r i n g s h o o t s .  The degree o f e p i p h y t i s m may  have a f f e c t e d the death r a t e o f  shoots.  Ruppia remained r e l a t i v e l y e p i p h y t e - f r e e u n t i l  ment was  complete and l e a f t i p s eroded; Z o s t e r a shoots  i n c r e a s i n g amounts o f e p i p h y t e s w i t h age u n t i l shoot l o s s may  fruit  develop-  accumulated  the shoots d i e d .  Thus  have reduced the r e s p i r a t o r y burden o f e p i p h y t e - l a d e n  97 l e a v e s to the remaining The  plant.  t o t a l d e n s i t y o f shoots showed mixed responses to t i d a l  height;  i n some i n s t a n c e s f l u x e s o f v e g e t a t i v e and r e p r o d u c t i v e shoots appeared to behave independently.  Despite  number between Z o s t e r a and o f each s p e c i e s was  the g r e a t d i f f e r e n c e s i n t o t a l  Ruppia, the r e d u c t i o n i n v e g e t a t i v e  p r o p o r t i o n a l to the g r e a t e r d e s i c c a t i o n at  shoot  shoots station  1 as compared to s t a t i o n 2 ( i . e . , 8 to 10% more exposure to the a i r d u r i n g the day,  see S e c t i o n 1 ) .  showed a d i f f e r e n t p a t t e r n . v e g e t a t i v e shoots,  and  Reproductive  shoot numbers, however,  Z o s t e r a r e f l e c t e d the p a t t e r n seen i n the  Ruppia remained r e l a t i v e l y constant  i n density  at a l l t h r e e s t a t i o n s . Recruitment and death r a t e s combined to y i e l d c h a r a c t e r i s t i c s t r u c t u r e s at each t i d a l h e i g h t  ( F i g . 13).  Noble et a l . (1979) found  death r a t e s i n ramets , o f Carex a r e n a r i a L. to be " r e l a t i v e l y o f i t s age  and o f i t s season o f b i r t h . "  age  T h i s i s o b v i o u s l y not  independent the  s i t u a t i o n i n e i t h e r Z. j a p o n i c a or R. maritima a t the l o c a t i o n s s t u d i e d , presumably because o f the more or l e s s u n p r e d i c t a b l e c o n d i t i o n s i n the i n t e r t i d a l i n temperature and  environmental  ( H a r r i s o n 0.979) s t a t e s t h a t f l u c t u a t i o n s  s a l i n i t y can be l a r g e and u n p r e d i c t a b l e d u r i n g  the  long d a i l y exposures to the a i r ) , whereas the dunes where C. a r e n a r i a grow are environmentally, s t a b l e . The v a r i a t i o n i n Z o s t e r a and i l l u s t r a t e how  Ruppia cohort  shoot l i f e spans change with  S u r v i v o r s h i p curves  s u r v i v o r s h i p curves  environmental c o n d i t i o n s .  tend to change when d e s i c c a t i o n i n c r e a s e s a t a  g i v e n s t a t i o n d u r i n g the growing season (e.g. Deevey Types I to II or I I I at s t a t i o n 2).  The p a t t e r n i s r e v e r s e d  the l o n g e s t and most f r e q u e n t  i n winter;  s t a t i o n 1 had  exposure to low a i r temperatures, and  the  longest  l i v e d shoots.  the w i n t e r may  The  shoot l o n g e v i t y a t s t a t i o n 1 i n  have allowed growth to resume as r a p i d l y as  when s u i t a b l e c o n d i t i o n s Survivorship  steady l o g r e d u c t i o n s species-specific).  by Harper (1967) from d a t a  of established plants  (Tamm 1948,  1956,  Sagar 1959,  A n t o n o v i c s 1972)  i n numbers over time (although  Williams  showed  the r a t e may  T h i s l e d Harper to suggest t h a t , i n the  throughout the l i f e o f the  on  s t u d i e d by a number o f  o f d r a s t i c environmental change, the r i s k o f m o r t a l i t y may constant  possible  returned.  curves c o n s t r u c t e d  natural populations researchers  increased  be  absence be  a  plant.  (1970), i n a study o f ramets o f Danthonia  caespitosa  Gaudich. i n v a r i o u s h a b i t a t s found t h a t the s u r v i v o r s h i p o f  populations  may  described  approximate a l l t h r e e main types o f s u r v i v o r s h i p curves  by Deevey (1947).  Williams  expanded on the i d e a s o f Harper (1967)  suggested t h a t "steady m o r t a l i t y i n p o p u l a t i o n s mental regime t h a t i s c o n s i s t e n t l y f a v o u r a b l e , other  words, an environment which i s s t a b l e .  than the p r e s e n t Williams My  1968,  one,  r e f l e c t s an  and  environ-  or u n f a v o u r a b l e " or i n Several  a l s o support t h i s h y p o t h e s i s  studies,  (e.g. Watt  other 1960,  Noble 1979).  r e s u l t s demonstrate t h a t the amount o f exposure to the a i r and  the p h y s i o l o g i c a l s t a t e o f a mature shoot w i n t e r quiescence) are f e a t u r e s f a c t that several cohorts  t h a t i n f l u e n c e shoot s u r v i v o r s h i p .  of various  s i t u a t i o n i n which a s i n g l e genet may physiological  ( r a p i d growth, f l o w e r i n g ,  ages are a l i v e s i m u l t a n e o u s l y , have shoots i n d i f f e r e n t  s t a t e s or phases, underscores the need f o r deomgraphic  s t u d i e s to understand the dynamics o f seagrass  populations.  or The a  99 From these a n a l y s e s o f v e g e t a t i v e p o p u l a t i o n s , i t i s e v i d e n t t h a t Z. j a p o n i c a and R. m a r i t i m a employ g e n e r a l l y t h e same l i f e  history  s t r a t e g i e s ; both p l a n t s would be c o n s i d e r e d " r " s e l e c t e d s p e c i e s ( G a d g i l and S o l b r i g 1972, H a r r i s o n 1979).  Both s p e c i e s behave as annuals o r  s h o r t - l i v e d p e r e n n i a l s h a v i n g i n d e t e r m i n a t e growth systems.  (Ruppia  f l o w e r e d year-round i n the l a b when m a i n t a i n e d a t a c o n s t a n t 10°C.) The observed d i f f e r e n c e s i n the f i e l d may be e x p l a i n e d from two approaches. city  First,  (as i n Baker's  s e l e c t i o n has a c t e d t o m a i n t a i n l i f e c y c l e (1965) a l l - p u r p o s e genotype)  to d i f f e r e n t  and s e c o n d l y , p l a n t s p e r c e i v e o r respond t o d e s i c c a t i o n  plastidegrees;  differently.  Ruppia s p e c i e s p r i m a r i l y i n h a b i t i n l a n d permanent o r temporary  waters  which have marked environmental f l u c t u a t i o n s from season t o season (Verhoeven 1979).  The r e - o c c u r r e n c e o f d i s t i n c t p e r i o d i c  environmental  hazards which do not p e r m i t the s u r v i v a l o f l o n g - l i v e d o r s l o w l y reproducing adults w i l l  s e l e c t i n f a v o r o f a s h o r t seed-to-seed  life  c y c l e , as has o c c u r r e d i n many annuals o f the d e s e r t s and c u l t i v a t e d habitats  (Harper and White 1974, A n t o n o v i c s  1976).  The v e r y s h o r t time r e q u i r e d f o r Ruppia t o complete at  its life  cycle  Roberts Bank, as compared to Z o s t e r a , i s due t o s e l e c t i o n p r e s s u r e s  on t h i s s p e c i e s when i t i n h a b i t e d p r e d i c t a b l e temporal h a b i t a t s Both Ruppia and Z o s t e r a have t h e p l a s t i c i t y t o e x p l o i t which,  i f t h e season o r s p e c i f i c  q u i c k l y proceed. genial  inland.  environments i n  l o c a t i o n i s u n f a v o r a b l e , f l o w e r i n g can  On the o t h e r hand, i f the environment  remains  con-  (as observed i n the l a b o r a t o r y ) , growth and f l o w e r i n g can  c o n t i n u e , although Ruppia's performance because o f heavy e p i p h y t e l o a d s .  rapidly declines,  possibly  100 D i f f e r e n c e s i n the way Z o s t e r a and Ruppia respond t o the environment can be a t t r i b u t e d t o t h e i r morphologies.  Ruppia g e n e r a l l y grows p o o r l y  i n the c o n t i n u a l l y f l u c t u a t i n g water l e v e l s and t u r b u l e n c e o f the i n t e r tidal.  Ruppia l e a v e s a r e t h i n  c u t i c l e o f Z. j a p o n i c a .  (see F i g . 16) and l a c k t h e w e l l - d e v e l o p e d  These f e a t u r e s i n c r e a s e t h e s e v e r i t y o f  d e s i c c a t i o n d u r i n g p e r i o d s o f exposure. a r e b r i t t l e and may not w i t h s t a n d  The u p r i g h t stems o f Ruppia  the t u r b u l e n c e o f the i n t e r t i d a l as  w e l l as the f l e x i b l e , f i b e r - s u p p o r t e d l e a v e s o f Z o s t e r a .  Ruppia i s  also a shallowly rooted species. In t h i s d i s c u s s i o n , r e l a t i o n s h i p s have been drawn between  shoot  f l u x and the r e s u l t a n t p o p u l a t i o n i n terms o f a b s o l u t e number, age s t r u c t u r e and s u r v i v o r s h i p ; the growth phases o f p l a n t s ; and the environment as a l t e r e d by t i d a l p a r a l l e l s have been observed t h e i r shoot  dynamics.  exposure.  Many d i f f e r e n c e s and c l o s e  between Z o s t e r a and Ruppia  concerning  In the next d i s c u s s i o n comparisons a r e c o n t i n u e d  between the s p e c i e s a t t h e t h r e e d i f f e r e n t t i d a l h e i g h t s by examining d i f f e r e n c e s i n the components o f the shoots  (e.g., l e a v e s , rhizomes and  flowers).  Leaf and rhizome i n t e r n o d e  lengths  S i t e - s p e c i f i c comparisons o f l e a f l e n g t h s and rhizome  internode  lengths i n d i c a t e morphogenic responses o f Z o s t e r a and Ruppia t o e n v i r o n mental d i f f e r e n c e s and a l s o r e f l e c t a s p e c t s o f a p l a n t ' s growth phase. The  appearance o f t h i n l e a v e s , such as was observed  corresponded  d i r e c t l y t o the onset o f quiescence  T i d a l h e i g h t d i c t a t e d when quiescence  would o c c u r  by A r a s a k i  (1950b),  i n rhizome growth. ( F i g . 17).  101 F l u c t u a t i o n s i n winter  l e a f l e n g t h s a t a l l s t a t i o n s may  to shoot-removal by storms, e.g. i s not known why  a t s t a t i o n s 1 and  s t a t i o n 3 d i d not  be r e l a t e d  2 i n February.  It  show a s i m i l a r decrease i n February;  perhaps i t s d i s t a n c e from shore spared i t from the t u r b u l e n c e  encountered  c l o s e r to shore. V a r i a t i o n i n l e a f dimensions o f Z o s t e r a j a p o n i c a with f a c t o r s was  recognized  t i o n s , t h e r e were two  by M i k i  (1933).  with and  l e a v e s 4 - 6 cm  At the time o f h i s i n v e s t i g a -  species of Z o s t e r e l l a reported  Roth (Z. j a p o n i c a , den Hartog 1970)  and  Z.  b r a c k i s h waters and had  from Japan, Z. nana  japonica.  l o n g , grew i n shallow  what M i k i c o n s i d e r e d  environmental  Z o s t e r a nana,  areas along  the  seashore,  a form o f Z. nana, Z. j a p o n i c a , grew o n l y i n narrower l e a v e s , 50  - 65 cm  long.  Differences  i n l e a f l e n g t h o f t h i s magnitude are a l s o observed i n Z_. j a p o n i c a i n North America.  Miki  (1933) a l s o found d i f f e r e n c e s i n l e a f width,  sheath l e n g t h , rhizome t h i c k n e s s , and j a p o n i c a on the open coast and Phenotypic p l a s t i c i t y ,  internode  l e n g t h between  e s p e c i a l l y of l e a f characters, Phillips  w r i g h t i i Aschers) to be r e l a t e d to amount o f t i d a l  and  sediment depth  Water depth  have a l s o been c o r r e -  (1978) s t u d i e d the v a r i a t i o n o f f i v e seagrass  He  (= H a l o d u l e  testudinum.  each c o l l e c t e d from s e v e r a l l o c a t i o n s and conditions.  and  inundation.  conditions.  (Zieman 1974)  l a t e d with changes i n l e a f l e n g t h o f T. McMillan  recog-  (1967) found l e a v e s o f T h a l a s s i a testudinum Bank  ex Kb'nig to be s h o r t e r under h y p e r s a l i n e (Straw 1961)  is a  (1960) found l e a f  rhizome dimensions o f D i p l a n t h e r a w r i g h t i i du P e t i t - t h o u a r s  and Mosely  Z.  in estuaries.  n i z e d phenomenon i n many s e a g r a s s e s .  McMillan  leaf  species,  grown under c o n t r o l l e d  found t h a t seagrass l e a f widths v a r i e d w i t h  their  102 immediate environmental  surroundings,  and  t h a t the degree o f p l a s t i c i t y  c o u l d v a r y g e o g r a p h i c a l l y , depending on the genotype. I t i s not known whether the d i f f e r e n c e s M i k i (1933) observed the r e s u l t o f l o c a l g e n o t y p i c  were  d i f f e r e n c e s o r whether v a r i a t i o n s seen i n  North American p o p u l a t i o n s o f Z_. j a p o n i c a are e c o t y p i c , r e f l e c t i n g h i g h degree o f phenotypic  p l a s t i c i t y e x h i b i t e d by t h i s p l a n t .  the  Phillips  (1972) found through r e c i p r o c a l t r a n s p l a n t s t h a t Z. marina e x h i b i t e d -  phenotypic  plasticity  ( i n terms o f l e a f length) a c r o s s t i d a l  marked as t h a t which I observed  zones as  i n Z. j a p o n i c a a t Roberts Bank.  American p o p u l a t i o n s o f Z. j a p o n i c a may  North  have d i v e r g e d from t h e i r  parentage i n the warmer waters o f Japan i n a s i m i l a r manner to the d i v e r gence d e s c r i b e d by M c M i l l a n  (1978).  Ruppia l e a v e s showed the same g e n e r a l response i n l e n g t h to  the  i n c r e a s e d exposure a t s t a t i o n 1 as d i d Z o s t e r a , i . e . an e a r l y b u r s t o f growth and  lower maximum, but the magnitude o f the d i f f e r e n c e was  l e s s i n Ruppia.  L a b o r a t o r y and  f i e l d o b s e r v a t i o n s and  herbarium  c o n f i r m t h a t Ruppia can e x h i b i t g r e a t v a r i a t i o n i n l e a f Leaves are arranged  h i e r a r c h i c a l l y on shoots  much records  lengths.  o f both s p e c i e s .  m a j o r i t y o f Z o s t e r a l e a v e s were u s u a l l y w i t h i n c e n t i m e t e r s  of  The the  l e n g t h o f the dominant l e a f , whereas the l o n g e s t p a i r o f Ruppia l e a v e s was  u s u a l l y about twice as l o n g as the remaining  leaves.  Thus, mean  maximum l e a f l e n g t h s g i v e a more a c c u r a t e r e p r e s e n t a t i o n o f Z o s t e r a than Ruppia l e a f l e n g t h s .  A more d e t a i l e d study o f Ruppia l e a v e s  r e v e a l more marked responses to t i d a l h e i g h t than those r e p o r t e d Z o s t e r a and corresponded T h i s suggests  may here.  Ruppia rhizome i n t e r n o d e l e n g t h s showed p a t t e r n s t h a t  to those o f t h e i r l e a f l e n g t h s at d i f f e r e n t t i d a l  heights.  a p h a s i c development o f p l a n t growth, the t i m i n g o f which  103 i s i n p a r t r e l a t e d to t i d a l  exposure.  P a t t e r n s o f shoot r e c r u i t m e n t ,  r e t e n t i o n , and l o s s f u r t h e r support such an i d e a (see F i g . 11). During the e a r l y p a r t o f the growing season l o n g i n t e r n o d e s were produced as each Z o s t e r a genet expanded Later, during lateral  through ramet  production.  . v e r t i c a l b r a n c h i n g , f l o w e r i n g , and seed development,  expansion was de-emphasized  and i n t e r n o d e l e n g t h d e c r e a s e d .  Ruppia rhizome i n t e r n o d e l e n g t h s , however, peaked a t each s t a t i o n the same time as l e a f l e n g t h s and f l o w e r i n g shoot numbers ( F i g s . 15 and 17). These r e s u l t s support o b s e r v a t i o n s made on shoot f l u c t u a t i o n s i . e . t h a t the growth o f Ruppia e x h i b i t s a p h a s i c development little  ( F i g . 11) which has  plasticity.  Verhoeven  (1979) p l o t t e d the t o t a l  ( h o r i z o n t a l and v e r t i c a l )  l e n g t h o f stems o f t h r e e Ruppia s p e c i e s , i n c l u d i n g R.. m a r i t i m a , and found e x p o n e n t i a l growth i n each c a s e .  S i m i l a r c u r v e s would be o b t a i n e d  by p l o t t i n g the t o t a l  l e n g t h o f a stem i n a genet o f Z. j a p o n i c a because  of their s i m i l a r i t i e s  i n b r a n c h i n g and growth  form.  The type o f s u b s t r a t e on which Z o s t e r a and Ruppia grow may  dictate  a s p e c t s o f t h e i r rhizome growth.  Z o s t e r a j a p o n i c a rhizome  observed i n areas o f g r a v e l l y mud  were s u b s t a n t i a l l y s h o r t e r than those  i n t h e a d j a c e n t sandy mud. e x p o n e n t i a l growth was  Verhoeven  internodes  (1979) found t h a t the time a t which  i n i t i a t e d i n Ruppia v a r i e d w i t h s u b s t r a t e and  water s a l i n i t y ; p l a n t s grew b e s t i n muddy sediment i n low s a l i n i t y  water.  The slow downward growth o f Z. j a p o n i c a rhizome a p i c e s i n t h e w i n t e r , as seen at Roberts Bank, has a l s o been observed i n Japan 1950a) and may  ( M i k i 1933,  Arasaki  p r o v i d e p r o t e c t i o n from o c c a s i o n a l f r e e z i n g i n the upper  sediment d u r i n g the w i n t e r .  104 In a study o f Ruppia rhizomes, Verhoeven t r a n s i t i o n from slow to r a p i d growth was temperature-dependent.  (1979) found t h a t the  always abrupt and c o m p l e t e l y  Budding o f rhizomes began a f t e r the mean d a i l y  maximum temperature had been above 15°C f o r 10 days w i t h a minimum temperature above 10°C.  A s i m i l a r mechanism i s l i k e l y  i n v o l v e d i n the  i n i t i a t i o n o f r a p i d growth from q u i e s c e n t rhizomes o f Z. j a p o n i c a (Arasaki  Genet  1950a).  growth The schematic r e p r e s e n t a t i o n s o f Z o s t e r a and Ruppia genets h e l p i n  comprehending  some o f the phases and geometry o f t h e i r growth.  e s t i m a t i o n s o f ramets per genet f o r b o t h s p e c i e s a r e poor  The  because  rhizomes fragment e a s i l y ; they do p r o v i d e an i d e a o f r e l a t i v e s i z e , how  an i n d i v i d u a l  expands and fragments i n t o a c o l o n y o f c l o n a l  and  parts.  I t i s a l s o c l e a r t h a t i t would take a l a r g e d i s t u r b a n c e t o remove an e n t i r e genet from the p o p u l a t i o n once b r a n c h i n g o c c u r r e d .  Mapping  rhizomes o f i n d i v i d u a l s would a l s o be important i n demographic  the  studies  f o c u s i n g on meristems as suggested by Tomlinson (1974).  Numbers o f f l o w e r s and  inflorescences  The number o f Z o s t e r a f l o w e r s per i n f l o r e s c e n c e v a r i e s from one l o c a t i o n to another.  I t i s my o b s e r v a t i o n t h a t s p a d i c e s o f p l a n t s  growing i n p r o t e c t e d p o o l s grow c o n s i s t e n t l y t o f i l l and may  have as many as 11 f u n c t i o n a l o v a r i e s .  t h e i r e n t i r e spathe  P l a n t s growing i n areas  t h a t a r e r e p e a t e d l y exposed to the a i r f o r extended p e r i o d s may  produce  s p a d i c e s t h a t a r e o n l y o n e - h a l f or o n e - t h i r d the s i z e o f t h e spathe and c o n t a i n few o v a r i e s .  The i d e n t i f i c a t i o n o f s p e c i f i c f a c t o r s which  control  105 the amount o f spaclix growth and  thus ovary p r o d u c t i o n  i s beyond the  o f t h i s study, but as i n d i c a t e d by these o b s e r v a t i o n s ,  scope  s p a d i x growth i s  r e l a t e d to the v i g o r o f p l a n t growth as c o n t r o l l e d by the p r e v a i l i n g environmental The  conditions.  majority  o f Ruppia i n f l o r e s c e n c e s produce e i g h t  (Verhoeven 1979).  However, a c c o r d i n g  o c c a s i o n a l l y there  can be as many as e i g h t o v a r i e s per  each i n f l o r e s c e n c e has per  two  flowers,  ovaries  to H i t c h c o c k et a l . (1973), flower  p o t e n t i a l l y 16 o v a r i e s  i n f l o r e s c e n c e ; the most I have observed i s 12.  w i t h fewer than e i g h t o v a r i e s a t Roberts Bank may  and  could  since form  Inflorescences have had  some phys-  i c a l l y removed by wave a c t i o n ; however the s i g n i f i c a n t drop i n ovary number a t s t a t i o n 1 i n age a r o l e i n reducing The  The  rapid reduction  they produce i s a f u n c t i o n o f  of Zostera  a r e s u l t o f the l o s s o f f l o w e r i n g  season d u r i n g longer  v i g o r o u s growth.  r e l a t i v e l y l o n g - l i v e d shoots  shoots produced e a r l y i n only  when l o s t were r e p l a c e d  ( F i g . 11a).  shoot  i n f l o r e s c e n c e s at s t a t i o n 1  These shoots were not  a t the o t h e r s t a t i o n s , but  flowering  play  ovary number.  number o f i n f l o r e s c e n c e s  longevity. was  c l a s s 2 suggests t h a t d e s i c c a t i o n may  Low  the  maintained by  other  m o r t a l i t y i n Ruppia  shoots r e s u l t e d i n c o n t i n u a l l y growing numbers o f  inflorescences.  Ovary f a t e s The  proportion  o f non-developing o v a r i e s  e v e r - p r e s e n t f a c t o r l i m i t i n g seed p r o d u c t i o n Roberts Bank.  Because there  c a l l e d ovary a b o r t i o n , impossible  e.g.  c o u l d be  ( f a t e 1) appears t o be i n Zostera  and  s e v e r a l causes f o r what I have  m a l f o r m a t i o n or n o n - p o l l i n a t i o n ,  with the o b s e r v a t i o n s  Ruppia at  i t is  made here to determine i f one  or a l l  an  106 o f t h e s e f a c t o r s remain constant  or i f they v a r y  through time and  space  to a common r e s u l t . Arasaki  (1950b)  pollination.  reported  From one  t h a t Z.  to f i v e f r u i t s  j a p o n i c a had  ( i n the m a j o r i t y  to f o u r ) would develop on a s i n g l e spathe. s e l f - c o m p a t i b i l i t y o f Z. place  through the water column and may how  be  o f cases,  submarine s e l f - p o l l i n a t i o n  l a b o r a t o r y environment, each p i s t i l  observed a t Roberts Bank may p i s t i l s by wave and The  higher  The  When  enclosed  In  the  successful  lower p o l l i n a t i o n success the  tide action.  ovary p r e d a t i o n  protected  is usually  and  flowers  be because p o l l e n i s c a r r i e d away from  ( f a t e 2)  seen on Ruppia than on  c o u l d be a t t r i b u t e d to Ruppia's morphology. c l o s e d and  of  inflorescence  reach the water s u r f a c e , the p o l l e n t r a v e l s on the s u r f a c e .  (Verhoeven 1979) .  the  inefficient.  a c t s as a s u r f a c e on which p o l l e n t r a v e l s t o the p i s t i l s .  i n producing a f r u i t  two  D i s p e r s a l o f p o l l e n takes  Ruppia takes p l a c e by an a i r bubble t h a t forms on the  undisturbed  of  Nothing i s known o f  japonica p o l l e n .  Verhoeven (1979) d e s c r i b e s  a poor r a t e  by the spathe.  o n l y by a t h i n p e r i c a r p .  Zostera  Zostera  o v a r i e s are  en-  Developing f r u i t s o f Ruppia are The  g e n e r a l l y low p r e d a t i o n  s t a t i o n 1 may  be a r e s u l t o f poor h a b i t a t c o n d i t i o n s  No  made to i d e n t i f y the a n i m a l ( s ) t h a t would remove v a r i o u s  e f f o r t was  f o r the  at  predator(s).  p o r t i o n s o f the f r u i t p e r i c a r p and u s u a l l y the e n t i r e c o n t e n t s o f seed o f both s p e c i e s .  Fungal or b a c t e r i a l i n f e c t i o n s o f t e n r e s u l t e d  f r u i t s , once damaged by a The  proportion  predator.  o f developing  fruits  l o s t before  they were mature  ( f a t e 3) r e f l e c t s e a r l y l o s s e s o f i n f r u i t e s c e n c e s w i t h d e s i c c a t i o n , e.g.  on  a t s t a t i o n 1, and  increased  a l s o the presence o f asynchronous  107 f r u i t development w i t h i n an i n f r u i t e s c e n c e . Table  IV shows how  g i v e n ovary success  rate  complex s e t s o f v a r i a b l e s i n t e g r a t e to y i e l d (fate 4).  Increased  s t a t i o n 1 over t h a t at 2 (see s e c t i o n one)  d e s i c c a t i o n experienced  does not  i n c r e a s e i n p a r t i c u l a r f a t e s , but a l t e r s p r o p o r t i o n s e.g.  the percentage l o s t to  Seed  production Because seed p r o d u c t i o n  j u s t cause an of s p e c i f i c fates,  i s the product o f f o u r y i e l d  the numbers o f o v a r i e s per  i n g shoot, and  i n producing  components: a mature seed,  i n f l o r e s c e n c e , i n f l o r e s c e n c e s per  f l o w e r i n g shoots per  area,  i t i s important t o  For Z o s t e r a , a l l y i e l d components a c t e d i n the estimated  together  seed p r o d u c t i o n  flower-  consider  the components s e p a r a t e l y when i n t e r p r e t i n g d i f f e r e n c e s i n seed  discrepancies  production.  to c r e a t e  the  between s t a t i o n s .  components at s t a t i o n 1 were g e n e r a l l y lower than a t the other  Yield  two  s t a t i o n s ; the combined e f f e c t o f these components on seed p r o d u c t i o n augmented by the shortened r e p r o d u c t i v e  o v a r i e s per  f l o w e r i n g shoot, and  f l u c t u a t e d p r i m a r i l y with  o v a r i e s i n producing  mature seed and  with  These d i f f e r e n c e s i n the behavior  the  to a l e s s e r extent  i n f l o r e s c e n c e remained r e l a t i v e l y constant  Seed p r o d u c t i o n  the success  at a l l s t a t i o n s . of i n d i v i d u a l  f l o w e r i n g shoot  density.  o f y i e l d components i n r e l a t i o n  to the environment r e f l e c t the g e n e r a l l y more p l a s t i c responses  of  Zostera  (as  to changing environmental c o n d i t i o n s compared to Ruppia  seen p r e v i o u s l y i n shoot demography and  was  p e r i o d a t s t a t i o n 1.  In Ruppia, however, the l e n g t h o f the r e p r o d u c t i v e p e r i o d , numbers o f i n f l o r e s c e n c e s per  at  predation.  the p r o b a b i l i t y o f i n d i v i d u a l ovary success and  a  l e a f and  rhizome  internode  108 lengths).  Because Z o s t e r a  l i v e s i n a wide range o f marine h a b i t a t s  1933), great f l e x i b i l i t y may  be r e q u i r e d to r e g u l a t e seed p r o d u c t i o n  s e v e r a l l e v e l s i n the developmental p r o c e s s able  (Miki at  to p r e c i s e l y a l l o c a t e a v a i l -  resources. The  r e l a t i o n s h i p s o f y i e l d components have been s t u d i e d  i n crop p l a n t s  (Adams 1967).  comparisons o f n a t u r a l and  extensively  However, Primack (1978) c a u t i o n s  a g r i c u l t u r a l populations  against  because o f pronounced  d i f f e r e n c e s i n the amount o f environmental h e t e r o g e n e i t y ,  differences  which can occur between r e p r o d u c t i v e l y mature p l a n t s , and  the p h e n o t y p i c  u n i f o r m i t y between i n b r e d l i n e s o f crop p l a n t s and  natural  populations.  SECTION 3.  THE SEED COMPONENT OF THE  POPULATION  Results Buried  seed  B u r i e d seed a t Roberts Bank was almost e n t i r e l y Z. j a p o n i c a and R. maritima, e x c e p t i o n s b e i n g seed-of Z. marina which o c c u r r e d i n 2 d e n s i t i e s o n l y o f a few per m maritima L.  During the w i n t e r Z o s t e r a and Ruppia  the upper 10 cm o f sediment range  and t h e o c c a s i o n a l f r u i t o f T r i g l o c h i n  ( F i g . 21).  seed was densest i n  and i n t h e summer, i n the 10 - 20 cm depth  Ruppia seed t y p i c a l l y outnumbered t h a t o f Z o s t e r a .  Both s p e c i e s showed a s i m i l a r p a t t e r n i n the d i s t r i b u t i o n o f t h e i r v i a b l e seed. deeper  The d i s t r i b u t i o n o f w i n t e r Z o s t e r a seed was u n i f o r m l y  i n 1981 compared w i t h the p r e v i o u s year as determined by a  cumulative p e r c e n t c u r v e . Both w i n t e r s Z o s t e r a a t s t a t i o n 2 had t h e h i g h e s t number o f b u r i e d 2 seed, a v e r a g i n g 65 per .1 m .  S t a t i o n s 1 and 3 had about  equal numbers  o f b u r i e d seed both w i n t e r s ; i n 1981 they were c l o s e r i n number t o those at s t a t i o n 2. In the f i r s t  5 cm o f sediment,  the t o t a l p e r c e n t o f v i a b l e Z o s t e r a  seed d u r i n g the w i n t e r decreased from s t a t i o n 1 t o 3. all  From 0 t o 20 cm,  s t a t i o n s i n 1980 c o n t a i n e d a p p r o x i m a t e l y the same p e r c e n t o f t h e i r  v i a b l e seed  (95%); i n 1981, however, the number s t i l l  w i t h d i s t a n c e from shore.  tended to decrease  Few, i f any, v i a b l e seeds were found below  15 cm i n the w i n t e r . General p r o f i l e s o f Ruppia seed numbers were v e r y s i m i l a r f o r both winters.  The number o f b u r i e d v i a b l e seed c o n s t a n t l y i n c r e a s e d from 2 s t a t i o n 1 to 3, a v e r a g i n g 77 per .1 m a t s t a t i o n 2; t h e range o f seed  110  F i g . 21 a - f .  Cumulative .percent o f a l l b u r i e d seed from t h r e e s t a t i o n s  ( s t a t i o n 1 = 3.17 m, 2 = 2.54 m, 3 = 2.60 m CD t i d a l h e i g h t ) a t Roberts Bank.  Bars show c u m u l a t i v e p e r c e n t o f v i a b l e seed.  a t the bottom o f each seed p r o f i l e from l e f t t o r i g h t :  Numbers  total  from t e n cores (20 X 8 cm d i a m e t e r ) , t o t a l e s t i m a t e d v i a b l e  seed  seed  2 from t e n c o r e s , and v i a b l e seed p e r 0.1 m .  The c o e f f i c i e n t o f  v a r i a t i o n o f c o r e s a t each s i t e and sampling date v a r i e d between 80 and 6%, w i t h a mean o f 21%.  Station 1  20  LO i  60 i  80  20  100  —i  - A -  1  60  80 100  1  1  20 I  1  2-  2-  L  4-  4-  6-  £ a  10-  10-  ~  12-  12-  c  LO  2-  —•  uE  Station 3  Station 2 Cumulative Percent  , .  L0 I  60 1  80 100  aj  .§  14-  CO  CO  1  .  16-  18-  18-  6  20  1.09  74  34.0  20-  181  F i g . 21a. Z o s t e r a j a p o n i c a , w i n t e r 1980.  120 60.1  130  65 32.5  '  I  Station 1  20 _i  40 i  60 i  Station 2 Cumulative Percent 80 i  20  100 i  J  2-  40  60  1  I  80 I  Station 3  100  20  I  t  •  40 '  60 JI  80 i  21  4.  • »  -  A  103  76  38.0  F i g . 21b. Ruppia m a r i t i m a ,  314  w i n t e r 1980.  174 87.5  296  196 98.4  100 i  Stat ion 1  20 i  ~  40 i  60 i  Station 2 Cumulative Percent 80 '  20  100 i  —I  2-  2  4 •  4-  61  6-  40 1  60 I  80 I  Station 3  100  20 i  I  40 i  60 i  80 i  6^  8 10'  10  12H  12  u  14  16-  16  18-  18  20  46  F i g . 21c.  32  16.0  Zostera japonica,  H  20 J  66  summer 1980.  34  17.0  56  22 11.0  100 i  Station 1  20  CO  60  . Station 2 Cumulative Percent 80 1QQ  20  • '  CO 1  1  60  Station 3  80 100 •  20  i  '  CO '  60 1  80 100 i  I  2-C  6  6-  8  8-  10 4  10  12  12-  U  U-  16-  16-  18-  18-  20  20 J  .g. 21d. Ruppia m a r i t i m a , summer 1980.  .  .  Station 1  20 i  40  60  Station 2 Cumulative Percent 80  —i  20  100  —i  1  40  1  60  1  Station 3  80 100  1  j  20 i  40 i  60 i  80 100  2H  4. — E  a.  6-  10  10  12H  12  cu  a  ~  c ca  U4 CD tO  16H  16.  18  18 • 20  J  14 7  109  55.0  20  177  F i g . 21e. Z o s t e r a j a p o n i c a , w i n t e r 1981.  137 69.0  141  109 55.0  i  i  Station 1  20  __i  40 i  60 1  Station 2 Cumulative Percent 20  80 100 i  _i  j  40 i  60 i  i  _j  40 i  60 ' 80 100 i  4-]  44 6  6-  u  _  i  2-  4-1  E  20  80 100  2-  —  Station 3  8 10'  10-  12H  12' 1H  15H  16H  18  18H  20  141  113 57.0  F i g . 21f.  Ruppia m a r i t i m a ,  20  205  w i n t e r 1981.  134 67.2  273  167 84.0  i  i  117 numbers was s m a l l e r i n 1981. the upper l a y e r  A h i g h e r p r o p o r t i o n o f v i a b l e seed was i n  ( 0 - 5 cm) a t s t a t i o n 1 than a t s t a t i o n s 2 and 3 i n both  w i n t e r s , but i f t h e top 10 cm a r e c o n s i d e r e d c o l l e c t i v e l y , i n the w i n t e r o f 1981 were about  a l l stations  equal w i t h a p p r o x i m a t e l y 80 - 85 p e r c e n t  o f the v i a b l e seed i n t h e w i n t e r o c c u r r i n g i n t h a t l a y e r .  Eight percent  or l e s s o f t h e v i a b l e seed i n a l l January samples was found below 15 cm. The d i s t r i b u t i o n s o f Z o s t e r a and Ruppia similar.  seed i n the summer were  The major d i f f e r e n c e was i n the mean number o f b u r i e d v i a b l e 2  seed; Z o s t e r a averaged  15, and Ruppia  found above the 5 cm sediment  level.  21 p e r .1 m .  No v i a b l e seed was  Both s p e c i e s showed a decrease i n  the p e r c e n t o f v i a b l e seed l o c a t e d i n the t o p 10 cm o f sediment. 30 p e r c e n t o f v i a b l e Z o s t e r a and Ruppia  Over  seed a t a l l s t a t i o n s was l o c a t e d  below 15 cm.  V i a b i l i t y o f u n t r e a t e d seed c o l l e c t i o n s s t o r e d a t 5°C. I n i t i a l v a l u e s o f new Z o s t e r a and Ruppia seed v i a b i l i t y averaged above 95% (Table V I ) .  i n July  Z o s t e r a seed i n September showed a  s i g n i f i c a n t decrease i n v i a b i l i t y from J u l y ' s e s t i m a t e .  Increases i n  m o r t a l i t y o f Z o s t e r a seed were not s i g n i f i c a n t a g a i n u n t i l A p r i l , when i t was e s t i m a t e d t h a t over t w o - t h i r d s o f the seed o r i g i n a l l y  collected  was a l i v e . V i a b i l i t y o f Ruppia seed d i d n o t change s i g n i f i c a n t l y from c o l l e c t i o n values u n t i l q u a r t e r s o f the o r i g i n a l  February.  By A p r i l ,  original  s l i g h t l y l e s s than t h r e e -  seed was v i a b l e .  Old Z o s t e r a seed showed no s i g n i f i c a n t d e c r e a s e s i n v i a b i l i t y throughout percent.  the study p e r i o d a l t h o u g h t h e mean v a l u e dropped O l d Ruppia  about 15,  seed, however, showed s i g n i f i c a n t m o r t a l i t y  after  118  Table VI.  Percent v i a b i l i t y o f seed s t o r e d a t 5°C and 27 o/oo  d u r i n g 1980 - 1981.  salinity  New seed o f Z o s t e r a j a p o n i c a and Ruppia  maritima was c o l l e c t e d from c u r r e n t y e a r shoots and o l d seed was c o l l e c t e d from the sediment  a t Roberts Bank, both i n J u l y ,  1980.  Standard d e v i a t i o n s are i n p a r e n t h e s e s .  New Seed Month  Zostera  O l d Seed Ruppia  Zostera  Ruppia  Jul.  96.7 (2.3)  95.3 (3.1)  87.3 (6.1)  82.0 (7.2)  Sep.  91.0 (2.6)  96.0 (2.0)  90.7 (7.0)  75.0 (5.6)  Oct.  88.0 (6.0)  93.3 (4.2)  83.3 (5.0)  73.7 (4.5)  Nov.  90.7 (4.2)  94.0 (2.0)  81.3 (9.9)  70.7 (6.1)  Jan.  89.3 (7.0)  87.3 (4.2)  76.0 (6.0)  66.0 (5.3)  Feb.  87.3 (3.1)  80.7 (4.2)  74.0 (8.0)  68.7 (3.1)  Apr.  68.7 (6.4)  73.3 (8.1)  76.0 (11.1)  64.7 (7.0)  119 s i x months o f s t o r a g e . significantly  F i n a l v i a b i l i t i e s o f a l l seeds were not  different.  E f f e c t s o f temperature and g e r m i n a t i o n  and a n a e r o b i c c o n d i t i o n s on seed  viability  New Z o s t e r a seed m a i n t a i n e d i n 5°C a e r o b i c c o n d i t i o n s i n the l a b o r a t o r y showed s i g n i f i c a n t l y h i g h e r v i a b i l i t y and s i g n i f i c a n t l y m o r t a l i t y i n February than i n A p r i l  (Table V I I ) .  Ruppia  lower  seed m a i n t a i n e d  at these c o n d i t i o n s showed no s i g n i f i c a n t d i f f e r e n c e s between the two test dates. period.  Few seed o f e i t h e r s p e c i e s germinated d u r i n g the study  Seed death was autonomic;  no f u n g a l o r b a c t e r i a l growth was  ever e v i d e n t i n the p e t r i d i s h e s . Values f o r Z o s t e r a and Ruppia seed m a i n t a i n e d i n 5°C a n a e r o b i c c o n d i t i o n s were not s i g n i f i c a n t l y d i f f e r e n t between s p e c i e s o r t e s t dates f o r percentages v i a b l e , dead, o r germinated.  These v a l u e s were  a l s o not s i g n i f i c a n t l y d i f f e r e n t from v a l u e s f o r 5°C a e r o b i c c o n d i t i o n s . The m a j o r i t y o f seed m a i n t a i n e d i n the a e r o b i c , a l t e r n a t i n g 7 - 15°C temperature  regime  germinated d u r i n g the t e s t p e r i o d .  Ten p e r c e n t o f  Z o s t e r a seed was v i a b l e i n February, but none were v i a b l e i n A p r i l . There was no v i a b l e Ruppia seed i n e i t h e r month. S i g n i f i c a n t l y l a r g e r percentages o f Z o s t e r a and Ruppia  seed were  v i a b l e i n both February and A p r i l when m a i n t a i n e d i n a n a e r o b i c 7 - 15°C c o n d i t i o n s as compared w i t h the a e r o b i c a l t e r n a t i n g temperature The percentage o f dead Ruppia  regime.  seed was s i g n f i c i a n t l y g r e a t e r i n A p r i l  a n a e r o b i c than i n a e r o b i c 15-7°C c o n d i t i o n s .  The percentages o f seed  g e r m i n a t i n g d u r i n g s t o r a g e under the a l t e r n a t i n g temprature regime always  significantly  lower under a n a e r o b i c c o n d i t i o n s .  were  Table V I I .  Percent v i a b i l i t y , death, and germination o f new  c o n t r o l l e d l a b o r a t o r y environments.  Eight 100-seed  Zostera japonica and Ruppia maritima seed from 1980 27 o/oo  constant 5'C,  or without oxygen.  The^seed was h e l d under t e s t conditions from October,  germination during storage.  u  s  Zostera  Dead  Germinated  5  Anaerobic  Aerobic  Feb.  85 .0 (4 •2)  81 .0 (5 •2)  10.3  (6.7)  50 .0 (7 .8)  Apr.  67 .5 (5 .0)  77 .0 (8 •1)  0.0 (0.0)  25 .0 (5 .3)  Feb.  11 .8 (3 •9)  14 .0 (3 • 7)  17.5 (9.8)  6 .5 (4 • 4)  Apr.  24 .0 (5 • 2)  19 .0 (6 .8)  15.0 (6.8)  . 19 .5 (6 • 0)  1 .5  2 .5 (1  72.0 (9.9)  46 .0 (12..3)  (6,.9)  4..0 (3, .6)  84.5  (6.8)  51 .0 (10 .9)  Feb.  81..3 (6. •9)  78,.3 (5. .0)  0.0 (0.0)  63..3 (3..8)  Apr.  71.,0  2)  80..0 (7. .8)  0.0 (0.0)  7..5 (3. .8)  Feb.  15. 5 (5. 7)  16.,5 (3. •0}  9.0 (5.0)  13..0 (4. 2)  Apr.  22. 0 (4. 3)  15. 0 (5. •3)  9.0 (7.5)  20. 5  Feb.  1. 5 (1. 9)  3. 0 (2. 6)  91.0 (5.0)  25. 0 (7. 6)  Apr.  7. 0 (5. 0)  5. 0 (2. 6)  91.0 (7.5)  72. 0 (9. 7)  Feb.  Apr.  7..5  C6.  Dead  Germinated  7 - 15 'C  C  Aerobic  (1 •9)  Viable  "Germinated" r e f e r s to  te  D a  Viable  1981.  Standard d e v i a t i o n s are given i n parentheses.  Recovery n  shoots were stored i n  or 12 h a t 7*C a l t e r n a t i n g with 12 h at 15 "C, with  1980 u n t i l February ( h a l f the seed) o r A p r i l ,  e  r e p l i c a t e s o f both  s a l i n i t y seawater under each o f four combinations o f temperature and  atmosphere:  G  seed maintained i n  Anaerobic  (6. 6)  121 V i a b i l i t y of buried  seed  The l o n g e v i t y o f e x p e r i m e n t a l l y b u r i e d seed g e n e r a l l y with sediment depth t o 15 cm i n February (Table V I I I ) . i f any v i a b l e seed remained  increased  In A p r i l , few  i n the upper 10 cm.  New seed o f both Z o s t e r a and Ruppia f o l l o w e d t h i s p a t t e r n , but Ruppia r e t a i n e d more v i a b l e seed a t each sediment  l e v e l i n February.  Although t h e i r p e r c e n t v i a b i l i t i e s a t the 20 cm depth i n A p r i l were s i m i l a r , seed v i a b i l i t i e s o f Z o s t e r a a t the 15 cm l e v e l were s i g n i f i c a n t l y h i g h e r than  Ruppia s. 1  Old seed o f both s p e c i e s g e n e r a l l y s u f f e r e d h i g h e r and/or more r a p i d m o r t a l i t y than new seed a t each sediment  level.  a t the 20 cm depth i n February were s i g n i f i c a n t l y Ruppia seed. recovery.  O l d Z o s t e r a seed  l e s s v i a b l e than o l d  The m a j o r i t y o f dead seed c o n s i s t e d o f o n l y t h e t e s t a upon  S e v e r a l o f t h e remaining dead seeds i n each r e p l i c a t e supported  f u n g a l growth d u r i n g v i a b i l i t y  tests.  New seed g e r m i n a t i o n From the time o f c o l l e c t i o n i n J u l y u n t i l October, no g e r m i n a t i o n o f new Z o s t e r a o r Ruppia seed o c c u r r e d (when seed was p l a c e d i n d i s t i l l e d water).  A s m a l l p r o p o r t i o n o f seed from both s p e c i e s germinated i n  November  ( F i g . 22), and by January, a l l v i a b l e seed was a b l e t o germinate.  The c o e f f i c i e n t o f v a r i a t i o n o f r e p l i c a t e s between 120 and 1.4% with a mean o f 10.  i n a l l germination tests  V i a b i l i t y averaged 86% i n  r e p l i c a t e s used i n g e r m i n a t i o n t e s t s . I n c r e a s i n g s a l i n i t i e s d e c r e a s e d the r a t e o f g e r m i n a t i o n o f both species  ( F i g . 23), but e s p e c i a l l y o f Z o s t e r a .  More than 65% o f new  seed was unable t o germinate i n s a l i n i t i e s o f 20 and 27 o/oo; 59% o f  varied  122  Table V I I I . New  Percent v i a b i l i t i e s o f b u r i e d seed at f o u r sediment  (from 1980 shoots) and o l d (from sediment)  depths.  seed o f Z o s t e r a  j a p o n i c a and Ruppia m a r i t i m a were c o l l e c t e d from Roberts Bank i n J u l y , 1980.  Seed was s t o r e d i n 27 o/oo seawater a t 5 °C u n t i l  burial  near s t a t i o n 2 (2.54 m CD t i d a l h e i g h t ) a t Roberts Bank on October 14, 1980.  Seed was r e c o v e r e d i n February and A p r i l ,  1981, and was  tested f o r v i a b i l i t y .  Sediment  Depth  Genus  Age  Recovery Date  Zostera  New  Feb.  18.0  47.5  69.5  66.0  Apr.  0.0  1.0  31.0  45.0  Feb.  10.0  24.0  28.5  29.5  Apr.  1.0  4.5  27.0  31.5  Feb.  26.0  63.0  82.5  80.0  Apr.  0.0  2.0  14.0  46.0  Feb.  5.3  12.0  41.0  52.0  Apr.  0.0  1.5  19.5  25.5  Old  Ruppia  New  Old  5 cm  10 cm  15 cm  20 cm  5  F i g . 22.  10  15  Days  20  P e r c e n t g e r m i n a t i o n r a t e o f c u r r e n t y e a r v i a b l e seed o f  Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a  i n 10°C  distilled  water.  124  Fig.  23 a, b.  P e r c e n t g e r m i n a t i o n r a t e o f c u r r e n t year v i a b l e seed o f  Z o s t e r a j a p o n i c a and Ruppia maritima i n 10 'C water a t f o u r salinities. distilled  At 30 days, ungerminated seeds were p l a c e d i n  water.  125  126  i  i  O  o  i  O  c  n  i  O  c  i  O  o  r  O  ^  i  i O  o  L  uoipuiujjeg  i O  O  -  i O  J  m  i O  f  N  i O  -  r  -  127 Ruppia would not germinate i n 27 o/oo.  Germination resumed when  nated seed was t r a n s f e r r e d from h i g h s a l i n i t i e s  ungermi-  t o d i s t i l l e d water.  The  s c o r i n g o f seed c o a t s i n c r e a s e d r a t e s o f g e r m i n a t i o n under low and h i g h s a l i n i t i e s , but d i d n o t i n c r e a s e t h e f i n a l percentage o f g e r m i n a t i o n under h i g h s a l i n i t i e s  (Fig-  24).  Increased temperatures promoted g e r m i n a t i o n r a t e s seed o f both s p e c i e s germinated most r a p i d l y 7  -. 15°C.  ( F i g . 25), but  i n a f l u c t u a t i n g regime o f  Germination d i m i n i s h e d t o zero when seed was h e l d a t 5°C.  The l a c k o f exposure t o white l i g h t had no e f f e c t on the g e r m i n a t i o n o f new seed o f e i t h e r s p e c i e s ( F i g .  26).  Regardless o f the temperature and atmosphere c o n d i t i o n s d u r i n g s t o r a g e , the g e r m i n a t i o n r a t e s o f seed p l a c e d i n 27 o/oo s a l i n i t y water a t a l t e r n a t i n g 7 - 15°C were e q u i v a l e n t .  sea-  The g e r m i n a t i o n o f new  seed i n February took p l a c e as r a p i d l y as o l d seed g e r m i n a t i o n , w i t h all  v i a b l e seed g e r m i n a t i n g w i t h i n f i v e  Old  seed g e r m i n a t i o n  t o t e n days.  The g e r m i n a t i o n r a t e s o f o l d Z o s t e r a and Ruppia seed s t o r e d a t 5°C and germinated a t 10°C i n d i s t i l l e d water remained time o f c o l l e c t i o n i n J u l y u n t i l  c o n s t a n t from the  t h e end o f t h e study i n A p r i l .  seed germinated sooner than Z o s t e r a seed  ( F i g . 27). Rate, but not the  amount, o f g e r m i n a t i o n o f o l d seed was slowed by i n c r e a s i n g (Fig.  Ruppia  salinity  28). The g e r m i n a t i o n o f o l d seed was not a f f e c t e d by l a c k o f  exposure to white l i g h t .  (Fig.  28).  128  . 24. a, b. unscored  Percent g e r m i n a t i o n r a t e o f s c o r e d  (solid  l i n e ) and  (dashed l i n e ) c u r r e n t y e a r v i a b l e seed o f Z o s t e r a  and Ruppia m a r i t i m a i n 10 "C water a t two s a l i n i t i e s . ungerminated seeds were p l a c e d i n d i s t i l l e d water.  japonica  At 30 days,  Percent Germination  6ZI  Percent Germination  131  F i g . 25. a, b.  Percent g e r m i n a t i o n r a t e o f c u r r e n t year v i a b l e seed o f  Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a i n 20 o/oo temperature  regimes  s a l i n i t y water a t  o f c o n s t a n t 10 °C and 18 *C and  a l t e r n a t i n g 15 - 7 "C.  12-hour  5  10  15  20  Days  F i g . 25a.  Zostera japonica.  No  germination  o c c u r r e d at  5"C.  Percent Germination  O  134  Fig.  26.  Percent g e r m i n a t i o n r a t e o f c u r r e n t year v i a b l e seed o f Z o s t e r a  j a p o n i c a and Ruppia m a r i t i m a i n 10 °C water a t two dark  (solid  l i n e ) and exposed t o white l i g h t  days, ungerminated  salinities  (dashed l i n e ) .  seeds were p l a c e d i n d i s t i l l e d water.  i n the At 30  I  5  10  15  20  Days  F i g . 27.  P e r c e n t g e r m i n a t i o n r a t e o f p r e v i o u s y e a r s ' v i a b l e seed  Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a  i n 10'C  d i s t i l l e d water.  of  138  Fig.  28. a, b. of and at  Percent germination r a t e o f previous years' v i a b l e  Z o s t e r a j a p o n i c a and Ruppia m a r i t i m a 20 o/oo 20 o/oo  salinities salinity  exposed to white  i n the dark  (solid  seed  i n 10 °C water at 10  o/oo  light  and  line).  (dashed  line)  139  uoipuiuLijeo  o  uoipuiuujaQ  juaDjaj  141 Germination i n seed bank Germination o f Z o s t e r a and Ruppia seed a t Roberts Bank was observed i n 1981,  on March 10.  Except f o r A p r i l  9 when equal numbers o f  s e e d l i n g s from each s p e c i e s were found, germinated twice as numerous as Ruppia  ( F i g . 29).  found below 12 cm.  seed o f Z o s t e r a was  The depth o f a l l germinated  seed o f both s p e c i e s averaged between 4 and 7 cm; was  first  no germinated  seed  S e e d l i n g counts w i t h i n p l o t s o f treatments.B  C i n d i c a t e d t h a t few s e e d l i n g s emerged a f t e r mid-June. June 23, an average o f l e s s than .3 Z o s t e r a and  and  From June 11 t o  .6 Ruppia  seedlings  2 emerged per .1 m  a t each s t a t i o n .  were r e c o r d e d and o n l y two  On J u l y 10, no new  Zostera seedlings  Ruppia s e e d l i n g s were found a t s t a t i o n  2.  Recruitment and death o f s e e d l i n g s and shoots from o v e r w i n t e r i n g rhizomes Shoots a r i s i n g from o v e r w i n t e r i n g rhizomes became i n c r e a s i n g l y from March to May  (Table I X ) .  T h e i r depth averaged between 4 and 5  rare cm.  Recruitment and death r a t e s were observed f o r s e e d l i n g s as a whole from March to May  ( F i g . 30a).  ,  The most severe l o s s e s  followed increased rates of recruitment.  generally  The t o t a l number o f s e e d l i n g s  p r e s e n t a t each sampling date, a l o n g w i t h the a b s o l u t e c o n t r i b u t i o n o f each c o h o r t a t s u c c e s s i v e sampling dates i s shown i n F i g u r e 30b. F i g u r e 30c,  . shows the percentage c o n t r i b u t i o n s o f c o h o r t s to the  t o t a l shoot p o p u l a t i o n a t each  station.  142  Fig.  29.  Percent o c c u r r e n c e o f s e e d l i n g s i n the sediment p r o f i l e near  station  2 (2.54 m CD t i d a l h e i g h t ) a t Roberts Bank, 1981.  number o f s e e d l i n g s i s i n d i c a t e d i n the lower r i g h t  Absolute  o f each graph.  143  Ruppia  Percent 0  0-1  10 1  maritima  Zostera  Seedlings  Percent  of 20  30  40  1  0  1  10  japonica  of 20  Seedlings 30  40  5'  March 10  10'  10—  15J  19  0  0  10  •  20  t  30  40  47  150  0  10  20  30  40  5  March 2U  5 10 10 13 "c  15  0  10  —1  20 1  30 1  15  40 1  0  27  J  0  10  20  30  40  0  April 9  CL CU  a  c  cu  5' 5 1010  E  I April 18  26 15  10  0-  20  30  40  0 01  10 ^  20  30  40  t _  510'  10-19  15 0  OH  May 1  25  15  l  10  -  20  30  40  0  5'  5  10  10  15  13  47  15-  15  0  J  10  20  30.  _40  29  144  T a b l e IX.  Shoot base depths and a b s o l u t e numbers o f Z o s t e r a shoots  e s t a b l i s h e d from o v e r w i n t e r i n g rhizomes i n h a p h a z a r d l y s e l e c t e d sediment c o r e s near s t a t i o n 2 a t Roberts Bank, 1981.  April  10  May 1  March 10  March 24  April 9  3  0  0  1  0  0  4  2  4  0  0  1  5  6  0  2  3  0  6  0  0  2  2  0  Depth  (cm)  145  30. a - c .  Recruitment and  l o s s , a b s o l u t e and p e r c e n t c o n t r i b u t i o n  of s e e d l i n g c o h o r t s of Z o s t e r a j a p o n i c a and t h r e e s t a t i o n s ( s t a t i o n 1 = 3.17 h e i g h t ) at Roberts Bank,  1981.  m,  2 = 2.54  Ruppia maritima m,  3 = 2.60  from  m CD  tidal  146  Station 2  Station 1 30-i  30-1  25-  25"  20Recruitment  15-  10-  10-  5-  5H  5-  51  10"  10 i  Loss  15  20-J  20 J 16 —j  17 1  18 19 20 1  1  1  Apr  Mar  20-  15-  15-  3  Station 3,  15H 20 J  16  —i  Mar  17 !  18 19 20 1  Apr  1  1  16  17  —1  1  Mar  18 19 20 1 — I  ^pr  Cohort Number and Month of Sampling F i g . 30a.  Recruitment and l o s s o f s e e d l i n g s between s u c c e s s i v e  sampling d a t e s . May  1,  1981.  S t i p p l i n g indicates seedlings  present  1  147  Cohort Number and Month of Sampling — Fig.  30b.  Absolute c o n t r i b u t i o n o f s e e d l i n g cohorts t o t o t a l  seedling population,  •  C  «  Mar  1  1 — i  Apr  1  i  and  i . Mar  1  total  seedling  1 — i  Apr  1  density.  i 1 Mar  1 — i  Apr  Cohort Number and Month of Sampling Fig.  30c.  Percent c o n t r i b u t i o n o f s e e d l i n g c o h o r t s t o t o t a l  seedling  population.  1  148 Discussion B u r i e d seed numbers B u r i e d v i a b l e seed o f Z o s t e r a and Ruppia e x i s t year-round i n the sediments o f Roberts Bank.  These p e r s i s t e n t seed banks appear to be  r e p l e n i s h e d to the p r e v i o u s y e a r ' s l e v e l each f a l l low numbers by the summer. i n the w i n t e r o f 1981  1981  The d i s t r i b u t i o n o f Z o s t e r a seed was  as compared w i t h 1980  i n sediment d i s t u r b a n c e .  and d e p l e t e d to v e r y  and may  deeper  indicate a difference  Ruppia seed, however, showed a mixed p a t t e r n ,  b u r i e d seed b e i n g e i t h e r h i g h e r or lower i n the p r o f i l e than the  previous year.  These v a r i a t i o n s i n b u r i a l depths may  have r e s u l t e d  d i f f e r e n c e s i n the time o f b u r i a l and/or b u r i a l p r o c e s s e s , e.g.  from  sediment  s o r t i n g c o n d i t i o n s a c t i n g on the d i f f e r e n t s i z e s and shapes o f the seed (see Harper et a l . 1970 b e h a v i o r i n the  f o r a d i s c u s s i o n o f seed morphology and  soil).  Most data on b u r i e d seed numbers have been based on e n t i r e counts.  Researchers who  have examined the d i s t r i b u t i o n o f seed through  the seed p r o f i l e have been few S t r i c k l e r and Edgerton 1976, 1979) .  A comparison  profile  (e.g. Major and P y o t t 1966,  Moore and Wein 1977,  Kellman  1970,  Leek and G r a v e l i n e  o f the d i s t r i b u t i o n o f b u r i e d seed a t Roberts Bank  with b u r i e d seed o f o t h e r ecosystems  ( T a b l e X) shows t h a t a h i g h e r p r o p o r -  t i o n o f seed i n i n t e r t i d a l  i s b u r i e d deeper.  sediments  Leek and G r a v e l i n e  (1979) suggested t h a t the reason t h a t s u r f a c e l a y e r s o f the marsh they were s t u d y i n g d i d not accumulate terrestrial  ecosystems  marsh which may  was  seed.  because o f the c o n s i d e r a b l e water f l u x i n the  r a f t away s u r f a c e d e b r i s c o n t a i n i n g seed.  a l s o p a r t i a l l y e x p l a i n why few  as h i g h a p r o p o r t i o n o f seed as o t h e r  This  s u r f a c e l a y e r s a t Roberts Bank had  could  relatively  Table X.  R e l a t i o n s h i p o f seed depth i n v a r i o u s  Ecosystem  Depth  ecosystems.*  ratio  Seed r a t i o  Reference  L i t t e r : 0 - 2 : 2 - 4 cm  12:5:1  S t r i c k l e r and E d g e r t o n 1976  O r g a n i c layer-0-2:2-4:4-6 cm  6.5:3:1  Moore and Wein 1977  Freshwater t i d a l marsh  0-2:4-6:8-10 cm  3:2:1  Leek and G r a v e l i n e 1979  Marine i n t e r t i d a l  0-2:4-6:8-10 cm  1:6.5:6**  p r e s e n t study w i n t e r 1981  Coniferous  forest  Deciduous-dominated  forest  * a f t e r Leek and G r a v e l i n e 1979. ** s t a t i o n 2 a t Roberts Bank (2.54 m CD t i d a l  height).  150 The  depth o f b u r i a l  frequency and  i s a l s o r e l a t e d to sediment t e x t u r e and  s e v e r i t y of disturbances  d r i v e n e r o s i o n a l and  to the sediment s t r a t a .  d e p o s i t i o n a l c y c l e s may  t i d a l b u r i a l process.  be  the Tide-  important i n the  inter-  Animals w i t h i n the sediment a l s o t u r n over  tremendous amounts o f sediment on a r e g u l a r b a s i s at Roberts Bank, and are l i k e l y the most important f o r c e a l t e r i n g sediment s t r a t a and contents.  Burrowing e r r a n t and  v a r i o u s prosobranchs and and  horizontally.  sedentary p o l y c h a e t e s ,  as w e l l  their  as  b i v a l v e s t r a n s p o r t sediments both v e r t i c a l l y  At Roberts Bank, Swinbanks (1979) found t h a t where 2  the p o l y c h a e t e completely  Abarenicola  had  a d e n s i t y o f 200  per m  , the animals would  t u r n over the sediment to the depth o f 10 cm  i n one  hundred  days. B u r i e d mats o f r o o t s and ( A r a s a k i 1950b) and tidal  rhizomes may  a i d sediment  c r e a t e b a r r i e r s to seed movement.  seagrass r o o t s are p r e s e n t  only during  high proportions  ments r e f l e c t and 1940,  Thus newly  little  impedance by  o f seed i n s u r f a c e l a y e r s o f f o r e s t e d  the s h o r t l o n g e v i t y o f many woodland seeds (Oosting and A l l e s s i o 1968).  Thus, b a r r i n g major  the time i t takes to become b u r i e d i n a f o r e s t may o f seed from l a t e s u c c e s s i o n a l It  (Major and  environintertidal  Humphreys disturbance,  exceed the l i f e  span  species.  i s g e n e r a l l y thought i n t e r r e s t r i a l  seed i s the o l d e s t  by  roots.  the slow r a t e o f b u r i a l as compared to the marine  L i v i n g s t o n and  any  deposited  Ruppia seeds c o u l d be worked down through the sediment  the s h i f t i n g o f sediments with The  However, i n t e r -  the growing season and  s t a b i l i z i n g e f f e c t s q u i c k l y d i m i n i s h i n the f a l l . Z o s t e r a and  stabiliziation  Pyott  1966).  over o f sediment i n the i n t e r t i d a l , any  ecosystems t h a t the  deeper  Because o f the r a p i d t u r n -  r e l a t i o n s h i p between age  and  151 depth would be banks and  incidental.  Another d i f f e r e n c e between i n t e r t i d a l  those i n o t h e r h a b i t a t s i s the amount o f  r e f l e c t i o n o f the s u r f a c e v e g e t a t i o n . (e.g. Major and P y o t t , 1966, Whipple 1978)  and  species-specific  B u r i e d seed banks i n t e r r e s t r i a l  L i v i n g s t o n and A l l e s s i o 1968,  s a l t marsh h a b i t a t s ( M i l t o n 1939)  resemblance to the growing f l o r a .  seed  Kellman  1970,  show l i t t l e or  no  I n t e r t i d a l seed banks, l i k e those  of  p r a i r i e g l a c i a l marshes which undergo drawdown d u r i n g p e r i o d s o f drought (van der Valk and  Davis  1978)  and  freshwater  t i d a l marshes (Leek  G r a v e l i n e 1979), do m i r r o r the s u r f a c e v e g e t a t i o n . r e l a t i o n s h i p to the s u r f a c e v e g e t a t i o n may o f seed b u r i a l , seed lishment  l o n g e v i t y and  a f t e r a disturbance  be due  This d i f f e r e n c e i n to the d i f f e r e n t  the importance o f s e e d l i n g r e - e s t a b -  t h e o r e t i c a l c o n s i d e r a t i o n s which  i n f l u e n c e the d e n s i t y o f b u r i e d seed.  of disturbance  because  " s p e c i e s s u b j e c t e d to f r e q u e n t and  severe d i s t u r b a n c e should  high proportion o f t h e i r resources  i n methods o f s u r v i v i n g the  m o r t a l i t y o f seed  and  Dawkins 1967), o n l y v e g e t a t i o n  s u f f i c i e n t p r o d u c t i v i t y to support banks.  l a r g e seed  disturbance,"  outputs  high  with  can m a i n t a i n  seed  Thus, because s t r e s s l i m i t s p r o d u c t i o n o f biomass o f a l l or  p a r t o f the v e g e t a t i o n , the accumulation low  invest a  Second, he contends t h a t because o f the  (Roberts  may  F i r s t , he proposed t h a t b u r i e d  seed d e n s i t i e s should r e l a t e to the frequency  b u r i e d seed banks.  rates  i n an ecosystem.  Thompson (1978) d i s c u s s e d two  e.g.  and  o f b u r i e d seed  i s favoured  by  levels of stress. Table XI compiles  vegetation types.  d a t a on b u r i e d seed d e n s i t i e s i n a number o f  Caution  because experimental  i s needed when i n t e r p r e t i n g these  methods vary; however a l l except  i n v o l v e d enumeration o f germinated seed  only.  data  the p r e s e n t  study  T a b l e XI.  E s t i m a t e s o f b u r i e d seed numbers  Ecosystem  Depth o f core  (m)  from v a r i o u s ecosystems.  Seeds p e r m  2  Reference  Pasture, f o r m e r l y a r a b l e  0.30  12,259  Grass c u t f o r hay  0.30  28,310  Desert  0.005  2,900  Went (1949)  Upland Eriphorum moor  0.18  2,483  Chippendale t> M o r r i s (1948)  S a l t marsh  0.18  877  Freshwater t i d a l Marine  intertidal  marsh  -  69,903  Chippendale § M i l t o n  (1934)  Chippendale § M i l t o n  (1934)  Milton  (1939)  0.10  6,405 •- 32,400  Leek and G r a v e l i n e (1979)  0.20  2,580  p r e s e n t study ( w i n t e r 1981)  153 As would be p r e d i c t e d by Thompson, l a r g e seed banks are a s s o c i a t e d with h i g h l y disturbed vegetation,  e.g.  the freshwater  t i d a l marsh which  i s s u b j e c t to annual f l o o d i n g and r i v e r s c o u r i n g , the d e s e r t  (note  core depth) with l o n g r a i n l e s s p e r i o d s , and  a g r i c u l t u r a l areas  h a r v e s t and  areas  grazing pressures.  have small seed banks, e.g. The  Conversely,  disturbance  s a l t marsh and moor v e g e t a t i o n  second p a r t o f Thompson's h y p o t h e s i s  productivity of vegetation.  o f low  with  types.  concerned l e v e l s  of  Although i d e a l i s t i c a l l y sound, i t l a c k s  p r e d i c t i v e power o f seed bank s i z e because o f i t s extreme g e n e r a l i t y . For example, s u b a r c t i c and  d e s e r t h a b i t a t s share h i g h s t r e s s e s on  p r o d u c t i v i t y i n t h e i r r e s p e c t i v e extreme temperatures and seasons.  s h o r t growing  As might be p r e d i c t e d from Thompson's h y p o t h e s i s ,  (1975) found no v i a b l e seed i n s u b a r c t i c f o r e s t f l o o r s , but  Johnson i n apparent  c o n t r a d i c t i o n , Went (1949) found l a r g e s t o r e s o f dormant seed i n d e s e r t soils.  Our  knowledge o f b u r i e d seed o u t s i d e temperate t e r r e s t r i a l  i s v e r y poor and perhaps Johnson (1975) was has  areas  c o r r e c t i n s a y i n g the time  not come f o r a s y n t h e s i s o f what i s known o f b u r i e d seed; however,  Thompson's ideas p r o v i d e  l i m i t e d p r e d i c t i o n and  a d i r e c t i o n for future  research. The number o f seagrass  seed i n sediments at Roberts Bank g r o s s l y  underestimates seed p r o d u c t i o n on the s i t e .  At f i r s t  examination i t  appears t h a t b u r i e d seed i n i n t e r t i d a l h a b i t a t s (high d i s t u r b a n c e seasonal  p r o d u c t i v i t y ) are s i m i l a r i n number to t h a t found i n an  moor (low d i s t u r b a n c e seed p r o d u c t i o n potential  i s taken i n t o account  intertidal  intermediate  and p r o d u c t i v i t y ) .  But  f o r a g r i c u l t u r a l areas,  upland  i f site-specific viable  (Table V), i t i s revealed  seed banks c o u l d r e a c h  and  l e v e l s which would  i f seed remained i n s i t u .  that be  154 The reason f o r the l a r g e d i s c r e p a n c i e s between seed produced the number d e p o s i t e d a t a s i t e seeds mature.  During August  and  i s the d i s p e r s a l t h a t takes p l a c e as  as the bases o f f l o w e r i n g shoots decay o r  are uprooted, e x t e n s i v e f l o a t i n g mats o f shoots form.  These mats advance  and r e t r e a t w i t h the t i d e , a p p a r e n t l y r e s u l t i n g i n the evenness  o f seed  d e p o s i t i o n seen at the study s i t e d e s p i t e the l a r g e d i f f e r e n c e s i n l o c a l seed p r o d u c t i o n . seawater greater  Mature seed o f Z o s t e r a and Ruppia s i n k immediately i n  ( s p e c i f i c g r a v i t y o f v i a b l e Z. j a p o n i c a  (= Z. nana) i s 1.9  ( A r a s a k i 1950b)) upon s e p a r a t i o n from the p a r e n t shoot.  c l o s e r agreement between s i t e - s p e c i f i c  or  The  seed p r o d u c t i o n and d e p o s i t i o n o f  Ruppia than o f Z o s t e r a i s e x p l a i n e d by o b s e r v a t i o n s t h a t much o f the Ruppia seed i s shed b e f o r e the r e p r o d u c t i v e shoot i s detached, Z o s t e r a where mature seed u s u a l l y remains  unlike  e n c l o s e d by the s p a d i x and  i s p r o b a b l y removed e i t h e r by wave a c t i o n o r w i t h decay o f the s p a d i x . In e i t h e r s i t u a t i o n , the m a j o r i t y o f seed i s r a f t e d w i t h v e g e t a t i v e shoots and i s not b u r i e d where produced. Arasaki  (1950b) noted t h a t Z_. j a p o n i c a seed i n Japanese waters i s  d i s p e r s e d over 2 to 3 months by the f l o a t i n g s h o o t s .  He a l s o  s i z e d t h a t because o f the . s i n k i n g o f seed, most was  d e p o s i t e d around  :  the p a r e n t p l a n t .  hypothe-  I t i s p o s s i b l e t h a t i n the Japanese waters where  A r a s a k i worked, shoots were r e t a i n e d l o n g e r a f t e r seed matured thus having a l o n g e r time to drop seed a t t h a t l o c a t i o n b e f o r e the few  remain-  i n g seeds were c a r r i e d away. The i n c r e a s e s o f seed numbers from s t a t i o n 1 to 3 may  indicate in  p a r t the r e l a t i v e time t h a t unattached mats c o n t a i n i n g seed spent a t various t i d a l heights.  Because the d i s t r i b u t i o n o f f l o a t i n g  materials  can be e a s i l y a l t e r e d , a p p a r e n t l y minor changes i n water movement c o u l d  155 r a d i c a l l y a l t e r seed d e p o s i t i o n and t h e r e s u l t a n t seed bank.  My r e s u l t s  show t h a t v a s t numbers o f seed a r e exported from t h e study s i t e ;  this  f a c t h e l p s t o e x p l a i n t h e r a p i d spread o f Z. j a p o n i c a and the wide o c c u r r e n c e o f R. m a r i t i m a .  Seed  viability "There a r e many f a c t o r s a c t i n g between seed d i s s e m i n a t i o n and seed  e s t a b l i s h m e n t which can a f f e c t the number o f i n d i v i d u a l s s u r v i v i n g i n p l a n t p o p u l a t i o n s " (Watkinson  1978).  Determining what these f a c t o r s  are and t h e i r e f f e c t s on v i a b l e seed numbers has been t h e major o b s t a c l e to t h e u s e o f b u r i e d seed i n f o r m a t i o n i n the study o f p o p u l a t i o n dynamics. The d e c l i n e s i n v i a b i l i t y o f new and o l d seed o f Z o s t e r a and Ruppia m a i n t a i n e d a t 5°C were s i m i l a r ; however, o l d seed b u r i e d i n t h e f i e l d d i e d o r was l o s t through g e r m i n a t i o n a t a much g r e a t e r r a t e than new seed was.  New seed was i n n a t e l y dormant and unable t o germinate d u r i n g  p a r t o f the b u r i e d p e r i o d have r e s u l t e d  (see f o l l o w i n g d i s c u s s i o n ) , a f a c t which may  i n i t s lower m o r t a l i t y .  C a u t i o n i s needed when r e l a t i n g  l a b o r a t o r y r e s u l t s t o those i n the f i e l d .  The r a t e o f seed death i n  the l a b o r a t o r y r e f l e c t e d a p p a r e n t l y autonomous causes o f death may have been d i f f e r e n t  from causes under f i e l d  l e n d support t o the o b s e r v a t i o n s o f Johnson  conditions.  which  These d a t a  (1975) who found t h a t t h e  decrease i n seed s u r v i v a l w i t h age i s n o t due t o the l o s s o f v i a b i l i t y , but t o e x t e r n a l f a c t o r s r e s u l t i n g i n g e r m i n a t i o n o r death by p r e d a t i o n . There a r e two environmental g r a d i e n t s i n t h e sediment which appear to a f f e c t seed p e r s i s t e n c e . i n temperature  First,  profile  there i s a d i f f e r e n c e  f l u c t u a t i o n between s u r f a c e and s u b s u r f a c e sediments  (see s e c t i o n 1 ) .  Turner (1933) suggested t h a t low s t a b l e  temperatures,  156 which are c h a r a c t e r i s t i c o f deeper s o i l depths i n many i n c r e a s e the p e r s i s t e n c e o f seed. have supported t h i s statement S t e i n b a u e r 1961, Lewis  environments,  Several studies besides t h i s  ( T o o l e and Brown 1946,  S c h a f e r and C h i l c o t e 1970,  one  D a r l i n g t o n and  Roberts and Feast  1972,  1973). More r e c e n t l y , Weaver and Cavers  a t i o n s near the s o i l  (1979) found temperature  fluctu-  s u r f a c e to be the main cause o f b u r i e d Rumex seed  g e r m i n a t i o n and thus d e p l e t i o n .  As w i l l be e l a b o r a t e d on i n the f o l l o w -  i n g s e c t i o n , f l u c t u a t i o n s i n s u r f a c e sediment  temperature may  play a  major r o l e i n the r a p i d d e p l e t i o n , through g e r m i n a t i o n o f Z o s t e r a and Ruppia seed from n e a r - s u r f a c e sediments. Secondly, t h e r e i s a g r a d i e n t i n redox p o t e n t i a l which  i n the  sediment  i m p l i e s a d e c r e a s i n g oxygen a v a i l a b i l i t y i n the sediment below the  s u r f a c e (see S e c t i o n 1 ) .  My r e s u l t s show t h a t a n a e r o b i c c o n d i t i o n s  the r a t e o f Z o s t e r a and Ruppia seed g e r m i n a t i o n . (1948), and Roberts  slow  Turner (1933), B i b b l y  (1972) have found t h a t low oxygen a v a i l a b i l i t y  dis-  couraged p r e c o c i o u s g e r m i n a t i o n o f seed and thus a i d e d i n i t s p e r s i s t e n c e . The e n f o r c e d dormancy o f seed i n a n a e r o b i c environments discussed l a t e r within this It i s d i f f i c u l t  will  be  section.  to determine how  my  r e s u l t s r e l a t e to b u r i e d seed  p o p u l a t i o n s i n o t h e r wetlands where t h e r e e x i s t marked g r a d i e n t s i n redox p o t e n t i a l , because o f l a c k o f i n f o r m a t i o n from these a r e a s .  It  has been known f o r some time t h a t t h e r e i s a postponement o f g e r m i n a t i o n o f seed i n a q u a t i c sediments.  Guppy (1897) showed t h a t g e r m i n a t i o n o f  some a q u a t i c seed can be d e l a y e d f o u r o r f i v e y e a r s w i t h o u t to i t s v i t a l i t y , w h i l e S h u l l  impairment  (1914) proved e x p e r i m e n t a l l y t h a t seed o f  many l a n d and water p l a n t s w i l l  germinate a f t e r b e i n g kept i n mud  water f o r p e r i o d s o f f o u r to seven y e a r s .  and  157 Few attempts have been made t o determine the reasons f o r seed p e r s i s t e n c e i n wet a r e a s .  I t i s known, however, t h a t reduced oxygen  p r e s s u r e s do not impede t h e g e r m i n a t i o n o f a l l seed.  Morigaga  found t h a t by r e p l a c i n g the a i r around Typha l a t i f o l i a n i t r o g e n , g e r m i n a t i o n percentages i n c r e a s e d . Morigaga,  seed o f few s p e c i e s i s encouraged  (1926)  L. seed w i t h  Even i f , as admitted by to germinate i n t h i s way,  Typha p r o v i d e s example enough not t o make g e n e r a l i z a t i o n s about the f a c t o r s which  e n f o r c e dormancy i n wetland  seed.  The s p e c i f i c causes o f Z o s t e r a and Ruppia seed m o r t a l i t y w i t h i n the sediment were d i f f i c u l t  to-determine, i n p a r t because o f the r a p i d  deterioration of soft tissue. sediment  temperatures  p r o b a b l y had l i t t l e  Because g e r m i n a t i o n i s u n l i k e l y a t w i n t e r  (around 5°C, see f o l l o w i n g d i s c u s s i o n ) , g e r m i n a t i o n  t o do w i t h t h e n e a r l y complete m o r t a l i t y o f seed  b u r i e d near the s u r f a c e by February.  A more f e a s i b l e e x p l a n a t i o n would be  t h a t t h e m o r t a l i t y r e s u l t e d from p h y s i c a l damage t o t h e seed by t h e r e p e a t e d f r e e z i n g observed i n s u r f a c e sediments a t Roberts Bank i n t h e winter. April  Germination o c c u r s n a t u r a l l y i n t h e f i e l d  between February and  (see f o l l o w i n g d i s c u s s i o n ) , and thus was a major means o f b u r i e d  seed d e p l e t i o n i n t h a t  period.  S p e c i f i c seed p r e d a t o r s have not been i d e n t i f i e d , a l t h o u g h as found i n t e r r e s t r i a l s i t u a t i o n s , f u n g a l pathogens  may p l a y a r o l e i n the d e p l e -  t i o n o f seed (Harper e t a l . 1961, Lawrence and Rediske 1962, T a y l o r s o n 1970).  Fungal d e g r a d a t i o n o f seagrass seed may be a i d e d by mechanical  i n j u r y t o seed r e s u l t i n g from s h i f t i n g o f sediments. the  I t i s not known i f  apparent p r e d a t i o n t h a t took p l a c e w h i l e seed was a t t a c h e d t o t h e  v e g e t a t i v e p l a n t s o c c u r r e d w i t h i n the sediment as w e l l .  158 I t i s p o s s i b l e t h a t causes than those f o r Ruppia.  o f Z o s t e r a seed d e p l e t i o n a r e d i f f e r e n t  Sarukhan (1974) found dramatic  d i f f e r e n c e s i n the  f a t e s o f seed from t h r e e Ranunculus s p e c i e s i n terms o f p r e d a t i o n and decay.  There i s now  c o n s i d e r a b l e evidence t h a t the c o n d i t i o n s under which  some seed r i p e n p l a y a r o l e i n d e t e r m i n i n g t h e i r l o n g e v i t y ( T a y l o r s o n 1970).  G e n e t i c v a r i a t i o n w i t h i n a p o p u l a t i o n can a l s o a f f e c t  viability  ( S t e i n e r 1968, Sawhney and N a y l o r 1979).  out t h a t i t may  Harper (1965) p o i n t s  be i n c o r r e c t to assume t h a t the dormancy and  c h a r a c t e r i s t i c s o f seed from the same p l a n t are P a t t e r n s o f seed s u r v i v a l  i n the s o i l  i n t e r e s t , but o f g r e a t p r a c t i c a l date few attempts  importance  seed  germination  alike.  are not o n l y o f e c o l o g i c a l to a g r i c u l t u r a l i s t s , but to  have been made to a n a l y z e the parameters o f b u r i e d seed  p e r s i s t e n c e and d e p l e t i o n .  S c h a f e r and C h i l c o t e  (1969) p r e s e n t e d a model  which p r o v i d e s a c o n c e p t u a l framework f o r problems i n v o l v i n g b u r i e d  seed.  I t simply s t a t e s t h a t the t o t a l b u r i e d seed p o p u l a t i o n o f a s p e c i e s a t a p o i n t i n time i s equal t o the number o f seed i n a s t a t e o f e n f o r c e d dormancy, p l u s the number i n i n n a t e and undergoing  g e r m i n a t i o n , and  induced dormancies, the number  the number which have l o s t v i a b i l i t y .  Roberts  (1972) expanded S c h a f e r ' s and C h i l c o t e ' s model t o d i f f e r e n t i a t e p e r s i s t e n c e by i n n a t e v s . induced dormancies, d e p l e t i o n through  g e r m i n a t i o n o f seed  from deep v s . shallow depths, and death by a g i n g o f seed v s . death predation.  by  To date, n e i t h e r model has advanced our knowledge o f the means  o f seed d e p l e t i o n i n the sediment p a r t l y because i t i s d i f f i c u l t  to  d i s t i n g u i s h between l o s s o f seed by p r e d a t i o n , p h y s i o l o g i c a l aging or g e r m i n a t i o n , thus d e f e a t i n g a major o b j e c t i v e o f the model (e.g., Rampton and  Ching  1970).  159 Because germination  has r e p e a t e d l y been found  o f b u r i e d seed d e p l e t i o n (Roberts  t o be a major cause  1972, Watkinson 1978, Weaver and  Cavers 1979), t h e key t o understanding  and p r e d i c t i n g p a t t e r n s o f  b u r i e d seed d e p l e t i o n l i e s w i t h o b t a i n i n g i n f o r m a t i o n on how  seed  i n t e r a c t with f a c t o r s which can l e a d t o v a r i o u s p e r i o d s and degrees o f dormancies.  On the o t h e r hand, attempts t o q u a n t i f y p r e d a t i o n on seed  may be u n r e a l i s t i c ,  f o r i t l i k e l y v a r i e s g r e a t l y i n both time and space  as p r e d a t o r p o p u l a t i o n s and food s u p p l i e s change. U n f o r t u n a t e l y , because seed b u r i a l experiments were conducted d u r i n g o n l y p a r t o f t h e year, extended p r e d i c t i o n s o f Z o s t e r a and Ruppia b u r i e d seed d e p l e t i o n cannot be made.  M o r t a l i t y d u r i n g the  summer i s p o s s i b l y q u i t e d i f f e r e n t than t h a t experienced  i n the w i n t e r .  I t i s i n t e r e s t i n g to c o n s i d e r , however, t h a t a small p o r t i o n o f t h e more deeply b u r i e d Z o s t e r a and Ruppia seed does s u r v i v e i n excess o f a year and may c o n t r i b u t e i n p a r t t o f u t u r e g e n e r a t i o n s means o f p o p u l a t i o n r e - e s t a b l i s h m e n t f a i l u r e by t h e most c u r r e n t  Germination "One  i n the case o f seed  and s e e d l i n g r e c r u i t m e n t  o f the most c r i t i c a l  o f halophytes  understood"  production  generation.  stages  i n the l i f e c y c l e o f halophytes  (or any p l a n t ) i s the p e r i o d o f g e r m i n a t i o n behavior  o r a c t as a  and e s t a b l i s h m e n t .  The  a t t h i s stage o f development i s r a t h e r p o o r l y  (Waisel 1972, quoted by Ungar 1978) .  The g e r m i n a t i o n o f  Z o s t e r a and Ruppia r e q u i r e s t h e removal o f a t l e a s t one, and p o s s i b l y two,  types o f dormancy.  dormancy t e r m i n o l o g y  Because much c o n f u s i o n h i s t o r i c a l l y  (Roberts  surrounds  1972), i t i s advantageous, i f n o t n e c e s s a r y ,  to d e f i n e what i s meant by v a r i o u s types o f dormancy.  Three types o f  160 dormancy ( i n n a t e , induced, and enforced) a r e now  r e c o g n i z e d (Harper  1957) . Innate dormancy i s t h a t which i s p r e s e n t when the new ceases to grow w h i l e i t i s s t i l l 1972).  embryo  a t t a c h e d to the p a r e n t p l a n t  (Roberts  Such a dormancy p r e v e n t s the seed from g e r m i n a t i n g u n t i l  dispersed.  A f t e r a seed has  o f dormancy may  be induced.  l o s t i t s i n n a t e dormancy, a s i m i l a r Induced  i t is type  dormancy i s u s u a l l y the r e s u l t  the seed b e i n g s u p p l i e d w i t h water, but i n an environment other f a c t o r i s unfavorable f o r germination.  of  where some  I t i s the p e r s i s t e n c e o f  induced dormancy a f t e r i n h i b i t o r y f a c t o r s have been removed which d i s t i n g u i s h e s i t from e n f o r c e d dormancy. Seed o f Z o s t e r a and Ruppia are shed i n n a t e l y dormant. o f i n n a t e dormancy may surrounding t i s s u e s  The b r e a k i n g  i n v o l v e f u r t h e r development o f the embryo o r  (Harper 1957).  This " a f t e r - r i p e n i n g " process  was  m a n i f e s t e d i n seed o f Z o s t e r a and Ruppia, as i t i s i n most p l a n t s ( K o l l e r et a l . 1962), as a g r a d u a l r e l a x a t i o n i n the s t r i c t n e s s o f requirements f o r subsequent o f g e r m i n a t i o n o f new  germination.  F i g u r e 23 shows a r e d u c t i o n  Z o s t e r a and Ruppia seed by h i g h s a l i n i t i e s i n  January; by February, g e r m i n a t i o n c o u l d take p l a c e i n a l l v i a b l e seed a t 27 o/oo  as i n d i c a t e d by the r e s u l t s o f T a b l e V I I .  A r a s a k i (1950b)  a l s o noted t h a t seed o f Z. j a p o n i c a c o l l e c t e d i n the summer would not germinate u n t i l sediments  the f o l l o w i n g January to March.  a t Roberts Bank germinated  o f p e r s i s t e n c e was Kidd  Old seed r e c o v e r e d from  r e a d i l y , i n d i c a t i n g t h a t t h e i r means  an e n f o r c e d r a t h e r than an induced dormancy.  (1941), Bibbey  (1948), Thornton  (1945), and K e l l e r e t a l .  (1962) have suggested t h a t the r a i s e d carbon d i o x i d e and lowered oxygen c o n c e n t r a t i o n s i n the s o i l  atmosphere are l a r g e l y r e s p o n s i b l e f o r  m a i n t a i n i n g the e n f o r c e d dormancy o f b u r i e d seed.  Although carbon  d i o x i d e l e v e l s were not monitored, my r e s u l t s show the r a p i d  germina-  t i o n o f Z o s t e r a and Ruppia seed i n a f a v o r a b l e temperature regime  can  be slowed, and the amount p o s s i b l y reduced, by r e p l a c i n g the atmosphere with nitrogen.  T h i s suggests t h a t a n a e r o b i c c o n d i t i o n s a l o n e a d v e r s e l y  a f f e c t the g e r m i n a t i o n o f Z o s t e r a and Ruppia seed. of the  The lowest depth  seed g e r m i n a t i o n a t Roberts Bank corresponded a p p r o x i m a t e l y w i t h boundary  between a e r o b i c and a n a e r o b i c sediments.  This lends  support to the h y p o t h e s i s t h a t w i t h i n a n a e r o b i c sediments, seed o f Z o s t e r a and Ruppia were e n f o r c e d i n t o dormancy.  Although experimental  b u r i a l s o f seed i n d i c a t e d h i g h w i n t e r m o r t a l i t y a t 5 cm below the s u r f a c e o f the sediment, F i g u r e 29 shows t h a t some seed a t t h a t depth s u r v i v e d to c o n t r i b u t e to the f l u s h o f g e r m i n a t i o n i n the l a t e w i n t e r and  spring. S e v e r a l mechanisms f o r a n a e r o b i c i n h i b i t i o n o f g e r m i n a t i o n have  been suggested, i n c l u d i n g inadequate s u p p l i e s o f oxygen f o r embryo respiration  (Thurston 1960), and more r e c e n t l y the s t i m u l a t o r y  of  oxygen have been a t t r i b u t e d to i t s p a r t i c i p a t i o n i n the  of  some endogenous i n h i b i t o r It  inactivation  ( K o l l e r et a l . 1962).  i s w e l l r e c o g n i z e d t h a t abnormally h i g h atmospheric c o n c e n t r a -  t i o n s o f carbon d i o x i d e o r o t h e r u n i d e n t i f i e d gaseous are  inhibitors  m e t a b o l i c p r o d u c t s from the seed or from microorganisms  Wareing  effects  1969)  (Wesson and  are i n v o l v e d i n the dormancy o f many s p e c i e s o f seed  (Kozlowski 1972).  Harper  (1957) suggested t h a t e s p e c i a l l y where s o i l  pores are s m a l l and s o i l water c o n t e n t i s h i g h , the l o c a l atmospheres  which  micro-  ( l i k e those s u r r o u n d i n g a seed i n the s o i l ) may  become exhausted, o f oxygen and r e p l a c e d by carbon d i o x i d e .  quickly  162 The replacement o f oxygen w i t h carbon d i o x i d e i n c r e a s e s w i t h depth and can be v e r y marked i n wet  soils  (Russell  1973).  down through the Roberts Bank sediment p r o f i l e ,  Thus as seed moves  by animal a c t i v i t y  o t h e r d i s t u r b a n c e , from a e r o b i c to a n a e r o b i c atmospheres, e f f e c t s d e s c r i b e d by Kidd (1941), T h o r t o n (1945), Bibbey R o l l e r et a l . (1962) would become i n c r e a s i n g l y  or  the dormancy (1948) and  pronounced.  The seed g e r m i n a t i o n o f a g r e a t number o f s p e c i e s i s i n f l u e n c e d by i r r a d i a t i o n now  w i t h white l i g h t  ( K a r r s s e n 1970)  a r e c o g n i z e d form o f dormancy c o n t r o l  1977).  i n many s p e c i e s (McDonough  Seed o f Z o s t e r a and Ruppia were found to be t o t a l l y  photoblastic as was  and absence o f l i g h t i s  non-  ( g e r m i n a t i o n took p l a c e i n l i g h t as w e l l as i n darkness)  seed o f Z o s t e r a marina  (R.C. P h i l l i p s p e r s o n a l  communication).  A p o s i t i v e p h o t o b l a s t i c response i n seagrass seed would be maladaptive because  i t would r e s u l t  e s t a b l i s h m e n t may  i n s e e d l i n g s a t the sediment  s u r f a c e where  be p r e v e n t e d by a p o o r l y anchored r o o t system, and the  r i s k o f d r y i n g would be g r e a t . The i n c r e a s e d r a t e s o f g e r m i n a t i o n caused by the s c o r i n g o f seed c o a t s c o u l d be due to a r e l e a s e from water uptake r e s t r i c t i o n s a l e s s e n i n g o f the mechanical r e s i s t a n c e to embryo expansion by the seed c o a t . seed was  imposed  The r e c o v e r y o f g e r m i n a t i o n i n d i s t i l l e d water  soaked i n seawater w i t h i n h i b i t o r y  c a t e s t h a t no permanent s p e c i f i c i n f l u e n c e o f excess s a l t s may Temperature  or to  after  s a l t concentrations i n d i -  ion toxicity  o c c u r s and t h a t the c h i e f  be osmotic.  e x e r t e d a powerful i n f l u e n c e , as d i d s a l i n i t y , on the  a b i l i t y to germinate and the r a t e o f g e r m i n a t i o n o f both Z o s t e r a and Ruppia seed.  Verhoeven  (1979) found t h a t g e r m i n a t i o n o f R. m a r i t i m a  seed took p l a c e s i m u l t a n e o u s l y when water temperatures  exceeded  the  d a i l y minimum-maximum i n t e r v a l o f 10 to 15°C. e s t a b l i s h e d t h a t temperature was  Setchell  (1924) a l s o  the c o n t r o l l i n g f a c t o r i n R. m a r i t i m a  seed g e r m i n a t i o n , the optimum o c c u r r i n g between 10 and 18°C.  Arasaki  (1950b) found t h a t seed o f Z. j a p o n i c a would germinate i n water  temper-  a t u r e s from 1 to 10°C; however, based on my o b s e r v a t i o n s o f Z.  japonica,  I would not expect g e r m i n a t i o n t o take p l a c e at o r below  Perhaps  5°C.  the seed A r a s a k i used d i f f e r e d from mine g e n o t y p i c a l l y , or s i n c e i n g environmental c o n d i t i o n s d u r i n g development  differ-  and i n n a t e dormancy can  i n f l u e n c e the g e r m i n a t i o n r e q u i r e m e n t s o f seed (Kozlowski 1972), perhaps the environment t h a t the seed A r a s a k i used was germinate a t 1°C.  Sediment  exposed to a l l o w them to  temperatures underwent a marked  increase  when the lowest low t i d e s switched from n i g h t to day i n e a r l y March (see S e c t i o n 1 ) .  The n a t u r a l g e r m i n a t i o n o f Z o s t e r a and Ruppia seed  at Roberts Bank c o i n c i d e d w i t h , and was  probably a d i r e c t r e s u l t of,  the i n c r e a s e i n sediment temperature. Poor s e e d l i n g e s t a b l i s h m e n t a t s t a t i o n 1 as compared to s t a t i o n s 2 and 3 i n March was 1).  l i k e l y a r e s u l t o f b u r i a l by sand waves (see S e c t i o n  S e v e r a l s e e d l i n g s were found f r e e - f l o a t i n g o r l y i n g on the sediment  s u r f a c e , a p p a r e n t l y d i s l o d g e d from the sediment a f t e r g e r m i n a t i o n ; t h i s c o u l d be a major source o f m o r t a l i t y o f seeds g e r m i n a t i n g near or on the sediment s u r f a c e .  The s e e d l i n g s which appeared a f t e r the major  f l u s h o f g e r m i n a t i o n (March t o May(?)) may  r e p r e s e n t seed which were  under e n f o r c e d dormancy a t a deep, a n a e r o b i c sediment depth and were r e l e a s e d from dormancy by t r a n s p o r t to a e r o b i c sediments through animal activity.  164 SUMMARY The  o b j e c t i v e o f t h i s study was n o t t o make a p r e c i s e i n v e n t o r y o f  components i n the p o p u l a t i o n s , but t o i d e n t i f y some o f t h e p r o c e s s e s which a f f e c t p o p u l a t i o n numbers, so t h a t changes o r d i f f e r e n c e s i n intertidal The  seagrass  processes  p o p u l a t i o n s can be b e t t e r p r e d i c t e d and e x p l a i n e d .  t h a t c o n t r o l t h e numbers i n a p o p u l a t i o n a r e t i g h t l y  i n t e g r a t e d and i n v a r i a b l y complex. The  f o l l o w i n g a r e some g e n e r a l c o n c l u s i o n s c o n c e r n i n g the  maintenance o f Z o s t e r a j a p o n i c a and Ruppia maritima Roberts Bank. determining  populations at  The amount o f exposure t o the a i r was a major i n f l u e n c e  the b e h a v i o r  o f shoot  flux.  s m a l l e r w i t h i n c r e a s e d time o f exposure.  Peak shoot  d e n s i t i e s were  Z o s t e r a w i t h the g r e a t e s t  exposure to the a i r r e t a i n e d a l a r g e r p r o p o r t i o n o f shoots  produced  e a r l y i n the growing season than d i d Z o s t e r a a t l e s s e r exposures.  Ruppia  r e t a i n e d a l a r g e p r o p o r t i o n o f e a r l y shoots r e g a r d l e s s o f exposure  level.  Z o s t e r a and Ruppia w i t h the g r e a t e s t exposure a l s o had a l a r g e r proport i o n o f shoots than v e g e t a t i v e  which f l o w e r e d .  Shoots t h a t f l o w e r e d u s u a l l y l i v e d  shoots.  Phases o f growth, v e g e t a t i v e , r e p r o d u c t i v e , and q u i e s c e n t c o u l d be r e c o g n i z e d  i n shoot  Ruppia shoots  During  (Zostera),  s u r v i v o r s h i p and morphology o f both  Deevey Type I s u r v i v o r s h i p curves were c h a r a c t e r i s t i c o f both and  longer  species.  Zostera  ( p r i m a r i l y v e g e t a t i v e ) e a r l y i n the growing season.  t h e r e p r o d u c t i v e phase, s u r v i v o r s h i p curves were o f Deevey Types  II o r I I I ; shoots produced as Z o s t e r a entered  the quiescent  showed a Deevey Type I p a t t e r n o f s u r v i v o r s h i p .  phase  Leaves and newly  produced rhizome i n t e r n o d e s were l o n g e r i n the e a r l y , p r i m a r i l y v e g e t a t i v e , phase; soon a f t e r p l a n t s began t o f l o w e r , new l e a f and  165 rhizome  internode lengths declined.  developed s h o r t , t h i n l e a v e s .  Z o s t e r a shoots e n t e r i n g q u i e s c e n c e  Each phase o f growth o c c u r r e d i n Ruppia  s i m u l t a n e o u s l y r e g a r d l e s s o f the amount o f exposure; i n Z o s t e r a , however, phases began e a r l i e r a t the g r e a t e s t  exposure.  Seed p r o d u c t i o n o f Z o s t e r a and Ruppia d e c r e a s e d w i t h i n c r e a s i n g exposure t o the a i r .  S p e c i f i c f a c t o r s i n f l u e n c i n g seed p r o d u c t i o n v a r i e d  between s p e c i e s and w i t h time.  In g e n e r a l , seed p r o d u c t i o n f l u c t u a t e d  w i t h the s u c c e s s o f i n d i v i d u a l o v a r i e s i n p r o d u c i n g mature seed and w i t h f l o w e r i n g shoot d e n s i t y .  Most seed was  e x p o r t e d from the s i t e o f  p r o d u c t i o n by the d r i f t i n g o f detached f l o w e r i n g s h o o t s . Z o s t e r a and Ruppia seed d i s p e r s e d through the summer and f a l l p r e v e n t e d from g e r m i n a t i n g f i r s t by i n n a t e dormancy, a c o n d i t i o n  was  which  e x p i r e d by January, and then p r i m a r i l y by low w i n t e r temperatures. b u r i e d near the s u r f a c e o f the sediment  Seed  s u f f e r e d high overwinter mortali-.  t i e s p o s s i b l y l i n k e d w i t h the f r e e z i n g o f sediments.  Mortality  was  g e n e r a l l y reduced w i t h depth, owing most l i k e l y t o a combination o f f a c t o r s which i n c l u d e d an i n c r e a s i n g l y a n a e r o b i c environment  o r unknown  carbon d i o x i d e e f f e c t r e s u l t i n g i n an e n f o r c e d dormancy.  The g e r m i n a t i o n  of  seed was  emerging  p r e v e n t e d by l o c a l seawater s a l i n i t i e s o n l y when seed  from i n n a t e dormancy.  The n a t u r a l g e r m i n a t i o n o f seed  s t i m u l a t e d by the warming o f sediment  the sediment  c o n f i n e d t o a e r o b i c sediments.  e n f o r c e d dormancy i n a n a e r o b i c sediment through A p r i l  was  i n March which o c c u r r e d a f t e r a  p r e d i c t a b l e a l t e r a t i o n i n t i d e s exposed Germination was  was  t o the midday sun.  Seed remained  year-round.  New  under  s e e d l i n g s emerged  and p o s s i b l y as l a t e as June, but o n l y a s m a l l p o r t i o n  became e s t a b l i s h e d . contributed l i t t l e  Z o s t e r a shoots a r i s i n g from o v e r w i n t e r i n g rhizomes t o the r e - e s t a b l i s h m e n t o f the growing p o p u l a t i o n .  166 T h i s work began w i t h the r e c o g n i t i o n t h a t p o p u l a t i o n s o f j a p o n i c a and  R. maritima  c o n s i s t o f growing and  t h a t i n o r d e r to understand both  produced the observed t h e r e was  The  are  maintained,  demographic approach to  population.  Until  such i n f o r m a t i o n was  the  gathered,  to e x p l a i n changes i n the numbers  Shoot demography, d e s p i t e i t s time-consuming  l i k e l y p l a y a prominant r o l e i n f u t u r e i n v e s t i g a t i o n s i n t o  dynamics o f seagrass  and  i n f o r m a t i o n on the u n d e r l y i n g f l u x e s which  l i t t l e hope i n b e g i n n i n g  in a population.  seed components,  p o p u l a t i o n s a r i s e and  components must be c o n s i d e r e d .  study o f shoots p r o v i d e d  will  how  Z.  populations.  Laboratory  nature, the  s t u d i e s p r o v i d e d much a i d  i n i n t e r p r e t i n g f i e l d i n v e s t i g a t i o n s i n t o the p e r s i s t e n c e and d e p l e t i o n of  seed.  the seed should  Future s t u d i e s aimed a t a more comprehensive u n d e r s t a n d i n g i n the p o p u l a t i o n maintenance o f Z. j a p o n i c a and  focus on long-term  i n t o how  specific  seed b u r i a l  environmental  R.  maritima  experiments and i n v e s t i g a t i o n s  c o n d i t i o n s i n f l u e n c e seed l o n g e v i t y .  of  167 LITERATURE  CITED  A n t o n o v i c s , J . 1972. P o p u l a t i o n dynamics o f the grass Anthoxanthum odoratum on a z i n c mine. J . E c o l . 60:351-365. A n t o n o v i c s , J . 1976. The n a t u r e o f l i m i t s t o n a t u r a l s e l e c t i o n . of the M i s s o u r i Bot. Garden 63:224-247.  Ann.  Adams, M.W. 1967. 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P o p u l a t i o n dynamics o f two p e r e n n i a l g r a s s e s i n A u s t r a l i a n semi-arid grassland. J . Ecol. 58:869-875. Yamanaka, K. 1975. Primary p r o d u c t i v i t y o f the F r a s e r R i v e r d e l t a f o r e shore: Y i e l d estimates o f emergent v e g e t a t i o n . M.Sc. T h e s i s . U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, B.C. Zieman, J.C. 1974. Methods f o r t h e study o f the growth and p r o d u c t i o n o f t u r t l e g r a s s , T h a l a s s i a i testudinum Ko'nig. A q u a c u l t u r e 4:139-142. Zieman, J.C. and R.G. W e t z e l . 1980. P r o d u c t i v i t y i n s e a g r a s s e s : Methods and r a t e s , p.87-116. Iri_ R.C. P h i l l i p s and C P . McRoy, eds. Handbook o f seagrass b i o l o g y : An ecosystem p e r s p e c t i v e . Garland STPM P r e s s , New York.  Appendix  1.  Taxonomy o f Z o s t e r a  japonica  177 INTRODUCTION  In  1957,  a thin-leaved, i n t e r t i d a l  N. H o t c h k i s s i n W i l l a p a Bay, Washington was  s e a g r a s s was  collected  ( H i t c h c o c k et a l . 1969).  the f i r s t r e c o r d o f a member o f the Z o s t e r a subgenus  growing i n North America.  (45°24'N;  and as f a r n o r t h as B u r r a r d I n l e t , Vancouver, B r i t i s h  This  Zosterella  S i n c e then, i t has been found on mud  f l a t s r a n g i n g as f a r south as N e t a r t s Bay, Oregon  (49°17'N;  by  and sand  124°53'W)  Columbia  123°13'W).  H i t c h c o c k et a l . (1969) i d e n t i f i e d the H o t c h k i s s c o l l e c t i o n as Z o s t e r a nana Roth, a now the  i n v a l i d name which a t the time i n c l u d e d a l l o f  Z o s t e r e l l a s p e c i e s used i n t h i s study.  In a monograph o f w o r l d s e a -  g r a s s e s , den Hartog (1970), d e s c r i b e d the H o t c h k i s s specimens as a s p e c i e s , based p r i m a r i l y on r e t i n a c u l a spadix) and l e a f t i p morphology.  new  ( s t e r i l e f l a p s on t h e f l o w e r i n g  He named the s p e c i e s Z o s t e r a americana  den H a r t o g . P h i l l i p s and Shaw (1976) compared specimens o f Z. americana from f o u r Washington  c o l l e c t i o n s with a v e g e t a t i v e c o l l e c t i o n o f Z o s t e r a  n o l t i i Hornem. from England, and den Hartog's i l l u s t r a t i o n s o f Z.  noltii.  They found t h a t l e a f t i p s and r e t i n a c u l a i n Z. americana were too v a r i a b l e t o d i f f e r e n t i a t e i t from the European s p e c i e s , Z. n o l t i i . c h a l l e n g e d den Hartog's d e t e r m i n a t i o n o f Z. americana as a new and c o n c l u d e d Z. americana s h o u l d be c a l l e d Z. n o l t i i  until  They species,  further  i n v e s t i g a t i o n s c o u l d be conducted. Harrison  (1976), a l s o q u e s t i o n i n g den Hartog's d e t e r m i n a t i o n ,  compared r e t i n a c u l a and l e a f t i p c h a r a c t e r s from B r i t i s h  Columbia  c o l l e c t i o n s o f Z. americana w i t h den Hartog's i l l u s t r a t i o n s o f Z. j a p o n i c a  178 Aschers § Graebn. was  H a r r i s o n c o n c l u d e d t h a t the North American  Z. j a p o n i c a , p r o b a b l y i n t r o d u c e d from Japan by o y s t e r  species  growers.  B i o l o g i s t s have c a l l e d the North American Z o s t e r e l l a s p e c i e s any o f f o u r names, and a r e o f t e n unsure i f o t h e r r e s e a r c h e r s a r e r e f e r r i n g to the same s p e c i e s .  P r e v i o u s workers, t r y i n g to show t h e r e l a t i o n s h i p  between the North American Z o s t e r e l l a and i t s c l o s e r e l a t i v e s , have n e i t h e r q u a n t i f i e d s p e c i e s c h a r a c t e r i s t i c s nor examined to r e s o l v e the i s s u e .  The purpose o f t h i s study was  enough m a t e r i a l  to c l a r i f y  the  taxonomic p o s i t i o n o f Z o s t e r a americana, u s i n g n u m e r i c a l taxonomy.  METHODS F l o w e r i n g Z o s t e r e l l a specimens were c o l l e c t e d i n 5% (v/v) formaldehyde seawater.  Z o s t e r a americana was  W i l l a p a Bay on t h e southwest c o a s t o f Washington  (46°24'N,  and from Roberts Bank i n s o u t h e r n B r i t i s h Columbia Z o s t e r a n o l t i i was (51°37'N, Scotland Bay  and p r e s e r v e d  collected  from  123°57'W),  (49°02*N,  123°08'W).  c o l l e c t e d from Krabben Kreek, the N e t h e r l a n d s  04°03'E), and from the Tay E s t u a r y , on the east c o a s t o f (56°27'N,  (39°29'N,  Japan.  i n 1980,  02°53'W).  Z o s t e r a j a p o n i c a was  141°51'W) and Odawa Bay  (35°12'N,  c o l l e c t e d from Yamada  139°39'W)  i n central  A c o l l e c t i o n of. Z. c a p r i c o r n i A s c h e r s . from Smiths Bay,  South Wales (35°36'S,  137°27'E), was  also  C h a r a c t e r s o f the Z o s t e r e l l a subgenus  New  examined. used i n den Hartog's monograph  which appeared to d i f f e r e n t i a t e taxa were chosen f o r q u a n t i f i c a t i o n (see T a b l e XII and F i g . 31).  Three new  c h a r a c t e r s which v a r i e d between  s p e c i e s were a l s o measured (see T a b l e X I I , c h a r a c t e r s 4, 5 and 16). minimize c h a r a c t e r d i f f e r e n c e s due t o age, o n l y specimens  i n which  had d e h i s c e d but o v u l e s had not e l o n g a t e d were s e l e c t e d .  The f i r s t  To pollen 12  Table XII:  Mean c h a r a c t e r values and standard d e v i a t i o n s o f four species i n the Zostera subgenus,  Z. n o l t i i  Characters  X 1. No. o f female flowers w i t h i n spathe 2. Retinaculum  length, mm  3. Retinaculum width,  X  S  s (1.00)  (.42)  .97  (.10)  1. 31  (.11)  (.08)  .59  (.06)  83  (.25)  .21  (.03)  37  (.02) (.01)  (.17)  74  (.06)  57 17  (.04)  (.02)  14  (.02)  .15  (.02)  10  (.23)  1. 96  (.39)  2.21  (.30)  2. 79  (.34)  22. 17  (3.56)  19.,17  (3.95)  6.,17  (1.53)  2..42  (.26)  5. Thickness of spathe at midrib, mm  .11  7. Spathe length, mm  14.58  (7.07)  23.,54  (2.39)  18.29  (5.27)  8. Prophyllum length, mm  22.79  (33.96)  20..04  (3.67)  15.42  (4.88)  (5.93)  8..25  (2.60)  8.17  11.87  X; 6. 58  .94  (.02)  9. Generative l e a f length, mm  Z. c a p r i c o r n i  (1.78)  (1.34)  1.58  Z. j aponica  5.67  6. 67  .10  mm  S  (1.00)  4. Thickness of spathal corners, mm  6. Spathe width,  X"  3.13  .33  mm  S  Z. americana  Zosterella.  (3.37) .  1.64  (.49)  1.35  (.28)  1.33  (.26)  .11  (.02)  .13  (.03)  .14  (.02)  .12  (.03)  12. No. of accessory f i b r e bundles between mid and l a s t l a t e r a l nerves, gen. l e a f  4.71  (.90)  4 .17  (.86)  5.42  (1.21)  5,.00  (1.12)  13. No. o f accessory f i b r e bundles ext. to marginal nerves, gen. l e a f  1.25  (.44)  3 .42  (1.02)  3.50  (.83)  1 .33  (.65)  14. No. of accessory f i b r e bundles between mid and l a s t l a t . nerves, spathal sheath  5.33  (.96)  4 .58  (.97)  6.37  (.44)  6 .25  (.14)  15. No. accessory f i b r e bundles ext. to marginal nerves, spathal sheath  9.71  (2.91)  4 .21  (1.18)  9.96  (2.53)  3 .25  ' (.96)  16. Length to width r a t i o o f retinaculum  2.94  (.60)  1 .80  (.26)  1.65  (.25)  1.44  (.30)  10. Generative l e a f width,  mm  11. Thickness of gen. l e a f at midrib, mm  31. shoot  C h a r a c t e r s used to d i f f e r e n t i a t e Z o s t e r e l l a t a x a . showing  g e n e r a t i v e l e a f , spathe,  and prophyllum.  showing the p o s i t i o n s of r e t i n a c u l a and have been o m i t t e d . Generative  C.  Retinaculum.  leaf cross section.  numbers from T a b l e I .  A. B.  Spadix  female f l o w e r s ; male f l o w e r s  D.  Spathe c r o s s s e c t i o n . E.  Numbers r e f e r to c h a r a c t e r  Drawings not to  Flowering  scale.  181 specimens encountered from each c o l l e c t i o n which were complete, nondeformed, and met the age c r i t e r i o n , were used f o r m i c r o s c o p i c and m a c r o s c o p i c s e t s o f c h a r a c t e r measurements. To o b t a i n measurements on anatomical embedded  in paraffin  micrometers.  (Feder and O'Brien,  From p r e p a r e d  slides,  c h a r a c t e r s , specimens were 1968) and s e c t i o n e d a t 12  seven c h a r a c t e r s  through 15) were measured under a c a l i b r a t e d compound Bulked  (4, 5, and 11 microscope.  specimens were grouped by c o l l e c t i o n s i t e , c r e a t i n g o p e r a t i o n a l  taxonomic u n i t s ( o t u ' s ) . Characters  from each s p e c i e s were compared u s i n g a n a l y s i s o f v a r i -  ance with a s i g n i f i c a n c e l e v e l o f 5%.  C h a r a c t e r d a t a f o r a l l specimens  were e v a l u a t e d u s i n g p r i n c i p a l components a n a l y s i s .  RESULTS T a b l e XII shows the mean v a l u e s o f c h a r a c t e r s f o r t h e f o u r s p e c i e s . Z o s t e r a n o l t i i was s i g n i f i c a n t l y d i f f e r e n t  from the o t h e r s p e c i e s f o r  9 o f the 16 c h a r a c t e r s ; Z o s t e r a americana and Z. j a p o n i c a were s i g n i f i c a n t l y d i f f e r e n t from the o t h e r s p e c i e s , but not from each o t h e r , for  c h a r a c t e r s 3, 10, and 13. In the p r i n c i p a l  of  the t o t a l v a r i a n c e .  components a n a l y s i s , component 1 accounted f o r 28% The main c o n t r i b u t o r s to component 1 i n o r d e r o f  d e c r e a s i n g importance were r e t i n a c u l u m width,  the r e t i n a c u l u m  width r a t i o , and the t h i c k n e s s o f the s p a t h a l c o r n e r s .  l e n g t h to  These were  f o l l o w e d by s p a t h a l sheath width and number o f female f l o w e r s . The separated noltii  t h r e e c h a r a c t e r s with t h e h e a v i e s t l o a d i n g s on component 1 Z. j a p o n i c a and Z. americana from the o t h e r s p e c i e s .  Zostera  r e t i n a c u l a were l o n g and t h i n , g i v i n g them a h i g h l e n g t h to width  182 ratio  (Table X I I ) . Z o s t e r a c a p r i c o r n i r e t i n a c u l a d i d n o t have a s i g n i f -  i c a n t l y s m a l l e r l e n g t h t o width r a t i o than Z. j a p o n i c a r e t i n a c u l a , b u t they were s i g n i f i c a n t l y l a r g e r .  The mean t h i c k n e s s e s o f s p a t h a l  corners  were s i g n i f i c a n t l y d i f f e r e n t f o r a l l f o u r s p e c i e s , but the mean v a l u e s for  Z. americana and Z. j a p o n i c a spathes were most s i m i l a r  (see T a b l e X I I ,  c h a r a c t e r 4, and F i g . 32). P r i n c i p a l component 1 v a l u e s were p l o t t e d a g a i n s t component 2 values  f o r individual plants  ( F i g . 33). Together, these  accounted f o r 45% o f t h e t o t a l v a r i a n c e . c o r n i c l e a r l y separated  components  Zostera n o l t i i  and Z. c a p r i -  from t h e o t h e r s ; Z. americana and Z. j a p o n i c a  overlapped.  DISCUSSION  It  i s my judgment, based on PCA r e s u l t s and s i m i l a r i t i e s o f major  c h a r a c t e r s , t h a t Z o s t e r a americana and Z o s t e r a j a p o n i c a a r e t h e same species.  The wide spread  o f p o i n t s i n t h e Z. j a p o n i c a - Z .  americana c l u s t e r  ( F i g . 33) i l l u s t r a t e s the p l a s t i c i t y o f t h i s taxon; i t has a l s o been shown that other  seagrass  d i f f e r i n climate  taxa vary morphologically  (McMillan  1978).  Zostera n o l t i i  range o f p o i n t s between i t s two c o l l e c t i n g In h i s monograph, den Hartog  when grown i n areas  which  displayed a similar  sites.  (1970) emphasized s p e c i e s d i f f e r e n c e s  i n l e a f t i p and r e t i n a c u l a r morphology i n a key t o Z o s t e r e l l a s p e c i e s and  through i l l u s t r a t i o n .  I found l e a f t i p morphologies were too v a r i -  a b l e w i t h i n each o f my c o l l e c t i o n s t o use as d i s t i n g u i s h i n g c h a r a c t e r istics.  Phillips  (1960) found t h a t l e a f t i p s , used to d i s t i n g u i s h  s p e c i e s o f the seagrass Harrison  D i p l a n t h e r a , v a r i e d w i t h t h e environment.  ( p e r s o n a l communication, 1981) observed t h a t r e t i n a c u l a r  183  Z.  Z.  Z.  Z.  32.  nolfii  ame  japonica  Capricorni  R e p r e s e n t a t i v e spathe  Nerve bundles  have been  cross sections of Z o s t e r e l l a  omitted.  taxa.  184  -2  •+-  e  t-  8  o  •• •  •o  •  -2  +  A  +  Fig.  33.  A  - 4  P r i n c i p a l component a n a l y s i s o f Z o s t e r e l l a  taxa;  p r o j e c t i o n s o f c h a r a c t e r s on components I and I I . • noltii  from Tay E s t u a r y ,  Scotland,  Kreek, The N e t h e r l a n d s , • U.S.A., •  Characters  Z. n o l t i i  Z. americana from Roberts Bank B.C.,  A  o  i n Table XII.  Canada,  WA,  •  Z. j a p o n i c a from Odawa  Z_. c a p r i c o r n i from Smiths Bay,  are l i s t e d  from Krabben  Z. americana from W i l l a p a Bay,  Z. j a p o n i c a from Yamada Bay, Japan, Bay, Japan,  v  Zostera  Australia.  185 morphology v a r i e d with age o f the specimen. by  I c o n t r o l l e d the age i n f l u e n c e  s e l e c t i n g p l a n t s o f t h e same stage o f r e p r o d u c t i o n ;  l e a f t i p characters  were n o t used. Because P h i l l i p s and Shaw (1976) l a c k e d f l o w e r i n g specimens o f Z. n o l t i i ,  they d i d not see c r o s s s e c t i o n s o f t h e spathes,  which a r e  d i s t i n c t l y d i f f e r e n t from those o f Z. americana ( F i g . 32). c o n t r o l c o u l d e x p l a i n t h e v a r i a b i l i t y they r e t i n a c u l a from d i f f e r e n t c o l l e c t i o n s .  Lack o f age  found between Z. americana  Immature Z. americana r e t i n a c u l a  a r e as narrow as mature Z. n o l t i i r e t i n a c u l a . Harrison  (1976) suggested t h a t Z. j a p o n i c a had been i n t r o d u c e d  Japan through t h e o y s t e r i n d u s t r y . B r i t i s h Columbia began i m p o r t i n g 1900s. and  growers i n Washington and  P a c i f i c Oysters  from Japan i n t h e e a r l y  By the 1930s, s u c c e s s f u l i n d u s t r i e s had developed i n Puget Sound,  e s p e c i a l l y i n W i l l a p a Bay on the Washington Coast  (1976) l i s t e d and  Oyster  from  8 animal s p e c i e s , a c c i d e n t a l l y i n t r o d u c e d  Puget Sound from Japan.  tors o f the P a c i f i c Scagel  i n t o W i l l a p a Bay  l i s t e d are p a r a s i t e s or preda-  Oyster.  from Japan t o Washington, Oregon, and southern  Columbia waters. i n t h e Northeast  attached  Most o f those  Sayce  (1956) r e p o r t e d t h a t Sargassum muticum (Yendo) F e n s h o l t had  been i n t r o d u c e d  Oyster beds.  ( E l s e y 1933) .  British  Sargassum, a common i n t e r t i d a l a l g a i n Japan, appeared P a c i f i c by t h e mid 1940s, o f t e n i n o r near P a c i f i c  By 1954, Sargassum was abundant i n n o r t h e r n W i l l a p a Bay,  to oyster  shells.  Z o s t e r a j a p o n i c a was p r o b a b l y  introduced to the Northeast  Pacific  as dormant seed, e i t h e r i n sediment a s s o c i a t e d with P a c i f i c O y s t e r s , o r attached  to adult p l a n t s .  There i s a n e c d o t a l  o y s t e r s were packed and shipped  evidence  t h a t Japanese  i n some s p e c i e s o f e e l g r a s s  (Harrison  186 1976).  Uprooted  p l a n t s can r e - e s t a b l i s h themselves,  not have s u r v i v e d t h e two-week l o n g voyage from  but would p r o b a b l y  Japan.  In t h i s study, s p e c i e s c h a r a c t e r i s t i c s which have p r e v i o u s l y o n l y been examined s u b j e c t i v e l y have been q u a n t i f i e d . and Shaw (1976) t h a t den Hartog based  I agree w i t h  t h e Z. americana  on a g e o g r a p h i c a l than a m o r p h o l o g i c a l b a s i s .  Phillips  d e s i g n a t i o n more  A f t e r e v a l u a t i n g PCA  r e s u l t s and o b s e r v i n g t h e s i m i l a r i t i e s o f major c h a r a c t e r i s t i c s , I conclude, as d i d H a r r i s o n (1976), t h a t Z. americana  i n t h e Northeast .  P a c i f i c a r e d i s j u n c t p o p u l a t i o n s o f Z. j a p o n i c a .  ACKNOWLEDGEMENTS  I thank E.A. Drew o f t h e G a t t y Marine  Lab.,  S t . Andrews, S c o t l a n d ,  R.P.M.W. Jacobs, o f t h e C e n t r a a l b u r e a u voor Schimmelcultures,  Baarn,  The N e t h e r l a n d s , V. H o l l a n d o f t h e Univ. o f New South Wales, Dept. o f Botany, A u s t r a l i a , and K. A i o i , o f t h e Ocean Res. Japan,  f o r c o l l e c t i n g and sending Z o s t e r a  I n s t . , Univ. o f Tokyo,  specimens.  LITERATURE CITED  E l s e y , C.R. 1933. O y s t e r s i n B r i t i s h Columbia. No. 34.  B i o l . Bd. Can. B u l l . ,  Feder, N. and T.P. O'Brien. 1968. P l a n t m i c r o t e c h n i q u e : some p r i n c i p l e s and new methods. Amer. J . Bot. 55:112-142. H a r r i s o n , P.G. 1976. Z o s t e r a j a p o n i c a (Aschers § Graebn.) i n B r i t i s h Columbia, Canada. S y e s i s 9:359-360. den Hartog, C. 1970. The Sea-grasses P u b l . Co., Amsterdam.  o f t h e World.  North-Holland  H i t c h c o c k , C.L., A. C r o n q u i s t , M. Ownbey, and J.W. Thompson. 1969. V a s c u l a r P l a n t s o f the P a c i f i c Northwest. Univ. o f Washington Press, S e a t t l e .  187 M c M i l l a n , C. 1978. Morphogeographic v a r i a t i o n under c o n t r o l l e d cond i t i o n s i n f i v e s e a g r a s s e s . T h a l l a s s i a testudinum. H a l o d u l e w r i g h t i i . Syringondium f i l i f o r m e , H a l o p h i l a engelmannii, and Z o s t e r a marina. A q u a t i c Bot. 4:169-189. P h i l l i p s , R.C. 1960. Environmental e f f e c t on l e a v e s o f D i p l a n t h e r a du petit-thouars. B u l l , o f Mar. S c i . o f t h e G u l f and Caribbean 10:346-353. P h i l l i p s , R.C. and R.F. Shaw. S y e s i s 9:355-358.  1976.  Zostera n o l t i i  i n Washington, U.S.A.  Sayce, C.S. 1976. The o y s t e r i n d u s t r y o f W i l l a p a Bay. P r o c . o f t h e Symposium on T e r r e s t r i a l and A q u a t i c E c o l . S t u d i e s o f t h e Northwest. E. Wash. S t a t e C o l l e g e P r e s s , Cheney, WA., pp.347-356. S c a g e l , R.F. 1956. I n t r o d u c t i o n o f a Japanese a l g a , Sargassum muticum, i n t o t h e Northeast P a c i f i c . F i s h . Res. Papers, Wash. Dept. F i s h . V o l . 1 No. 4.  Appendix 2. O x i d i z i n g p o t e n t i a l s o f Roberts Bank sediment.  189  Appendix 2.  Oxidizing  (redox) p o t e n t i a l s o f the sediment  to 20 cm  near s t a t i o n 2 (2.54 m CD t i d a l h e i g h t ) a t Roberts Bank, 1980  depth -  1981.  SEDIMENT DEPTH  11 JUNE  10 JULY  15 AUG.  12 SEPT.  14 OCT.  Surface  155  115  100  140  160  2  110  65  60  80  100  4  90  -5  40  45  60  6  10  -35  -10  -20  10  8  -40  -100  -120  -80  -20  10  -60  -120  -130  -110  -60  12  -85  -120  -140  -130  -100  14  -105  -120  -140  -135  -110  16  -130  -135  -145  -135  -110  18  -150  -140  -145  -135  -125  20  -155  -140  -155  -135  -125  3 DEC. 200 125 100 -30 -60 -100 -100 -100 -100 -100 -100  10 MAR.  18 APR.  23 JAN.  21 FEB.  230  185  200  190  165  170  185  120  140  180  150  90  120  165  130  45  80  125  105  -15  -10  0  -40  -45  -50  -40  -70  -100  -100  -120  -110  -120  -120  -100  120  -105  -110  -130  -140  -140  -130  -130  -140  -140  1 MAY 185 100 60 -10 -40 -80 -110 -120 -120 -130 -150  Appendix 3. Shoot demography d a t a .  192  Appendix 3.  Demographic data showing mapping dates which e s t a b l i s h e d  c o h o r t s , c o h o r t s p r e s e n t a t each sampling date, the average  number  o f v e g e t a t i v e and r e p r o d u c t i v e shoots p r e s e n t i n p l o t s a t each s t a t i o n , and the f a t e o f shoots i n each c o h o r t i n terms o f when they were r e c r u i t e d i n t o the v e g e t a t i v e o r r e p r o d u c t i v e phase o f the p o p u l a t i o n .  The number o f new shoots found a t each  sampling  date = G, the number o f shoots r e t a i n e d from p a s t sampling = R, and the number o f shoots l o s t = L.  dates  193 Station Zostera 1 VEGETATIVE MAPPING DATE May 12 June 2 June 11  June 23  J u l y 10  J u l y 21  August 6  COHORT NUMBER 1 1 2 1 2 3 1 2 3 4 1 2 3 4 5 1 2 3 4 5 6 1 2 3 4  19 35  August 26  September 12  October 6  G  L  T  R  L  G  19 16  51.7  9.7 14  81.7  2.7 9.7 23.7  5 .2  4.3  4.3  28 3 2.3 4.3  10.3  4.3  2.7 1 3 8.3  22  8.3  4 2  45.7 97 2 13.7 37.3  6.7 7  2  44 89  45 2 3 3.7 5  2.3 7.7 29  .7  8.3 26 10  8.3 6.7 6.3  50 34.3  •5 6 7 1 2 3 4 5 6 7 8 4 5 6 7 8 9 8 9 10  R  T  REPRODUCTIVE  34.3 2.3 7.7 12 35  3.3 15  10.7 10 13.7  9 15.3  16 16  39.7  10.7 10  3.3 4 8  13.7 11 8  16 27.7  39.7  11.7  4.3 16  8.7  11.7 11.3  4.7 4  10.7 10 11 8  Z o s t e r a 1 (cnt'd) REPRODUCTIVE  VEGETATIVE MAPPING DATE October 21  December 3  January 6  February 6  March 3  March 10  March 24  April  April May 1  9  18  COHORT NUMBER 8 9 10 11 8 9 10 11 12 10 12 13 12 13 14 12 13 14 15 13 15 16 13 15 16 17 13 16 17 18 16 18 16 18  T  R  G  T  L  7 1.7  3 4 0 6.3  3 2  2 4.3  2 1.3  5 3 2 5.3  1.7 2  1.3 1.7 1.7 .3 1.7  4.7 1.7 3 4.7  1.7 2  1 1  4.3  1.3 2  .3 1 3  3.7  .3 1 3 2.7  2 2  1 1 1 1  1.7  R  G  L  195 Zostera 2 REPRODUCTIVE  VEGETATIVE MAPPING DATE May 12 June 2 June 11  June 23  J u l y 10  J u l y 21  August 6  August 26  September 12  October 6  COHORT NUMBER 1 1 2 1 2 3 1 2 3 4 1 2 3 4 5 1 2 3 4 5  6 2 3 4 5 6 7 3 4 5 6 7 8 4 5 6 7 8 9 4 5 6 7 8 9 10  22.3 64.3  22.3 6.3  16 48.3  86.7  11 46.3  122.3  2 36.3 27.3  29.3 4.7 10 2  4.3  2 2.3 1 3  18.3  4.3  56.7 145.7 20 26.3 53.7  4.3 14  45.7 4.3 7.3  34.3  187.7 20 2.7 3 3  4 42.7 42.7  6.7 19.7  98.3 6.7 6.7  67  200.7  13  4 14.3 6 12  7.3 28.7 86.2  35.3  78.3 95.3  119  37.3 6 2 22 19 6.7  1.7 3 24.7 19  3.7 42.7 52.7  13 6 6  20 89.3  81.7 19 30.3 17.3  6.7 2.7  4 11.3 3.7 16 23.7 22.3  39.3 12.7 3  22.7 36  27 19 25.3 8 17.7 27  16  5 10 5  4 15 39.7 6.3  196 Z o s t e r a 2 (cnt'd) VEGETATIVE MAPPING DATE October 21  December 3  January 6  February 6  March 10  March 24  April 9  A p r i l 18  May 1  COHORT NUMBER 7 8 9 10 11 9 10 11 12 11 12 13 11 12 13 14 11 13 14 15 14 15 16 14 15 16 17 16 17 18 17 18 19  T  R  G  REPRODUCTIVE L  T  2.3  R  1 1  G  L 21 10 4  27 2.3 3.3  1 1.3  1 2  3.7  1 1  .3 1 1.7  4.7  .7  .3 1  1.3  .3 2.7  5.7  .7 1.3 1.3  1.3 4.3 4.7  .3 1.3  1 3 3  8  .3 1.3 3 5  5  3 2  3 2 4  3 1  1 0  197 Zostera 3 REPRODUCTIVE  VEGETATIVE  MAPPING DATE May 12 June 2 June 11  June 23  J u l y 10  J u l y 21  August 6  August 26  COHORT NUMBER 1 1  R 18.3 25.7  18.3  2 1 2 3 1 2 3 4 1 2 3 4 5 2 3 4 5 6 3 4 5 6 7 2 3 4 5 6 7  4.3  14 11.7  49.7  3 9.3  70.7  3 4 26.7  11 2.3 37.3 2.7 2.7  2.7 10.3 37 8.3  79.3  2.7  4 10.7 18.7  5.7  10.3 18.3 46  116 3 4 41.7  4 2.3 1 4.3  24.7  3  33.7  5.7  5.3 13.7  2.7 5.3  67.3 124 12.7 59.3  1.3 3  3.7  4 25.3  9.7 10.7  52 61.3  134  9.7 5 31.7  1.7| 7 21.31  3 5.3 12  49 8.3  87.7 September 12  October 6  5 6 7 8 9 6 7 8 9 10  9.7 5 4.7 38.7  72.7  49  61.7 26.3 8.3 27  4 22.71  23.7 26.3| 22  25  26  13.3 11.7  29 12  11.7  198 Z o s t e r a 3 (cnt'd) REPRODUCTIVE  VEGETATIVE MAPPING DATE October 21  December 3  January 6  February 6  March 3  March 10  March 24  April 9  A p r i l 18  May 1  COHORT NUMBER 7 8 9 10 11 10 11 12 10 12 13 10 12 13 14 10 13 15 13 15 16 15 16 17 15 16 17 18 16 18 19 16 18 20  T  G  R  T  L  R  G  13.3 11.7  1  2 8.3 11.7 3  2  L  1  0 4  1  2 2  4  1.7 1  .3 1 1.3  1  1.3 1 .7  .3 .7 0  .3 .3  4.7 .3 4.3  .3 .7  3.7 3 2.3 3  1.3 2  2 3  .3 2 1  1 1 1 1  2  199 Ruppia 1 REPRODUCTIVE  VEGETATIVE  MAPPING DATE May 12 June 2 June 11  June 23  J u l y 10  J u l y 21  COHORT NUMBER 1 1 2 1 2 3 1 2 3 4 1 2 3 4 5 1 2 3 4 5  T  G  1.3 2.3  1.3 1.3  T _0 0 1.3 .3  ~T7T 8.3  14  1.3 .3  .7 .3  .71  19.3 1 4.3 7  (3  August 6  August 26  1 2 3 4 5 6 7 5 6  1.3 3 3.7  1.71  1.7  1.7  5.7| 10 2  1.7  200 Ruppia 2 VEGETATIVE  MAPPING DATE May 12 June 2 June 11  June 23  J u l y 10  J u l y 21  COHORT NUMBER 1 1 2 1 2 3 1 2 3 4 1 2 3 4 5 1 2 3 4 5  REPRODUCTIVE  G 3 13.7 10.7 3 4.3  6.3 6.3 1.3  11.3  ~3 4.3 .3  12.3 6.3 3.7  15  17 4.3 .3 2  4.7  6_  8.3 6.7  August 26  2 4 5 6 7 2 4 5 6 7  1.7 3.7  19.3 1.3 .3 1 3.7  1 2.3 6.3 3.7  1.7  (3  August 6  1.7  12 1 3.7 1  3.3 1 3 1  3 4 3 1  1.3 1.3 3.3! 3.7  10.7  3 4 3 2 27.6  201 Ruppia 3 VEGETATIVE  MAPPING DATE May 12 June 2 June 11  June 23  J u l y 10  J u l y 21  August 6  August 26  September 12  COHORT NUMBER 1_ 1 2_ 1 2 3_ 1 2 3 4_ 1 2 3 4 5_ 1 2 3 4 5 6_ 2 3 4 5 6 7_ 5 6 7 6 7  R  REPRODUCTIVE  G 6  12.7 6.7 10.3  6 2.7  11.3  5.7  1.7 7.7 2 1.7 0  5.7 7.3  5.7  18 6 1.7 5.7 4.7  7.3 4.7  24 3.7 1.7 5.7 4.7  1.7 2.7  9.3  1.7 1  4.3 2.7  1.7 2.3  5.7 277 3.7 1.7 5.7 6  2.7 1.7 2.3  . .3  1.3 .3  4.3 3.3  1.3 .3  Appendix 4. Averages and s t a n d a r d d e v i a t i o n s o f m o r p h o l o g i c a l  data  203  Appendix 4.  Averages and standard  ( L . L . L . ) , rhizome i n t e r n o d e shoots p e r 0.1 m inflorescence  2  deviations o f longest l e a f  length  length  ( R . I . L . ) , number o f f l o w e r i n g  2 ( # f l . s h . / . l m ) , and number o f o v a r i e s p e r  ( # 0 . / i n f l . ) o f Z o s t e r a j a p o n i c a and Ruppia  m a r i t i m a a t t h r e e s t a t i o n s ( s t a t i o n 1 = 3.17 m, 2 = 2.54 m, and 3 = 2.60 m CD t i d a l h e i g h t )  a t Roberts Bank, 1980 - 1981.  Zostera R.I. .L.  L.L. L.  Date  //fl.sh. /.lm  2  i H n f l . / f l . sh •  #0./infl •  X  S  X  S  X  S  X  s  X  S  15 May  10.5  4 .1  2.5  1  0  0  0  0  0  0  11 June  15.4  4.4  2.0  .6  7.3  2.5  3.2  .8  4. 3  1  10 J u l y  8.4  2.7  1.2  .4  33.5  3.9  1.8  .8  4. 5  •6  26 Aug.  3.8  1.3  .3  .14 37  9.5  1.3  .61  4..1  •8  12 Sept.  3.0  1.2  .4  .1  0  0  0  0  0  0  6 Oct.  3.9  2.1 '  .4  .23  0  0  0  0  0  0  3 Dec.  3.0  1.5  .2  0  0  0  0  0  0  0  6 Jan.  5.1  2,2  .3  .2  0  0  0  0  0  0  6 Feb.  3.4  1.5  .5  .2  0  0  0  0  0  0  10 Mar.  6.4  1.6  .9  .6  0  0  0  0  0  0  9 Apr.  8.1  2.3  1  .8  0  0  0  0  0  0  15 May  10.6  4.3  2.0  1.2  11 June  11.2  3.9  2.1  10 J u l y  23.4  6.4  26 August  15.8  12 Sept.  STATION 1  STATION 2 0  0  0  0  0  0  .6  2.2  1  2  .8  6.2  1.2  2.6  .4  26.3  6.8  2. 3  2  6.3  1. 1  1.5  1.5  .5  81.2  19.7  5. 5  2  7.3  1. 1  6.2  .5  .5  .2  82.3  16.5  4. 6  2. 2  6.5  8  6 Oct.  6.6  .7  .6  .1  18.2  4.1  •6  6.1  2  3 Dec.  8.2  1.2  .3  .1  0  0  0  0  0  0  6 Jan.  6.9  2.0  .3  .5  0  0  0  0  0  0  6 Feb.  4.1  2.2  .3  .1  0  0  0  0  0  0  10 Mar.  6.5  2.6  1.2  1.5  0  0  0  0  0  0  ? Apr.  11.2  4.8  1.3  .9  0  0  0  0  0  0  15 May  11.8  1.6  2.2  1.4  0  0  0  0  0  0  11 June  12.6  3  2.4  .8  1.3  .8  1..6  6  6.1  1..3  10 J u l y  18.3  6.2  2.2  .3  13.7  3.4  1..8  96  6.0  .6  26 Aug.  12.3  1.7  1  .2  47.5  6.5  4..1  1. 1  6.5  1  12 Sept.  8.2  3.4  .5  .3  61.6  10.2  3..6  1  5.9  1..1  6 Oct.  7.4  1.2  .5  .1  13  6.9  1..6  6.2  1 .6  3 Dec.  6.6  2.1  .2  0  0  0  0  0  0  6 Jan.  6.3  2.5  .3  .2  0  0  0  0  0  0  6 Feb.  6.8  l.S  .4  .3  0  0  0  0  0  0  10 Mar.  6.4  2.5  1.2  1.8  0  0  0  0  0  0  10.4  6.1  1.5  1.1  0  0  0  0  0  0  2  STATION 3  9 Apr.  0  4  205  Ruppia Date  L.,L.L. X  R.I. , L. S  X  # f l .,sh./,,1m  2  #infl . / f l . s h .  #0./infl.  s  X  S  X  S  X  s  .1  0  0  0  0  0  0  4.7  1..6  2  .6  7.4  1.2  3,.1  ' 4.3  1.4  6.5  1.5  2  6.6  1.2  0  STATION 1 15 May  6.3  1.3  11 June  6.8  2.1  1.  .2  10 J u l y  13.5  3.7  1.7  .3  9  4.3  1  15 May  4.2  1.2  .3  .2  0  0  0  0  0  11 June  6.5  1.9  1.2  .2  9.3  2..9  2.7  1.4  7.9  .5  10 J u l y  16.7  2  1.7  .6  18.2  3..1  5.3  1.8  7.4  .1  3.1  1  .4  6  1.,5  8.0  2.1  7.7  1.2  . .3  .1  0  0  0  0  0  0  2  1  .3  5.9  1.,6  3.5  1.4  7.9  .5  1.8  1.5  .3  21.9  6.. 3  4.7  2.4  7.6  .8  2.3  1  .2  10.2  2. 3  7.5  3.2  7.6  1.2  26 Aug.  .3  1  16 1.5  ,9  5.5  STATION 2  26 Aug.  8  •  STATION 3 15 May  4.6  11 June  5.8  10 J u l y 26 Aug.  16 7.8  .8  

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