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Habitat, population and leaf characteristics of Zostera marina L. on Roberts Bank, British Columbia 1978

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HABITAT, POPULATION AND LEAF. CHARACTERISTICS OF Zostera marina L. ON ROBERTS BANK, BRITISH COLUMBIA by ROBERT MOODY B . S c , U n i v e r s i t y of B r i t i s h Columbia, 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department o f P l a n t Science We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA May, 19 78 ©ROBERT MOODY, 1978 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make i t f ree l y ava i lab le for reference and study. I fur ther agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my writ ten permission. Department of Plant Science The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date May 1. 1978 5 i i ABSTRACT The sand and mud f l a t s o f the F r a s e r R i v e r f o r e - shore support e x t e n s i v e meadows of the seagrass Zostera marina L. ( e e l g r a s s ) . I n d u s t r i a l , r e s i d e n t i a l and r e c r e a t i o n a l developments t h r e a t e n these v a l u a b l e f o r e s h o r e areas. A study was undertaken i n t o the h a b i t a t requirements and p o p u l a t i o n and m o r p h o l o g i c a l c h a r a c t e r i s t i c s of e e l g r a s s on southern Roberts Bank, B r i t i s h Columbia t o p r o v i d e i n f o r m a t i o n which would h e l p minimize the p o t e n t i a l l y d e l e t e r i o u s e f f e c t s o f such developments on the e e l g r a s s r e s o u r c e . Watecr temperatures and s a l i n i t i e s and wave motion on southern Roberts Bank a l l approach the world-wide optima f o r e e l g r a s s . The upper d i s t r i b u t i o n a l l i m i t of e e l g r a s s was lower than those of other P a c i f i c Coast e e l g r a s s p o p u l a t i o n s . The sandy nature o f the s u b s t r a t e i n f l u e n c e s "desiccation" which, i n t u r n , c o n t r o l s the i n t e r t i d a l l i m i t of e e l g r a s s growth. L i g h t a v a i l a b i l i t y determines the lower d i s t r i b u - t i o n a l l i m i t o f e e l g r a s s i n other areas. These two f a c t o r s , the sandy s u b s t r a t e and reduced l i g h t a v a i l a b i l i t y i n the t u r b i d e s t u a r i n e waters of the F r a s e r R i v e r f o r e s h o r e , appear to be r e s p o n s i b l e f o r the narrow depth range of e e l g r a s s on southern Roberts Bank. A s t r a t i f i e d random sampling technique was used t o determine seasonal changes i n e e l g r a s s s t a n d i n g crop, t u r i o n d e n s i t y and l e a f dimensions a t f i v e e l e v a t i o n s , l o c a t e d a t 0.5 m depth i n t e r v a l s , from the upper to the lower l i m i t s of e e l g r a s s growth. A pronounced d e c l i n e i n both t u r i o n d e n s i t y and l e a f s t a n d i n g crop o c c u r r e d i n l a t e summer. Throughout the study p e r i o d , l e a f s t a n d i n g crops and t u r i o n d e n s i t i e s were g r e a t e s t ' a t the three i n t e r m e d i a t e study e l e v a t i o n s . Reduced l e a f s t a n d i n g crops were found near the upper and lower edges of the e e l g r a s s bed; no s i g n i f i c a n t d i f f e r e n c e i n stan d i n g crops was found f o r these two e l e v a t i o n s . T u r i o n d e n s i t i e s were a l s o lower near the upper and lower depth l i m i t s o f e e l g r a s s and a s i g n i f i c a n t d i f f e r e n c e i n t u r i o n d e n s i t i e s was found between these two e l e v a t i o n s , w i t h the lowest t u r i o n d e n s i t y recorded near the lower l i m i t of e e l - g r a s s . Near the upper edge of the e e l g r a s s bed, t u r i o n weights and mean l e a f lengths were one-half those o f the lower e l e v a t i o n s . " A s y n t h e s i s of the a v a i l a b l e i n f o r m a t i o n i n d i c a t e s t h a t d e p t h - r e l a t e d f a c t o r s s t r o n g l y i n f l u e n c e c e r t a i n m o r p h o l o g i c a l and p o p u l a t i o n c h a r a c t e r i s t i c s o f e e l g r a s s on southern Roberts Bank. i v TABLE OF CONTENTS Page 1. INTRODUCTION 1 1.1. Purpose o f the Study 1 1.2. Previ o u s Research 2 1.3. O b j e c t i v e s of the Study 9 2. THE STUDY AREA 10 3. ENVIRONMENTAL FACTORS IN RELATION TO EELGRASS HABITAT 17 3.1. M a t e r i a l s and Methods 17 3.2. H a b i t a t F a c t o r s 21 3.2.1. S a l i n i t y 21 3.2.1.1. Seasonal Changes 21 3.2.1.2. D i u r n a l Changes 24 3.2.2. Temperature 24 3.2.2.1. Seasonal Changes 24 3.2.2.2. D i u r n a l Changes 27 3.2.3. L i g h t 2 7 3.2.3.1. Seasonal Changes 27 3.2.3.2. D i u r n a l Changes 2 7 3.2.4. T i d a l Range and Percentage Exposure 32 3.2.5. Subs t r a t e 3 3 3.2.5.1. Surface L e v e l Changes 33 3.2.5.2. P h y s i c a l and Chemical C h a r a c t e r i s t i c s 33 3.2.6. Waves and Cu r r e n t s 39 3.3. D i s c u s s i o n 39 4. STANDING CROP, TURION DENSITY, BIOMASS AND LEAF MEASUREMENT STUDIES 45 4.1. M a t e r i a l s and Methods 45 4.2. Standing Crop 4 8 4.2.1. Temporal Changes 50 4.2.2. I n f l u e n c e o f Depth 52 V Page 4.3. T u r i o n D e n s i t y 56 4.3.1. I n f l u e n c e of Time and E l e v a t i o n on T o t a l T u r i o n D e n s i t y 56 4.3.2. I n f l u e n c e of Time and E l e v a t i o n on Reproductive T u r i o n D e n s i t y ... 64 4.4. The I n f l u e n c e o f Depth on Organic Weight per T u r i o n 4.5. Biomass 4.6. Leaf Measurements 4.7. D i s c u s s i o n 5. SUMMARY AND CONCLUSIONS 7 9 GLOSSARY BIBLIOGRAPHY APPENDICES .. 64 70 70 75 83 86 91 v i LIST OF TABLES Table Page 1. P a r t i c l e s i z e composition o f sediments 36 2. Organic and carbonate carbon contents of sediments 40 3. Comparisons of h a b i t a t f a c t o r s a f f e c t i n g e e l - grass growth (modified from Stout 1976, and P h i l l i p s 1972) 41 4. A n a l y s i s o f v a r i a n c e summary t a b l e f o r mean l e a f s t a n d i n g crop (organic dry weight i n grams per 0.25 square meter quadrat) 51 5. Newman-Keuls M u l t i p l e Range T e s t f o r mean l e a f s t a n d i n g stocks (organic dry weight i n grams per 0.2 5 square meter quadrat) a t f i v e e l e v a t i o n s 55 6. A n a l y s i s o f v a r i a n c e summary t a b l e f o r mean t o t a l t u r i o n d e n s i t y ( t u r i o n s per 0.25 square meter quadrat 58 7. Newman-Keuls M u l t i p l e Range T e s t f o r t o t a l t u r i o n d e n s i t y ( t u r i o n s per 0.25 square meter quadrat) means a t f i v e e l e v a t i o n s 59 8. T o t a l t u r i o n d e n s i t i e s ( t u r i o n s per 0.25 square meter quadrat) f o r f o u r t e e n sampling s e s s i o n s , May to December 1976 61 9. A n a l y s i s of v a r i a n c e summary t a b l e f o r mean r e p r o d u c t i v e t u r i o n d e n s i t y ( t u r i o n s per square meter) 65 10. L i n e a r r e g r e s s i o n equations of o r g a n i c dry weight (g) on t u r i o n numbers per quadrat f o r f i v e e l e v a t i o n s 66 11. A n a l y s i s of co v a r i a n c e summary t e s t i n g f o r s i g n i f i c a n t d i f f e r e n c e s between slo p e s of l i n e a r r e g r e s s i o n l i n e s o f o r g a n i c dry weight on t u r i o n numbers f o r f i v e e l e v a t i o n s 6 8 12. Newman-Keuls M u l t i p l e Range T e s t f o r d i f f e r - ences between slo p e s o f l i n e a r r e g r e s s i o n s of or g a n i c dry weight on t u r i o n numbers f o r f i v e e l e v a t i o n s 69 v i i T able Page 13. Percentages of above-substrate ( l e a f ) and below-substrate (roots and rhizomes) s t a n d i n g crops, A p r i l 1976 to January 1977 ... 71 14. Leaf measurements f o r f i v e e l e v a t i o n s , August 1976 to January 1977 72 15. Leaf and rhizome measurements f o r samples c o l l e c t e d a t 0.8 meters ( i n r e l a t i o n t o Chart Datum), August 19 76 to January 19 77. Number of o b s e r v a t i o n s i n b r a c k e t s 74 v i i i LIST OF FIGURES F i g u r e Page 1. A e r i a l photo mosaic of the F r a s e r R i v e r D e l t a showing l o c a t i o n o f the study area 11,12 2. Diagram of the study s i t e showing t r a n s e c t l o c a t i o n s 13,14 3. Schematic p r o f i l e o f the study s i t e showing t r a n s e c t e l e v a t i o n s i n r e l a t i o n to Chart Datum 18,19 4. Surface and 1.5 m s a l i n i t i e s and temperatures at the study s i t e and mean monthly a i r temper- ature a t Vancouver I n t e r n a t i o n a l A i r p o r t (Monthly Record, M e t e o r o l o g i c a l Observations i n Canada, Atmospheric Environment, F i s h e r i e s and Environment Canada, A p r i l 19 76 to^January 19 77). Mean monthly a i r temperature p l o t t e d a t the midpoint of each month 22,23 5. D i u r n a l s u r f a c e and 1.5 m s a l i n i t i e s . May 2, J u l y 2 8 and October 4, 19 76. January 18, 1977 : 25,26 6. D i u r n a l a i r temperatures and s u r f a c e and 1.5 m water temperatures. May 2, J u l y 2 8 and October 4, 1976. January 18, 1977 28,29 7. S e c c h i depth (meters) a t the study s i t e and maximum d a i l y d i s c h a r g e (thousands of c u b i c meters per second) of the F r a s e r R i v e r a t Hope, B.C. f o r each month from March 19 76 to January 1977 30,31 8. Net o s c i l l a t i o n s o f sediment s u r f a c e l e v e l s , J u l y 1976 t o January 1977. Mean + Standard E r r o r 34,35 9. Sediment samples taken a t 10-meter i n t e r v a l s from the upper t o the lower l i m i t s o f e e l g r a s s growth: a. Percentage of f i n e s b. Percentages of o r g a n i c and carbonate carbon 37,38 10. Mean l e a f s t a n d i n g crop (grams per square meter) f o r f i v e e l e v a t i o n s ( i n r e l a t i o n t o Chart Datum), A p r i l 1976 to January 1977 53,54 i x F i g u r e Page 11. Mean t o t a l t u r i o n numbers per square meter f o r f i v e e l e v a t i o n s ( i n r e l a t i o n t o Chart Datum), A p r i l 1976 to January 1977 62,63 X LIST OF APPENDICES Appendix Page 1. S e c c h i depth and s u r f a c e and subsurface (1.5 m) s a l i n i t y and temperature measure- ments. March 1976 t o January 1977 92 2. D i u r n a l s u r f a c e and subsurface (1.5 m) s a l i n i t y (parts per thousand) measurements. May 2, J u l y 2 8 and October 4, 19 76. January 18, 1977 93 3. D i u r n a l a i r , s u r f a c e and subsurface (1.5 m) temperature (°C) measurements. May 2, J u l y 28 and October 4, 1976. January 18, 1977 .... 94 4. D i u r n a l S e c c h i depth and 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) measurements. May 2, J u l y 28 and October 4, 19 76. January 18, 1977 95 5. Net o s c i l l a t i o n s of sediment s u r f a c e l e v e l s - measurements and s t a t i s t i c s . June 19 76 to January 1977 96 6. S t a t i s t i c s o f s t a n d i n g crop i n f o r m a t i o n (organic dry weight per quadrat) used f o r optimum quadrat s i z e d e t e r m i n a t i o n 9 7 7. Organic dry weight i n grams per square meter f o r f i v e e l e v a t i o n s (Chart Datum). A p r i l 1976 t o January 1977 98 8. A n a l y s i s o f v a r i a n c e summary t a b l e f o r mean l e a f s t a n d i n g crop (organic dry weight i n grams per 0.25 square meter quadrat) 99 9. D e n s i t y i n t u r i o n s per square meter f o r f i v e e l e v a t i o n s (Chart Datum). A p r i l 19 76 to January 1977 100 10. A n a l y s i s of v a r i a n c e summary t a b l e f o r mean t u r i o n d e n s i t y ( t u r i o n s per 0.25 square meter quadrat) 101 11. Reproductive t u r i o n d e n s i t y (per square meter) f o r f i v e e l e v a t i o n s . June to August, 1976 102 12. A n a l y s i s of v a r i a n c e summary f o r slo p e s of the r e g r e s s i o n s o f t u r i o n numbers on o r g a n i c dry weight f o r f i v e e l e v a t i o n s (Chart Datum) 103 x i Appendix Page 13. Mean biomass o f i n t e r t i d a l (0.8 m) e e l g r a s s i n grams per square meter (organic dry weight) . A p r i l 1976 to January 1977 104 x i i ACKNOWLEDGEMENTS Fina n c i a l assistance for t h i s study was provided by the B r i t i s h Columbia Hydro and Power Authority. I am espe c i a l l y indebted to Mr. R. Dundas and Dr. R. Ferguson of the Environmental Group of t h i s agency. The assistance received from t h i s agency and these individuals i s g r a t e f u l l y acknowledged. My committee members, Dr. R. E. Foreman, Dr. P. G. Harrison and Dr. C. D. Levings, provided encouragement, advice and constructive c r i t i c i s m during the study. I am also indebted to my committee chairman, Dr. Runeckles. I am sincerely g r a t e f u l to my fellow students, Herb Klassen, Ed Medley and Dave Swinbanks, for t h e i r valuable f i e l d assistance. T i d a l information was provided by Mr. W. J. Rapatz, Regional Tide Superintendent. Mr. B i l l Tupper of the B r i t i s h Columbia Inst i t u t e of Technology gave valued informa- t i o n on a e r i a l photography. Dr. J. Luternauer of the Geological Survey of Canada was most h e l p f u l i n providing information concerning the geological setting of the Fraser River foreshore. I appreciate the assistance of these i n d i v i d u a l s . I am p a r t i c u l a r l y indebted to my supervisor, Professor V. C. Brink, for his help, patience and guidance throughout the course of t h i s work. F i n a l l y , I am deeply moved by the support, assistance and extreme patience received from my wife, f r i e n d , confidante and colleague, Anne. 1. INTRODUCTION 1.1. Purpose of the Study Most of the B r i t i s h Columbia c o a s t l i n e i s t y p i c a l l y p r e c i p i t o u s ; the shallow p r o t e c t e d areas necessary f o r the s u c c e s s f u l e s t a b l i s h m e n t o f seagrass meadows are r e l a t i v e l y r a r e along our c o a s t . The e x t e n s i v e sand and mud f l a t s o f the F r a s e r R i v e r D e l t a support l a r g e meadows o f the n o r t h temperate seagrass Zostera marina L. ( e e l g r a s s ) . Z. marina, a marine Angiosperm, i s a member of the f a m i l y Potamogetonaceae, subfamily Z o s t e r o i d e a e , genus Z o s t e r a , and subgenus Z o s t e r a (den Hartog 19 70). The importance of e e l g r a s s t o i n v e r t - e b r a t e s , f i s h and waterfowl p o p u l a t i o n s i s well-documented i n the North American and European l i t e r a t u r e ( P h i l l i p s 1975, Thayer e t a l 1975). In r e c e n t y e a r s , p r o p o s a l s t o develop the t i d a l f l a t s f o r r e s i d e n t i a l , i n d u s t r i a l and r e c r e a t i o n a l purposes have been i n c r e a s i n g . In a d d i t i o n t o d i r e c t l o s s e s of e e l g r a s s h a b i t a t , these developments may a l s o have d e t r i - mental e f f e c t s on the remaining e e l g r a s s h a b i t a t through a l t e r a t i o n o f c u r r e n t p a t t e r n s and water q u a l i t y , and i n c r e a s e d i n d u s t r i a l and r e c r e a t i o n a l t r a f f i c a long the f o r e - shore. To minimize the d e l e t e r i o u s e f f e c t s of v a r i o u s developments on the e e l g r a s s resource of the F r a s e r R i v e r D e l t a , i n f o r m a t i o n i s r e q u i r e d on the h a b i t a t requirements and growth c h a r a c t e r i s t i c s of e e l g r a s s i n the area. The purpose o f t h i s study i s to pr o v i d e some o f t h a t i n f o r m a t i o n . 2 1 . 2 . Previous Research In a comprehensive study of the seasonal growth of some seventy taxa of benthic marine plants i n Great Pond estuary, Massachusetts, Conover ( 1 9 58) found that the rel a t i o n s of environmental factors to the growth and d i s t r i - bution of Z. marina were not well-defined. High standing crop values of eelgrass were found i n those sections of the estuary where s a l i n i t i e s ranged from 1 2 to 3 2 % o , lower values were obtained i n areas where the s a l i n i t y range was 1 to 3 0 % o , and eelgrass was not present i n areas having less than l % o s a l i n i t y . Standing crop maxima and minima for eelgrass were associated with the annual maxima and minima of i n s o l a t i o n and water temperature. Conover suggests that these two factors, temperature and l i g h t , play leading roles i n the seasonal growth of eelgrass i n Great Pond. Setchell's scheme ( 1 9 2 9 ) describing various growth, developmental and phenological a c t i v i t i e s of eelgrass based on 5°C water temperature increments has not been borne out i n the recent works of Burkholder and Doheny ( 1 9 6 8), McRoy ( 1 9 6 9 ) and P h i l l i p s ( 1 9 7 2 ) . Based on information from transplant experiments, P h i l l i p s ( 1 9 7 4 ) suggests that the lower depth l i m i t of e e l - grass growth i n Puget Sound, Washington i s determined by l i g h t a v a i l a b i l i t y . Controlled f i e l d experiments i n southern C a l i f o r n i a by Backman and B a r i l o t t i ( 1 9 7 6 ) confirmed that eelgrass turion density i s a function of irradiance received by the plants. A turion i s a leafy branch a r i s i n g from the 3 h o r i z o n t a l rhizome. In Chesapeake Bay on the A t l a n t i c Coast, Orth (19 73) found t h a t the sediments a s s o c i a t e d with dense stands of e e l g r a s s are more p o o r l y s o r t e d and c o n t a i n h i g h e r f i n e f r a c t i o n s than the sediments from areas of l e s s dense e e l - grass growth. S i m i l a r l y , Stout (19 76) d e s c r i b e s a r e l a t i o n - s h i p between the occurrence of very f i n e - g r a i n e d sands and s i l t s and the presence o f e e l g r a s s beds. These sediment c h a r a c t e r i s t i c s are a t t r i b u t e d by both authors t o a t r a p p i n g a c t i o n by e e l g r a s s . E e l g r a s s has not been observed growing on sand i n p r e v i o u s s t u d i e s o f e e l g r a s s p o p u l a t i o n s on the P a c i f i c Coast. P h i l l i p s (1972) and Stout (1976) d e s c r i b e the h a b i t a t f a c t o r s a s s o c i a t e d with e e l g r a s s f o r Puget Sound, Washington and N e t a r t s Bay, Oregon r e s p e c t i v e l y . Taxonomic c l a s s i f i c a t i o n of the members of the genus Zostera has been, t o a l a r g e e x t e n t , based on l e a f measurement i n f o r m a t i o n and the v e r t i c a l d i s t r i b u t i o n of the p l a n t s . Two forms of Zostera marina are re c o g n i z e d on the A t l a n t i c Coast of North America ( S e t c h e l l 1920, H a r r i s o n and Mann 1975) and A l a s k a (McRoy 1972) . A s h o r t , narrow-leafed form i n h a b i t s the shallow i n t e r t i d a l and upper s u b t i d a l zones of these areas. The t a l l e r , b r o a d - l e a f e d form i s found i n the deeper s u b t i d a l waters. Along the P a c i f i c Coast of North America, from B r i t i s h Columbia t o C a l i f o r n i a , the shallow-water and deeper- water forms are prese n t but a s i z e s h i f t appears t o have o c c u r r e d . The narrow, s h o r t form of the i n t e r t i d a l and 4 shallow s u b t i d a l reaches of t h i s area corresponds t o the t a l l , b r o a d - l e a f e d form of the A t l a n t i c Coast (Scagel 1961) and A l a s k a . ( P h i l l i p s 1972). The t a l l , w i d e - l e a f e d form of the c e n t r a l P a c i f i c Coast, o f t e n r e f e r r e d to as Z. marina var. l a t i f o l i a Morong, has much wider and l o n g e r l e a v e s than the t y p i c a l form ( S e t c h e l l 1927). C o n s i d e r a b l e taxonomic con- f u s i o n e x i s t s w i t h i n g e o g r a p h i c a l areas; l e a f l e n g t h o f the l a r g e r form Z. marina f . l a t i f o l i a d e s c r i b e d by Outram (1957) f o r southern B r i t i s h Columbia i s the same as t h a t f o r the s h o r t , narrow-leafed form Z. marina v a r . typioa {marina) d e s c r i b e d by Scagel (1961) f o r B r i t i s h Columbia c o a s t a l waters. S e t c h e l l (1927) f e l t t h a t the slow r i s e i n water temperature observed f o r areas i n h a b i t e d by Z. marina v a r . l a t i f o l i a r e s u l t e d , i n a l o n g e r growing season which allowed f o r the f u l l v e g e t a t i v e development of the p l a n t . The t y p i c a l form of the A t l a n t i c Coast was thus merely an underdeveloped form of v a r . l a t i f o l i a . S e t c h e l l (1927) d i d not attempt t o account f o r the s h o r t , narrow growth form (var. angustifolia) o f the A t l a n t i c Coast d e s c r i b e d i n an e a r l i e r work ( S e t c h e l l 19 20) and makes no mention o f the presence of the t y p i c a l form of the A t l a n t i c Coast along the P a c i f i c Coast. Den Hartog (19 70) f e l t t h a t there was c o n s i d e r a b l e o v e r l a p o f the upper s i z e l i m i t of the t y p i c a l form and the lower s i z e l i m i t of v a r . l a t i f o l i a and regarded the two forms as phenotypes of the taxon, Z. marina. In Humboldt Bay, no r t h e r n C a l i f o r n i a K e l l e r (196 3) found an i n c r e a s e i n mean t u r i o n l e n g t h of i n t e r t i d a l Z. marina 5 w i t h i n c r e a s e d depth but f a i l e d to remark on the s i g n i f i c a n c e of t h i s r e l a t i o n s h i p i n t h i s and i n a l a t e r paper ( K e l l e r and H a r r i s 1966) . A s i m i l a r r e l a t i o n s h i p of i n c r e a s e d l e a f dimensions wi t h depth was observed by P h i l l i p s (19 72) i n Puget Sound, Washington. He used r e c i p r o c a l t u r i o n t r a n s p l a n t s across two t i d a l zones ( i n t e r t i d a l and s u b t i d a l ) and l e a f measurements of t u r i o n s from three broad t i d a l zones (MLLW, MLLW to LLLW, and below LLLW) to i n v e s t i g a t e the i n f l u e n c e of depth on l e a f dimensions. In the U n i t e d S t a t e s , mean low water (MLW), the average of a l l low waters, i s the plane which r e p r e s e n t s Chart Datum on the A t l a n t i c Coast and mean lower low water (MLLW), the average of the lower of the two low waters each day, i s the plane f o r the P a c i f i c Coast (Chapman 1960). P h i l l i p s (1972) concluded t h a t the v a r i a t i o n i n l e a f dimensions ac r o s s t i d a l zones was a t t r i - b u t a b l e to phenotypic p l a s t i c i t y and d i s c o u n t e d the v a l i d i t y o f v a r i e t a l d i s t i n c t i o n s based on l e a f measurement i n f o r m a t i o n f o r Puget Sound e e l g r a s s . An i n c r e a s e i n l e a f l e n g t h w i t h depth has been r e p o r t e d f o r other seagrasses (Strawn 1961). An i n v e r s e r e l a t i o n s h i p of l e a f l e n g t h and depth f o r Z. marina i s r e p o r t e d by Burkholder and Doheny (1968) f o r Long I s l a n d , New York but i s not s u b s t a n t i a t e d elsewhere i n the l i t e r a t u r e . T i d a l e l e v a t i o n e x e r t s c o n s i d e r a b l e i n f l u e n c e on o t h e r c h a r a c t e r i s t i c s of e e l g r a s s p o p u l a t i o n s . These i n c l u d e r e p r o d u c t i v e and v e g e t a t i v e t u r i o n d e n s i t y , l e a f s t a n d i n g crop, biomass and phenology. S t u d i e s of e e l g r a s s t u r i o n d e n s i t y on the P a c i f i c Coast of North America r e p o r t 6 c o n f l i c t i n g r e s u l t s . K e l l e r and H a r r i s (1966) found t h a t the h i g h e s t e l e v a t i o n they c o n s i d e r e d (0.3 meters above MLLW) had the lowest t u r i o n d e n s i t y ; more s i g n i f i c a n t l y , however, t h e i r data r e v e a l t h a t t u r i o n d e n s i t y decreased above and below mean lower low water (MLLW). T h i s r e l a t i o n - s h i p was a l s o r e p o r t e d from Puget Sound, Washington ( P h i l l i p s 19 72) where t u r i o n d e n s i t y decreased from MLLW with g r e a t e r depth and A l a s k a (McRoy 19 72) where s u b t i d a l e e l g r a s s d e n s i t y was l e s s than i n t e r t i d a l t u r i o n d e n s i t y . Reproductive t u r i o n d e n s i t y was a l s o g r e a t e r i n the i n t e r - t i d a l zone o f Puget Sound ( P h i l l i p s 1972). Co n v e r s e l y , Stout (1976), working i n N e t a r t s Bay, Oregon, found t h a t deep water e e l g r a s s had s i g n i f i c a n t l y h i g h e r t o t a l and r e p r o d u c t i v e t u r i o n d e n s i t i e s than shallow water e e l g r a s s . She c o n s i d e r e d shallow and deep water e e l g r a s s as d i s t i n c t groups but f a i l e d t o p r o v i d e any e l e v a t i o n a l or mo r p h o l o g i c a l i n f o r m a t i o n f o r the two types. In the same study Stout found t h a t the deep water e e l g r a s s had a much hi g h e r biomass per square meter than the shallow water e e l g r a s s . These r e s u l t s do not agree with those o f ot h e r P a c i f i c Coast e e l g r a s s s t u d i e s . P h i l l i p s (1972) r e p o r t e d t h a t i n t e r t i d a l biomass always exceeded s u b t i d a l biomass a t h i s Bush P o i n t , Washington study s i t e and a t A l k i P o i n t , Washington s u b t i d a l biomass o n l y exceeded i n t e r t i d a l biomass from J u l y t o September when a l a r g e i n c r e a s e i n sub- t i d a l l e a f s t a n d i n g crop o c c u r r e d . E e l g r a s s biomass i n - creased from the upper l i m i t of e e l g r a s s growth (0.5 meters above MLLW) to -0.5 meters and decreased g r a d u a l l y t h e r e a f t e r 7 to i t s lower l i m i t o f -2.75 meters i n southern C a l i f o r n i a (Backman and B a r i l o t t i 1976). S i m i l a r l y , K e l l e r and H a r r i s (1966) d e s c r i b e an i n c r e a s e i n l e a f s t a n d i n g crop of i n t e r - t i d a l e e l g r a s s from i t s upper l i m i t o f 0.3 meters above MLLW to -0.3 meters and a s l i g h t decrease at the lowest e l e - v a t i o n (-0.5 meters) they s t u d i e d . The i n f l u e n c e of t i d a l e l e v a t i o n , across broad t i d a l zones, on such p h e n o l o g i c a l events as seasonal changes i n l e a f and rhizome s t a n d i n g c r o p s , t o t a l biomass and t u r i o n d e n s i t y i s d e s c r i b e d f o r Puget Sound by P h i l l i p s (1972). T h i s review of p r e v i o u s e c o l o g i c a l s t u d i e s of Z. marina i n d i c a t e s t h a t c e r t a i n m o r p h o l o g i c a l , biomass, and p o p u l a t i o n c h a r a c t e r i s t i c s of e e l g r a s s are i n f l u e n c e d by environmental f a c t o r s which change w i t h depth. The c o n f u s i o n which e x i s t s i n the l i t e r a t u r e as to the t r u e nature of the change i n these c h a r a c t e r i s t i c s w i t h depth can be a t t r i b u t e d t o : 1. s t u d i e s conducted over on l y a p o r t i o n of the t i d a l range of e e l g r a s s ( K e l l e r 1963, K e l l e r and H a r r i s 1966) 2. s t u d i e s d e s c r i b i n g the i n f l u e n c e of t i d a l e l e v a t i o n on o n l y one or two parameters (Burkholder and Doheny 196 8, P h i l l i p s 1974) 3. s t u d i e s comparing e e l g r a s s c h a r a c t e r i s t i c s a c r o s s broad t i d a l zones, e.g. i n t e r t i d a l and s u b t i d a l (McRoy 1972), shallow and deep (Stout 1976). L i e b i g ^ s law o f the minimum, t h a t p l a n t y i e l d i s dependent on the n u t r i e n t p r e s e n t i n minimum q u a n t i t y , has been g e n e r a l l y expanded to the broader e c o l o g i c a l concept of 8 l i m i t i n g f a c t o r s , i . e . , t h a t the c o n d i t i o n which approaches or exceeds the l i m i t s o f t o l e r a n c e o f an organism i s s a i d t o be a l i m i t i n g f a c t o r . The upper l i m i t o f Z. marina growth i s determined by d e s i c c a t i o n of the p l a n t which, i n t u r n , i s a f u n c t i o n o f t i d a l exposure and s u b s t r a t e composition (den Hartog 19 70). The f a c t o r c o n t r o l l i n g the lower l i m i t of e e l g r a s s i s l i g h t a v a i l a b i l i t y ( P h i l l i p s 1972, Backman and B a r i l o t t i 1976). In t u r b i d c o a s t a l and e s t u a r i n e waters, water c l a r i t y i n - f l u e n c e s the l i g h t environment of e e l g r a s s (Burkholder and Doheny 196 8) and, consequently, the p h o t o s y n t h e t i c a c t i v i t y o f the p l a n t . I t i s reasonable to expect t h a t these two very d i f f e r e n t l i m i t i n g f a c t o r s , l i g h t and d e s i c c a t i o n , i n f l u e n c e the p r e v i o u s l y d e s c r i b e d c h a r a c t e r i s t i c s o f e e l g r a s s i n d i f f e r e n t ways as i t s upper and lower d i s t r i b u t i o n a l l i m i t s are approached. A study of seasonal changes i n t o t a l and reproduc- t i v e t u r i o n d e n s i t i e s , l e a f s t a n d i n g crop and l e a f and rhizome dimensions, from the upper t o the lower l i m i t s o f e e l g r a s s growth, p r o v i d e s a means of determining the i n f l u e n c e of t i d a l e l e v a t i o n on e e l g r a s s c h a r a c t e r i s t i c s . Such a study would a l s o p r o v i d e i n s i g h t i n t o the ways i n which l i m i t i n g f a c t o r s i n f l u e n c e the v e g e t a t i v e c h a r a c t e r i s t i c s o f e e l g r a s s near i t s t o l e r a n c e l i m i t s . 1.3. O b j e c t i v e s of the Study- C o n s i d e r i n g the purpose o f the study, and p r e v i o u s a u t e c o l o g i c a l r e s e a r c h on e e l g r a s s , the f o l l o w i n g o b j e c t i v e s were e s t a b l i s h e d : 1. To assess the s e a s o n a l and d i u r n a l changes i n e n v i r o n - mental f a c t o r s of e e l g r a s s h a b i t a t on southern Roberts Bank. 2. To determine the i n f l u e n c e of t i d a l e l e v a t i o n , from the upper to the lower l i m i t s o f e e l g r a s s d i s t r i b u t i o n , on e e l g r a s s s t a n d i n g crop, r e p r o d u c t i v e and t o t a l t u r i o n d e n s i t i e s , and l e a f and rhizome dimensions d u r i n g the growing season. 3. To d e s c r i b e biomass changes of e e l g r a s s d u r i n g a growing season. 4. To c o l l a t e the above i n f o r m a t i o n to b e t t e r understand the h a b i t a t requirements and growth c h a r a c t e r i s t i c s o f e e l - grass on southern Roberts Bank. 10 2. THE STUDY AREA The study area, shown i n Figure 1, i s approximately 20 kilometers south of the C i t y of Vancouver- The geograph- i c a l location of the study s i t e , adjacent to and south of the Tsawwassen Ferry Terminal Causeway, i s 49° 00' N. l a t i t u d e , 123° 07' W. longitude. Roberts Bank adjoins the southern S t r a i t of Georgia between the main d i s t r i b u t a r y channel of the Fraser River and the Canada-USA International Boundary. The study s i t e i s approximately 6 kilometers due south of the mouth of the south arm of the Fraser River. F i e l d reconnaissance and information from a e r i a l photographs and topographic maps were used i n the selection of the study s i t e , as shown i n Figure 2. A uniform cover of eelgrass from the upper to the lower elevational l i m i t s of eelgrass growth, and a c c e s s i b i l i t y , both on foot and by boat, were major con- siderations i n selecting the study s i t e . The Fraser River Delta i s composed of recent sedi- ments several hundreds of feet thick over Pleistocene sediments (Mathews and Shepard 1962). An excellent summary of the geology of the Fraser River Delta i s given by Luternauer (Hoos and Packman 19 74) . Kellerhals and Murray (1969) describe the sedimentary c h a r a c t e r i s t i c s of the t i d a l f l a t s covered by eelgrass i n Boundary Bay. Previous vegetation studies of the Fraser River estuary have been largely descriptive and a l l but two have ignored the submerged vascular plants. General marsh des- c r i p t i o n s are provided by Forbes (1972a,b), McLaren (1972) 11 F i g . 1. A e r i a l photo mosaic of the F r a s e r R i v e r D e l t a showing l o c a t i o n o f the study area.  13 F i g . 2. Diagram of the study s i t e showing t r a n s e c t l o c a t i o n s . 14 CANADA U.S.A.'' 15 and H i l l a b y and B a r r e t t (1976). Forbes (1972c) provides rough maps and estimates of eelgrass coverage f o r the Fraser R i v e r foreshore and Boundary Bay. H i s t o r i c a l changes i n the Roberts Bank eelgrass bed and h a b i t a t and population char- a c t e r i s t i c s of Roberts Bank eelg r a s s are described i n an environmental impact assessment of Roberts Bank port expansion prepared f o r the N a t i o n a l Harbours Board, Port of Vancouver (1977) by Beak Consultants L t d . Y i e l d estimates of the major emergent marsh p l a n t s are given by Yamanaka (19 75) but i n f o r m a t i o n on the submergent vegetation i s l a c k i n g . S i m i l a r l y , Burgess (1970) describes the importance of various emergent species to s e v e r a l species of dabbling ducks on the Fraser foreshore marshes. Burgess repo r t s t h a t the p h y s i c a l environment of the t i d a l marshes exe r t s strong i n f l u e n c e s on the composition and d i s t r i b u t i o n of the v e g e t a t i o n . The e s t u a r i n e waters adjacent to the Fraser R i v e r foreshore are h i g h l y s t r a t i f i e d (Hoos and Packman 19 74) , a f a c t o r which i s s t r o n g l y i n f l u e n c e d by wind and t i d e - d r i v e n c u r r e n t s . Tides i n the southern p o r t i o n of the S t r a i t of Georgia are of the mixed, mainly d i u r n a l type. At the study s i t e the mean t i d a l range i s 3.05 meters; f o r l a r g e t i d e s the range averages 4.69 meters. Mean water l e v e l , the average of a l l hourly observations, i s 2.96 meters. During the summer, extreme lower low water as s o c i a t e d w i t h 'the s p r i n g t i d e s occurs near midday; i n the w i n t e r , near midnight. The times are reversed f o r extreme higher high water (Canadian Hydrographic Service 19 76). In Canada, Chart Datum (CD) i s 16 the plane o f lowest normal t i d e s and i s t h e r e f o r e below mean lower low water (MLLW). At the study s i t e MLLW i s 1 meter above CD. Development p r o p o s a l s f o r areas along the F r a s e r R i v e r f o r e s h o r e have i n c r e a s e d g r e a t l y i n r e c e n t y e a r s . The p r o x i m i t y of the F r a s e r R i v e r E s t u a r y to the l a r g e and r a p i d l y growing m e t r o p o l i s of Vancouver, the i n c r e a s i n g r e c r e a t i o n a l demands of the populace, and the p r o g r e s s i v e i n d u s t r i a l i z a t i o n of the area are a l l important f a c t o r s i n the encroachment on f o r e s h o r e lands. S e v e r a l of the proposed developments are d i s c u s s e d i n Hoos and Packman (1974) and H a r r i s and T a y l o r (1973). The i n f l u e n c e o f the adjacent urban and i n d u s t r i a l areas on the water q u a l i t y of the lower reaches of the F r a s e r R i v e r i s d i s c u s s e d a t l e n g t h by Dorcey (1976). On southern Roberts Bank r e c e n t developments have taken the form of p o r t and causeway c o n s t r u c t i o n . The Tsawwassen F e r r y Terminal and Causeway were c o n s t r u c t e d i n 1960. In 1970 the Westshore Terminal p o r t f a c i l i t y and cause- way were b u i l t across southern Roberts Bank. In a d d i t i o n , s e v e r a l power and telecommunication c a b l e s have been l a i d a cross the i n t e r t i d a l sand f l a t s of Roberts Bank. Cu r r e n t p r o p o s a l s t o f u r t h e r develop southern Roberts Bank i n c l u d e a m u l t i - f o l d expansion o f the Westshore Terminal p o r t f a c i l i t y . Depending on the u l t i m a t e form of the p o r t expansion, the e f f e c t s on the e e l g r a s s resource of southern Roberts Bank w i l l vary from s l i g h t to c o n s i d e r a b l e . 17 3. ENVIRONMENTAL FACTORS IN RELATION TO EELGRASS HABITAT 3.1. M a t e r i a l s and Methods Seasonal changes i n s a l i n i t y , temperature and water c l a r i t y were determined from measurements made every 2 weeks from A p r i l t o August 19 76 and monthly t h e r e a f t e r t o January 1977. D i u r n a l changes i n s a l i n i t y , temperature, water c l a r i t y and l i g h t were monitored on f o u r o c c a s i o n s d u r i n g the study p e r i o d , c o r r e s p o n d i n g to the s p r i n g , summer, f a l l and w i n t e r c o n d i t i o n s i n the study area. F i g u r e 3 i s a schematic p r o f i l e o f the study s i t e . A l l measurements were taken j u s t seaward of the lower boundary of the e e l g r a s s bed and, w i t h the e x c e p t i o n of the d i u r n a l m o n i t o r i n g program, were made between 10.0 0 and 14.0 0 hours. S a l i n i t y and temper- ature were measured in situ, a t the s u r f a c e and 1.5 meters below s u r f a c e , w i t h a YSI Model 14 86 p o r t a b l e S a l i n i t y - Conductivity-Temperature meter. T h i s instrument measures e l e c t r i c a l c o n d u c t i v i t y and temperature and computes s a l i n i t y from these measurements. The manufacturer l i s t s i t s accuracy at +0.1°C a t -2°C f o r temperature and +0.7%o a t 20% o f o r s a l i - n i t y . A 30 cm (diameter) S e c c h i d i s c was used to measure the t r a n s m i s s i o n of v i s i b l e l i g h t through the water column. The d i s c was lowered i n t o the water u n t i l i t disappeared and s l o w l y r a i s e d u n t i l i t reappeared. S e c c h i depth, a measure of water c l a r i t y , was recorded as the average o f these two r e a d i n g s . D i u r n a l changes i n p h o t o s y n t h e t i c a l l y a c t i v e 18 F i g . 3. Schematic p r o f i l e o f the study s i t e showing t r a n s e c t e l e v a t i o n s i n r e l a t i o n to Chart Datum.  20 r a d i a t i o n (PAR) were measured w i t h a LI-COR Model LI-185 Quantum/Radiometer/Photometer equipped w i t h an underwater quantum sensor. The upper l i m i t o f e e l g r a s s growth was determined u s i n g p r e d i c t e d t i d a l i n f o r m a t i o n f o r the Secondary P o r t of Tsawwassen c o n t a i n e d i n the 19 76 T i d e and C u r r e n t Tables of the Canadian Hydrographic S e r v i c e . T r a n s e c t A was e s t a b - l i s h e d j u s t w i t h i n the upper boundary o f the e e l g r a s s bed and the o t h e r four t r a n s e c t s were l o c a t e d a t 0.5^ meter depth i n t e r v a l s w i t h a survey s t a d i a rod. The lower l i m i t of e e l g r a s s growth was determined a t the same time. The e l e v a - t i o n of t r a n s e c t A was l a t e r confirmed u s i n g h o u r l y t i d a l r eadings from the Tsawwassen T i d a l S t a t i o n f o r 19 76 o b t a i n e d from the I n s t i t u t e o f Ocean S c i e n c e s , F i s h e r i e s and Marine S e r v i c e , Environment Canada, V i c t o r i a . T h i s i n f o r m a t i o n was a l s o used to determine t i d a l exposure of t r a n s e c t s A and B f o r 1976. As there was a need f o r very accurate i n f o r m a t i o n c o n c e r n i n g t i d a l e l e v a t i o n s , t r a n s e c t s A and B were surveyed from Bench Mark "Geod. No. 66-C-045" l o c a t e d i n the w a l l of the H u l l Maintenance B u i l d i n g , Tsawwassen F e r r y T e r m i n a l , on March 12, 1977. A K e u f f e l and E s s e r a l i d a d e and plane t a b l e were used f o r the survey. There was good agreement (+3 cm) between the surveyed e l e v a t i o n s and those determined from i n t e r - p o l a t i o n of h o u r l y t i d e h e i g h t s . A technique s i m i l a r t o t h a t d e s c r i b e d by Ranwell e t a l (1974) was used to monitor sediment s u r f a c e l e v e l o s c i l l a t i o n s w i t h i n the e e l g r a s s bed. Twenty 2.5 cm diameter and 30 cm long wooden stakes were pushed i n t o the s u b s t r a t e u n t i l 10 cm protruded a t 10 meter i n t e r v a l s a c r o s s the e e l g r a s s bed from the upper to the lower l i m i t s of e e l - grass growth. The l e n g t h of stake p r o t r u d i n g was measured at i n t e r v a l s from J u l y 1976 to January 1977. - P l e x i g l a s tubes 10 cm long ( i n s i d e diameter 4 cm) were used to remove sediment cores from areas adjacent to the stakes i n October 19 76, and the upper 5 cm of each core was s u b j e c t e d to v a r i o u s p h y s i c a l and chemical d e t e r m i n a t i o n s . Carbonate carbon was determined f o l l o w i n g the g r a v i m e t r i c method f o r l o s s of carbon d i o x i d e d e s c r i b e d by Black (1965). Organic matter content was found by l o s s i n weight on i g n i t i o n a t 550°C (Wood 1975) and was converted to o r g a n i c carbon content by d i v i s i o n w i t h a f a c t o r of 1.8 as recom- mended by Trask (19 39). Dry s i e v i n g with a s e t of nested US Standard Sieves (4.0 to 0.1 cm openings) was used to perform the p a r t i c l e s i z e a n a l y s i s . Approximately 40 g of dry sediment were p l a c e d i n the top s i e v e and the s e t of s i e v e s was shaken on a ROTAP machine f o r 2 minutes. 3.2. H a b i t a t F a c t o r s 3.2.1. S a l i n i t y 3.2.1.1. Seasonal Changes The 1.5 m s a l i n i t y (Figure 4) was c o n s i s t e n t l y g r e a t e r than s u r f a c e s a l i n i t y except f o r one anomalous s e t 22 F i g . 4. Surface and 1.5 m s a l i n i t i e s and temperatures at the study s i t e and mean monthly a i r temperature at Vancouver International Airport (Monthly Record, Meteorological Observations i n Canada, Atmospheric Environment, Fisheries and Environment Canada, A p r i l 1976 to January 1977). Mean monthly a i r temperature plotted at the midpoint of each month. 23 A 1 M I j I j I A I S I 6 I N I fj I J I MONTH \ \ \ A I M I J I J I A I S I 0 I ti I fj I J I MONTH 24 of measurements i n mid-winter. Surface and 1.5 m s a l i n i t y d i f f e r e n c e s are on the order o f 1 to 2%o i n the s p r i n g and e a r l y summer, and i n c r e a s e two- to t h r e e f o l d by l a t e summer. The pronounced s a l i n i t y s t r a t i f i c a t i o n i s maintained u n t i l w i n t e r . 3.2.1.2. D i u r n a l Changes The d i u r n a l s a l i n i t y measurements of F i g u r e 5 r e f l e c t , to a gre a t e x t e n t , the p e r t i n e n t f e a t u r e s o f the seasonal s a l i n i t y changes. Observations o f May 2, 19 76 and January 18, 1977 show t h a t the water column was w e l l mixed i n the w i n t e r and s p r i n g . On.July 28, 19 76 the h i g h e r s a l i - n i t y a t 1.5 meters was maintained across two complete t i d a l c y c l e s . By October the s a l i n i t y d i f f e r e n c e o f s u r f a c e and subsurface waters was g r e a t e r than t h a t observed d u r i n g the summer. 3.2.2. Temperature 3.2.2.1. Seasonal Changes Seasonal trends i n water temperature resemble s a l i n i t y i n t h a t the thermal s t r a t i f i c a t i o n apparent i n the summer disappears d u r i n g the r e s t o f the year (Figure 4). The seasonal i n c r e a s e and decrease i n water temperature f o l - lows the mean monthly a i r temperature curve f o r Vancouver I n t e r n a t i o n a l A i r p o r t , 20 k i l o m e t e r s n o r t h , c l o s e l y u n t i l f a l l when the curves d i v e r g e and the mean monthly a i r temperature becomes i n c r e a s i n g l y lower than the sea temperature. 25 F i g . 5. D i u r n a l s u r f a c e and 1.5 m s a l i n i t i e s . May 2, J u l y 2 8 and October 4, 19 76. January 18, 19 77. 26 3.2.2.2. D i u r n a l Changes F i g u r e 6 i n d i c a t e s t h a t w i n t e r and s p r i n g s u r f a c e and subsurface water temperatures were very constant over the 24-hour sampling p e r i o d . The water column i s w e l l mixed d u r i n g these seasons. In the summer the temperature of the a i r i s warmer than t h a t of the s u r f a c e water which i s , i n t u r n , warmer than the deeper water. The d i u r n a l temperature i n f o r m a t i o n f o r October 4, 1976 i l l u s t r a t e s how the warming e f f e c t of the sun can i n f l u e n c e the temperature r e l a t i o n s h i p s o f the a i r and s u r f a c e and subsurface waters. As the sun rose above the h o r i z o n , a i r temperature i n c r e a s e d and surpassed f i r s t s u bsurface, then s u r f a c e water temperature; a concomitant r i s e i n s u r f a c e water temperature above subsurface water temperature a l s o o c c u r r e d . 3.2.3. L i g h t 3.2.3.1. Seasonal Changes There i s an obvious i n v e r s e r e l a t i o n s h i p between the seasonal d i s c h a r g e c y c l e of the F r a s e r R i v e r and the S e c c h i depth of waters at the study s i t e ( F i gure 7). 3.2.3.2. D i u r n a l Changes Se c c h i depth measurements and l i g h t data c o l l e c t e d d u r i n g the d i u r n a l m o n i t o r i n g s e s s i o n s show more v a r i a b i l i t y w i t h i n than between sampling s e s s i o n s . No trends c o u l d be d i s c e r n e d from the i n f o r m a t i o n as gathered (Appendix 4). D i u r n a l a i r temperatures and s u r f a c e and 1.5 m water temperatures. May 2, J u l y 2 8 and October 4, 1976. January 18, 1977. PACIFIC DAYLIGHT SAVING TIME 30 F i g . 7. S e c c h i depth (meters) a t the study s i t e and maximum d a i l y d i s c h a r g e (thousands o f c u b i c meters per second) of the F r a s e r R i v e r at Hope, B.C. f o r each month from March 19 76 to January 19 77.  32 Atmospheric c o n d i t i o n s on the four days s e l e c t e d f o r d i u r n a l m o n i t o r i n g were h i g h l y v a r i a b l e . May 2, 1976 was o v e r c a s t w i t h p e r i o d s of r a i n showers. Morning fog which c l e a r e d away bef o r e noon, b r i g h t sunshine d u r i n g midday and h i g h clouds by l a t e a f t e r n o o n o c c u r r e d on J u l y 28, 19 76. October 4, 1976 was sunny wi t h cloudy p e r i o d s and January 18, 19 7 7 was cloudy w i t h a few sunny p e r i o d s . 3.2.4. T i d a l Range and Percentage Exposure At the study s i t e the upper l i m i t of e e l g r a s s growth was 0.85 meters Chart Datum (-0.15 m MLLW) (Figure 2) and the lower l i m i t was -1.25 m CD (-2.25 m MLLW); thus the depth range f o r e e l g r a s s i n t h i s area i s approximately 2 meters. Percentage exposures were c a l c u l a t e d f o r the' two i n t e r t i d a l t r a n s e c t s (A and B) from h o u r l y t i d a l readings a t the Tsawwassen T i d a l S t a t i o n , l o c a t e d 1 k i l o m e t e r west of the study s i t e , f o r 19 76. Two methods were used. The f i r s t method t o t a l l e d the number of hours d u r i n g which the study e l e v a t i o n s were exposed i n 1976 and t h i s t o t a l was expressed as a percentage of the t o t a l number of hours i n 19 76. T h i s method i n d i c a t e d t h a t t r a n s e c t A was exposed 1.00% of the year and t r a n s e c t B, 0.034% of 1976. The second, more d e t a i l e d method e n t a i l e d d i r e c t i n t e r p o l a t i o n of t i d a l h e i g h t s between a l l h o u r l y o b s e r v a t i o n s which i n c l u d e d but d i d not encompass the two e l e v a t i o n s . T h i s method r e v e a l e d t h a t t r a n s e c t A had a percentage exposure of 0.9 36 and t r a n s e c t B was exposed 0.006% of the year. The f i r s t method over- 33 estimated the percentage exposure o f the lower e l e v a t i o n ( t r a n s e c t B) by more than f i v e f o l d . 3.2.5. Sub s t r a t e 3.2.5.1. Surface L e v e l Changes F i g u r e 8 d e p i c t s net s u b s t r a t e s u r f a c e l e v e l o s c i l l a t i o n s observed at the study s i t e w i t h i n the boundaries o f the e e l g r a s s bed. There was an accumulation of sediments u n t i l l a t e summer when sediments were t r a n s p o r t e d out of the e e l g r a s s bed. The o v e r a l l e r o s i o n observed d u r i n g the study p e r i o d was approximately 2 cm. 3.2.5.2. P h y s i c a l and Chemical C h a r a c t e r i s t i c s R e s u l t s of a mechanical a n a l y s i s of sediment samples c o l l e c t e d at 10 meter i n t e r v a l s a c r o s s the e e l g r a s s bed a t the study s i t e are shown i n Table 1. The sample taken at the upper edge of the e e l g r a s s bed i s b e t t e r s o r t e d than samples taken a t 10, 20 and 30 meters i n s i d e the upper edge , which are the most p o o r l y s o r t e d o f a l l . S o r t i n g of samples more than 30 meters from the upper edge i n c r e a s e s with depth u n t i l j u s t b e f o r e the lower edge of e e l g r a s s i s reached. A moderate decrease i n degree of s o r t i n g occurs near the lower d i s t r i b u t i o n a l l i m i t of e e l g r a s s . F i n e s content (Figure 9) e x h i b i t s a s i m i l a r d e c l i n e w i t h depth a t d i s t a n c e s g r e a t e r than 30 meters from the upper edge and a s l i g h t i n c r e a s e near the lower l i m i t . 34 \ F i g . 8. Net o s c i l l a t i o n s o f sediment s u r f a c e l e v e l s , J u l y 19 76 to January 19 77. Mean + Standard E r r o r . 35 -3.0 J 1 A 1 S 1 6 1 N 1 D 1 J MONTH 36 Table 1. Particle size composition of sediments Particle Size (%) Distance (m) 0.10 mm 0.25 mm 0.50 mm from Upper Edge to to to of Eelgrass Growth <0.10 mm .0.25 mm 0.50 mm 1.0 mm > 1.0 mm 0 33.86 57.70 5.11 1.44 1.89 10 32.21 44.03 21.22 1.23 1.31 20 21.06 47.67 27.66 1.78 1.83 30 22.29 43.47 29.55 2.42 2.26 40 33.87 54.22 6.96 1.72 3.23 50 26.78 62.26 5.47 1.08 4.40 60 23.87 66.48 4.58 .88 4.19 70 21.75 69.22 4.85 .66 3.51 80 18.82 71.96 5.30 .64 3.28 90 18.68 69.77 4.75 3.35 3.45 100 14.74 74.25 6.94 .86 3.06 110 11.57 77.61 7.66 6.26 2.53 120 11.89 76.68 8.02 .80 2.61 130 10.31 76.98 8.29 1.36 3.06 140 9.61 80.47 6.88 .65 2.38 150 8.05 79.95 8.61 1.27 2.12 160 8.47 78.80 9.12 1.06 2.56 170 14.17 73.26 7.73 1.34 3.51 175 15.34 70.52 8.90 1.70 3.55 180 12.23 72.36 12.17 1.54 1.69 F i g . 9. Sediment samples taken a t 10-meter i n t e r v a l s from the upper to the lower l i m i t s of e e l g r a s s growth: a. Percentage of f i n e s b. Percentages of o r g a n i c and carbonate carbon. i 38 39 The apparent anomaly t h a t the s t a t i o n s l o c a t e d 10, 20 and 30 meters i n s i d e the upper edge have lower percentages o f f i n e s than adjacent s t a t i o n s and y e t are more p o o r l y s o r t e d i s e x p l a i n e d by the high l a r g e r sand f r a c t i o n s ( g r e a t e r than 0.5 mm diameter) of these s t a t i o n s . Percentage contents of carbonate carbon and o r g a n i c carbon (Figure 9, Table 2) d e c l i n e w i t h d i s t a n c e from the upper l i m i t of e e l g r a s s growth. A moderate i n c r e a s e i s noted f o r both near the lower edge o f e e l g r a s s . 3.2.6. Waves and C u r r e n t s Although c u r r e n t v e l o c i t i e s were not measured at the study s i t e , g e n e r a l o b s e r v a t i o n s made d u r i n g the study p e r i o d i n d i c a t e o n l y g e n t l e c u r r e n t s occur a c r o s s the e e l - grass bed. E x c e s s i v e wave a c t i o n d i d not appear t o be an important f a c t o r a t the study s i t e as i t i s p r o t e c t e d by the a d j a c e n t Tsawwassen F e r r y Terminal Causeway and, to a l e s s e r extent, by nearby P o i n t Roberts p e n i n s u l a . 3.3. D i s c u s s i o n Zostera marina L. i s a e u r y h a l i n e , eurythermal seagrass which i n h a b i t s the shallow, 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 (Table 3). The s a l i n i t y , temperature and water motion c o n d i t i o n s of southern Roberts Bank are c l o s e to the world-wide optima f o r these h a b i t a t f a c t o r s as i n d i c a t e d by Table 3. The other h a b i t a t f a c t o r s s t u d i e d , l i g h t , s u b s t r a t e and exposure, appear to account Table 2. Organic and carbonate carbon contents of sediments Content (%) Distance (m) from Upper Edge of Eelgrass Growth Organic Carbon Carbonate Carbon 0 .96 2.45 10 1.12 3.03 20 .89 2.14 30 .83 1.90 40 1.19 2.68 50 1.03 2.42 60 .86 1.96 70 .97 1.86 80 .88 2.02 90 .84 2.09 100 .96 1.81 110 .64 1.54 120 .69 1.93 130 .62 1.90 140 .71 1.53 150 .62 1.26 160 .62 1.48 170 .79 1.98 175 .70 2.17 180 .59 1.81 4 1 Table 3 . Comparisons of habitat factors affecting eelgrass growth (modified from Stout 1 9 7 6 , and Phillips 1 9 7 2 ) TEMPERATURE Range World-wide Optimum World-wide Southern Roberts Bank 0 - 4 0 . 5 ° C 1 0 - 2 0 ° C Range 7 . 8 - 1 7 . 5 ° C SALINITY Range World-wide Optimum World-wide Southern Roberts Bank Range SUBSTRATE Range World-wide Optimum World-wide Southern Roberts Bank Range Freshwater - 4 2 % o 1 0 - 3 0 % o 1 3 . 8 - 3 0 . 0 % o pure firm sand to pure soft mud mixed sand and mud sand to mixed sand and mud WAVE MOTION Range World-wide Optimum World-wide Southern Roberts Bank waves to.stagnant water l i t t l e wave action, gentle currents gentle currents, low wave shock DEPTH Range World-wide Optimum Puget Sound Southern Roberts Bank Range MLLW to - 3 0 meters - 1 to - 4 meters MLLW to - 2 meters 42 for the narrow depth d i s t r i b u t i o n of eelgrass on southern Roberts Bank. Den Hartog (19 70) states that the depth attained by eelgrass depends greatly on l i g h t i n t e n s i t y and hence water c l a r i t y , suspended materials i n the water column, etc. The a b i l i t y of eelgrass to extend to greater depths i n other areas of the P a c i f i c Coast having clearer waters ( P h i l l i p s 1972, Backman and B a r i l o t t i 1976) suggests that the turbid water of the Fraser River discharge i s responsible for the elevated lower l i m i t of eelgrass on the Fraser River foreshore. In F l o r i d a , Strawn (1961) found that t i d a l exposure was the major factor influencing the zonation of t r o p i c a l seagrasses. Based on a sample of six 1-week periods over the year, percentage exposures were calculated for s i x elevations in Humboldt Bay, northern C a l i f o r n i a (Keller and Harris 1966). These determinations indicated that the upper l i m i t of e e l - grass growth (0.3 m above MLLW) was exposed to the air.about 15 percent of the time. In my study area, transect A (0.8m above CD, 0.2 m below MLLW), located just inside the upper boundary of eelgrass, was exposed approximately 1 percent of the time during 1976. If desiccation, and hence t i d a l expos- ure, does indeed control the upper l i m i t of eelgrass as postulated by den Hartog (1970) and K e l l e r and Harris (1966), how then can t h i s great d i s p a r i t y i n percentage exposure for the upper l i m i t of two P a c i f i c Coast eelgrass populations be accounted for? The answer l i e s i n the f a c t t h a t d e s i c c a t i o n i s determined, t o a g r e a t e x t e n t , by s u b s t r a t e c h a r a c t e r i s t i c s as w e l l as exposure p e r i o d s . The o n l y sediment i n f o r m a t i o n p r o v i d e d f o r Humboldt Bay ( K e l l e r and H a r r i s 1966) are r e f e r e n c e s to patches o f bare mud w i t h i n the e e l g r a s s bed; the sediment i n my study area was sand. The g r e a t e r water- h o l d i n g c a p a c i t y of mud may account f o r the presence of e e l - g rass h i g h e r i n the i n t e r t i d a l zone o f areas having muddy s u b s t r a t e s . On southern Roberts Bank the sandy s u b s t r a t e l i m i t s the exposure t o l e r a n c e of e e l g r a s s and thereby i n - f l u e n c e s the upper d i s t r i b u t i o n a l l i m i t o f the p l a n t . Net changes i n s u b s t r a t e s u r f a c e l e v e l s observed a t the study s i t e are the r e s u l t of changes i n p r e v a i l i n g seasonal winds and wave a c t i o n . The study s i t e i s i n the l e e of the Tsawwassen F e r r y Terminal Causeway and p r o t e c t e d from the p r e v a i l i n g northwest summer winds; a d e p o s i t i o n a l e n v i r o n - ment i s thus maintained w i t h i n the boundaries of the e e l g r a s s bed. During the f a l l and w i n t e r the p r e v a i l i n g winds are from the southeast and the study s i t e r e c e i v e s more wave a c t i o n . There i s a r e s u l t a n t net decrease i n sediment s u r f a c e l e v e l s a t t h i s time of year. The high percentage of f i n e s ( l e s s than 0.1 mm diameter) and o r g a n i c carbon and the p o o r l y s o r t e d sediments observed near the edges of e e l g r a s s growth p r o v i d e s t r o n g support f o r the b a f f l i n g a c t i o n o f the v e r t i c a l edge o f an e e l g r a s s bed proposed by Orth (19 7 3). Organic carbon content and the percentage o f f i n e s was p o s i t i v e l y c o r r e l a t e d (r = 0.89) f o r the samples. Carbonate carbon ( l a r g e l y s h e l l fragments) a l s o had high v a l u e s near the upper and lower l i m i t s of e e l g r a s s growth. F i e l d o b s e r v a t i o n s i n d i c a t e d t h a t b e n t h i c i n f a u n a p o p u l a t i o n s of b i v a l v e s were h i g h e s t near the edges of e e l g r a s s growth. My i n t e r p r e t a t i o n of the s t r o n g c o r r e l a t i o n of o r g a n i c and carbonate carbon (r = 0.79) a c r o s s the e e l g r a s s bed i s t h a t the i n f a u n a l d i s t r i b u t i o n r e f l e c t s food abundance (organic carbon) which i s c o n c e n t r a t e d near the upper and lower edges of the e e l - grass bed as the n u t r i e n t - l a d e n c u r r e n t s are slowed by e e l g r a s s . V a r i o u s aspects of the data r e q u i r e f u r t h e r con- s i d e r a t i o n and e l a b o r a t i o n t o assess the v a l i d i t y of the data as gathered. The s a l i n i t y , temperature and S e c c h i depth measurements have the l i m i t a t i o n of b eing " p o i n t i n time" o b s e r v a t i o n s . T h i s l i m i t a t i o n becomes even more apparent when the h i g h l y v a r i a b l e c o n d i t i o n s of the e s t u a r i n e environment are c o n s i d e r e d . The d i u r n a l m o n i t o r i n g program was undertaken t o , among other t h i n g s , p l a c e the seasonal changes i n a b e t t e r p e r s p e c t i v e . As noted e a r l i e r , weather c o n d i t i o n s f o r three of the four d i u r n a l m o n i t o r i n g s e s s i o n s were u n s e t t l e d ; the e x t e n t to which the v a r i a b l e c o n d i t i o n s are r e f l e c t e d i n the measurements taken i s u n c e r t a i n and f o r t h i s reason o n l y g e n e r a l trends were e x t r a p o l a t e d from the data. Sediment samples were c o l l e c t e d i n October 1976. F i g u r e 8 i n d i c a t e s t h a t the s u r f a c e l e v e l s o f the s u b s t r a t e f l u c t u a t e d d u r i n g the study p e r i o d and f o r t h i s reason i t i s reasonable t o assume t h a t the r e s u l t s o f the sediment analyses may have been q u i t e d i f f e r e n t had the samples been c o l l e c t e d at some other time. Future studies on the i n t e r - actions of sediments and marine angiosperms should include the dynamic nature of the sediments i n experimental design considerations. 4. STANDING CROP, TURION DENSITY, BIOMASS AND LEAF , MEASUREMENT STUDIES 4.1. Materials and Methods A s t r a t i f i e d random sampling technique was used to determine seasonal changes i n eelgrass standing crop, turion density and leaf dimensions at f i v e t i d a l elevations. Anchor blocks were placed at the upper and lower edges of eelgrass growth and joined by a rope which thus bisected the eelgrass bed (Figure 2). Transect A was established just within the upper edge of eelgrass growth and the remaining four tran- sects were located at 0.5 meter depth in t e r v a l s across the eelgrass bed. The lowest transect, transect E, was just inside the lower l i m i t of eelgrass and was 2.0 meters below the highest transect. Fifty-meter long nylon l i n e s , marked at 1 meter i n t e r v a l s , were anchored p a r a l l e l to the depth contours at 0.5 meter depth i n t e r v a l s . The transect l i n e s were placed i n such a way that they were bisected by the rope joining the anchor blocks at the upper and lower eelgrass l i m i t s . A ran- dom number generator was used to select two numbers between 1 and 50 for each elevation and sampling s i t e s were located along the study t r a n s e c t s at these numbers. A 0.25 square meter (0.5 m x 0.5 m) s t e e l quadrat was p l a c e d on e i t h e r s i d e o f the t r a n s e c t at each of the two l o c a t i o n s and a l l of the t u r i o n s rooted w i t h i n the quadrat were c l i p p e d a t sediment l e v e l and p l a c e d i n c o t t o n sacks. To av o i d the p o s s i b l e e f f e c t s o f i n c r e a s e d i n s o l a t i o n experienced by areas immediately adjacent t o sampled quadrats, only a l t e r - nate p o s s i b l e sample l o c a t i o n s were i n c l u d e d , t h a t i s to say, sample s i t e s were l o c a t e d a t whole meter i n t e r v a l s . SCUBA was used f o r underwater sampling o f the v e g e t a t i o n . Samples were t r a n s p o r t e d t o the l a b o r a t o r y and t o t a l and r e p r o d u c t i v e t u r i o n counts were made. I n d i v i d u a l samples were then washed f o r 2 minutes i n a p o r t a b l e Hoover washing machine t o remove epiphytes and spun f o r 1 minute i n the machine t o remove adherent water. The machine proved t o be very e f f e c t i v e i n removing epiphytes from the e e l g r a s s l e a v e s . The weight o f the sample a f t e r s p i n n i n g i s r e f e r r e d t o as wet weight. Dry weight and o r g a n i c (ash-free) dry weight d e t e r - minations were made f o l l o w i n g the techniques and terminology of Westlake (1963). T r a n s e c t E was not e s t a b l i s h e d i n time f o r the f i r s t sampling s e s s i o n ( A p r i l 5 and 6, 1976) but an a n a l y s i s o f st a n d i n g crop (organic dry weight) data from the f o u r 0.25 square meter quadrats c o l l e c t e d from each o f the oth e r f o u r e l e v a t i o n s i n d i c a t e d t h a t t r a n s e c t A had a hi g h e r r e l a t i v e v a r i a b i l i t y than the o t h e r s . The f o l l o w i n g data i l l u s t r a t e t h i s : T r a n s e c t C o e f f i c i e n t o f V a r i a t i o n A 0.46 B 0.17 C 0.18 D 0.29 The number of samples f o r t r a n s e c t A was i n c r e a s e d to s i x f o r the remainder o f the study p e r i o d t o reduce sample v a r i a b i l i t y f o r t h i s e l e v a t i o n . On A p r i l 15, 1976 a program u s i n g f i v e d i f f e r e n t quadrat s i z e s was conducted t o determine the optimum quadrat s i z e f o r sampling e e l g r a s s . The f o l l o w i n g f i g u r e s i n d i c a t e the e f f e c t o f quadrat s i z e on r e l a t i v e v a r i a b i l i t y (sample v a r i a b i l i t y r e l a t i v e to the mean of the sample): Quadrat C o e f f i c i e n t of Percentage Area (m2) V a r i a t i o n Standard E r r o r f 1.0 0.27 13.33 0.5 „ 0.33 11.82 0.25 0.22 6.52 0.04 0.56 11.22 0.01 1.90 26.98 Percentage standard e r r o r s were c a l c u l a t e d by the method of Bordeau (1953). Appendix 6 c o n t a i n s a d d i t i o n a l i n f o r m a t i o n . The 0.25 square meter quadrat had the lowest r e l a t i v e v a r i a b i l i t y and i t s use was continued f o r the remain der o f the study. S e v e r a l attempts were made to sample the r o o t and rhizome components of the v e g e t a t i o n t o complement the l e a f s t a n d i n g crop s t u d i e s . The use of a c o r i n g d e v i c e and a post hole auger met wit h very l i m i t e d success due to the sandy 48 nature of the sediments, and underwater d i g g i n g reduced v i s i b i l i t y t o n i l i n a matter of seconds. Consequently the underwater biomass sampling program was dropped; however, i n t e r t i d a l biomass sampling i n areas a d j a c e n t to t r a n s e c t A was conducted from A p r i l 1976 to January 1977 d u r i n g s u i t a b l y low t i d e s . Four random samples (0.25 square meter quadrat) were gathered on each c o l l e c t i o n date. T u r i o n s were c l i p p e d a t sediment l e v e l and l a t e r enumerated. , The sediment was excavated to the lowest r o o t l e v e l , g e n e r a l l y 20 cm t o 30 cm, and s i e v e d through a 0.4 cm metal screen. The r o o t and rhizome m a t e r i a l r e t a i n e d by the screen was l a t e r hand cleaned and s o r t e d i n the l a b o r a t o r y . Dimensions of the l o n g e s t i n - t a c t l e a f of each t u r i o n and random rhizome diameters were recorded f o r f o u r sampling s e s s i o n s from August 19 76 to January 19 77. Two samples were s e l e c t e d a t random from the f o u r c o l l e c t e d a t each e l e v a t i o n d u r i n g the s i x s t a n d i n g crop and d e n s i t y sampling s e s s i o n s of August 19 76 to January 19 77. Leaf l e n g t h and width were measured from the l o n g e s t i n t a c t l e a f of each t u r i o n . I n t a c t l eaves were i d e n t i f i e d by t h e i r rounded t i p s . 4.2. Standing Crop E e l g r a s s samples were c o l l e c t e d from each of f i v e e l e v a t i o n s on 16 o c c a s i o n s d u r i n g the p e r i o d of A p r i l 19 76 to January 19 77 (Appendix 7). A t o t a l o f 36 4 quadrats were sampled d u r i n g the study p e r i o d f o r l e a f s t a n d i n g crop 49 d e t e r m i n a t i o n s . A l l of the s t a t i s t i c a l analyses f o l l o w Zar (1974 ) . Percentage dry weight (of wet weight) and percentage ash content (of dry weight) s t a t i s t i c s are i l l u s t r a t e d : Percent Dry Weight Percent Ash Content Determinations 323 343 Mean 12.45 13.98 SD 1.68 4.79 SE 0.09 0.26 Range 9.71 to 18.95 5.58 to 25.72 A t h r e e - f a c t o r a n a l y s i s of v a r i a n c e (Zar 19 74) w i t h f a c t o r s A ( e l e v a t i o n ) and B (time) f i x e d and f a c t o r C (sample l o c a t i o n ) random was performed on the quadrat l e a f s t a n d i n g crop data. The f i r s t sampling s e s s i o n was not i n c l u d e d i n the a n a l y s i s o f v a r i a n c e due to m i s s i n g informa- t i o n . In a d d i t i o n , one l o c a t i o n , r e p r e s e n t i n g two samples, was randomly d e l e t e d from the t r a n s e c t A data f o r each sampling s e s s i o n . T h i s was done so t h a t the number of samples f o r each e l e v a t i o n and sampling time were i d e n t i c a l . The a n a l y s i s o f v a r i a n c e c a l c u l a t i o n s were performed on a hand c a l c u l a t o r . The f o l l o w i n g n u l l hypotheses were formulated and t e s t e d : 1. Ho: Organic dry weight per quadrat the same f o r a l l f i v e e l e v a t i o n s 2. Ho: Organic dry weight per quadrat the same f o r a l l 15 sampling times 3. Ho: Organic dry weights per quadrat between l o c a - t i o n s w i t h i n e l e v a t i o n s and times are the same 50 4. HQ: Organic dry weight per quadrat d i f f e r e n c e s among e l e v a t i o n s are independent o f d i f f e r e n c e s among times ( i . e . , absence of A x B i n t e r a c t i o n ) Table 4 summarizes the a n a l y s i s o f v a r i a n c e f o r l e a f s t a n d i n g crop; an expanded v e r s i o n i s presented i n Appendix 8. 4 . 2 . 1 . Temporal Changes The a n a l y s i s o f v a r i a n c e f o r l e a f s t a n d i n g crop showed t h a t o r g a n i c dry weight per quadrat was not the same f o r a l l 15 sampling s e s s i o n s . A Newman-Keuls M u l t i p l e Range Te s t was employed t o determine between which sampling dates d i f f e r e n c e s e x i s t e d . U n f o r t u n a t e l y , the s i g n i f i c a n c e l e v e l f o r t h i s type o f t e s t i s the p r o b a b i l i t y o f encountering at l e a s t one Type I e r r o r w h ile comparing a l l the p a i r s o f means. The t e s t was not powerful enough t o d i s c e r n where, among the 1 5 sampling s e s s i o n means, t r u e d i f f e r e n c e s i n o r g a n i c dry weights o c c u r r e d . A si m p l e r , although much l e s s s e n s i t i v e , approach was t r i e d . The means of the 1 5 sampling s e s s i o n s were d i v i d e d i n t o three groups of f i v e and a grand mean, i n grams o r g a n i c dry weight per quadrat, was c a l c u l a t e d f o r each group. The r e s u l t s were: Ses s i o n s 2 - 6 7 - 1 1 1 2 - 1 6 P e r i o d A p r i l 18-June 13 June 28-Aug. 25 Sept. 28-Jan. 18 Mean (g) 8.73 8.40 3.42 T h i s i n f o r m a t i o n suggests t h a t e e l g r a s s s t a n d i n g crop p e r s i s t s a t a f a i r l y h i g h and constant l e v e l from l a t e 51 Table 4. Analysis of variance summary table for mean leaf standing crop (organic dry weight i n grams per 0.25 square meter quadrat) Hypothesis Calculated F C r i t i c a l F Conclusion Elevation (factor A) Time (factor B) Location (factor C) 4. A x B 16.55** FO.01(1),4,70 = 3 - 6 0 Reject HQ 8.36** F0.01(1),14,70 = 2.35 Reject HQ 3.21** Fo.Ol(l),70,140 = 1-60 Reject HQ 1.14ns F0.01(l),50,70 = 1-83 Accept HQ spring u n t i l late summer. There appears to be a d r a s t i c decline i n the late summer and early f a l l period during which more than 50 percent of the standing stock i s l o s t . A low and constant standing stock i s maintained during much of the winter. Appendix 7 reveals the same general trends. Figure 10 graphically portrays t h i s seasonal cycle of mid- summer abundance, late summer decline, and reduced standing crop throughout the winter. 4.2.2. Influence of Depth The analysis of variance conducted for leaf standing crop revealed that organic dry weight per quadrat i s not the same for a l l f i v e elevations (F = 16.55**). Results of a Newman-Keuls Multiple Range Test show that the mean standing crops of the highest and lowest transects (0.8 and -1.2 m respectively) are not s i g n i f i c a n t l y d i f f e r e n t (q = 2.10) from one another. S i m i l a r l y the standing stocks of the three middle elevations are not s i g n i f i c a n t l y d i f f e r e n t (q = 2.16) from each other; however, they are s i g n i f i c a n t l y d i f f e r e n t (q = 5.11*) from those of the highest and lowest elevations (Table 5 ) . The differences i n leaf standing crops for the fi v e study elevations are shown i n Figure 10. The l a t e r summer and early f a l l decline i n standing stocks mentioned i n section 4.2.1. i s . very pronounced for the three middle elevations (0.3, -0.2 and -0.7 m). Both the magnitude and rate of decline i n leaf standing stock are noticeably less for 53 F i g . 10. Mean l e a f s t a n d i n g crop (grams per square meter) f o r f i v e e l e v a t i o n s ( i n r e l a t i o n t o Chart Datum), A p r i l 19 76 to January 19 77. 9 0 0.8 A r M I 1 I J I "A I S 1 6 I N I D I 7 I MONTH Table 5. Newman-Keuls Multiple Range Test for the mean leaf standing stocks (organic dry weight in grams per 0.25 square meter quadrat) at five elevations Elevation (m) 0.8 -1.2 0.3 -0.2 -0.7 Ranks of Sample Means 1 2 3 4 5 Ranked Sample Means 3.60 4.88 7.98 8.51 9.29 tomparison Difference SE q P ^0.05,120,p Conclusion 5 us 1 5.69 .61 9.37 5 3.917 Reject HQ* Reject Ho* 5 us 2 4.42 .61 7.27 4 3.685 5 us 3 1.31 .61 2.16 3 3.356 Accept HQ 5 us 4 0.79 .61 1.30 2 Do not test 4 us 1 4.90 .61 8.07 4 3.685 Reject HQ* 4 us 2 3.63 .61 5.97 3 3.356 Reject HQ* 4 us 3 0.53 .61 0.87 2 Do not test 3 us 1 4.38 .61 7.21 3 3.356 Reject HQ* 3 us 2 3.10 .61 5.11 2 2.800 Reject Ho* 2 us 1 1.27 .61 2.10 2 2.800 Accept HQ Overall Conclusion 0.8 = -1.2 * 0.3 = -0.2 = -0.7 transects A and E (0.8 and -1.2 m, respectively) which are nearest the upper and lower edges of the eelgrass bed. 4.3. Turion Density The vegetative axes of eelgrass consist of both horizontal, indeterminate rhizomes and erect annual axes with determinate growth. Clusters of foliage leaves, c a l l e d turions, arise from both vegetative axes. Reproductive turions are terminal i n Z. marina (den Hartog 1970) and during the study were d i f f e r e n t i a t e d from vegetative turions on the basis of t h e i r l i g h t yellow-green colour and sympodial branching habit. Total and reproductive turion counts from a t o t a l of 338 quadrats (0.25 square meter) were co l l e c t e d from A p r i l 1976 to January 1977. A three-factor analysis of variance (Zar 1974) with factors A (elevation) and B (time) fixed and factor C (sample locations) random was conducted on the t o t a l and reproductive turion density data. 4.3.1. Influence of Time and Elevation on Total Turion Density Turion counts were not made on a l l of the samples from the f i r s t and second sampling sessions (April 1976). To f a c i l i t a t e the turion density analysis of variance p a r t i a l information from the f i r s t two sampling sessions were ex- cluded from the calcu l a t i o n s . Thus, only the l a s t 14 sampling sessions were included i n the analysis of variance. To further f a c i l i t a t e the analysis of variance 57 calculations data for two of the six quadrats from transect A were deleted at random from each sampling session. Thus, turion counts of four quadrats from each of f i v e elevations sampled on 14 occasions were used i n the analysis of v a r i - ance calculations to te s t the following n u l l hypotheses: 1. Ho: Turion density per quadrat i s the same for a l l f i v e elevations (Factor A) 2 . H o : Turion density per quadrat i s the same for a l l 15 sampling sessions (Factor B) 3. Ho: Turion density per quadrat between locations within elevations and times i s . the same (Factor C) 4 . H o : Turion density per quadrat differences among elevations are independent of differences among times (Absence of A x B interaction) Appendix 9 contains turion density information c o l l e c t e d during the study. Table 6 summarizes the analysis of variance for turion density and Appendix 10 presents more analysis of variance information for mean turion density. Highly s i g n i f i c a n t differences i n t o t a l turion density existed between elevations and times, and between locations within elevations and times (Table 6 ) . There was no s i g n i f i c a n t i n t e r a c t i o n of elevation and time on t o t a l turion density. Newman-Keuls Multiple Range Tests were used to determine which treatment means (of f i v e elevations and 15 sessions) were d i f f e r e n t . Table 7 shows the re s u l t s for the mean turion densities of the f i v e elevations. Turion densities of the highest and lowest transects ( 0 . 8 and - 1 . 2 m respectively) were s i g n i f i c a n t l y d i f f e r e n t from one another 58 Table 6. Analysis of variance summary table for mean total turion density (turions per 0.25 square meter quadrat) Hypothesis Calculated F C r i t i c a l F Conclusion 1. Elevation (factor A) 2. Time (factor B) 3. Location (factor C) 4. A x B 13.52** 8.59** 2.345** 1.393ns F 0 . 0 1 ( l ) , 4 , 7 0 = 3 - 6 0 Reject HQ FO.Ol(l),13,70 = 2.40 Reject HQ F0.01(l),70,140 = 1-60 Reject HQ FQ.OKI) ,50,70 = 1-83 Accept HQ 59 Table 7. Newman-Keuls Multiple Range Test for total turion density (turions per 0.25 square meter quadrat) means at five elevations Elevation (m) - 1 . 2 0 . 8 - 0 . 2 0 . 3 - 0 . 7 Ranks of Sample Means 1 2 3 4 5 Ranked Sample Means 9 . 9 3 1 3 . 2 3 1 6 . 8 9 1 7 . 2 0 1 9 . 3 8 Comparison Difference SE q p 30.05,120,p Conclusion 5 vs 1 9.45 1.02 5 vs 2 6.14 1.02 5 vs 3 2.48 1.02 5 vs 4 2.18 1.02 4 vs 1 7.27 1.02 4 vs 2 3.96 1.02 4 vs 3 0.30 1.02 3 vs 1 6.97 1.02 3 vs 2 3.66 1.02 2 vs 1 3.30 1.02 9 . 2 9 5 3 . 9 1 7 Reject Ho* 6 . 0 4 4 3 . 6 8 5 Reject H Q - 2 . 4 4 3 3 . 3 5 6 Accept H Q 2 . 1 4 2 Do not test 7 . 1 5 4 3 . 6 8 5 Reject H Q * 3 . 9 0 3 3 . 3 5 6 Reject H Q * 0 . 3 0 2 Do not test 6 . 8 5 - 3 3 . 3 5 6 Reject H Q * 3 . 6 0 2 2 . 8 0 0 Reject H Q * 3 . 2 5 2 2 . 8 0 0 Reject H Q * Overall Conclusion - 1 . 2 * 0 . 8 * - 0 . 2 = 0 . 3 = 0.7 60 and from the three middle e l e v a t i o n s , between which no s i g n i f i c a n t d i f f e r e n c e s e x i s t e d . The lowest e l e v a t i o n s (-1.2 m) had the lowest t u r i o n d e n s i t y (40 t u r i o n s per square meter). D e n s i t i e s f o r the middle e l e v a t i o n s ranged from 67 t o 77 t u r i o n s per square meter. The h i g h e s t e l e v a - t i o n had an i n t e r m e d i a t e d e n s i t y (53 t u r i o n s per square meter). The Newman-Keuls M u l t i p l e Range T e s t gave i n c o n - c l u s i v e r e s u l t s f o r comparisons of mean t u r i o n d e n s i t i e s between sampling s e s s i o n s . T h i s t e s t o f t e n produces ambiguous r e s u l t s f o r comparisons w i t h l a r g e numbers of treatment means (Zar 19 74). However, an o v e r a l l seasonal t r e n d showing a d e c l i n e i n t o t a l t u r i o n d e n s i t y from summer to w i n t e r i s seen i n Table 8. Summer t u r i o n d e n s i t y i s halved by mid-winter. F i g u r e 11 d e p i c t s the seasonal d e c l i n e i n t o t a l t u r i o n d e n s i t y f o r the f i v e t r a n s e c t e l e v a t i o n s . The g e n e r a l t i m i n g of t u r i o n l o s s e s seems constant f o r a l l e l e v a t i o n s ; there do, however, appear to be g r e a t d i f f e r e n c e s i n the r a t e and magnitude of the d e c l i n e i n d e n s i t y between e l e v a t i o n s . S i m i l a r w i n t e r t u r i o n d e n s i t y (approximately 40 t u r i o n s per square meter) appears to be reached at the same time (October) f o r a l l e l e v a t i o n s . During the summer the three middle e l e v a t i o n s had t u r i o n d e n s i t i e s twice as g r e a t as those of the upper and lower e l e v a t i o n s and, consequently, both the r a t e ( t u r i o n l o s s per u n i t time) and e x t e n t ( t u r i o n l o s s per square meter) of the observed d e c l i n e must have been much g r e a t e r f o r these middle e l e v a t i o n s . Table 8. Total turion densities (turions per 0.25 square meter quadrat) for fourteen sampling sessions, May to December 1976 Ranks of Sample Means Ranked Sample Means Month Sampled 1 22.95 May 2 21.90 May 3 21.05 July 4 20.05 June 5 18.95 August 6 16.55 May 7 15.30 June 8 14.65 August 9 13.00 July 10 11.60 September 11 10.70 January 12 10.15 November 13 9.20 October 14 8.50 December 62 F i g . 11. Mean t o t a l t u r i o n numbers per square meter f o r f i v e e l e v a t i o n s ( i n r e l a t i o n to Chart Datum), A p r i l 1976 to January 1977. 63 A f M I ~J I 3 n A I S I 0 I N I fj I J I MONTH 4.3.2. I n f l u e n c e of Time and E l e v a t i o n on Reproductive T u r i o n D e n s i t y A t w o - f a c t o r a n a l y s i s o f v a r i a n c e without r e p l i - c a t i o n was performed on the r e p r o d u c t i v e t u r i o n d e n s i t y i n f o r m a t i o n (Appendix 11) c o l l e c t e d d u r i n g the study. During the p e r i o d i n which r e p r o d u c t i v e t u r i o n s were pr e s e n t (May to August) 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 r e p r o d u c t i v e t u r i o n d e n s i t i e s were found between e l e v a t i o n s or sampling times (Table 9 ) , but may occur. However, c e r t a i n g e n e r a l trends are apparent i n the r e p r o d u c t i v e t u r i o n d e n s i t y data of Appendix 11. Peak f l o w e r i n g o c c u r r e d d u r i n g June and J u l y . The three middle e l e v a t i o n s had a longer p e r i o d d u r i n g which r e p r o d u c t i v e t u r i o n s were prese n t than had the h i g h e s t and lowest e l e v a - t i o n s . F l o w e r i n g was e s s e n t i a l l y completed a t the h i g h e s t e l e v a t i o n b e f o r e i t began at the lowest e l e v a t i o n s . 4.4. The I n f l u e n c e of Depth on Organic Weight per T u r i o n To i n v e s t i g a t e the r e l a t i o n s h i p of o r g a n i c dry weight per t u r i o n and t i d a l e l e v a t i o n , a simple l i n e a r r e - g r e s s i o n equation was c a l c u l a t e d f o r each o f the f i v e e l e v a t i o n s u s i n g the t u r i o n d e n s i t y (per quadrat) and s t a n d i n g crop (grams per quadrat) data. The l i n e a r r e g r e s - s i o n o f o r g a n i c dry weight (dependent v a r i a b l e ) on t u r i o n number (independent v a r i a b l e ) f o r the f i v e e l e v a t i o n s i s presented i n Table 10. The equations i n d i c a t e t h a t the 65 Table 9. Analysis of variance summary table for mean reproductive turion density (turions per square meter) Source of Variation SS D F MS Total 46.97 27 Elevation 11.13 4 2.78 Time 4.57 5 0.91 Remainder 31.27 18 1.74 To test H Q : No difference among elevations. Calculated F = 1.60 Fo.05(1),4,18 = 2.93ns To test H Q : N O difference among times. Calculated F = 0.53 FQ.05(1),5,18 = 2.77ns , Table 10. Linear regression equations of organic dry weight (g) on turion numbers per quadrat for five elevations Elevation Number of Coefficient of (CD) Observations Equation Determination 0.8 m 88 Y = 0.21 x +0.79 0.57 0.3 m 64 Y = 0.51 x -0.71 0.64 -0.2 m 62 Y = 0.56 x -1.34 0.80 -0.7 m 64 Y = 0.45 x -0.06 0.68 -1.2 m 60 Y = 0.53 x -0.57 0.78 * 67 r e g r e s s i o n c o e f f i c i e n t (slope) o f the bes t f i t r e g r e s s i o n l i n e f o r the h i g h e s t e l e v a t i o n (0.8 m) d i f f e r s from those of the oth e r e l e v a t i o n s . An a n a l y s i s o f v a r i a n c e procedure was used t o t e s t the s i g n i f i c a n c e o f each of the r e g r e s s i o n s . The n u l l h y pothesis HQ: P = 0 was r e j e c t e d f o r a l l f i v e e l e v a t i o n s as h i g h l y s i g n i f i c a n t d i f f e r e n c e s e x i s t e d f o r each (Appendix 12). The next s t a t i s t i c a l procedure employed was an a n a l y s i s o f c o v a r i a n c e t e s t i n g f o r s i g n i f i c a n t d i f f e r e n c e s between the r e g r e s s i o n s o f the f i v e e l e v a t i o n s . The n u l l h y p o t hesis t h a t the slop e s o f a l l f i v e r e g r e s s i o n s ( f o r f i v e e l e v a t i o n s ) were equal was r e j e c t e d due to the h i g h l y s i g n i - f i c a n t c a l c u l a t e d F value (Table 11). A Newman-Keuls M u l t i p l e Range T e s t was used t o determine which slo p e s were d i f f e r e n t from which o t h e r s . Table 12 r e v e a l s t h a t the slope o f . t h e b e s t f i t r e g r e s s i o n l i n e f o r the h i g h e s t e l e v a t i o n (0.8 m) e x h i b i t s a h i g h l y s i g n i f i c a n t d i f f e r e n c e from the sl o p e s o f the r e g r e s s i o n s f o r the ot h e r e l e v a t i o n s . My i n t e r - p r e t a t i o n i s t h a t the t u r i o n s o f the h i g h e s t e l e v a t i o n have a much lower f o l i a g e (per t u r i o n ) than i s found a t the lower e l e v a t i o n s . Using, the same .data the f o l l o w i n g c a l c u - l a t i o n taken from the l e a f s t a n d i n g crop and t u r i o n d e n s i t y analyses of v a r i a n c e i s recorded. E l e v a t i o n (m) 0.8 0.3 -0.2 -0.7 -1.2 .Organic Dry Weight (g) 3.60 7.98 8.51 9.29 4.87 T u r i o n D e n s i t y 13.23 17.19 16.89 19.37 9.93 Organic Dry Weight (g) 0.27 0.46 0.50 0.48 0.49 per T u r i o n 68 Table 11. Analysis of covariance summary testing for significant differences between slopes of linear regression lines of organic dry weight on turion numbers for five elevations Regression Number of Regression Residual Residual Observations Coefficient SS DF Elevation (m) 0.8 88 0.21 96.98 86 0.3 64 0.51 586.75 62 -0.2 62 0.57 489.28 60 -0.7 64 0.45 524.51 62 -1.2 ' 60 0.53 182.83 58 Pooled 1880.35 Common 0.45 4669.32 Calculated F = 12.62** Fo.Ol(l),4,300 = 3.38 Conclusion: Reject %:£().8 =£0.3 =£-0.2 =£-0.7 =£-1.2 6 9 Table 12. Newman-Keuls Multiple Range Test for differences between slopes of linear regressions of organic dry weight on turion numbers for five elevations Elevation (m) 0 . 8 0 . 3 - 0 . 2 - 0 . 7 - 1 . 2 Ranks of Regression Coefficients 1 3 5 2 4 Ranked Regression Coefficients 0 . 2 1 0 . 5 1 0 . 5 7 0 . 4 5 0 . 5 3 Comparison Difference SE q p 30.01,300,p Conclusion 5 vs 1 . 3 6 . 0 3 2 1 1 . 4 2 5 4 . 6 0 3 Reject H Q 5 vs 2 . 1 2 . 0 3 8 3 . 1 1 4 4 . 4 0 3 Accept Ho 5 vs 3 . 0 7 . 0 4 2 1 . 5 5 3 Do not test 5 vs 4 . 0 5 . 0 4 1 1 . 1 5 2 Do not test 4 vs 1 . 3 2 . 0 2 7 1 1 . 6 6 4 4 . 4 0 3 Reject H Q 4 vs 2 . 0 7 . 0 4 2 1 . 7 0 3 Do not test 4 vs 3 . 0 2 . 0 4 6 0 . 4 1 2 Do not test 3 vs 1 . 3 0 . 0 3 7 8 . 1 2 3 4 . 1 2 0 Reject H Q 3 vs 2 . 0 5 . 0 4 4 1 . 2 1 2 Do not test 2 vs 1 . 2 5 . 0 3 3 3 . 3 8 2 3 . 6 4 3 Reject H Q Overall Conclusion of Slopes 0.8 ̂ 0.3 = -0.2 = -0.7 = -1.2 70 4.5. Biomass I n t e r t i d a l eelgrass biomass was sampled during low tides from A p r i l 1976 to January 19 77. Sampling sessions were undertaken at approximately 1-month i n t e r v a l s and were conducted during very low tides when the i n t e r t i d a l eelgrass was exposed. The res u l t s of the biomass sampling program are contained i n Appendix 13. Percentages of above and below substrate parts were constant from A p r i l to July 1976 (Table 13). A dr a s t i c decline i n i n t e r t i d a l leaf standing crop i n August 19 76 greatly altered the r a t i o i n subsequent samplings. Rhizome standing crop did not appear to change during the sampling period. During the spring and early summer the leaf standing crop was about two-thirds and the root and rhizome standing crops about one-third of the t o t a l biomass. By late summer and f a l l the above and below substrate portions each constituted about 50 percent of the biomass. 4.6. Leaf Measurements Leaf length and width were measured on the longest i n t a c t leaf of each turion c o l l e c t e d during the regular standing crop and turion density sampling sessions from August 1976 to January 1977. The information i s summarized i n Table 14. There i s a general decline i n leaf width from August to January for a l l f i v e elevations. A s i m i l a r decline i n leaf length i s apparent for the same period but there i s Table 13. Percentages of above substrate (leaf) and below substrate (roots and rhizomes) standing crops, A p r i l 1976 to January 1977 Date Percentage Percentage Above Substrate Below Substrate 16.4.76 61.9 38.1 15.5.76 72.7 27.3 12.6.76 67.2. 32.8 10.7.76 64.4 35.6 7.8.76 42.1 57.9 24.8.76 49.8 50.2 25.10.76 56.1 43.9 23.11.76 47.3 52.7 17.1.77 53.0 47.0 Mean 59.3 40.7 72 Table 14. Leaf measurements for five elevations, August 1976 to January 1977 Elevation (m) 0.8 0.3 -0,2 -0.7 -1.2 Leaf Length (cm) August . Mean 54. .9 104. ,3 102, .8 99, .9 94, .5 SE 5. ,53 20. ,0 9, .37 8, .03 8, .25 September Mean 56. ,0 71. ,4 80, .7 87 .9 69, .8 SE 4. ,09 8. ,51 9 .65 7 .90 9, .56 October Mean 55. ,0 59. ,3 49 .7 69 .3 70, .3 SE 5. ,67 8. .11 11 .23 9 .40 8, .30 November Mean 39. ,3 42. .6 54 .7 40 .5 60, .7 SE 3. .45 6. .79 5, .71 4 .63 7, .85 December Mean 39. .6 45. .6 42 .7 55 .0 54, .0 SE 3. ;43 4. .30 5 .72 6 .90 11, .37 January Mean 31. ,6 29. .6 41 .4 41 .0 42 .6 SE '3. .89 2. .61 3 .91 2 .23 2 .96 Leaf Width (cm) August Mean 0. .61 0. .69 0 .60 0 .66 0 .66 SE 0. .022 0, .058 0 .029 0 .031 0 .036 September Mean 0. .58 0. .62 0 .65 0 .60 0 .56 SE 0. .027 0, .029 0 .027 0 .026 0 .041 October Mean 0. .51 0, .57 0 .61 0 .56 0 .55 SE 0, .028 0, .028 0 .040 0 .039 0 .031 November Mean 0, .53 0, .56 0 .49 0 .46 0 .56 SE 0, .021 0, .043 . 0 .020 0 .019 0 .029 December Mean 0, .52 0, .54 0 .54 0 .57 0 .52 SE 0, .025 0 .022 0 .033 0 .025 0 .037 January Mean 0, .50 0 .40 0 .52 0 .58 0 .58 SE 0, .025 0 .017 0 .020 0 .016 0 .023 a s t r i k i n g d i s s i m i l a r i t y between the highest elevation (0.8 m) and the others. In August, mean leaf length for the highest elevation i s approximately one-half that of the other elevations. By January, mean leaf length for the upper elevation has been reduced by 40 percent; however, mean leaf length for the other elevations has declined by about 60 percent. Mean winter leaf length (of the longest i n t a c t leaf on each turion) appears to be the same for a l l f i v e elevations and thus the lower elevations experience a greater and more rapid change i n mean leaf length during the f a l l . There appears to be a time lag associated with increasing depth for the observed changes i n mean leaf length. In August the 0.3 and -0.2 m elevations had the greatest mean leaf length, i n September the -0.2 and -0.7 m elevations, October the lowest two elevations, and by November the greatest mean leaf length was observed at the lowest elevation. Table 15 shows the same seasonal decline i n leaf length and width of samples c o l l e c t e d adjacent to the 0.8 m elevation for the biomass determinations (August 19 76 to (Vide Table 14) January 1977). Disregarding the anomalous readings vfor August, which may be largely attributed to sampling error, the other values are s i m i l a r to those obtained during the regular sampling sessions (Table 14). The changes i n mean rhizome diameter are d i f f i c u l t to interpret because of the r e l a t i v e l y short period i n which measurements were taken. During excavation the rhizomes were often cut with the shovel 74 Table 15. Leaf and rhizome measurements for samples collected at 0.8 meters (in relation to Chart Datum), August 1976 to January 1977. Number of observations i n brackets Aug. 76 Oct. 76 Nov. 76 Jan. 77 Leaf Length (cm) Mean 30 .80 (87)- 55 .48 (27) 48 .74 (22) 26. 89 (43) SE 1 .08 4 .76 4 .39 1. 43 Leaf Width (cm) Mean 0 .45 (87) 0 .54 (27) 0 .56 (22) 0. 47 (43) SE 0 .01 0 .02 0 .03 0. 01 Rhizome Mean 0 .37 (87) . 0 .41 (92) 0 .47 (61) 0. 40 (96) Diameter (cm) SE 0 .02 0 .01 0 .01 0. 01 b l a d e . As diameters were measured on i n d i v i d u a l rhizome segments, each rhizome may have been rep r e s e n t e d s e v e r a l times i n each sample. 4.7. D i s c u s s i o n The i n f l u e n c e of f a c t o r s a s s o c i a t e d w i t h t i d a l e l e v a t i o n on e e l g r a s s l e a f dimensions, v e g e t a t i v e and r e p r o - d u c t i v e t u r i o n d e n s i t i e s and s t a n d i n g stocks have been i n v e s t i g a t e d i n s e v e r a l o t h e r P a c i f i c Coast e e l g r a s s s t u d i e s (see s e c t i o n 1.2.). Leaf measurements taken d u r i n g t h i s study i n d i c a t e t h a t the e e l g r a s s of southern Roberts Bank corresponds to the s h o r t , narrow-leafed form (Z. marina var. typiea) o f Scagel (1961). The l a r g e r form Z. marina var. l a t i f o l i a was not encountered d u r i n g the study. Leaf dimen- s i o n s o f Roberts Bank e e l g r a s s are s i m i l a r to those o f Puget Sound e e l g r a s s ( P h i l l i p s 19 72). The r e l a t i o n s h i p s of i n c r e a s e d l e a f l e n g t h w i t h g r e a t e r depth d e s c r i b e d f o r o t h e r P a c i f i c Coast e e l g r a s s p o p u l a t i o n s ( P h i l l i p s 1972, K e l l e r and H a r r i s 1966) and o t h e r seagrasses (Strawn 1961) i s f u r t h e r supported by t h i s study. On Roberts Bank, t u r i o n d e n s i t i e s were h i g h e s t a t the three middle e l e v a t i o n s s t u d i e d , i n t e r m e d i a t e near the upper l i m i t of e e l g r a s s growth and the lowest near the lower l i m i t of e e l g r a s s d i s t r i b u t i o n . K e l l e r and H a r r i s (1966) found the same r e l a t i o n s h i p of depth and t u r i o n d e n s i t y i n n o r t h e r n C a l i f o r n i a . In Puget Sound, Washington P h i l l i p s (19 72) found t h a t i n t e r t i d a l t u r i o n d e n s i t y was f i v e times as great as subtidal turion density i n the cle a r waters i surrounding Bush Point and only twice as great i n the turbid waters o f f A l k i Point. Both Puget Sound study s i t e s also exhibited a decrease i n turion density with increasing depth. Eelgrass density on Roberts Bank i s low compared to other P a c i f i c Coast eelgrass populations ( P h i l l i p s 1972, Ke l l e r 1963, Stout 1976) and a lack of comparable habitat information (e.g. water c l a r i t y ) from these other areas l i m i t s speculation as to the reasons for these regional differences i n population c h a r a c t e r i s t i c s . , The findings of thi s study reveal that the mean leaf standing crops of the highest and lowest elevations were s i g n i f i c a n t l y lower than the mean leaf standing crops of the three middle elevations, which, i n turn, were not s i g n i f i c a n t l y d i f f e r e n t from each other. This relationship of reduced i standing crop near the upper and lower l i m i t s of growth i s si m i l a r to that reported by K e l l e r and Harris (1966) i n C a l i f o r n i a . The standing crop values of eelgrass on Roberts Bank clo s e l y resemble the values obtained by P h i l l i p s (1972) at his A l k i Point, Washington study s i t e . The standing crops of eelgrass at A l k i Point, where the water was turbid, were much lower than at his Bush Point study s i t e , where the water was clearer. S i m i l a r l y , t o t a l biomass at A l k i Point was much lower than at Bush Point. Both standing crop and biomass appear to be strongly influenced by water c l a r i t y . Sampling d i f f i c u l t i e s did not allow me to c o l l e c t information on subtidal biomass. I n t e r t i d a l biomass of eelgrass on southern Roberts Bank i s comparable to the biomass of one of the i n t e r t i d a l stations at A l k i Point, Washington ( P h i l l i p s 1972). Seasonal changes i n vegetative and reproductive turion d e n sities, leaf standing crop, biomass and, to a li m i t e d extent, leaf measurements have been studied i n Puget Sound, Washington by P h i l l i p s (1972). The information c o l l e c t e d during t h i s study indicates that southern Roberts Bank eelgrass undergoes seasonal cycles s i m i l a r to Puget Sound eelgrass. For both locations, leaf standing crop and turion density reach minimum values i n January and maximum values from May to July. However, P h i l l i p s did not record the great losses i n leaf standing crop and turion densities in the late summer which were observed i n t h i s study. Previous studies on eelgrass productivity and leaf dynamics have not considered the loss of whole turions as being a s i g n i f i c a n t factor i n the determination of net production.and for t h i s reason may have grossly underestimated actual net production. P h i l l i p s did not report seasonal changes i n mean leaf dimensions but did f i n d that reproductive turions f i r s t appeared i n A p r i l i n Puget Sound. On southern Roberts Bank, reproductive eelgrass turions were f i r s t observed i n mid-May and had disappeared by mid-August. The reasons for the shortened reproductive season observed during t h i s study were not investigated; however, Backman and B a r i l o t t i (1976) found that flowering i s affected by reduced irradiance. The turbid estuarine waters of Roberts Bank reduce the amount of l i g h t available to eelgrass and a s i m i l a r i n h i b i t i o n 78 i n f l o w e r i n g may be the r e s u l t o f reduced i r r a d i a n c e i n t h i s area. During the study, two problem areas arose which warrant f u r t h e r comment i n regard t o f u t u r e i n v e s t i g a t i o n s o f seagrasses. One of the c r i t e r i a used i n the s e l e c t i o n of the study s i t e was the apparent homogeneity of the e e l - grass bed. No areas of bare s u b s t r a t e or sparse e e l g r a s s growth were observed a t the study s i t e ; however, the data c o l l e c t e d i n d i c a t e t h a t c o n s i d e r a b l e p a t c h i n e s s e x i s t e d w i t h i n the e e l g r a s s meadow. H i g h l y s i g n i f i c a n t d i f f e r e n c e s between l o c a t i o n s w i t h i n study e l e v a t i o n s and sampling s e s s i o n s were found f o r both t u r i o n d e n s i t y (Table 6) and l e a f s t a n d i n g crop (Table 5). The patchy d i s t r i b u t i o n o f e e l g r a s s p l a n t s w i t h i n an e e l g r a s s meadow should be i n c o r p o r - ated i n t o sampling schemes of f u t u r e i n v e s t i g a t i o n s . The problems encountered i n t r y i n g t o assess t o t a l p l a n t biomass o r i g i n a t e i n the d i f f i c u l t i e s o f sampling the r o o t and rhizome components of e e l g r a s s . C o n s i s t e n t r e s u l t s were not ob t a i n e d f o r r o o t t o rhizome t o shoot r a t i o s or f o r the o r g a n i c dry weight determinations o f these components d u r i n g the study, even a f t e r l a b o r i o u s hand s o r t i n g and c l e a n i n g of the ro o t s and rhizomes. A much g r e a t e r degree o f s o p h i s t i c a t i o n i n approach and technique w i l l be r e q u i r e d to o b t a i n c o n s i s t e n t and u s e f u l r e s u l t s . 79 5. SUMMARY AND CONCLUSIONS The r e s u l t s o f the study have been d i s c u s s e d i n each s e c t i o n . The purpose of t h i s p o r t i o n o f the study i s to s y n t h e s i z e the p r e v i o u s d i s c u s s i o n s and f i n d i n g s i n view of the s t a t e d o b j e c t i v e s o f the study. The d i s c u s s i o n o f e e l g r a s s h a b i t a t f a c t o r s on southern Roberts Bank showed t h a t the r e s t r i c t e d depth range encountered there was the r e s u l t o f d e s i c c a t i o n and reduced l i g h t . In a d d i t i o n , the d i s c u s s i o n o f t u r i o n d e n s i t i e s , l e a f s t a n d i n g crops and l e a f dimensions showed t h a t s i g n i f i - cant d i f f e r e n c e s e x i s t e d f o r some of these parameters a t the d i f f e r e n t study e l e v a t i o n s . How do the environmental f a c t o r s o f the study s i t e r e l a t e t o the d i f f e r e n c e s i n mo r p h o l o g i c a l , biomass and p o p u l a t i o n ^ c h a r a c t e r i s t i c s o f e e l g r a s s a t the study s i t e ? What are the adaptive s t r a t e g i e s which e e l g r a s s has evolved to d e a l w i t h the depth dependent f a c t o r s c o n t r o l l i n g i t s upper and lower d i s t r i b u - t i o n a l l i m i t s ? The i n f o r m a t i o n presented i n t h i s study i n d i c a t e s t h a t the e e l g r a s s o f southern Roberts Bank can be grouped, on the b a s i s o f l e a f s t a n d i n g crop, t u r i o n d e n s i t y and l e a f measurements, i n t o three d i s t i n c t c a t e g o r i e s which correspond to three t i d a l zones. Near the upper l i m i t o f e e l g r a s s growth, comparatively low s t a n d i n g crops and i n t e r m e d i a t e t u r i o n d e n s i t i e s are observed. Mean l e a f l e n g t h i s l e s s than at lower e l e v a t i o n s , as i s o r g a n i c dry weight per t u r i o n . In othe r areas, the upward e x t e n s i o n o f e e l g r a s s depends g r e a t l y 80 on the degree of'desiccation" (den Hartog 1970); reduced blade length appears to be the adaptive mechanism employed by eelgrass i n response to increase desiccation on Roberts .Bank. The three middle elevations studied exhibited high turion densities and large leaf standing crops. Mean leaf length and mean organic dry weight per turion were greater than at the highest elevation. I t appears that optimal conditions for eelgrass growth and development are found at the intermediate portions of the depth range of eelgrass. The lowest elevation (-1.2 m) had the lowest mean turion density of a l l and yet maintained an intermediate leaf standing crop. Leaf length and organic dry weight per turion were the same as those of the middle elevations. Near the lower d i s t r i b u t i o n a l l i m i t , eelgrass responds to decreased l i g h t i n t e n s i t y by reducing turion density. Where l i g h t i s l i m i t i n g self-shading may become an important consideration and a mechanism which w i l l reduce turion density, and thus shading w i l l be advantageous to the plant. The major conclusions of the study are: 1. The s a l i n i t y , temperature and water motion conditions of southern Roberts Bank are close to the world-wide optima for eelgrass growth. 2. The r e s t r i c t e d depth d i s t r i b u t i o n of eelgrass on southern Roberts Bank i s due to the l i g h t environment and substrate c h a r a c t e r i s t i c s of the area., 3. Reduced l i g h t a v a i l a b i l i t y i n the turbid estuarine waters of southern Roberts Bank i s responsible for the elevated 81 lower d i s t r i b u t i o n a l l i m i t of eelgrass found there. 4. The sandy nature of the sediments of the study area controls the upper d i s t r i b u t i o n a l l i m i t of eelgrass on southern Roberts Bank. 5. Sediments within an eelgrass bed experience pronounced seasonal changes i n surface l e v e l s . 6. Fine sediment fractions and part i c u l a t e organic matter are concentrated near the edges of eelgrass meadows. 7. Eelgrass undergoes pronounced seasonal changes i n leaf 1 standing crop and turion density; a large decline i n both takes place i n late summer. 8. Flowering of eelgrass on southern Roberts Bank occurs from mid-May to mid-August; t h i s r e l a t i v e l y short reproductive season observed may be the r e s u l t of reduced l i g h t a v a i l a b i l i t y . 9. Leaf standing crops are lower near the upper and lower l i m i t s of eelgrass beds. Leaf standing crop i s greatest at intermediate elevations. 10. Turion density i s highest at intermediate elevations, lower near the upper edge of the eelgrass bed and lowest near the subtidal d i s t r i b u t i o n a l l i m i t of eelgrass growth. 11. Organic dry weight per turion near the upper edge of . eelgrass growth i s approximately one-half of the value of lower elevation turions. 12. During the summer the mean leaf length near the upper edge of the eelgrass bed i s approximately one-half of the mean length of leaves from lower elevations; i n winter mean l e a f l e n g t h i s the same f o r a l l e l e v a t i o n s . 13. The r a t i o o f above s u b s t r a t e t o below s u b s t r a t e s t a n d i n g crops i s 2:1; d u r i n g w i n t e r the r a t i o i s 1:1. 14. Reduced l e a f l e n g t h appears t o be a response t o d e s i c c a t i o n i n e e l g r a s s . 15. Reduced t u r i o n d e n s i t y appears to be a response to reduced l i g h t a v a i l a b i l i t y i n e e l g r a s s . 83 GLOSSARY 5 84 Biomass. The weight of a l l p a r t s of a l l the p l a n t s on a u n i t area a t a given time. Carbonate carbon. Carbonate carbon was used as an i n d i r e c t measure of b e n t h i c b i v a l v e p o p u l a t i o n s i n t h i s study. The source o f carbonate i n marine sediments i s g e n e r a l l y s h e l l fragments. Chart Datum (CD). In Canada, Chart Datum r e p r e s e n t s the plane of lowest normal t i d e s . In the t e x t p o s i t i v e and ne g a t i v e e l e v a t i o n s r e f e r to e l e v a - t i o n s above and below the s p e c i f i e d r e f e r e n c e plane (MLLW or CD). Dry weight. The weight of p l a n t m a t e r i a l a f t e r h e a t i n g i n z an oven a t 105OC to constant weight. F i n e s . For the purpose of t h i s study the sediments which passed through the f i n e s t (0.1 mm) s i e v e a v a i l a b l e c o n s t i t u t e d the f i n e f r a c t i o n . F r e s h weight. The t r u e weight of the l i v i n g p l a n t . Organic carbon. The o r g a n i c content of a sediment r e f l e c t s the amount of p a r t i c u l a t e p l a n t and animal r e s i d u e s p r e s e n t and thus p r o v i d e s a rough estimate o f the food a v a i l a b l e f o r f i l t e r f e e d i n g i n f a u n a f o r the purposes of t h i s study. Organic dry weight. The l o s s i n weight of p l a n t matter a f t e r i g n i t i o n a t 550°C. A l s o known as as h - f r e e dry weight. P r o s t r a t e . H o r i z o n t a l , t r a i l i n g along the ground. Quadrat. A square or r e c t a n g u l a r area used to q u a n t i t a t i v e l y sample v e g e t a t i o n . A 0.25 m2 (0.5 x 0.5 m) quadrat was used i n t h i s study. Reproductive t u r i o n . An e r e c t stem b e a r i n g i n f l o r e s c e n c e s . Rhizome. H o r i z o n t a l , elongated, subterranean stem. Se c c h i d i s c . A round white d i s c which i s lowered i n t o the water column t o provide an estimate of the t r a n s - m i s s i o n o f v i s i b l e l i g h t i n water and hence, water c l a r i t y . Standing crop. The weight of p l a n t m a t e r i a l t h a t can be sampled or harvested by normal methods, at any one time, from a gi v e n area. Does not n e c e s s a r i l y i n c l u d e a l l p a r t s of p l a n t s o r a l l p l a n t s . 85 Sympodial Branching. Occurs when the t e r m i n a l bud l o s e s i t s c a p a c i t y f o r a c t i v e growth and a l l subsequent growth occurs a t the a u x i l i a r y shoots. T o t a l t u r i o n d e n s i t y . T o t a l number of t u r i o n s ( v e g e t a t i v e and r e p r o d u c t i v e ) per u n i t area. T u r i o n . A c l u s t e r of f o l i a g e leaves a r i s i n g from a v e g e t a t i v e a x i s . 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P r e n t i c e - H a l l , Inc., New J e r s e y . 620 pp. 91 APPENDICES 92 APPENDIX 1: SECCHI DEPTH AND SURFACE AND SUBSURFACE (1.5 m) SALINITY AND TEMPERATURE MEASUREMENTS MARCH 1976 TO JANUARY 1977 Date Secchi Depth (meters) Salinity (parts per Tenperature (°C) thousand) Surface 1.5 m Surface 1.5 m 31.3.76 5.25 2.4.76 6.75 3.4.76 5.40 5.4.76 5.25 26.0 10.5 28.5 8.0 6.4.76 3.25 19.4.76 3.30 27.2 9.0 27.6 9.0 3.5.76 1.80 14.5.76 1.60 28.0 11.0 28.0 10.5 31.5.76 2.30 26.3 11.6 27.0 10.8 13.6.76 2.00 24.0 11.8 24.3 11.9 28.6.76 2.30 22.7 15.5 23.7 14.3 10.7.76 2.30 22.5 15.0 23.5 14.0 28.7.76 2.90 22.8 17.5 24.0 16.0 10.8.76 2.60 19.9 17.0 21.2 15.0 24.8.76 1.80 13.8 16.0 18.2 14.8 4.10.76 1.60 20.1 11.2 26.2 10.8 20.10.76 2.90 22.9 10.3 23.8 10.4 23.11.76 4.10 21.4 8.0 30.0 7.8 22.12.76 4.10 22.5 8.2 27.6 8.6 18.1.77 5.40 26.5 8.0 26.0 8.0 APPENDIX 2: DIURNAL SURFACE AND SUBSURFACE (1.5 m) SALINITY (PARTS PER THOUSAND) MEASUREMENTS. MAY 2, JULY 28 AND OCTOBER 4, 1976. JANUARY 18, 1977. Time (PDST) May 2 July 28 October 4 January 18 Surface 1.5 m Surface 1.5 m Surface 1.5 m . Surface 1.5 r 0000 26.3 26.3 21.8 23.2 15.7 19.3 01.00 02.00 26.3 26.3 15.5 22.0 03.00 04.00 18.0 19.2 05.00 24.2 24.3 06.00 24.2 24.2 23.8 25.1 19.5 22.5 07.00 08.00 24.0 25.0 22.9 26.0 24.0 25.8 09.00 10.00 23.7 24.2 20.8 25.2 20.1 26.2 11.00 27.2 27.2 12.00 24.0 24.7 24.0 24.7 20.4 22.5 13.00 26.5 26.0 14.00 24.7 25.0 22.8 24.0 21.2 22.3 15.00 27.2 27.2 16.00 23.6 23.5 20.8 22.2 21.8 24.7 17.00 27.0 27.3 18.00 23.5 24.6 22.2 23.8 21.75 23.8 19.00 27.2 27.5 20.00 24.0 26.0 24.2 27.2 20.5 21.9 21.00 27.2 27.3 22.00 24.0 21.5 23.0 21.3 20.4 23.00 26.8 26.8 24.00 24.0 23.8 26.5 21.0 20.2 APPENDIX 3: DIURNAL AIR, SURFACE AND SUBSURFACE -(1.5 m) TEMPERATURE (°C) MEASUREMENTS MAY 2, JULY 28 AND OCTOBER 4, 1976. JANUARY 18, 1977. Time May 2 July 28 October 4 January 18 Surface 1.5 m Surface 1.5 m Ai r Surface 1.5 m A i r Surface • 1.5 m Ai r oooo 12.5 12.5 14.5 13.8 16.3 10.4 10.8 9.5 01.00 7.5 7.5 14.0 02.00 12.5 12.5 10.0 11.5 10.4 03.00 04.00 10.0 10.8 9.0 05.00 8.0 8.0 12.0 06.00 11.0 11.0 13.4 12.8 14.2 10.1 11.0 9.2 07.00 08.00 11.0 11.5 14.75 12.25 20.5 10.8 11.0 9.8 09.00 10.00 11.33 11.5 17.0 14.0 26.25 11.2 10.8 10.8 11.00 7.6 7.6 7.5 12.00 11.5 11.75 16.0 14.0 23.0 11.8 .10.3 14.1 13.00 8.0 8.0 9.6 14.00 11.6 12.0 17.5 16.0 20.0 12.6 11.8 14.5 15.00 8.2 8.1 12.9 16.00 11.75 12.0 15.3 14.8 18.2 12.5 11.2 14.8 17.00 8.2 8.0 10.6 18.00 11.5 11.25 14.8 13.8 17.2 12.1 11.5 12.5 19.00 8.0 7.9 8.2 20.00 11.0 10.5 14.8 12.6 15.8 12.5 12.1 11.8 21.00 7.8 7.8 8.2 22.00 11.5 15.0 14.8 16.0 11.8 12.2 12.9 23.00 7.8 7.8 8.0 24.00 12.0 15.0 12.5 15.9 11.5 11.8 12.9 95 APPENDIX 4: DIURNAL SECCHI DEPTH AND PHOTOSYNTHETICALLY ACTIVE RADIATION (PAR) MEASUREMENTS MAY 2, JULY 23 AND OCTOBER 4, 1976. JANUARY 18, 1977. Time (PDST) Secchi Depth (meters) PAR Quanta (microeinsteins per square meter per second) 10 cm Above Surface 1.5 m Surface May 2 06.00 2.1 30 7 08.00 2.1 49 12 10.00 2.2 180 42 12.00 2.2 150 23.5 14.00 2.2 195 52.5 16.00 1.0 350 78 18.00 1.8 100 35 20.00 2.2 12 3 July 28 06.00 3.1 170 45 19 08.00 3.9 1200 500 200 10.00 3.5 1900 1100 550 12.00 2.8 2200 1450 650 14.00 2.9 2500 1600 800 16.00 1.5 310 170 53 18.00 2.1 250 150 80 20.00 2.75 150 33 17 October 4 08.00 2.2 114 64 27 10.00 1.6 500 220 44 12.00 1.8 2150 975 325 14.00 2.4 2100 1050 450 16.00 2.4 2000 850 275 18.00 2.5 500 90 29 January 18 11.00 5.7 13.00 5.4 15.00 5.2 17.00 5.2 APPENDIX 5: NET OSCILLATIONS OF SEDIMENT SURFACE LEVELS - MEASUREMENTS AND STATISTICS. JUNE 1976 TO JANUARY 1977 Date 30.6.76 29.7.76 11.8.76 26.8.76 4.10.76 20.10.76 23.11.76 22.12.76 19.1.77 Number of 20 12 14 9 15 19 17 12 12 Observations sMean height (cm) 10.00 9.64 9.36 9.29 9.83 10.10 10.90 11.74 -11.87 of pegs above sediment surface Net change +0.36 +0.64 +0.71 +0.17 -0.10 -0.90 -1.74 -1.87 Standard Deviation 2.04 1.21 0.65 1.38 1.41 1.71 1.76 1.92 Standard Error 0.59 0.32 0.22 0.36 0.32 0.42 0.51 0.55 vo APPENDIX 6: STATISTICS OF STANDING CROP INFORMATION (ORGANIC DRY WEIGHT PER QUADRAT) USED FOR OPTIMUM QUADRAT SIZE DETERMINATION Quadrat Area Number of Quadrats Quadrat Dimensions Mean (g) SD (g) SE (g) Percentage SE CV. 1.0 m2 4 1 m x 1 m 16.69 4.45 2.22 13.33 0.27 0.5 8 0.71 m x 0.71 m 12.21 4.08 1.44 11.82 0.33 0.25 12 0.5 m x 0.5 m 5.53 1.25 0.36 6.52 0.22 0.04 25 0.2 m x 0.2 m 0.81 0.46 0.09 11.22 0.56 0.01 50 0.1 m x 0.1 m 0.20 0.37 0.05 26.98 1.90 APPENDIX 7: ORGANIC DRY WEIGHTS IN GRAMS PER SQUARE METER FOR FIVE ELEVATIONS (CHART DATUM) APRIL 1 9 7 6 to JANUARY 1 9 7 7 . 0 . 8 m 0 . 3 m - 0 . 2 m - 0 . 7 m - 1 . 2 m Date Mean Date Mean Date Mean Date Mean Date Mean SE SE SE SE SE Apr. 6 9 . 9 1 Apr. 6 4 3 . 2 5 Apr. 6 4 3 . 3 7 Apr. 6 3 4 . 6 7 2 . 2 7 3 . 7 7 3 . 8 2 5 . 0 8 Apr. 1 7 1 8 . 6 1 3 3 . 0 , Apr. 1 9 3 6 . 7 8 Apr. 1 9 3 3 . 3 3 Apr. 1 9 3 0 . 3 0 3 . 3 1 4 . 4 1 8 . 8 2 4 . 3 7 6 . 8 0 May 2 1 6 . 3 2 May 3 4 2 . 4 3 May 3 3 3 . 6 0 May 3 3 7 . 3 1 May 3 1 7 . 9 3 2 . 6 3 5 . 4 3 3 . 8 4 1 . 7 7 9 . 8 2 May 14 2 2 . 0 2 May 14 4 9 . 9 8 May 14 5 0 . 2 9 May 1 5 5 3 . 4 1 May 1 5 1 2 . 4 3 4 . 1 7 9 . 1 3 1 1 . 8 6 8 . 6 0 5 . 1 9 May 3 0 1 3 . 6 8 May 3 1 3 2 . 0 1 May 3 1 . 4 9 . 4 7 May 3 1 6 1 . 8 1 May 3 1 3 8 . 4 5 1 . 9 0 4 . 8 3 9 . 3 2 1 1 . 4 4 7 . 3 8 June 1 2 1 8 . 6 7 June 1 2 5 7 . 2 6 > June 1 2 3 8 . 6 1 June 1 3 5 5 . 6 7 June 1 3 2 2 . 3 5 2 . 1 4 1 0 . 9 1 9 . 1 4 9 . 3 5 6 . 8 5 June 2 7 1 6 . 0 5 July 2 4 7 . 9 7 July 2 4 6 . 9 1 July 2 3 7 . 0 7 July 3 . 1 2 . 6 9 3 . 0 5 1 5 . 1 6 5 . 6 3 2 . 1 7 4 . 4 3 July 1 0 1 6 . 3 0 July 1 0 4 7 . 4 4 July 1 0 8 8 . 4 0 July 1 0 5 9 . 3 8 July 1 0 3 8 . 4 2 2 . 4 3 1 7 . 9 3 2 3 . 7 4 1 7 . 0 5 1 1 . 2 2 July 28 1 7 . 7 2 July 2 9 4 1 . 1 2 July 2 9 1 5 . 0 2 July 2 8 2 6 . 1 2 July 2 8 8 . 8 2 3 . 5 8 4 . 2 2 7 . 4 3 1 1 . 1 5 2 . 9 0 Aug. 7 1 6 . 1 6 Aug. 1 0 4 1 . 2 2 Aug. 1 0 4 9 . 5 2 Aug. 1 0 5 3 . 2 3 Aug. 1 0 3 1 . 6 8 1 . 4 0 4 . 3 6 4 . 0 1 8 . 0 9 4 . 7 9 Aug. 2 5 1 3 . 0 3 Aug. 2 5 2 0 . 2 2 Aug. 2 6 3 5 . 6 9 Aug. 2 5 4 3 . 4 4 Aug. 2 5 1 8 . 8 1 2 . 1 4 3 . 6 6 6 . 8 8 8 . 7 7 9 . 5 1 Sept. 28 1 4 . 1 9 Oct. 4 1 1 . 3 5 Oct. 4 2 0 . 4 8 Oct. 4 3 2 . 2 3 Oct. 4 1 7 . 1 0 2 . 0 7 3 . 3 1 3 . 2 3 2 . 9 0 1 . 6 4 Oct. 2 5 1 4 . 2 1 Oct. 2 0 1 6 . 8 4 Oct. 2 0 1 0 . 6 2 Oct. 2 0 1 7 . 4 6 Oct. 2 0 1 2 . 0 4 1 . 7 4 3 . 8 8 5 . 2 6 .' 3 . 4 1 5 . 1 2 Nov. 23 9 . 5 7 Nov. 2 3 1 1 . 2 3 Nov. 23 1 7 . 5 9 Nov. 23 1 4 . 9 7 Nov. 2 3 1 6 . 1 0 1 . 8 0 0 . 8 7 3 . 3 8 2 . 9 9 3 . 3 2 Dec. 20 1 1 . 9 3 Dec. 2 0 1 4 . 1 4 D G C • 2 2 1 0 . 4 6 D G C • 22 1 1 . 6 5 Dec. 22 3 . 6 8 2 . 4 6 2 . 1 2 1 . 9 0 2 . 2 9 1 . 2 5 Jan. 1 8 1 0 . 4 6 Jan. 1 8 1 2 . 2 3 Jan. 1 9 7 . 0 0 Jan. 1 9 2 0 . 5 2 Jan. 1 9 1 1 . 9 0 1 . 5 1 1 . 5 4 1 . 7 2 3 . 2 4 3 . 7 3 APPENDIX 8: ANALYSIS OF VARIANCE SUMMARY TABLE FOR MEAN LEAF STANDING CROP (ORGANIC DRY WEIGHT IN GRAMS PER 0.25 SQUARE METER QUADRAT) Source of Variation SS DF MS Calculated F C r i t i c a l F Conclusion Total 8,170.13 299 Elevation (A) 1,465.82 4 366.45 16.55** FO.Ol(l),4,70 =' 3.60 Reject HQ Time (B) 2,592.68 14 185.19 8.36** FO.Ol(l),14,70 = 2.34 Reject HQ Location (C) . 1,415.65 56 22.14 3.21** FO.Ol(l),70,140 = 1-60 Reject HQ A x B 1,660.57 75 25.28 l-14ns FO.Ol(l),50,70 = 1-83 Accept HQ Error 1,035.41 150 6.90 VD VD APPENDIX 9: DENSITY IN TURIONS PER SQUARE METER FOR FIVE ELEVATIONS (CHART DATUM) APRIL 1976 TO JANUARY 1977 0.8 m 0.3 m -0. 2 m -0. 7 m -1.2 m Date Mean Date Mean Date Mean Date Mean Date Mean SE SE SE SE SE Apr. 6 43 Apr. 6 89 Apr. 6 86 Apr. 6 119 9.84 3.77 0.86 4.07 Apr. 9 66 Apr. 19 106 Apr. 19 64 1.56 2.47 2.80 May 2 36 May 3 95 May 3 83 May 3 81 May 3 43 .2.05 3.30 2.56 3.09 5.72 May 14 63 May 14 106 May 14 123 May 15 123 May 15 36 3.74 ' 5.39 5.35 2.87 3.49 May 30 53 May 31 71 May 31 105 May 31 134 May 31 77 1.54 3.35 5.94 4.52 3.38 June 12 61 June 12 107 June 13 86 June 13 110 June 13 44 1.85 3.64 2.10 2.26 2.35 June 27 67 July 2 82 July 2 66 July 2 67 July 3 35 2.51 0.96 1.04 1.38 3.40 July 10 66 July 10 70 July 10 133 July 10 93 July 10 55 2.80 4.74 6.05 7.19 3.64 July 28 79 July 29 86 July 29 29 July 28 49 July 28 27 2.06 3.57 1.44 1.44 2.25 Aug. 7 79 Aug. 10 87 Aug. 10 72 Aug. 10 94 Aug. 10 47 1.30 2.28 0.42 3.28 1.11 Aug. 25 51 Aug. 25 44 Aug. 26 73 Aug. 25 81 Aug. 25 33 2.14 1.78 3.28 3.09 3.68 Sept. 28 53 Oct. 4 39 Oct. 4 44 Oct. 4 62 Oct. 4 40 2.07 2.56 2.49 1.19 2.28 Oct. 25 51 Oct. 20 38 Oct. 26 27 Oct. 20 43 Oct. 20 33 1.71 1.85 3.30 2.14 2.75 Nov. 23 43 Nov. 23 37 Nov. 23 46 Nov. 23 48 Nov. 23 35 1.68 1.03 1.66 1.36 0.86 Dec. 20 42 Dec. 20 43 Dec. 22 34 Doc• 22 _ 42 Dec. 22 14 1.58 1.75 0.65 1.85 1.19 Jan. 18 42 Jan. 18 58 Jan. 19 25 Jan. 19 58 Jan. 19 37 1.48 3.86 1.11 1.76 0.86 APPENDIX 10: ANALYSIS OF VARIANCE SUMMARY TABLE FOR MEAN TURION DENSITY (TURIONS PER 0.25 SQUARE METER QUADRAT) Source of Variation SS DF MS Calculated F C r i t i c a l F Conclusion Total 21,287.43 279 Elevation (A) 3,128.41 4 782.10 13.52** F0.01(l),4,70 = 3 - 6 0 Reject HQ Time (B) 6,462.38 13 497.11 8.59** F0.01(l),13,70 = 2.40 Reject HQ Location (C) 4,050.25 70 57.86 2.345** F0.01(l),70,140 =1-60 Reject HQ A x B 4,191.89 52 80.61 1.393ns F0.01(l) ,50,70 = L83 Accept HQ Error 3,454.50 140 24.67 102 APPENDIX 11 : REPrClDUCITVE TURION DENSITY (PER SQUARE METER) FOR FIVE ELEVATIONS. JUNE TO AUGUST, 1976. Elevation (m) Date 0.8 0.3 -0.2 -0.7 -1.2 May 14, 15 Reproductive 0 3 0 0 0 Total 71 106 123 123 36 - % Reproductive 0 2.83 0 0 0 May 30,31 Reproductive 1 0 2 1 0 Total 51 71 105 134 77 % Reproductive 1.96 0 1.90 0.75 0 June 12, 13 Reproductive 5 3 0 1 0 Total 91 107 86 110 44 % Reproductive 5.49 2.80 0 0.91 0 July 2, 3 Reproductive 0 2 4 0 3 Total 100 82 66 67 35 % Reproductive 0 2.44 6.06 0 8.57 July 10 Reproductive 0 2 3 0 0 Total 70 70 133 93 55 % Reproductive 0 2.86 2.26 0 0 July ,28, 29 Reproductive 0 2 0 2 0 Total 69 86 29 49 27 % Reproductive 0 2.33 0 4.08 0 August 7 Reproductive 0 0 N 0 0 0 Total 79 87 72 94 47 % Reproductive 0 0 0 0 0 APPENDIX 12: ANALYSIS OF VARIANCE SUMMARY FOR SLOPES OF THE REGRESSIONS OF TURION NUMBERS ON ORGANIC DRY WEIGHT FOR FIVE ELEVATIONS (CHART DATUM) Elevation Number of Source of (meters) Observations Variation SS DF MS Calculated F F0.01(l),l,n-2 Conclusion 0.8 88 Total 224.74 87 Linear Regression Residual 127.76 96.98 1 86 127.76 1.13 113.30 6.96 Reject B Q - . B = 0 0.3 64 Total 1643.43 63 Linear Regression Residual 1056.68 586.75 1 62 1056.68 9.46 111.66 7.08 Reject HQ:P = 0 -0.2 62 Total 2481.98 61 Linear Regression Residual 1992.71 489.28 1 60 1992.71 8.15 244.36 7.08 Reject HQ: P = 0 -0.7 ~ 64 Total 1636.33 63 Linear Regression Residual 1111.82 524.51 1 62 1111.82 8.46 131.42 7.08 Reject HQ:£ = 0 -1.2 60 Total 841.38 59 Linear Regression Residual . 658.55 182.83 1 58 658.55 3.15 208.92 7.08 Reject EQ-.P = 0 I— 1 o co 104 APPENDIX 13.: MEAN BIOMASS OF INTERTIDAL (0.8 m) EELGRASS IN GRAMS PER SQUARE METER (ORGANIC DRY WEIGHT) . APRIL 1976 TO JANUARY 1977. Leaves Roots Rhizomes Date Mean SE Mean SE Mean SE 16.4.76 28.80 0.25 4.36 0.20 13.37 0.26 15.5.76 16.98 1.18 1.80 0.15 4.58 0.34 12.6.76 27.45 1.64 3.70 1.18 9.69 1.88 10.7.76 25.33 2.62 3.09 0.24 10.91 1.84 7.8.76 7.90 1.84 1.00 0.24 9.85 1.85 24.8.76 10.68 0.68 1.76 0.29 9.01 2.29 25.10.76 10.64 3.77 1.05 0.47 7.27 2.93 23.11.76 10.10 1.82 0.97 0.21 10.29 1.76 17.1.77 9.29 1.58 1.30 0.23 6.95 1.21

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