UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

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

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1991_A6_7 N53.pdf [ 3.29MB ]
Metadata
JSON: 831-1.0098621.json
JSON-LD: 831-1.0098621-ld.json
RDF/XML (Pretty): 831-1.0098621-rdf.xml
RDF/JSON: 831-1.0098621-rdf.json
Turtle: 831-1.0098621-turtle.txt
N-Triples: 831-1.0098621-rdf-ntriples.txt
Original Record: 831-1.0098621-source.json
Full Text
831-1.0098621-fulltext.txt
Citation
831-1.0098621.ris

Full Text

SEED AND SEEDLING DYNAMICS OF THE SEAGRASS ZOSTERA JAPONICA ASCHERS. AND GRAEBN. AND THE INFLUENCE OF ZOSTERA MARINA L. by MICHELE ERIN NIELSEN B . S c , The U n i v e r s i t y o f Iowa, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Botany) We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA December 1990 © Michele E r i n N i e l s e n , 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of PrSTAr-W  The University of British Columbia Vancouver, Canada Date n prr/<ft> DE-6 (2/88) ABSTRACT The s e a g r a s s Z o s t e r a i a p o n i c a A s c h e r s . and G r a e b n . o c c u r s as p u r e p o p u l a t i o n s and i n m i x t u r e w i t h Z o s t e r a m a r i n a L. a l o n g t h e i n t e r t i d a l r e g i o n s o f s o u t h w e s t B r i t i s h C o l u m b i a . A t t h e R o b e r t s Bank s t u d y a r e a s e e d and s e e d l i n g d y n a m i c s were s t u d i e d i n t h r e e v e g e t a t i o n z o n e s : a l a n d w a r d m o n o s p e c i f i c z o n e o f Z. i a p o n i c a , a zone o f c o - e x i s t i n g Z. i a p o n i c a a n d Z. m a r i n a , and a s e a w a r d m o n o s p e c i f i c zone o f Z. m a r i n a . Many more s e e d s were p r o d u c e d t h a n were f o u n d i n 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 d . Z o s t e r a j a p o n i c a s e e d s were most a b u n d a n t i n t h e s e e d bank i n t h e u p p e r z o n e s where t h e r e i s h i g h Z. i a p o n i c a d e n s i t y . E v e n t h o u g h s e e d s r e m a i n e d i n t h e w a t e r c o l u m n f o r up t o two months, v e r y few s e e d s d i s p e r s e d i n t o t h e l o w e r zone p o p u l a t e d b y Z. m a r i n a . t h u s l i m i t i n g Z.. i a p o n i c a ' s c o l o n i z a t i o n o f t h e l o w e r z o n e s . I t i s u n c l e a r what l i m i t s t h e d i s p e r s a l o f Z. i a p o n i c a s e e d s . Of t h e s e e d s t h a t were 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 few g e r m i n a t e d ( 5 % o r l e s s ) . When s e e d s were p l a n t e d i n b u c k e t s p l a c e d i n t o t h e s e d i m e n t , w i t h and w i t h o u t Z. m a r i n a , Z. i a p o n i c a was a b l e t o g e r m i n a t e , grow, and r e p r o d u c e i n one y e a r t h r o u g h o u t t h e s t u d y a r e a . S e e d l i n g s t h a t emerged e a r l i e s t ( i n A p r i l ) e i t h e r d i d n o t e s t a b l i s h o r d i d n o t s u r v i v e a s l o n g a s t h o s e s e e d l i n g s t h a t emerged l a t e r i n May a n d J u n e . S e e d l i n g s were o f t e n f o u n d u p r o o t e d , f l o a t i n g i n t h e w a t e r . The r i m o f t h e b u c k e t s and t h e p r e s e n c e o f Z. m a r i n a s h o o t s a p p e a r e d t o p r o t e c t t h e Z. i a p o n i c a s e e d l i n g s , p r e v e n t i n g u p r o o t i n g , b u t i i t h e r e s u l t s w e r e n o t c o n c l u s i v e . O n c e s e e d l i n g s became e s t a b l i s h e d , t h e y s p r e a d v e g e t a t i v e l y a t a r a p i d r a t e a n d c a n p e r s i s t t h r o u g h o u t t h e w i n t e r , e i t h e r a s r e d u c e d s h o o t s o r a s o v e r w i n t e r i n g r h i z o m e s . T h e s e o v e r w i n t e r i n g p l a n t s c o n t r i b u t e g r e a t l y t o t h e f o l l o w i n g y e a r ' s p o p u l a t i o n . i i i TABLE OF CONTENTS ABSTRACT i i L I S T OF FIGURES v i ACKNOWLEDGEMENTS x i INTRODUCTION 1 SEDIMENT STUDIES 3 I n t r o d u c t i o n 3 S t u d y A r e a 5 Metho d s 7 R e s u l t s 10 S e e d s 10 T e s t a e 19 G e r m i n a t i n g s e e d s 19 D i s c u s s i o n 35 SEEDLING ESTABLISHMENT 42 I n t r o d u c t i o n 42 Metho d s . . . . . 44 R e s u l t s . . . 49 S e e d l i n g s 49 i v V e g e t a t i v e ramets 57 Reproductive Shoots 57 T o t a l ramets . . 67 A d u l t Shoots 74 N a t u r a l Survey 78 D i s c u s s i o n 80 REFERENCES 84 v LIST OF FIGURES F i g . 1 Mean number of Z. i a p o n i c a seeds per 625 cm 2 of sediment i n each zone. 11 F i g . 2 Mean number of Z. i a p o n i c a seeds produced p e r 625 cm 2 ( d a t a = l o g 1 0 (X+l)) i n each zone 12 F i g . 3 Mean number of Z. i a p o n i c a seeds per 625 cm 2 o f sediment a t each depth. a. J a p o n i c a zone • 13 b. T r a n s i t i o n zone 14 c. Marina zone 15 F i g . 4 Percent of the t o t a l number of v i a b l e and non-v i a b l e Z. i a p o n i c a seeds per 625 cm 2 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 found a t each date. a. J a p o n i c a zone 16 b. T r a n s i t i o n zone 17 c. Marina zone 18 F i g . 5a J a p o n i c a zone. Percent o f the t o t a l number o f v i a b l e Z. i a p o n i c a seeds per 625 cm 2 o f sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, separated by depth. 20 v i F i g . 5b J a p o n i c a zone. Percent of the 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 seeds per 625 cm 2 of sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, s e p a r a t e d by depth. 21 F i g . 5c T r a n s i t i o n zone. Percent o f the t o t a l number o f v i a b l e Z. i a p o n i c a seeds per 625 cm 2 o f sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, separated by depth 22 F i g . 5d T r a n s i t i o n zone. Percent of the t o t a l number of n o n - v i a b l e Z. i a p o n i c a seeds p e r 625 cm 2 o f sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, s e p a r a t e d by depth. 23 F i g . 5e Marina zone. Percent of the 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 seeds p e r 625 cm 2 o f sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, s e p a r a t e d by depth. 24 F i g . 5f Marina zone. Percent of the 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 seeds p e r 625 cm 2 o f sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date t h a t were n o n - v i a b l e sep a r a t e d by depth 25 F i g . 6 Mean number of Z. i a p o n i c a t e s t a e p e r 625 cm 2 o f sediment i n each zone. 26 F i g . 7 Mean number o f Z. i a p o n i c a t e s t a e per 625 cm 2 of sediment a t each depth. a. J a p o n i c a zone 27 v i i b. T r a n s i t i o n zone 28 c. Marina zone . 29 F i g . 8 Mean number of germinated Z. i a p o n i c a seeds per 625 cm 2 of sediment i n each zone. 31 F i g . 9 Mean number of Z. i a p o n i c a germinated seeds per 625 cm 2 of sediment a t each depth. a. J a p o n i c a zone 32 b. T r a n s i t i o n zone 33 c. Marina zone 34 F i g . 10 Study S i t e Layout 45 F i g . 11 Mean number of Z. i a p o n i c a s e e d l i n g s per 625 cm 2 i n each treatment. a. J a p o n i c a zone 50 b. T r a n s i t i o n zone 51 c. Marina zone 52 F i g . 12 Mean number o f s e e d l i n g p e r 625 cm 2 i n t h e n a t u r a l survey i n each zone. 53 F i g . 13 Mean number of newly emerged s e e d l i n g s p e r 625 cm 2 a t each date i n each treatment. a. J a p o n i c a zone 54 b. T r a n s i t i o n zone . 55 c. Marina zone 56 F i g . 14 Mean number of weeks t h a t genets from each date s u r v i v e d i n each treatment. a. J a p o n i c a zone. 58 b. T r a n s i t i o n zone 59 v i i i c. Marina zone 60 F i g . 15 Mean number of v e g e t a t i v e shoots from s e e d l i n g s per 625 cm 2 i n each treatment. a. J a p o n i c a zone 61 b. T r a n s i t i o n zone 62 c. Marina zone 63 F i g . 16 Mean number o f r e p r o d u c t i v e shoots from s e e d l i n g s per 625 cm 2 i n each treatment. a. J a p o n i c a zone 64 b. T r a n s i t i o n zone 65 c. Marina zone 66 F i g . 17 Mean number o f spathes p e r r e p r o d u c t i v e shoot i n treatments and n a t u r a l survey. a. J a p o n i c a zone 68 b. T r a n s i t i o n zone. 69 c. Marina zone 70 F i g . 18 Mean number of t o t a l ramets produced from s e e d l i n g s per 625 cm 2 i n each treatment. a. J a p o n i c a zone 71 b. T r a n s i t i o n zone 72 c. Marina zone 73 F i g . 19 Mean number of a d u l t s p e r 625 cm 2 i n each treatment. a. J a p o n i c a zone 75 b. T r a n s i t i o n zone 76 c. Marina zone 77 i x F i g . 20 Mean number of a d u l t s per 625 cm 2 i n each zone i n the n a t u r a l survey. ACKNOWLE DGEMENTS I would l i k e t o thank Dr. Paul G. H a r r i s o n f o r h i s guidance and f i n a n c i a l a s s i s t a n c e i n t h i s r e s e a r c h . I a p p r e c i a t e h i s d i l i g e n c e and p a t i e n c e i n the e d i t i n g o f t h i s t h e s i s . I wish t o acknowledge C y n t h i a Durance f o r s h a r i n g her knowledge and e x p e r t i s e i n f i e l d r e s e a r c h and the seagrass ecosystem. I a p p r e c i a t e her c o n s i d e r a b l e e f f o r t on the mudflats, e s p e c i a l l y when w e l l i n t o the l a t e stages o f pregnancy. F i n a l l y , I would l i k e t o thank my husband, B a r r i e N i e l s e n , whose common sense and understanding kept me going a l l these months. He not o n l y boosted me s p i r i t u a l l y , but c o n t r i b u t e d h i s s t r e n g t h h a u l i n g buckets o f wet sediment t o and from the f i e l d s i t e d u r i n g those c o l d , dark, r a i n y , low t i d e s o f January. x i INTRODUCTION Seagrasses are widely d i s t r i b u t e d a l o n g the c o a s t a l r e g i o n s of temperate and t r o p i c a l seas and c o n s t i t u t e one of the most conspicuous and p r o d u c t i v e ecosystems ( P h i l l i p s and Menez 1988). The seagrass ecosystem has both p h y s i c a l and b i o l o g i c a l r o l e s . The presence o f seagrasses i s important i n the s t a b i l i z a t i o n of sediments and shore p r o t e c t i o n and i s e s s e n t i a l t o the p e r s i s t e n c e and growth of many s p e c i e s o f marine l i f e ( P h i l l i p s and Watson 1984). The seagrass Z o s t e r a i a p o n i c a Aschers. and Graebn. i s an annual o r s h o r t - l i v e d p e r e n n i a l ( B i g l e y 1981) which oc c u r s as pure stands and c o - e x i s t i n g w i t h Z o s t e r a marina L. i n Japan ( A r a s a k i 1950a), on the southwest c o a s t o f Canada and on the northwest c o a s t o f the U n i t e d S t a t e s ( H a r r i s o n and B i g l e y 1982). E a r l i e r s t u d i e s have r e f e r r e d t o Z. i a p o n i c a as Z. nana and a l s o Z. americana ( B i g l e y and Barreca 1982). I t i n h a b i t s the upper and m i d - i n t e r t i d a l r e g i o n s but i s a b l e t o grow i n lower r e g i o n s where Z. marina i s not p r e s e n t (Nomme 1989). Z. marina ( e e l g r a s s ) i n h a b i t s the i n t e r t i d a l and shallow s u b t i d a l r e g i o n s of p r o t e c t e d c o a s t a l waters where s u i t a b l e s u b s t r a t e i s a v a i l a b l e (Moody 1978). The purpose o f t h i s r e s e a r c h was t o examine th e p r o d u c t i o n and d i s p e r s a l of Z. i a p o n i c a seeds and the r e c r u i t m e n t o f Z. i a p o n i c a s e e d l i n g s t o determine i f i t s p o p u l a t i o n growth i s l i m i t e d by the e f f e c t s of Z. marina on these stages o f i t s l i f e h i s t o r y . 1 N e i g h b o r i n g v e g e t a t i o n can i n f l u e n c e seed d i s p e r s a l , g e r m i n a t i o n , and re c r u i t m e n t i n b a s i c a l l y t h r e e ways: 1) the impact of a l i v i n g p l a n t canopy, 2) the impact o f p l a n t l i t t e r , and 3) c o m p e t i t i o n among s e e d l i n g s (van der V a l k 1986). T h i s study focuses on the f i r s t type o f l i m i t a t i o n . Due t o the s c a r c i t y o f data on Z. i a p o n i c a . i n f o r m a t i o n on the annual form o f Z. marina was used t o h e l p formulate hypotheses and methodology i n t h i s r e s e a r c h . T h i s study asks the q u e s t i o n s : 1) Do Z. i a p o n i c a seeds reach the sediment i n the deeper r e g i o n s where Z. marina v e g e t a t i o n dominates? and 2) Do Z. marina p l a n t s reduce the r e c r u i t m e n t o f Z.. i a p o n i c a from t h e seed bank?. The t h e s i s i s d i v i d e d i n t o two s e c t i o n s ; f i r s t i s an a n a l y s i s o f the seed bank and second i s an a n a l y s i s o f experimental treatments where Z. i a p o n i c a seeds were p l a n t e d w i t h and without Z. marina v e g e t a t i o n . 2 SEDIMENT STUDIES I n t r o d u c t i o n Z o s t e r a i a p o n i c a overwinters as b u r i e d seeds which germinate i n the s p r i n g ( H a r r i s o n and B i g l e y 1982). Seeds germinate i n the sediment and although " g e r m i n a t i o n " can be c o n s i d e r e d as the emergence of any s e e d l i n g p a r t from t h e seed, f r u i t , o r s o i l s u r f a c e (Garwood 1983), most s t u d i e s a c t u a l l y r e c o r d g e r m i n a t i o n when the s e e d l i n g appears out o f the s o i l (Orth and Moore 1983). Pre-emergence m o r t a l i t y (Harper 1957) i s an important f a c t o r but i s r a r e l y r e c orded. Z o s t e r a i a p o n i c a seeds are e l l i p s o i d and approximately 2 mm l o n g . The t e s t a i s brown when r i p e , and smooth ( A r a s a k i 1950b). The seeds have a s p e c i f i c g r a v i t y o f 1.19 o r more. These seeds o f t e n remain i n the ovary and i n many cases are s c a t t e r e d w h i l e the f l o w e r i n g shoots d r i f t ( A r a s a k i 1950b). The f l o w e r i n g shoots of Z.. i a p o n i c a decay a t the bases o r are uprooted forming e x t e n s i v e f l o a t i n g mats of shoots ( B i g l e y 1981). Mats flow w i t h the t i d e so t h a t the m a j o r i t y o f seeds are r a f t e d t o o t h e r l o c a t i o n s and are not b u r i e d where they are produced. Seeds drop from t h e f l o w e r i n g shoots as they r i p e n ( A r a s a k i 1950b). B i g l e y (1981) suggests t h a t t h i s r e s u l t s i n an evenness o f seed d e p o s i t i o n . The seed bank i s d e f i n e d as the number o f seeds b u r i e d i n the s o i l and can be c o n s i d e r e d e i t h e r t r a n s i e n t o r p e r s i s t e n t . A t r a n s i e n t seed bank c o n t a i n s seeds where the m a j o r i t y are 3 v i a b l e and i n the s o i l f o r no more than one y e a r (Bewley and Black 1985) o r w i t h i n one year of d i s p e r s a l (Hutchings 1986). A p e r s i s t e n t seed bank c o n t a i n s a s i g n i f i c a n t p r o p o r t i o n of seeds t h a t remain v i a b l e f o r many yea r s . D i sturbance of the s o i l may cause seeds from the seed bank t o germinate ( L i v i n g s t o n and A l l e s s i o 1968). There are few s t u d i e s of any k i n d on i n t e r t i d a l o r s u b t i d a l b u r i e d seed banks ( B i g l e y 1981, Fukuda e t a l . 1983, Hutchings and R u s s e l l 1989). The o b j e c t i v e s of t h i s p a r t of the r e s e a r c h a r e t o examine the seed bank t o determine the q u a n t i t y , d i s p e r s a l p a t t e r n , and v i a b i l i t y o f Z.. i a p o n i c a seeds and thus t o determine whether t h e r e 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 decreases i t s chances of c o l o n i z a t i o n i n t o deeper zones. The n u l l h y p o t h e s i s i s t h a t t h e r e i s no d i f f e r e n c e i n the numbers or v i a b i l i t y o f Z. j a p o n i c a seeds i n the sediment a t any r e g i o n where Z. i a p o n i c a can grow. 4 Study Area F i e l d s t u d i e s were conducted a t Roberts Bank, on the P a c i f i c c o a s t of Canada, approximately 5 km south of the lower arm of the F r a s e r R i v e r (49 02'N; 123 08*W). The area i s bounded by the Roberts Bank c o a l p o r t causeway t o t h e northwest and the Tsawwassen f e r r y t e r m i n a l causeway t o the southeast. The c o a l p o r t causeway d e f l e c t s sediment c a r r i e d by t h e F r a s e r R i v e r , r e s u l t i n g i n improved water c l a r i t y i n the study area. A r i p - r a p d i k e was c o n s t r u c t e d i n e a r l y 1982 a t the seaward margin o f t h e seagrass bed t o reduce e r o s i o n o f d e n d r i t i c d r a inage channels and the adjacent seagrass beds. The study area i s s u b j e c t t o mixed s e m i - d i u r n a l t i d e s . Drainage o f the embayment occurs a t a slower r a t e than a t a d j a c e n t non-enclosed areas. The incoming t i d e waters flow around t h e d i k e i n t o t h e embayment u n t i l the water l e v e l r i s e s above the d i k e and q u i c k l y f l o o d s the a r e a . The a r e a between the causeways c o n t a i n e d approximately 400 ha o f seagrass v e g e t a t i o n i n 1984 ( H a r r i s o n 1987). Z o s t e r a  marina o c c u r s i n a m o n o s p e c i f i c p o p u l a t i o n i n the lower i n t e r t i d a l and shallow s u b t i d a l zones. S i n c e 1969 t h e coverage o f Z. marina has g r e a t l y expanded through v e g e t a t i v e growth p r i m a r i l y because o f the improved water c l a r i t y ( H a r r i s o n 1987). Z o s t e r a i a p o n i c a f i r s t c o l o n i z e d h i g h i n the i n t e r t i d a l zone and s e p a r a t e l y i n t h e area j u s t landward o f where Z o s t e r a marina grows. Now i t o c c u r s i n expanded m o n o s p e c i f i c p o p u l a t i o n i n the upper t o m i d - i n t e r t i d a l zones (+1 t o +3 m r e l a t i v e t o lowest 5 l o w w a t e r ) ( H a r r i s o n 1984) b u t h a s a l s o b e e n f o u n d i n d e e p e r a r e a s n o r m a l l y o c c u p i e d b y Z . m a r i n a (Nomine 1989) . F o r r e f e r e n c e , t h e r e g i o n p o p u l a t e d b y Z . i a p o n i c a w i l l b e c a l l e d t h e " j a p o n i c a z o n e " , t h e r e g i o n c o n t a i n i n g b o t h s p e c i e s w i l l : c a l l e d t h e " t r a n s i t i o n z o n e " , a n d t h e r e g i o n p o p u l a t e d b y Z . m a r i n a w i l l b e c a l l e d t h e " m a r i n a z o n e " (Nomme 1 9 8 9 ) . Methods The number and d i s t r i b u t i o n o f seeds and seed products ( t e s t a e , germinated seeds) were e v a l u a t e d monthly from A p r i l 1989 t o A p r i l 1990. From each of the t h r e e zones, f i f t e e n sediment c o r e s were taken u s i n g random c o o r d i n a t e s from an area o f 450 m2. Samples were c o l l e c t e d by i n s e r t i n g a P l e x i g l a s tube (77 mm i n s i d e diameter) i n t o the sediment t o a t l e a s t a 20-cra depth. To determine the depth d i s t r i b u t i o n o f t h e seeds, c o r e s were s l i c e d i n the f i e l d a t 2-cm i n t e r v a l s , from the s u r f a c e t o 12 cm. Each s l i c e was marked and p l a c e d i n a p l a s t i c bag. Bags were r e t u r n e d t o the l a b and s t o r e d i n the dark a t 5° C f o r one t o f o u r t e e n days u n t i l they c o u l d be examined. The c o n t e n t s o f each bag were washed w i t h t a p water through two s i e v e s . A 2 mm mesh was used t o remove i n v e r t e b r a t e s , d e t r i t u s , and p l a n t m a t e r i a l ; the m a t e r i a l r e t a i n e d was examined f o r t h e presence of germinated seeds. A 0.850 mm mesh r e t a i n e d a l l o t h e r seeds and seed products a l o n g w i t h some i n o r g a n i c m a t e r i a l . The m a t e r i a l i n t h i s mesh was c o l l e c t e d and examined v i s u a l l y o r by d i s s e c t i n g microscope. V i a b i l i t y was t e s t e d u s i n g the t e t r a z o l i u m t e s t on seeds t h a t were f i r s t p r i c k e d w i t h a needle (Grabe 1970). Seeds were monitored every twelve hours. V i a b i l i t y was confirmed i f the h y p o c o t y l s t a i n e d r e d . 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 cm 2 t o be c o n s i s t e n t w i t h s e e d l i n g e s t a b l i s h m e n t data. To a c h i e v e e q u a l i t y o f 7 v a r i a n c e s , the square r o o t t r a n s f o r m a t i o n was employed (Benoit e t a l . 1989). Comparisons of seeds and seed p r o d u c t s by zone and by depth were analyzed u s i n g ANOVA when v a r i a n c e s were g r e a t e r than zero. K r u s k a l - W a l l i s was employed when one or more o f the v a r i a n c e s were zero (Zar, 1984), as was o f t e n the case i n the marina zone. A survey of the t h r e e zones was conducted t o compare the number o f seeds produced t o the number o f seeds i n the sediment and t o compare the experimental p l o t s (see s e e d l i n g e s t a b l i s h m e n t s e c t i o n , page 67) on the t r a n s e c t s t o the n a t u r a l p o p u l a t i o n . From A p r i l 1989 t o January 1990 f i f t e e n samples were taken a t every low t i d e c y c l e from a 450 m2 area c o n t a i n i n g the t r a n s e c t s i n each zone. Quadrats were p l a c e d u s i n g random c o o r d i n a t e s . W i t h i n the quadrat, emerged Z. i a p o n i c a s e e d l i n g s were counted a l o n g w i t h the numbers of mature 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 spathe, and seeds per spathe. In the j a p o n i c a zone a 625 cm 2 quadrat was used due t o the h i g h d e n s i t y o f Z. i a p o n i c a ramets but i n the lower zones where shoots were l e s s dense, a 2500 cm 2 quadrat was used. A l l v a l u e s were s t a n d a r d i z e d t o 625 cm 2. These data were used i n t h e s e e d l i n g e s t a b l i s h m e n t s e c t i o n . ANOVA was used t o t e s t f o r z o n a l d i f f e r e n c e s . Numbers of seeds produced per 625 cm 2 were c a l c u l a t e d by m u l t i p l y i n g the mean number o f f l o w e r i n g (seed-producing) shoots by the mean number o f spathes per shoot by the mean number o f seeds per 8 s p a t h e . O n l y a r o u g h e s t i m a t e o f s e e d s p r o d u c e d was r e q u i r e d , s o v a r i a n c e s w e r e n o t t a k e n i n t o a c c o u n t . 9 R e s u l t s Seeds The most seeds of Z.. i a p o n i c a were found i n the j a p o n i c a zone, fewer i n the t r a n s i t i o n zone, and v e r y few i n the marina zone. The v a l u e s f o r each zone were s i g n i f i c a n t l y d i f f e r e n t (p<.05) a t a l l dates except i n the months o f A p r i l and September 1989 ( K r u s k a l - W a l l i s p>.05), and March, 1990 (ANOVA p>.05) ( F i g . 1) . Standard e r r o r s overlapped and t h e r e f o r e were not i n c l u d e d f o r c l a r i t y o f graphs. The survey of the n a t u r a l p o p u l a t i o n showed t h a t seeds were p r i m a r i l y produced from mid-August t o the f i r s t p a r t of October i n t h e j a p o n i c a zone, from mid-September t o mid-October i n the t r a n s i t i o n zone, and i n l a t e September i n the marina zone ( F i g . 2) . The number o f seeds i n the sediment f i r s t began t o i n c r e a s e i n October f o r t h e upper two zones and i n November i n the marina zone ( F i g . 1). These seeds were found a t the s u r f a c e (0-2 cm). A l a r g e r p r o p o r t i o n of the seeds was found a t a g r e a t e r depth (8-12 cm) i n the s p r i n g than any o t h e r time i n the j a p o n i c a and t r a n s i t i o n zones ( F i g . 3a-c). Few seeds were found i n the marina zone except i n the l a t e f a l l 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 o f seeds i n the sediment was c o n s i s t e n t i n a l l t h r e e zones ( F i g . 4a-c). An i n c r e a s e d number o f v i a b l e seeds was noted i n the f a l l . Between zones, from May t o Nov 1 t h e r e was no d i f f e r e n c e i n numbers o f v i a b l e seeds and from Nov 30, 1989 t o A p r i l 1990 t h e r e was no d i f f e r e n c e i n t h e numbers of 10 40 3 © B o t/3 © CO o fl> a a cd © 30 20 10 0 ^ — 6 — & — & — & — & — 9 9 9 9--^ Date F i g . 1 Mean number o f Z. i a p o n i c a seeds p e r 625 cm 2 of sediment i n each zone. «=japonica zone, A = t r a n s i t i o n zone, o=marina zone. 11 Date F i g . 2 Mean number of Z. i a p o n i c a seeds produced per 625 cm 2 ( d a t a = l o g 1 Q ( x + 1 ) ) i n each zone. •=japonica z o n e , A = t r a n s i t i o n zone, o=marina zone. 12 40 fl a •1-1 o a Ui o CO o M 4> a .55 a 30 20 10 0 1 7 7 7 1 H 0-2 cm §§§ 2-4 cm • 4-6 cm §|j 6-8 cm ^ 8-10 cm H 10-12 cm K P ^ tf** S**e S^ 1 K»* S ^ 1 0<* ^  pc* j * * ?<^ 0 £ 9 tV£° Date F i g . 3a J a p o n i c a zone. Mean number o f Z. i a p o n i c a seeds per 625 cm 2 of sediment a t each depth. 13 Date F i g . 3b T r a n s i t i o n zone. Mean number o f Z. i a p o n i c a seeds p e r 625 cm 2 o f sediment a t each depth. 14 40 © a © c o C O © © CO 30 • 0-2 cm §§§ 2-4 cm • 4-6 cm ^ 6-8 cm 8-10 cm IH 10-12 cm 20 © yd a a © 10 0 i i i I i i i i H i i in iii wm Date F i g . 3c Marina zone. Mean number of Z, i a p o n i c a seeds per 625 cm 2 o f sediment a t each depth. 15 8 Date F i g . 4a J a p o n i c a zone. Percent of the t o t a l number of v i a b l e ( s t r i p e d ) and n o n - v i a b l e ( s o l i d ) Z. i a p o n i c a seeds p e r 62 5 cm 2 of 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 found a t each date. 16 © © c o © a T—< a) -«-> O 8 7 H 3 a © o u © 0 Date F i g . 4b T r a n s i t i o n zone. Percent o f t h e t o t a l number of v i a b l e ( s t r i p e d ) and n o n - v i a b l e ( s o l i d ) Z. i a p o n i c a seeds per 625 cm 2 of 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 found a t each date. 17 8 co O © CO o JO B z cd O H 3 © O © 0 • H B a a L Date F i g . 4c Marina zone. Percent o f the t o t a l number o f v i a b l e ( s t r i p e d ) and n o n - v i a b l e ( s o l i d ) Z. i a p o n i c a seeds p e r 625 cm 2 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 found a t each date. 18 n o n - v i a b l e seeds (p>.05). The percentage o f v i a b l e seeds decreased from the time of i n c o r p o r a t i o n i n t o the sediment u n t i l l a t e s p r i n g ( F i g . 5 a - f ) . V i a b l e seeds i n i t i a l l y were l o c a t e d i n the upper l a y e r s (0-4 cm) of sediment i n the f a l l . The percentage of n o n - v i a b l e seeds i n c r e a s e d from l a t e f a l l t o summer. In the j a p o n i c a zone t h e r e appears t o be an i n c r e a s e i n the number of seeds i n the sediment i n June but these seeds are n o n - v i a b l e and t h i s i n c r e a s e may be due t o h e t e r o g e n e i t y of the sampling area ( F i g . 1 and F i g . 3a vs F i g . 4a). In the f a l l , n o n - v i a b l e seeds were l o c a t e d i n the upper l a y e r s of sediment but were found a t i n c r e a s i n g l y lower l e v e l s (8-12 cm) i n t h e s p r i n g and summer. Testa e 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 d i f f e r e n t (ANOVA, p<.05) ( F i g . 6). The marina zone was always lower than the o t h e r two but the j a p o n i c a zone was not d i f f e r e n t from the t r a n s i t i o n zone except i n September and December, 1989 and February, 1990 when a l l t h r e e zones were d i f f e r e n t from each o t h e r (Tukey t e s t p<.05). Testae were g e n e r a l l y found i n the deeper p a r t s o f the sediment sample (6-12 cm), w i t h a few on top and i n c r e a s i n g numbers wi t h depth ( F i g . 7 a - c ) . Germinating seeds Germination was r e s t r i c t e d t o t h e p e r i o d between February 19 © a 4 © 09 © © co O a © © © 2 -0 • 0-2 cm §§§ 2-4 cm O 4-6 cm §§ 6-8 cm 8-10 cm I I 1 0 - 1 2 cm Date F i g . 5a J a p o n i c a zone. Percent of the t o t a l number of v i a b l e Z. i a p o n i c a seeds p e r 625 cm 2 of sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, separated by depth. 20 Date F i g . 5b J a p o n i c a zone. Percent o f the t o t a l number of no n - v i a b l e Z. i a p o n i c a seeds p e r 625 cm 2 of sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, s e p a r a t e d by depth. 21 a © .§ 4 © CO © © CO (2 o •«-> a © o © P i 0 B 0-2 cm §§] 2-4 cm • 4 - 6 cm f § 6-8 cm jg3 8 - 1 0 cm Hi 10 -12 cm i i Date F i g . 5c T r a n s i t i o n z o n e . 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 cm 2 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 d e p t h . 22 c o a 4 u GO to © © co r—< cd (2 a © o © 3 -2 -0 • 0-2 cm §§§ 2 - 4 cm L J | 4 - 6 cm H 6-8 cm £gj ; 8 - 1 0 cm II 1 0 - 1 2 cm i l \*3 V Date F i g . 5d T r a n s i t i o n zone. Percent of the t o t a l number of n o n - v i a b l e Z. i a p o n i c a seeds p e r 625 cm 2 o f sediment c o l l e c t e d from May 1 9 8 9 t o A p r i l 1 9 9 0 t h a t were found a t each date, s e p a r a t e d by depth. 2 3 5 r S 4 X ) c o O S o CO • 4 - » <2 • 0-2 cm §§§ 2-4 cm O 4-6 cm §1 6-8 cm ^ 8-10 cm Il 10-12 cm a © O U fl> 0 Date F i g . 5e Marina zone. Percent o f the t o t a l number o f no n - v i a b l e Z. i a p o n i c a seeds p e r 625 cm 2 of sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date, s e p a r a t e d by depth. 24 5 0-2 cm a a 4 © CO ^ 3 © © CQ 03 I 2 © o © o Date F i g . 5f Marina zone. Percent o f t h e t o t a l number of non - v i a b l e Z. i a p o n i c a seeds p e r 625 cm 2 o f sediment c o l l e c t e d from May 1989 t o A p r i l 1990 t h a t were found a t each date t h a t were non-v i a b l e separated by depth. 25 200 o B •*-< o CO 150 -100 o © a d cd © 50 0 Date F i g . 6 Mean number o f Z. i a p o n i c a t e s t a e p e r 625 cm 2 of sediment i n each zone. •=japonica zone, * = t r a n s i t i o n zone, o=marina zone. 26 200 r rt © B • T - ( o CO © cd Cm o l - l © B rt cd © 150 100 50 -0 • 0-2 cm §§§ 2-4 cm • 4-6 cm fH 6-8 cm ^ 8-10 cm M 10-12 cm i 1 ^ **** j**6 s^ 1 K » * ^ o°x ^ t*0 *°V* 0 }^ 0 Date F i g . 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 per 625 cm 2 o f sediment a t each depth. 27 2 0 0 © •T-< © co © +-> E2 O t-t © © 150 100 50 -0 1 I • 0-2 cm §§§ 2-4 cm O 4-6 cm 6-8 cm .8-10 cm H 10-12 cm H • ^ tf** j * * 6 5*** K»» S«* v <** ^ t>e* J * * t ^ s ^ s 9 ° D a t e F i g . 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 per 625 cm 2 o f sediment a t each depth. 28 2 0 0 a © o +-> <•-< o © a a © 150 100 50 0 • 0-2 cm §§§ 2-4 cm • 4 - 6 cm § § 6 -8 cm ffl 8 - 1 0 cm H 10 -12 cm r-r4 L i o i o i )a4x& ^ S**6 ^ K » * ° o V ^ 3** * e V * ° M ^ ° Date F i g . 7c Marina zone. Mean number o f Z. j a p o n i c a t e s t a e per 625 cm 2 of sediment a t each depth. 29 and J u n e . 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 i n d e n s i t y o f g e r m i n a t i n g s e e d s between z o n e s e x c e p t i n J u n e 1989 a n d A p r i l 1990 ( K r u s k a l - W a l l i s p<.05) ( F i g . 8 ) . T h e r e were more g e r m i n a t i n g Z_. i a p o n i c a s e e d s i n t h e j a p o n i c a zone, f e w e r i n t h e t r a n s i t i o n zone, and f e w e s t i n t h e m a r i n a zone. I n F e b r u a r y , M a r c h , and A p r i l t h e m a j o r i t y o f g e r m i n a t i o n o c c u r r e d a t s h a l l o w d e p t h s (0-4 cm) ; l a t e r g e r m i n a t i o n o c c u r r e d s l i g h t l y d e e p e r ( F i g . 9 a - c ) . 30 10 C O © © CO © cd fl a © o o u © B & Z fl cd © 2 8 h 0 D a t e F i g . 8 Mean number of germinated Z. i a p o n i c a seeds per 625 cm 2 of sediment i n each zone. «=japonica zone, = t r a n s i t i o n zone, o=marina zone. 31 10 «> T3 H> <D CO © cd fl •1-1 a M CO o o u © a z A cd cu 8 -6 -2 -0 I • 0-2 cm §D 2 -4 cm • 4 - 6 cm ^ 6-8 cm jgj 8 - 1 0 cm IH 10 -12 cm I I L Date F i g . 9a J a p o n i c a zone. Mean number o f Z. i a p o n i c a germinated seeds per 625 cm 2 o f sediment a t each depth. 32 10 © O OO o -«-» (=1 o U o cd © 8 -6 -0 L l • 0-2 cm §§§ 2-4 cm • 4 - 6 cm ^§ 6-8 cm [gj 8 - 1 0 cm M 10 -12 cm 1 L l J * * 6 S^3 K 8 * fW« f ° V t 0 K ^ ° Date F i g . 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 germinated seeds p e r 625 cm 2 o f sediment a t each depth. 33 10 C O © © CO © -•-> cd a •1-1 © o (f-l o © a a © 8 0 Li • 0-2 cm §g] 2-4 cm • 4-6 cm §§ 6-8 cm ^ 8-10 cm H 10-12 cm J I I L I I I 1 Date F i g . 9c Marina zone. Mean number o f Z. i a p o n i c a germinated seeds p e r 625 cm 2 o f sediment a t each depth. 34 D i s c u s s i o n Of the many seeds t h a t are produced, few are i n c o r p o r a t e d i n t o the sediment and even fewer germinate. Given t h a t Z o s t e r a  i a p o n i c a has been d e s c r i b e d as an annual i n t h i s a r e a ( H a r r i s o n 1979), t h i s r e s u l t was unexpected and suggests t h a t Z. i a p o n i c a must r e l y on c l o n a l growth t o m a i n t a i n the p o p u l a t i o n (see s e e d l i n g e s t a b l i s h m e n t d i s c u s s i o n ) . S t u d i e s c o u l d be done t o determine the importance of o c c a s i o n a l genet e s t a b l i s h m e n t i n the p o p u l a t i o n g e n e t i c s o f t h i s s p e c i e s . Seed p r o d u c t i o n d e c l i n e d from a peak i n the landward j a p o n i c a zone towards the sea. Even h i g h e r seed p r o d u c t i o n , more than t h r e e times the maximum number produced i n t h e j a p o n i c a zone, has been observed h i g h e r i n the i n t e r t i d a l zone ( B i g l e y 1981). Z o s t e r a j a p o n i c a responds l i k e o t h e r seagrasses w i t h an i n c r e a s e i n sexual r e p r o d u c t i v e output i n t h e hi g h e r , more exposed areas ( H a r r i s o n 1979). Seed p r o d u c t i o n f o r Z. i a p o n i c a began e a r l i e r i n the upper r e g i o n s o f the i n t e r t i d a l than i n the lower r e g i o n s . T h i s was a l s o noted i n o t h e r l o c a l s t u d i e s ( B i g l e y 1981, Nomme 1989). T h i s may be due t o environmental d i f f e r e n c e s as one p r o g r e s s e s seaward such as water depth, l i g h t q u a l i t y and q u a n t i t y , as w e l l as temperature and s a l i n i t y . None o f these has been s t u d i e d i n the l o c a l area f o r Z. i a p o n i c a . I t i s unknown how long r e p r o d u c t i v e shoots s t a y a t t a c h e d o r how long the seeds s t a y i n the spathe b e f o r e they a r e r e l e a s e d . In the survey o f n a t u r a l p o p u l a t i o n s , many o f the r e p r o d u c t i v e 35 shoots might have been counted i n more than one sampling time. A l s o , seeds may have dropped from the spathes b e f o r e they were counted. Even so, a t the time of peak seed p r o d u c t i o n (August t o mid-October) t h e r e were up t o t e n times more seeds being produced per area than were found i n the sediment. The presence of the new seed crop i n the sediment was i n d i c a t e d by an i n c r e a s e i n the number o f v i a b l e seeds i n the upper sediment l a y e r s i n October and November ( F i g . 5a,c,e). The h i g h e r seed d e n s i t y i n areas of h i g h Z. i a p o n i c a a d u l t d e n s i t y i n d i c a t e s t h a t d i s p e r s a l i s l o c a l . In s t u d i e s of the annual form o f Z.. marina i n Europe, the m a j o r i t y o f the seeds a l s o s t a y e d i n the area i n which they were produced (Jacobs 1982) . Other s t u d i e s of t e r r e s t r i a l systems have found t h a t seeds are o f t e n shed next t o or near the parent (Benoit e t a l . 1989). Because t h e r e are more seeds d e p o s i t e d i n t h e s e h i g h e r zones, even i f few o f these seeds produce s u c c e s s f u l s e e d l i n g s , they may c o n t r i b u t e t o the h i g h d e n s i t y o f a d u l t Z.. i a p o n i c a i n these zones. The January sample was the one time t h a t the numbers of seeds and t e s t a e i n the t r a n s i t i o n zone exceeded those i n the j a p o n i c a zone. T h i s may be due t o the h e t e r o g e n e i t y o f the system (Moody 1978). Sampling was done randomly and i t may be t h a t areas t h a t c o n t a i n e d more seeds and seed p r o d u c t s (such as d e p r e s s i o n s ) were sampled on t h i s date. Another cause may be sediment s h i f t i n g due t o w i n t e r storms. 36 The l a r g e number of new seeds d i d not d i s p e r s e i n t o the lower i n t e r t i d a l areas (marina zone). Nomme (1989) had the same r e s u l t although B i g l e y (1981) suggested t h a t the seeds were i n the water column l o n g enough t o produce a more even d i s t r i b u t i o n o f seed. B i g l e y (1981), however, s t u d i e d Z. i a p o n i c a much h i g h e r i n the i n t e r t i d a l than my j a p o n i c a zone and the two s i t e s may be s u b j e c t t o d i f f e r e n t water flow regimes. Thus my n u l l h y p o t h e s i s t h a t t h e r e i s no d i f f e r e n c e i n the d i s p e r s a l o f Z. i a p o n i c a seeds i s f a l s e . I t i s u n c l e a r why Z. i a p o n i c a seeds d i d not d i s p e r s e i n t o more seaward r e g i o n s ; perhaps they were washed onto shore. There was l i t t l e 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 . Most o f the seeds were i n the top 4-6 cm o f the sediment i n the w i n t e r and as time went on the seeds became more deeply i n c o r p o r a t e d i n t o the sediment. Whether these seeds n a t u r a l l y work t h e i r way down due t o the water flow p a s s i n g through the sediment o r t o the s h i f t i n g o f sediments by i n v e r t e b r a t e s i s unknown. Swinbanks (1979), working i n the a d j a c e n t F r a s e r R i v e r d e l t a , 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 a t a d e n s i t y of 200/m 2 c o u l d completely t u r n over the sediment down t o a depth o f 10 cm i n 100 days. S e v e r a l i n v e r t e b r a t e s i n h a b i t the sediment i n the study area and the same type o f sediment mixing i s p r o b a b l y o c c u r r i n g . A v e r y s m a l l number of Z. i a p o n i c a seeds germinated from the seed bank. The f a t e of the remaining seeds i n the seed bank i s unknown. Some seeds may have become more deeply embedded i n 37 the sediment. Other seeds may have been consumed o r destroyed i n the s p r i n g by the i n c r e a s i n g a c t i v i t y o f i n v e r t e b r a t e s i n the sediment. Common cr u s t a c e a n i n h a b i t a n t s of e e l g r a s s meadows and 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 shown t o be p o t e n t i a l p r e d a t o r s o f Z. marina seeds (Wigand and C h u r c h i l l 1988). I t has been suggested f o r Z. marina t h a t the t e s t a e found i n the sediment are the remnants o f t h a t y e a r ' s g e r m i n a t i o n (Fukuda e t al.1983, Fukuda and T s u c h i y a 1987). In Z. i a p o n i c a . the numbers o f t e s t a e f a r exceeded the numbers o f germinated seeds. I t i s probable t h a t the remnants of the seed do not decompose i n one year but how l o n g they remain i s u n c e r t a i n . One would expect 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 a p e r i o d o f germination and i n the j a p o n i c a zone, where ge r m i n a t i o n peaked i n June t h e r e was a c o r r e s p o n d i n g peak i n t e s t a e i n J u l y ( F i g . 8 vs F i g . 6). In the t r a n s i t i o n zone, g e r m i n a t i o n peaked i n June and so d i d the number o f t e s t a e found i n the sediment. There were too few seeds g e r m i n a t i n g i n the marina zone f o r any comparisons t o be made. B i g l e y (1981) found 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 depth o f 4-7 cm and none below 12 cm. My r e s u l t s concur w i t h t h i s a lthough s e v e r a l seeds germinated from the 0-2 cm range. Most o f t h e l a t t e r o c c u r r e d i n the e a r l y s p r i n g b e f o r e any o f the o v e r w i n t e r i n g p o p u l a t i o n had renewed growth. Many of the s e e d l i n g s t h a t emerged e a r l y were found l a t e r f l o a t i n g i n the water, uprooted and unable t o r e - e s t a b l i s h . These f l o a t i n g 38 s e e d l i n g s c o u l d be a major source o f m o r t a l i t y ( B i g l e y 1981) (See s e e d l i n g e s t a b l i s h m e n t s e c t i o n ) . A l a r g e p e r s i s t e n t seed bank was not e v i d e n t i n t h i s study. By summer, most seeds i n the seed bank o f t h i s study were no l o n g e r v i a b l e and some were a t shallow depths. B i g l e y (1981) r e p o r t e d a p e r s i s t e n t seed bank below 5 cm w i t h a mean number i n the summer o f 72.5 v i a b l e seeds/625 cm 2. D i f f e r e n c e s between 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 i n sediment d i s t u r b a n c e regimes. A l t e r n a t e l y , i f seed m o r t a l i t y from v a r i o u s causes i s not density-dependent, then the much s m a l l e r seed p r o d u c t i o n i n the area o f t h i s study compared t o t h a t o f B i g l e y (1981) c o u l d be t h e cause. Z o s t e r a i a p o n i c a has not been p r e s e n t i n the study area 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 response t o d i s t u r b a n c e but a low o r n o n - e x i s t e n t seed bank would suggest 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 t o draw from i n case o f major d i s t u r b a n c e . One study t h a t d i s c u s s e s seed bank dynamics and the 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 systems i s Grime (1989) which d e s c r i b e s f o u r types o f seed banks and f i v e r e g e n e r a t i v e s t r a t e g i e s . Although the seed bank t y p e s are determined 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 , some o f t h e c h a r a c t e r i s t i c s used i n the key can 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 seeds found i n t h i s study and B i g l e y ' s (1981) study. L i g h t i s not r e q u i r e d f o r g e r m i n a t i o n and requirements f o r s c a r i f i c a t i o n o f Z. i a p o n i c a seeds have not been determined. Laboratory work i n v o l v i n g the d r y i n g o f Z. 39 i a p o n i c a seeds has not been done. Even so, the key l e a d s one to b e l i e v e t h a t Z. i a p o n i c a seeds belong t o e i t h e r Type I I I or IV seed banks. Type I I I d e s c r i b e s annual and p e r e n n i a l herbs t h a t p r i m a r i l y germinate i n autumn but m a i n t a i n a s m a l l seed bank. Type IV d e s c r i b e s annual and p e r e n n i a l herbs and shrubs w i t h l a r g e p e r s i s t e n t seed banks. N e i t h e r seeds bank type a c c u r a t e l y d e s c r i b e s Z. i a p o n i c a i n my study area because the seeds germinate p r i m a r i l y i n the s p r i n g and t h e r e i s l i t t l e o r no p e r s i s t e n t seed bank. Of t h e r e g e n e r a t i v e s t r a t e g i e s d e s c r i b e d i n Grime (1989), the s e a s o n a l r e g e n e r a t i o n s t r a t e g y f i t s b e s t . The p l a n t u s i n g t h i s s t r a t e g y has independent o f f s p r i n g (seeds o r v e g e t a t i v e propagules) produced by a s i n g l e c o h o r t . The c o n d i t i o n s under which t h i s s t r a t e g y appears t o have a s e l e c t i v e advantage are h a b i t a t s s u b j e c t e d t o s e a s o n a l l y p r e d i c t a b l e d i s t u r b a n c e by c l i m a t i c o r b i o t i c f a c t o r s . These c o n d i t i o n s seem t o f i t the i n t e r t i d a l h a b i t a t , but the s e a s o n a l r e g e n e r a t i o n s t r a t e g y a l s o i n c l u d e s seed bank Types I and I I . Z o s t e r a i a p o n i c a seeds do not appear t o belong i n e i t h e r o f these t y p e s . V a r i a b i l i t y i n the data may have obscured some important d i f f e r e n c e s i n seed dynamics. The sampling regime i t s e l f may be t o blame because l a r g e numbers o f s m a l l sampling u n i t s have been shown t o be b e t t e r than s m a l l numbers of l a r g e u n i t s (Benoit e t a l . 1989). By sampling deeper i n t o the sediment, one might d i s c o v e r how deep seeds and seed p r o d u c t s are l o c a t e d . I t might a l s o be u s e f u l t o compare the i n v e r t e b r a t e s c o n t a i n e d w i t h i n the samples t o determine i f t h e i r numbers and a c t i v i t i e s are a s s o c i a t e d w i t h the depth of seeds and p o s s i b l e t u r n o v e r w i t h i n the sediment. 4 1 SEEDLING ESTABLISHMENT I n t r o d u c t i o n E s t a b l i s h m e n t i s the process d u r i n g which a g e r m i n a t i n g seed t a k e s r o o t , uses up p r o v i s i o n s p r o v i d e d by the p arent and assumes independent growth as a s e e d l i n g (Howe and Smallwood 1982). The s u r v i v o r s h i p of s e e d l i n g s i s d i f f i c u l t t o monitor a c c u r a t e l y u n l e s s frequent o b s e r v a t i o n s are made, because those s e e d l i n g s which d i e b e f o r e emergence w i l l not be r e c o r d e d (Watkinson 1986). The e s t a b l i s h m e n t of the s e e d l i n g i s one of the weakest l i n k s i n the c o l o n i z a t i o n of new t e r r i t o r y by p l a n t s . In p e r e n n i a l t e r r e s t r i a l g r a s s e s n e a r l y a l l m o r t a l i t y i s w i t h i n the f i r s t y e a r o f l i f e (Stebbins 1971). H a r r i s o n and B i g l e y (1982) found t h a t the chance of a Z. i a p o n i c a s e e d l i n g becoming e s t a b l i s h e d was s m a l l but once s e c u r e l y r o o t e d the p l a n t can grow q u i c k l y . The shading of the annual by the p e r e n n i a l form o f Z. marina decreases the s u r v i v a l and r e p r o d u c t i v e p o t e n t i a l o f the annual, s u g g e s t i n g i n t e r s p e c i f i c c o m p e t i t i o n f o r l i g h t (Keddy 1987). There i s i n d i r e c t evidence s u g g e s t i n g t h a t shading by Z. marina may i n t e r f e r e w i t h Z. i a p o n i c a i n deeper zones a t Roberts Bank (Nomme 1989). F i e l d measurements i n d i c a t e t h a t 30% of s u r f a c e p h o t o s y n t h e t i c a l l y a c t i v e r a d i a t i o n (PAR, 400-700 nm) p e n e t r a t e s t o the sediment through 1.5 m o f sea water and a canopy o f Z. marina compared t o 43% of s u r f a c e PAR t h a t reaches 42 the sediment beneath a Z. i a p o n i c a canopy (Nomme 1989). T h i s shading may be r e s p o n s i b l e f o r the su p p r e s s i o n o f l a t e r a l b r a n c h i n g o f Z. i a p o n i c a o r may a f f e c t i t s growth i n some other way (Nomme 1989). The o b j e c t i v e o f t h i s phase o f the r e s e a r c h was t o determine i f the canopy o f Z. marina i n t e r f e r e s w i t h the s e e d l i n g emergence o r establishment o f Z. i a p o n i c a . The n u l l h y p o t h e s i s i s t h a t Z. i a p o n i c a seeds p l a n t e d w i t h Z. marina w i l l grow and 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 a f t e r the e e l g r a s s i s removed. 43 Methods For f i e l d s t u d i e s o f seed germination, and s e e d l i n g e s t a b l i s h m e n t and growth, i t was necessary t o use a c o n t a i n e r t h a t r e t a i n e d c l e a n e d sediment, kept out rhizomes from surrounding p l a n t s , and allowed water t o c i r c u l a t e through the sediment. F o u r - l i t r e p l a s t i c buckets (20-cm diameter) w i t h bottoms removed and r e p l a c e d by n y l o n s t o c k i n g m a t e r i a l were used. Seeds were c o l l e c t e d from f r u i t i n g shoots and from the sediment. Reproductive shoots o f Z. i a p o n i c a were c o l l e c t e d from the f i e l d s i t e i n August 1988, p l a c e d i n p l a s t i c bags and brought back t o the l a b . Shoots were kept i n c i r c u l a t i n g , a e r a t e d s a l t w a t e r a q u a r i a a t approximately 5° C u n t i l the seeds matured and dropped t o the bottoms o f the ta n k s . C o l l e c t e d seeds were s t o r e d i n seawater i n the dark a t 5° C. Sediment was c o l l e c t e d t o a depth o f 10 cm i n January 1989 from the f i e l d s i t e . The sediment was s i f t e d f o r seeds u s i n g the same method as used f o r seed bank a n a l y s i s . Cleaned sediment was saved f o r l a t e r use. The number o f seeds per area was determined and seeds were s t o r e d i n seawater i n t h e dark a t 5° 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 the se 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 and 5 meters a p a r t were s e t up i n each zone. These t r a n s e c t s ran p e r p e n d i c u l a r t o the t i d a l flow, about 500 m from the c o a l p o r t causeway and 1500 m from the Tsawwassen causeway ( F i g . 10). One-meter square 44 F i g . 10 Study S i t e Layout SHORE C O A L P O R T C A U S E W A Y J a p o n i c a Zone T r a n s i t i o n Zone <- 500 m [ -50 m-Marina Zone r 5m t t 200 m t 200 m 2m t 2m 1500 m T S A W W A S S E N 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 randomly on each s i d e of the t r a n s e c t l i n e s . The space between the p a i r e d t r a n s e c t s allowed access t o the p l o t s without d i s t u r b i n g them. P l a n t i n g o c c u r r e d d u r i n g the l a s t two weeks o f January, 1989. Cleaned sediment was p l a c e d i n the m o d i f i e d buckets and taken t o the study s i t e . B i g l e y (1981) found t h a t Z. i a p o n i c a seeds f i r s t germinated a t a depth o f 4-7 cm. Thus t e n Z. i a p o n i c a seeds were p l a c e d approximately 5 cm i n t o the sediment. The buckets were p l a n t e d i n the c e n t r e o f randomly chosen 1 m2 p l o t s a long the t r a n s e c t s o f each zone such t h a t the to p s o f t h e buckets were approximately l e v e l w i t h the s u r r o u n d i n g sediment. To t e s t the i n f l u e n c e of Z o s t e r a marina on seed g e r m i n a t i o n and s e e d l i n g e s t a b l i s h m e n t of Z. i a p o n i c a . two types o f seeded p l o t s were used, with the n a t u r a l Z. marina removed o r i n t a c t . Nine buckets o f each type were p l a n t e d i n the t r a n s i t i o n and marina zones. Because t h e r e i s no n a t u r a l l y o c c u r r i n g Z. marina i n the j a p o n i c a zone, the treatment of p l a n t i n g buckets i n p l o t s w i t h Z. marina was unnecessary and t h e r e f o r e excluded. C o n t r o l s were used t o monitor the e f f e c t s o f t h e buckets and o f c l e a r i n g Z. marina from the p l o t s . The f i r s t c o n t r o l was 1 m 2 p l o t s w i t h Z. marina removed. The second c o n t r o l i n v o l v e d p l a c i n g buckets without bottoms i n t o 1 m 2 p l o t s w i t h Z. marina removed. There were f i f t e e n o f each o f t h e s e c o n t r o l s p l a c e d randomly a l o n g the t r a n s e c t s i n each o f the t h r e e zones. 46 To monitor s e e d l i n g emergence and s u r v i v a l , c o n t r o l p l o t s had two 30-cm l e n g t h s of PVC p l a s t i c p i p e i n s e r t e d i n t o the sediment t o a depth of 29 cm. These were permanent p l o t markers. Two of the f o u r l e g s of a p l o t frame (20x50 cm i n s i d e dimensions) were p l a c e d i n t o the p i p e s . A P l e x i g l a s sheet f i t i n t o the frame forming a t a b l e - l i k e s u r f a c e 10 cm above the sediment s u r f a c e . An a c e t a t e sheet p l a c e d over t h e P l e x i g l a s was used t o mark the area v e r t i c a l l y p r o j e c t e d through the i n s i d e of the frame. V e r t i c a l alignment was i n s u r e d by use of a p a r a l l a x tube. T h i s P l e x i g l a s tube was 10 cm l o n g by 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 both ends. When the tube was p l a c e d v e r t i c a l l y on the p l o t frame s u r f a c e , shoot l o c a t i o n s c o u l d be i d e n t i f i e d . E x perimental and c o n t r o l p l o t s were mapped every low t i d e c y c l e , approximately every two weeks, from A p r i l through November 1989 and then once a month u n t i l the end o f December. Each ramet was i d e n t i f i e d t o s p e c i e s , whether i t was a mature shoot or a s e e d l i n g , and i t s p o s i t i o n was mapped t o i n d i c a t e the date o f emergence, branching, f l o w e r i n g , and disappearance. I t became e v i d e n t t h a t some Z. i a p o n i c a shoots were growing from o v e r w i n t e r i n g rhizomes; thus from June 1 these a d u l t shoots were a l s o counted. Temperatures of the sediment were taken and v i s u a l i n s p e c t i o n of i n v e r t e b r a t e burrow openings was conducted i n p l o t s w i t h and without buckets as i n d i c a t o r s o f p o s s i b l e changes i n the environment induced by the buckets. 47 To determine whether 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 experimental p l o t s , both w i t h i n and among zones, data were f i r s t s t a n d a r d i z e d t o numbers per 625 cm 2 (which c l o s e l y approximated the areas o f the buckets and a c e t a t e sheets) and square-root transformed (Zar 1984). A two-way ANOVA ( s i g n i f i c a n c e l e v e l , p<.05) was used when v a r i a n c e s were g r e a t e r than zero and the K r u s k a l - W a l l i s t e s t (p<.05) was used when v a r i a n c e s were zero (Zar 1984). Because SYSTAT onl y does the 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 ad-j u s t e d by u s i n g the B o n f e r r o n i procedure ( W i l k i n s o n 1988) t o a v o i d a type one e r r o r . When the B o n f e r r o n i procedure was a p p l i e d t o a 0.05 p r o b a b i l i t y the new p r o b a b i l i t y was 0.0125. In each case, the s i g n i f i c a n c e l e v e l i s s t a t e d i n t h e t e s t . C o n t r o l p l o t s were compared wit h the n a t u r a l survey (see sediment s t u d i e s methods) u s i n g a o n e - f a c t o r ANOVA (p<.05) t o t e s t t he e f f e c t s o f c l e a r i n g Z. marina. 48 R e s u l t s S e e d l i n g s The i n i t i a l ramet t h a t emerged from the seed w i l l be termed the s e e d l i n g . Any other ramets t h a t may have branched from t h i s s e e d l i n g w i l l 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 shoots, depending on t h e i r f u n c t i o n . Standard e r r o r s were h i g h and overlapped, thus they were not i n c l u d e d i n the graphs f o r c l a r i t y . The number of s e e d l i n g s per 625 cm 2 i n the n a t u r a l survey was not s t a t i s t i c a l l y d i f f e r e n t from the number found i n the c o n t r o l p l o t s i n each zone ( F i g . 11 a-c vs F i g . 12). The numbers observed i n seeded buckets i n the j a p o n i c a zone appeared t o be lower than i n the c o n t r o l p l o t s , but t h i s was not s t a t i s t i c a l l y d i f f e r e n t ( F i g . 11a) (p>.0125). In the t r a n s i t i o n zone t h e r e were d i f f e r e n c e s between t h e c o n t r o l p l o t s and the seeded bucket p l o t s from A p r i l 24 t o J u l y 1 (p<.0125) ( F i g . l i b ) . I t appears t h a t i n the seeded buckets p l a n t e d w i t h Z. marina 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 than i n the seeded buckets p l a n t e d without Z. marina but the d i f f e r e n c e was not s t a t i s t i c a l l y s i g n i f i c a n t (p>.0125). There was no d i f f e r e n c e among p l o t s i n the marina zone, but i n many p l o t s Z. i a p o n i c a s e e d l i n g s were found clumped j u s t o u t s i d e the bucket. The mean number of Z. i a p o n i c a s e e d l i n g s emerging was g r e a t e s t i n A p r i l and May, d e c r e a s i n g s h a r p l y a f t e r w a r d s ( F i g . 13a-c). O f t e n more than h a l f o f the s e e d l i n g s would d i s a p p e a r by the f o l l o w i n g survey. Many s e e d l i n g s were found uprooted, 49 Date F i g . 11a J a p o n i c a zone. Mean number of Z.. i a p o n i c a s e e d l i n g s per 625 cm 2 i n each treatment. o=unseeded p l o t s without bucket, ^=unseeded buckets, «=seeded buckets without Z. marina. 50 2 -0 Date F i g . 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 per 625 cm 2 i n each treatment. o=unseeded p l o t s without bucket, A =unseeded buckets, «=seeded buckets without Z.. marina. •=seeded buckets w i t h Z. marina. 51 'J 4 r co DO .1-1 J o o *-< 2 CD a a c3 1 © 1 0 N rt V W ^ i W W ^ ***** ftp-Date F i g . 11c Marina zone. Mean number of Z. i a p o n i c a s e e d l i n g s per 625 cm 2 i n each treatment. o=unseeded p l o t s without b u c k e t ,A =unseeded buckets, »=seeded buckets without Z. marina, • =seeded buckets w i t h Z.. marina. 52 * * * * * * * * * * * Date F i g . 12 Mean number o f s e e d l i n g per 625 cm 2 i n the n a t u r a l survey i n each zone. •= j a p o n i c a zone, A = t r a n s i t i o n zone, o= marina zone. 53 F i g . 13a J a p o n i c a z o n e . Mean number o f n e w l y emerged s e e d l i n g s p e r 625 cm 2 a t e a c h d a t e i n e a c h 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 , ^ = 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 . 54 4 « w o a w CO a © CO o u © a p* z a © 0 n ^ n ^ u i Date F i g . 13b T r a n s i t i o n zone. Mean number o f newly emerged s e e d l i n g s per 625 cm 2 a t each date i n each treatment. o= unseeded p l o t s without bucket, A=unseeded buckets, «=seeded buckets without Z, marina. «=seeded buckets w i t h Z. marina. 55 4 to a Date F i g . 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 cm 2 a t e a c h d a t e i n e a c h 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 , 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 . « = s e e d e d b u c k e t s w i t h Z. m a r i n a . 56 f l o a t i n g i n the water. S e e d l i n g s c o n t i n u e d t o emerge i n t o August. In the seeded buckets w i t h Z. marina and the unseeded buckets of the t r a n s i t i o n zone, Z. i a p o n i c a s e e d l i n g s continued t o emerge i n t o September. S e e d l i n g genets t h a t emerged between 24 A p r i l and 23 May i n a l l zones s u r v i v e d the l o n g e s t , w i t h one or more ramets s u r v i v i n g p a s t the end of October ( F i g . 14a-c). A c o n s i d e r a b l e number of genets t h a t emerged much l a t e r (30%), from June 1 t o J u l y 1, s u r v i v e d i n t o the winter. V e g e t a t i v e ramets O v e r a l l , b ranching was l e s s f r e q u e n t i n the marina zone than i n the o t h e r two zones. Although t h e r e appeared t o be more bra n c h i n g w i t h c e r t a i n treatments ( F i g . 15a-c), t h e r e was no s t a t i s t i c a l l y s i g n i f i c a n t e f f e c t o f p l o t type i n any zone. S e e d l i n g s i n seeded buckets without Z. marina e x h i b i t e d l i t t l e b r a n c h i n g i n t h e j a p o n i c a zone and none i n t h e o t h e r zones. Rep r o d u c t i v e Shoots Rep r o d u c t i v e shoots began t o appear August 1 and t o detach o r d i s a p p e a r a t the end of September ( F i g . 16a-c). The d e n s i t y o f r e p r o d u c t i v e shoots was v e r y low i n a l l t h r e e zones. The means were not s i g n i f i c a n t l y d i f f e r e n t (p>.0125). There were more i n t h e j a p o n i c a zone, fewer i n the t r a n s i t i o n zone, and o n l y one p l o t had r e p r o d u c t i v e shoots i n the marina zone. There were no r e p r o d u c t i v e shoots produced from seeded buckets i n 57 25 cd > 20 GO cd © 2 15 -© a © O o M 10 © © 5 -l^h-M> ' Date F i g . 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 g e n e t s f r o m e a c h d a t e s u r v i v e d i n e a c h 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 , 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 . 58 K ^ J S V M> *H>^  Date F i g . 14b T r a n s i t i o n z o n e . Mean number o f weeks t h a t s e e d l i n g g e n e t s f r o m e a c h d a t e s u r v i v e d i n e a c h 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 , 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=seeded b u c k e t s w i t h Z. m a r i n a . 59 M> v6 Date F i g . 14c M a r i n a zone. Mean number o f weeks t h a t s e e d l i n g g e n e t s f r o m e a c h d a t e s u r v i v e d i n e a c h 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 , 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 F i g . 15a J a p o n i c a z o n e . 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 cm 2 i n e a c h 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 , ^ = 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 . 61 oo a Date F i g . 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 shoots from s e e d l i n g s p e r 625 cm 2 i n each treatment. o=unseeded p l o t s w i thout bucket, A=unseeded buckets, «=seeded buckets without Z. marina, B=seeded buckets w i t h Z. marina. 62 F i g . 15c Marina zone. Mean number o f v e g e t a t i v e shoots from s e e d l i n g s p e r 625 cm 2 i n each treatment. o=unseeded p l o t s without bucket, ^=unseeded buckets, «=seeded buckets without Z. marina. •=seeded buckets w i t h Z. marina. 63 F i g . 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 cm 2 i n e a c h 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 , 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 . 64 1.0 C O •«-> O O .a GO £ o o a o o a « © 0.8 0.6 0.4 0.2 0.0 Date F i g . 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 shoots from s e e d l i n g s p e r 625 cm 2 i n each treatment. o=unseeded p l o t s w i thout bucket, A=unseeded buckets, «=seeded buckets without Z. marina and seeded buckets w i t h Z. marina. 65 C O •*-> O O 43 GO © •T-l -»-» o o CM O O © a a 03 1.0 0.8 0.6 -0.4 -0.2 0.0 * * * * * Date F i g . 16c Marina zone. Mean number o f r e p r o d u c t i v e shoots from s e e d l i n g s p e r 625 cm 2 i n each treatment. «=unseeded p l o t s w i thout bucket, unseeded buckets, and seeded buckets without Z. marina. • =seeded buckets w i t h Z. marina. (Note: f i l l e d symbols o v e r l a p on x - a x i s . ) 6 6 e i t h e r the j a p o n i c a or t r a n s i t i o n zone. The o n l y Z . i a p o n i c a r e p r o d u c i n g i n the marina zone was from a seeded bucket with Z . marina. There was no d i f f e r e n c e i n the number of spathes produced per r e p r o d u c t i v e shoot i n any of the zones (p>.05). E l e v a t i o n of the p l o t s d i d not a f f e c t the number of spathes produced per shoot. The number of spathes per shoot i n the n a t u r a l p o p u l a t i o n a d j a c e n t t o the study p l o t s was the same as i n the c o n t r o l p l o t s i n each zone (p>.05) ( F i g . 17a-c). The mean numbers o f spathes per shoot i n the j a p o n i c a and t r a n s i t i o n zones ranged from 1.30 t o 4.22. There was a mean o f 2 spathes per shoot from the p l o t i n the marina zone. T o t a l ramets The numbers o f t o t a l ramets from s e e d l i n g s ( F i g . 18a-c) r e f l e c t the i n i t i a l s e e d l i n g emergence i n l a t e A p r i l t o June. The i n c r e a s e i n mid-July t o the end of August demonstrates the p r o d u c t i o n o f branching and r e p r o d u c t i v e shoots from e s t a b l i s h e d s e e d l i n g s . The d e c l i n e i n ramets i n l a t e September i l l u s t r a t e s t h e d e t a c h i n g of the r e p r o d u c t i v e shoots and t h e b e g i n n i n g of t h e r e d u c t i o n i n numbers of the ramets b e f o r e w i n t e r . 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 among p l o t types i n the j a p o n i c a and marina zones. In the t r a n s i t i o n zone, t h e r e 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 (p<.0125) o n l y on June 19 and J u l y 1 when ramets i n the seeded p l o t s without 67 D a t e F i g . 17a J a p o n i c a zone. Mean number o f spathes p e r r e p r o d u c t i v e shoot i n treatments and n a t u r a l survey. o=unseeded p l o t s without bucket, A=unseeded b u c k e t s , a =natural survey. 68 D a t e F i g . 17b T r a n s i t i o n z o n e . 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 a n d n a t u r a l s u r v e y . 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 , • = n a t u r a l s u r v e y . 69 Date F i g . 17c Marina zone. Mean number o f spathes p e r r e p r o d u c t i v e shoot i n treatments and n a t u r a l survey. «=seeded buckets w i t h Z. marina, • = n a t u r a l survey. 70 F i g . 18a J a p o n i c a z o n e . 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 cm 2 i n e a c h 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 . 71 10 r oo fl D a t e F i g . 18b T r a n s i t i o n z o n e . 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 cm 2 i n e a c h 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 , 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 . 72 F i g . 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 cm 2 i n e a c h 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 , ^ = 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 . a=seeded b u c k e t s w i t h Z. m a r i n a . 73 Z. m a r i n a a l l b u t d i s a p p e a r e d . E v e n t h o u g h t h e r e were few s t a t i s t i c a l d i f f e r e n c e s , t h e r e a r e some i n t e r e s t i n g t r e n d s . The s e e d e d b u c k e t s h a d l o w e r i n i t i a l numbers b u t i n t h e t r a n s i t i o n z one and t h e m a r i n a zone, 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 s o o n e q u a l l e d t h e u n s e e d e d c o n t r o l p l o t s . The b u c k e t c o n t r o l s and 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 h a d r a m e t s t h a t p e r s i s t e d when o t h e r p l o t s d i e d o u t . A d u l t S h o o t s The number o f a d u l t s h o o t s d e c r e a s e d w i t h d e c r e a s i n g e l e v a t i o n ( F i g . 1 9 a - c ) . T h e r e were f e w e r s h o o t s i n t h e u n s e e d e d p l o t s w i t h b u c k e t s t h a n i n t h o s e w i t h o u t i n t h e j a p o n i c a zone f r o m J u l y 1 t o A u g u s t 1 and i n t h e t r a n s i t i o n z o n e f r o m A u g u s t 16 t o O c t o b e r 15 (p<.0125). A l t h o u g h t h e same t r e n d was s e e n i n t h e m a r i n a zone, t h e r e was no s i g n i f i c a n t d i f f e r e n c e . The few a d u l t s h o o t s t h a t d i d a p p e a r i n s e e d e d b u c k e t s were r a m e t s t h a t e i t h e r grew i n f r o m t h e s u r r o u n d i n g a r e a o v e r t h e b u c k e t edge o r t h a t u p r o o t e d , f l o a t e d i n t o t h e b u c k e t , a n d r e - e s t a b l i s h e d t h e r e . T h e s e s h o o t s were removed. E v e n t h o u g h t h e b u c k e t s were p l a n t e d a t s e d i m e n t l e v e l , o f t e n t h e s e d i m e n t s washed away, e x p o s i n g b u c k e t r i m s s l i g h t l y a b o v e s e d i m e n t l e v e l . T h e r e was no d i f f e r e n c e i n s e d i m e n t t e m p e r a t u r e s t a k e n among p l o t s (p>.05). V i s u a l l y 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 i n v e r t e b r a t e b u r r o w o p e n i n g s b e t w e e n p l o t s w i t h a n d w i t h o u t b u c k e t s . 74 100 r oi tt-t O O & .0 cd <0 80 -60 -4 0 -2 0 -0 D a t e F i g . 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 2 i n each treatment. o=unseeded p l o t s without b u c k e t ,A=unseeded buckets, «=seeded buckets without Z. marina. 75 F i g . 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 2 i n each treatment. o=unseeded p l o t s without b u c k e t , A =unseeded buckets, »=seeded buckets without Z. marina. «=seeded buckets w i t h Z.. marina. (Note: f i l l e d symbols o v e r l a p ) 7 6 •*-» o © a « © 100 r 80 -60 40 20 -0 D a t e F i g . 19c Marina zone. Mean number o f a d u l t s p e r 625 cm 2 i n each treatment. o=unseeded p l o t s w i thout bucket, =unseeded buckets, •=seeded buckets without Z. marina. •=seeded buckets w i t h Z. marina. (Note: f i l l e d symbols o v e r l a p ) 77 N a t u r a l S u r v e y T h e r e was no s i g n i f i c a n t d i f f e r e n c e i n t h e d e n s i t y o f s e e d l i n g s among z o n e s e x c e p t on J u n e 1 ( m a r i n a < o t h e r two z o n e s ) a n d J u l y 4 ( m a r i n a < t r a n s i t i o n < j a p o n i c a ) (p<.05) ( F i g . 1 2 ) . T h e s e s h o o t s h a d n o t been mapped a n d s e e d l i n g s c o u l d n o t be d i s t i n g u i s h e d f r o m t h e a d u l t p o p u l a t i o n a f t e r J u l y 4 s o t h e numbers were c o m b i n e d a f t e r t h i s d a t e . T h e r e were no d i f f e r e n c e s when c o m p a r i n g t h e t o t a l number o f r e p r o d u c t i v e s h o o t s i n t h e c o n t r o l p l o t s t o what was f o u n d i n t h e n a t u r a l p o p u l a t i o n and when c o m p a r i n g t h e number o f s p a t h e s p e r s h o o t i n t h e c o n t r o l p l o t s a n d t h e n a t u r a l p o p u l a t i o n (p>.05). Numbers o f r e p r o d u c t i v e s h o o t s were v e r y l o w i n t h e m a r i n a z o n e . The d e n s i t y o f t o t a l r a m e t s i n t h e n a t u r a l s u r v e y was n o t s t a t i s t i c a l l y d i f f e r e n t f r o m t h e sum o f a d u l t s ( i . e . f r o m o v e r w i n t e r i n g g e n e t s ) p l u s t h e t o t a l r a m e t s f r o m s e e d l i n g s i n t h e c o n t r o l p l o t s i n e a c h zone (p>.05). T h e r e were d i f f e r e n c e s i n t h e d e n s i t y o f a d u l t s among z o n e s o f t h e n a t u r a l s u r v e y f r o m J u l y 4 t o O c t o b e r 15 and on November 30 (p<.05) ( F i g . 2 0 ) . On a l l o f t h e s e d a t e s t h e m a r i n a zone d e n s i t y was l o w e r t h a n t h a t i n t h e o t h e r z o n e s . D e n s i t i e s d e c l i n e d s h a r p l y a f t e r A u g u s t 1. S h o o t s a l s o b e g a n t o r e d u c e i n l e n g t h a n d l e a f w i d t h i n l a t e S e p t e m b e r . T h u s i n t h e f a l l a n d w i n t e r r a m e t s w o u l d o f t e n be l e s s t h a n 2 cm h i g h and 1 mm w i d e . 78 F i g . 20 Mean number o f a d u l t s p e r 625 cm 2 i n each zone i n the n a t u r a l survey. »=japonica zone, A = t r a n s i t i o n zone, o=marina zone. 79 D i s c u s s i o n In a l l of the t e s t s t h e r e was no d i f f e r e n c e o f mean numbers between the c o n t r o l p l o t s and the n a t u r a l p o p u l a t i o n ad-j a c e n t t o t h e study p l o t s . Because o f t h i s , i t w i l l be assumed t h a t t h e removal o f Z o s t e r a marina from the study p l o t s d i d not d i s r u p t Z. i a p o n i c a seeds or shoots i n the sediment. Genets became d i f f i c u l t t o i d e n t i f y as the p l a n t s grew due t o t h e underground rhizomes and rhizome fragmentation ( B i g l e y 1981, B i g l e y and H a r r i s o n 1986). In o r d e r not t o d i s t u r b the p l o t s , t o t a l e x c a v a t i o n of ramets t o determine which genet they were from was i m p o s s i b l e . There may be some e r r o r due t o t h i s u n c e r t a i n t y , but c a r e f u l mapping o f ramets reduced the e r r o r t o a minimum. There were, however, problems w i t h the use o f seeded buckets which had lower numbers o f emerging s e e d l i n g s than the c o n t r o l p l o t s . Two f a c t o r s may have c o n t r i b u t e d t o t h e d i f f e r e n c e . F i r s t , the d e n s i t y o f seeds t h a t were p l a n t e d i n the buckets was i n a d v e r t e n t l y lower than t h a t i n the u n d i s t u r b e d seed bank (See sediment s t u d i e s r e s u l t s , page 10). Second, Z. i a p o n i c a was a l s o seen t o be growing j u s t o u t s i d e many o f these p l a n t e d buckets, so i t appears t h a t some o f the p l a n t e d seeds washed out o f t h e buckets. Z o s t e r a 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 s t r a t e g y . High i n t h e i n t e r t i d a l zone where the f i r s t c o l o n i z e r s were observed, the p l a n t i s l a r g e l y annual and produces many seeds ( H a r r i s o n and B i g l e y 1982). A t p r o g r e s s i v e l y lower e l e v a t i o n s , i n the 80 area o f the j a p o n i c a and t r a n s i t i o n zones of t h i s study, o v e r w i n t e r i n g shoots and shoots t h a t came from o v e r w i n t e r i n g rhizomes made up a c o n s i d e r a b l e p a r t o f the p o p u l a t i o n . Perhaps rhizomes ov e r w i n t e r more s u c c e s s f u l l y i n sediment t h a t i s not exposed t o t h e c o l d w i n t e r a i r common d u r i n g the n i g h t t i m e low t i d e s . T h i s s t r e s s occurs a t the h i g h e l e v a t i o n s and dormant seeds may be r e s i s t a n t t o c o l d s t r e s s . I t appears t h a t t h e r e i s no advantage t o s e e d l i n g s which emerge e a r l y , as t h e r e i s i n many ot h e r systems. In A p r i l t h e r e was a f l u s h o f emerging s e e d l i n g s but many o f thes e e a r l y s e e d l i n g s d i e d , mostly through u p r o o t i n g as was observed by B i g l e y (1981). The s e e d l i n g s t h a t emerged i n l a t e A p r i l through May, as w e l l as a few l a t e emerging s e e d l i n g s i n J u l y , were the genets t h a t s u r v i v e d the l o n g e s t . The i n t e r t i d a l sediment h a b i t a t i s s u b j e c t t o both r e g u l a r ( i . e . t i d a l ) and u n p r e d i c t a b l e ( i . e . storm-induced) d i s t u r b a n c e s t h a t may modify the s e a s o n a l p r o g r e s s i o n from c o o l w i n t e r days w i t h low l i g h t l e v e l s t o t h e warmer, b r i g h t e r , and l o n g e r s p r i n g days t h a t are more f a v o r a b l e t o p l a n t growth. E a r l y s p r i n g i s s t i l l a h i g h -r i s k p e r i o d f o r Z.. i a p o n i c a s e e d l i n g s . When a r t i f i c i a l l y p l a n t e d i n each zone, even the marina zone, seeds were a b l e t o produce r e p r o d u c t i v e shoots, thus e n a b l i n g t h e p l a n t t o propagate s e x u a l l y throughout t h e study area even where p l a n t s a re absent from the n a t u r a l v e g e t a t i o n . In Japan, Z. i a p o n i c a grew r a p i d l y from seeds but no p l a n t s developed f l o w e r i n g stems w i t h i n the f i r s t y e a r ( A r a s a k i 1950b). 8 1 T h i s 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 s p e c i e s . Nomme (1989) showed t h a t t r a n s p l a n t s o f mature shoots a l s o were a b l e t o grow throughout the same study area. Now we know t h a t both a d u l t s and s e e d l i n g s can mature throughout t h i s e l e v a t i o n g r a d i e n t , so the 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 from the l o c a l d i s p e r s a l p a t t e r n i d e n t i f i e d i n the sediment s t u d i e s s e c t i o n (page 37). The b i o l o g y o f Z. i a p o n i c a a t the seaward edge o f i t s c u r r e n t 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 shoots were found i n the marina zone and these were g e n e r a l l y i n sparse areas w i t h few Z. marina. The o c c a s i o n a l s e e d l i n g o f Z. i a p o n i c a t h a t might e s t a b l i s h n a t u r a l l y among the Z. marina may have d i f f i c u l t y p e n e t r a t i n g the extremely t h i c k rhizome mats of the p e r e n n i a l Z. marina. Pre-emption of r o o t i n g space by Z. marina may a f f e c t Z. i a p o n i c a as i t grows, perhaps d u r i n g the w i n t e r and second year o f growth. There i s i n d i r e c t evidence t h a t suggests belowground i n t e r a c t i o n between t h e two Z o s t e r a s p e c i e s (Nomme 1989). More r e s e a r c h needs t o be done i n order t o determine t h e exte n t o f i n t e r f e r e n c e between t h e two s p e c i e s . I t appears, however, t h a t Z. i a p o n i c a i s not l i k e l y t o r e p l a c e Z. marina. I t i s p o s s i b l e t h a t the buckets and Z. marina p l a y e d the same b e n e f i c i a l r o l e i n promoting e s t a b l i s h m e n t and growth. The presence o f a bucket o r a Z. marina canopy was a s s o c i a t e d w i t h s e e d l i n g s and t h e i r ramets p e r s i s t i n g l o n g e r o r w i t h h i g h e r ramet d e n s i t i e s . T h i s l e a d s t o the c o n c l u s i o n t h a t both of 82 t h e s e must s l o w w a t e r a c t i o n o r s t a b i l i z e s e d i m e n t s t o a l l o w b e t t e r s e e d l i n g e s t a b l i s h m e n t and s u b s e q u e n t g r o w t h ( T h a y e r e t a l . 1975, F o n s e c a and F i s h e r 1986, F o n s e c a and K e n w o r t h y 1987). I must t h e r e f o r e a c c e p t t h e n u l l h y p o t h e s i s t h a t t h e r e i s no n e g a t i v e e f f e c t o f Z. m a r i n a on t h e emergence a n d e s t a b l i s h m e n t o f Z. i a p o n i c a . 83 R E F E R E N C E S A r a s a k i , M. 1950a. S t u d i e s on the ecology of Z o s t e r a marina 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):567-572. A r a s a k i , M. 1950b. S t u d i e s on the ecology of Z o s t e r a marina and Z o s t e r a nana I I . B u l l . Jap. Soc. S c i . F i s h . 16:70-76. B e n o i t , D.L., N.C. Kenkel, and P.B. Cavers. 1989. F a c t o 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 bank e s t i m a t e s . Can. J . Bot. 67:2833-2840. Bewley, J.D., and M. Black. 1985. Seeds. P h y s i o l o g y o f Development and Germination. Plenum P r e s s . New York. Ch. 6 (some e c o p h y s i o l o g i c a l a s p e c t s of g e r m i n a t i o n ) . pp.237-252. B i g l e y , R.E. 1981. The p o p u l a t i o n b i o l o g y of two i n t e r t i d a l s e a g r asses, Z o s t e r a i a p o n i c a and Ruppia maritima. a t Roberts Bank, B r i t i s h Columbia. 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. 205p. B i g l e y , R.E. and J.L. Barreca. 1982. Evidence f o r synonymizing Z o s t e r a americana den Hartog w i t h Z o s t e r a i a p o n i c a Aschers. and Graebn. Aquat. Bot. 14:349-3 56. B i g l e y , R.E. and P.G. H a r r i s o n . 1986. Shoot demography and morphology of Z o s t e r a i a p o n i c a and Ruppia maritima from B r i t i s h Columbia, Canada. Aquat. Bot. 24:69-82. C h u r c h i l l , A.C. 1983. F i e l d s t u d i e s on seed g e r m i n a t i o n and s e e d l i n g development i n Z o s t e r a marina L. Aquat. Bot. 16: 21-29. Fonseca, M.S. and J.S. F i s h e r . 1986. A comparison o f canopy f r i c t i o n and sediment movement between f o u r s p e c i e s of seagrass w i t h r e f e r e n c e t o t h e i r ecology and r e s t o r a t i o n . Mar. E c o l . Prog. Ser. 29:15-22. Fonseca, M.S. and W.J. Kenworthy. 1987. E f f e c t s o f c u r r e n t on p h o t o s y n t h e s i s and d i s t r i b u t i o n of s e a g r a s s e s . Aquat. Bot. 27:59-78. Fukuda, T., Y. T s u c h i y a , and S. Terashima. 1983. R e l a t i o n s h i p between seed d i s t r i b u t i o n and a d u l t growth i n an e e l g r a s s ( Z o s t e r a marina) bed: I n v e s t i g a t i o n i n a narrow zone. B u l l , o f the F i s h e r i e s Experiment S t a t i o n , Okayama P r e f e c t u r e 1982:61-65. 84 Fukuda, T. and Y. T s u c h i y a . 1987. R e l a t i o n between shoot and seed d i s t r i b u t i o n s of e e l g r a s s bed. Nippon S u i s a n G a k k a i s h i 53(10):1755-1758. Garwood, N.C. 1983. Seed germination i n a s e a s o n a l t r o p i c a l f o r e s t i n Panama: A community study. E c o l . Monog. 53(2): 159-181. Grabe, D.F. (ed.) 1970. T e t r a z o l i u m T e s t i n g Handbook f o r A g r i c u l t u r a l Seeds. C o n t r i b u t i o n No. 29 t o the Handbook on Seed T e s t i n g . The T e t r a z o l i u m T e s t i n g Committee of the A s s o c i a t i o n o f O f f i c i a l Seed A n a l y s t s . 61p. Grime, J.P. 1989. Seed banks i n e c o l o g i c a l p e r s p e c t i v e . In: Ecology o f S o i l Seed Banks. Leek, M.A., V.T. Parker, and R.L. Simpson (eds). Acedemic Pr e s s , Inc. Toronto, pp. x v - x x i i . Harper, J.L. 1957. The e c o l o g i c a l s i g n i f i c a n c e o f dormancy and i t s importance i n weed c o n t r o l . Proceedings o f the I V ^ n I n t e r n a t i o n a l Congress of Crop P r o t e c t i o n ; 1957. Hamburg. 1:415-420. Harper. J.L., P.A. Landragin, and J.W. Ludwig. 1955. The i n f l u e n c e o f environment on seed and s e e d l i n g m o r t a l i t y : I. The i n f l u e n c e of time o f p l a n t i n g on the g e r m i n a t i o n of Maize. New Phyt. 54(2):107-118. Harper, J.L. and J . White. 1970. The dynamics o f p l a n t p o p u l a t i o n s . In: Proceeding o f the Advanced Study  I n s t i t u t e on Dynamics of Numbers o f P o p u l a t i o n s ; 1970; Oosterbeek. den Boer, P.J. and G.R. Gradwell ( e d s ) . Centre f o r A g r i c u l t u r a l P u b l i s h i n g and Documentation. Wageningen, West Germany, pp. 419-463. Harper, J.L. and J . White. 1974. The demography o f p l a n t s . Ann. Rev. E c o l . S y s t . 5:419-463. H a r r i s o n , P.G. 1979. Reproductive s t r a t e g i e s i n i n t e r t i d a l p o p u l a t i o n s o f two c o - o c c u r r i n g seagrasses ( Z o s t e r a spp.). Can. J . Bot. 57(23):2635-2638. H a r r i s o n , P.G. 1984. The B i o l o g y o f Seagrasses i n the Intercauseway Area o f Roberts Bank, B.C. A r e p o r t submitted t o the P o r t of Vancouver. 168p. H a r r i s o n , P.G. 1987. N a t u r a l expansion and e x p e r i m e n t a l m a n i p u l a t i o n o f seagrass ( Z o s t e r a spp.) abundance and the response o f i n f a u n a l i n v e r t e b r a t e s . E s t . Coast. S h e l f S c i . 24:799-812. 85 H a r r i s o n , P.G. and R.E. B i g l e y . 1982. The r e c e n t i n t r o d u c t i o n of the seagrass Zo s t e r a i a p o n i c a Aschers. and Graebn. t o the P a c i f i c c o a s t of North America. Can. J . F i s h . Aquat. S c i . 39:1642-1648. Hootsmans, M.J.M., J.E. Vermaat, and W. van V i e r s s e n . 1987. Seed bank development, germination, and e a r l y s e e d l i n g s u r v i v a l of two seagrass s p e c i e s from The N e t h e r l a n d s : Z o s t e r a marina L. and Z o s t e r a n o l t i i Hornem. Aquat. Bot. 28:275-285. Howe, H.F. and J . Smallwood. 1982. Ecology o f seed d i s p e r s a l . Ann. Rev. E c o l . S y s t . 13:201-228. Hutchings, M.J. 1986. The s t r u c t u r e of p l a n t p o p u l a t i o n s . In: P l a n t Ecology. Crawley, M.J. (ed). B l a c k w e l l . pp.97-136. Hutchings, M.J. and P.J. R u s s e l l . 1989. The seed r e g e n e r a t i o n dynamics o f an emergent s a l t marsh. J . E c o l . 77:615-637. Jacobs, R.P.W.M. 1982. Reproductive s t r a t e g i e s o f two seagrass s p e c i e s ( Z o s t e r a marina and Z o s t e r a n o l t i i ) a l o n g West European c o a s t s . In: S t u d i e s on Acruatic V a s c u l a r P l a n t s . Symoens, J . J . , S.S. Hooper, and P. Compere ( e d s ) . Royal B o t a n i c a l S o c i e t y o f Belgium, B r u s s e l s , pp.150-155. Keddy, C.J. 1987. Reproduction o f annual e e l g r a s s : v a r i a t i o n among h a b i t a t s and comparison w i t h p e r e n n i a l e e l g r a s s ( Z o s t e r a marina L . ) . Aquat. Bot. 27:243-256. L i v i n g s t o n , R.B. and M.L. A l l e s s i o . 1968. B u r i e d v i a b l e seed i n s u c c e s s i o n a l f i e l d and f o r e s t stands, Harvard F o r e s t , Massachusetts. B u l l . T o r r . Bot. Club 95(l):58-69. Moody, R. 1978. H a b i t a t , p o p u l a t i o n and l e a f c h a r a c t e r i s t i c s o f seagrass (Zostera marina L.) on Roberts Bank, B.C. 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. 104p. Nomme, K.M. 1989. I n t e r a c t i v e b i o l o g y o f two s e a g r a s s e s , Z o s t e r a marina L. and Z o s t e r a i a p o n i c a A s c h e r s . and Graebn. M.Sc. t h e s i s . U n i v e r s i t y of B r i t i s h Columbia, Vancouver. 118p. Orth, R.J. and K.A. Moore. 1983. Seed g e r m i n a t i o n and s e e d l i n g growth o f Z o s t e r a marina L. ( e e l g r a s s ) i n the Chesapeake Bay. Aquat. Bot. 15:117-131. P h i l l i p s , R.C. and J.F. Watson. 1984. The E c o l o g y o f E e l g r a s s  Meadows i n the P a c i f i c Northwest: A Community P r o f i l e . U.S. Department of the I n t e r i o r , FWS/OBS-84/24. Washington D.C. 86 P h i l l i p s , R.C. and E.G. Menez. 1988. Seagrasses. Smithsonian c o n t r i b u t i o n s t o the marine s c i e n c e s . No. 34. Smithsonian I n s t i t u t e P r e s s . Washington, D.C. 104p. Ste b b i n s , G.L. 1971. Adaptive r a d i a t i o n of r e p r o d u c t i v e c h a r a c t e r i s t i c s i n angiosperms. I I . Seeds and s e e d l i n g s . Ann. Rev. E c o l . S y s t . 2:237-260. S u l t a n , S.E. 1987. E v o l u t i o n a r y i m p l i c a t i o n s o f phenotypic p l a s t i c i t y i n p l a n t s . E v o l . B i o l . 21:127-178. Swinbanks, D.D. 1979. Environmental f a c t o r s c o n t r o l l i n g z o n a t i o n and the d i s t r i b u t i o n of burrowing and tube-d w e l l i n g organisms of F r a s e r d e l t a t i d a l f l a t s , B r i t i s h Columbia. Ph.D. t h e s i s . U n i v e r s i t y o f B r i t i s h Columbia, Vancouver. Thayer, G.W., D.A. Wolfe, and R.B. W i l l i a m s . 1975. The impact o f man on seagrass systems. Am. S c i e n t . 63:288-296. Thayer, G.W., M.S. Fonseca, and E. Pendleton. 1984. The  Ecology o f E e l g r a s s Meadows o f the A t l a n t i c Coast: A  Community P r o f i l e . U.S. Department of the I n t e r i o r , FWS/OBS-84/02. Washington D.C. van der V a l k , A.G. 1986. The impact o f l i t t e r and annual p l a n t s on r e c r u i t m e n t from the seed bank o f a l a c u s t r i n e wetland. Aquat. Bot. 24:13-26. Watkinson, A.R. 1986. P l a n t p o p u l a t i o n dynamics. In: P l a n t  Ecology. Crawley, M.J. (ed). B l a c k w e l l . pp.137-184. Wigand, C. and A.C. C h u r c h i l l . 1988. L a b o r a t o r y s t u d i e s on e e l g r a s s seed and s e e d l i n g p r e d a t i o n . E s t u a r i e s 11(3):180-183. W i l k i n s o n , L. 1988. SYSTAT. Evanston, IL: SYSTAT, Inc. Zar, J.H. 1984. B i o s t a t i s t i c a l A n a l y s i s . Englewood C l i f f s , N.J. P r e n t i c e - H a l l Inc. 719p. 87 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0098621/manifest

Comment

Related Items