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Seed and seedling dynamics of the seagrass, Zostera japonica Aschers. and Graebn. and the influence of… Nielsen, Michele Erin 1990

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SEED AND  SEEDLING DYNAMICS OF THE SEAGRASS  ZOSTERA JAPONICA ASCHERS.  AND  GRAEBN. AND  THE  INFLUENCE OF ZOSTERA MARINA L .  by MICHELE ERIN NIELSEN B.Sc,  The U n i v e r s i t y  A THESIS SUBMITTED  o f Iowa, 1981  IN PARTIAL FULFILLMENT OF  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY OF GRADUATE STUDIES (Department o f Botany)  We a c c e p t t h i s t h e s i s a s to the required  conforming  standard  THE UNIVERSITY OF BRITISH COLUMBIA December 1990 © Michele E r i n Nielsen,  1990  In  presenting  degree  this  thesis  in  at the University of  partial  fulfilment  British Columbia,  freely available for reference and study. copying  of  department  this or  thesis by  for scholarly  his  publication of this thesis  or  her  PrSTAr-W  The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  n  prr/<ft>  the  I agree  requirements  for  an  advanced  that the Library shall make it  I further agree that permission for extensive  purposes  may  representatives.  It  be is  granted  by the head  understood  that  for financial gain shall not be allowed without  permission.  Department of  of  of  my  copying  or  my written  ABSTRACT  The pure  seagrass  p o p u l a t i o n s and  intertidal Roberts in  a  zone  than  germinated. seed  bank  two  with  British  a landward Z.  months, by  the lower  Z.  iaponica  sediment  Columbia.  though very  seeds  buckets  Z.  iaponica  zones.  April)  were  t h e sediment,  t h e Z.  area.  that  emerged  found  iaponica  When s e e d s  column  colonization  Z.  the  emerged  marina,  i n one earliest as  long  June.  i n t h e water.  o f Z. m a r i n a  seedlings,  into  of  were p l a n t e d  and reproduce  floating  f o r up  zone  or d i d not survive  uprooted,  were  iaponica  and w i t h o u t  and  a  i n the  incorporated  i n May  and  the dispersal  Seedlings that  and t h e presence  Z.  Z.. i a p o n i c a ' s  were  Z.  fewer  the lower  limits  of  seeds  abundant  i s high  with  later  studied  marina,  and even  into  grow,  d i d not establish  often  of the buckets protect  that  (5% or l e s s ) .  the study  seedlings  Seedlings  limiting  able t o germinate,  Z.  i n the water  dispersed  Of t h e seeds  placed into  either  there  I t i s u n c l e a r what  seeds.  throughout  thus  were  Many more  were most  remained  few s e e d s  Z. m a r i n a .  was  where  and  as  L. a l o n g t h e  m o n o s p e c i f i c zone  iaponica  seeds  occurs  At the  dynamics  i n the sediment,  zones  few g e r m i n a t e d  in  those  found  and Graebn.  Zostera marina  and s e e d l i n g  Zostera japonica  of  year  were  Even  populated  to  seed  of co-existing  i n t h e upper  density.  rim  area  Aschers.  m o n o s p e c i f i c z o n e o f Z. m a r i n a .  produced  as  study  t h r e e v e g e t a t i o n zones:  seaward  (in  i n mixture  r e g i o n s o f southwest  Bank  iaponica,  to  Zostera iaponica  shoots  The  appeared  preventing uprooting, but  i i  the  results  were  established, persist  they  throughout  overwintering greatly  not  to  the  conclusive.  Once s e e d l i n g s  spread vegetatively the  winter,  rhizomes. following  These year's  either  at  a  rapid  as  reduced  overwintering  became rate  and  shoots  plants  or  can as  contribute  population.  i i i  T A B L E OF CONTENTS  ABSTRACT  LIST  i  OF FIGURES  i  v i  ACKNOWLEDGEMENTS  x i  INTRODUCTION  1  SEDIMENT  3  STUDIES  Introduction  3  Study  5  Area  Methods  7  Results  10  Seeds  10  Testae  19  Germinating  seeds  19  Discussion  SEEDLING  35  ESTABLISHMENT  42  Introduction  42  Methods  44  . . . . .  Results Seedlings  . . .  49 49  iv  V e g e t a t i v e ramets  57  Reproductive Shoots  57  Total  ramets  67  Adult  Shoots  Natural Discussion  REFERENCES  Survey  . .  74 78 80  84  v  L I S T OF FIGURES  Fig.  1  Mean number o f Z. i a p o n i c a  s e e d s p e r 625 c m  2  of  s e d i m e n t i n e a c h zone. Fig.  2  Mean number o f Z. i a p o n i c a 625  Fig.  3  11  cm  ( d a t a = l o g (X+l))  2  1 0  seeds produced p e r i n e a c h zone  Mean number o f Z. i a p o n i c a  12  s e e d s p e r 625 c m  2  of  sediment a t each depth.  Fig.  4  a.  Japonica  zone  b.  Transition  c.  M a r i n a zone  •  zone  14 15  Percent of the t o t a l viable  Z. i a p o n i c a  number o f v i a b l e a n d n o n -  s e e d s p e r 625 c m  c o l l e c t e d May 1989 t o A p r i l  Fig.  5a  at  each date.  a.  Japonica  b.  Transition  c.  M a r i n a zone  Japonica  o f sediment  1990 t h a t w e r e f o u n d  16  zone  17 18  Percent of the t o t a l  s e e d s p e r 625 c m  f r o m May 1989 t o A p r i l date,  2  zone  zone.  Z. i a p o n i c a  13  2  number o f v i a b l e  o f sediment  collected  1990 t h a t were f o u n d a t e a c h  s e p a r a t e d by depth.  20  vi  Fig.  5b  J a p o n i c a zone.  Percent of the t o t a l  n o n - v i a b l e Z.. i a p o n i c a sediment c o l l e c t e d  number o f  s e e d s p e r 625 c m  f r o m May  2  of  1989 t o A p r i l  1990  t h a t were f o u n d a t e a c h d a t e , s e p a r a t e d b y d e p t h . Fig.  5c  Transition viable  zone.  Z. i a p o n i c a  collected  f r o m May  Percent of the t o t a l s e e d s p e r 625 c m 1989 t o A p r i l  2  number o f  o f sediment  1990 t h a t  were  found a t each d a t e , s e p a r a t e d by d e p t h Fig.  5d  Transition  zone.  Percent of the t o t a l  n o n - v i a b l e Z. i a p o n i c a sediment c o l l e c t e d  22 number o f  s e e d s p e r 625 c m  f r o m May  2  1989 t o A p r i l  of 1990  t h a t were f o u n d a t e a c h d a t e , s e p a r a t e d b y d e p t h . Fig.  5e  M a r i n a zone.  Percent of the t o t a l  n o n - v i a b l e Z.  iaponica  sediment c o l l e c t e d  2  1989 t o A p r i l  of 1990  t h a t were f o u n d a t e a c h d a t e , s e p a r a t e d b y d e p t h . Fig.  5f  M a r i n a zone.  Percent of the t o t a l  n o n - v i a b l e Z. i a p o n i c a sediment c o l l e c t e d  23  number o f  s e e d s p e r 625 c m  f r o m May  21  24  number o f  s e e d s p e r 625 c m  2  f r o m May 1989 t o A p r i l  of 1990  t h a t were f o u n d a t e a c h d a t e t h a t were n o n - v i a b l e s e p a r a t e d by d e p t h Fig.  6  Mean number o f Z. i a p o n i c a t e s t a e p e r 625 c m sediment  Fig.  7  25 2  of  i n each zone.  Mean number o f Z. i a p o n i c a t e s t a e p e r 625 c m  26 2  of  sediment a t each depth. a.  J a p o n i c a zone  27 vii  Fig.  8  b.  Transition  c.  M a r i n a zone  9  28 .  cm  2  625  cm  a.  Japonica  b.  Transition  c.  M a r i n a zone  2  o f sediment a t each depth. zone  32  zone  33 34  Study S i t e Layout  Fig.  11  Mean number o f Z. i a p o n i c a in  13  a.  Japonica  b.  Transition  c.  M a r i n a zone  14  s e e d l i n g s p e r 625  cm  2  zone  50  zone  51 52  Mean number o f s e e d l i n g p e r 625 c m  2  2  i n the  s u r v e y i n each zone.  Mean number o f n e w l y cm  Fig.  45  each treatment.  natural Fig.  31  Mean number o f Z. i a p o n i c a g e r m i n a t e d s e e d s p e r  10  12  seeds p e r  o f sediment i n each zone.  Fig.  Fig.  29  Mean number o f g e r m i n a t e d Z. i a p o n i c a 625  Fig.  zone  53  emerged s e e d l i n g s p e r 625  a t each date i n each treatment.  a.  Japonica  zone  b.  Transition  c.  M a r i n a zone  zone  54 .  55 56  Mean number o f weeks t h a t g e n e t s f r o m e a c h d a t e survived  i n each treatment.  a.  Japonica  zone.  b.  Transition  zone  58 59 viii  c. Fig.  15  M a r i n a zone  Mean number o f v e g e t a t i v e p e r 625 cm  Fig.  16  60  2  17  a.  Japonica  zone  b.  Transition  c.  M a r i n a zone  61  zone  62 63  Mean number o f r e p r o d u c t i v e s h o o t s f r o m  a.  Japonica  b.  Transition  c.  M a r i n a zone  i n each treatment.  2  zone  64  zone  65 66  Mean number o f s p a t h e s p e r r e p r o d u c t i v e s h o o t i n t r e a t m e n t s and n a t u r a l  Fig.  18  a.  Japonica  b.  Transition  c.  M a r i n a zone  19  survey.  zone  68  zone.  69 70  Mean number o f t o t a l s e e d l i n g s p e r 625 cm  Fig.  seedlings  i n each t r e a t m e n t .  s e e d l i n g s p e r 625 cm  Fig.  s h o o t s from  a.  Japonica  b.  Transition  c.  M a r i n a zone  ramets produced from 2  i n each treatment.  zone  71  zone  72 73  Mean number o f a d u l t s p e r 625 c m  2  i n each  treatment. a.  Japonica  zone  b.  Transition  c.  M a r i n a zone  zone  75 76 77 ix  Fig.  20  Mean number o f a d u l t s the  natural  survey.  p e r 625 c m  2  i n e a c h zone i n  ACKNOWLE DGEMENTS  I would l i k e and  financial  t o thank Dr. P a u l  assistance i n this  d i l i g e n c e and p a t i e n c e  research.  i n the editing  I w i s h t o acknowledge C y n t h i a knowledge and e x p e r t i s e i n f i e l d ecosystem. mudflats,  G. H a r r i s o n  for his  guidance  I appreciate h i s  of this  thesis.  Durance f o r s h a r i n g h e r  r e s e a r c h and t h e seagrass  I appreciate her considerable e f f o r t e s p e c i a l l y when w e l l i n t o t h e l a t e  on t h e  stages o f  pregnancy. Finally,  I would l i k e  t o t h a n k my h u s b a n d , B a r r i e N i e l s e n ,  whose common s e n s e a n d u n d e r s t a n d i n g months.  He n o t o n l y b o o s t e d  kept  me g o i n g  me s p i r i t u a l l y ,  a l l these  but contributed h i s  s t r e n g t h h a u l i n g b u c k e t s o f wet s e d i m e n t t o a n d f r o m t h e f i e l d site  during those  c o l d , dark, r a i n y , low t i d e s o f J a n u a r y .  xi  INTRODUCTION  Seagrasses are widely of  t e m p e r a t e and  conspicuous  and  tropical  s e a s and  productive  The  seagrass  e c o s y s t e m has  The  presence of seagrasses  s e d i m e n t s and  shore  p e r s i s t e n c e and and  Watson The  distributed  i s important  pure stands  Zostera  and  and  of  americana  Menez  1988).  roles. of  the (Phillips  marina  G r a e b n . i s an  which occurs  States  Barreca  regions but  i a p o n i c a as  1982).  Z.  on  and  Z.  shallow  1982).  n a n a and  I t i n h a b i t s the  (Nomme 1 9 8 9 ) .  intertidal  the  Bigley  i s a b l e t o grow i n l o w e r  i s not present  i n h a b i t s the  ( H a r r i s o n and  as  i n Japan  s o u t h w e s t c o a s t o f Canada and  ( B i g l e y and  mid-intertidal  also  upper regions  marina  subtidal regions  p r o t e c t e d c o a s t a l w a t e r s where s u i t a b l e s u b s t r a t e i s  available  (Moody 1 9 7 8 ) .  examine t h e p r o d u c t i o n the  to  Z o s t e r a m a r i n a L.  s t u d i e s h a v e r e f e r r e d t o Z.  (eelgrass)  most  stabilization  and  ( B i g l e y 1981)  co-existing with  1 9 5 0 a ) , on t h e  where Z.  and  i s essential  iaponica Aschers.  northwest coast of the United  Z.  of the  biological  i n the  regions  1984).  annual or s h o r t - l i v e d p e r e n n i a l  Earlier  (Phillips  p h y s i c a l and  p r o t e c t i o n and  coastal  g r o w t h o f many s p e c i e s o f m a r i n e l i f e  seagrass  (Arasaki  the  c o n s t i t u t e one  ecosystems both  along  recruitment  o f Z.  The and  purpose of t h i s  dispersal  stages  i a p o n i c a seeds  to and  iaponica seedlings t o determine i f i t s  p o p u l a t i o n g r o w t h i s l i m i t e d by these  o f Z.  r e s e a r c h was  of i t s l i f e  the  effects  o f Z.  marina  on  history. 1  Neighboring v e g e t a t i o n can i n f l u e n c e germination,  and r e c r u i t m e n t  in basically  seed  dispersal,  t h r e e ways:  impact o f a l i v i n g  p l a n t c a n o p y , 2) t h e i m p a c t o f p l a n t  and  among s e e d l i n g s  3) c o m p e t i t i o n  study  f o c u s e s on t h e f i r s t  scarcity of  Z. m a r i n a was u s e d t o h e l p  methodology i n t h i s  divided and  Due t o t h e form  f o r m u l a t e h y p o t h e s e s and  research. 1) Do Z. i a p o n i c a  seeds  i n t h e d e e p e r r e g i o n s where Z. m a r i n a  v e g e t a t i o n dominates? recruitment  This  i n f o r m a t i o n on t h e a n n u a l  T h i s study asks the questions: reach t h e sediment  litter,  (van d e r V a l k 1986).  type o f l i m i t a t i o n .  o f d a t a on Z. i a p o n i c a .  1) t h e  a n d 2) Do Z. m a r i n a p l a n t s r e d u c e t h e  o f Z.. i a p o n i c a  i n t o two s e c t i o n s ;  f r o m t h e s e e d bank?. first  The t h e s i s i s  i s a n a n a l y s i s o f t h e s e e d bank  s e c o n d i s a n a n a l y s i s o f e x p e r i m e n t a l t r e a t m e n t s where Z.  iaponica  s e e d s were p l a n t e d w i t h a n d w i t h o u t Z.  marina  vegetation.  2  SEDIMENT STUDIES  Introduction Zostera  iaponica  o v e r w i n t e r s as b u r i e d  germinate  i n the spring  germinate  i n t h e sediment  considered  (Harrison and  and  or s o i l  record  g e r m i n a t i o n when t h e s e e d l i n g  an  important Zostera  long. The  (Garwood 1983),  and Moore 1 9 8 3 ) .  The  remain  seeds a r e e l l i p s o i d  i n t h e o v a r y and shoots d r i f t  s h o o t s o f Z.. i a p o n i c a extensive  decay  Bigley  actually  out of the  soil  ( H a r p e r 1957)  is  and  and  approximately 2  smooth  (Arasaki  o r more.  mm  1950b). seeds  i n many c a s e s a r e s c a t t e r e d  while  (Arasaki  1950b).  a t the bases  t h e t i d e so t h a t t h e m a j o r i t y  The  or are uprooted  ( B i g l e y 1981).  o f seeds  flowering  are r a f t e d to  shoots as t h e y r i p e n  (1981) s u g g e s t s t h a t t h i s  forming  Mats flow w i t h other  a r e n o t b u r i e d where t h e y a r e p r o d u c e d .  from t h e f l o w e r i n g  seed,  These  f l o a t i n g mats o f s h o o t s  l o c a t i o n s and  be  i s r a r e l y recorded.  t e s t a i s brown when r i p e ,  the flowering  drop  appears  s e e d s h a v e a s p e c i f i c g r a v i t y o f 1.19  often  Seeds  from t h e  most s t u d i e s  Pre-emergence m o r t a l i t y  f a c t o r but iaponica  1982).  seedling part  fruit,  (Orth  Bigley  which  although "germination" can  a s t h e emergence o f any surface  seeds  (Arasaki  Seeds 1950b).  r e s u l t s i n an e v e n n e s s  of  seed  deposition. The the s o i l  s e e d bank i s d e f i n e d and  c a n be  considered  A t r a n s i e n t s e e d bank c o n t a i n s  a s t h e number o f s e e d s b u r i e d  in  either transient or persistent. s e e d s where t h e m a j o r i t y  are  3  viable  and  i n the s o i l  B l a c k 1985) persistent that  f o r no more t h a n one y e a r  s e e d bank c o n t a i n s  a significant proportion  1968).  s e e d banks  H u t c h i n g s and R u s s e l l  the  ( B i g l e y 1981,  o f Z.. i a p o n i c a  on  intertidal  a r e t o examine  dispersal pattern,  and  s e e d s and t h u s t o d e t e r m i n e w h e t h e r  i s a l i m i t e d d i s p e r s a l p a t t e r n which d e c r e a s e s i t s chances  of c o l o n i z a t i o n i n t o deeper zones. there  may  1989).  s e e d bank t o d e t e r m i n e t h e q u a n t i t y ,  there  seeds  F u k u d a e t a l . 1983,  objectives of t h i s part of the research  viability  A  ( L i v i n g s t o n and  T h e r e a r e few s t u d i e s o f any k i n d  or s u b t i d a l buried  of  Disturbance of the s o i l  c a u s e s e e d s f r o m t h e s e e d bank t o g e r m i n a t e  The  and  o r w i t h i n one y e a r o f d i s p e r s a l ( H u t c h i n g s 1 9 8 6 ) .  r e m a i n v i a b l e f o r many y e a r s .  Allessio  (Bewley  The n u l l  hypothesis i s that  i s no d i f f e r e n c e i n t h e numbers o r v i a b i l i t y  japonica  s e e d s i n t h e s e d i m e n t a t any  of  r e g i o n where Z.  Z. iaponica  c a n grow.  4  Study  Area Field  Pacific arm  s t u d i e s were c o n d u c t e d a t R o b e r t s Bank, on  coast  of the  b o u n d e d by  o f Canada, a p p r o x i m a t e l y  Fraser River  (49  02'N;  123  5 km  south  08*W).  The  t h e R o b e r t s Bank c o a l p o r t causeway t o t h e  t h e Tsawwassen f e r r y t e r m i n a l causeway t o t h e  The  c o a l p o r t causeway d e f l e c t s resulting  r i p - r a p d i k e was of the  seagrass  channels  and  The  the  the  Fraser area.  study  constructed  at the  seaward  i n e a r l y 1982  to reduce e r o s i o n of d e n d r i t i c  adjacent  at a slower  seagrass  r a t e than  the water l e v e l  beds.  tides.  The  study  area  areas.  into the  r i s e s a b o v e t h e d i k e and  is  embayment  non-enclosed dike  margin  drainage  Drainage of the  at adjacent  A  embayment  quickly floods  area. The  ha  northwest  southeast.  s e d i m e n t c a r r i e d by  incoming t i d e waters flow around the  until  is  i n the  bed  the  lower  i n improved water c l a r i t y  s u b j e c t t o mixed s e m i - d i u r n a l occurs  of the area  and  River,  the  a r e a between t h e causeways c o n t a i n e d  of seagrass  marina occurs intertidal  and  vegetation  i n a monospecific shallow  o f Z. m a r i n a h a s  grows.  Now  i n the  population  i n the  Since  1969  area  i t occurs  improved water c l a r i t y  colonized high just  i n the  lower the  the upper to m i d - i n t e r t i d a l  growth  ( H a r r i s o n 1987).  l a n d w a r d o f where Z o s t e r a  zones  (+1  t o +3  coverage  intertidal  i n expanded m o n o s p e c i f i c  400  Zostera  g r e a t l y expanded t h r o u g h v e g e t a t i v e  iaponica f i r s t  separately  ( H a r r i s o n 1987).  s u b t i d a l zones.  p r i m a r i l y because of the Zostera  i n 1984  approximately  zone  marina  population  m relative  and  to  in lowest  5  low  water)  areas  normally  reference, the  ( H a r r i s o n 1984)  the  "japonica  called  the  marina  will  occupied region zone",  called  by  has  the  region  zone", the  also  Z. marina  populated  "transition be  but  by  Z.  been  (Nomine  1989)  iaponica  containing  and the  found  both  region  "marina zone"  .  will  in  For be  species  populated  (Nomme  deeper  1989).  called will : by  Z.  Methods The  number  (testae,  germinated  1989 t o A p r i l sediment  1990.  seeds)  o f seeds  and s e e d  were e v a l u a t e d m o n t h l y  products from  From e a c h o f t h e t h r e e z o n e s ,  April  fifteen  c o r e s were t a k e n u s i n g random c o o r d i n a t e s f r o m an a r e a  o f 450 m .  S a m p l e s were c o l l e c t e d b y i n s e r t i n g  2  (77 mm  and d i s t r i b u t i o n  i n s i d e diameter)  i n t o t h e sediment  a Plexiglas  tube  to at least  a 20-cra  o f t h e seeds,  cores  depth. To d e t e r m i n e were s l i c e d 12 cm.  the depth d i s t r i b u t i o n  i n the f i e l d  Each  a t 2-cm  intervals,  s l i c e was marked a n d p l a c e d i n a p l a s t i c  were r e t u r n e d t o t h e l a b and s t o r e d to  f o u r t e e n days u n t i l The  A 2 mm  i n t h e d a r k a t 5° C f o r one  mesh was u s e d t o remove  and p l a n t m a t e r i a l ;  the material seeds.  visually  The m a t e r i a l  r e t a i n e d was e x a m i n e d  A 0.850 mm  retained  inorganic and examined  microscope.  V i a b i l i t y was t e s t e d u s i n g t h e t e t r a z o l i u m t h a t were f i r s t  mesh  i n t h i s mesh was c o l l e c t e d  o r by d i s s e c t i n g  through  invertebrates,  o t h e r s e e d s a n d s e e d p r o d u c t s a l o n g w i t h some  material.  Bags  t h e y c o u l d be examined.  f o r t h e presence o f germinated all  bag.  c o n t e n t s o f e a c h b a g were washed w i t h t a p w a t e r  two s i e v e s . detritus,  from t h e s u r f a c e t o  pricked with a needle  monitored  every twelve hours.  hypocotyl  stained red.  (Grabe  Viability  1970).  on  seeds  S e e d s were  was c o n f i r m e d i f t h e  D e n s i t i e s were s t a n d a r d i z e d t o 625 c m with seedling establishment data.  test  2  t o be  consistent  To a c h i e v e e q u a l i t y o f  7  variances,  t h e s q u a r e r o o t t r a n s f o r m a t i o n was e m p l o y e d  e t a l . 1989).  Comparisons  (Benoit  o f s e e d s and s e e d p r o d u c t s by  zone  and b y d e p t h were a n a l y z e d u s i n g ANOVA when v a r i a n c e s were greater than  zero.  K r u s k a l - W a l l i s was e m p l o y e d when one o r more  o f t h e v a r i a n c e s were z e r o the marina  ( Z a r , 1984),  a s was o f t e n t h e c a s e i n  zone.  A s u r v e y o f t h e t h r e e z o n e s was c o n d u c t e d number o f s e e d s p r o d u c e d and  t o t h e number o f s e e d s  t o compare t h e e x p e r i m e n t a l p l o t s  establishment population.  i n t h e sediment  (see s e e d l i n g  s e c t i o n , p a g e 67) on t h e t r a n s e c t s t o t h e n a t u r a l From A p r i l  1989 t o J a n u a r y  were t a k e n a t e v e r y low t i d e c y c l e containing the transects  i n each  u s i n g random c o o r d i n a t e s . iaponica  t o compare t h e  1990 f i f t e e n  f r o m a 450 m  zone.  2  Quadrats  samples  area were p l a c e d  W i t h i n t h e q u a d r a t , emerged  Z.  s e e d l i n g s were c o u n t e d a l o n g w i t h t h e numbers o f m a t u r e  v e g e t a t i v e shoots, r e p r o d u c t i v e shoots, spathes p e r shoot, f l o w e r s p e r s p a t h e , and s e e d s p e r s p a t h e . a 625 c m iaponica dense,  2  In the japonica  zone  q u a d r a t was u s e d due t o t h e h i g h d e n s i t y o f Z. ramets  b u t i n t h e l o w e r z o n e s where s h o o t s were  a 2500 c m  2  q u a d r a t was u s e d .  s t a n d a r d i z e d t o 625 c m .  These  2  establishment  A l l v a l u e s were  d a t a were u s e d  i n the seedling  section.  ANOVA was u s e d t o t e s t seeds produced  less  p e r 625 cm  mean number o f f l o w e r i n g  2  f o r zonal differences.  Numbers o f  were c a l c u l a t e d b y m u l t i p l y i n g t h e  ( s e e d - p r o d u c i n g ) s h o o t s b y t h e mean  number o f s p a t h e s p e r s h o o t by t h e mean number o f s e e d s p e r  8  spathe. so  Only  variances  a  rough estimate  were  not  taken  of  into  seeds  p r o d u c e d was  required,  account.  9  Results Seeds The most s e e d s o f Z.. i a p o n i c a were f o u n d i n t h e zone,  fewer  zone.  i n the t r a n s i t i o n  zone,  and v e r y few  i n the marina  The v a l u e s f o r e a c h zone were s i g n i f i c a n t l y  (p<.05) a t a l l d a t e s e x c e p t i n t h e months o f A p r i l 1990  japonica  different and  1989  ( K r u s k a l - W a l l i s p>.05), and M a r c h ,  1) .  S t a n d a r d e r r o r s o v e r l a p p e d and t h e r e f o r e were n o t  September  (ANOVA p>.05) ( F i g . included  f o r c l a r i t y of graphs. The  survey of the natural population  p r i m a r i l y produced in  the japonica  transition 2) . in  from mid-August  zone,  zone,  and  t o the f i r s t  i n l a t e September i n t h e m a r i n a  O c t o b e r f o r t h e u p p e r two ( F i g . 1).  These  z o n e s and  cm)  i n t h e s p r i n g t h a n any  transition marina  zones  of October  first  ( F i g . 3a-c).  zone e x c e p t i n t h e l a t e  i n the  zone ( F i g .  began t o  increase  i n November i n t h e m a r i n a  s e e d s were f o u n d a t t h e s u r f a c e  A l a r g e r p r o p o r t i o n o f t h e s e e d s was (8-12  part  s e e d s were  from mid-September t o mid-October  The number o f s e e d s i n t h e s e d i m e n t  zone  showed t h a t  (0-2  found a t a g r e a t e r  cm).  depth  other time i n the japonica  Few fall  and  s e e d s were f o u n d i n t h e and w i n t e r a t s h a l l o w  depths. The v i a b i l i t y all  t h r e e zones  o f s e e d s i n t h e s e d i m e n t was  ( F i g . 4a-c).  s e e d s was  noted i n the f a l l .  t h e r e was  no d i f f e r e n c e  30,  1989  to April  1990  An  consistent i n  i n c r e a s e d number o f  Between z o n e s ,  viable  f r o m May  i n numbers o f v i a b l e s e e d s and t h e r e was  no d i f f e r e n c e  t o Nov  1  from  Nov  i n t h e numbers o f 10  40 3 ©  B o  30  t/3  © CO  20  o fl> a  10 a  cd ©  0  ^—6—&—&—&—&—9  9  9  9--^  Date Fig.  1  Mean number o f Z. i a p o n i c a s e e d s p e r 625 c m sediment i n each zone. «=japonica zone, A = t r a n s i t i o n z o n e , o=marina z o n e .  2  of  11  Date Fig.  2  Mean number o f Z. i a p o n i c a s e e d s p r o d u c e d p e r 625 c m (data=log Q( )) i each zone. • = j a p o n i c a z o n e , A = t r a n s i t i o n z o n e , o=marina zone. 2  x + 1  n  1  12  40 H fl  0-2 cm  §§§ 2-4 cm  a  •  o 30  §|j 6-8 cm  a  ^  8 - 1 0 cm  H  1 0 - 1 2 cm  •1-1  Ui  4-6 cm  o CO  20  o  777  M 4>  1  a  .55 10 a  1  0 K P ^ tf** S** S ^ e  1  K»* S ^  1  0<* ^  pc* j * *  ?<^ £ tV£° 0  9  Date Fig.  3a  J a p o n i c a zone. Mean number o f Z. i a p o n i c a p e r 625 cm o f s e d i m e n t a t e a c h d e p t h .  seeds  2  13  Date Fig.  3b  T r a n s i t i o n zone. s e e d s p e r 625 c m  2  Mean number o f Z. i a p o n i c a o f sediment a t each depth.  14  40 0-2  cm  ©  §§§ 2-4  cm  a  •  4-6  cm  ^  6-8  cm  •  © co  30  8-10  IH 10-12 cm  CO  © ©  CO  cm  20  ©  yd  a  10 a ©  0  i  i  i  I  i  i  i  i  H  i  i  in  iii  wm  Date Fig.  3c  M a r i n a zone. Mean number o f Z, i a p o n i c a p e r 625 cm o f s e d i m e n t a t e a c h d e p t h .  seeds  2  15  8  Date Fig.  4a  J a p o n i c a zone. P e r c e n t o f t h e t o t a l number o f v i a b l e ( s t r i p e d ) a n d n o n - v i a b l e ( s o l i d ) Z. i a p o n i c a s e e d s p e r 62 5 c m o f sediment c o l l e c t e d May 1989 t o A p r i l 1990 t h a t were f o u n d a t e a c h date. 2  16  8  © © co  7  © a  T—<  a) -«-> O  H  3  a ©  o u ©  0 Date Fig.  4b  T r a n s i t i o n zone. P e r c e n t o f t h e t o t a l number o f v i a b l e ( s t r i p e d ) a n d n o n - v i a b l e ( s o l i d ) Z. i a p o n i c a s e e d s p e r 625 c m o f sediment c o l l e c t e d May 1989 t o A p r i l 1990 t h a t were f o u n d a t e a c h date. 2  17  8 co O  © CO  o  JO  B  z  cd O  H  3  © O  ©  0  •  H  B  a  a  L  Date Fig.  4c  M a r i n a zone. P e r c e n t o f t h e t o t a l number o f v i a b l e ( s t r i p e d ) a n d n o n - v i a b l e ( s o l i d ) Z. i a p o n i c a s e e d s p e r 625 c m o f sediment c o l l e c t e d May 1989 t o A p r i l 1990 t h a t were f o u n d a t e a c h date. 2  18  non-viable decreased until  spring  The p e r c e n t a g e o f v i a b l e  (Fig. 5a-f).  i n the upper  layers  Viable  (0-4 cm)  In the japonica  n o n - v i a b l e and t h i s  the  sampling area  fall,  i n c r e a s e may  were  i n the  from l a t e  fall. fall  to  increase  i n June but t h e s e seeds  be due  to heterogeneity  ( F i g . 1 and F i g . 3a v s F i g . 4 a ) . i n the upper  s e d i m e n t b u t were f o u n d a t i n c r e a s i n g l y and  sediment  zone t h e r e a p p e a r s t o be an  n o n - v i a b l e s e e d s were l o c a t e d  the spring  seeds  seeds i n i t i a l l y  of sediment  t h e number o f s e e d s i n t h e s e d i m e n t  are  in  into the  percentage o f n o n - v i a b l e seeds i n c r e a s e d  summer. in  (p>.05).  from t h e time o f i n c o r p o r a t i o n  late  located The  seeds  of  In the  layers  lower l e v e l s  of  (8-12  cm)  summer.  Testae The  numbers o f t e s t a e by zone were s i g n i f i c a n t l y  (ANOVA, p<.05) the  o t h e r two  transition February, other  ( F i g . 6).  The m a r i n a  but the japonica  zone was  always lower than  not d i f f e r e n t  zone e x c e p t i n S e p t e m b e r and December, 1990  (Tukey t e s t p<.05).  T e s t a e were g e n e r a l l y  i n c r e a s i n g numbers w i t h d e p t h  Germinating  (6-12  cm),  from t h e  1989  when a l l t h r e e z o n e s were d i f f e r e n t  d e e p e r p a r t s o f t h e sediment sample and  zone was  different  from  and each  found i n the  w i t h a few  on t o p  ( F i g . 7a-c).  seeds  G e r m i n a t i o n was  restricted  t o t h e p e r i o d between F e b r u a r y 19  © a  4  •  0-2  cm  §§§  2-4  cm  O  4-6  cm  §§  6-8  cm  ©  8-10  II  10-12  cm cm  09  © ©  co 2  -  O  a © © ©  0  Date Fig.  5a  J a p o n i c a zone. P e r c e n t o f t h e t o t a l number o f v i a b l e Z. i a p o n i c a s e e d s p e r 625 c m o f sediment c o l l e c t e d f r o m May 1989 t o A p r i l 1990 t h a t were found a t each d a t e , s e p a r a t e d by d e p t h . 2  20  Date Fig.  5b  J a p o n i c a zone. P e r c e n t o f t h e t o t a l number o f n o n - v i a b l e Z. i a p o n i c a s e e d s p e r 625 c m o f s e d i m e n t c o l l e c t e d f r o m May 1989 t o A p r i l 1990 t h a t were f o u n d a t e a c h d a t e , s e p a r a t e d by depth. 2  21  a ©  .§ 4 © CO  B  0-2  cm  §§]  2-4  cm  •  4-6  cm  f§  6-8  cm  jg3  8-10  Hi  10-12  i  cm cm  © © CO  i  (2  o •«-> a ©  o ©  Pi  0  Date Fig.  5c  T r a n s i t i o n zone. Percent of the v i a b l e Z. i a p o n i c a s e e d s p e r 6 2 5 c o l l e c t e d f r o m May 1989 t o A p r i l found a t each d a t e , s e p a r a t e d by  t o t a l number o f cm o f sediment 1990 t h a t were depth. 2  22  c o a  u  4  GO  to  •  0-2  cm  §§§  2-4  cm  LJ|  4-6  cm  H  6-8  cm  £gj 3  -  2  -  II  ;  8-10 10-12  cm cm  © © co r—<  cd (2  a © o ©  i  l  0 V  \*3  Date Fig.  5d  T r a n s i t i o n zone. P e r c e n t o f t h e t o t a l number o f n o n - v i a b l e Z. i a p o n i c a s e e d s p e r 625 c m o f s e d i m e n t c o l l e c t e d f r o m May 1 9 8 9 t o A p r i l 1 9 9 0 t h a t were f o u n d a t e a c h d a t e , s e p a r a t e d b y depth. 2  23  5  r  •  S  4  X)  co  OS  0-2  cm  §§§ 2-4  cm  O  4-6  cm  §1  6-8  cm  ^  8-10  Il  10-12 cm  cm  o CO •4-»  <2  a  © O  U  fl>  0  Date Fig.  5e  M a r i n a zone. P e r c e n t o f t h e t o t a l number o f n o n - v i a b l e Z. i a p o n i c a s e e d s p e r 625 c m o f s e d i m e n t c o l l e c t e d f r o m May 1989 t o A p r i l 1990 t h a t were f o u n d a t e a c h d a t e , s e p a r a t e d b y depth. 2  24  5 0-2  cm  a a  4  © CO  ^ ©  3  © CQ  I 03  2  ©  o © o  Date Fig.  5f  M a r i n a zone. P e r c e n t o f t h e t o t a l number o f n o n - v i a b l e Z. i a p o n i c a s e e d s p e r 625 c m o f s e d i m e n t c o l l e c t e d f r o m May 1989 t o A p r i l 1990 t h a t were f o u n d a t e a c h d a t e t h a t were n o n v i a b l e s e p a r a t e d by d e p t h . 2  25  200 o  B  •*-<  o CO  150 -  100 o  © a  50 d cd ©  0 Date Fig.  6  Mean number o f Z. i a p o n i c a t e s t a e p e r 625 c m sediment i n each zone. • = j a p o n i c a zone, * = t r a n s i t i o n zone, o=marina zone.  2  of  26  200  r  •  rt ©  §§§ 2-4 cm  B  •  •T-(  o CO  0-2 cm  150  4-6 cm  fH 6-8 cm  © cd  ^  8-10 cm  M  10-12 cm  100 Cm  o l-l  ©  B  50 i  rt cd ©  1 0  ^  **** j** s^ K»* ^ 6  1  o° ^ t* x  0  *°V* }^ 0  0  Date Fig.  7a  J a p o n i c a zone. Mean number o f Z. i a p o n i c a t e s t a e p e r 625 c m o f s e d i m e n t a t e a c h d e p t h . 2  27  200  •  ©  0-2  cm  §§§ 2-4  cm  O  4-6  cm  6-8  cm  •T-<  © co  150  .8-10 H  ©  10-12  cm cm  +->  E2  100  O  t-t © 50  -  1 I  ©  H  0 ^  tf**  j**  6  5*** K»» S « * <** ^ v  t>e* J * *  •  t ^ s ^ s 9 °  Date  Fig.  7b  T r a n s i t i o n zone. Mean number o f Z. i a p o n i c a t e s t a e p e r 625 c m o f s e d i m e n t a t e a c h d e p t h . 2  28  200  a ©  150  o +->  •  0-2  cm  §§§  2-4  cm  •  4-6  cm  §§  6-8  cm  ffl  8-10  H  10-12  cm cm  100 <•-<  o © a  50  a  ©  0  r-r4  ^  Lioioi  )a4x&  K»*  S** ^ 6  °  o V  ^  3  ** * V * ° M ^ ° e  Date Fig.  7c  M a r i n a zone. Mean number o f Z. j a p o n i c a p e r 625 c m o f s e d i m e n t a t e a c h d e p t h .  testae  2  29  and  June.  germinating 1990  There seeds  were  transition  p<.05)  Z_. i a p o n i c a zone,  significant  between zones  (Kruskal-Wallis  germinating  no  and  fewest  March,  and A p r i l  depths  ( 0 - 4 cm) ; l a t e r  except  (Fig.  seeds  differences  8).  i n June There  i n the japonica  i n the marina  the majority  i n density  1989 were  and  fewer  i n the  In February,  of germination occurred  germination occurred  April  more  zone,  zone.  of  slightly  at shallow deeper ( F i g .  9a-c).  30  10 CO  © © CO  8  h  © cd fl a  ©  o  o u © B & Z fl cd © 2  0  Date  Fig.  8  Mean number o f g e r m i n a t e d Z. i a p o n i c a s e e d s p e r 625 c m o f s e d i m e n t i n e a c h z o n e . «=japonica zone, = t r a n s i t i o n z o n e , o=marina z o n e . 2  31  10 0-2  cm  §D 2 - 4  cm  •  4-6  cm  ©  ^  6-8  cm  cd fl  jgj 8 - 1 0  • «> T3 H> <D CO  •1-1 a  M CO  8 -  IH 1 0 - 1 2  6 -  cm cm  o o u  ©  a z A  2  cd cu  0  -  I  I  I  L  Date Fig.  9a  J a p o n i c a zone. Mean number o f Z. i a p o n i c a g e r m i n a t e d s e e d s p e r 625 c m o f s e d i m e n t a t e a c h depth. 2  32  10 ©  O  OO  8 -  o -«-»  (=1  •  0-2  cm  §§§  2-4  cm  •  4-6  cm  ^§  6-8  cm  [gj  8-10  M  10-12  cm cm  6 -  o U  o  cd ©  0  Ll  Ll  1 J * * S^ 6  3  K * 8  fW«  f °V  t  0  K^°  Date Fig.  9b  T r a n s i t i o n zone. Mean number o f Z. i a p o n i c a g e r m i n a t e d s e e d s p e r 625 c m o f s e d i m e n t a t e a c h depth. 2  33  10  •  CO  © © CO  0-2 cm  §g] 2-4 cm  8  © -•-> cd a •1-1  •  4-6 cm  §§  6-8  ^  8-10 cm  H  10-12 cm  cm  ©  o (f-l  o © a  a ©  0  Li  J  I  I  L  I  I  I  1  Date Fig.  9c  M a r i n a zone. Mean number o f Z. i a p o n i c a g e r m i n a t e d s e e d s p e r 625 c m o f s e d i m e n t a t e a c h depth. 2  34  Discussion Of  t h e many s e e d s t h a t a r e p r o d u c e d ,  few a r e i n c o r p o r a t e d  i n t o t h e s e d i m e n t and e v e n f e w e r g e r m i n a t e . i a p o n i c a has been d e s c r i b e d 1979), t h i s must r e l y seedling  result  Given that  as an a n n u a l i n t h i s  area  Zostera  (Harrison  was u n e x p e c t e d a n d s u g g e s t s t h a t Z. i a p o n i c a  on c l o n a l growth t o m a i n t a i n establishment  discussion).  t h e p o p u l a t i o n (see  Studies  c o u l d b e done t o  determine t h e importance o f o c c a s i o n a l genet establishment the population  genetics of this  Seed p r o d u c t i o n japonica  japonica (Bigley with  Even h i g h e r  zone, has been o b s e r v e d h i g h e r 1981).  Zostera  production,  i n the i n t e r t i d a l  output  local  studies  i n t h e upper  the  local It  how  area  was  light quality  progresses  and q u a n t i t y ,  None o f t h e s e  as w e l l  has been s t u d i e d i n  f o r Z. i a p o n i c a .  i s unknown how  long t h e seeds s t a y  In t h e survey  This  ( B i g l e y 1981, Nomme 1 9 8 9 ) .  T h i s may b e due t o e n v i r o n m e n t a l d i f f e r e n c e s a s one  as t e m p e r a t u r e and s a l i n i t y .  seagrasses  1979).  than i n t h e lower r e g i o n s .  seaward such as water depth,  zone  i n the higher,  f o r Z. i a p o n i c a b e g a n e a r l i e r  of the i n t e r t i d a l i n other  reproductive  (Harrison  Seed p r o d u c t i o n  i n the  japonica responds l i k e other  i n sexual  more e x p o s e d a r e a s  a l s o noted  seed  t i m e s t h e maximum number p r o d u c e d  an i n c r e a s e  regions  species.  d e c l i n e d from a peak i n t h e landward  zone towards t h e s e a .  more t h a n t h r e e  in  long reproductive  shoots stay attached  i n the spathe before  of natural populations,  they  or  are released.  many o f t h e r e p r o d u c t i v e  35  s h o o t s m i g h t h a v e b e e n c o u n t e d i n more t h a n one Also,  s e e d s may  counted. to  Even  have dropped  f r o m t h e s p a t h e s b e f o r e t h e y were  so, a t t h e time o f peak seed p r o d u c t i o n  mid-October)  The p r e s e n c e o f t h e new i n d i c a t e d b y an i n c r e a s e sediment  layers  seed crop i n the sediment  i n t h e number o f v i a b l e  i n a r e a s o f h i g h Z.  indicates that dispersal  a n n u a l f o r m o f Z.. m a r i n a also  stayed  1982) .  sediment.  i n O c t o b e r and November  The h i g h e r s e e d d e n s i t y density  i s local.  i n Europe,  iaponica  these  seeds  (Jacobs that  (Benoit et a l . i n these higher  successful  contribute to the high density of adult  seedlings,  Z.. i a p o n i c a i n  zones. The J a n u a r y s a m p l e was  s e e d s and t e s t a e japonica system that  adult  systems have found  B e c a u s e t h e r e a r e more s e e d s d e p o s i t e d  t h e y may  i n the  In s t u d i e s of the  i n t h e a r e a i n w h i c h t h e y were p r o d u c e d  i f few o f t h e s e s e e d s p r o d u c e  was  ( F i g . 5a,c,e).  seeds a r e o f t e n shed next t o o r near the p a r e n t  zones, even  seeds  the majority of the  Other studies of t e r r e s t r i a l  1989).  (August  t h e r e were up t o t e n t i m e s more s e e d s b e i n g  p r o d u c e d p e r a r e a t h a n were f o u n d i n t h e  upper  sampling time.  zone.  i n the t r a n s i t i o n T h i s may  (Moody 1 9 7 8 ) .  areas that  zone e x c e e d e d  those i n the  be due t o t h e h e t e r o g e n e i t y o f t h e  S a m p l i n g was  done r a n d o m l y  and  i t may  be  c o n t a i n e d more s e e d s and s e e d p r o d u c t s ( s u c h a s  d e p r e s s i o n s ) were sampled sediment  t h e one t i m e t h a t t h e numbers o f  shifting  due  on t h i s  date.  A n o t h e r c a u s e may  be  t o w i n t e r storms.  36  The  l a r g e number o f new  lower i n t e r t i d a l result  areas  seeds d i d not d i s p e r s e  (marina zone).  although Bigley  (1981) s u g g e s t e d t h a t t h e s e e d s were i n  c o l u m n l o n g enough t o p r o d u c e  of seed.  Bigley  may  t h a n my  japonica  be s u b j e c t t o d i f f e r e n t water  hypothesis that there  did  Z.  much  zone a n d t h e two T h u s my  i n the d i s p e r s a l  I t i s u n c l e a r why  i n t o more s e a w a r d  distribution  iaponica  flow regimes.  i s no d i f f e r e n c e  seeds i s f a l s e .  not disperse  a more e v e n  ( 1 9 8 1 ) , however, s t u d i e d  i n the i n t e r t i d a l  iaponica  the  Nomme (1989) h a d t h e same  the water  higher  into  Z.  sites  null of  iaponica  Z.  seeds  r e g i o n s ; p e r h a p s t h e y were  washed o n t o s h o r e . T h e r e was  little  m o r t a l i t y o f seeds d u r i n g t h e w i n t e r .  M o s t o f t h e s e e d s were i n t h e t o p 4-6  cm  o f the sediment  i n the  w i n t e r and a s t i m e went on t h e s e e d s became more d e e p l y incorporated  i n t o the sediment.  work t h e i r way  down due  t o the water  sediment o r t o the s h i f t i n g unknown.  Swinbanks  Whether t h e s e s e e d s  flow passing through the  o f s e d i m e n t s by  (1979), w o r k i n g  naturally  invertebrates i s  i n the adjacent Fraser  delta,  found t h a t the p o l y c h a e t e A b a r e n i c o l a  200/m  c o u l d c o m p l e t e l y t u r n o v e r t h e s e d i m e n t down t o a d e p t h  of  2  10 cm  sediment  i n 100  days.  Several  invertebrates  at a density  River  inhabit  of  the  i n t h e s t u d y a r e a and t h e same t y p e o f s e d i m e n t m i x i n g  i s probably occurring. A v e r y s m a l l number o f Z. i a p o n i c a t h e s e e d bank. is  unknown.  The  seeds germinated  from  f a t e o f t h e r e m a i n i n g s e e d s i n t h e s e e d bank  Some s e e d s may  h a v e become more d e e p l y embedded i n  37  the sediment.  O t h e r s e e d s may  have been  consumed o r d e s t r o y e d  i n t h e s p r i n g by t h e i n c r e a s i n g a c t i v i t y sediment. the s n a i l  I l y a n n a s s a o b s o l e t a have been  I t has been  seeds  (Wigand  o f g e r m i n a t i o n and  i n July  i n the sediment. zone  Bigley d e p t h o f 4-7 this  I n Z.  i n the japonica  i n J u n e t h e r e was  o f t h e s e e d do  not  zone,  a  where  a c o r r e s p o n d i n g peak i n In the t r a n s i t i o n  zone,  i n J u n e and s o d i d t h e number o f t e s t a e T h e r e were t o o few  found  seeds g e r m i n a t i n g i n the  f o r any c o m p a r i s o n s t o be made. (1981) f o u n d t h a t most g e r m i n a t i o n o c c u r r e d a t a cm  and none below  although several  12 cm.  My  results  concur with  s e e d s g e r m i n a t e d f r o m t h e 0-2  Most o f t h e l a t t e r o c c u r r e d  i n the early  cm  range.  s p r i n g b e f o r e any  t h e o v e r w i n t e r i n g p o p u l a t i o n h a d renewed g r o w t h . s e e d l i n g s t h a t emerged e a r l y were f o u n d l a t e r water,  iaponica.  l o n g they remain i s u n c e r t a i n .  ( F i g . 8 vs F i g . 6).  g e r m i n a t i o n peaked  marina  found  e x p e c t an i n c r e a s e i n t h e number o f t e s t a e a f t e r  g e r m i n a t i o n peaked testae  1988).  of that year's germination  I t i s p r o b a b l e t h a t t h e remnants  would  potential  f a r e x c e e d e d t h e numbers o f g e r m i n a t e d  decompose i n one y e a r b u t how  period  and C h u r c h i l l  e t a l . 1 9 8 3 , Fukuda and T s u c h i y a 1 9 8 7 ) .  t h e numbers o f t e s t a e  One  shown t o be  s u g g e s t e d f o r Z. m a r i n a t h a t t h e t e s t a e  i n t h e s e d i m e n t a r e t h e remnants  seeds.  i n the  Common c r u s t a c e a n i n h a b i t a n t s o f e e l g r a s s meadows and  p r e d a t o r s o f Z. m a r i n a  (Fukuda  of invertebrates  u p r o o t e d and u n a b l e t o r e - e s t a b l i s h .  Many o f t h e  floating These  of  i n the  floating  38  s e e d l i n g s c o u l d be a m a j o r s o u r c e o f m o r t a l i t y (See s e e d l i n g  establishment  A large persistent By  summer, most s e e d s  longer viable reported  section).  s e e d bank was n o t e v i d e n t i n t h i s  i n t h e s e e d bank o f t h i s  a n d some were a t s h a l l o w d e p t h s .  a persistent  s t u d i e s may i n d i c a t e a d i f f e r e n c e Alternately,  not density-dependent,  be t h e c a u s e .  s t u d y were no Bigley  Differences  2  the area o f t h i s  study.  (1981)  s e e d bank b e l o w 5 cm w i t h a mean number i n  t h e summer o f 72.5 v i a b l e s e e d s / 6 2 5 c m .  regimes.  ( B i g l e y 1981)  i n sediment  i f seed m o r t a l i t y  between  disturbance  from v a r i o u s causes i s  t h e n t h e much s m a l l e r s e e d p r o d u c t i o n i n  s t u d y compared t o t h a t o f B i g l e y  (1981) c o u l d  Z o s t e r a i a p o n i c a has n o t been p r e s e n t i n t h e  s t u d y a r e a l o n g enough f o r o b s e r v a t i o n s o f i t s p o p u l a t i o n r e s p o n s e t o d i s t u r b a n c e b u t a low o r n o n - e x i s t e n t s e e d would suggest from  t h a t t h i s p o p u l a t i o n would have l i t t l e  bank  t o draw  i n case o f major d i s t u r b a n c e . One s t u d y t h a t d i s c u s s e s s e e d bank d y n a m i c s a n d t h e  r e l a t i o n s h i p s w i t h p o p u l a t i o n dynamics i n t e r r e s t r i a l Grime  (1989) w h i c h d e s c r i b e s f o u r t y p e s o f s e e d b a n k s a n d f i v e  regenerative strategies. determined  A l t h o u g h t h e seed bank t y p e s a r e  by l a b o r a t o r y c h a r a c t e r i s t i c s ,  c h a r a c t e r i s t i c s used  Bigley's  (1981) s t u d y .  requirements  been determined.  some o f t h e  i n t h e k e y c a n be a p p l i e d t o  c h a r a c t e r i s t i c s o f Z. i a p o n i c a  and  systems i s  Light  seeds  found  i n this  i s not required  forscarification  s t u d y and  f o r germination  o f Z. i a p o n i c a  seeds have n o t  L a b o r a t o r y work i n v o l v i n g t h e d r y i n g o f Z. 39  iaponica  s e e d s has  not  b e e n done.  believe that  Z.  seed banks.  Type I I I d e s c r i b e s  primarily Type IV  iaponica  describes  a n n u a l and  Z.  iaponica  i n my  germinate p r i m a r i l y i n the persistent  the this  a n n u a l and  g e r m i n a t e i n autumn b u t  describes  seed  the  has  perennial Neither  s p r i n g and  strategy  strategy  climatic  or b i o t i c  factors.  habitat,  there  fits  Variability  but  the  seasonal  i n the  II.  d a t a may  i n seed dynamics.  shown t o be  b e t t e r than small  al.  By  a l s o be  how  that  accurately  seeds  is little  or  best.  i n Grime The  The  no  (1989),  plant  using  vegetative  conditions  Zostera  under  The  iaponica  f i t the also  seeds  do  types. important may  be  s a m p l i n g u n i t s have been large units  (Benoit  s e d i m e n t , one  might  seed products are  u s e f u l t o compare t h e  by  sampling regime i t s e l f  numbers o f  are  strategy  h a v e o b s c u r e d some  sampling deeper i n t o the  d e e p s e e d s and  seem t o  regeneration  t o b l a m e b e c a u s e l a r g e numbers o f s m a l l  discover  IV  with  predictable disturbance  appear t o belong i n e i t h e r of these  1989).  to  bank.  shrubs  because the  These c o n d i t i o n s  s e e d bank T y p e s I and  differences  seed  appears t o have a s e l e c t i v e advantage to seasonally  not  one  herbs  s e e d s bank t y p e  a s i n g l e cohort.  subjected  includes  h e r b s and  study area  habitats  intertidal  maintain a small  independent o f f s p r i n g (seeds o r  p r o p a g u l e s ) p r o d u c e d by which t h i s  leads  perennial  strategies described  regeneration  strategy  key  bank.  regenerative  seasonal  the  seeds b e l o n g t o e i t h e r Type I I I o r  l a r g e p e r s i s t e n t seed banks.  Of  Even so,  invertebrates  located.  contained  et  I t might within  the  s a m p l e s t o d e t e r m i n e i f t h e i r numbers and a c t i v i t i e s associated the  are  w i t h t h e d e p t h o f s e e d s and p o s s i b l e t u r n o v e r w i t h i n  sediment.  41  SEEDLING ESTABLISHMENT  Introduction Establishment seed takes root,  i s the  u s e s up  process during  provisions provided  assumes i n d e p e n d e n t g r o w t h as 1982).  The  accurately seedlings  links  establishment  perennial  a seedling  seedlings  by  germinating the  (Howe and  to  monitor  a r e made, b e c a u s e  emergence w i l l  not  be  and  Smallwood  is difficult  observations  parent  those  recorded  1986).  i n the  first  frequent  which d i e before  (Watkinson The  s u r v i v o r s h i p of unless  which a  of the  seedling  c o l o n i z a t i o n o f new  terrestrial  year of  life  found t h a t the e s t a b l i s h e d was  c h a n c e o f a Z. small  but  of the  t e r r i t o r y by  grasses nearly  (Stebbins  i s one  plants.  a l l mortality  1971).  Harrison  iaponica  and  seedling  once s e c u r e l y  weakest  rooted  In  i s within Bigley  the  (1982)  becoming the  plant  can  grow q u i c k l y . The  shading of the  marina decreases the  a n n u a l by  s u r v i v a l and  annual,  suggesting  1987).  There i s i n d i r e c t  m a r i n a may Bank  canopy o f  to the Z.  reproductive competition  iaponica  form o f  for light that  m a r i n a compared t o 43%  of  m of  (PAR, sea  surface  s h a d i n g by  30%  of  400-700  that  Z.  Roberts  w a t e r and PAR  the  (Keddy  i n deeper zones a t  active radiation  s e d i m e n t t h r o u g h 1.5  Z.  p o t e n t i a l of  F i e l d measurements i n d i c a t e t h a t  photosynthetically  penetrates  perennial  evidence suggesting  i n t e r f e r e w i t h Z.  (Nomme 1 9 8 9 ) .  surface  interspecific  the  nm) a  reaches  42  the  s e d i m e n t b e n e a t h a Z. i a p o n i c a c a n o p y  (Nomme 1 9 8 9 ) .  This  s h a d i n g may be r e s p o n s i b l e f o r t h e s u p p r e s s i o n o f l a t e r a l branching way  o f Z. i a p o n i c a o r may a f f e c t  (Nomme The  i t s growth  i n some o t h e r  1989).  o b j e c t i v e o f t h i s p h a s e o f t h e r e s e a r c h was t o  d e t e r m i n e i f t h e canopy  o f Z. m a r i n a i n t e r f e r e s w i t h t h e  s e e d l i n g emergence o r e s t a b l i s h m e n t hypothesis  o f Z. i a p o n i c a .  The n u l l  i s t h a t Z. i a p o n i c a s e e d s p l a n t e d w i t h Z. m a r i n a  grow a n d e s t a b l i s h no d i f f e r e n t l y  than those  seeds p l a n t e d  will after  t h e e e l g r a s s i s removed.  43  Methods For  field  s t u d i e s o f seed g e r m i n a t i o n , and  e s t a b l i s h m e n t and growth, that  retained  i t was n e c e s s a r y t o u s e a  c l e a n e d sediment, k e p t out rhizomes  surrounding plants, sediment.  seedling container  from  and a l l o w e d water t o c i r c u l a t e t h r o u g h t h e  F o u r - l i t r e p l a s t i c buckets  (20-cm d i a m e t e r ) w i t h  b o t t o m s removed a n d r e p l a c e d b y n y l o n s t o c k i n g m a t e r i a l  were  used. S e e d s were c o l l e c t e d sediment.  from f r u i t i n g  s h o o t s and from t h e  R e p r o d u c t i v e s h o o t s o f Z. i a p o n i c a w e r e  from t h e f i e l d  site  i n August  brought back t o t h e l a b .  1988, p l a c e d  collected  i n p l a s t i c bags and  S h o o t s were k e p t i n c i r c u l a t i n g ,  aerated  s a l t w a t e r a q u a r i a a t a p p r o x i m a t e l y 5° C u n t i l  matured  and dropped t o t h e bottoms o f t h e t a n k s .  s e e d s were s t o r e d Sediment  i n t h e d a r k a t 5° C.  site.  The s e d i m e n t was s i f t e d  saved f o r l a t e r use.  1989  using  Cleaned  The number o f s e e d s p e r a r e a  was d e t e r m i n e d a n d s e e d s were s t o r e d 5°  f o r seeds  same method a s u s e d f o r s e e d b a n k a n a l y s i s .  s e d i m e n t was  Collected  was c o l l e c t e d t o a d e p t h o f 10 cm i n J a n u a r y  from t h e f i e l d the  i n seawater  t h e seeds  i n seawater  i n the dark a t  C. Due t o t h e s p a t i a l h e t e r o g e n e i t y o f t h e s e a g r a s s e s (Moody  1978),  two f i f t y - m e t e r t r a n s e c t s p a r a l l e l  were s e t up i n e a c h z o n e . the  tidal  and 5 meters  apart  These t r a n s e c t s r a n p e r p e n d i c u l a r t o  f l o w , a b o u t 500 m f r o m t h e c o a l p o r t  m f r o m t h e Tsawwassen causeway ( F i g . 1 0 ) .  c a u s e w a y a n d 1500  One-meter  square  44  Fig.  10  Study S i t e Layout  SHORE Japonica  C O A L P O R T C A U S E W A Y  Zone 2m t  2m  t 200 m Transition <-  Zone 1500 m  500 m  [  -50 mt 200 m  Marina  T S A W W A S S E N  Zone  r  5m t  C A U S E W A y  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx RIP-RAP DIKE  STRAIT OF GEORGIA  45  p l o t s were p l a c e d The  randomly  on e a c h s i d e o f t h e t r a n s e c t  lines.  space between t h e p a i r e d t r a n s e c t s a l l o w e d a c c e s s t o t h e  p l o t s without disturbing Planting 1989.  them.  occurred during the l a s t  C l e a n e d s e d i m e n t was  taken to the study s i t e . seeds f i r s t iaponica  Bigley  weeks o f J a n u a r y ,  i n the modified buckets  (1981) f o u n d t h a t  g e r m i n a t e d a t a d e p t h o f 4-7  cm.  The b u c k e t s were p l a n t e d  1 m  Z.  into  and  iaponica  Thus t e n  s e e d s were p l a c e d a p p r o x i m a t e l y 5 cm  sediment. chosen  placed  two  Z.  the  i n the centre of  randomly  p l o t s a l o n g t h e t r a n s e c t s o f e a c h zone s u c h t h a t  2  the  t o p s o f t h e b u c k e t s were a p p r o x i m a t e l y l e v e l w i t h t h e surrounding  sediment.  To t e s t and  t h e i n f l u e n c e o f Z o s t e r a m a r i n a on s e e d g e r m i n a t i o n  s e e d l i n g e s t a b l i s h m e n t o f Z. i a p o n i c a .  p l o t s were u s e d , w i t h t h e n a t u r a l  Z.  in  zones.  the japonica  with  occurring  2  intact. and  Z.  marina  zone, t h e t r e a t m e n t o f p l a n t i n g b u c k e t s i n p l o t s u n n e c e s s a r y and t h e r e f o r e e x c l u d e d .  C o n t r o l s were u s e d t o m o n i t o r t h e e f f e c t s  1 m  seeded  i n the t r a n s i t i o n  B e c a u s e t h e r e i s no n a t u r a l l y  Z. m a r i n a was  and o f c l e a r i n g  types of  m a r i n a removed o r  N i n e b u c k e t s o f e a c h t y p e were p l a n t e d marina  two  Z. m a r i n a  from t h e p l o t s .  p l o t s w i t h Z. m a r i n a removed.  p l a c i n g b u c k e t s w i t h o u t bottoms i n t o removed.  T h e r e were f i f t e e n  randomly  along the transects  The 1 m  The  of the buckets first  control  second c o n t r o l 2  involved  p l o t s w i t h Z.  of each o f t h e s e c o n t r o l s i n each o f the t h r e e  was  marina placed  zones.  46  To m o n i t o r had  two  s e e d l i n g emergence and  30-cm l e n g t h s o f PVC  sediment markers.  t o a depth Two  dimensions)  plastic  o f 29 cm.  survival,  control  pipe inserted  into  T h e s e were p e r m a n e n t  of the four legs of a p l o t  frame  were p l a c e d i n t o t h e p i p e s .  (20x50 cm  sediment  surface.  was  t o mark t h e a r e a v e r t i c a l l y p r o j e c t e d t h r o u g h  i n s i d e o f t h e frame. p a r a l l a x tube.  r a m e t was  and  the  i n s u r e d by u s e  10 cm  l o n g by  frame s u r f a c e ,  identified  8  shoot  of a  cm  When t h e  tube  locations  and  i t s p o s i t i o n was  became e v i d e n t t h a t  some Z.  o v e r w i n t e r i n g rhizomes;  of  disappearance.  as i n d i c a t o r s o f  i n d u c e d by t h e  was  the It  from  s h o o t s were  were t a k e n  o f i n v e r t e b r a t e burrow openings  changes i n t h e environment  a mature  s h o o t s were g r o w i n g  of the sediment  i n p l o t s w i t h and w i t h o u t b u c k e t s  December.  mapped t o i n d i c a t e  thus from June 1 t h e s e a d u l t  Temperatures  inspection  t h e end  f l o w e r i n g , and  iaponica  tide  through  t o s p e c i e s , w h e t h e r i t was  d a t e o f emergence, b r a n c h i n g ,  a l s o counted.  weeks, f r o m A p r i l  t h e n o n c e a month u n t i l  shoot or a s e e d l i n g ,  visual  Plexiglas  c o n t r o l p l o t s were mapped e v e r y low  a p p r o x i m a t e l y e v e r y two  November 1989 Each  on t h e p l o t  the  identified.  E x p e r i m e n t a l and cycle,  above  w i t h c r o s s - h a i r s a t b o t h ends.  placed v e r t i c a l l y  c o u l d be  a l i g n m e n t was  T h i s P l e x i g l a s t u b e was  ( i n s i d e diameter) was  s u r f a c e 10 cm  acetate sheet p l a c e d over the  Vertical  inside  A P l e x i g l a s sheet f i t  frame f o r m i n g a t a b l e - l i k e  used  the  plot  into the  An  plots  and conducted  possible  buckets.  47  To  d e t e r m i n e w h e t h e r t h e r e were s i g n i f i c a n t d i f f e r e n c e s  between c o n t r o l s and e x p e r i m e n t a l zones, data  were f i r s t  (which c l o s e l y acetate  and s q u a r e - r o o t  (significance  were g r e a t e r t h a n  both  w i t h i n a n d among  s t a n d a r d i z e d t o numbers p e r 625 c m  approximated t h e areas  sheets)  way ANOVA  plots,  level,  o f t h e buckets and  transformed  ( Z a r 1984).  p<.05) was u s e d when  zero and t h e K r u s k a l - W a l l i s t e s t  u s e d when v a r i a n c e s were z e r o  2  ( Z a r 1984).  A two-  variances (p<.05) was  B e c a u s e SYSTAT  only  does t h e o n e - f a c t o r K r u s k a l - W a l l i s t e s t ,  p r o b a b i l i t i e s were a d -  j u s t e d by u s i n g t h e B o n f e r r o n i p r o c e d u r e  (Wilkinson  avoid  a type  one e r r o r .  1988) t o  When t h e B o n f e r r o n i p r o c e d u r e was  a p p l i e d t o a 0.05 p r o b a b i l i t y t h e new p r o b a b i l i t y was 0.0125. In each case,  the significance  level  C o n t r o l p l o t s were compared w i t h  i s stated i n the test. t h e n a t u r a l survey (see  s e d i m e n t s t u d i e s methods) u s i n g a o n e - f a c t o r ANOVA test the effects  of clearing  (p<.05) t o  Z. m a r i n a .  48  Results Seedlings The the  initial  seedling.  seedling w i l l depending  ramet t h a t emerged f r o m t h e s e e d w i l l  Any  o t h e r ramets  t h a t may  be  have b r a n c h e d  termed  from  this  be c a l l e d v e g e t a t i v e o r r e p r o d u c t i v e s h o o t s ,  on t h e i r  function.  S t a n d a r d e r r o r s were h i g h  o v e r l a p p e d , t h u s t h e y were n o t i n c l u d e d  i n the graphs  and  for  clarity. The was  number o f s e e d l i n g s p e r 625  not s t a t i s t i c a l l y  control plots  i n each  numbers o b s e r v e d to  be  different zone  i n seeded  cm  different  i n the natural  f r o m t h e number f o u n d  ( F i g . 11 a - c v s F i g . 1 2 ) . buckets  i n the japonica  lower than i n the c o n t r o l p l o t s ,  statistically  2  ( F i g . 11a)  b u t t h i s was  (p>.0125).  (Fig.  bucket p l o t s lib).  from A p r i l  I t appears  that  24 t o J u l y  1  i n the seeded  i n the The  zone  appeared  not  In the  zone t h e r e were d i f f e r e n c e s b e t w e e n t h e c o n t r o l p l o t s seeded  survey  transition and  the  (p<.0125) buckets p l a n t e d with  Z. m a r i n a more s e e d l i n g s s u r v i v e d a f t e r m i d - J u l y t h a n i n t h e s e e d e d b u c k e t s p l a n t e d w i t h o u t Z. m a r i n a not  statistically  significant  d i f f e r e n c e among p l o t s iaponica  but the d i f f e r e n c e  (p>.0125).  i n the marina  zone,  s e e d l i n g s were f o u n d c l u m p e d j u s t  The mean number o f Z. greatest  in April  13a-c).  O f t e n more t h a n h a l f  by t h e f o l l o w i n g  and May,  iaponica  survey.  T h e r e was  was  no  b u t i n many p l o t s outside the  s e e d l i n g s emerging  Z.  bucket. was  decreasing sharply afterwards (Fig. o f t h e s e e d l i n g s would d i s a p p e a r  Many s e e d l i n g s were f o u n d  uprooted, 49  Date  Fig.  11a  J a p o n i c a zone. Mean number o f Z.. i a p o n i c a s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , ^ = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a . 2  50  2  -  0 Date Fig.  l i b T r a n s i t i o n zone. Mean number o f Z.. i a p o n i c a s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , A =unseeded b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z.. m a r i n a . •=seeded b u c k e t s w i t h Z. m a r i n a . 2  51  'J  4  r  co DO .1-1  J  o o *-< CD  2  a  a  c3 ©  1 1  0  N VW^iWW^  *****  rt  ftp-  Date Fig.  11c  M a r i n a zone. Mean number o f Z. i a p o n i c a s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , » = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a , • =seeded b u c k e t s w i t h Z.. m a r i n a . 2  52  * * * * * * * * * * * Date Fig.  12  Mean number o f s e e d l i n g p e r 625 c m i n the n a t u r a l s u r v e y i n each zone. •= j a p o n i c a z o n e , = t r a n s i t i o n zone, o= m a r i n a z o n e . 2  A  53  Fig.  13a  J a p o n i c a zone. Mean number o f n e w l y emerged s e e d l i n g s p e r 625 c m a t each date i n each treatment, o =unseeded p l o t s w i t h o u t bucket, ^ = u n s e e d e d b u c k e t s , » = s e e d e d b u c k e t s w i t h o u t Z. marina. 2  54  4  « w  o a  w CO  a © CO  o u  © a p* z  a ©  n  0  ^ n  ^  u  i  Date Fig.  13b  T r a n s i t i o n zone. Mean number o f n e w l y emerged s e e d l i n g s p e r 625 c m a t each date i n each treatment. o= u n s e e d e d p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z, m a r i n a . « = s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  55  4 to  a  Date Fig.  13c  M a r i n a zone. Mean number o f n e w l y emerged s e e d l i n g s p e r 625 c m a t each date i n each treatment. o=unseeded p l o t s w i t h o u t bucket, A=unseeded b u c k e t s , «=seeded b u c k e t s w i t h o u t m a r i n a . « = s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  Z.  56  floating  i n t h e water.  S e e d l i n g s c o n t i n u e d t o emerge  August.  I n t h e s e e d e d b u c k e t s w i t h Z. m a r i n a and t h e  b u c k e t s o f t h e t r a n s i t i o n zone, to  emerge i n t o  Z.  iaponica  into unseeded  seedlings  continued  September.  S e e d l i n g g e n e t s t h a t emerged b e t w e e n 24 A p r i l a n d all  z o n e s s u r v i v e d t h e l o n g e s t , w i t h one o r more  surviving  p a s t t h e end o f O c t o b e r  July  1, s u r v i v e d  Vegetative  (30%),  in  ramets  ( F i g . 14a-c).  number o f g e n e t s t h a t emerged much l a t e r  23 May  A  considerable  from June  1 to  into the winter.  ramets  Overall,  b r a n c h i n g was  t h a n i n t h e o t h e r two  zones.  branching with certain statistically  less  frequent  i n the marina  A l t h o u g h t h e r e a p p e a r e d t o be more  t r e a t m e n t s ( F i g . 1 5 a - c ) , t h e r e was  significant effect of plot  t y p e i n any  i n s e e d e d b u c k e t s w i t h o u t Z. m a r i n a e x h i b i t e d  branching  i n the japonica  zone and none i n t h e o t h e r  no  zone.  Seedlings  Reproductive  zone  little  zones.  Shoots  R e p r o d u c t i v e s h o o t s began t o appear August or  d i s a p p e a r a t t h e end o f S e p t e m b e r  of  r e p r o d u c t i v e s h o o t s was  ( F i g . 16a-c).  v e r y low i n a l l t h r e e  means w e r e 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 more i n t h e j a p o n i c a o n l y one p l o t h a d  zone,  1 and t o d e t a c h The  density  zones.  (p>.0125).  T h e r e were  fewer i n t h e t r a n s i t i o n zone,  reproductive shoots i n the marina  The  and  zone.  There  w e r e no r e p r o d u c t i v e s h o o t s p r o d u c e d f r o m s e e d e d b u c k e t s i n 57  25  cd  >  20  GO  © a ©  15  -  O o 10 © ©  M  cd ©  5 -  2  l^h-M>  ' Date  Fig.  14a  J a p o n i c a zone. Mean number o f weeks t h a t s e e d l i n g genets from each date s u r v i v e d i n each treatment. o=unseeded p l o t s w i t h o u t bucket, A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. marina.  58  K^JSV  M>  *H>^  Date Fig.  14b  T r a n s i t i o n zone. Mean number o f weeks t h a t s e e d l i n g genets from each date s u r v i v e d i n each treatment. o=unseeded p l o t s w i t h o u t bucket, A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. i = s e e d e d b u c k e t s w i t h Z. m a r i n a .  59  M>  v6  Date Fig.  14c  M a r i n a zone. Mean number o f weeks t h a t seedling genets from each date s u r v i v e d i n each treatment. o=unseeded p l o t s w i t h o u t bucket, A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a , « = s e e d e d b u c k e t s w i t h Z. m a r i n a .  60  Date Fig.  15a  J a p o n i c a zone. Mean number o f v e g e t a t i v e s h o o t s f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , ^ = u n s e e d e d b u c k e t s , » = s e e d e d b u c k e t s ^ w i t h o u t Z. m a r i n a . 2  61  oo  a  Date Fig.  15b  T r a n s i t i o n zone. Mean number o f v e g e t a t i v e s h o o t s f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a , B = s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  62  Fig.  15c  M a r i n a zone. Mean number o f v e g e t a t i v e s h o o t s f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , ^ = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a . • = s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  63  Fig.  16a  J a p o n i c a zone. Mean number o f r e p r o d u c t i v e s h o o t s f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t bucket, A=unseeded buckets, «=seeded buckets w i t h o u t marina. 2  Z.  64  1.0 CO  •«-> O O  .a 0.8 GO  £ o  o 0.6  a o  o 0.4 a  «  0.2  © 0.0  Date Fig.  16b  T r a n s i t i o n zone. Mean number o f r e p r o d u c t i v e s h o o t s f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a and s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  65  1.0 CO  •*->  O O 43 GO  ©  0.8  •T-l -»-»  o o  0.6 -  CM  O O  0.4 -  © a  a  0.2  03  * * * **  0.0 Date Fig.  16c  M a r i n a zone. Mean number o f r e p r o d u c t i v e s h o o t s f r o m s e e d l i n g s p e r 625 c m i n each treatment. «=unseeded p l o t s w i t h o u t bucket, u n s e e d e d b u c k e t s , a n d s e e d e d b u c k e t s w i t h o u t Z. m a r i n a . • =seeded b u c k e t s w i t h Z. m a r i n a . (Note: f i l l e d s y m b o l s o v e r l a p on x - a x i s . ) 2  66  e i t h e r the japonica or t r a n s i t i o n reproducing  i n the marina  zone.  zone was  The  only  Z.  iaponica  from a seeded b u c k e t w i t h Z .  marina. T h e r e was  no d i f f e r e n c e  i n t h e number o f s p a t h e s p r o d u c e d  p e r r e p r o d u c t i v e s h o o t i n any o f t h e z o n e s of the p l o t s d i d not a f f e c t  (p>.05).  Elevation  t h e number o f s p a t h e s p r o d u c e d  per  shoot. The number o f s p a t h e s p e r s h o o t i n t h e n a t u r a l a d j a c e n t t o t h e s t u d y p l o t s was i n e a c h zone  (p>.05)  t h e same a s i n t h e c o n t r o l  ( F i g . 17a-c).  4.22.  T h e r e was  i n the marina  Total  from  1.30  a mean o f 2 s p a t h e s p e r s h o o t f r o m t h e  plot  zones ranged  zone.  ramets The numbers o f t o t a l  reflect The  plots  The mean numbers o f s p a t h e s  p e r s h o o t i n t h e j a p o n i c a and t r a n s i t i o n to  population  the i n i t i a l  increase  ramets  from s e e d l i n g s  ( F i g . 18a-c)  s e e d l i n g emergence i n l a t e A p r i l  i n m i d - J u l y t o t h e end o f August  t o June.  demonstrates  p r o d u c t i o n o f b r a n c h i n g and r e p r o d u c t i v e s h o o t s f r o m seedlings.  The d e c l i n e  i n ramets  in late  September  the  established illustrates  t h e d e t a c h i n g o f t h e r e p r o d u c t i v e s h o o t s and t h e b e g i n n i n g o f the reduction  i n numbers o f t h e r a m e t s b e f o r e w i n t e r .  T h e r e w e r e no s i g n i f i c a n t t h e j a p o n i c a and m a r i n a  zones.  d i f f e r e n c e s among p l o t In the t r a n s i t i o n  were s t a t i s t i c a l  d i f f e r e n c e s between p l o t s  June  1 when r a m e t s  19 and J u l y  types i n  zone,  there  (p<.0125) o n l y  on  i n t h e seeded p l o t s w i t h o u t  67  Date  Fig.  17a  J a p o n i c a zone. Mean number o f s p a t h e s p e r r e p r o d u c t i v e shoot i n t r e a t m e n t s and n a t u r a l survey. o=unseeded p l o t s w i t h o u t b u c k e t , A=unseeded b u c k e t s , a = n a t u r a l s u r v e y .  68  Date  Fig.  17b  T r a n s i t i o n zone. Mean number o f s p a t h e s p e r reproductive shoot i n treatments and n a t u r a l survey. o=unseeded p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z.. marina, • =natural survey.  69  Date Fig.  17c  M a r i n a zone. Mean number o f s p a t h e s p e r r e p r o d u c t i v e shoot i n t r e a t m e n t s and n a t u r a l s u r v e y . « = s e e d e d b u c k e t s w i t h Z. m a r i n a , •=natural survey.  70  Fig.  18a  J a p o n i c a zone. Mean number o f t o t a l ramets p r o d u c e d f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t bucket, *=unseeded b u c k e t s , «=seeded b u c k e t s w i t h o u t marina. 2  Z.  71  10  r  oo fl  Date  Fig.  18b  T r a n s i t i o n zone. Mean number o f t o t a l ramets p r o d u c e d f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , « = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a , B = s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  72  Fig.  18c  M a r i n a zone. Mean number o f t o t a l r a m e t s p r o d u c e d f r o m s e e d l i n g s p e r 625 c m i n each treatment. o=unseeded p l o t s w i t h o u t bucket, ^=unseeded buckets, «=seeded b u c k e t s w i t h o u t m a r i n a . a = s e e d e d b u c k e t s w i t h Z. m a r i n a . 2  Z.  73  Z.  marina  a l l but  statistical The  seeded  the  plots  number  lower  the  though  some  initial  the marina  seeded  of  buckets died  t h e r e were  interesting  numbers  zone,  unseeded  adult  July  to  marina  15  zone,  few  the  control  with  Z.  but  seeded  few  trends.  in  the  buckets  plots.  marina  The  had  with  Z.  bucket  ramets  that  out.  that  either  bucket  edge  or  buckets  without  of  no that  no  transition the  the  floated  sediment rims  Visually  invertebrate  burrow  zone  from  i n seeded  the  August  was  seen  buckets over  bucket,  removed.  slightly  openings  zone  in  difference.  level,  t h e r e was  unseeded  japonica  same t r e n d  into  i n sediment  (p>.05).  i n the  surrounding area  shoots were  difference  i n the  d i d appear  i n from  These  shoots  significant  uprooted,  there.  with decreasing  fewer  Although  exposing bucket  was  among p l o t s  shoots  that  were  i n the  were p l a n t e d a t  away,  There  1 and  grew  decreased  i n those without  t h e r e was  adult  re-established  There  (p<.0125).  ramets  number  than  1 t o August  October  washed  shoots  ( F i g . 19a-c).  with buckets  The  the  there are  when o t h e r p l o t s  elevation  the  and  Even  Shoots The  16  had  equalled  and  persisted  from  zone  soon  controls  Adult  differences, buckets  transition marina  disappeared.  often above  though sediments  sediment  temperatures no  level.  taken  difference  between p l o t s  the  and  Even the  were  in  the  with  and  buckets.  74  100  oi  tt-t O  r  80  -  60  -  40  -  20  -  O  & .0 cd <0  0  Date Fig.  19a  J a p o n i c a zone. Mean number o f a d u l t s p e r 625 cm i n each treatment. o=unseeded p l o t s w i t h o u t b u c k e t , A = u n s e e d e d b u c k e t s , «=seeded b u c k e t s w i t h o u t Z. m a r i n a . 2  75  Fig.  19b  T r a n s i t i o n zone. Mean number o f a d u l t s p e r 6 2 5 cm i n each t r e a t m e n t . o=unseeded p l o t s w i t h o u t b u c k e t , =unseeded b u c k e t s , » = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a . « = s e e d e d b u c k e t s w i t h Z.. marina. (Note: f i l l e d symbols o v e r l a p ) 2  A  76  100  r  80 •*-»  o © a  60  40  « ©  20 -  0 Date  Fig.  19c  M a r i n a zone. Mean number o f a d u l t s p e r 625 cm i n each treatment. o=unseeded p l o t s w i t h o u t bucket, =unseeded b u c k e t s , • = s e e d e d b u c k e t s w i t h o u t Z. m a r i n a . • = s e e d e d b u c k e t s w i t h Z. marina. (Note: f i l l e d symbols o v e r l a p )  2  77  Natural  Survey  There  was  no  seedlings  among  zones)and  July  12). be  These  4  per  shoot  after  shoots  density  plots  of total  genets)  in  control  plots  the density  from  could  July  not  4 so the  date.  plots  the total  t o w h a t was  t h e number  and t h e n a t u r a l  of  number found i n spathes  population  s h o o t s were v e r y  i n each  the total zone  among  September. than  began Thus  2 cm  zones  t o reduce i n the f a l l  high  zone  Densities  a n d 1 mm  of adults ramets  (p>.05).  15 a n d o n N o v e m b e r  t h e other zones. also  i n the natural  t h e sum  o f these dates the marina  less  after  two  (p<.05) ( F i g .  and s e e d l i n g s  when c o m p a r i n g  ramets  plus  of adults  4 t o October  Shoots  < japonica)  of  low i n t h e  zone.  overwintering  all  this  of reproductive  different  July  (marina < o t h e r  a n d when c o m p a r i n g  statistically  in  i n the density  population  i n the control  population  Numbers  The  the  1  mapped  the adult  i n the control  (p>.05). marina  from  no d i f f e r e n c e s  reproductive natural  on June  (marina < t r a n s i t i o n  combined  were  the  except  difference  s h o o t s had n o t been  were  There of  zones  distinguished  numbers  significant  seedlings i n  were  of the natural 30  (p<.05)  declined  was  sharply  not  ( i . e . from  from  There  density  i n length  s u r v e y was  differences survey  from  ( F i g . 20). lower after  than  On that  August  and l e a f  width  i n  and w i n t e r ramets  would  often  1.  late be  wide.  78  Fig.  20  Mean number o f a d u l t s p e r 625 c m i n each i n the natural survey. »=japonica zone, A = t r a n s i t i o n z o n e , o=marina z o n e . 2  zone  79  Discussion In a l l of the t e s t s there  was  no d i f f e r e n c e o f mean  numbers b e t w e e n t h e c o n t r o l p l o t s and t h e n a t u r a l p o p u l a t i o n jacent  t o the study p l o t s .  Because  t h a t the removal o f Zostera disrupt  Z.  iaponica  marina  1981, plots,  total  1986).  be  assumed  sediment.  as t h e p l a n t s  grew  due  fragmentation (Bigley  In order not t o d i s t u r b  the  e x c a v a t i o n o f ramets t o determine which genet t h e y  were f r o m was uncertainty,  to identify  r h i z o m e s and r h i z o m e  B i g l e y and H a r r i s o n  i t will  from t h e s t u d y p l o t s d i d not  seeds o r shoots i n the  G e n e t s became d i f f i c u l t t o the underground  of this,  ad-  impossible.  T h e r e may  be some e r r o r due  to  this  b u t c a r e f u l mapping o f r a m e t s r e d u c e d t h e e r r o r t o  a minimum. T h e r e were, however, p r o b l e m s w i t h t h e u s e o f buckets which had control plots. difference. the  iaponica planted  than the  f a c t o r s may  have c o n t r i b u t e d  First,  the density  o f s e e d s t h a t were p l a n t e d  inadvertently  lower than t h a t  (See s e d i m e n t s t u d i e s was  seedlings  Two  b u c k e t s was  seed bank  l o w e r numbers o f e m e r g i n g  seeded  results,  a l s o s e e n t o be g r o w i n g j u s t  b u c k e t s , so i t appears t h a t  to the in  i n the undisturbed  page 1 0 ) . outside  Second,  Z.  many o f t h e s e  some o f t h e p l a n t e d  seeds  washed o u t o f t h e b u c k e t s . Zostera  i a p o n i c a has a v a r i e d r e p r o d u c t i v e  in the i n t e r t i d a l the  plant  and B i g l e y  zone where t h e f i r s t  strategy.  c o l o n i z e r s were o b s e r v e d ,  i s l a r g e l y a n n u a l and p r o d u c e s many s e e d s 1982).  At progressively  High  lower e l e v a t i o n s ,  (Harrison i n the  80  area  of the japonica  overwintering  and t r a n s i t i o n  zones o f t h i s  s h o o t s and s h o o t s t h a t came f r o m  r h i z o m e s made up a c o n s i d e r a b l e rhizomes overwinter  overwintering  part of the population.  more s u c c e s s f u l l y i n s e d i m e n t t h a t  exposed t o t h e c o l d winter  a i r common d u r i n g  tides.  at the high  This  study,  s t r e s s occurs  Perhaps i s not  the nighttime  low  e l e v a t i o n s and dormant  s e e d s may b e r e s i s t a n t t o c o l d s t r e s s . It  appears that there  emerge e a r l y , a s t h e r e there  was a f l u s h  seedlings Bigley May,  (1981).  o f emerging s e e d l i n g s  systems.  The s e e d l i n g s  l e v e l s t o t h e warmer, favorable  risk period  b r i g h t e r , and l o n g e r  f o r Z.. i a p o n i c a  When a r t i f i c i a l l y  area  t h a t may m o d i f y  days w i t h  low l i g h t  s p r i n g days t h a t a r e  Early spring i s s t i l l  a  high-  seedlings.  planted  i n each zone, even t h e marina  zone, s e e d s were a b l e t o p r o d u c e r e p r o d u c t i v e enabling  sediment  ( i . e . t i d a l ) and  from c o o l w i n t e r  t o p l a n t growth.  through  i n J u l y , were t h e  ( i . e . storm-induced) d i s t u r b a n c e s progression  early  a s was o b s e r v e d b y  The i n t e r t i d a l  i s subject t o both r e g u l a r  seasonal  In April  t h a t emerged i n l a t e A p r i l  survived the longest.  unpredictable  which  b u t many o f t h e s e  a s w e l l a s a few l a t e e m e r g i n g s e e d l i n g s  habitat  more  i s i n many o t h e r  died, mostly through uprooting  genets that  the  i s no a d v a n t a g e t o s e e d l i n g s  shoots,  thus  t h e p l a n t t o propagate s e x u a l l y throughout t h e study  e v e n where p l a n t s a r e a b s e n t f r o m t h e n a t u r a l  vegetation.  In Japan,  Z. i a p o n i c a grew r a p i d l y f r o m s e e d s b u t no p l a n t s  developed  flowering  stems w i t h i n t h e f i r s t  year  (Arasaki  1950b).  81  This  i s f u r t h e r evidence f o r v a r i a b i l i t y w i t h i n the species.  Nomme (1989) showed t h a t t r a n s p l a n t s o f m a t u r e s h o o t s a l s o were able  t o grow t h r o u g h o u t t h e same s t u d y a r e a .  both adults  and s e e d l i n g s  Now we know  can mature throughout t h i s  gradient,  s o t h e l i m i t e d d i s t r i b u t i o n must d e r i v e  dispersal  pattern  identified  that  elevation  from t h e l o c a l  i n t h e sediment s t u d i e s  section  (page 3 7 ) . The current  biology  o f Z. i a p o n i c a a t t h e s e a w a r d edge o f i t s  range deserves s p e c i a l a t t e n t i o n .  Very  few a d u l t  were f o u n d  i n t h e m a r i n a zone a n d t h e s e were g e n e r a l l y  areas with  few Z.  marina.  The o c c a s i o n a l  seedling of  i a p o n i c a t h a t m i g h t e s t a b l i s h n a t u r a l l y among t h e Z. have d i f f i c u l t y the  perennial  penetrating  Z.  marina.  m a r i n a may a f f e c t winter that  Z.  Z. may  t h e e x t r e m e l y t h i c k r h i z o m e mats o f  Pre-emption o f r o o t i n g space by  Z.  i a p o n i c a a s i t grows, p e r h a p s d u r i n g t h e  and second y e a r o f growth.  (Nomme 1 9 8 9 ) .  to determine t h e extent  There i s i n d i r e c t  More r e s e a r c h  evidence Zostera  n e e d s t o b e done i n o r d e r  o f i n t e r f e r e n c e b e t w e e n t h e two s p e c i e s .  It  a p p e a r s , however, t h a t  Z.  marina. It  i n sparse  marina  s u g g e s t s b e l o w g r o u n d i n t e r a c t i o n b e t w e e n t h e two  species  shoots  Z. i a p o n i c a  i s not l i k e l y  t o replace  i s p o s s i b l e t h a t t h e b u c k e t s a n d Z. m a r i n a p l a y e d t h e  same b e n e f i c i a l  r o l e i n promoting establishment  and growth.  p r e s e n c e o f a b u c k e t o r a Z. m a r i n a c a n o p y was a s s o c i a t e d seedlings  and t h e i r  ramet d e n s i t i e s .  ramets p e r s i s t i n g l o n g e r  This  leads  or with  to the conclusion  The  with  higher  that both of 82  these better al. I  must  Z.  action or  Fonseca  and  effect  of  Z.  stabilize  and  the n u l l  marina  on  sediments  subsequent  F i s h e r 1986,  therefore accept  negative of  water  seedling establishment  1975,  must  slow  Fonseca  hypothesis the  growth  and  allow  (Thayer  Kenworthy  that  emergence  to  and  there  i s  et  1987). no  establishment  iaponica.  83  REFERENCES  A r a s a k i , M. 1950a. S t u d i e s on t h e e c o l o g y o f Z o s t e r a m a r i n a and Z o s t e r a nana I . B u l l . Jap. Soc. S c i . F i s h . 15(10):567572. A r a s a k i , M. 1950b. S t u d i e s on t h e e c o l o g y o f Z o s t e r a m a r i n a and Z o s t e r a nana I I . B u l l . J a p . S o c . S c i . F i s h . 16:70-76. B e n o i t , D.L., N.C. K e n k e l , and P.B. C a v e r s . i n f l u e n c i n g the p r e c i s i o n o f s o i l seed Can. J . B o t . 67:2833-2840.  1989. Factors bank e s t i m a t e s .  B e w l e y , J.D., and M. B l a c k . 1985. Seeds. 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