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The biological determinants of the structure of harpacticoid copepod communities on an estuarine intertidal… Harrison, Brenda Jane 1981

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THE BIOLOGICAL DETERMINANTS OF THE STRUCTURE OF HARPACTICOID COPEPOD COMMUNITIES ON AN ESTUARINE INTERTIDAL FLAT . • (FRASER RIVER DELTA, B.C.) .'• by '•• BRENDA JANE HARRISON B.Sc., D a l h o u s i e U n i v e r s i t y , 1 9 7 5 A THESIS SUBMITTED IN PARTIAL FULFILLMENT. OF THE REQUIREMENTS FOR THE DEGREE OF . DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA 24 J u l y 1981 (c) Brenda Jane H a r r i s o n , 1981 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. It i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Z o o l o g y The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 D a t e 16 O c t 81 7 Q ^ One mau not Jcnfct t(\aty S<nne(u>w7 aooa cAncCJure, tfie r e v e r e n t e u e mutt s e c A . , r . d \ u j e r t Brooke " i i ABSTRACT . The abundance and m i c r o s p a t i a l d i s t r i b u t i o n of h a r p a c t i c o i d copepods were s t u d i e d from Jan 1977 t o Jan 1980 a t two i n t e r t i d a l s i t e s on the F r a s e r R i v e r D e l t a , B.C.: one (Sand) on the c r e s t of a sand wave and the o t h e r (Mud) on the edge of i t s • muddy t r o u g h . E i g h t s p e c i e s formed the communities a t the two s i t e s . The c o m p o s i t i o n of the communities was s t u d i e d by b i w e e k l y survey i n 1978. Longer term changes i n the o r g a n i z a t i o n of the sand community were f o l l o w e d by annual m i d - w i n t e r s u r v e y s over f o u r y e a r s . F a c t o r a n a l y s i s was used t o group s p e c i e s w i t h s i m i l a r p a t t e r n s of s e a s o n a l o c c u r r e n c e and m a c r o h a b i t a t • d i s t r i b u t i o n s . M i c r o s p a t i a l p a t t e r n s i n the two communities were compared by h e t e r o g e n e i t y c h i - s q u a r e a n a l y s i s from random c o r e samples c o l l e c t e d monthly. The d i s t r i b u t i o n of s p e c i e s r e l a t i v e t o s m a l l - s c a l e h y d r a u l i c bedforms (sand r i p p l e s ) was s t u d i e d a t the sand s i t e . D i s t i n c t p a t t e r n s of community o r g a n i z a t i o n were seen a t the two s i t e s . The mud community was c h a r a c t e r i z e d by h i g h t e m p o r a l o v e r l a p of s p e c i e s ; the sand s p e c i e s showed a d i s t i n c t i v e p a t t e r n of te m p o r a l s e g r e g a t i o n . A l t h o u g h s p e c i e s i n both communities were s e g r e g a t e d a t s m a l l s p a t i a l s c a l e s , m i c r o s p a t i a l p a r t i t i o n i n g was s t r o n g e r and s e a s o n a l l y more v a r i a b l e i n the mud. S p a t i a l p a t t e r n s i n the sand were r e l a t e d t o the r i p p l e d bedforms. B i o g e n i c s t r u c t u r i n g by macrobenthos and d i s t u r b a n c e by p r e d a t o r s were i m p l i c a t e d as the causes of m i c r o s p a t i a l p a t t e r n s observed i n the mud community i n summer. A l t h o u g h the two communities showed d i s t i n c t f e a t u r e s of o r g a n i z a t i o n they were not c o m p l e t e l y i s o l a t e d . Two mud s p e c i e s , S c o t t o l a n a c a n a d e n s i s and T a c h i d i u s t r i a n g u l a r i s , 'migrated' t o the sand i n summer. The r o l e of b i o l o g i c a l i n t e r a c t i o n s i n s t r u c t u r i n g the communities was i n v e s t i g a t e d . P r e d a t i o n by s m a l l t i d e p o o l f i s h , C l e v e l a n d i a i o s and L e p t o c o t t u s armatus, was s t u d i e d by gut a n a l y s i s . P r e d a t i o n was s p e c i e s - and s i z e - s e l e c t i v e , w i t h two e p i p e l i c s p e c i e s , S. c a n a d e n s i s and T. t r i a n g u l a r i s , o c c u r r i n g most f r e q u e n t l y i n f i s h gut samples. A morphometric b a s i s f o r o n t o g e n e t i c v a r i a t i o n i n p r e d a t i o n by C. i o s was proposed. E v i d e n c e t o support the h y p o t h e s i s t h a t c o m p e t i t i v e i n t e r a c t i o n s h e l p t o s t r u c t u r e h a r p a c t i c o i d copepod communities was found i n changing p a t t e r n s of abundance, changing p a t t e r n s of m i c r o h a b i t a t use and morphometric c h a r a c t e r d i s p l a c e m e n t over f o u r y e a r s . C o m p e t i t i v e i n t e r a c t i o n s were h i g h l y dynamic and appeared t o be p a r t of the cause of both the t e m p o r a l and m i c r o s p a t i a l s e g r e g a t i o n o b s e r v e d i n the sand community i n 1979. By 1980, the e i g h t s p e c i e s p r e s e n t i n the January sand community formed a d i s p l a c e m e n t s e r i e s i n body s i z e s . A l t h o u g h each h a r p a c t i c o i d community i s u n i q u e , numerous p a r a l l e l s e x i s t between the s t r u c t u r e and f u n c t i o n of the Iona N o r t h assemblage and those from s h a l l o w water h a b i t a t s , w o r l d w i d e . I t i s c l e a r , t h e r e f o r e , t h a t the c o n c l u s i o n s from t h i s r e s e a r c h have more than l o c a l s i g n i f i c a n c e . i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES i x LIST OF FIGURES . x i ACKNOWLEDGEMENTS . x v i i I . INTRODUCTION 1 11 . GENERAL METHODS . 8 A. Sampling the B i o t a 8 1. Sampling d e s i g n 14 B. F i e l d o b s e r v a t i o n s of a b i o t i c environment !.... 18 1. Annual c y c l e 18 2. D i e l c y c l e 19 C. L a b o r a t o r y treatment of samples 20 1 . E x t r a c t i o n of the fauna 20 2. Q u a n t i t a t i v e h a r p a c t i c o i d samples 21 3. Sediment pigment a n a l y s i s ....21 4. Scanning E l e c t r o n M i c r o s c o p y (SEM) 23 D. E n v i r o n m e n t a l measurements 24 1. Redox p o t e n t i a l s _ 24 2. Sediment g r a i n s i z e 24 E. Data a n a l y s i s 25 I I I . THE STUDY SITE AND ITS BIOTA 27 A. I n t r o d u c t i o n t o the Iona N o r t h h a b i t a t 27 B. Choice of s i t e f o r study of the meiobenthos 35 C. S e a s o n a l V a r i a t i o n i n E n v i r o n m e n t a l F a c t o r s 36 V 1 . T i d e s and Exposure 36 2. S a l i n i t y 40 3. Temperature 40 4. Redox 43 5. Sediment g r a i n s i z e 49 D. D i e l v a r i a t i o n s i n e n v i r o n m e n t a l f a c t o r s 52 E. Sediment pigments and m i c r o a l g a e 56 F. S e a s o n a l abundance p a t t e r n s of the fauna 61 1. T o t a l meiobenthos 61 2. I n d i v i d u a l t a x a 70 a. Permanent meiobenthos 70 b. S m a l l macrobenthos 76 c. M i c r o b e n t h o s 76 IV. AUTECOLOGY OF IONA NORTH HARPACTICOID COPEPODS 78 A. I n t r o d u c t i o n 78 B. A u t e c o l o g y 85 1. S c o t t o l a n a c a n a d e n s i s 85 2. H a l e c t i n o s o m a sp 95 3. Pseudobradya sp 104 4. T a c h i d i u s t r i a n g u l a r i s 108 5. L e p t a s t a c u s c o n s t r i c t u s 116 6. P a r a l e p t a s t a c u s s p i n i c a u d a 121 7. Huntemannia j a d e n s i s 129 8. • L i m n o c l e t o d e s b e h n i n g i 135 C. D i s c u s s i o n 1 40 D. Summary 149 V. FACTOR ANALYSIS OF IONA NORTH HARPACTICOID COMMUNITIES 152 v i A. I n t r o d u c t i o n 152 B . Methods . . . 155 1. R-mode: S p e c i e s as v a r i a b l e s 155 2. Q-mode: Samples as v a r i a b l e s .158 C. R e s u l t s 159 1. R-mode f a c t o r a n a l y s i s 159 a. I d e n t i f i c a t i o n of groups of s p e c i e s from f a c t o r l o a d i n g s 159 b. I d e n t i f i c a t i o n of s e a s o n a l p a t t e r n s of groups from f a c t o r s c o r e s 162 2. Q-mode f a c t o r a n a l y s i s : Sand 166 3. Q-mode f a c t o r a n a l y s i s : Mud ...169 D. D i s c u s s i o n 178 1. C l u s t e r i n g of s p e c i e s (R-mode a n a l y s i s ) 178 2. S e a s o n a l p a t t e r n s of community change (Q-mode a n a l y s i s ) 180 V I . SPATIAL PATTERNS 183 A. I n t r o d u c t i o n 183 B. H e t e r o g e n e i t y C hi-Square A n a l y s i s 187 1 . Methods 187 2. R e s u l t s 189 C. Sand R i p p l e A n a l y s i s 201 1. I n t r o d u c t i o n 201 2. Methods 202 3. R e s u l t s 205 a. Sand r i p p l e s 205 b. Wi n t e r f a u n a l samples [ J a n u a r y 1977] 206 v i i c. Summer f a u n a l samples [ J u l y 1978]- 216 d. M i c r o h a b i t a t d i s p l a c e m e n t 221 D. D i s c u s s i o n 224 E. Summary 232 V I I . PREDATION BY SMALL TIDEPOOL FISH 234 A. I n t r o d u c t i o n .234 B. Methods 240 1. D e s c r i p t i o n of d i e t s of t i d e p o o l f i s h ...241 2. E l e c t i v i t y .........243 C. R e s u l t s and d i s c u s s i o n , 246 1. C l e v e l a n d i a i o s 246 2. L e p t o c o t t u s armatus 250 3. S e l e c t i v e p r e d a t i o n by C l e v e l a n d i a i o s 254 •4. Comparison of the two p r e d a t o r s 264 5. S i g n i f i c a n c e of p r e d a t i o n by l i t t o r a l f i s h 272 D. Summary ....277 V I I I . INTERSPECIFIC COMPETITION AND COMMUNITY STRUCTURE ..284 A. i n t r o d u c t i o n 284 B. Methods . . 290 1. D e t e c t i o n of v a r i a t i o n between y e a r s ....290 2. Q u a n t i f i c a t i o n of morphometric and t r o p h i c r e l a t i o n s h i p s 290 3. A n a l y s i s of community s t r u c t u r e 292 C. R e s u l t s and D i s c u s s i o n 296 1. Body s i z e and t r o p h i c r e l a t i o n s h i p s 296 2. I n t e r a c t i o n s between P a r a l e p t a s t a c u s s p i n i c a u d a and H a l e c t i n o s o m a sp 310 v i i i a. R e l a t i v e abundance . . . . . 3 1 3 b. M i c r o h a b i t a t d i s t r i b u t i o n s 316 c. Body s i z e r e l a t i o n s h i p s 319 3. Community S t r u c t u r e 330 a. S e a s o n a l changes i n community s t r u c t u r e through 1 978 330 b. Niche b r e a d t h of i n d i v i d u a l s p e c i e s 335 c. Changes i n the m i d - w i n t e r sand community between y e a r s .338 D. Summary 343 IX. SUMMARY AND DISCUSSION 347 A. The s t r u c t u r e of m e i o b e n t h i c h a r p a c t i c o i d communities 347 B. The s t r u c t u r e of the Iona N o r t h communities 350 1. P a t t e r n of r e s o u r c e a l l o c a t i o n among s p e c i e s ....350 2. P a t t e r n s of s p a t i a l abundance 352 3. P a t t e r n s of t e m p o r a l abundance 353 4. C o m p e t i t i o n .. 356 a. Changing p a t t e r n s of abundance 356 b. Changing p a t t e r n s of m i c r o h a b i t a t use 359 c. Morphometric c h a r a c t e r d i s p l a c e m e n t 360 5. P r e d a t i o n ....362 C. P r o s p e c t u s : S i m i l a r o p t i m a l s o l u t i o n s t o community s t r u c t u r e 367 X. BIBLIOGRAPHY 370 XI. APPENDICES ..394 i x LIST OF TABLES Table 1 . ' C a l c u l a t i o n of minimum number of r e p l i c a t e s 18 Table 2. Range of d e n s i t i e s of t o t a l meiobenthos i n 1978. 62 Table 3. E s t i m a t e s of m e i o f a u n a l d e n s i t i e s from p r o d u c t i v e i n t e r t i d a l and s h a l l o w s u b t i d a l h a b i t a t s 66 Table 4. S c o t t o l a n a c a n a d e n s i s . R e p r o d u c t i o n and temperature i n the mud, 1978 93 Table 5. C o r r e l a t i o n s between d e n s i t y of ovi.gerous females and t o t a l p o p u l a t i o n d e n s i t y f o r 7 s p e c i e s 95 Table 6. S e a s o n a l v a r i a t i o n i n T o t a l C h i - s q u a r e (TCS) of h a r p a c t i c o i d s in.1978. 196 Table 7. C o m p o s i t i o n of sand on 22 Jan 1977 206 Table 8. The s t r u c t u r e of the m e i o b e n t h i c assemblage of the sand r i p p l e s i n w i n t e r and summer 207 Table 9. M i c r o h a b i t a t s e l e c t i o n by sand r i p p l e ha r p a c t i c o i d spec i e s 2 1 2 Table 10. Average PS of assemblages from c o r e s c o l l e c t e d i n the same and i n d i f f e r e n t m i c r o h a b i t a t s 213 Tab l e 11. P. s p i n i c a u d a and H a l e c t i n o s o m a sp. . C h i - s q u a r e t e s t f o r independence 222 Tab l e 12. C l e v e l a n d i a i o s . C h a r a c t e r i s t i c s of f i s h used i n gut a n a l y s i s 246 Table 13. C l e v e l a n d i a i o s . D i e t i n Iona N o r t h t i d e p o o l s . 249 Tab l e 14. R e l a t i v e c o n t r i b u t i o n s of macro- and meiobenthos and d e t r i t u s t o d i e t s 248 X T a b l e 15. L e p t o c o t t u s armatus. C h a r a c t e r i s t i c s of f i s h used i n gut a n a l y s i s .....251 Ta b l e 16. L e p t o c o t t u s armatus. D i e t i n Iona N o r t h t i d e p o o l s 252 Tab l e 17. S p e c i e s c o m p o s i t i o n of the prey community. .....254 Tab l e 1 8 . Summary of r e p o r t s of f i s h p r e d a t i o n on h a r p a c t i c o i d s . .278 Tab l e 19. Summary of a u t e c o l o g y of h a r p a c t i c o i d s from Jan sand samples 297 Ta b l e 20. Body, s i z e and food s i z e r a t i o s of h a r p a c t i c o i d s p e c i e s i n Jan 1980 301 Table 21. Summary of y e a r - t o - y e a r changes i n the s t r u c t u r e of the m i d - w i n t e r sand community .......341 LIST OF FIGURES F i g u r e - 1 . Map of the F r a s e r R i v e r d e l t a , B.C. showing . l o c a t i o n of study s i t e ......... 9 F i g u r e .2. D e t a i l of framed a r e a from F i g . 1 11 F i g u r e 3. Placement of c o r e s i n monthly sand r i p p l e s a m p l i n g 15 F i g u r e 4. Photographs of the Iona N o r t h study s i t e 28 F i g u r e 5. T i d e c u r v e s f o r P t . A t k i n s o n , 18-21 J u l y .1978 and20-23 Jan 1977. ............ 38 F i g u r e *6. Se a s o n a l v a r i a t i o n i n s a l i n i t y and temperature of Iona N o r t h t i d e p o o l s . 41 F i g u r e 7. Sediment temperature and Redox p r o f i l e s ........ 44 F i g u r e 8. Redox c o n d i t i o n s i n the t o p 10 cm of sediment through, 1978 . 46 F i g u r e 9, S e a s o n a l v a r i a t i o n s i n sediment t e x t u r e . ....... 50 F i g u r e 10. D i u r n a l v a r i a t i o n of p h y s i c a l c o n d i t i o n s i n the South P o o l on 19-20 J u l y , 1978. 53 F i g u r e 11. Se a s o n a l v a r i a t i o n s i n sediment c o n c e n t r a t i o n s of p h o t o s y n t h e t i c pigments •••• 57 F i g u r e 12. Se a s o n a l v a r i a t i o n i n abundance of t o t a l meiobenthos 63 F i g u r e 13. Se a s o n a l v a r i a t i o n i n c o n t r i b u t i o n of major t a x a t o the t o t a l abundance of meiobenthos 68 F i g u r e 14. S e a s o n a l v a r i a t i o n s i n abundance of major m e i o b e n t h i c t a x a a t the sand s i t e t h r o u g h 1 978 71 F i g u r e 15. Seasonal v a r i a t i o n s i n abundance of major m e i o b e n t h i c t a x a a t the mud s i t e through 1978 73 F i g u r e 16. L i m n o c l e t o d e s b e h n i n q i . SEM montage ( h a b i t u s ) of an a d u l t female 81 F i g u r e 17. S c o t t o l a n a c a n a d e n s i s • H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and. s e a s o n a l abundance p a t t e r n at the two • study s i t e s through 1978 87 F i g u r e .18 .Halectinosoma sp. . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two s i t e s t h r o ugh 1978 97 F i g u r e 19. Ha l e c t i n o s o m a sp. . D e t a i l of mouthparts 99 F i g u r e 20. Pseudobradya sp. . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two s i t e s t h r o ugh 1978 105 F i g u r e 21. T a c h i d i u s t r i a n q u l a r i s . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two study s i t e s through 1978 109 F i g u r e 22. L e p t a s t a c u s c o n s t r i c t u s . H a b i t u s drawing and s e a s o n a l abundance p a t t e r n a t the sand s i t e through 1978 117 F i g u r e 23. P a r a l e p t a s t a c u s . s p i n i c a u d a . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the sand s i t e through 1978 .122 F i g u r e 24. P a r a l e p t a s t a c u s s p i n i c a u d a . D e t a i l of mouthparts 125 F i g u r e 25. Huntemannia j a d e n s i s . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two s i t e s t h r o u g h 19.78. 130 F i g u r e 26. L i m n o c l e t o d e s b e h n i n q i . Habitus, d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the mud s i t e t h r o u g h 1978 136 F i g u r e 27. I n t e r h a b i t a t m i g r a t i o n s by S c o t t o l a n a c a n a d e n s i s and T a c h i d i u s t r i a n q u l a r i s . 145 F i g u r e 28. H a r p a c t i c o i d s p e c i e s p l o t t e d i n the space d e f i n e d by the f i r s t two p r i n c i p a l f a c t o r s (R-mode) ...160 F i g u r e 29. F a c t o r s c o r e s d e r i v e d from s e a s o n a l abundance da t a i n the sand and mud h a b i t a t s p l o t t e d a g a i n s t time (R-mode) .163 F i g u r e 30. S e a s o n a l samples from sand p l o t t e d i n the space d e f i n e d by the f i r s t two p r i n c i p a l f a c t o r s (Q-mode). ...167 F i g u r e 31. S e a s o n a l samples from mud p l o t t e d i n the space d e f i n e d by the f i r s t two p r i n c i p a l f a c t o r s (Q-mode) ...170 F i g u r e 32. P a t t e r n s of s e a s o n a l change of abundance of the h a r p a c t i c o i d s of Iona N o r t h 173 F i g u r e 33. P a t t e r n s of s e a s o n a l change i n d i v e r s i t y and d e n s i t y of the two communities i n 1978. 175 F i g u r e 34. D e n s i t y and s p e c i e s d i v e r s i t y of h a r p a c t i c o i d copepods a t Iona N o r t h i n 1978 190 F i g u r e 35. S e a s o n a l v a r i a t i o n i n p o o l e d c h i - s q u a r e and i t s r e l a t i o n s h i p t o s p e c i e s d i v e r s i t y and abundance 193 F i g u r e 36. S e a s o n a l v a r i a t i o n i n h e t e r o g e n e i t y c h i - s q u a r e and i t s r e l a t i o n s h i p t o d i v e r s i t y and abundance 198 F i g u r e 37. Counts of nematodes and h a r p a c t i c o i d s i n t r a n s e c t s t h r o u g h r i p p l e s 22 Jan 1 977 208 x i v F i g u r e 38. M i c r o h a b i t a t d i s t r i b u t i o n s of h a r p a c t i c o i d s p e c i e s on 22 Jan 1977. 210 F i g u r e 39. T r e l l i s diagram f o r the 24 sand r i p p l e samples c o l l e c t e d on 22 Jan 1977 ...214 F i g u r e 40. Counts of nematodes and h a r p a c t i c o i d s i n t r a n s e c t s t h rough sand r i p p l e s 21 J u l y .1978. .217 F i g u r e 41. M i c r o h a b i t a t d i s t r i b u t i o n s of h a r p a c t i c o i d s p e c i e s on 21 J u l y 1978 ...219 F i g u r e 42. S e a s o n a l change i n v e r t i c a l d i s t r i b u t i o n of sand r i p p l e h a r p a c t i c o i d s through 1978. .228 F i g u r e 43. P o t e n t i a l p r e d a t o r s on h a p a c t i c o i d s i n Iona N o r t h t i d e p o o l s ........238 F i g u r e 44. C l e v e l a n d i a i o s . R e l a t i o n s h i p between f i s h l e n g t h and s p e c i e s - s p e c i f i c e l e c t i v i t y i n 1979 257 F i g u r e 45. R e l a t i o n s h i p between f i s h l e n g t h and s p e c i e s -s p e c i f i c e l e c t i v i t y i n 1980 260 F i g u r e 46. R e l a t i o n s h i p between f i s h l e n g t h and s i z e -s p e c i f i c e l e c t i v i t y 262 F i g u r e 47. C o n t r i b u t i o n of h a r p a c t i c o i d s t o the d i e t s of d i f f e r e n t s i z e s of p r e d a t o r s ....265 F i g u r e 48. R e l a t i o n s h i p between the s i z e of the f i s h and the number of h a r p a c t i c o i d s found i n t h e i r g u t s 268 F i g u r e 49. C l e v e l a n d i a i o s . O r a l morphology 273 F i g u r e 50. R e l a t i o n s h i p between o n t o g e n e t i c v a r i a t i o n i n f r o n t a l p i t w i d t h and s i z e of dominant p r e y 275 F i g u r e 51. Length f r e q u e n c y d i s t r i b u t i o n s of the 8 h a r p a c t i c o i d s p e c i e s c o l l e c t e d from the sand on 22 Jan XV 1 980. 286 F i g u r e .52. H a b i t u s drawings of the 8 s p e c i e s which o c c u r r e d a t the sand i n m i d - w i n t e r . 298 F i g u r e 53. Length f r e q u e n c y d i s t r i b u t i o n s of diatoms i n g e s t e d by the 5 most abundant s p e c i e s on 22 Jan 1980. 302 F i g u r e 54. S c a t t e r diagram showing r e l a t i o n s h i p between body l e n g t h s of copepods and l e n g t h of diatoms i n g e s t e d . . 304 F i g u r e 55.. R e l a t i o n s h i p between mean body l e n g t h of each. s p e c i e s and mean l e n g t h of diatoms i n g e s t e d . 306 F i g u r e 56. Summary of body s i z e and d i e t o v e r l a p s among the 5 most abundant h a r p a c t i c o i d s p e c i e s i n Jan 1980. .308 F i g u r e 57. Length f r e q u e n c y d i s t r i b u t i o n s of Ha l e c t i n o s o m a sp. ,. P. s p i n i c a u d a and Pseudobradya sp. 1977-1979. . . . . 311 F i g u r e 58. The r e l a t i v e abundance of 8 sand s p e c i e s i n January over 4 c o n s e c u t i v e y e a r s • 314 F i g u r e 59. R e l a t i v e f r e q u e n c y of m i c r o h a b i t a t use by P. s p i n i c a u d a and H a l e c t inosoma sp. i n Ja n u a r y 1977 and 1978. 317 F i g u r e 60. Mean l e n g t h of i n d i v i d u a l s of P. s p i n i c a u d a and H a l e c t inosoma sp. i n Jan over 4 c o n s e c u t i v e y e a r s . ...320 F i g u r e 61. P a r a l e p t a s t a c u s s p i n i c a u d a . Length of females and number of eggs per o v i s a c a t h e i g h t of the b r e e d i n g season 323 F i g u r e 62. Number of eggs per eggsac of d i f f e r e n t s i z e d x v i females i n Jan 1977 and 1978 325 F i g u r e 63. R e l a t i v e m i c r o h a b i t a t use by P. s p i n i c a u d a and S c h i z o p e r a sp. i n Jan 1980 327 F i g u r e 64. Seas o n a l v a r i a t i o n s i n the n i c h e parameters of the sand community through 1978. 332 F i g u r e 65. Seas o n a l v a r i a t i o n i n c a l c u l a t e d n i c h e b r e a d t h of sand h a r p a c t i c o i d s p e c i e s i n 1978. 336 F i g u r e 6 6 . . M i c r o h a b i t a t o v e r l a p m a t r i c e s f o r the mid-w i n t e r sand h a r p a c t i c o i d community 339 F i g u r e 67. R e l a t i o n s h i p , between s p e c i e s d i v e r s i t y and c o e f f i c i e n t of v a r i a t i o n of mean s p a t i a l o v e r l a p 344 x v i i ACKNOWLEDGEMENTS I w i s h t o e x p r e s s . my s i n c e r e a p p r e c i a t i o n t o my s u p e r v i s o r . Dr. T.R. Parsons f o r h i s w i l l i n g n e s s t o support even my most e s o t e r i c r e s e a r c h over the p a s t 6 y e a r s . I am g r a t e f u l a l s o f o r the sup p o r t and h e l p f u l c r i t i c i s m s of my guidance committee,. D rs.' S.C. C a l v e r t , .. P. J . ..Harri son , C D . L e v i n g s and A.G. L e w i s . I have a l s o b e n e f i t t e d from d i s c u s s i o n s w i t h the o t h e r members of DOUBC, p a r t i c u l a r l y D r s . J . P a r s l o w , F.J.R. T a y l o r , P. Crean, C. L a l l i and P.H. L e B l o n d . Mr. L. Veto p r o v i d e d i n c o m p a r a ble guidance w i t h the SEM. My en c o u n t e r s w i t h UBC computers were b u f f e r e d somewhat w i t h the a s s i s t a n c e of M. D. L a p l a n t e and Dr. D. Z i t t i n . E i g h t hardy i n d i v i d u a l s , Dr.,P.G. H a r r i s o n , I. P e r r y , C. McNamee, E. Nutbrown, D. Skraba, P. S t y f f e , B.C. H a r r i s o n and J . Pa r s l o w p a r t i c i p a t e d i n the e x p e d i t i o n s t o Iona I s l a n d . P. S t y f f e began h i s s u r g i c a l t r a i n i n g on the f i s h of Iona i n 1979; L. Gormican c o n t i n u e d h i s f i n e work i n 1980. T.G. B j o r n p r o v i d e d moral support d u r i n g a l l phases of the r e s e a r c h . The G r e a t e r Vancouver Sewerage and Drainage D i s t r i c t g e n e r o u s l y p r o v i d e d a c c e s s t o the Iona J e t t y . I have b e n e f i t t e d g r e a t l y from the c o n g e n i a l encouragement I have r e c e i v e d from c o l l e g u e s i n the I n t e r n a t i o n a l A s s o c i a t i o n of M e i o b e n t h o l o g i s t s . Taxonomic a d v i c e was p r o v i d e d by B.A. Kask, D r s . B.M. M a r c o t t e , R.J. F e l l e r , B.C. C o u l l and J . B . J . W e l l s . S p e c i a l t h a n k s a re due t o Dr. B.M. M a r c o t t e who f i r s t i n t r o d u c e d me t o the w o r l d of the meiobenthos and who has c o n t i n u e d t o p r o v i d e i n s p i r a t i o n "and encouragement t h r o u g h the x v i i i c o u r s e of t h i s s t u d y . F i n a l l y , T wish t o thank my f r i e n d s and f a m i l y f o r t h e i r c o n t i n u i n g s u p p o r t . My husband, P a u l , has a c t e d as my f i e l d a s s i s t a n t , c r i t i c and p r o o f r e a d e r . Without h i s c o n s t a n t encouragement, a d v i c e and support I would not have completed t h i s t h e s i s . I r e c e i v e d f i n a n c i a l s u p port from the N a t u r a l S c i e n c e s and E n g i n e e r i n g Research C o u n c i l of Canada and an H.R. M a c M i l l a n F a m i l y F e l l o w s h i p . I d e d i c a t e t h i s t h e s i s w i t h a f f e c t i o n t o Win H a l l i d a y who i n s i s t e d always t h a t I do my b e s t . 1 I . INTRODUCTION "We have reason t o b e l i e v e t h a t s p e c i e s i n a s t a t e of n a t u r e a r e l i m i t e d i n t h e i r , range by the c o m p e t i t i o n of o t h e r - o r g a n i c b e i n g s q u i t e as much a s , or more t h a n , by a d a p t a t i o n t o p a r t i c u l a r c l i m a t e s . " C. Darwin (1859) The l i m i t a t i o n of a s p e c i e s i n na t u r e t o a range of h a b i t a t s s m a l l e r than may be p r e d i c t e d from a study ( i n the absence of o t h e r s p e c i e s ) of i t s p h y s i c a l t o l e r a n c e s and food r e q u i r e m e n t s remains one of the fundamental problems of modern e c o l o g y . The n o t i o n e n u n c i a t e d by Darwin i n "The O r i g i n of S p e c i e s " (1859, pp.76-77) and quoted a t the b e g i n n i n g of t h i s c h a p t e r , t h a t p a r t of t h i s l i m i t a t i o n may d e r i v e from the presence of o t h e r s p e c i e s i n the environment, both c o m p e t i t o r s ( s p e c i e s w i t h the same r e q u i r e m e n t s of "food or r e s i d e n c e " ) and p r e d a t o r s ( " s p e c i e s from which i t has t o e s c a p e " ) , was e l a b o r a t e d by many of the e c o l o g i s t s of the f i r s t h a l f of t h i s c e n t u r y ( n o t a b l y by G r i n n e l l 1917 and E l t o n 1927) i n t o the concept of the n i c h e . The m a t h e m a t i c a l f o r m a l i z a t i o n of the n i c h e i s due t o H u t c h i n s o n (1957). H u t c h i n s o n made a d i s t i n c t i o n between the "fundamental" n i c h e , "an n - d i m e n s i o n a l hypervolume... ev e r y p o i n t i n which c o r r e s p o n d s t o a s t a t e of the environment which would p e r m i t the s p e c i e s . . . t o p e r s i s t i n d e f i n i t e l y " , and the " r e a l i z e d " n i c h e , a subset of the fundamental n i c h e t o which the s p e c i e s i s r e s t r i c t e d by b i o l o g i c a l i n t e r a c t i o n s . L e v i n s (1968) f u r t h e r r e f i n e d the 2 n i c h e concept t o i n c l u d e a f i t n e s s measure a t each p o i n t i n the hypervolume i n r e c o g n i t i o n of the f a c t t h a t not a l l c o m b i n a t i o n s of e c o l o g i c a l f a c t o r s which a l l o w p e r s i s t e n c e of a s p e c i e s w i l l be e q u a l l y f a v o r a b l e . The h i s t o r y of the concept of the n i c h e has been r e v i e w e d r e c e n t l y by C h r i s t i a n s e n and F e n c h e l (1977 pp.68-9) and Hu t c h i n s o n (1978 pp. 152-8). In h i s 1978 book, H u t c h i n s o n made a d i s t i n c t i o n between two c l a s s e s of n i c h e d i m e n s i o n s , the " s c e n o p o e t i c " or those axes which r e p r e s e n t f a c t o r s of the environment which the s p e c i e s must t o l e r a t e , such as s a l i n i t y and t e m p e r a t u r e , and the "bionomic" or those axes which r e p r e s e n t r e s o u r c e s such as t i m e , space and food f o r which s p e c i e s may compete. The purpose of t h i s t h e s i s i s t o d e s c r i b e the " n i c h e r e l a t i o n s h i p s " of a group of m e i o b e n t h i c h a r p a c t i c o i d s ( C r u s t a c e a : Copepoda) w i t h p r i n c i p a l emphasis on the bionomic n i c h e axes. The term 'meiobenthos' [Gk. meion l e s s + benthos depth (of the s e a ) ] was c o i n e d by Mare (1942) t o d e s c r i b e those b o t t o m - d w e l l i n g metazoa i n t e r m e d i a t e i n s i z e between the l a r g e r macrobenthos and s m a l l e r m i c r o b e n t h o s ( b a c t e r i a and p r o t o z o a ) . M c l n t y r e (1969) proposed a f u n c t i o n a l d e f i n i t i o n f o r the meiobenthos (=meiofauna) which w i l l be f o l l o w e d i n t h i s t h e s i s : " a group of s m a l l metazoans m o s t l y p a s s i n g a l/2mm mesh, which by t h e i r s i z e , number, g e n e r a t i o n time and a d a p t a t i o n s can c o n v e n i e n t l y be c o n s i d e r e d s e p a r a t e l y from the l a r g e r members of the benthos." 3 S p e c i a l i z e d r e p r e s e n t a t i v e s of most i n v e r t e b r a t e p h y l a occur i n the meiobenthos a l t h o u g h by f a r the most abundant i n most h a b i t a t s are the nematodes and h a r p a c t i c o i d copepods ( F e n c h e l 1978; C o u l l and B e l l 1979). U n l i k e the i n t e r s t i t i a l fauna which i s l i m i t e d t o sandy h a b i t a t s , the meiobenthos as a whole i s not l i m i t e d t o p a r t i c u l a r b i o t o p e s and can be c o n s i d e r e d u b i q u i t o u s i n marine and e s t u a r i n e b e n t h i c h a b i t a t s . The members of the meiobenthos, due t o t h e i r s m a l l s i z e , h i g h d e n s i t i e s ( 1 0 s t o 10 7 m" 2), s h o r t g e n e r a t i o n times ( l e s s than 1 year) and enormous d i v e r s i t y of form and f u n c t i o n , are an i d e a l p r o v i n g ground f o r the f o r m u l a t i o n and t e s t i n g of e c o l o g i c a l and e v o l u t i o n a r y t h e o r i e s of community o r g a n i z a t i o n . The e c o l o g y of the meiobenthos and the h i s t o r y of i t s study t h r o u g h t o the 1960's has been the s u b j e c t of s e v e r a l e x t e n s i v e r e v i e w s (Swedmark 1964; M c l n t y r e 1969; G e r l a c h 1971; C o u l l 1973). The emphasis of r e s e a r c h through t h i s p e r i o d was on the i d e n t i f i c a t i o n of the m u l t i t u d e of s p e c i e s i n c l u d e d i n the meiobenthos, t h e i r m o r p h o l o g i c a l a d a p t a t i o n s t o t h e i r unique h a b i t a t , the i d e n t i f i c a t i o n of f a u n a l a s s o c i a t i o n s , the c o l l e c t i o n of q u a n t i t a t i v e e s t i m a t e s of the d e n s i t y of major groups on a v a r i e t y of s u b s t r a t e t y p e s and the r e l a t i o n s h i p s of i n d i v i d u a l s p e c i e s t o t h e i r p h y s i c a l environment ( i . e . H u t c h i n s o n ' s s c e n o p o e t i c n i c h e a x e s ) . In the past decade a major s h i f t i n the emphasis of m e i o b e n t h i c r e s e a r c h has o c c u r r e d toward s t u d i e s of the "bionomic" n i c h e r e l a t i o n s h i p s of m e i o b e n t h i c s p e c i e s i n c l u d i n g i n c r e a s e d a t t e n t i o n t o the f u n c t i o n a l as w e l l as q u a n t i t a t i v e r e l a t i o n s h i p s of i n d i v i d u a l s 4 i n m u l t i s p e c i e s assemblages. The development of t h i s r e l a t i v e l y new approach t o m e i o b e n t h i c e c o l o g y has been reviewed r e c e n t l y by F e n c h e l (1978), C o u l l and B e l l (1979) and Warwick (1980a). The v e r y a t t r i b u t e s which make the meiobenthos so p r o m i s i n g f o r community s t u d i e s a l s o make i t l o g i s t i c a l l y v e r y d i f f i c u l t t o study s i m u l t a n e o u s l y the r e l a t i o n s h i p s , of a l l s p e c i e s w i t h i n a community t o a l l t h r e e major bionomic axes ( t i m e , space and f o o d ) . Most s t u d i e s have c o n c e n t r a t e d on one or a p a i r of axes; the d i s t r i b u t i o n of m e i o b e n t h i c s p e c i e s t h r o u g h , time and i n space have r e c e i v e d the most a t t e n t i o n ( F e n c h e l 1978). U n f o r t u n a t e l y , a complete u n d e r s t a n d i n g of the dynamics of m e i o b e n t h i c h a r p a c t i c o i d communities may r e q u i r e r e s o l u t i o n of a l l t h r e e n i c h e d i m e n s i o n s . No one study has a c c o m p l i s h e d t h i s , a l t h o u g h our u n d e r s t a n d i n g of the dynamics of h a r p a c t i c o i d communities has been c o n s i d e r a b l y enhanced by s e v e r a l r e c e n t l y r e p o r t e d s t u d i e s . I v e s t e r (1975, 1980) and M a r c o t t e (1977a) e l u c i d a t e d the s t r u c t u r e of m a r s h - d w e l l i n g h a r p a c t i c o i d communities over l a r g e s p a t i a l s c a l e s ( c o v e r i n g a v a r i e t y of sediment t y p e s , thus a v a r i e t y of d i s t i n c t h a b i t a t s ) . These s t u d i e s i n c l u d e d c o n s i d e r a t i o n of the t r o p h i c r e l a t i o n s h i p s of the s p e c i e s i n v o l v e d but not of the f i n e - s c a l e t e m p o r a l or s p a t i a l p a t t e r n s . More r e c e n t l y , workers have decre a s e d the number of s i t e s sampled which a l l o w s i n c r e a s e d frequency of s a m p l i n g and, hence, r e s o l u t i o n of tempor a l p a t t e r n s . B e l l (1979) r e s t r i c t e d her a t t e n t i o n t o a s i n g l e high-marsh s i t e and sampled monthly t o r e s o l v e t e m p o r a l p a t t e r n s . Her study a l s o i n c l u d e d a 5 c o n s i d e r a t i o n of s m a l l - s c a l e s p a t i a l d i s t r i b u t i o n at two p o i n t s d u r i n g the year (March and May) and l o n g e r term v a r i a b i l i t y (over 19 months). A study of p r e d a t i o n by g r a s s shrimp i n the same h a b i t a t was r e p o r t e d s e p a r a t e l y ( B e l l 1980). C a s t e l and L a s s e r r e (1979) s t u d i e d two communities, one i n an i n t e r t i d a l p o o l and one i n an a q u a c u l t u r e ( f i s h ) impoundment, over one year and r e s o l v e d t e m p o r a l changes i n community o r g a n i z a t i o n but d i d not c o n s i d e r m i c r o s p a t i a l p a t t e r n s . F l e e g e r (1980) s t u d i e d t h r e e s i t e s (two s u b t i d a l and one low-marsh, i n t e r t i d a l ) b i w e e k l y f o r one year and i n c l u d e d s m a l l - s c a l e s p a t i a l p a t t e r n s i n h i s s a m p l i n g d e s i g n . Both m i c r o h a b i t a t s p e c i a l i z a t i o n and p r e d a t i o n were suggested as i m p o r t a n t s t r u c t u r i n g mechanisms i n the communities, a l t h o u g h F l e e g e r d i d not e x p l i c i t l y study e i t h e r . Such c o m p a r a t i v e s t u d i e s of community dynamics l i m i t e d t o a few s i t e s h o l d the most promise, p a r t i c u l a r l y those employing c o n t r o l l e d f i e l d m a n i p u l a t i o n s ( B e l l 1980) and those employing s h o r t - i n t e r v a l s a m p l i n g f o r s e v e r a l y e a r s . The N o r t h I n l e t , South C a r o l i n a i n v e s t i g a t i o n of C o u l l and F l e e g e r (1977), which now c o v e r s 5 y e a r s a t two s u b t i d a l marsh s i t e s ( C o u l l and B e l l 1979) and the Dievengat (a s h a l l o w , b r a c k i s h p o o l i n - n o r t h e r n Belgium) i n v e s t i g a t i o n of H e i p (1977,1980) which c o v e r s 9 y e a r s , a r e the most e x t e n s i v e s t u d i e s of community dynamics made t o d a t e . Both have s t r e s s e d the importance of l o n g e r term (on the o r d e r of y e a r s ) f l u c t u a t i o n s i n s p e c i e s abundances t o our u n d e r s t a n d i n g of community dynamics. From t h e s e and o t h e r s t u d i e s on m e i o b e n t h i c h a r p a c t i c o i d 6 communities which w i l l be d i s c u s s e d i n subsequent c h a p t e r s , s e v e r a l i m p o r t a n t g e n e r a l i z a t i o n s emerge ( F e n c h e l 1978; C o u l l and B e l l 1979): 1) a s t r o n g dichotomy e x i s t s between sand- and mud-d w e l l i n g h a r p a c t i c o i d communities i n terms of s p e c i e s c o m p o s i t i o n and e c o l o g y 2) no s i n g l e measure of community s t r u c t u r e (e.g. s p e c i e s d i v e r s i t y ) e x i s t s which can a d e q u a t e l y c h a r a c t e r i z e a m u l t i s p e c i e s h a r p a c t i c o i d assemblage 3) m e i o b e n t h i c s p e c i e s show complex temporal p a t t e r n s of v a r i a t i o n s i n abundance both w i t h i n and between y e a r s .4) m e i o b e n t h i c s p e c i e s are h e t e r o g e n e o u s l y d i s t r i b u t e d i n space at s e v e r a l s c a l e s 5) s t r o n g i n t e r s p e c i f i c i n t e r a c t i o n s (both c o m p e t i t i v e and p r e d a t o r - p r e y ) are o f t e n i m p l i c a t e d . Any study of community dynamics which aims t o r e s o l v e the " bionomic" r e l a t i o n s h i p s of the community must employ a d i v e r s e s e t of s a m p l i n g t e c h n i q u e s and both s h o r t - and l o n g i n t e r v a l s a m p l i n g . The r e s e a r c h I am about t o d e s c r i b e was d e s i g n e d t o i d e n t i f y and compare the s t r u c t u r e of a p a i r of i n t e r t i d a l h a r p a c t i c o i d communities on the F r a s e r R i v e r d e l t a and t o e x p l o r e the b i o l o g i c a l d e t e r m i n a n t s of t h a t s t r u c t u r e ; t h a t i s , t o d e t e r m i n e the "bionomic" n i c h e r e l a t i o n s h i p s of an e s t u a r i n e 7 h a r p a c t i c o i d assemblage. To t h i s end the study was d e s i g n e d t o i n c l u d e c o n s i d e r a t i o n of the t e m p o r a l , s p a t i a l and food ( s i z e ) r e l a t i o n s h i p s of the s p e c i e s , as w e l l as t h e i r r e l a t i o n s h i p s t o p r e d a t o r s , and so i s r e a l l y a c o l l e c t i o n of s m a l l i n v e s t i g a t i o n s , each employing s p e c i f i c methods t o answer s p e c i f i c q u e s t i o n s , but a l l j o i n e d by the common theme of b i o t i c i n t e r a c t i o n s w i t h i n a community. 8 I I . GENERAL METHODS The study a r e a , Iona N o r t h , i s l o c a t e d on the i n t e r t i d a l f l a t on Sturgeon Bank n o r t h of the Iona I s l a n d causeway on the F r a s e r R i v e r D e l t a , B r i t i s h Columbia ( 49° 1 2 ' 54 ' ' N , 1 23° 1 3 \3 ' ' W). ( F i g . 1). The meiobenthos on the c r e s t of a s i n g l e sand wave and i t s a s s o c i a t e d t i d e p o o l s ( F i g . 2) was sampled p e r i o d i c a l l y between January 1977 and January 1980. To e s t a b l i s h p a t t e r n s of s e a s o n a l change i n the b i o t a and i t s environment, two s t a k e d s i t e s were sampled at a p p r o x i m a t e l y f o r t n i g h t l y i n t e r v a l s from 4 Feb 1978 t o 22 Jan 1979. T h i s p e r i o d w i l l be r e f e r r e d t o as the year 1978. Longer term changes i n community c o m p o s i t i o n were i n v e s t i g a t e d by samp l i n g one s i t e , 'Sand', i n l a t e J a n uary f o r f o u r c o n s e c u t i v e y e a r s b e g i n n i n g i n 1977. P a t t e r n s of p r e d a t i o n on the meiobenthos were s t u d i e d by monthly a n a l y s e s of the gut c o n t e n t s of t i d e p o o l f i s h e s from May t o August 1979 and i n A p r i l and June 1980. A l l samples were taken when the stu d y s i t e was exposed by a f a l l i n g t i d e . A. Sampling the B i o t a Q u a n t i t a t i v e samples of the meiobenthos were o b t a i n e d by p u s h i n g p l a s t i c c o r e tubes made from 10 cc d i s p o s a b l e s y r i n g e s 5 cm i n t o the sediment. Each c o r e sampled 1.65 cm 2. Sediment was e x t r u d e d t h r o u g h the bottom of the tubes w i t h the p l u n g e r and c u t i n t o two s e c t i o n s , 0-1 cm (= ' s u r f a c e ' ) and 1-5 cm (= ' s u b s u r f a c e ' ) , which were t r e a t e d s e p a r a t e l y . D e f o r m a t i o n of the c o r e s by t h i s p rocedure was m i n i m a l . Samples were p l a c e d i n (R) W h i r l - p a c s w and t r a n s p o r t e d w i t h i n 2 hours t o the l a b o r a t o r y 9 F i g u r e 1. Map of the F r a s e r R i v e r d e l t a , B.C. showing l o c a t i o n of the study s i t e . Framed a r e a t o the west of Iona I s l a n d i s e n l a r g e d a t . r i g h t showing major t o p o g r a p h i c f e a t u r e s . Contours are e l e v a t i o n s i n meters above c h a r t datum. [ E l e v a t i o n s from a survey undertaken 16 Jan 1979 by Northwest H y d r o g r a p h i c Surveys L t d . , S u r r e y , B.C.; k i n d l y p r o v i d e d by Dr. C D . L e v i n g s ] . The study s i t e was l o c a t e d i n framed a r e a . .11 F i g u r e 2. D e t a i l of framed a r e a from F i g . V showing l o c a t i o n s of sand (=S a t +3.0m) and mud (=M a t +2.8m) sampling s i t e s ( t o p ) . . P r o f i l e (bottom) through study s i t e a l o n g A--B t r a n s e c t showing r e l a t i v e l o c a t i o n s of sand and mud s i t e s and n o r t h and south t i d e p o o l s . 12 " — ' 1 —i 1 0 50 100 150 200 DISTANCE FROM J E T T Y (m) 13 where they were f i x e d i n a 4% (v/v) s o l u t i o n of g l u t a r a l d e h y d e i n seawater. A d d i t i o n a l , ' q u a l i t a t i v e ' samples of sediment and macroalgae were c o l l e c t e d on v a r i o u s o c c a s i o n s and r e t u r n e d u n f i x e d t o the l a b o r a t o r y f o r v i s u a l o b s e r v a t i o n s of the f e e d i n g and b e h a v i o r of the meiobenthos. A l l o b s e r v a t i o n s were conducted a t room te m p e r a t u r e . T r i p l i c a t e sediment samples f o r q u a n t i t a t i v e d e t e r m i n a t i o n of p h o t o s y n t h e t i c pigments were c o l l e c t e d from each s i t e on each s a m p l i n g o c c a s i o n a f t e r 11 May 1978 w i t h c o r e tubes made from 50 cc d i s p o s a b l e s y r i n g e s (each sampled a s u r f a c e a r e a of 5.31 c m 2 ) . Cores were s p l i t i n t o s u r f a c e (0-1 cm) and s u b s u r f a c e (1-5 cm) l a y e r s , p l a c e d i n j a r s i n a c o o l e r and r e t u r n e d t o the l a b o r a t o r y f o r immediate a n a l y s i s . On d a t e s when ' r i p p l e ' f a u n a ! samples (see next s e c t i o n ) were c o l l e c t e d from the sand s i t e , t r i p l i c a t e t r o u g h and t r i p l i c a t e c r e s t samples were taken f o r pigment d e t e r m i n a t i o n s . W i n t e r l e v e l s of pigments were determined by samp l i n g b i - w e e k l y between 11 Jan and 27 A p r i l 1979. In a d d i t i o n t o q u a n t i t a t i v e samples, s m a l l q u a n t i t i e s of s u r f a c e sediments were c o l l e c t e d p e r i o d i c a l l y and r e t u r n e d u n f i x e d t o the l a b o r a t o r y f o r m i c r o s c o p i c e x a m i n a t i o n and c o a r s e d e t e r m i n a t i o n of m i c r o a l g a l s p e c i e s c o m p o s i t i o n ( k i n d l y p r o v i d e d by Dr. F.J.R. T a y l o r , Department of Oceanography, U.B.C.). 1 4 J _ . . Sampling d e s i g n M e i o b e n t h i c samples were c o l l e c t e d i n two c o n f i g u r a t i o n s : s h o r t t r a n s e c t s of c o n t i g u o u s c o r e s t o study f i n e - s c a l e p a t t e r n s a s s o c i a t e d w i t h s h o r t wavelength h y d r a u l i c bedforms (sand r i p p l e s ) and non-contiguous c o r e s p l a c e d a t randomly s e l e c t e d p o i n t s w i t h i n an area of 0.25 m2 t o study l a r g e r - s c a l e s p a t i a l p a t t e r n s and changes i n p o p u l a t i o n d e n s i t y w i t h t i m e . " R i p p l e " samples were c o l l e c t e d a t monthly i n t e r v a l s from 22 Jan 1 9 7 8 t o 22 Jan 1 9 7 9 a t the sand s i t e o n l y . On each o c c a s i o n 22 c o n t i g u o u s c o r e s were c o l l e c t e d i n an H-shaped c o n f i g u r a t i o n ( F i g . 3 ) . The f i r s t arm of the H was a t r a n s e c t of e i g h t c o n t i g u o u s c o r e s ( d e s i g n a t e d C r e s t samples 1 through 8) a l o n g a sand r i p p l e c r e s t ; the second arm, a p a r a l l e l t r a n s e c t of e i g h t c o n t i g u o u s c o r e s a l o n g the a d j a c e n t t r o u g h ( d e s i g n a t e d Trough samples 1 t h r o u g h 8 ) . A t h i r d t r a n s e c t of s i x c o r e s i n t e r s e c t e d the f i r s t two a t r i g h t ' a n g l e s thus c u t t i n g a c r o s s the r i p p l e p a t t e r n ( A c r o s s s a m p l e s ) . The c o r e s were t r e a t e d as d e s c r i b e d above. Random samples were c o l l e c t e d b i w e e k l y from the mud s i t e t h r o ugh 1 9 7 8 and monthly from the sand s i t e from 4 Feb 1 9 7 8 , a l t e r n a t i n g w i t h the r i p p l e samples. A complete l i s t of s a m p l i n g d a t e s and c o n f i g u r a t i o n s used a t each s i t e i s g i v e n i n Appendix 1. Twelve r e p l i c a t e c o r e samples were t a k e n w i t h i n a 0.25 m2 quadrat a t p o s i t i o n s w i t h i n a 1 0 0 - c e l l g r i d ; sample c o o r d i n a t e s were s e l e c t e d from a t a b l e of random numbers. 1 5 F i g u r e 3. Placement of c o n t i g u o u s c o r e s i n monthly sand r i p p l e s a m p l i n g . Each c o r e sampled a s u r f a c e a r e a of 1.65 cm 2. 17 S t a t i s t i c a l d e t e r m i n a t i o n of number of r e p l i c a t e random samples The minimum number of r e p l i c a t e s r e q u i r e d t o d e t e c t s e a s o n a l changes i n abundance of the dominant m e i o b e n t h i c t a x a (nematodes and h a r p a c t i c o i d copepods) was determined from p r e l i m i n a r y samples c o l l e c t e d from the two s i t e s on 23 Oct 1977. At each s i t e , 30 c o r e s were taken i n a 1 0 0 - c e l l , 0.25 m2 g r i d a t c o o r d i n a t e s chosen from a t a b l e of random numbers. The c o r e s were not s e c t i o n e d but were o t h e r w i s e t r e a t e d i n the u s u a l manner. A s t a n d a r d e r r o r of 20% of the p o p u l a t i o n mean (x) was chosen as the minimum a c c e p t a b l e l e v e l of p r e c i s i o n . The minimum number of r e p l i c a t e s (n) r e q u i r e d i s then g i v e n by (1 ) n = 25 s 2 / x 2 f o r a 20% e r r o r ( E l l i o t 1971) where s 2 i s the sample v a r i a n c e . The r e s u l t s f o r the p r e l i m i n a r y samples are g i v e n i n T able 1. A minimum of n i n e samples were r e q u i r e d t o e s t i m a t e d e n s i t i e s of the sand h a r p a c t i c o i d s and mud nematodes a t a p r e c i s i o n of 20%, but o n l y f o u r samples were r e q u i r e d f o r the mud h a r p a c t i c o i d s . A l t h o u g h 16 r e p l i c a t e s were r e q u i r e d f o r the sand nematodes, a compromise of 12 r e p l i c a t e s f o r each s i t e was chosen a f t e r a c o n s i d e r a t i o n of the time r e q u i r e d t o p r o c e s s samples. A l a r g e r number of r e p l i c a t e s (n = 22) was taken monthly at the sand s i t e and p r o v i d e d e s t i m a t e s of the nematode p o p u l a t i o n w i t h i n the r e q u i r e d p r e c i s i o n . 18 Table 1, C a l c u l a t i o n of the minimum number of r e p l i c a t e random samples (it) r e q u i r e d t o e s t i m a t e the mean p o p u l a t i o n s i z e of the m e i o b e n t h i c t a x a w i t h a p r e c i s i o n of 20%. SITE TAXON MEAN ( x ) ' VARIANCE ( s 2 ) ' * n Sand Harpact i c o i d s .102.4 3942.7. 9.4 Nematodes 68.8 •3073.1 16.2 Mud H a r p a c t i c o i d s 19.2 53.9 3.7 Nematodes 146.8 8140.4 9.4 estimated from counts of 30 Random cores (each 1.65 cm2 and 5 cm deep) w i t h i n 0.25 m taken on 23 Oct 1977. B. F i e l d o b s e r v a t i o n s of a b i o t i c environment J_. Annual c y c l e S a l i n i t y and temperature of the s t a n d i n g water i n the n o r t h and so u t h t i d e p o o l s ( F i g . 2) were r e c o r d e d w i t h a YSI Model 33 p o r t a b l e s a l i n i t y - t e m p e r a t u r e - c o n d u c t i v i t y meter ( Y e l l o w S p r i n g s Instrument Co., Y e l l o w S p r i n g s , Ohio, U.S.A.) imm e d i a t e l y b e f o r e b i o t i c samples were c o l l e c t e d . Sediment temperature p r o f i l e s were measured by pus h i n g a mercury thermometer v e r t i c a l l y i n t o the.sediment a d j a c e n t t o the s i t e marker and r e c o r d i n g the temperature a t 1 cm i n t e r v a l s . Two l a r g e c o r e s (each s a m p l i n g a s u r f a c e a r e a of 20 cm 2) were taken a t each s i t e ; one t o a depth of 15 t o 20 cm f o r measurement of 19 redox p o t e n t i a l s , the o t h e r t o a depth of 10 cm f o r sediment g r a i n s i z e a n a l y s i s . These c o r e s were capped t o p and bottom and r e t u r n e d i n t a c t t o the l a b o r a t o r y . Cores f o r g r a i n s i z e a n a l y s i s were s t o r e d f r o z e n b e f o r e a n a l y s i s ; redox p o t e n t i a l s were measured w i t h i n 2 t o 4 hours of c o l l e c t i o n . On a l l o c c a s i o n s when samp l i n g was conducted d u r i n g d a y l i g h t h o u r s , photographs of the s i t e were taken from a r e f e r e n c e l o c a t i o n on the causeway i n o r d e r t o document any l a r g e s c a l e changes i n topography which might occur through the course of the s t u d y , p a r t i c u l a r l y the m i g r a t i o n of l a r g e sand waves t h r o u g h the a r e a . 2. D i e l e y e l e S i g n i f i c a n t f l u c t u a t i o n s i n p h y s i c a l c o n d i t i o n s at Iona N o r t h were expected over a t i d a l c y c l e , e s p e c i a l l y d u r i n g summer when the f l a t i s exposed a t mid-day. The e f f e c t s of exposure.on the r e g u l a r l y m o n i t o r e d p h y s i c a l v a r i a b l e s were s t u d i e d by s h o r t - i n t e r v a l s a m p l i n g of the South t i d e p o o l on 19-20 J u l y 1978. D u r i n g the day, i r r a d i a n c e was measured on the sewage j e t t y a d j a c e n t t o Iona N o r t h a t 15-minute i n t e r v a l s w i t h a Quantum-Radiometer Photometer ( L i - C o r Model LI-185) equipped w i t h a c o s i n e quantum c o l l e c t o r . Temperature, s a l i n i t y and d i s s o l v e d oxygen c o n c e n t r a t i o n s were measured i n the t i d e p o o l s at 15-minute i n t e r v a l s d u r i n g the p e r i o d of emergence of the sand s i t e and a t 30-minute i n t e r v a l s d u r i n g submergence. S a l i n i t y and temperature were measured as d e s c r i b e d above; d i s s o l v e d oxygen c o n c e n t r a t i o n s were measured w i t h a G a l v a n i c 20 C e l l Oxygen A n a l y s e r ( P r e c i s i o n S c i e n t i f i c • C o . ) . C. L a b o r a t o r y t r e a t m e n t of samples J_. E x t r a c t i o n of the fauna At l e a s t 24 hours b e f o r e f a u n a l samples were s o r t e d they were s t a i n e d w i t h Rose B e n g a l . Organisms were s e p a r a t e d from p r e s e r v e d sediment by s h a k i n g the samples i n a j a r w i t h 0.2 jam-f i l t e r e d seawater and, a f t e r a l l o w i n g . t h e h e a v i e r p a r t i c l e s t o s e t t l e o u t , d e c a n t i n g the s u p e r n a t a n t and fauna through a 0.035 mm mesh. T h i s p r o c e d u r e was r e p e a t e d t h r e e times and the r e s i d u a l sediment.was scanned f o r u n e x t r a c t e d a n i m a l s . The m a t e r i a l r e t a i n e d on the mesh was washed i n t o an 8 x 12 cm Plexiglas®counting t r a y and examined a t X16 and x40 m a g n i f i c a t i o n s w i t h a Z e i s s d i s s e c t i n g m i c r o s c o p e . The d i s c r i m i n a t i o n of the fauna from r e s i d u a l sediment and d e t r i t u s was g r e a t l y f a c i l i t a t e d by the use of Rose Bengal which s t a i n e d a n i m a l t i s s u e deep r e d . The organisms r e t a i n e d on the mesh were s o r t e d t o major taxon (e.g. nematodes, o s t r a c o d s , o l i g o c h a e t e s ) and counted. Manayunkia a e s t u a r i n a , n u m e r i c a l l y the most abundant p o l y c h a e t e s p e c i e s of Sturgeon Bank ( L e v i n g s and C o u s t a l i n 1975), was counted s e p a r a t e l y from the o t h e r p o l y c h a e t e s p e c i e s . A l l h a r p a c t i c o i d copepods were p i c k e d from the samples and r e t a i n e d f o r f u r t h e r i d e n t i f i c a t i o n and a n a l y s i s . 21 2. Q u a n t i t a t i v e h a r p a c t i c o i d samples H a r p a c t i c o i d copepods ( c o p e p o d i t e s and a d u l t s ) were i d e n t i f i e d t o s p e c i e s and c o u n t e d . N a u p l i i of d i f f e r e n t s p e c i e s were d i f f i c u l t t o d i s c r i m i n a t e and so were combined i n t o a s i n g l e c a t e g o r y . Females b e a r i n g e x t e r n a l o v i s a c s were counted s e p a r a t e l y as an index of r e p r o d u c t i v e a c t i v i t y . S p e c i e s i d e n t i f i c a t i o n s were made u s i n g the p r o c e d u r e s recommended by C o u l l (1977). P r e l i m i n a r y i d e n t i f i c a t i o n s were based on the keys of Lang (1948,1965) and W e l l s (1976). O r i g i n a l d e s c r i p t i o n s were c o n s u l t e d f o r c o n f i r m a t i o n . On some o c c a s i o n s s i z e f r e q u e n c y d i s t r i b u t i o n s of the a d u l t and c o p e p o d i t e h a r p a c t i c o i d s were c o n s t r u c t e d . Body l e n g t h s were measured from the base of the r o s t r u m to the i n s e r t i o n of the c a u d a l rami ( C o u l l 1977). For permanent s t o r a g e , a n i m a l s were e i t h e r put i n t o 4% (v/v) f o r m a l i n / s e a w a t e r or mounted on microscope s l i d e s i n Hoyer's mounting medium ( C o u l l 1977). Whole mounts of a n i m a l s were used f o r gut c o n t e n t s a n a l y s e s (see c h a p t e r V I I I ) . 3_. Sediment pigment a n a l y s i s Sediment pigment c o n c e n t r a t i o n s were measured by a c o m b i n a t i o n of the s p e c t r o p h o t o m e t r i c methods of T i e t j e n (1966) and S t r i c k l a n d and Parsons (1972). Samples were t r a n s f e r r e d t o a mortar and ground f o r 5 minutes i n 30 ml of 90% (v/v) acetone i n d i s t i l l e d water w i t h a few drops of a s u s p e n s i o n of MgC03 t o speed e x t r a c t i o n of pigments. The sediment-acetone s l u r r y was 22 t r a n s f e r r e d t o a grad u a t e d , capped p l a s t i c c e n t r i f u g e tube and the t o t a l volume made up t o 50 ml w i t h a d d i t i o n a l 90% ac e t o n e . The samples were e x t r a c t e d f o r 2 hours i n the dark a t 5° C, warmed t o room temperature and c e n t r i f u g e d . A f t e r c e n t r i f u g a t i o n , the volume of the sediment p l u g was r e c o r d e d . A f r a c t i o n of the e x t r a c t was decanted i n t o a 1 cm p a t h c u v e t t e . E x t i n c t i o n s of the e x t r a c t s were measured a g a i n s t a 90% acetone blank i n a P e r k i n - E l m e r Double Beam Spectrophotometer (Model:Coleman 124D) a t wavelengths of 665 and 750 nm. For d e t e r m i n a t i o n of phaeo p h y t i n a c o n c e n t r a t i o n s , the samples were a c i d i f i e d by the a d d i t i o n of 10% HC1 and a f t e r 5 minutes the e x t i n c t i o n s were remeasured a t 665 and 750 nm. The c o n c e n t r a t i o n s of c h l o r o p h y l l a and ph a e o p h y t i n a were c a l c u l a t e d by the e q u a t i o n s of S t r i c k l a n d and Parsons (1972) (2) C h l o r o p h y l l a (mg-m"3) = [ 26.7(665o-665a)v ] / V (3) P h a e o p h y t i n a (mg-m"3) = [ 26.7(1.7{665a-665o})v ] / V where 665o and 665a a re the e x t i n c t i o n s a t 665 nm b e f o r e and a f t e r a c i d i f i c a t i o n ( c o r r e c t e d f o r e x t i n c t i o n s a t 750 nm), v i s the acetone volume i n ml, and V i s the sediment volume i n l i t r e s . The pigment c o n c e n t r a t i o n s i n g n r 2 were then (4) Pigment ( g - n r 2 ) = g - n r 3 - ( V / 1 0 0 0 ) - 1 8 8 3 23 Where 1883 i s a c o r r e c t i o n f a c t o r d e r i v e d by d i v i d i n g 1.0 m2 (= 10' cm 2) by the a r e a of sediment sampled by the c o r i n g d e v i c e (5.31 c m 2 ) . 4. Scanning E l e c t r o n M i c r o s c o p y (SEM) The. morphology, of the mouthparts of the dominant h a r p a c t i c o i d s p e c i e s a t Iona N o r t h and t h e i r major p r e d a t o r s was s t u d i e d w i t h SEM. A l l specimens f o r SEM were f i x e d i n a 4% (v/v) g l u t a r a l d e h y d e / s e a w a t e r s o l u t i o n and p o s t - f i x e d i n a 1% (v/v) s o l u t i o n of osmium t e t r o x i d e i n d i s t i l l e d water f o r 2 hour s . For c r i t i c a l p o i n t d r y i n g , h a r p a c t i c o i d s were r a p i d l y d e h y d r a t e d through a s e r i e s of i n c r e a s i n g l y c o n c e n t r a t e d a l c o h o l s o l u t i o n s (30, 50, 70, 85, 95, 100%). A f t e r 30 minutes, i n 100% EtOH the specimens were bathed i n a s e r i e s of EtOH: amyl a c e t a t e m i x t u r e s (3:1, 1:1, 1:3) f o r 15 minutes each and f i n a l l y i n 100% amyl a c e t a t e , the t r a n s i t i o n a l f l u i d , f o r 30 min u t e s . The specimens were then t r a n s f e r r e d t o envelopes made from n u c l e o p o r e f i l t e r s which were p l a c e d i n w i r e mesh b a s k e t s i n a CO 2 bomb. The bomb was f l o o d e d w i t h C 0 2 under p r e s s u r e (the C 0 2 r e p l a c e s the amyl a c e t a t e i n the sp e c i m e n s ) . The C 0 2 was e v a p o r a t e d a t 1400 p s i and 46° C. D r i e d copepods were mounted, v e n t r a l s i d e up, on s t u b s w i t h m e t a l t a p e . Mounted specimens were c o a t e d w i t h a 20 t o 40 nm l a y e r of g o l d i n a M i k r o s model VE10 Vacuum E v a p o r a t o r and observ e d w i t h a Cambridge S t e r e o s c a n Mark 2A SEM ( a c c e l e r a t i n g v o l t a g e = 20KV). Images were r e c o r d e d on E f k e (Adox) 120 f i l m . F i s h specimens were d i s s e c t e d p r i o r t o p o s t - f i x i n g and whole heads or 24 s e p a r a t e d jaws were mounted on s t u b s w i t h c o n d u c t i v e carbon g l u e but o t h e r w i s e r e c e i v e d the same tr e a t m e n t as the h a r p a c t i c o i d s . D. E n v i r o n m e n t a l measurements J _ . Redox p o t e n t i a l s The sediment c o r e f o r redox measurements was e x t r u d e d through the t o p of the c o r e tube i n t o a p r o t e c t i v e s l e e v e p r o v i d e d w i t h a l o n g i t u d n a l s l i t t hrough which an e l e c t r o d e c o u l d be i n s e r t e d . Measurements were made at 1 cm i n t e r v a l s down the c o r e . P o t e n t i a l s (Eh) were measured f o l l o w i n g F e n c h e l (1969) u s i n g an Accumet Model 320 pH meter f i t t e d w i t h a P l a t i n u m Combination E l e c t r o d e ( F i s h e r #13-639-82). The e l e c t r o d e was c a l i b r a t e d w i t h Z o B e l l ' s s o l u t i o n (Dybern e t a l . 1976). 2. Sediment g r a i n s i z e The sediment g r a i n s i z e c h a r a c t e r i s t i c s of the two s i t e s were de t e r m i n e d by s i e v e a n a l y s i s (Buchanan 1971). Samples were d r y - s i e v e d t h r o u g h a n e s t e d s e r i e s of Canada S t a n d a r d s i e v e s (1.0, 0.595, 0.355, 0.180, 0.075, and 0.053 mm). The m a t e r i a l r e t a i n e d on each s c r e e n was weighed and the weight of the s u b s i e v e m a t e r i a l was e s t i m a t e d by d i f f e r e n c e . Median p a r t i c l e d i a m e t e r and s o r t i n g ( q u a r t i l e d e v i a t i o n ) were d e t e r m i n e d g r a p h i c a l l y from c u m u l a t i v e f r e q u e n c y c u r v e s (Buchanan 1971). 25 The s i n g l e most i m p o r t a n t sediment c h a r a c t e r i s t i c t o which m e i o b e n t h i c organisms respond i s the p e r c e n t of s i l t - c l a y s i z e d p a r t i c l e s ( F e n c h e l 1 9 6 9 ) ; the c o n t r i b u t i o n of t h i s f r a c t i o n t o the t o t a l d r y weight of the sediment sample was measured from monthly samples. The s u r f a c e cm was s e c t i o n e d from f r o z e n c o r e s and d r i e d a t 60 p C t o a c o n s t a n t w e i g h t . Ten t o 15 g of the s u r f a c e m a t e r i a l was w e t - s i e v e d on a 0.064 mm s c r e e n . The f r a c t i o n r e t a i n e d on the mesh was d r i e d t o a c o n s t a n t weight. The f r a c t i o n of f i n e m a t e r i a l i n the sample was e s t i m a t e d by d i f f e r e n c e and e x p r e s s e d as a p e r c e n t of the t o t a l d r y weight of the sample. E.' Data a n a l y s i s S p e c i f i c s of d a t a a n a l y s i s w i l l be p r o v i d e d i n the b r i e f methods s e c t i o n i n each c h a p t e r . U n l e s s o t h e r w i s e s p e c i f i e d , the f o l l o w i n g c o n v e n t i o n s were f o l l o w e d . C a l c u l a t i o n s were performed on the UBC Amdahl computer u s i n g F o r t r a n programs w r i t t e n by the a u t h o r or programs from the S t a t i s t i c a l Package f o r the S o c i a l S c i e n c e s . To reduce the number of t r a n s c r i p t i o n e r r o r s i n e v i t a b l e w i t h a l a r g e d a t a base, where p o s s i b l e , programs were d e s i g n e d t o m a n i p u l a t e raw d a t a and p r e s e n t r e s u l t s i n t a b u l a r form and/or p l o t s . Where d a t a t r a n s f o r m a t i o n s were n e c e s s a r y , a ln(x+1) t r a n s f o r m a t i o n was used. The s t a n d a r d e r r o r of the mean [v s ^ / n ] ( E l l i o t 1971) was c a l c u l a t e d as a measurement of v a r i a n c e among samples. Where graphed v a l u e s were c a l c u l a t e d from more than one sample, the p o i n t s r e p r e s e n t the mean ± 1 s t a n d a r d e r r o r . In t e s t s of 26 s i g n i f i c a n c e , n u l l hypotheses were r e j e c t e d i f the p r o b a b i l i t y t h a t the d i f f e r e n c e between observed and e x p e c t e d v a l u e s was due t o chance was l e s s than 5%. 27 I I I . THE STUDY SITE AND ITS BIOTA A. I n t r o d u c t i o n t o the Iona N o r t h h a b i t a t . The a c t i v e d e l t a f r o n t of the F r a s e r R i v e r c o n s i s t s of two broad t i d a l f l a t s , Sturgeon Bank t o the n o r t h and R o b e r t s Bank to the s o u t h , which form the i n t e r f a c e between the r i v e r and the S t r a i t of G e o r g i a ( F i g . 1a). The main p l a t f o r m of the f l a t s e xtends seawards f o r an average of 6 Km w i t h a mean s l o p e of 0.08° (Hoos and Packman 1974). The f l a t s a re mantled m a i n l y w i t h w e l l - s o r t e d medium t o f i n e sands (0.35 t o 0.125 mm) ( L u t e r n a u e r and Murray 1973). The g e n e r a l l y f e a t u r e l e s s topography of the f l a t s i s i n t e r r u p t e d o n l y by t i d a l - c h a n n e l s and h y d r a u l i c bedforms ( L u t e r n a u e r and Murray 1973). The h y d r a u l i c bedforms on Sturgeon Bank occur a t two s c a l e s . The dominant f e a t u r e s are the l a r g e , p e r s i s t e n t bedforms. F o l l o w i n g Swinbanks (1979) I w i l l r e f e r t o those f e a t u r e s w i t h wavelengths on the o r d e r of 100 m as "sand waves" [='sand s w e l l s ' of L u t e r n a u e r (1980)] ( F i g . 4 a ) . The sand waves on n o r t h e r n Sturgeon Bank p r o b a b l y o r i g i n a t e d i n w i n t e r storms (see d i s c u s s i o n i n Swinbanks 1979), and a t Iona N o r t h have p e r s i s t e d w i t h no n o t i c e a b l e change i n p o s i t i o n from January 1977 t o January 1 9 8 1 . At a much s m a l l e r s c a l e , w i t h wavelengths on the o r d e r of 10 cm, a r e ephemeral wave- and c u r r e n t -g e n e r a t e d bedforms which I w i l l r e f e r t o as 'sand r i p p l e s ' ( F i g . 4b); they a r e a s h o r t - l i v e d ( l a s t i n g s e v e r a l hours) but h i g h l y p r e d i c t a b l e source of e n v i r o n m e n t a l h e t e r o g e n e i t y on the sand wave c r e s t s . The sand r i p p l e s a re g e n e r a l l y a s y m m e t r i c a l 28 F i g u r e 4. Photographs of the Iona N o r t h study s i t e a. Sand wave c r e s t , f a c i n g . south-west w i t h j e t t y i n background. Note sand r i p p l e s . [14 Oct 1978] b. Sand r i p p l e s . Core tubes a re samples C1-C3. [ 18 March 1978] c. R i p - r a p of j e t t y ( l a r g e , i r r e g u l a r s t o n e s ) w i t h s o u t h p o o l i n f o r e g r o u n d . [11 J u l y 1978] d. Study s i t e ( f a c i n g n o r t h - w e s t ) from j e t t y w i t h s o u t h p o o l i n f o r e g r o u n d . Large s t a k e on f i r s t sand wave c r e s t marks sand s i t e . . S m a l l s t a k e behind marks mud s i t e a t edge of n o r t h p o o l . [11 May 1978] e. Z o s t e r a a m e r i c a n a , U l v a sp. and t u b e - f o r m i n g N a v i c u l o i d s (brown t u f t s ) i n n o r t h p o o l . . [27 A p r i l 1979] b 32 l a n d w a r d ( i . e . t h e d i s t a n c e from c r e s t t o t r o u g h i s l e s s on t h e l a n d w a r d t h a n on the. . seaward s i d e of t h e r i p p l e ) w h i c h i n d i c a t e s t h a t t h e y a r e formed on t h e f l o o d t i d e ( K e l l e r h a l s and Murray 1969). They p e r s i s t u n t i l d e s t r o y e d by wave a c t i o n i n t h e f i r s t few m i n u t e s o f i n u n d a t i o n of t h e s u c c e e d i n g t i d a l c y c l e . The n a t u r a l t o p o g r a p h y o f t h e s a n d f l a t of Iona N o r t h and t h e man-made sewage . j e t t y p r o v i d e t h r e e d i s t i n c t t y p e s of b e n t h i c h a b i t a t . The l a r g e , i r r e g u l a r s t o n e s ( " r i p - r a p " ) of t h e sewage j e t t y . p r o v i d e a' s o l i d s u b s t r a t e f o r c o l o n i z a t i o n by a t t a c h e d m a c r o a l g a e , s e s s i l e i n v e r t e b r a t e s and a s s o c i a t e d forms ( F i g . 4 c ) . The c r e s t s of t h e s a n d waves a r e an u n s t a b l e , s h i f t i n g s u b s t r a t e , p o o r l y c o l o n i z e d by m a c r o i n v e r t e b r a t e s . The t r o u g h s of t h e sand waves a r e s t a b i l i z e d by f i n e s e d i m e n t s d e p o s i t e d d u r i n g t h e a n n u a l f r e s h e t of t h e F r a s e r . These t r o u g h s r e m a i n c o v e r e d by a s h a l l o w l a y e r of water a t low t i d e and so form n a t u r a l t i d e p o o l s ( F i g . 4d) w h i c h h a r b o r a r i c h and d i v e r s e f a u n a . The s o l i d s u b s t r a t e o f t h e j e t t y m a i n t a i n s a t y p i c a l , z o n e d a s s e m b l a g e of m a c r o b e n t h o s . The d o m i n a n t m a c r o p h y t e s a r e P o r p h y r a spp., F u c u s d i s t i c h u s , E n t e r o m o r p h a sp. and U l v a s p . . The s e s s i l e i n v e r t e b r a t e community i s d o m i n a t e d by t h e m u s s e l M y t i l u s e d u l i s and t h e b a r n a c l e B a l a n u s q l a n d u l a . L a r g e numbers of amphipods, m o s t l y Eogammarus c o n f e r v i c o l u s , f e e d on t h e a l g a e . A l a r g e community o f c r a b s , H e m i g r a p s u s o r e g o n e n s i s , l i v e s among t h e a l g a e and s m a l l s t o n e s . The major p r e d a t o r s on t h e m a c r o i n v e r t e b r a t e s a r e r a t s , R a t t u s n o r v e g i c u s , and 33 p o p u l a t i o n s of s h o r e b i r d s , e s p e c i a l l y h e r r i n g g u l l s , L a r u s  a r g e n t a t u s , and g r e a t b l u e h e r o n s , Ardea h e r o d i a s . The b i r d s f e e d m a i n l y on the' t i d e p o o l f i s h ' (Hoos and Packman 1974; Brown et a l . 1977) . The t i d e p o o l s a r e s p a r s e l y v e g e t a t e d through most of the y e a r . In l a t e w i n t e r and s p r i n g , most of the a v a i l a b l e h a r d s u b s t r a t e ( s m a l l s t o n e s and fragments of d r i f t wood) i s c o l o n i z e d by l a r g e t u f t s of a c o l o n i a l diatom, N a v i c u l a sp. ( F i g . 4 e ) . Amphipods, Eogammarus c o n f e r v i c o l u s and Corophium spp. and the h a r p a c t i c o i d copepod, H a r p a c t i c u s u n i r e m i s , a r e v e r y abundant i n the t u f t s u n t i l l a t e May when the diatom d i s a p p e a r s from the p o o l s . In summer, the dominant macrophyte of the p o o l s i s U l v a sp. which accumulates i n J u l y and August. At the b e g i n n i n g of o b s e r v a t i o n s , January 1977, t h e r e were no r o o t e d macrophytes i n the p o o l s . In the s p r i n g of 1978 the n o r t h p o o l was c o l o n i z e d by the temperate s e a g r a s s , Z o s t e r a  americana ( F i g . 4e) which, by the summer of 1980, had e s t a b l i s h e d a p a t c h y but a p p a r e n t l y permanent bed i n the n o r t h p o o l and had s p r e a d a l s o t o the s o u t h p o o l . T h i s c o l o n i z a t i o n i s under study by Dr. P.G. H a r r i s o n , U.B.C. The s m a l l e e l g r a s s bed and i t s a s s o c i a t e d e p i p h y t e s s h o u l d p r o v i d e a t t r a c t i v e c o v e r f o r both macro- and m e i o b e n t h i c i n v e r t e b r a t e s and f i s h . The dominant m a c r o i n v e r t e b r a t e s of the t i d e p o o l s a r e the amphipods mentioned above, the t u b i c o l o u s p o l y c h a e t e s Manayunkia a e s t u a r i n a and P y g o s p i o e l e g a n s , the b i v a l v e m o l l u s c Macoma b a l t h i c a , the cumacean, Cumel l a sp. and mysids. Three s p e c i e s of f i s h i n h a b i t the p o o l s , and are most common i n 34 summer: the arrow goby, C l e v e l a n d i a i o s , and j u v e n i l e P a c i f i c s t a g h o r n s c u l p i n , L e p t o c o t t u s armatus, a re the most common but j u v e n i l e s t a r r y f l o u n d e r , P l a t i c h t h y s s t e l l a t u s , may be found o c c a s i o n a l l y ( p e r s o n a l o b s e r v a t i o n s through 1978-1980). As s t a t e d above, the sand wave c r e s t ( F i g . 4a) i s a s h i f t i n g , u n s t a b l e h a b i t a t f o r macrobenthic c o l o n i z a t i o n . U n l i k e the t r o u g h s , the wave c r e s t s l i e exposed f o r up t o 6 hours per day, a l t h o u g h they never c o m p l e t e l y d r y . Macroalgae are never found on the wave c r e s t a l t h o u g h , as w i l l be d i s c u s s e d l a t e r , m i c r o a l g a e are abundant. The m a c r o i n v e r t e b r a t e community.of the c r e s t s i s i m p o v e r i s h e d , both i n terms of s p e c i e s r i c h n e s s and abundance. Manayunkia a e s t u a r i n a were never .found on the c r e s t , a l t h o u g h o t h e r p o l y c h a e t e s and Macoma  b a l t h i c a o c c u r r e d i n s m a l l numbers d u r i n g a r e s t r i c t e d p a r t of the y e a r . The geology and e c o l o g y of the F r a s e r R i v e r e s t u a r y were reviewed by Hoos and Packman (1974). The oceanography and ec o l o g y of the n e i g h b o r i n g S t r a i t of G e o r g i a were re v i e w e d by Parsons (1979). More d e t a i l e d i n f o r m a t i o n on the geomorphology of the banks and s e d i m e n t a t i o n p r o c e s s e s on the d e l t a i s a v a i l a b l e i n Mathews and Shepard (1962), L u t e r n a u e r and Murray (1973), L u t e r n a u e r (1980) and M i l l i m a n (1980). F u r t h e r i n f o r m a t i o n on i n v e r t e b r a t e b i o l o g y i s a v a i l a b l e i n Bawden e t a l . (1973), O t t e and L e v i n g s (1975), L e v i n g s and C o u s t a l i n (1975), Brown et a l . (1977), McGreer (1979), Sharma (1979), and Pomeroy and L e v i n g s (1980). 35 B. C h o i c e of s i t e f o r study of the meiobenthos From p r a c t i c a l c o n s i d e r a t i o n s , the n o r t h e r n Sturgeon Bank s i t e p r o v i d e d an e x c e l l e n t l o c a t i o n f o r the study of m e i o b e n t h i c communities. The s i t e was c o n v e n i e n t l y l o c a t e d ( o n e - h a l f hour d r i v e from UBC). The sewage j e t t y (beyond a l o c k e d gate) p r o v i d e d c o n t r o l l e d a c c e s s t o the f l a t s and so the s i t e c o u l d be marked and r e v i s i t e d f r e q u e n t l y over s e v e r a l y e a r s w i t h l i t t l e p o s s i b i l i t y t h a t i t would be d i s t u r b e d . F i n a l l y , a l t h o u g h i n t e r e s t i n the b i o l o g y and e c o l o g y of the e s t u a r y had i n c r e a s e d i n the e a r l y p a r t of the 1970's (see Hoos and Packman 1974) t h e r e had been no s y s t e m a t i c study of i t s meiobenthos. From t h e o r e t i c a l c o n s i d e r a t i o n s , the p a r t i c u l a r c l a s s e s and s c a l e s of h a b i t a t h e t e r o g e n e i t y at Iona N o r t h p r o v i d e d a unique o p p o r t u n i t y t o study b i o l o g i c a l i n t e r a c t i o n s i n a n a t u r a l m e i o b e n t h i c community. Because the s i t e was l o c a t e d i n an e s t u a r i n e i n t e r t i d a l zone, i t s m e i o b e n t h i c community was expected t o be r i c h e r i n numbers and poorer i n s p e c i e s than the communities of comparable marine s i t e s ( C o u l l 1973). The p h y s i c a l v a r i a b l e s which p l a y the most i m p o r t a n t r o l e i n d e t e r m i n i n g the d i s t r i b u t i o n s of m e i o b e n t h i c s p e c i e s are those r e l a t i n g t o sediment t e x t u r e ( P o l l o c k 1971; C o u l l and F l e e g e r 1977; F e n c h e l 1978; M a r c o t t e 1977a; Moore 1979a and b; I v e s t e r 1980). At Iona N o r t h , the j u x t a p o s i t i o n of a sandy (wave c r e s t ) and a s i l t y (wave trough) h a b i t a t a l l o w e d the study of two v e r y d i s t i n c t m e i o b e n t h i c communities s i m i l a r t o t h a t conducted by C o u l l and F l e e g e r (1977) but w i t h i n a r e s t r i c t e d l o c a t i o n . 36 P h y s i c a l c o n d i t i o n s such as s a l i n i t y and temperature were e x p e c t e d t o be s i m i l a r f o r both sediment t y p e s . Two s i t e s were chosen t o be c l o s e t o g e t h e r but s t i l l on d i s t i n c t sediment t y p e s . The sand s i t e was a t +3.0 m e l e v a t i o n on the peak of a sand wave c r e s t ( F i g . 2 ) ; i t s sediment was w e l l s o r t e d medium sand. The mud. s i t e was l o c a t e d 20.4 m seaward a t the edge of the wave t r o u g h i n the n o r t h t i d e p o o l ( e l e v a t i o n = +2.8 m) ( F i g . 2 ) ; i t s sediments were an uncompacted, p o o r l y s o r t e d m i x t u r e of sand, f i n e s i l t and o r g a n i c d e t r i t u s . S e v e r a l i m p o r t a n t d i f f e r e n c e s were known a p r i o r i t o e x i s t between the sand and the mud s i t e s . F i r s t was the o b v i o u s d i f f e r e n c e i n sediment t e x t u r e . Second, the sand s i t e had no s i g n i f i c a n t m a c r o i n v e r t e b r a t e community. T h i r d , d u r i n g p e r i o d s of emergence, the most l i k e l y meiofauna p r e d a t o r s , the s m a l l f i s h , were l i m i t e d t o the muddy t i d e p o o l s . F i n a l l y , the sand s i t e was d i v i d e d i n t o p r e d i c t a b l e and w e l l -d e f i n e d m i c r o h a b i t a t s by the sand r i p p l e s w h i l e f o r most of the year the mud s i t e appeared f e a t u r e l e s s . C. S e a s o n a l V a r i a t i o n i n E n v i r o n m e n t a l F a c t o r s J _ . T i d e s and Exposure The t i d e s on the F r a s e r D e l t a are a mixed, s e m i - d i u r n a l type w i t h i n e q u a l i t i e s i n both h e i g h t and t i m i n g of s u c c e e d i n g h i g h and low w a t e r s . These i n e q u a l i t i e s v a r y w i t h l u n a r d e c l i n a t i o n and a r e maximal when the moon has passed i t s minimum d e c l i n a t i o n (Defant 1 9 6 1 ) . The mean t i d a l range f o r P t . 37 A t k i n s o n , t h e c l o s e s t l o c a t i o n f o r w h i c h t a b u l a t e d t i d e d a t a a r e a v a i l a b l e , i s 3.3 m (HHW = 4 . 9 m, LLW = 0.1 m, HLW = 3.4 m, LHW = 3.1 m) ( C a n a d i a n T i d e and C u r r e n t T a b l e s . V o l . 5 1978). At an e l e v a t i o n of +3.0 m, t h e san d s i t e i s l o c a t e d i n t h e upper r n i d - i n t e r t i d a l z o n e . The t i m i n g and d u r a t i o n of emergence of t h e s i t e v a r i e s b o t h w i t h t h e m o n t h l y t i d a l v a r i a t i o n and s e a s o n a l l y . D e p e n d i n g on t h e t i m e of month t h e s i t e i s e i t h e r u n c o v e r e d ( f o r up t o 9 h o u r s ) by o n l y one low water i n e a c h 24.8-hour p e r i o d or i s u n c o v e r e d by b o t h low w a t e r s ( f o r as l o n g as 4 h o u r s each) i n e v e r y 24.8-hour p e r i o d . Due t o t h e l o c a l t o p o g r a p h y w h i c h c a u s e s r e t e n t i o n of water i n t h e t r o u g h a t low t i d e t h e mud s i t e i s o n l y r a r e l y c o m p l e t e l y u n c o v e r e d a t low w a t e r . The t i m i n g of l o w e s t low water v a r i e s s e a s o n a l l y . Hence t h e maximum p e r i o d of emergence o c c u r s n e a r mid-day i n summer and nea r m i d - n i g h t i n w i n t e r ( F i g . 5 ) ; b e f o r e noon i n s p r i n g and a f t e r noon i n f a l l . The s i g n i f i c a n c e of t h e s e complex t i d a l p a t t e r n s f o r t h e Iona N o r t h m e i o b e n t h o s w i l l be d i s c u s s e d f u r t h e r i n t h i s and s u b s e q u e n t c h a p t e r s . Two major i m p l i c a t i o n s s h o u l d be m e n t i o n e d h e r e . F i r s t , t h e d a i l y t i d a l v a r i a t i o n s w i l l a m p l i f y v a r i a t i o n s i n o t h e r p h y s i c a l f a c t o r s , p a r t i c u l a r l y i n summer. F o r a c o m p r e h e n s i v e r e v i e w o f t h e e f f e c t s of emergence on t h e p h y s i o l o g y o f i n t e r t i d a l i n v e r t e b r a t e s see N e w e l l ( 1 9 7 9 ) . S e c o n d , t h e san d s i t e i s e f f e c t i v e l y i s o l a t e d f r o m t h e s u r r o u n d i n g b e n t h i c h a b i t a t s f o r a s i g n i f i c a n t p r o p o r t i o n of e a c h day. T i d a l emergence, t h e r e f o r e , e s s e n t i a l l y " c a g e s " t h e sand from b o t h p r e d a t o r s and c o m p e t i t o r s on a r e g u l a r and 38 F i g u r e 5. T i d e c u r v e s from t a b u l a t e d p r e d i c t e d t i d e data f o r P t . A t k i n s o n , B . C . f o r 18-21 -July 1978 and 20-23 January 1977 showing s e a s o n a l v a r i a t i o n i n t i m i n g of- lower low water. H o r i z o n t a l bars i n d i c a t e approximate d u r a t i o n of exposure of the sand s i t e (+3.0m). Exposure o c c u r r e d near mid-day i n summer and near m i d - n i g h t i n w i n t e r . •: T a b u l a t e d t i d e h e i g h t . 5 r i 4 • EC ' < . I U Ul ( • < V 12 18 0 6 12 18 0 6 12 T I M E O F D A Y P S T (h) I S J U L Y 18 I S J U L Y S O J U L Y 0 12 18 2 1 J U L Y h I CD UJ I UJ • 3 ^ r 1 12 18 S O J A M 6 12 18 0 6 12 18 T I M E O F D A Y P S T (h) 2 1 J A N 2 2 J A I M 12 18 2 3 J A I M GO 40 p r e d i c t a b l e s c h e d u l e . 2. S a l i n i t y S e a s o n a l v a r i a t i o n i n s a l i n i t y measured i n the Iona N o r t h t i d e p o o l s i n 1978 ( F i g . 6) f o l l o w e d the s e a s o n a l p a t t e r n i n F r a s e r . R i v e r d i s c h a r g e (Hoos and Packman 1974). H i g h e s t s a l i n i t i e s (20.0 .to 27.3 ppt) were r e c o r d e d i n f a l l and w i n t e r when r i v e r r u n o f f was low. S a l i n i t i e s of deeper S t r a i t , of G e o r g i a waters i n the v i c i n i t y of the r i v e r a re between 28 and 31 ppt (Parsons 1979). The f a l l and w i n t e r t i d e p o o l s a l i n i t i e s a t Iona N o r t h i n d i c a t e , t h e r e f o r e , d i l u t i o n b o th by the F r a s e r and by r a i n f a l l . Between May and June s a l i n i t i e s f e l l below 20.0 ppt w i t h i n c r e a s e d r i v e r d i l u t i o n d u r i n g the f r e s h e t . A l t h o u g h 1978 was a year of lower than average f r e s h e t f l o w (Chapman 1979) s a l i n i t i e s remained low from June u n t i l l a t e September ( F i g . 6 ) . The minimum s a l i n i t y r e c o r d e d i n t h i s p e r i o d was 6.3 ppt i n the south p o o l on 4 Aug. The s e a s o n a l p a t t e r n of s a l i n i t y f l u c t u a t i o n was the same f o r both t i d e p o o l s a l t h o u g h on any g i v e n day t h e i r s a l i n i t i e s d i f f e r e d by as much as 3.5 p p t . 3_. Temperature Water temperature i n the Iona N o r t h t i d e p o o l s i n 1978 v a r i e d s e a s o n a l l y i n a p p r o x i m a t e l y the o p p o s i t e p a t t e r n t o s a l i n i t y ( F i g . 6 ) . Lowest t e m p e r a t u r e s (-0.5 and 0.0° C) were r e c o r d e d on 27 Dec. Temperatures remained below 10° C from the 41 F i g u r e 6. S e a s o n a l v a r i a t i o n i n s a l i n i t y and temperature measured i n the Iona N o r t h t i d e p o o l s t h r o u g h the study p e r i o d . Readings were taken i n s t a n d i n g water i m m e d i a t e l y b e f o r e c o l l e c t i o n of f a u n a l samples. 42 U J DC D 32.0 h Z CC - J £ 16.0 | -H- 8.0 0.0 SOUTH POOL {_ I- 2 4 . 0 h A A A/ \ v x^ ^ A A A - A - ^ -I 1 1 I • A ^ s / x i \ . A A A — A i A A > A ^ A / v i , A A - A A ' ' V / X ' I x I J L 'A A J L F M A M J J • A S O N D J 1978 79 L U 32.0 QC > H 24.0 —' CL 16.0 f- 8.0 0.0 NORTH POOL h • S % o / \ .a ' q \ • / .Q l -B ^ H " - T ° C -i 1 1 1 i • 'a / • • J L F M A M J J A S O N D J 1978 7 9 43 b e g i n n i n g of November u n t i l e a r l y March. • From l a t e A p r i l t h r o ugh the end of September the temperature remained above 15° C. The h i g h e s t water temperature r e c o r d e d was 28° C i n the s o u t h p o o l , 8 June. As would be expected f o r an i n t e r t i d a l s i t e , the observed annual temperature range a t Iona N o r t h , 0.5 t o 28°C, i s g r e a t e r than the range r e p o r t e d by Parsons (1979) f o r the s u r f a c e waters of the S t r a i t of G e o r g i a i n the v i c i n i t y of the F r a s e r R i v e r , 7 t o 22°C. Temperatures i n the upper few cm of sediment a t the sand and mud s i t e showed a p a t t e r n of s e a s o n a l v a r i a t i o n s i m i l a r t o the t i d e p o o l t e m p e r a t u r e s ( F i g . 7 ) . Sediment t e m p e r a t u r e s were o f t e n 1 t o 2° C h i g h e r i n w i n t e r and lower i n summer than c o r r e s p o n d i n g t i d e p o o l t e m p e r a t u r e ; however, g i v e n the 28.5° C range of temperature o b s e r v e d t h i s i s a minor e f f e c t . Marked t h e r m o c l i n e s i n sediment p r o f i l e s (e.g. 25 May, mud, F i g . 7) were observed more f r e q u e n t l y i n mud than i n sand but a g a i n , temperature d i f f e r e n c e s were s m a l l over the t o p 5 cm ( F i g . 7 ) . 4. Redox Redox p r o f i l e s ( F i g s . 7 and 8) were d i s t i n c t l y d i f f e r e n t a t the two s i t e s and a l s o showed s e a s o n a l v a r i a t i o n . Reducing c o n d i t i o n s , i n d i c a t e d by Eh < +100 mV ( F e n c h e l 1969 ) , were never o b s e r v e d i n the upper sediment l a y e r s a t the sand s i t e . P o t e n t i a l s i n the upper cm u s u a l l y exceeded +300 mV. A redox p o t e n t i a l d i s c o n t i n u i t y l a y e r (RPD) where Eh v a l u e s f e l l r a p i d l y w i t h depth was u s u a l l y d i s c e r n a b l e between 2 and 6 cm below the sediment s u r f a c e ; however, n e g a t i v e p o t e n t i a l s were 44 F i g u r e 7. Temperature (T; s o l i d t r i a n g l e s ) and redox (Eh; s o l i d s q u ares) p r o f i l e s from the sand (a) and mud (b) s i t e s on s e l e c t e d s a m p l i n g dates..' Dashed l i n e i n d i c a t e s +100 mV ( l i m i t of f r e e oxygen). 46 F i g u r e 8. Redox c o n d i t i o n s i n the t o p 10cm of sediment at the sand (a) and mud (b) s i t e s t h r ough the study p e r i o d . I s o p l e t h s connect depths w i t h e q u a l Eh r e a d i n g s . The +100 mV i s o p l e t h i s i n d i c a t e d w i t h a d a s h e d . l i n e . 47 48 never r e c o r d e d i n the sand. These o b s e r v a t i o n s are s u p p o r t e d by the c o n c l u s i o n of F e n c h e l (1969) t h a t w e l l s o r t e d medium sands low i n both f i n e m a t e r i a l s and o r g a n i c matter are o x i d i z e d t h r o u g h o u t . The o x i d i z e d c o n d i t i o n s of the sand s i t e were i n sharp c o n t r a s t t o the redox p r o f i l e s o b s e r v e d i n the p o o r l y s o r t e d , s i l t y sediments of the mud s i t e ( F i g s . 7 and 8 ) . P o t e n t i a l s a t 1 cm depth were c o n s i d e r a b l y lower than.1 cm r e a d i n g s i n the sand c o r e s . Reducing c o n d i t i o n s (Eh < +100 mV) were g e n e r a l l y , found w i t h i n 5 cm of the sediment s u r f a c e ( F i g . 8 ) ; on 25 May the sediments were r e d u c i n g a t the 1 cm l e v e l . A marked RPD was always p r e s e n t a l t h o u g h i t s depth m i g r a t e d s e a s o n a l l y . In w i n t e r the RPD was l o c a t e d from 4 t o 6 cm below the mud s u r f a c e . The RPD rose toward the sediment s u r f a c e (perhaps due t o i n c r e a s e d o r g a n i c i n p u t ) i n the s p r i n g and remained near the s u r f a c e u n t i l November when i t sank ( p r o b a b l y due t o i n c r e a s e d storm a c t i v i t y ) . P o t e n t i a l s i n the upper l a y e r were h i g h e r i n e a r l y summer i n f r e s h l y d e p o s i t e d s i l t - c l a y due p a r t l y t o the i n c r e a s e d a c t i v i t y of p o l y c h a e t e s a t t h a t t i m e . E x t r e m e l y low p o t e n t i a l s were r e c o r d e d from August onwards under t h i s b l a n k e t of f i n e , c o h e s i v e m a t e r i a l which p r e v e n t e d the p e n e t r a t i o n of oxygen. The p o r t i o n of t h e sediment c o r e s below 3 cm was u s u a l l y b l a c k and s m e l l e d s t r o n g l y of H 2S. 49 5_. Sediment g r a i n s i z e No s i g n i f i c a n t changes i n sediment t e x t u r e were observed at the sand s i t e t h r o u g h the c o u r s e of the study ( F i g . 9 ) . The p r o p o r t i o n of f i n e p a r t i c l e s (<• 0.064 mm d i a m e t e r ) i n the s u r f a c e cm of sand ranged from 0.99 % (June 1978) t o 3.55 % (Feb r u a r y 1978); the mean v a l u e f o r 10 months from March t o December 1978 was 1.21 ± 0.06 % f i n e s by w e i g h t . S l i g h t i n c r e a s e s i n - s i l t - c l a y r e c o r d e d i n F e b r u a r y 1978 and January 1979 (1.85 %) were p r o b a b l y due t o f i n e m a t e r i a l t r a n s p o r t e d from the t r o u g h t o the c r e s t by w i n t e r storm waves. In marked c o n t r a s t t o the u n i f o r m i t y of sediment t e x t u r e a t the sand s i t e t h r o u g h 1978, l a r g e changes i n t e x t u r e of the s u r f i c i a l sediment o c c u r r e d a t the mud s i t e ( F i g . 9 ) . From November t o March, the sediment was a p o o r l y s o r t e d m i x t u r e of sand, s i l t - c l a y and d e t r i t u s . Throughout t h i s p e r i o d , the pe r c e n t a g e of f i n e m a t e r i a l , 6.3 t o 15.45%, was g r e a t e r than the upper l i m i t f o r the e s t a b l i s h m e n t of an i n t e r s t i t i a l fauna (3 t o 4 % ) ( F e n c h e l 1969). The r e l a t i v e c o a r s e n e s s of mud s u r f a c e sediments i n w i n t e r was p r o b a b l y due t o the r e s u s p e n s i o n of f i n e m a t e r i a l and the import of sand from the sand wave c r e s t . W i t h calmer c o n d i t i o n s i n l a t e s p r i n g , the mud sediments were much f i n e r i n A p r i l and May. The c o n t r i b u t i o n of f i n e s d e c r e a s e d a g a i n i n May and June due t o b i o g e n i c r e w o r k i n g by i n c r e a s e d p o p u l a t i o n s of p o l y c h a e t e s , e s p e c i a l l y P y g o s p i o  e l e g a n s , a s m a l l s p i o n i d which i n c o r p o r a t e s f i n e sediment p a r t i c l e s i n t o i t s membranous tubes (Gosner 1971), and t u b i c o l o u s o l i g o c h a e t e s (see s e c t i o n F ) . With f r e s h i n p u t s of 50 F i g u r e 9. S e a s o n a l v a r i a t i o n i n t h e p e r c e n t a g e of f i n e m a t e r i a l (<0.064mm) i n t h e s u r f a c e cm of s e d i m e n t a t t h e two s i t e s i n 1978. 100 52 s i l t froir. the F r a s e r f r e s h e t , the mud s i t e was u n i f o r m l y b l a n k e t e d w i t h a 1 t o 2 cm l a y e r of f i n e m a t e r i a l , i n e a r l y August, i n c r e a s i n g the s i l t - c l a y f r a c t i o n t o 50.46% by we i g h t . The sediments remained v e r y f i n e (> 50% s i l t - c l a y ) u n t i l r e d i s t u r b e d by storms i n e a r l y October ( F i g . 9 ) . The s e a s o n a l c y c l e of sediment t e x t u r a l changes i n the sand wave tr o u g h s a t Iona N o r t h a r e , t h e r e f o r e the r e s u l t of t h r e e major p r o c e s s e s : r e s u s p e n s i o n and t r a n s p o r t of sediments by w i n t e r storm waves, the d e p o s i t i o n of s i l t - c l a y by the F r a s e r plume i n l a t e summer and the c o n s o l i d a t i o n of f i n e m a t e r i a l i n t o c o a r s e r , b i o g e n i c s t r u c t u r e s , p r i n c i p a l l y by p o l y c h a e t e and o l i g o c h a e t e worms. D. D i e l v a r i a t i o n s i n e n v i ronmental f a c t o r s P h y s i c a l c o n d i t i o n s i n the i n t e r t i d a l zone may change s i g n i f i c a n t l y d u r i n g a s i n g l e t i d a l c y c l e . On 19-29 J u l y 1978 some of thes e changes were m o n i t o r e d i n the s o u t h t i d e p o o l t h r o u g h a complete c y c l e of two h i g h and two low w a t e r s . The r e s u l t s a r e shown i n F i g . 10. The p r e d i c t e d t i d a l range a t P t . A t k i n s o n on 19 J u l y was 4.5 m, c l o s e t o the maximum range of 4.9 m. The day was warm ( a i r temperature from 15.8 t o 26° C) and c l e a r a l t h o u g h t h e r e was a b r i s k n o r t h w e s t wind. The maximum i r r a d i a n c e measured on t h e j e t t y was 2000 j j E i n n r 2 s - 1 a t 1300 h. T i d e p o o l t e m p e r a t u r e s i n c r e a s e d from 20.8° C t o 28.0° C w i t h i n c r e a s i n g i r r a d i a n c e . S a l i n i t y a l s o i n c r e a s e d s l i g h t l y from 8 ppt t o 10 ppt by e v a p o r a t i o n d u r i n g the p e r i o d of emergence. D i s s o l v e d oxygen c o n c e n t r a t i o n s i n the p o o l were v a r i a b l e but were g e n e r a l l y h i g h e r a f t e r 1200 h; they reached a 53 F i g u r e 10. D i u r n a l v a r i a t i o n i n t e m p e r a t u r e , s a l i n i t y a n d d i s s o l v e d o x y g e n c o n c e n t r a t i o n i n t h e s o u t h t i d e p o o l m e a s u r e d on 19-20 J u l y 1978. S h a d i n g i n d i c a t e s p e r i o d o f e mergence of t h e s a n d s i t e . I r r a d i a n c e was m e a s u r e d a t 15 m i n u t e i n t e r v a l s on t h e j e t t y . T i d a l c u r v e i s p l o t t e d f r o m t a b u l a t e d p r e d i c t i o n s f o r P t . A t k i n s o n . 0 28 26 24 22 20 12 10 8 6 4 10 8 5 4 3 2 1 0 I I I l — J I I I I 1 ! ! 1 1 1 1 1 1 L 1000 1200 1400 1600 1800 2000 2200 0000 0200 0400 0600 0800 19 JULY 1978 SO JULY 55 peak of 10.6 mg 1~ 1 a t 1400 h presumably from the combined e f f e c t s of wind d r i v e n d i f f u s i o n from the atmosphere and h i g h mid-day r a t e s of p r i m a r y p r o d u c t i v i t y of the macroalgae i n the p o o l . The r i s i n g t i d e swept over the study s i t e a t 1530 h. The i n u n d a t i n g water was warm (26 t o 28° C ) , from i t s passage over the warm sand f l a t s and r e l a t i v e l y s a l i n e (10—12 p p t ) . Between 1645 and 1815 h p h y s i c a l c o n d i t i o n s changed r a p i d l y as f r e s h e r ( s a l i n i t y as low as 4.4 p p t ) , c o l d e r . (temperature as low as 21.6° C) F r a s e r R i v e r plume water reached Iona N o r t h . In 1.5 hours the drop of s a l i n i t y i n the t i d e p o o l (7.5 ppt) was e q u i v a l e n t t o 37.1% of t h e ' a n n u a l s a l i n i t y range; the drop i n temperature (4.9° C ) , 17.2% of i t s annual range. These changes are i m p o r t a n t t o the a n i m a l s s i n c e a h i g h r a t e of change i s l i k e l y t o be more s t r e s s f u l than a l a r g e annual range of c o n d i t i o n s ( B a r n e t t 1968). A f t e r the time of h i g h low water (0445 h) the more s a l i n e water (9 ppt) of the s a l t wedge p e n e t r a t e d the study s i t e ( F i g . 10). Two p o i n t s s h o u l d be made from the f o r e g o i n g d i s c u s s i o n . F i r s t , c a r e must be taken when comparing the annual f a u n a l abundance p a t t e r n s of F i g s . 12 t o 15 w i t h the annual s a l i n i t y and t e m p e r a t u r e p a t t e r n s p r e s e n t e d i n F i g . 6. The l a t t e r r e p r e s e n t n o t h i n g more than the c o n d i t i o n s measured at the time t h a t f a u n a l samples were t a k e n . By comparing s p e c i e s ' o c c u r r e n c e s w i t h t h e s e t e m p e r a t u r e s and s a l i n i t i e s , we can e s t a b l i s h , the minimum s a l i n i t y and temperature ranges of the Iona N o r t h s p e c i e s ; the maximum range i s p r o b a b l y somewhat 56 l a r g e r . Second, s h o r t i n t e r v a l v a r i a t i o n s i n p h y s i c a l c o n d i t i o n s f o r e s t u a r i n e i n t e r t i d a l meiofauna may be v e r y l a r g e , even when compared w i t h the a m p l i t u d e of v a r i a b i l i t y over the e n t i r e annual c y c l e . In the example above the temperature v a r i a t i o n over 24 hours (20.0 t o 28.0° C) was 28.1% of the measured annual temperature range (-0.5 t o 28.0° C ) ; the 24-hr s a l i n i t y range (4.4 t o 12.0 ppt) was 37.6% of the measured annua l range (6.3 t o 26.5 p p t ) . E. Sediment pigments and m i c r o a l g a e Large s e a s o n a l v a r i a t i o n s i n both c h l o r o p h y l l a and p h a e o p h y t i n a c o n c e n t r a t i o n s were measured i n the s u r f a c e 5 cm of sediment a t Iona N o r t h i n 1978-1979 ( F i g . 11) ( o b s e r v a t i o n s ar e g i v e n i n Appendix 2) and the p a t t e r n of v a r i a t i o n was d i f f e r e n t a t the two s i t e s . At the sand s i t e c h l o r o p h y l l a c o n c e n t r a t i o n s were u n i f o r m l y low from November t o A p r i l and i n c r e a s e d t o a p p r o x i m a t e l y double w i n t e r l e v e l s d u r i n g the summer months. P h a e o p h y t i n c o n c e n t r a t i o n s were h i g h f o l l o w i n g the f a l l o u t of the s p r i n g p h y t o p l a n k t o n bloom on 25 May 1978 but f o r the r e s t of the year were m o s t l y v e r y low. The t o t a l range of c h l o r o p h y l l a c o n c e n t r a t i o n s o b s e r v e d through the p e r i o d was 32.0 t o 180.6 mg n r 2 . C h l o r o p h y l l a and p h a e o p h y t i n a c o n c e n t r a t i o n s were both h i g h e r and s e a s o n a l l y more v a r i a b l e a t the mud s i t e . At the mud s i t e c h l o r o p h y l l a c o n c e n t r a t i o n s were r e l a t i v e l y low between January and June. A l t h o u g h a l a r g e , mid-summer bloom o c c u r r e d i n J u l y the most i n t e n s e blooms of m i c r o a l g a e were r e c o r d e d on 57 F i g u r e 1 1 . S e a s o n a l v a r i a t i o n i n s e d i m e n t p h o t o s y n t h e t i c • p i g m e n t c o n c e n t r a t i o n s , a t t h e s a n d ( t o p ) and mud ( b o t t o m ) s i t e s o f I o n a N o r t h . S o l i d s y m b o l s a r e c h l o r o p h y l l , a c o n c e n t r a t i o n s ; open s y m b o l s a r e p h a e o p h y t i n a c o n c e n t r a t i o n s V e r t i c a l b a r s i n d i c a t e ± 1 s t a n d a r d e r r o r o f . t h e mean o f n = r e p l i c a t e s f o r t h e mud and n = 3 o r 6 r e p l i c a t e s f o r t h e s a n d 58 S A N D CN i E I -0.4 0.3 Phaeophytin a LU 0.2] 0 A Chlorophyll a F M A 1979 M J A S O N D J 1978 M U D CN ' E 0.41 Ui H LU 0.2 Chlorophyll a Phaeophytin CD \ 0.1 ^0- 1 »•  Q t n / 1 I L,H__i n H 0 ^ s i a ^ ^ a l ^ D i ^ , ^ F M A M J . J A S O N D J 1979 1978 59 29 Sept and 27 Dec 1978. A s p r i n g i n c r e a s e i n p h a e o p h y t i n a c o n c e n t r a t i o n s i n the mud o c c u r r e d from March t o June, w i t h a secondary peak on 27 Dec. The i n c r e a s e i n p h a e o p h y t i n a c o n c e n t r a t i o n s observed between March and June was l a r g e l y due t o the s e d i m e n t a t i o n of p h y t o d e t r i t u s , e s p e c i a l l y c h a i n - f o r m i n g diatoms,- from the water column. A s i m i l a r annual p a t t e r n of ph a e o p h y t i n d e p o s i t i o n was obser v e d i n sediment t r a p s p l a c e d a t 30 m depth ( a p p r o x i m a t e l y 2 m above the sediment s u r f a c e ) i n De p a r t u r e Bay, B r i t i s h Columbia (Stephens e t a l . 1967). The range of c h l o r o p h y l l a c o n c e n t r a t i o n s o b s e r v e d was 62.7 t o 423.7 mg n r 2 . Bawden et a l . ( 1 973) r e p o r t e d c h l o r o p h y l l a c o n c e n t r a t i o n s i n the sediments of R o b e r t s and Sturgeon Banks of 26-244 mg n r 2 . T h i s i s e q u i v a l e n t t o the range of c o n c e n t r a t i o n s I. found s i n c e these a u t h o r s sampled o n l y the top 1 t o 2 cm,• and I g e n e r a l l y found as. much c h l o r o p h y l l a below t h a t depth as above i t . The s e a s o n a l p a t t e r n of v a r i a t i o n i n c h l o r o p h y l l a c o n c e n t r a t i o n s i n the sediments of Iona N o r t h agrees q u a l i t a t i v e l y w i t h the p a t t e r n on the n o r t h p a r t of R o b e r t s Bank where maximum c o n c e n t r a t i o n s o c c u r r e d i n w i n t e r [November 1975] ( L e v i n g s e t a l . 1978). The s e a s o n a l v a r i a t i o n i n c h l o r o p h y l l a c o n c e n t r a t i o n s i n the S t r a i t of G e o r g i a i s g i v e n i n Parsons (1979). C h l o r o p h y l l a c o n c e n t r a t i o n s a re low from October through F e b r u a r y . There i s a s i n g l e a n n u a l i n c r e a s e t o a June maximum (80mg n r 2 i n a l a y e r 20 m deep) which l a g s b e h i n d the p r i m a r y p r o d u c t i v i t y maximum by one month (Parsons 1979 [ F i g . 6 . 2 ] ) . Compared w i t h the s u r f a c e waters of the S t r a i t , the F r a s e r m u d f l a t s p r o v i d e a 60 h i g h l y c o n c e n t r a t e d s o u r c e o f m i c r o a l g a l f o o d f o r s m a l l h e r b i v o r e s . T h e m i c r o a l g a e o f I o n a N o r t h a l s o c h a n g e d q u a l i t a t i v e l y t h r o u g h t h e y e a r ( s e e A p p e n d i x 3 ) . T h e m u d m i c r o a l g a e w e r e d o m i n a t e d i n a l l s e a s o n s b y p e n n a t e d i a t o m s . T h e s p e c i e s c o m p o s i t i o n o f t h e p e n n a t e s - p r o b a b l y v a r i e d s e a s o n a l l y ; t h e s i z e c o m p o s i t i o n a l m o s t c e r t a i n l y d i d . I n s p r i n g t h e m i c r o a l g a e w e r e a l m o s t a l l 30 t o 6 0 um l o n g n a v i c u l o i d s . A g r e a t e r d i v e r s i t y o f f o r m s w a s p r e s e n t i n m i d - s u m m e r i n c l u d i n g c o d o m i n a n t p e n n a t e s C y l i n d r o t h e c a f u s i f o r m i s ( 1 . 7 5 um l o n g ) a n d 10 t o 15 ;um n a v i c u l o i d s . O n 1 S e p t s m a l l n a v i c u l o i d s ( 2 0 um l o n g ) w e r e d o m i n a n t . T h e s e c e l l s w e r e r e s p o n s i b l e f o r t h e h u g e b l o o m o b s e r v e d o n 2 9 S e p t . T h e s a n d m i c r o a l g a l c o m m u n i t y g e n e r a l l y h a r b o r e d a g r e a t e r d i v e r s i t y o f f o r m s t h a n t h e m u d . T h e s p r i n g s a m p l e w a s d o m i n a t e d b y 6 0 um l o n g p e n n a t e s . B y m i d - s u m m e r t h e s a n d d i a t o m s w e r e g r e a t l y o u t n u m b e r e d b y a d i v e r s e a s s e m b l a g e o f s m a l l ( 6 t o 10 um) c r y p t o m o n a d s a n d d i n o f l a g e l l a t e s . T h i s d i v e r s i t y w a s r e d u c e d o n 1 S e p t b y a l a r g e b l o o m o f A m p h i d i n i u m  t e s t u d o ( 3 0 um) w h i c h w e r e m o s t l y g o n e b y 2 9 S e p t . A l t h o u g h t h e s a n d m i c r o a l g a e r e t a i n e d t h e i r d i v e r s i t y i n t o t h e w i n t e r , d i a t o m s a g a i n b e c a m e r e l a t i v e l y m o r e a b u n d a n t . 61 F. Seasonal abundance p a t t e r n s of the fauna J _ . T o t a l meiobenthos The range i n the t o t a l d e n s i t y of meiobenthos ( a l l t a x a ) a t Iona N o r t h i s g i v e n i n Ta b l e 2; mean coun t s of dominant t a x a on each s a m p l i n g date'appear i n Appendix 4. D i f f e r e n t s e a s o n a l abundance p a t t e r n s of the t o t a l meiobenthos were observed a t the two s i t e s ( F i g . 12). In the sand t o t a l abundance peaked i n e a r l y A p r i l (a 385% i n c r e a s e i n 2 months) f o l l o w e d by an even s h a r p e r peak i n June (66.4% of which were h a r p a c t i c o i d n a u p l i i ) . The meiobenthos then c r a s h e d a b r u p t l y t o moderate d e n s i t i e s which were m a i n t a i n e d , w i t h 3 minor peaks, u n t i l l a t e September, a f t e r which they d e c l i n e d t o low w i n t e r d e n s i t i e s . The mud s i t e was c h a r a c t e r i z e d by h i g h e r s u s t a i n e d d e n s i t i e s of meiobenthos through most of the y e a r . The major s p r i n g i n c r e a s e i n the mud lagged 6 weeks beh i n d the sand bloom w i t h peak d e n s i t i e s r e c o r d e d on 11 May. T h i s bloom c r a s h e d t o l a t e w i n t e r d e n s i t i e s one month l a t e r . A s m a l l secondary peak, 45 % of which were h a r p a c t i c o i d copepods, o c c u r r e d i n m i d - J u l y f o l l o w e d by a s u s t a i n e d peak, 45-60% h a r p a c t i c o i d copepods, i n September. The mud m e i o b e n t h i c p o p u l a t i o n s then d e c r e a s e d s t e a d i l y t h r o u g h the f a l l and w i n t e r . Compared w i t h o t h e r a r e a s Iona N o r t h h a r b o r s a r i c h m e i o b e n t h i c assemblage. The t o t a l d e n s i t y of meiobenthos r e c o r d e d i n 1978 (Table 2) i n d i c a t e s t h a t the F r a s e r i n t e r t i d a l r a n ks among the most p r o d u c t i v e of m e i o b e n t h i c h a b i t a t s ( T a b l e 3; see a l s o : M c l n t y r e 1971; Brickman 1972; C o u l l 1973 T a b l e 2. Range o f d e n s i t i e s o f t o t a l me iobenthos a t two s i t e s o f I o n a N o r t h (1978) . S i t e Date T o t a l d e n s i t y o f m e i o b e n t h o s c o r e - 1 m - 2 10 cm -2 X SE x SE X SE n SAND MIN 25 Nov 63.58 12.01 3 . 8 5 - 1 0 5 935 .0 385 .3 29 .6 * 22 MAX 8 J u n 797 .67 72.48 4 . 8 3 - 1 0 6 5640 .0 4830 .0 '178..4 12 MUD MIN 22 J a n 79 136.92 12 .45 8 . 3 0 - 1 0 5 969.2 829 .7 30 .65 12 MAX 11 May 591.83 74 .23 3 . 5 9 - 1 0 6 5780.0 3590.0 182.7 12 dens i ty - •m 2 = d e n s i t y p e r c o r e • ( 6 0 6 0 . 6 ) ; each c o r e samples 1 .65 <cm2 d e n s i t y •10 c m " 2 = d e n s i t y p e r c o r e « ( 6 . 06) 63 F i g u r e 12. S e a s o n a l v a r i a t i o n i n abundance of t o t a l meiofauna at the sand and mud s i t e s t h r o u g h 1978. Each p o i n t i s the mean of n = 12 r e p l i c a t e c o u n t s f o r the mud and n = 12 or 22 r e p l i c a t e c o u n t s f o r the sand. V e r t i c a l b a rs r e p r e s e n t ±1 s t a n d a r d e r r o r of the mean. Each c o r e sampled a sediment area of 1.65 cm 2 t o a depth of 5 cm. MEAN NUMBER PER CORE 65 and J u a r i o 1975). A l t h o u g h comparison among s i t e s i s made d i f f i c u l t by the d i v e r s i t y of methods used by d i f f e r e n t a u t h o r s , h i g h e r abundances of t o t a l meiobenthos than those found a t Iona N o r t h were r e p o r t e d o n l y from s a l t marshes and o t h e r e s t u a r i n e i n t e r t i d a l f l a t s . In terms of major t a x a r e p r e s e n t e d , the Iona N o r t h meiobenthos conformed t o the e x p e c t e d p a t t e r n ( C o u l l and B e l l 1979) of n u m e r i c a l dominance by nematodes and h a r p a c t i c o i d copepods ( F i g . 13). Together t h e s e two t a x a c o n s t i t u t e d 57.8 t o 99.3% of the t o t a l meiobenthos i n the sand and 74.8 t o 96.9% i n the mud. The r e l a t i v e abundances of t a x a changed d u r i n g 1978 a t both s i t e s ( F i g . 13). O l i g o c h a e t e s dominated the sand b r i e f l y i n F e b r u a r y but the dominant p o s i t i o n was q u i c k l y t aken by the h a r p a c t i c o i d copepods and h e l d u n t i l l a t e A p r i l when the nematodes became dominant. H a r p a c t i c o i d s a g a i n d o m i n a t e d , i n mid-summer and nematodes i n f a l l and w i n t e r . P o l y c h a e t e s and o l i g o c h a e t e s were a g r e a t e r f r a c t i o n of the mud fauna a l t h o u g h t o g e t h e r they c o n s t i t u t e d , a t most, 24.8% of the t o t a l numbers. The mud meiobenthos was dominated by h a r p a c t i c o i d copepods from J u l y t o November, by nematodes the r e s t of the y e a r . One v e r y s i g n i f i c a n t d i f f e r e n c e between s i t e s was the p r o p o r t i o n a l r e p r e s e n t a t i o n of a d u l t and c o p e p o d i t e h a r p a c t i c o i d s and n a u p l i i . The r a t i o of [ a d u l t s + c o p e p o d i t e s ] / n a u p l i i i n the sand ranged from 0.12 t o 2.86; through most of the y e a r , n a u p l i i g r e a t l y outnumbered p o s t - n a u p l i a r i n d i v i d u a l s . The r e v e r s e s i t u a t i o n o c c u r r e d i n the mud; through most of the year n a u p l i i were r e l a t i v e l y r a r e w i t h the r a t i o of [ a d u l t s + 66 T a b l e 3. C o m p a r i s o n o f Iona N o r t h w i t h o t h e r p r o d u c t i v e i n t e r t i d a l and s h a l l o w s u b t i d a l h a b i t a t s . R e f e r e n c e L o c a t i o n / h a b i t a t M e i o f a u n a d e n s i t y ( remarks ) (number -m" 2 )  INTERTIDAL Rees (1940) B a r n e t t (1968) Dye (1979) H a r r i s o n ( t h i s s t u d y ) B r i s t o l C h a n n e l / 0 . 9 - 1 1 2 - l O 5 sewage p o l l u t e d f l a t Southampton / m u d f l a t F r a s e r E s t u a r y / m u d f l a t s SALT MARSH t o 1 . 0 2 - 1 0 6 ( b r a c k i s h ) (copepods o n l y ) Mngazana e s t u a r y , 2 . 5 9 « 1 0 5 - 7 . 2 7 * 1 0 6 T r a n s k e i 3 . 8 5 . 1 0 5 - 4 . 8 3 » 1 0 6 W i e s e r § K a n w i s h e r (1961) T e a l 5 W i e s e r (1966) B r i c k m a n (1972) M a r c o t t e (1977a) M c l n t y r e (1964) F e n c h e l (1969) T i e t j e n (1969) Warwick § Buchanan (1970) Wood's H o l e / P enzance marsh 1 . 4 - 2 . 1 - 1 0 6 (nematodes o n l y ) S a p e l o I s l a n d , G a . to 1 6 . 3 - 1 0 6 New J e r s e y marsh West Lawrence town, Nova S c o t i a SUBTIDAL N e v i s § F l a d e n Ground D a n i s h E s t u a r y sands New E n g l a n d e s t u a r i e s Nor thumber1 and s u b t i d a l t o 10 .59* 10 6 t o 8 . 8 4 - 1 0 6 0 . 5 4 - 3 . 1 6 ' 1 0 6 5 - 1 0 5 - 2 - 1 0 6 1.18 - 5 . 1 6 - 1 0 s 1 . 8 4 - 1 0 5 - 7 . 1 3 - 1 0 5 C o u l l (1970) Bermuda 1 2 . 2 - 1 3 3 - 1 0 t + 67 T a b l e 3. c o n t ' d J u a r i o (1975) J e n s e n (1977) V i t i e l l o § A i s s a (1977) German B i g h t 0resund,D k . Lake o f T u n i s ( e u t r o p h i e d l a g o o n ) 3.05 - 5 . 2 6 « 1 0 6 0 .2 - 1 . 0 2 - 1 0 6 5 . 9 - 1 0 6 (nematodes o n l y ) 68 F i g u r e 13. S e a s o n a l v a r i a t i o n i n p e r c e n t a g e c o n t r i b u t i o n of most abundant t a x a t o the t o t a l number of m e i o b e n t h i c organisms c o l l e c t e d from each s i t e t h r ough 1978. -SAND MEIOBENTHOS 1978 01-1 1 1 1 1 1 1 1 i i i • i F M A M J J A S 0 N D J MUD MEIOBENTHOS 1978 0 U 1 1 1 J 1 1 1 1 I I l L F M A M J J A S 0 N D J 70 c o p e p o d i t e s ] / n a u p l i i r a n g i n g from 0.6 t o 19.7. 2. I n d i v i d u a l t a x a a. Permanent meiobenthos The s e a s o n a l abundance p a t t e r n of each of the major t a x a i s shown i n F i g . 14 (sand) and F i g . 15 (mud) and i n Appendix 4. NEMATODES bloomed o n l y once i n 1978, i n l a t e s p r i n g . The i n c r e a s e c o r r e s p o n d e d w i t h the i n c r e a s e i n temperature and p h a e o p h y t i n a and was synchronous between the two h a b i t a t s a l t h o u g h s u b s t a n t i a l l y h i g h e r d e n s i t i e s were reached i n the mud than i n the sand. Sharma (1978) p r o v i d e s a d d i t i o n a l , s p e c i e s -s p e c i f i c d a t a on the s e a s o n a l v a r i a t i o n i n nematode abundances at a s i m i l a r s i t e n o r t h of the Iona J e t t y . She r e p o r t e d an i n c r e a s e i n d e n s i t i e s i n May 1977; however her s a m p l i n g s c h e d u l e ( f i v e s a m p l i n g s through 1977) d i d not p e r m i t f u l l r e s o l u t i o n of the s e a s o n a l p a t t e r n of v a r i a t i o n i n abundance and the " s p r i n g bloom" i n nematode d e n s i t i e s appears t o have been u n d e t e c t e d . TURBELLARIA a l s o showed a s i m i l a r s e a s o n a l abundance p a t t e r n a t the two s i t e s ; a s u b s t a n t i a l i n c r e a s e i n p o p u l a t i o n i n s p r i n g (peak on 28 A p r i l ) c o i n c i d e n t w i t h i n c r e a s i n g nematode d e n s i t i e s . The t u r b e l l a r i a were f a r l e s s abundant than the major t a x a . These d a t a a r e c o n s i s t e n t w i t h the s u g g e s t i o n t h a t some m e i o b e n t h i c t u r b e l l a r i a may be nematode p r e d a t o r s ( M c l n t y r e 1 9 6 9 ) . The s e a s o n a l p a t t e r n s of the o t h e r major m e i o b e n t h i c t a x a 71 F i g u r e 14. S e a s o n a l v a r i a t i o n s i n abundance of major m e i o b e n t h i c t a x a a t the sand s i t e t h r o u g h 1978. P o i n t s are means of n = 12 or n = 22 r e p l i c a t e s depending on the date of c o l l e c t i o n . V e r t i c a l b a rs i n d i c a t e ±1 s t a n d a r d e r r o r . -Each c o r e sampled a sediment a r e a of 1.65 cm 2 t o a depth of 5 cm. 7 2 S A N D MEIDFAUNA" 1978 a. permanent NEMATODES HARPACTICOIDS OLIGOCHAETES F M A M J J A S O N D J MONTH b. temporary < macrofauna> 10 r-5 POLYCHAETES 0<—£=» 2 1 0 Macoma . " * -y -s A A c. temporary <microfauna> LARGE CILIATES 73 F i g u r e 15. S e a s o n a l v a r i a t i o n s i n abundance of major m e i o b e n t h i c t a x a a t the mud s i t e t h r o u g h 1978. P o i n t s are means of n = 12 r e p l i c a t e s f o r each d a t e . V e r t i c a l b ars i n d i c a t e .-.± .  1 s t a n d a r d e r r o r . Each c o r e sampled a sediment a r e a of 1.65 cm 2 t o a depth of 5 cm. 74 M U D M E I O F A U N A • 1 9 7 8 a. permanent NEMATODES I I I—I—1 l_J I I I I I F M A M J J A S O N D J MONTH b. temporary < macrofauna > Manayunkia 15 r OTHER POLYCHAETES 1.0 h 0.5 0 Macoma 0.51-o AMPHIPODS c. temporary <microfauna> 5|-o •21 LARGE CILIATES 75 showed l a r g e m a c r o h a b i t a t (sand v e r s u s mud) d i f f e r e n c e s . OSTRACODS were v i r t u a l l y absent from the sand s i t e . In the mud they reached peak abundance i n F e b r u a r y but were a minor p a r t of the t o t a l number of meiobenthos (maximum = 1.9% of t o t a l numbers). OLIGOCHAETES reached peak d e n s i t y i n the sand i n February w i t h a secondary i n c r e a s e i n m i d - A p r i l . The p o p u l a t i o n f e l l t o e x t r e m e l y low d e n s i t i e s d u r i n g the l o w - s a l i n i t y summer months and r e c o v e r e d s l i g h t l y when s a l i n i t y i n c r e a s e d i n the f a l l . The mud o l i g o c h a e t e p o p u l a t i o n showed the r e v e r s e s e a s o n a l p a t t e r n . The p o p u l a t i o n i n c r e a s e d t o a s m a l l peak i n e a r l y June as s a l i n i t y d e c r e a s e d f o l l o w e d by a l a r g e r peak i n e a r l y August.* Only the mud p o p u l a t i o n f o l l o w e d the s e a s o n a l abundance p a t t e r n f o r b r a c k i s h o l i g o c h a e t e s i n the F r a s e r R i v e r (Chapman 1979). The s e a s o n a l abundance p a t t e r n of HARPACTICOID COPEPODS w i l l be one of the t o p i c s c o n s i d e r e d i n depth i n f u t u r e c h a p t e r s . S e v e r a l f e a t u r e s bear m e n t i o n i n g a t t h i s s t a g e . F i r s t , as w i t h the o l i g o c h a e t e s , the t e m p o r a l p a t t e r n of abundance observed i n 1978 was not a t a l l s i m i l a r i n the two h a b i t a t s . In the sand, the major peaks o c c u r r e d i n e a r l y A p r i l and e a r l y June; i n the mud, i n l a t e J u l y and l a t e September. Second, much h i g h e r p o p u l a t i o n d e n s i t i e s were a c h i e v e d i n the mud and they were s u s t a i n e d f o r a l o n g e r p e r i o d . T h i r d , as mentioned above, n a u p l i i were r e l a t i v e l y r a r e t h r o u g h the year i n the mud; i n the sand the peaks of abundance of h a r p a c t i c o i d s were accompanied by the p r o d u c t i o n of l a r g e numbers of n a u p l i i . 76 b. S m a l l macrobenthos The sand was c h a r a c t e r i z e d t h r o u g h 1978 by a p a u c i t y of s m a l l macrobenthos. P o l y c h a e t e s were most abundant i n l a t e summer. Manayunkia a e s t u a r i n a were o n l y r a r e l y found i n the sand, m o s t l y i n w i n t e r . S m a l l b i v a l v e m o l l u s c s , Macoma  b a l t h i c a , o c c u r r e d i n s m a l l numbers i n ' m i d - w i n t e r and mid-summer . A v a r i e t y of s m a l l macrobenthic t a x a o c c u r r e d i n the mud. The p o l y c h a e t e M. a e s t u a r i n a peaked- i n mid-September. The remainder of the p o l y c h a e t e s ( m o s t l y Pygospio e l e g a n s ) peaked i n l a t e June, f o l l o w i n g the nematode d e c l i n e and p r e c e d i n g the o l i g o c h a e t e and h a r p a c t i c o i d i n c r e a s e s . Low numbers of Macoma b a l t h i c a were found throughout the year i n the mud. S m a l l amphipods, m o s t l y Corophium spp. were found m a i n l y i n l a t e w i n t e r and e a r l y s p r i n g . c. M i c r o b e n t h o s The s e a s o n a l sampling program d i d not i n c l u d e c o n s i d e r a t i o n of the c i l i a t e d p r o t o z o a n s and o t h e r m i c r o f a u n a ; however, l a r g e ( a p p r o x i m a t e l y 0.5 mm) i n t e r s t i t i a l c i l i a t e s were o b s e r v e d i n the meiofauna samples from the sand, w i t h h i g h e s t numbers o c c u r r i n g i n f a l l and w i n t e r . C i l i a t e s were a l s o found i n the mud i n m i d - w i n t e r when the sediment was sandy ( F i g . 9) . The c i l i a t e s a r e u n i c e l l u l a r and t h e r e f o r e do not f i t the d e f i n i t i o n of meiobenthos as " s m a l l e r metazoans". T h i s p a r t i c u l a r group of c i l i a t e s were so l a r g e , however, t h a t they 77 c o u l d c o n c e i v a b l y compete w i t h the meiobenthos f o r food ( F e n c h e l 1978). At numbers c o n s i s t e n t l y l e s s than 1.5 c o r e " 1 , i t i s u n l i k e l y t h a t the c i l i a t e s were s i g n i f i c a n t c o m p e t i t o r s i n 1978. 78 IV. AUTECOLOGY OF IONA NORTH HARPACTICOID COPEPODS A. I n t r o d u c t i o n T h i s s e c t i o n d e a l s w i t h the a u t e c o l o g y of the e i g h t s p e c i e s of h a r p a c t i c o i d copepods c o l l e c t e d a t Iona N o r t h between January 1 9 7 7 and January 1 9 8 0 . The, i n f o r m a t i o n p r o v i d e d here i s i n t e n d e d as a b r i e f i n t r o d u c t i o n t o the s a l i e n t f e a t u r e s of the b i o l o g y of each s p e c i e s and i s a ne c e s s a r y p r e r e q u i s i t e f o r u n d e r s t a n d i n g f u t u r e s e c t i o n s of the t h e s i s . The f o l l o w i n g i n f o r m a t i o n ( i f known) i s p r o v i d e d f o r each of the h a r p a c t i c o i d s p e c i e s s t u d i e d from Iona N o r t h : a) type l o c a t i o n and ge o g r a p h i c range b) taxonomic a f f i n i t y t o o t h e r s p e c i e s i n the c o l l e c t i o n c) morphology, i n c l u d i n g body form and s i z e , s t r u c t u r e of c e p h a l i c appendages ( i n c l u d i n g SEM photographs of o r a l morphology) and s t r u c t u r e of t h o r a c i c appendages d) b e h a v i o r d u r i n g movement, f e e d i n g and p r e c o p u l a t i o n and e) s e a s o n a l v a r i a t i o n i n p o p u l a t i o n d e n s i t y , r e p r o d u c t i v e a c t i v i t y and m a c r o h a b i t a t (mud v s . sand) use. The i n f o r m a t i o n g i v e n was d e r i v e d from a b i - w e e k l y survey of the Iona N o r t h s i t e s i n 1978, annual m i d - w i n t e r s u r v e y s between 79 1977 and 1980, l a b o r a t o r y o b s e r v a t i o n s of the b e h a v i o r of l i v e i n d i v i d u a l s , o b s e r v a t i o n s of whole and d i s s e c t e d i n d i v i d u a l s w i t h both l i g h t and s c a n n i n g e l e c t r o n m i c r o s c o p y (SEM) and a review of the l i t e r a t u r e . The H a r p a c t i c o i d a i s one of the t h r e e f r e e - l i v i n g o r d e r s of the s u b c l a s s Copepoda (Phylum A r t h r o p o d a ; C l a s s C r u s t a c e a ) ; the o t h e r two o r d e r s are the C a l a n o i d a and the . C y c l o p o i d a . Three c h a r a c t e r i s t i c s s e r v e t o demarcate the o r d e r s ( C o u l l 1977): 1) the p o s i t i o n of the prosome-urosome a r t i c u l a t i o n : between the f i f t h and s i x t h postcephalosome segments i n the H a r p a c t i c o i d a and C y c l o p o i d a ; between the s i x t h and s e v e n t h i n the C a l a n o i d a 2) the number of segments i n the A.1: fewer than 10 i n the H a r p a c t i c o i d a ; u s u a l l y 10-22 i n the C y c l o p o i d a ; and u s u a l l y more than 22 i n the C a l a n o i d a 3) the number of rami i n the A.2: two i n the H a r p a c t i c o i d a and C a l a n o i d a ; one (the endopod) i n the C y c l o p o i d a . F o l l o w i n g the t e r m i n o l o g y used by C o u l l (1977), the h a r p a c t i c o i d body i s d i v i d e d i n t o two r e g i o n s : an a n t e r i o r 80 prosome and p o s t e r i o r urosome ( F i g . 16). The prosome may be f u r t h e r s u b d i v i d e d i n t o the c e p h a l o t h o r a x which c o n s i s t s of the f o l l o w i n g , f u s e d segments: a) the cephalosome b e a r i n g the head appendages (A.1, A. 2, Md, Mx . 1., Mx . 2 ) b) the f i r s t t h o r a c i c segment b e a r i n g the m a x i l l i p e d s (Mxp) and ( u s u a l l y ) c) the second t h o r a c i c segment b e a r i n g the f i r s t p a i r of swimming (or w a l k i n g ) l e g s (P.1) and the metasome which c o n s i s t s of the r e m a i n i n g t h r e e ( i f the f i r s t i s f u s e d t o the cephalosome) or f o u r f r e e t h o r a c i c segments b e a r i n g the r e m a i n i n g swimming l e g s (P.2, P.3, P.4). The urosome i s g e n e r a l l y o n l y s l i g h t l y narrower than the prosome and c o n s i s t s of the r e m a i n i n g segments from the g e n i t a l somite which bears the h i g h l y m o d i f i e d f i f t h l e g s (P.5) t o the a n a l segment which t e r m i n a t e s i n a p a i r of p r o j e c t i o n s , the c a u d a l rami (CR) which bear the ( o f t e n e l o n g a t e d ) c a u d a l s e t a e . The h a r p a c t i c o i d c e p h a l o t h o r a x bears s i x p a i r s of h i g h l y m o d i f i e d appendages which s e r v e a s ensory and f e e d i n g f u n c t i o n . They are l i s t e d here i n o r d e r from a n t e r i o r t o p o s t e r i o r a l o n g w i t h the a b b r e v i a t i o n s by which I w i l l r e f e r t o them i n the remainder of the t e x t : A. 1 A.2 Md -- A n t e n n u l e or f i r s t antenna - Antenna or second antenna M a n d i b l e 81 F i g u r e 16. L i m n o c l e t o d e s b e h n i n g i . SEM montage ( h a b i t u s ) of a d u l t female; v e n t r a l view i l l u s t r a t i n g f e a t u r e s of h a r p a c t i c o i d morphology. ( i n s e t ) D o r s a l view of a d u l t female. A 1 - f . i r s t antenna . . . A2-second antenna Md-mandible M x 1 - f i r s t m a x i l l a Mx2-second m a x i l l a M x p - m a x i l l i p e d P1 -P4-walking/'swimming l e g s P 5 - f i f t h l e g Exp-exopod Enp-endopod CR-caudal rami fjimnocfetoifes hftninab 83 Mx.1 - M a x i l l u l a o r . f i r s t m a x i l l a Mx.2 - M a x i l l a or second m a x i l l a Mxp - M a x i l l i p e d A l l 6 p a i r s of appendages may be used i n . f e e d i n g ( M a r c o t t e 1977a) and so w i l l be r e f e r r e d t o as ' o r a l appendages'. More thorough t r e a t m e n t s of h a r p a c t i c o i d morphology are a v a i l a b l e i n Lang (1948, 1965) and C o u l l (1977). The morphology of o r a l appendages of s e l e c t e d s p e c i e s i s g i v e n i n I v e s t e r (1975) and I v e s t e r and C o u l l (1977). The f u n c t i o n a l morphology of o r a l appendages and f e e d i n g b e h a v i o r of s e l e c t e d s p e c i e s were s t u d i e d by M a r c o t t e (1977a,b). M a r c o t t e ' s (1977a) t r o p h i c c l a s s i f i c a t i o n s , which a re based on a c o m b i n a t i o n of m o r p h o l o g i c a l and b e h a v i o r a l c h a r a c t e r i s t i c s , were used t o group the Iona N o r t h h a r p a c t i c o i d s . E i g h t s p e c i e s of h a r p a c t i c o i d copepods b e l o n g i n g t o 5 f a m i l i e s were c o l l e c t e d as p a r t of the r o u t i n e sampling conducted through the c o u r s e of 1978 ( s p e c i e s marked w i t h an * were p r e v i o u s l y r e p o r t e d from the western c o a s t of N o r t h A m e r i c a ) : F a m i l y CANUELLIDAE Lang 1948 * S c o t t o l a n a c a n a d e n s i s ( W i l l e y 1923) C o u l l 1972 F a m i l y ECTINOSOMATIDAE Sa r s 1903 p a r t i m ; O l o f s s o n 1917 H a l e c t inosoma sp. Pseudobradya sp. 84 F a m i l y TACHIDII DAE Sa'rs 1909; Char . r e v . Lang 1948 T a c h i d i u s t r i a n g u l a r i s Shen and T a i 1963 F a m i l y CYLINDROPSYLLIDAE Sars 1909; C h a r . r e v . Lang 1948 * L e p t a s t a c u s c o n s t r i c t u s Lang 1965 P a r a l e p t a s t a c u s s p i n i c a u d a (T.& A. S c o t t 1895) F a m i l y C'LETODIDAE T . S c o t t 1904 *Huntemannia j a d e n s i s Poppe 1884 L i m n o c l e t o d e s b e h n i n q i B o r u t z k y 1926 In a d d i t i o n t o these e i g h t s p e c i e s which I w i l l c o n s i d e r i n some d e t a i l , f o u r o t h e r s p e c i e s were i d e n t i f i e d from spot c o l l e c t i o n s and f i s h gut samples from Iona N o r t h : * H a r p a c t i c u s * u n i r e m i s K r o y e r 194.2 ( F a m i l y HARPACTICIDAE) L e i m i a vaga W i l l e y 1923 ( F a m i l y CLETODIDAE) Ammonardia spp. ( F a m i l y DIOSACCIDAE) S c h i z o p e r a sp. ( F a m i l y DIOSACCIDAE) 85 B. A u t e c o l o g y 1. S c o t t o l a n a c a n a d e n s i s ( W i l l e y 1923) C o u l l 1972 N u m e r i c a l l y , the most abundant h a r p a c t i c o i d copepod at Iona N o r t h through the study p e r i o d was a b e n t h o - p e l a g i c s p e c i e s , S c o t t o l a n a c a n a d e n s i s . T h i s s p e c i e s , . o r i g i n a l l y i n the genus C a n u e l l a , was d e s c r i b e d from p l a n k t o n c o l l e c t i o n s i n the Shubenacadie R i v e r , Nova S c o t i a (about 45° N). In h i s r e d e s c r i p t i o n , C o u l l (1972) c a l l e d S. c a n a d e n s i s a s h a l l o w , b r a c k i s h , water form r e c o r d e d .from e s t u a r i e s and s a l t marshes. I t has s i n c e been found as f a r south as the G u l f of Mexico ( C o u l l 1977). S c o t t o l a n a c a n a d e n s i s was one of the dominant s p e c i e s i n two s h a l l o w , western N o r t h A t l a n t i c ecosystems; i t comp r i s e d up t o 31.0% of the h a r p a c t i c o i d community of D i v i d i n g Creek, New J e r s e y (Brickman 1972) and was an im p o r t a n t component of the h a r p a c t i c o i d copepod community of the Patuxent R i v e r e s t u a r y , M a r y l a n d ( H a r r i s 1977). In the P a t u x e n t , n a u p l i i o c c u r r e d i n l a r g e numbers (100,000-300,000 n r r 3 ) from June t o November ( H a r r i s 1977). There a r e two p r e v i o u s r e p o r t s of S. c a n a d e n s i s from the n o r t h e a s t P a c i f i c : i n Columbia R i v e r e s t u a r y p l a n k t o n ( H a e r t e l and O s t e r b e r g 1967) and the Nanaimo e s t u a r y , Vancouver I s l a n d , B.C. where i t made up o n l y 0.6% of the t o t a l b e n t h i c h a r p a c t i c o i d fauna ( S i b e r t 1979). 86 Morphology The body of S. c a n a d e n s i s i s f u s i f o r m ; i t s P.I i s n o n p r e h e n s i l e ( F i g . 17). A d u l t females i n W i l l e y ' s (1923) and C o u l l ' s (1972) c o l l e c t i o n s ranged from 1.21 t o 1.30 mm t o t a l l e n g t h ; C o u l l (1972) r e p o r t e d no s i z e d i f f e r e n c e r e s u l t i n g from the 10° d i f f e r e n c e i n l a t i t u d e between the two c o l l e c t i n g s i t e s . A d u l t females a t Iona N o r t h were somewhat s m a l l e r , 0.79 ± 0.012 mm, n = 23 on. 26 June 1980 ( e x c l u d i n g c a u d a l rami and s e t a e which add about 35% t o the t o t a l body l e n g t h ) . L i k e o t h e r members of the f a m i l y C a n u e l l i d a e , S. c a n a d e n s i s i s m o r p h o l o g i c a l l y w e l l - a d a p t e d f o r swimming; i t s t h o r a c i c l e g s remain r e l a t i v e l y u n d i f f e r e n t i a t e d , w i t h 3-segmented rami w e l l armed w i t h s e t a e . The c e p h a l i c appendages of S. c a n a d e n s i s are d e s c r i b e d and f i g u r e d i n C o u l l (1972). The major d i s t i n c t i o n between S. c a n a d e n s i s and the o t h e r Iona N o r t h s p e c i e s i s i n the morphology of t h e s e appendages ( F i g . 17) and Hooper (1981); t h e i r plumose s e t a e , p a r t i c u l a r l y on the exopods of the Md and Mx.1 and the endopods of the Mxp, s t r o n g l y suggest a d a p t a t i o n t o f i l t e r f e e d i n g ( H a r r i s 1977). B e h a v i o r S c o t t o l a n a c a n a d e n s i s i s the o n l y s p e c i e s i n the Iona N o r t h c o l l e c t i o n w i t h p l a n k t o n i c s t a g e s i n i t s l i f e c y c l e ; i t s n a u p l i i a r e p o s i t i v e l y p h o t o t a c t i c ( H a r r i s 1977) and e n t e r the p l a n k t o n soon a f t e r h a t c h i n g . Upon metamorphosis from the s i x t h 87 F i g u r e 17. S c o t t o l a n a c a n a d e n s i s . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n at the two study s i t e s t hrough 1978. SEM i s l a t e r a l view. Shaded c u r v e i s mean d e n s i t y (± 1 SE c o r e - 1 ) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded c u r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; double bar 0.05 mm. 88 89 n a u p l i a r s t a g e the c o p e p o d i t e s become n e g a t i v e l y p h o t o t a c t i c and s e t t l e t o the benthos. C o p e p o d i t e s and a d u l t s remain good swimmers and are f r e q u e n t l y e n c ountered i n e s t u a r i n e p l a n k t o n samples ( W i l l e y 1923; H a e r t e l and O s t e r b e r g 1967). I n d i v i d u a l s I o b s e r v e d i n the l a b "swam" e a s i l y through f l u i d mud and d e t r i t u s . They made f r e q u e n t , s h o r t e x c u r s i o n s i n t o the water above the sediment, " f l i t t i n g " w i t h s t r o n g , synchronous beats of t h e i r t h o r a c i c l e g s . S c o t t o l a n a c a n a d e n s i s was e q u a l l y a c t i v e when p l a c e d i n sand; i n d i v i d u a l s were observed,at t i m e s t o c r a w l a c r o s s the sand s u r f a c e but g e n e r a l l y remained b u r i e d under a few mm of sediment, a c t i v e l y t u n n e l i n g i n l o n g t r a c k s p a r a l l e l t o the s u r f a c e . P r e - c o p u l a t o r y c o u p l i n g was observed f r e q u e n t l y . I t was a m o d i f i c a t i o n of t h a t of C a n u e l l a p e r p l e x a d e s c r i b e d by V i n c x and H e i p (1979). The male c l a s p e d the female, v e n t r a l s i d e s t o g e t h e r , a t the base of her P.4 w i t h h i s g e n i c u l a t e A.1. T h i s compact arrangement d i d not v i s i b l y impede the a c t i v i t y of the f e m a l e s . Males were o c c a s i o n a l l y found c l a s p i n g females c a r r y i n g e x t e r n a l o v i s a c s . S c o t t o l a n a  canadens i s was the most fecund of the s e d i m e n t - d w e l l i n g h a r p a c t i c o i d s a t Iona N o r t h . Females c a r r i e d a p a i r of e x t e r n a l o v i s a c s , each sac c o n t a i n i n g 13-22 eggs (mean = 16.7 ± 0.42, n = 3 2 ) . S c o t t o l a n a c a n a d e n s i s i n the l a b o r a t o r y e x h i b i t e d the a b i l i t y t o f e e d w i t h a v a r i e t y of mechanisms on a broad range of food t y p e s . The most commonly used mechanism was not " f i l t e r f e e d i n g " i n the c l a s s i c a l sense of M a r s h a l l and Orr (1955); but r a t h e r m o d i f i e d s u s p e n s i o n f e e d i n g . The a n i m a l e s t a b l i s h e d a 9 0 water current from anterior to posterior over the oral appendages with beats of the mandibular palps and maxillae. Small food p a r t i c l e s (usually unbroken) were ingested by the suction created by the strong p e r i s t a s i s and a n t i p e r i s t a l s i s of the oesophagus. Larger p a r t i c l e s , large diatoms for example, were f l i c k e d toward the mouth with a strong stroke of the maxilliped and either ingested d i r e c t l y or caught, presumably with the maxillae, and crushed with the mandibles before ingestion. This feeding behavior may be viewed as Marcotte's (1977a) 'rubble sorting' refined for removing p a r t i c l e s from a di l u t e suspension. Scottolana canadensis was repeatedly observed to s t i r up fine sediments with i t s thoracic appendages, f l i p onto i t s dorsal surface and sort through the suspension created. A closely related , species, Canuella  perplexa behaves s i m i l a r l y (Vincx and Heip 1 9 7 9 ) . Scottolana canadensis observed in the laboratory exhibited a p l a s t i c i t y of feeding behaviors depending both on the type of food and type of substrate. When offered small c e l l s (e.g. Cryptomonas spp.), adult females fed as described above. They also fed on a variety of other microalgae including sand-dwelling d i n o f l a g e l l a t e s , Amphidinium sp. and Gymnodinium  placidum, benthic diatoms, Nitzschia n i c h i e l l a , pelagic chain forming diatoms (Skeletonema costatum and T h a l l a s s i o s i ra  p a c i f i c a ) , and very large (200 um diameter) centric diatoms, Coscinodiscus astereomorpha (phytoplankton c e l l s kindly provided from the Northeast P a c i f i c Culture C o l l e c t i o n , Department of Oceanography, U.B.C. by R.M. Waters). The c e l l s 91 of G. p l a c i d u m o f f e r e d t o S. c a n a d e n s i s were i n a p a l m e l l o i d phase; t h a t i s , they had l o s t t h e i r f l a g e l l a and were embedded i n a v i s c o u s mass of m u c o p o l y s a c c h a r i d e . S c o t t o l a n a c a n a d e n s i s swam s l o w l y t h rough the j e l l y , p i c k i n g out and i n g e s t i n g c e l l s which i t e n c o u n t e r e d . S c o t t o l a n a c a n a d e n s i s was o b s e r v e d t o c a t c h l a r g e c e l l s w i t h i t s Mxp w h i l e s u s p e n s i o n f e e d i n g or t o approach c e l l s s i n g l y and feed on them r a p t o r i a l l y . T h i s was a c c o m p l i s h e d m a i n l y w i t h the Mx.1 and Mx.2. The Mx.1 i s adapted d i s t a l l y f o r f i l t e r i n g but the p r e c o x a l a r t h r i t e i s armed w i t h s t o u t s p i n e s w i t h which i t can g r a s p l a r g e p a r t i c l e s , as does C a n u e l l a  p e r p l e x a ( V i n c x and H e i p 1979). The b a s i s of the Mx.2 i s armed w i t h a r o b u s t claw which the a n i m a l a l s o appears t o use f o r g r a s p i n g l a r g e items ( i t s m a x i l l i p e d s a r e not p r e h e n s i l e ) . L i k e C a n u e l l a p e r p l e x a ( V i n c x and H e ip 1979), S. c a n a d e n s i s can be c l a s s i f i e d as a mixed f e e d e r . H e i n l e et a l . ( 1-977) r e a r e d S. c a n a d e n s i s i n the l a b on a d i e t of d e t r i t u s w i t h m i c r o o r g a n i s m s i n c l u d e d a l t h o u g h a m i c r o a l g a l supplement was r e q u i r e d f o r egg p r o d u c t i o n ; egg p r o d u c t i o n and growth were a l s o good on a d i e t of p r o t o z o a , e s p e c i a l l y c i l i a t e s . I once observed S. c a n a d e n s i s f e e d i n g on a l a r g e sand d w e l l i n g nematode. A l t h o u g h I don't know how the c a p t u r e was a c h i e v e d , the nematode appeared t o be a l i v e when I f i r s t o b s e r v e d i t p r o t r u d i n g h e a d - f i r s t from the mouth of an a d u l t female copepod swimming i n a p e t r i d i s h . The copepod h e l d the prey f i r m l y w i t h the s p i n e s and c l a w s of i t s Mx.2 as d e s c r i b e d above and abraded the p r e y ' s t i s s u e w i t h i t s Mx.1 and 92 Md. I t was observed t o c o n t i n u e f e e d i n g s l o w l y f o r about 15 minutes b e f o r e d i s c a r d i n g the uneaten p o r t i o n of the prey. Two i n d i v i d u a l s from p r e s e r v e d f i e l d c o l l e c t i o n s a l s o had nematodes p r o t r u d i n g from t h e i r mouths. S c o t t o l a n a c a n a d e n s i s has an e x t r e m e l y omnivorous d i e t . I t s f e e d i n g b e h a v i o r encompasses both s u s p e n s i o n f e e d i n g and r a p t o r i a l f e e d i n g . S e a s o n a l abundance p a t t e r n The s e a s o n a l abundance p a t t e r n of S c o t t o l a n a c a n a d e n s i s i s shown i n F i g . 17. In 1978, S. c a n a d e n s i s was p r e s e n t throughout the year, i n the mud h a b i t a t . R e p r o d u c t i o n began i n e a r l y A p r i l when the temperature i n the t i d e p o o l r o s e above 13°C and l a s t e d u n t i l mid-September when the temperature f e l l below 15° C. A l t h o u g h females b e a r i n g eggs were p r e s e n t throughout t h i s p e r i o d t h e r e were t h r e e peaks i n the number of g r a v i d f e m a l e s : 1 A p r i l , 26 June and 4 Aug. R e p r o d u c t i o n ceased a b r u p t l y a t the end of September a f t e r which the p o p u l a t i o n f e l l s t e a d i l y f o r 3 months. The minimum d e n s i t y of S. c a n a d e n s i s a t Iona N o r t h was 0.58 ± 0.23 c o r e " 1 on 18 March a t the end of the w i n t e r d i e -o f f . In the f o l l o w i n g two weeks d e n s i t y i n c r e a s e d t o 36.42 ± 4.68 c o r e " 1 , 63.6% of which were e g g - b e a r i n g females ( F i g . 17) p o s s i b l y from the s e t t l e m e n t of c o p e p o d i t e s from the p l a n k t o n . The p o p u l a t i o n i n c r e a s e d f o r the f o l l o w i n g 6 months u n t i l the end of September. A g a i n s t t h i s s t e a d y p o p u l a t i o n 93 i n c r e a s e t h e r e were t h r e e l a r g e peaks i n d e n s i t y which l a g g e d one t o two months behind the peaks i n d e n s i t y of g r a v i d f e m a l e s ; the d u r a t i o n of the l a g appeared t o be r e l a t e d t o temperature ( T a b l e . 4 ) . These o b s e r v a t i o n s agree q u a l i t a t i v e l y T a b l e 4. S c o t t o l a n a c a n a d e n s i s . R e l a t i o n s h i p between peak i n t o t a l p o p u l a t i o n d e n s i t y , time ( i n days) s i n c e l a s t observed peak i n d e n s i t y of g r a v i d females and the observed temperature range (°C) i n the i n t e r p e a k p e r i o d f o r the mud p o p u l a t i o n i n 1978. DATE DENSITY TIME SINCE PEAK TEMPERATURE (no. c o r e ' 1 ) REPRODUCTION 2 5 May • 68.. 08± 6.52 ' 54 13.5 - 20.0 21 J u l y 179.92±16.70 25 17.6 - 24.5 29 Sept 178.92± 8.31 56 22.2 - 1-4.0 w i t h H a r r i s ' (1977) c u l t u r e e x p e r i m e n t s . Under c o n t r o l l e d c o n d i t i o n s , i n c l u d i n g c o n s t a n t t e m p e r a t u r e , H a r r i s (1977) r e c o r d e d g e n e r a t i o n times of 12 t o 17 days a t 25° C and 23 t o 25 days a t 20° C. The i n c r e a s e d i n t e r p e a k p e r i o d f o r l a t e summer a t Iona N o r t h c o u l d be a d i r e c t r e s u l t of f a l l i n g t e mperature a t t h a t t i m e . The s e a s o n a l abundance p a t t e r n of S. c a n a d e n s i s i n the mud i n 1978 was p o s i t i v e l y c o r r e l a t e d w i t h temperature ( r = 0.44; df = 23; p<0.05). The d e n s i t y c u r v e was bimodal w i t h a sh a r p peak i n l a t e J u l y (1085 ±41.1 10 cm" 2) and a more s u s t a i n e d 94 peak (maximum = 1084.2 ± 20.5 10 cm" 2) i n September. These d e n s i t i e s are the h i g h e s t y e t r e p o r t e d f o r the s p e c i e s . The maximum r e p o r t e d by Brickman (1972) f o r a New J e r s e y s a l t marsh cree k was 652 10 cm" 2. P a r t of the s u c c e s s of S. c a n a d e n s i s i n the mud h a b i t a t of Iona N o r t h p r o b a b l y a r i s e s from i t s t o l e r a n c e t o both h i g h temperature and a n a e r o b i o s i s (Vernberg and C o u l l 1975). A l t h o u g h the mud s i t e was not g e n e r a l l y reduced.at the s u r f a c e , the RPD was v e r y s h a l l o w (1-3 cm) i n summer ( F i g . 8 b ) . In mid-summer a s m a l l p o p u l a t i o n of S. c a n a d e n s i s became e s t a b l i s h e d a t the sand s i t e . D e m o g r a p h i c a l l y , i t d i f f e r e d from the mud p o p u l a t i o n i n h a v i n g a s i g n i f i c a n t l y h i g h e r p r o p o r t i o n of e g g - b e a r i n g females ( F i g . 17) (W i l c o x o n ' s s i g n e d rank c o m p a r i s o n , p<0.005). A l t h o u g h the number of e g g - b e a r i n g females was - u n c o r r e l a t e d w i t h t o t a l p o p u l a t i o n d e n s i t y i n the mud the two v a r i a b l e s were s i g n i f i c a n t l y c o r r e l a t e d i n the sand (Table 5 ) . Peak sand d e n s i t i e s were r e c o r d e d on 4 Aug (15.92 ± 2.92 c o r e " 1 ) . The p o p u l a t i o n d e c l i n e d s h a r p l y i n mid-September and was v i r t u a l l y gone w i t h i n a month. 95 Table 5. C o r r e l a t i o n between the observed number of o v i g e r o u s females and the t o t a l number of i n d i v i d u a l s [ e x c l u d i n g n a u p l i i ] i n Iona N o r t h h a r p a c t i c o i d p o p u l a t i o n s i n 1978 (df= 23). P o p u l a t i o n s of s p e c i e s which o c c u r r e d a t both s i t e s a r e t r e a t e d s e p a r a t e l y . SPECIES SAND MUD . r P r P. S. c a n a d e n s i s + 0.98 <0.001 + 0.15 ns H a l e c t i n o s o m a sp. + 0.96 <0.001 + 0.56 <0.01 L. c o n s t r i c t u s +0.47' <0.02 -P. s p i n i c a u d a + 0.89 <0.001 -T. t r i a n g u l a r i s + 0.99 <0.001 + 0.24 ns H. j a d e n s i s +0.30'' ns -L. b e h n i n q i - +0.64 <0.001 ' r = +0.54 a t a l a g of 45 days (p<0.0l) ' ' r = +0.89 a t a l a g of 60 days (p<0.00l) 2. H a l e c t i n o s o m a sp. The E c t i n o s o m a t i d H a l e c t inosoma sp. was an imp o r t a n t member of the w i n t e r h a r p a c t i c o i d copepod assemblage a t Iona N o r t h . To d a t e , a t t e m p t s t o i d e n t i f y t h i s s p e c i e s have been u n s u c c e s s f u l and so i t s g e o g r a p h i c a l d i s t r i b u t i o n i s unknown. A second E c t i n o s o m a t i d , Pseudobradya sp. , was a l s o found a t t h e study s i t e . Morphology The body of H a l e c t i n o s o m a sp. i s f u s i f o r m - the tor p e d o 96 shape c h a r a c t e r i s t i c of the f a m i l y ( F i g . 18). The Iona N o r t h s p e c i e s i s s m a l l ; females b e a r i n g e x t e r n a l o v i s a c s were 0.429 ± 0.004 mm (n = 41 on 22 Jan 1979). The s i z e range f o r the f a m i l y g i v e n by Noodt (1971) i s 0.5 t o 1.2 mm w i t h the s m a l l e r forms l i v i n g i n t e r s t i t i a l l y . H a l e c t inosoma sp. d i d occur d u r i n g p a r t of the study a t the sand s i t e but was more common a t the mud s i t e i n w i n t e r when i t c o n t a i n e d a h i g h p e r c e n t a g e of sandy sediments ( F i g . 9 ) . L i k e o t h e r members of the f a m i l y , H a l e c t inosoma sp. has w e l l - d e v e l o p e d . t h o r a c i c swimming l e g s ; the endopod and exopod of a l l f o u r p a i r s of l e g s a re t r i r a m o u s and equipped w i t h numerous l o n g s e t a e . The swimming b e h a v i o r of H a l e c t inosoma sp. was observed i n p e t r i d i s h e s c o n t a i n i n g sediment c o v e r e d w i t h a p p r o x i m a t e l y 1 cm of seawater. I n d i v i d u a l s swam r a p i d l y upward i n l o o s e s p i r a l s w i t h s t r o n g l e g s t r o k e s , u s i n g the c a u d a l end as a ru d d e r . The a n i m a l then stopped a b r u p t l y , p r e s s e d i t s l e g s t o i t s abdomen and s l o w l y sank on i t s back toward the sediment i n t o which i t dove w i t h a sudden s t r o n g f l e x i n g of the body. S i m i l a r b e h a v i o r was d e s c r i b e d f o r the E c t i n o s o m a t i d s s t u d i e d by M a r c o t t e (1977a). H a l e c t i n o s o m a sp. has the t i n y c e p h a l i c appendages c h a r a c t e r i s t i c of the genus ( F i g . 18). I t s A.1 a r e reduced and not used i n f e e d i n g . The antennae a r e , however, v e r y prominent. The endopod, and t o a l e s s e r e x t e n t , exopod bear l o n g , s t o u t , barbed s e t a e ( F i g . 19). The labrum i s l a r g e and bulbous w i t h a s m a l l p i c k a t i t s t i p ( F i g . 19). The mandi b l e , Mx.1 and Mx.2 resemble those f i g u r e d by M a r c o t t e •( 1977a) f o r H a l e c t i n o s o m a 97 F i g u r e 1 8 . H a l e c t i n o s o m a sp. . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two s i t e s t h r ough 1 9 7 8 . Shaded c u r v e i s mean d e n s i t y (± 1 SE c o r e " 1 ) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded c u r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; double bar 0.05 mm. NUMBER PER CORE 99 F i g u r e 19. (top) H a l e c t i n o s o m a sp. . D e t a i l of mouthparts. L-labrum Md-mandibular p a l p s - s e t a of A2 (note s p i n e s ) . S c a l e 0.005 mm. (bottom) Diatom i n c r e v i c e on sand g r a i n . S c a l e 0.005 mm. 100 101 sp.1 e x c e p t t h a t t h e t e e t h of t h e Iona N o r t h s p e c i e s a r e much b l u n t e r t h a n t h o s e of M a r c o t t e ' s s p e c i e s . The m a x i l l i p e d o f H a l e c t i n o s o m a s p . i s not p r e h e n s i l e ( F i g . 18) but t h e Mx.2 i s armed w i t h two s t o u t , c l a w l i k e s p i n e s w h i c h may have a g r a s p i n g f u n c t i o n . B e h a v i o r H a l e c t inosoma s p . i s a s a n d f i l e r . I t f e e d s i n t h e same way as M a r c o t t e (1977a) d e s c r i b e d f o r a n o t h e r u n i d e n t i f i e d H a l e c t i n o s o m a s p . from t h e West Lawrencetown M a r s h , Nova S c o t i a ; t h a t i s , i t c r a d l e s s a n d g r a i n s i n i t s p r o m i n e n t m a n d i b u l a r p a l p s and Mx.1 and a b r a d e s f o o d ( p r i n c i p a l l y d i a t o m s ) from t h e sand s u r f a c e w i t h i t s A.2 s e t a e and l a b r a l p i c k . P r e s e r v e d i n d i v i d u a l s i n f i e l d c o l l e c t i o n s were o c c a s i o n a l l y f o u n d w i t h an egg i m p a l e d on t h e Mx.2 c l a w s . L i v e i n d i v i d u a l s were n e v e r o b s e r v e d t o e x h i b i t p r e d a t o r y b e h a v i o r . P r e c o p u l a t o r y c o u p l i n g o c c u r s i n H a l e c t i n o s o m a s p . w i t h t h e male c l a s p i n g t h e f e m a l e by h e r c a u d a l s e t a e w i t h h i s A.1. The f e m a l e b e a r s from 5 t o 14 eggs i n a s i n g l e o v i s a c w h i c h i s p r o t e c t e d by t h e l o n g s t o u t s e t a e o f h e r P.5. D e t a i l s o f t h e l i f e h i s t o r y o f t h e s p e c i e s a r e unknown. F e m a l e s b e a r i n g e x t e r n a l o v i s a c s were p r e s e n t t h r o u g h most o f t h e y e a r a t Iona N o r t h s u g g e s t i n g c o n t i n u o u s r e p r o d u c t i o n . 1 02 Seaso n a l abundance p a t t e r n The s e a s o n a l abundance p a t t e r n of H a l e c t inosoma sp. i s shown i n F i g . 18. A l t h o u g h t h e s p e c i e s o c c u r r e d t h r o u g h most of the year a t both s i t e s , most of the i n d i v i d u a l s c o l l e c t e d were found a t the mud s i t e . O v i g e r o u s females were p r e s e n t i n the mud p o p u l a t i o n on a l l s a m p l i n g o c c a s i o n s except 8 June and 29 Sept 1978 but f o u r w e l l - d e f i n e d peaks i n e g g - b e a r i n g were obs e r v e d . In the summer months r e p r o d u c t i o n c o n t i n u e d a t a low l e v e l . A s m a l l i n c r e a s e i n d e n s i t y of r e p r o d u c t i v e females o c c u r r e d i n e a r l y November f o l l o w e d by a l a r g e r , more s u s t a i n e d p e r i o d of e g g - b e a r i n g . from l a t e December t o l a t e F e b r u a r y (maximum = 3.50 ± 0.68 g r a v i d females c o r e " 1 ) . The l a r g e s t peak i n r e p r o d u c t i o n o c c u r r e d i n March (max = 1.67 ± 0.4 c o r e " 1 ) w i t h a s m a l l e r peak i n A p r i l . The t o t a l p o p u l a t i o n of H a l e c t i n o s o m a sp. i n c r e a s e d from a mid-summer low t o a maximum d e n s i t y of 18.83 ± 2.33 c o r e " 1 on 8 Nov w i t h a s m a l l e r peak i n mid- September. Three more peaks o c c u r r e d between the November maximum and the summer d e c l i n e , w i t h a p p r o x i m a t e l y 2 months between the f i r s t and second and second and t h i r d peaks but o n l y 1 month b e f o r e the l a s t . The number of g r a v i d females i n the p o p u l a t i o n was p o s i t i v e l y c o r r e l a t e d w i t h the t o t a l p o p u l a t i o n d e n s i t y (Table 5 ) . The s e a s o n a l abundance p a t t e r n i n the sand was s i m i l a r t o t h a t i n the mud a l t h o u g h sand d e n s i t i e s were much lo w e r . The p o p u l a t i o n d e c l i n e d from F e b r u a r y t o e a r l y August f o l l o w e d by a s m a l l but s u s t a i n e d peak t h r o u g h the f a l l . The p o p u l a t i o n 103 d i s a p p e a r e d c o m p l e t e l y from t h e s a n d i n November but h i g h numbers were r e c o r d e d a t t h e end of J a n u a r y 1979. The h i g h p r o p o r t i o n of g r a v i d f e m a l e s i n t h i s p o p u l a t i o n (43.7%) s u g g e s t s t h a t t h e y m ight a l s o be i m m i g r a n t s from t h e mud h a b i t a t . The s e a s o n a l abundance p a t t e r n of H a l e c t inosoma s p . p r e s e n t s an i n t r i g u i n g p u z z l e . In t h i s s p e c i e s t h e m a j o r r e c r u i t m e n t of c o p e p o d i t e s o c c u r r e d i n l a t e summer, a f u l l 5 t o 6 months a f t e r t h e maximum i n number of o v i g e r o u s f e m a l e s ; a s i g n i f i c a n t p r o p o r t i o n - of t h e s e i n d i v i d u a l s d i d not become o v i g e r o u s f o r a f u r t h e r .3 months. I f t h i s was i n s i t u p r o d u c t i o n , t h i s v e r y s m a l l * s p e c i e s must have a g e n e r a t i o n t i m e of 8 t o 9 months and a v e r y l o n g n a u p l i a r l i f e . W h i l e t h i s p o s s i b i l i t y c a n n o t be r u l e d o u t on t h e b a s i s of my d a t a , I t h i n k i t h i g h l y u n l i k e l y . A more p l a u s i b l e e x p l a n a t i o n i s i n s i t u p r o d u c t i o n i n w i n t e r (November t o March) f o l l o w e d by a l a r g e d e c l i n e i n t h e p o p u l a t i o n a t f r e s h e t and t h e r e i n t r o d u c t i o n of t h e s p e c i e s f r o m t h e l o w e r i n t e r t i d a l or s h a l l o w s u b t i d a l i n t h e f a l l . E n c y s t m e n t i n summer of a d u l t s (or any s t a g e ) , s u c h as r e c e n t l y d e s c r i b e d f o r an i n t e r t i d a l p o p u l a t i o n o f H e t e r o p s y l l u s n u n n i ( C o u l l and G r a n t 1981), c o u l d p r o d u c e t h e s e a s o n a l p a t t e r n d e s c r i b e d above was not o b s e r v e d i n H a l e c t i n o s o m a sp. or any o f t h e o t h e r Iona N o r t h h a r p a c t i c o i d s . 104 3.Pseudobradya sp. In the f a l l of 1978 another E c t i n o s o m a t i d b e l o n g i n g t o the genus Pseudobradya e s t a b l i s h e d a s m a l l p o p u l a t i o n a t Iona N o r t h . Pseudobradya sp. i s v e r y s i m i l a r t o Ha l e c t i n o s o m a sp. i n g r o s s morphology ( F i g . 20); the two s p e c i e s a r e both torpedo-shaped a l t h o u g h Pseudobradya sp. was l a r g e r ( g r a v i d females = 0.65 ± 0.009 mm , n = 8; 22 Jan 1979) . Morphology and B e h a v i o r The t h o r a c i c swimming l e g s of Pseudobradya sp. d i f f e r from those of H a l e c t inosoma sp. o n l y i n minor d e t a i l s of s e t a t i o n . The c e p h a l i c appendages of the two s p e c i e s a re a l s o s i m i l a r i n th o s e f e a t u r e s i m p o r t a n t i n f e e d i n g ; t h a t i s , i n the g r o s s morphology of A.2, Md p a l p s , Mx.2 claws and non-p r e h e n s i l e Mxp. C o r r e l a t e d w i t h the s i m i l a r i t i e s i n morphology of t h e i r c e p h a l i c and t h o r a c i c appendages, Pseudobradya sp. appeared t o swim and feed i n the same way as H a l e c t i n o s o m a sp. . P r e c o p u l a t o r y c o u p l i n g i n Pseudobradya sp. was as d e s c r i b e d f o r H a l e c t i n o s o m a sp. . Female Pseudobradya sp. c a r r i e d a l a r g e r number of eggs per o v i s a c (19-33; mean = 28.4 ± 2.24, n = 6 ) . 1 05 F i g u r e 20. Pseudobradya sp. . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two s i t e s through 1978. Shaded c u r v e i s mean d e n s i t y (± 1 SE c o r e " 1 ) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded c u r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; double bar 0.05 mm. 1 07 Sea s o n a l abundance p a t t e r n The s e a s o n a l abundance p a t t e r n of Pseudobradya sp. i s not known a l t h o u g h i t appeared t o re a c h i t s l a r g e s t p o p u l a t i o n s i z e i n w i n t e r ( F i g . 20). I t o c c u r r e d i n low numbers a t both s i t e s from November t o January w i t h a maximum d e n s i t y of 5.25 ± 0.84 c o r e " 1 observed on 8 Jan 1979. In subsequent y e a r s , Pseudobradya sp. became the dominant s p e c i e s i n the m i d w i n t e r sand community (see c h a p t e r V I I I ) . R e p r o d u c t i v e a c t i v i t y , s i m i l a r l y , can o n l y be p a r t l y d e s c r i b e d from the 1978 s t u d y . Females b e a r i n g an o v i s a c were found a t the two s i t e s from November through January s u g g e s t i n g a r e p r o d u c t i v e c y c l e s i m i l a r t o t h a t d e s c r i b e d f o r H a l e c t i n o s o m a sp. . 108 4 . T a c h i d i u s t r i a n g u l a r i s Shen and T a i 1963 The f o u r t h most abundant s p e c i e s of h a r p a c t i c o i d copepod at Iona N o r t h through the c o u r s e of 1978 was T a c h i d i u s  t r i a n g u l a r i s . T h i s i s the f i r s t known r e p o r t of t h i s s p e c i e s o u t s i d e the type l o c a t i o n , the d e l t a - of the P e a r l R i v e r , Kwangtung, South China (about 23° N, near Canton and Hong Kong). T a c h i d i u s t r i a n g u l a r i s i s v e r y s i m i l a r i n form t o a c o s m o p o l i t a n congener, T. d i s c i p e s , from which i t d i f f e r s i n the s e t a t i o n of i t s f i r s t t h o r a c i c l e g and i n the d i s t i n c t i v e , t r i a n g u l a r form of i t s f i f t h l e g f o r which the s p e c i e s was named (Shen and T a i 1963). In r e c o g n i t i o n of the resemblance between T. t r i a n g u l a r i s and members of the genus M i c r o a r t h r i d i o n , p a r t i c u l a r l y M. l i t t o r a l e , T. t r i a n g u l a r i s was p l a c e d i n a new subgenus, N e o t a c h i d i u s . T a c h i d i u s t r i a n g u l a r i s o c c u r s a l s o i n the Nanaimo E s t u a r y ( S i b e r t 1979 [ i n c o r r e c t l y i d e n t i f i e d i n T a ble 2 as T. d i s c i p e s , B.A.Kask, P a c i f i c B i o l o g i c a l S t a t i o n , Nanaimo, pers.comm.]). Morphology The body of T a c h i d i u s t r i a n g u l a r i s i s f u s i f o r m ; i t s P.1 i s non-p r e h e n s i l e ( F i g . 21). T a c h i d i u s t r i a n g u l a r i s i s an i n t e r m e d i a t e - s i z e d s p e c i e s a t Iona N o r t h ( g r a v i d females = 0.40 ± 0.008 mm , n = 8, 22 Jan 1979), somewhat s m a l l e r than the 0.60 t o 0.63 mm r e p o r t e d f o r w i n t e r specimens by Shen and T a i (1963). .1 09 F i g u r e 21. T a c h i d i u s t r i a n g u l a r i s . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the two study s i t e s t h r o u g h 1978. Shaded c u r v e i s mean d e n s i t y (± 1 SE c o r e " 1 ) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded cu r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; double bar 0.05 mm. 111 T a c h i d i u s t r i a n g u l a r i s i s a s t r o n g swimmer and f l i t s between f e e d i n g s i t e s t h r o u g h t h e water column a few mm above t h e s e d i m e n t s u r f a c e . In swimming t h e a n i m a l u s e s a c o m b i n a t i o n o f s t r o n g s t r o k e s of i t s t h o r a c i c a ppendages c o u p l e d w i t h d o r s o - v e n t r a l f l e x i n g o f i t s body. T a c h i d i u s t r i a n g u l a r i s c ombines body f l e x i n g , l i m i t e d l e g movement and t h e movement of i t s c e p h a l i c a p p e n d a g e s , i n c l u d i n g i t s A.1, t o move a c r o s s t h e s e d i m e n t s u r f a c e . When i t f e e d s i n s o f t s e d i m e n t , t h e a n i m a l r e s t s l i g h t l y on t h e s e d i m e n t w i t h i t s l o n g c a u d a l s e t a e , d i s t a l t i p s ' o f i t s t h o r a c i c l e g s and i t s c e p h a l i c appendages i n c o n t a c t w i t h t h e s u r f a c e . The m o r p h o l o g y of T. t r i a n g u l a r i s i s t y p i c a l of t h e " r u b b l e s o r t e r s " d e s c r i b e d by M a r c o t t e ( 1 9 7 7 a ) . T a c h i d i us  t r i a n g u l a r i s has w e l l - d e v e l o p e d A.1 armed w i t h numerous s t o u t , b a r b e d s e t a e . The A.2 and Mxp p r o t r u d e beyond t h e o t h e r c e p h a l i c a p p endages w h i c h a r e r e l a t i v e l y s m a l l . The Mx.1 and Mx.2 a r e e q u i p p e d w i t h numerous s m a l l , n aked, c u r v e d s e t a e and s p i n e s w h i c h form a f i n e , t o o t h - l i k e comb. The c u t t i n g edge of t h e m a n d i b l e has b l u n t , r o b u s t p a r s i n c i s i v a and a p r o m i n e n t , r o u n d e d p a r s m o l a r i s . The Mxp i s p r e h e n s i l e ; t h e f i r s t endopod segment i s g r e a t l y e l o n g a t e d ; t h e s e c o n d segment s m a l l and armed d i s t a l l y w i t h a l o n g , s l i g h t l y c u r v e d , naked c l a w . The swimming l e g s a r e w e l l - d e v e l o p e d w i t h numerous plumose s e t a e and o u t e r e d g e s f r i n g e d w i t h s h o r t h a i r s . The b a s e s of t h e swimming l e g s a r e b r o a d and f l a t w i t h a b u l b o u s i n n e r e x t e n s i o n and a r e l a t e r a l l y d i s p l a c e d p r o d u c i n g a " v a u l t e d s p a c e " between t h e i n t e r c o x a l p l a t e , b a s e s and endopods l i k e t h e one d e s c r i b e d 1 1 2 i n M i c r o a r t h r i d i o n l . i t t o r a l e by M a r c o t t e (1 977a ) . B e h a v i o r The f e e d i n g b e h a v i o r of T. t r i a n g u l a r i s conforms e x a c t l y t o the " r u b b l e s o r t i n g " p r e d i c t e d from i t s barbed A . l s e t a e and the v a u l t e d space between i t s swimming l e g s . In f l u i d , s i l t y s e d i ments, T. t r i a n g u l a r i s moves s l o w l y a l o n g the sediment-water i n t e r f a c e w i t h i t s v e n t r a l s i d e t o the s u b s t r a t e . Sediment i s g a t h e r e d i n an almost c o n t i n u o u s stream by the A . l and A.2 u s i n g the barbed s e t a e . The sediment stream i s passed a c r o s s the Mx.l-Mx.2 complex where food items a r e p i c k e d out and moved a n t e r i o r l y t o the p o w e r f u l mandibles which c r u s h them i f n e c e s s a r y b e f o r e they are swallowed. The " r e j e c t e d " sediment i s moved on toward the abdominal r e g i o n by the p r e h e n s i l e Mxp and back through the v a u l t e d space between the l e g s . The f e e d i n g p r o c e s s i s c o n t i n u o u s and the a n i m a l m a i n t a i n s i t s f o r w a r d p r o g r e s s a l o n g the sediment s u r f a c e t h r o u g h o u t . The e x a c t n a t u r e of the r u b b l e b e i n g s o r t e d i s unknown a l t h o u g h a n i m a l s i n the l a b o r a t o r y were o f t e n observed t o s o r t a l o n g the mucus t r a i l s of nematodes and t u r b e l l a r i a . I t has r e c e n t l y been shown (Riemann and Schrage 1978; Warwick 1980b) t h a t nematode t r a i l s p r o v i d e a n u t r i e n t - r i c h s u b s t r a t e f o r the growth of s e l e c t e d m i c r o a l g a e and b a c t e r i a . I t i s p o s s i b l e t h a t T. t r i a n g u l a r i s robs the r i c h m i c r o f l o r a which grows on the mucus t r a p s of these o t h e r meiofauna. T a c h i d i u s t r i a n g u l a r i s changes i t s f e e d i n g b e h a v i o r i n o t h e r sediment t y p e s . . When f e e d i n g i n sandy sediment or c o a r s e r , p a r t i c u l a t e . d e t r i t u s , i t feeds more l i k e the sphere c l e a n e r s ( M a r c o t t e 1977a). P a r t i c l e s of d e t r i t u s , or s m a l l sand g r a i n s a r e h e l d under the A.2 and m a n i p u l a t e d r a p i d l y by movements of the Mxp. Food, p a r t i c u l a r l y pennate dia t o m s , i s p i c k e d from the p a r t i c l e s by the Mx.1 and Mx.2 as b e f o r e . When the a n i m a l has c l e a n e d the p a r t i c l e i t i s r e l e a s e d by an outward t h r u s t of the Mxp. The t h o r a c i c l e g s a r e not used i n t h i s f e e d i n g mode and the a n i m a l s remain s t a t i o n a r y w h i l e the food packet i s m a n i p u l a t e d . In p r e - c o p u l a t o r y c o u p l i n g , males c l a s p e d females from above and be h i n d i n . a m o d i f i c a t i o n of the p a t t e r n d e s c r i b e d f o r the f a m i l y by Lang (1948). The male's g e n i c u l a t e A.1 e n c i r c l e d the t h o r a x of the female and grasped between the second and t h i r d f r e e t h o r a c i c segments. Lang (1948 [ F i g . 6 0 7 a ] ) d e s c r i b e d the g r a s p i n g s i t e as the base of the c e p h a l o t h o r a x . Females bore 13-22 eggs (mean = 18.2 ± 0.58, n = 29) i n a s i n g l e o v i s a c . 114. S easonal abundance p a t t e r n • . . The s e a s o n a l abundance p a t t e r n of T. t r i a n g u l a r i s i s g i v e n i n F i g . 21. In 1978, T. t r i a n g u l a r i s was p r e s e n t t h rough the year i n the mud h a b i t a t . The c o n t i n u o u s presence of females b e a r i n g e x t e r n a l o v i s a c s (except on 17 Aug and 25 Nov) p r o b a b l y i n d i c a t e s c o n t i n u o u s , l o w - l e v e l r e p r o d u c t i o n . The abundance of g r a v i d females d i d vary, s l i g h t l y t h r ough the year w i t h a s m a l l i n c r e a s e i n M a r c h - A p r i l ( t o 0.5 ± 0.29 c o r e " 1 ) , a l a r g e r peak i n l a t e June (1.92 ± 0.79 c o r e " 1 ) and a t h i r d peak i n the f a l l (max = 1.92 ± 0.42 c o r e " 1 ) . In the mud., except i n August, the whole p o p u l a t i o n , f o l l o w e d r o u g h l y the same p a t t e r n of changing d e n s i t y as the g r a v i d females ( F i g . 2 1 ) , w i t h two s p r i n g peaks, a minor i n c r e a s e i n August and a l a r g e f a l l i n c r e a s e (max = 13.33 ± 1.94 c o r e " 1 ) which l a s t e d two months. The p o p u l a t i o n remained at a low l e v e l t h r ough the w i n t e r (November t o A p r i l ) . T a c h i d i u s t r i a n g u l a r i s e s t a b l i s h e d a l a r g e summer p o p u l a t i o n i n the sand i n 1978 ( F i g . 21). The demographic s t r u c t u r e of t h i s p o p u l a t i o n was d i f f e r e n t from t h a t of the summer mud p o p u l a t i o n ; 41.7 ± 5.5 % of the t o t a l sand p o p u l a t i o n over the year c o n s i s t e d of o v i s a c - b e a r i n g females (max = 72.8%) compared w i t h 15.2 ± 2.12% i n the mud. T h i s d i f f e r e n c e was s i g n i f i c a n t t h r o u g h the year ( w i l c o x o n ' s s i g n e d rank c o m p a r i s o n , P < 0.005). The number of g r a v i d females was h i g h l y c o r r e l a t e d w i t h the t o t a l p o p u l a t i o n d e n s i t y i n the sand; the two v a r i a b l e s were u n c o r r e l a t e d i n the mud (Table 5 ) . . 1 1 5 The s e a s o n a l p a t t e r n of the sand p o p u l a t i o n was d i s t i n c t from t h a t o bserved i n the mud: a v e r y l a r g e , s harp peak i n e a r l y June (55.92 ± 10.11 c o r e " 1 ) , a s m a l l peak one month l a t e r and an even s m a l l e r f a l l peak. 1 16 5. L e p t a s t a c u s c o n s t r i c t u s Lang.1965 The r a r e s t and s m a l l e s t h a r p a c t i c o i d copepod at Iona N o r t h was a t i n y , i n t e r s t i t i a l s p e c i e s , L e p t a s t a c u s c o n s t r i c t u s . T h i s s p e c i e s has been p r e v i o u s l y r e c o r d e d from two i n t e r t i d a l l o c a t i o n s on the west c o a s t of N o r t h America; from the type l o c a t i o n , f i n e sands of t i d e p o o l s a t D i l l o n Beach, C a l i f o r n i a and from medium t o f i n e sands i n E a g l e Cove, San Juan I s l a n d , Wash. USA (Gray 1968). L e p t a s t a c u s c o n s t r i c t u s was v e r y abundant a t the l a t t e r s i t e . Morphology and b e h a v i o r L e p t a s t a c u s c o n s t r i c t u s i s v e r m i f o r m ( F i g . 22) w i t h the reduced appendages ( f i g u r e d i n Lang 1965). t y p i c a l of the f a m i l y C y l i n d r o p s y l l i d a e . I t i s a l s o minute, r e a c h i n g a maximum l e n g t h of 0.35 mm (Lang 1965). L e p t a s t a c u s c o n s t r i c t u s i s ' a s t r i c t l y i n t e r s t i t i a l s p e c i e s . In sand i t moves w i t h a " j e r k y c r a w l i n g motion u s i n g the t h o r a c i c l i m b s as attachment p o i n t s and f l e x i n g the body around the g r a i n s " (Gray 1968). I t can swim f e e b l y m o s t l y by ' r u d d e r i n g ' i t s body. The appendages of L. c o n s t r i c t u s e x h i b i t the m o r p h o l o g i c a l r e d u c t i o n t y p i c a l of i n t e r s t i t i a l s p e c i e s (Swedmark 1964). The number of segments on the endopods i s reduced t o two and the number of s e t a e on a l l r a m i , p a r t i c u l a r l y the endopods, i s reduced. The female P.5 i s reduced t o a s m a l l t r i a n g u l a r p l a t e 1 7 F i g u r e 22. L e p t a s t a c u s c o n s t r i c t u s . H a b i t u s d r a w i n g and s e a s o n a l a b u n d a n c e p a t t e r n a t t h e s a n d s i t e t h r o u g h 1978. S h aded c u r v e i s mean d e n s i t y (± 1 SE c o r e " 1 ) of f e m a l e s b e a r i n g e x t e r n a l o v i s a c s ; u n s h a d e d c u r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e b a r 0.10 mm. 119 w i t h f o u r s l e n d e r s e t a e . The females bear o n l y two eggs a t a time i n a s i n g l e o v i s a c . From the morphology of i t s c e p h a l i c appendages, L. c o n s t r i c t u s can be c l a s s i f i e d as a " p o i n t f e e d e r " or " s e l e c t i v e e p i s t r a t e f e e d e r " ( M a r c o t t e 1977a). I t s A . l i s l o n g (seven segments) w i t h a l o n g a e s t h e t a s c (chemoreceptor) on the f o u r t h segment, i t s A.2 i s reduced ( e s p e c i a l l y the e x o p o d i t e ) , both i t s Md and Mx.1 are s m a l l and compact and i t s labrum i s prominent and h a i r y . The Mxp i s p r e h e n s i l e and armed w i t h a l o n g , s l e n d e r c l a w . The Mx.2 i s compact and r o b u s t ; i t s b a s i s armed w i t h a s t r o n g c l a w . L e p t a s t a c u s c o n s t r i c t u s feeds r a p t o r i a l l y on d i s c r e t e p a c k e t s of food (eg. i n d i v i d u a l d i a t o m s , c l u s t e r s of b a c t e r i a ) which i t (presumably) l o c a t e s w i t h the a i d of the a e s t h e t a s c s mentioned above. Season a l abundance p a t t e r n L e p t a s t a c u s c o n s t r i c t u s i s s t r i c t l y l i m i t e d t o c l e a n sands and so was never found i n the t i d e p o o l s of Iona N o r t h . I t f i r s t appeared a t the sand s i t e i n e a r l y March and p e r s i s t e d u n t i l l a t e summer. A s i n g l e specimen was c o l l e c t e d i n Jan 1979. Ov i g e r o u s females were c o l l e c t e d i n March and A p r i l i n low numbers. Three minor peaks i n p o p u l a t i o n d e n s i t y o c c u r r e d : mid-A p r i l , e a r l y June and e a r l y August. L e p t a s t a c u s c o n s t r i c t u s o c c u r r e d i n much h i g h e r d e n s i t i e s i n q u a l i t a t i v e c o l l e c t i o n s of c o a r s e sands lower i n the i n t e r t i d a l zone and so t h i s s m a l l Iona N o r t h p o p u l a t i o n may be e i t h e r the upper . f r i n g e of the 120 p o p u l a t i o n or an a r t i f a c t of a s e a s o n a l m i g r a t o r y p a t t e r n such as d e s c r i b e d by Gray (1968). 121 6. P a r a l e p t a s t a c u s s p i n i c a u d a (T. and A. S c o t t 1895) Moore 1975 The most a b u n d a n t s a n d - d w e l l i n g h a r p a c t i c o i d c o p e p o d a t I o n a N o r t h was t h e C y l i n d r o p s y l l i d , P a r a l e p t a s t a c u s s p i n i c a u d a s . l a t . , an i n t e r s t i t i a l s p e c i e s w i t h w i d e s p r e a d d i s t r i b u t i o n on t i d a l a n d a t i d a l b e a c h e s o f n o r t h e r n E u r o p e (Moore 1 9 7 5 ) . P a r a l e p t a s t a c u s s p i n i c a u d a a l s o o c c u r s i n S o u t h C a r o l i n a ( I v e s t e r 1 9 7 5 ) . S p e c i e s w i t h i n t h e genus P a r a l e p t a s t a c u s e x h i b i t a l a r g e d e g r e e o f p h e n o t y p i c v a r i a b i l i t y and so t h e s y s t e m a t i c s o f t h e g e nus h a v e been r e c e n t l y d i s p u t e d ( M i e l k e 1975; Moore 1 9 7 5 ) . I have f o l l o w e d t h e k e y s i n Moore (1975) i n i d e n t i f y i n g t h e I o n a N o r t h s p e c i m e n s . M o r p h o l o g y P a r a l e p t a s t a c u s s p i n i c a u d a i s s m a l l a n d v e r m i f o r m ( F i g . 23) l i k e t h e o t h e r C y l i n d r o p s y l l i d a t I o n a N o r t h , L e p t a s t a c u s c o n s t r i c t u s . The two s p e c i e s a r e e a s i l y d i s t i n g u i s h a b l e by t h e m o r p h o l o g y o f t h e t e r m i n a l s e t a e on t h e c a u d a l r a m i . L i k e L. c o n s t r i c t u s , P. s p i n i c a u d a a l s o h a s t h e r e d u c e d t h o r a c i c a p p e n d a g e s c h a r a c t e r i s t i c o f an i n t e r s t i t i a l s p e c i e s ( b i r a m o u s e n d o p o d s on P.I t o P.4 a n d r e d u c e d s e t a t i o n ) a l t h o u g h i t s P.5 d i f f e r e d f r o m t h a t o f L. c o n s t r i c t u s i n h a v i n g a d i s t i n c t b a s o e n d o p o d a n d e x o p o d . F e m a l e s b e a r 4-12 e g g s i n a s i n g l e o v i s a c . The body s i z e o f P. s p i n i c a u d a showed a d i s t i n c t i v e p a t t e r n o f v a r i a t i o n i n t i m e w h i c h w i l l be t h e s u b j e c t o f c h a p t e r V I I I . 122 F i g u r e 23. - P a r a l e p t a s t a c u s s p i n i c a u d a . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l a b u n d a n c e . p a t t e r n • a t • t h e sand s i t e t h r o u g h 1978. Note: SEM.is of a d u l t male;,A1.and A2 a r e s e x u a l l y d i m o r p h i c . Shaded c u r v e i s mean d e n s i t y (± 1 SE c o r e " 1 ) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded cu r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; double bar 0.05 mm. 124 B e h a v i o r P a r a l e p t a s t a c u s s p i n i c a u d a i s a poor swimmer. I t l e a v e s the i n t e r s t i t i a l environment o n l y o c c a s i o n a l l y and swims by f l e x i n g i t s body i n a l o o s e s p i r a l . In c o a r s e sediments i t l i v e s i n t e r s t i t i a l l y , c r a w l i n g t h r o u g h the la c u n a e w i t h l e g movements and by f l e x i n g i t s body. P r e c o p u l a t o r y c o u p l i n g , was observed once i n the. l a b . The male c l a s p e d the female's c a u d a l s e t a e w i t h h i s A.1 and the tandem c o n t i n u e d t o move f r e e l y t h r o u g h the i n t e r s t i c e s . When f e e d i n g , P a r a l e p t a s t a c u s s p i n i c a u d a moves s l o w l y around a sand g r a i n u s i n g i t s A.1. Wnen a food item ( u s u a l l y a pennate diatom) i s l o c a t e d the an i m a l manoeuvers i t s body u n t i l i t s mouthparts are p r e s s e d t o the sand g r a i n , p i c k s o f f the food (presumably w i t h i t s Mx.1, Mx.2 and t o o t h e d l a b i u m [ F i g . 24]) and pokes i t i n t o i t s mouth w i t h the l o n g claws of i t s p r e h e n s i l e Mxp and Mx.2 , the t i p s of which i n s e r t i n t o the o r a l c a v i t y ( F i g . 23). The food i s e i t h e r swallowed whole or cr u s h e d w i t h the p o w e r f u l p a r s i n c i s i v a of i t s mandibles ( F i g . 2 4 ) . P a r a l e p t a s t a c u s s p i n i c a u d a has a v e r y prominent labrum ( F i g . 24) cover e d w i t h s m a l l naked h a i r s which may se r v e some s e n s o r y f u n c t i o n . From i t s morphology and b e h a v i o r P. s p i n i c a u d a may be c l a s s i f i e d as a " s e l e c t i v e e p i s t r a t e f e e d e r " ( M a r c o t t e 1977a). 125 F i g u r e 24. P a r a l e p t a s t a c u s s p i n i c a u d a . D e t a i l of mouthparts of a d u l t female, (top) A1 - f i r s t antenna A2-second antenna L-labrum 1-labium (note t e e t h ) Md-mandible Mx-1-f i r s t . m a x i l l a . S c a l e 0.02 mm. (bottom) Note mandibular t e e t h and h a i r s on l a b i u m . S c a l e 0.005 mm. 126 127 S e a s o n a l abundance p a t t e r n P a r a l e p t a s t a c u s s p i n i c a u d a was the dominant h a r p a c t i c o i d s p e c i e s a t the sand s i t e from F e b r u a r y through A p r i l 1978 ( F i g . 2 3 ) . Between A p r i l and May i t s d e n s i t y f e l l d r a m a t i c a l l y (from 66.33 ± 8.82 c o r e " 1 on 1 Apr t o 0.91 ± 0.25 c o r e " 1 on 11 May). I s o l a t e d i n d i v i d u a l s were e n c o u n t e r e d d u r i n g the r e s t of the y e a r . O v i g e r o u s females were p r e s e n t from F e b r u a r y through A p r i l and t h e i r d e n s i t y was c o r r e l a t e d w i t h the d e n s i t y of the p o p u l a t i o n as a whole ( r = +0.89; n = 25; P<0.001.). The v i r t u a l d i s a p p e a r a n c e of a d u l t s and c o p e p o d i t e s of t h i s s p e c i e s from the sand s i t e i n the l a t t e r p a r t of 1978 i s p u z z l i n g a l t h o u g h t h e r e are a t l e a s t t h r e e p o s s i b l e e x p l a n a t i o n s . The f i r s t i s mass m o r t a l i t y from i n c r e a s i n g t e m p e r a t u r e s or d e c r e a s i n g s a l i n i t i e s . C o n s i d e r i n g t h a t the temperature and s a l i n i t y i n the c r i t i c a l p e r i o d were w e l l w i t h i n the t o l e r a n c e s of P. s p i n i c a u d a g i v e n by Jansson (1968) t h i s seems an u n l i k e l y e x p l a n a t i o n a l t h o u g h a d m i t t e d l y , the Iona N o r t h p o p u l a t i o n i s l i k e l y t o be p h y s i o l o g i c a l l y d i s t i n c t from those s t u d i e d by J a n s s o n . The second e x p l a n a t i o n i s t h a t the p o p u l a t i o n may m i g r a t e t o a d i f f e r e n t t i d e h e i g h t d u r i n g summer (Gray 1968). The t h i r d i s t h a t the s p e c i e s may produce r e s t i n g n a u p l i i ( C o u l l and Dudley 1976). Large numbers of n a u p l i i were c o l l e c t e d from the sand through most of 1978 and some of t h e s e c o u l d have been from P. s p i n i c a u d a . Large numbers of P. s p i n i c a u d a ( i n c l u d i n g g r a v i d f e m ales) were c o l l e c t e d from the sand s i t e i n June and Oct 1977 and so i t would seem t h a t 128 t h e i r s c a r c i t y a t those times i n 1978 may not have been " t y p i c a l " of the p o p u l a t i o n . 1 29 7. Huntemannia j a d e n s i s Poppe 1884 The second most abundant s p e c i e s r e s i d e n t a t the sand s i t e i n 1978 was Huntemannia j a d e n s i s . I w i l l i n c l u d e H. j a d e n s i s w i t h the i n t e r s t i t i a l s p e c i e s a l t h o u g h o n l y i t s n a u p l i i and f i r s t two c o p e p o d i t e s are t r u l y i n t e r s t i t i a l ; l a t e r s t a g e s d i s p l a c e sand g r a i n s as they c r a w l through them and so a r e , s t r i c t l y s p e a k i n g , endopsammic ( F e l l e r 1980). Lang (1948) c h a r a c t e r i z e d H. j a d e n s i s as a b r a c k i s h , s a n d - d w e l l i n g s p e c i e s ; i t s deepest r e c o r d e d o c c u r r e n c e was 18 m. Huntemannia j a d e n s i s i s a b o r e a l s p e c i e s , r e p o r t e d from beaches and f l a t s i n N o r t h e r n Europe (Lang 1948; M i e l k e 1975). On some i n t e r t i d a l beaches of Puget sound H. j a d e n s i s i s the dominant h a r p a c t i c o i d copepod (26%; 10 t o 1000'lOcm" 2) ( F e l l e r 1980). In the the Nanaimo E s t u a r y 19% of the t o t a l h a r p a c t i c o i d copepods c o l l e c t e d were H. j a d e n s i s ( c a l c u l a t e d from Table 2 of S i b e r t 1979). Huntemannia j a d e n s i s i s a component of the d i e t of j u v e n i l e salmon i n the Nanaimo E s t u a r y ( S i b e r t 1979) and i s a l s o o c c a s i o n a l l y i n g e s t e d by u n s p e c i f i e d f i s h s p e c i e s i n Puget Sound ( F e l l e r 1977). The e c o l o g y and l i f e h i s t o r y of H. j a d e n s i s were t h o r o u g h l y i n v e s t i g a t e d by F e l l e r (1977,1980). Morphology Huntemannia j a d e n s i s i s a f u s i f o r m s p e c i e s w i t h a non-p r e h e n s i l e P.1 ( F i g . 2 5 ) . A d u l t females range from 0.83 t o 1.30 mm; males a r e d i m o r p h i c - the s m a l l morph i s 0.8 t o 1.15-mm and 1 30 F i g u r e 25. Huntemannia j a d e n s i s . H a b i t u s drawing, SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n at the two s i t e s t h rough 1978. SEM i s l a t e r a l view. Shaded.curve i s mean d e n s i t y (± 1 SE core". 1) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded curve i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; double bar 0.05 mm. 131 .132 the l a r g e morph from 1.10 t o 1.55 mm ( F e l l e r 1977). Only s m a l l morph males were c o l l e c t e d from Iona N o r t h . The e x o s k e l e t o n of H. j a d e n s i s i s u s u a l l y e n c r u s t e d w i t h s m a l l m i n e r a l p a r t i c l e s . L i k e many of the C l e t o i d s , H. j a d e n s i s has m o d i f i e d t h o r a c i c l e g s , w i t h r e d u c t i o n i n both the number of segments and the number of s e t a e . I t s f i r s t l e g has a t r i - s e g m e n t e d exopod and an endopod of o n l y one segment; both rami are armed w i t h s t o u t s p i n e s . I t s second t o f o u r t h l e g s are f u r t h e r reduced, w i t h bi-segmented exopods and the endopods r e p r e s e n t e d by a minute segment armed a p i c a l l y w i t h a s i n g l e l o n g s e t a . As might be e x p e c t e d from i t s l e g morphology, H. j a d e n s i s swims p o o r l y , m o s t l y by w r i g g l i n g i t s e n t i r e body. In sediments i t burrows, u s i n g i t s l e g s , A.1, and c u r v e d c a u d a l s e t a e . I f d i s t u r b e d , e i t h e r w h i l e swimming or b u r r o w i n g , i n d i v i d u a l s c u r l i n t o an a r m a d i l l o - l i k e p o s t u r e and . remain m o t i o n l e s s f o r a p r o t r a c t e d p e r i o d . B e h a v i o r The c e p h a l i c appendages of Huntemannia j a d e n s i s are f i g u r e d i n Lang (1948); i t s f e e d i n g b e h a v i o r i s d e s c r i b e d i n F e l l e r ( 1 9 8 0 ) . Huntemannia j a d e n s i s f i t s M a r c o t t e ' s ( 1 9 7 7 a ) c a t e g o r y of "sphere c l e a n e r " and feeds i n much the same way as T. t r i a n g u l a r i s i n sand. S m a l l g r a i n s of sand are m a n i p u l a t e d by i t s w e l l -d e v e l o p e d A.2, Mx.1, Mx.2, p r e h e n s i l e Mxp and hooked s e t a e on the c a u d a l r a m i . Food items a r e p i c k e d from the s u r f a c e of the g r a i n by the Mx.1 and Mx.2 which a r e c o m b - l i k e ( r e s e m b l i n g 133 those of T. T r i a n g u l a r i s ) . Huntemannia j a d e n s i s has s t r o n g , b l u n t p a r s i n c i s i v a e and a rounded p a r s m o l a r i s f o r c r u s h i n g diatoms. Males of H. j a d e n s i s c l a s p the females by the c a u d a l rami w i t h the males' p r e h e n s i l e c l a s p e r s ( F e l l e r 1980). Females c a r r y eggs i n a p a i r of e x t e r n a l o v i s a c s . F e c u n d i t y ranges from 14-58 eggs/brood w i t h an average brood s i z e of 27.9 t o 31.6 ( F e l l e r 1980). S e a s o n a l abundance p a t t e r n Huntemannia j a d e n s i s was m o s t l y r e s t r i c t e d t o the sand s i t e a t Iona N o r t h a l t h o u g h a few i n d i v i d u a l s were o c c a s i o n a l l y found at the mud s i t e , p a r t i c u l a r l y i n w i n t e r , when i t s sand c o n t e n t was h i g h ( F i g . 9 ) . In the sand, females c a r r y i n g p a i r e d e x t e r n a l o v i s a c s appeared from l a t e F e b r u a r y t o l a t e May ( F i g . 2 5 ) . The number of o v i g e r o u s females and t h e i r c o n t r i b u t i o n t o the t o t a l p o p u l a t i o n (42 t o 61%) i n c r e a s e d s l i g h t l y between 16 Feb and 1 Apr and then f e l l s h a r p l y as the number of o v i g e r o u s females d e c l i n e d and the r e c r u i t m e n t of c o p e p o d i t e s i n t o the p o p u l a t i o n began. The l a t t e r event was accompanied by a sharp i n c r e a s e i n the t o t a l p o p u l a t i o n and a s h a r p d e c l i n e i n the p e r c e n t c o n t r i b u t i o n of g r a v i d females t o the t o t a l ( t o 6.5%) 59 days a f t e r t h e i r f i r s t appearance. R e c r u i t m e n t b a l a n c e d m o r t a l i t y f o r a p p r o x i m a t e l y 2 months and then the p o p u l a t i o n d e c l i n e d as r e c r u i t m e n t slowed., i n May and June. A minor i n c r e a s e i n the 134 number of o v i g e r o u s females i n June and J u l y was f o l l o w e d 65 days l a t e r by a minor f a l l r e c r u i t m e n t of c o p e p o d i t e s which f a i l e d t o mature. A v e r y s m a l l number of i n d i v i d u a l s s u r v i v e d t o o v e r w i n t e r as a d u l t s . The number of o v i g e r o u s females i n the p o p u l a t i o n was not s i g n i f i c a n t l y c o r r e l a t e d w i t h the t o t a l p o p u l a t i o n s i z e (Table 5) i n the same sample. C o r r e l a t i o n c o e f f i c i e n t s were r e c a l c u l a t e d w i t h the t o t a l p o p u l a t i o n time s e r i e s l a g g e d by 1,2,3,... s a m p l i n g i n t e r v a l s b e h i n d the g r a v i d female time s e r i e s . Maximum c o r r e l a t i o n s were o b t a i n e d a t a l a g of 4 sam p l i n g i n t e r v a l s ( a p p r o x i m a t e l y 60 days) i n d i c a t i n g a development time of egg + n a u p l i a r s t a g e s combined between 40 and 60 days a t f i e l d t e m p e r a t u r e s (3.5 t o 12.5° C ) . T h i s e s t i m a t e a g r e e s r e a s o n a b l y w e l l w i t h F e l l e r ' s (1980) o b s e r v a t i o n of 49.3 days a t 8° C i n l a b o r a t o r y c u l t u r e s . 135 8. L i m n o c l e t o d e s b e h n i n g i B o r u t z k y 1926 The second most abundant h a r p a c t i c o i d copepod found i n the mud h a b i t a t a t Iona N o r t h i s a s m a l l , e p i p e l i c C l e t o i d , L i m n o c l e t o d e s b e h n i n g i . F i r s t c o l l e c t e d from S a r a t o v on the V o l g a R i v e r (51° N,47° E ) , L. b e h n i n g i has been c o l l e c t e d from f r e s h and b r a c k i s h waters over a wide p a r t of A s i a and from e s t u a r i n e beaches i n s o u t h e a s t I n d i a ( B o r u t z k y 1952; W e l l s 1971). C o r r e l a t e d w i t h i t s wide d i s t r i b u t i o n , the s p e c i e s i s p h e n o t y p i c a l l y v a r i a b l e , p a r t i c u l a r l y i n the form of the female P.5 ( W e l l s 1971). Specimens from Iona N o r t h f a l l w i t h i n the v a r i a b i l i t y r e p o r t e d by W e l l s (1971). Morphology and B e h a v i o r L i m n o c l e t o d e s b e h n i n g i has a f u s i f o r m body and n o n - p r e h e n s i l e P.1; i t s e x o s k e l e t o n i s o f t e n e n c r u s t e d w i t h m i n e r a l p a r t i c l e s ( F i g s . 16 and 2 6 ) . L i m n o c l e t o d e s b e h n i n g i was the s m a l l e s t of the r e g u l a r mud r e s i d e n t s ( g r a v i d females = 0.381 ± 0.005 mm; n = 49 on 26 June 1980). U n l i k e the o t h e r C l e t o i d , H. j a d e n s i s which was m o s t l y l i m i t e d t o the sand s i t e , L. b e h n i n g i i s an e p i p e l i c s p e c i e s l i m i t e d t o the mud s i t e . I t s t h o r a c i c l e g s ( F i g . 16) a r e much b e t t e r d e v e l o p e d than those of H. j a d e n s i s , a d a p t i n g i t t o a swimming, e p i p e l i c existence!. These l e g s a r e f i g u r e d i n Smirnov (1932). The P.1 t o P.4 exopods are t r i -segmented and well-armed w i t h s e t a e . The endopods a r e b i -segmented w i t h the d i s t a l segment g r e a t l y e l o n g a t e d and armed 1 36 F i g u r e 26. L i m n o c l e t o d e s b e h n i n g i . H a b i t u s d r a w i n g , SEM of o r a l r e g i o n and s e a s o n a l abundance p a t t e r n a t the mud s i t e t h r o u g h 1978. Shaded c u r v e i s mean d e n s i t y (± 1 SE c o r e " 1 ) of females b e a r i n g e x t e r n a l o v i s a c s ; unshaded c u r v e i n d i c a t e s t o t a l p o p u l a t i o n d e n s i t y ( a d u l t s + c o p e p o d i t e s ) . S i n g l e bar 0.10 mm; .double bar 0.05 mm. NUMBER PER CORE — K J CO O i o o o o o o 1 38 a p i c a l l y w i t h two (P.1 t o P.3) or t h r e e (P.4) s e t a e . The e l o n g a t i o n of rami (by the a d d i t i o n and/or l e n g t h e n i n g of segments) and setae a l l o w L. b e h n i n g i t o swim above the sediment or t o walk on i t s f l u i d s u r f a c e . L i m n o c l e t o d e s  b e h n i n g i i s a f a s t swimmer, f l i t t i n g from p l a c e t o p l a c e j u s t above the mud/water i n t e r f a c e and a l i g h t i n g o c c a s i o n a l l y t o f e e d . M o r p h o l o g i c a l l y , L. b e h n i n g i i s t y p i c a l of M a r c o t t e ' s (1977a) sphere c l e a n e r s ( F i g s . 16 and 26). I t s A.1 and exopod of i t s A.2 a r e both armed w i t h s t o u t barbed s e t a e ; i t s A.2 a r e prominent and p r o t r u d e v e n t r a l l y t o form an ar c h e d space over the mandibles and f i r s t and second m a x i l l a e ; i t s m a x i l l i p e d s are s t r o n g and armed w i t h a c u r v e d , p r e h e n s i l e c l a w . When i t f e e d s , L. b e h n i n g i a l i g h t s on the sediment s u r f a c e , p i c k s up a sphere ( g e n e r a l l y a b a l l of d e t r i t a l mud or a fragment of macrophyte d e t r i t u s ) w i t h the a i d of the barbed s e t a e on i t s A.1 and A.2, h o l d s the p a r t i c l e i n the a r c h e d space under i t s A.2 and Mxp and then w h i r l s the p a r t i c l e r a p i d l y by the combined a c t i o n of thes e two appendages as i t g l e a n s food from the s u r f a c e w i t h i t s f i n e , c o m b - l i k e Mx.1 and Mx.2. When t h e sphere has been c l e a n e d i t i s f l i c k e d away by the Mxp. The swimming l e g s do not f u n c t i o n i n f e e d i n g . S m a l l sand g r a i n s were sometimes c l e a n e d as d e s c r i b e d above. P r e c o p u l a t o r y c o u p l i n g may be b r i e f i n t h i s s p e c i e s ; tandems were o n l y r a r e l y seen i n p r e s e r v e d samples. Males c l a s p e d f e m a l e s , v e n t r a l s i d e s t o g e t h e r , w i t h t h e i r g e n i c u l a t e A.1, g r a s p i n g the p o s t e r i o r , v e n t r a l margin of the female's 139 g e n i t a l segment. Females c a r r i e d 12-23 eggs (mean = 17.25 ±0.8) i n a s i n g l e , e x t e r n a l o v i s a c . S e a s o n a l abundance p a t t e r n At Iona N o r t h L i m n o c l e t o d e s b e h n i n g i o c c u r r e d o n l y a t the mud s i t e ( F i g . 26). Ovi g e r o u s females were c o l l e c t e d i n a l l months except December and Ja n u a r y a l t h o u g h the d e n s i t y of o v i g e r o u s females v a r i e d s e a s o n a l l y , w i t h t h r e e peaks. The f i r s t peak i n r e p r o d u c t i v e a c t i v i t y o c c u r r e d i n l a t e w i n t e r and s p r i n g . O v i g e r o u s females were not found on 25 May but g r a d u a l l y i n c r e a s e d i n number u n t i l e a r l y August. A t h i r d peak o c c u r r e d i n f a l l , f o l l o w i n g the summer peak by 1.5 months. The s e a s o n a l p a t t e r n f o r the t o t a l p o p u l a t i o n of L. b e h n i n g i was s i g n i f i c a n t l y c o r r e l a t e d w i t h t h a t of the o v i g e r o u s females ( T a b l e 5 ) . The s p e c i e s was abundant when the mud s i t e was f i r s t sampled i n F e b r u a r y and d e c l i n e d s t e a d i l y f o r 2 months f o l l o w e d by a minor peak i n e a r l y A p r i l . T h i s peak was not s u s t a i n e d and the p o p u l a t i o n d e n s i t y remained low u n t i l J u l y when the summer i n c r e a s e began. The summer maximum c o i n c i d e d w i t h the peak d e n s i t y of o v i g e r o u s females on 4 Aug. The p o p u l a t i o n d e c l i n e d s l i g h t l y i n l a t e August f o l l o w e d by a v e r y l a r g e i n c r e a s e i n September (max = 43.17 ± 3.79 c o r e " 1 ) and a r a p i d i n c r e a s e i n m o r t a l i t y i n November which reduced the p o p u l a t i o n t o w i n t e r l e v e l s . 140 C. D i s c u s s i o n The s t a n d i n g s t o c k of a d u l t s and c o p e p o d i t e s of a g i v e n s p e c i e s i n a g i v e n h a b i t a t r e p r e s e n t s the b a l a n c e between r e c r u i t m e n t (the sum of the number of i n d i v i d u a l s metamorphosing from the l a s t n a u p l i a r t o f i r s t c o p e p o d i t e stage and the number of i n d i v i d u a l s m i g r a t i n g i n t o the h a b i t a t ) and l o s s of i n d i v i d u a l s (sum of p o s t - n a u p l i a r i n d i v i d u a l s l o s t t o a l l s o u r c e s of m o r t a l i t y and i n d i v i d u a l s which m i g r a t e out of the h a b i t a t ) d u r i n g the i n t e r s a m p l i n g p e r i o d . The most imp o r t a n t e x t r i n s i c f a c t o r d e t e r m i n i n g the r a t e of passage through immature st a g e s and thus r e c r u i t m e n t i n t o the a d u l t h a r p a c t i c o i d p o p u l a t i o n i s temperature (Heip and Smol 1976a; S a r v a l a 1979; F e l l e r 1980; Palmer and C o u l l 1980). Large d i f f e r e n c e s i n temperature between the Iona. N o r t h h a b i t a t s i n 1978 were not observed ( F i g . 6 ) . I f a s p e c i e s o c c u r r e d i n both h a b i t a t s , a s i g n i f i c a n t d i f f e r e n c e i n s e a s o n a l p o p u l a t i o n p a t t e r n between the two h a b i t a t s due s o l e l y t o temperature d i f f e r e n c e s would not.be a n t i c i p a t e d . No two s p e c i e s of h a r p a c t i c o i d s a t Iona N o r t h shared p r e c i s e l y the same s e a s o n a l p a t t e r n . The d i f f e r e n c e s observed were: 1) i n t e r s p e c i f i c , w i t h i n h a b i t a t 2) i n t e r s p e c i f i c , between h a b i t a t , and 3) i n t r a s p e c i f i c , between h a b i t a t . 141 I n t e r s p e c i £ i c , W i t h i n H a b i t a t D i f f e r e n c e s i n Se a s o n a l P a t t e r n s The t e m p o r a l d i s p l a c e m e n t of r e p r o d u c t i v e p e r i o d s among s y m p a t r i c h a r p a c t i c o i d s p e c i e s which has o f t e n been o b s e r v e d ( H a r r i s 1972a; H e i p 1973; C o u l l and Vernberg 1975; F e n c h e l 1978) i s p r e d i c t e d by c o m p e t i t i o n t h e o r y . At Iona N o r t h f o r example, the t h r e e s a n d - d w e l l i n g s p e c i e s a l l occur i n the same p l a c e and eat the same food (the e p i f l o r a of sand g r a i n s ) . A l t h o u g h each i s r e p r o d u c t i v e f o r 2 t o 3 months t h e r e i s a l a g i n the onset of r e p r o d u c t i o n among the s p e c i e s (P. s p i n i c a u d a i n J a n u a r y , H. j a d e n s i s i n F e b r u a r y and L. c o n s t r i c t u s i n March) and a c o r r e s p o n d i n g l a g i n peak r e c r u i t m e n t (1 Apr, 15 Apr and 11 May, and 11 J u l y and 4 Aug, r e s p e c t i v e l y ) . The l i f e h i s t o r y of H. j a d e n s i s ( F i g . 25) i s d i f f e r e n t from those of the o t h e r i n t e r s t i t i a l s p e c i e s i n t h r e e ways: slow development, almost synchronous p r o d u c t i o n and growth of a s i n g l e c o h o r t , and v e r y l o n g g e n e r a t i o n t i m e . The s e a s o n a l p a t t e r n of P. s p i n i c a u d a ( F i g . 2 3 ) , on the o t h e r hand, suggests a s h o r t g e n e r a t i o n time as may be ex p e c t e d of a s m a l l s p e c i e s . The shape of the i n i t i a l peak of L. c o n s t r i c t u s ( F i g . 22) i s s i m i l a r t o t h a t of P. s p i n i c a u d a as i s e x p e c t e d from a r e l a t e d s p e c i e s . The d a t a suggest t h a t subsequent peaks of L. c o n s t r i c t u s may be due t o i m m i g r a t i o n , not i n s i t u p r o d u c t i o n ( u n l e s s t h i s v e r y s m a l l s p e c i e s has a development time on the o r d e r of 4 months at t e m p e r a t u r e s e x c e e d i n g 20° C ) . 142 I n t e r s p e c i f i c , Between H a b i t a t D i f f e r e n c e s i n S e a s o n a l P a t t e r n s Whereas the sand s p e c i e s a l l peaked i n s p r i n g and reproduced f o r o n l y a b r i e f t i m e , the mud s p e c i e s peaked i n f a l l and w i n t e r and t h e i r r e p r o d u c t i v e a c t i v i t y extended over a p r o t r a c t e d p e r i o d . S c o t t o l a n a c a n a d e n s i s bred f o r 5 1/2 months i n s p r i n g and summer ( F i g . 17); r e c r u i t m e n t i n t o the a d u l t p o p u l a t i o n from the p l a n k t o n o c c u r r e d c o n t i n u a l l y over t h a t t i m e . Three l a r g e peaks i n r e c r u i t m e n t f o l l o w e d peaks i n r e p r o d u c t i o n w i t h a temperature-dependent time l a g . L i m n o c l e t o d e s b e h n i n g i r e p r o d u c e d through the year except December-January ( F i g . 26). Some r e c r u i t m e n t of c o p e p o d i t e s o c c u r r e d i n J u l y a l t h o u g h the major r e c r u i t m e n t was i n September. W i t h the almost c o n t i n u o u s r e p r o d u c t i o n of L. b e h n i n g i , i t i s v e r y d i f f i c u l t t o d i s c e r n the l i f e h i s t o r y of t h i s s p e c i e s w i t h the s a m p l i n g i n t e r v a l used. O v i g e r o u s females of H a l e c t inosoma sp. were found through most of the year ( F i g . 1 8 ) . The major r e p r o d u c t i v e peak of t h i s s p e c i e s was i n w i n t e r ; i t s major r e c r u i t m e n t o c c u r r e d i n f a l l and was a p p a r e n t l y from m i g r a t i o n from o u t s i d e the h a b i t a t . The s e a s o n a l c y c l e of T a c h i d i u s t r i a n g u l a r i s i n the mud h a b i t a t was the l e a s t d i s t i n c t , w i t h almost c o n t i n u o u s , low-l e v e l r e p r o d u c t i o n and s e v e r a l peaks of c o p e p o d i t e r e c r u i t m e n t (the l a r g e s t i n e a r l y f a l l ) ( F i g . 2 1 ) . F l e e g e r ( 1 9 8 0 ) suggested t h a t c o n t i n u o u s egg p r o d u c t i o n by a c l o s e l y r e l a t e d s p e c i e s , M i c r o a r t h r i d i o n l i t t o r a l e , may be a response t o h i g h l e v e l s of p r e d a t i o n a l t h o u g h he p r e s e n t e d no s u p p o r t i n g d a t a . The 143 o b s e r v a t i o n t h a t T. t r i a n g u l a r i s i s h e a v i l y preyed upon i n summer at Iona N o r t h (see c h a p t e r V I I ) may support F l e e g e r ' s argument f o r p r e d a t o r y c o n t r o l of some e p i p e l i c h a r p a c t i c o i d s p e c i e s . I n t r a s p e c i f i c , Between H a b i t a t D i f f e r e n c e s i n Seaso n a l P a t t e r n s Two s p e c i e s e s t a b l i s h e d p o p u l a t i o n s i n both h a b i t a t s i n 1978; unexpected i n t r a s p e c i f i c d i f f e r e n c e s i n s e a s o n a l c y c l e s were noted f o r both S. c a n a d e n s i s and T. t r i a n g u l a r i s ( F i g s . 1 7 and 21 ) . S e v e r a l l i n e s of e v i d e n c e suggest t h a t t h e i r sand p o p u l a t i o n s were r e c r u i t e d from the mud and t h a t the d i s p e r s e r s were m a i n l y a d u l t s . F i r s t , both s p e c i e s were absent from the sand i n w i n t e r and s p r i n g ; s u b s t a n t i a l d e n s i t i e s appeared s u d d e n l y . Second, f o r both s p e c i e s the p r o p o r t i o n of g r a v i d females i n the sand p o p u l a t i o n was s i g n i f i c a n t l y h i g h e r than the p r o p o r t i o n i n the mud p o p u l a t i o n . T h i r d , the h i g h p o s i t i v e c o r r e l a t i o n between the d e n s i t y of o v i g e r o u s females and t o t a l p o p u l a t i o n d e n s i t y f o r both s p e c i e s ( r = +0.98 and r = +0.99 r e s p e c t i v e l y ) ( T a b l e 5) i n d i c a t e s t h a t development t i m e s a r e much s h o r t e r than the i n t e r s a m p l i n g p e r i o d or t h a t i n d i v i d u a l s a r e b e i n g r e c r u i t e d i n t o the sand p o p u l a t i o n from another h a b i t a t . The f i r s t h y p o t h e s i s seems u n l i k e l y s i n c e the mud p o p u l a t i o n s g i v e no i n d i c a t i o n of slow development. A l s o , a l t h o u g h I have not measured g e n e r a t i o n t i m e s f o r t h i s s p e c i e s i n the l a b , the l i t e r a t u r e f o r S. c a n a d e n s i s ( H a r r i s 1977) would suggest a development time of a p p r o x i m a t e l y 20 t o 30 days 1 44 a t v a r i a b l e , l a t e summer tempe r a t u r e s (compared w i t h the i n t e r s a m p l i n g time of a p p r o x i m a t e l y 14 d a y s ) . From the b e h a v i o r of these two s p e c i e s and t h e i r r e l a t i v e demographics I propose the f o l l o w i n g , p a r t l y h y p o t h e t i c a l schemes ( F i g . 27) f o r the causes of i n t e r h a b i t a t d i f f e r e n c e s i n demography observed between May and October,1978. S c o t t o l a n a c a n a d e n s i s i n the mud produced p e l a g i c n a u p l i i which i m m e d i a t e l y e n t e r e d the p l a n k t o n . The mud h a b i t a t was r e -e n t e r e d a f t e r a v a r i a b l e l a g p e r i o d by c o p e p o d i t e s ; s e v e r a l peaks i n s e t t l e m e n t o c c u r r e d throughout the summer ( F i g . . 17). The c o p e p o d i t e s matured i n the mud' and egg p r o d u c t i o n was c o n t i n u o u s through the summer. The- i n i t i a l c o l o n i z e r s a r r i v e d i n the sand i n e a r l y J u l y and were not o v i g e r o u s ; they may have come from the mud or s e t t l e d d i r e c t l y from the p l a n k t o n . A s m a l l b r e e d i n g . p o p u l a t i o n grew, presumably w i t h a s m a l l , c o n t i n u o u s s u p p l y of a d u l t s from the mud u n t i l September. No n o t i c e a b l e c o p e p o d i t e r e c r u i t m e n t i n t o the sand o c c u r r e d through t h i s t i m e ; a l l n a u p l i i produced i n the sand e n t e r e d the p l a n k t o n . The f i r s t c o l o n i z e r s of T a c h i d i u s t r i a n g u l a r i s were m a i n l y (73%) o v i g e r o u s females ( F i g . 21) which appeared i n the sand i n l a t e A p r i l . The perc e n t a g e of o v i g e r o u s females i n the sand p o p u l a t i o n remained h i g h ; a s m a l l p r o p o r t i o n of the p o p u l a t i o n were c o p e p o d i t e s and no r e a l peaks of c o p e p o d i t e r e c r u i t m e n t were obs e r v e d . The major d i s p e r s e r s i n t o the sand, t h e r e f o r e , were a d u l t females. R e p r o d u c t i v e a c t i v i t y i n the sand was p a r t i c u l a r l y h i g h i n June and J u l y . C o r r e s p o n d i n g t o t h e 1 45 F i g u r e 27. Schematic diagram of h y p o t h e t i c a l i n t e r - h a b i t a t m i g r a t i o n s by S c o t t o l a n a c a n a d e n s i s (a) and T a c h i d i u s  t r i a n g u l a r i s ( b ) . The most abundant s t a g e ( s l observed i n each h a b i t a t a r e i n d i c a t e d as w e l l as the i n f e r r e d i d e n t i t y of d i s p e r s e r s . Width of arrow i n d i c a t e s r e l a t i v e magnitude of p o p u l a t i o n movements. Losses of i n d i v i d u a l s t o p r e d a t i o n a re i n d i c a t e d by shadow drawings of l a r g e ( L e p t o c o t t u s armatus) and s m a l l ( C l e v e l a n d i a i o s ) f i s h . The dashed l i n e r e p r e s e n t s the lower boundary of the p l a n k t o n . 146 a. Scottolana canadensis MIXED S A N D M U D b. Tachidius triangularis COPEPODITES 147 i n c r e a s e i n o v i g e r o u s females of T. t r i a n g u l a r i s t h e r e was a huge bloom of n a u p l i i (max = 529 ± 60.02 c o r e " 1 ) at a time when no o t h e r sand s p e c i e s were r e p r o d u c i n g . T h i s bloom of n a u p l i i was not f o l l o w e d by a l a r g e r e c r u i t m e n t of c o p e p o d i t e s . A l t h o u g h some l a r g e (unknown) m o r t a l i t y c o u l d have caused t h i s f a i l u r e of r e c r u i t m e n t , e m i g r a t i o n of c o p e p o d i t e s i s a r e a s o n a b l e a l t e r n a t e h y p o t h e s i s . I would suggest t h a t the e m i g r a t i n g c o p e p o d i t e s r e e n t e r e d the mud h a b i t a t where they s u f f e r e d s i g n i f i c a n t p r e d a t o r y m o r t a l i t y d u r i n g the summer (see c h a p t e r V I I ) . A s i m i l a r p a t t e r n of m i g r a t i o n by a h a r p a c t i c o i d copepod was d e s c r i b e d by H i c k s (1979). In s p r i n g , a p o p u l a t i o n of T h a l e s t r i s longimana invaded an ephemeral a l g a l e p i p h y t e of Fucus s e r r a t u s i n Robin Hood's Bay, U.K.. A v e r y l a r g e p r o p o r t i o n of i n d i v i d u a l s found on the a l g a d u r i n g summer was o v i g e r o u s f e m a l e s ; c o p e p o d i t e s r e c r u i t e d d i r e c t l y i n t o the o v e r w i n t e r i n g sand p o p u l a t i o n . H i c k s a t t r i b u t e d the m i g r a t i o n t o the e x p l o i t a t i o n of a r i c h , u n p r e d i c t a b l e source of food (the e p i p h y t e ) . T a c h i d i u s t r i a n g u l a r i s females may a l s o be e x p l o i t i n g a s e a s o n a l l y r e s t r i c t e d food s o u r c e , the sand-d w e l l i n g d i n o f l a g e l l a t e s which bloom i n summer (Appendix 3 ) . I n t e r h a b i t a t d i f f e r e n c e s i n s e a s o n a l p a t t e r n s of h a r p a c t i c o i d s p e c i e s have been documented a t the community l e v e l (Brickman 1972; C o u l l and Vern b e r g 1975; I v e s t e r 1975; C o u l l and F l e e g e r 1977; M a r c o t t e 1977a). In a d d i t i o n , Brickman (1972) noted i n t e r h a b i t a t d i f f e r e n c e s i n t o t a l p o p u l a t i o n s f o r s i n g l e s p e c i e s ( i n c l u d i n g S. c a n a d e n s i s ) which he a t t r i b u t e d t o 1 48 temperature and ( i n f e r r e d ) p r e d a t i o n . In the f i r s t study of i n t e r s i t e v a r i a t i o n of l i f e h i s t o r y p a t t e r n s w i t h i n a s i n g l e s p e c i e s , Palmer (1980) showed s i g n i f i c a n t d i f f e r e n c e s i n l i f e h i s t o r y parameters f o r M i c r o a r t h r i d i o n l i t t o r a l e between an i n t e r t i d a l and a s u b t i d a l marsh s i t e i n South C a r o l i n a i n c l u d i n g d i s p l a c e m e n t i n the month of maximum o c c u r r e n c e ( J u l y i n the i n t e r t i d a l and October i n the s u b t i d a l ) . T a c h i d i u s t r i a n g u l a r i s and M i c r o a r t h r i d i o n l i t t o r a l e a r e e c o l o g i c a l l y e q u i v a l e n t s p e c i e s ; they a re m o r p h o l o g i c a l l y s i m i l a r (Shen and T a i 1963), feed i n the same way ( M a r c o t t e 1977a and c h a p t e r I V . B . 4 ) , are e p i b e n t h i c and good swimmers, and reproduce y e a r - r o u n d (Palmer 1980 and F i g . 21, t h i s t h e s i s ) . T a c h i d i u s t r i a n g u l a r i s shows a s i m i l a r d i s p l a c e m e n t i n t i m i n g of peak p o p u l a t i o n s i z e between two h a b i t a t s ( J u n e - J u l y i n the sand and Sept-Nov i n the mud). A l t h o u g h Palmer (1980) d i s c o u n t e d p a s s i v e i m m i g r a t i o n between h a b i t a t s as a f a c t o r i n her study on the ground t h a t sediment was not d e p o s i t e d a t the i n t e r t i d a l marsh s i t e , up t o 48% of the s u r f a c e - d w e l l i n g h a r p a c t i c o i d copepods ( i n c l u d i n g M. l i t t o r a l e ) i n s o f t sediments may be t i d a l l y resuspended ( B e l l and Sherman 1980).. F u r t h e r , on the orde r of 20% of the resuspended copepods o c c u r r e d i n c l e a r water above the suspended sediment ( B e l l and Sherman 1980). I m m i g r a t i o n of e p i b e n t h i c copepods a t a s i t e need n o t , t h e r e f o r e , be accompanied by the d e p o s i t i o n of sediment. T h i s i n t e r p r e t a t i o n has been f u r t h e r r e i n f o r c e d by the r e c e n t f i n d i n g s of Palmer and Brandt (1981) who suggested t h a t s i g n i f i c a n t changes i n sediment d e n s i t i e s of M. l i t t o r a l e 149 d u r i n g a t i d a l c y c l e are the r e s u l t of e m i g r a t i o n ( e i t h e r a c t i v e or p a s s i v e ) i n t o the water column. The d i s p e r s a l of the meiobenthos has o n l y r e c e n t l y a t t r a c t e d i n t e r e s t ( G e r l a c h 1977a). The r a p i d r e c o l o n i z a t i o n of de f a u n a t e d s u b s t r a t e by h a r p a c t i c o i d copepods ( T h i s t l e 1980) and the presence, of meiofauna,above the sediment s u r f a c e ( B e l l and Sherman 1980) bo t h i n d i c a t e s i g n i f i c a n t t i d a l movement of the meiobenthos. Whil e too l i t t l e i s known of the phenomenon t o g e n e r a l i z e w i d e l y about i t s consequences, i t i s c l e a r t h a t i t i s p r o b a b l y of g r e a t e r importance f o r the l a r g e r , e p i b e n t h i c forms which a re good swimmers. I t c e r t a i n l y a c t s s e l e c t i v e l y on a subset of the community and so w i l l have im p o r t a n t i m p l i c a t i o n s f o r the community e c o l o g y of t i d a l systems. L a s t l y , i t s h o u l d be c l e a r t h a t a m e i o b e n t h i c s p e c i e s such as T. t r i a n g u l a r i s may use s e l e c t i v e t i d a l r e s u s p e n s i o n as a d i s p e r s a l mechanism w i t h i m p o r t a n t i m p l i c a t i o n s f o r i t s c o m p e t i t i v e and p r e d a t o r - p r e y i n t e r a c t i o n s . C o m p e t i t i o n w i l l be d i s c u s s e d i n c h a p t e r V I I I and p r e d a t i o n i n c h a p t e r V I I . D. Summary S c o t t o l a n a c a n a d e n s i s was an e x t r e m e l y s u c c e s s f u l component of the h a r p a c t i c o i d copepod community a t Iona N o r t h ; i t r e produced through the summer when the temperature was h i g h and the water b r a c k i s h and a t t a i n e d v e r y h i g h d e n s i t i e s i n September. The broad p h y s i o l o g i c a l t o l e r e n c e of the s p e c i e s c o u p l e d w i t h i t s d i e t a r y and b e h a v i o r a l p l a s t i c i t y u ndoubtedly a l l o w S. c a n a d e n s i s both t o dominate i t s own h a b i t a t and t o 150 invade n e i g h b o r i n g ones when c o n d i t i o n s a r e r i g h t . Other members of t h i s f a m i l y , eg. C a n u e l l a p e r p l e x a and C. f u r c i g e r a a re s i m i l a r l y s u c c e s s f u l members of b o r e a l , b r a c k i s h water, s h a l l o w or i n t e r t i d a l communities ( B a r n e t t 1968; Heip 1973). H a l e c t i n o s o m a sp. was a prominent member of the w i n t e r community a t both s i t e s a l t h o u g h i t was both more abundant and more p e r s i s t e n t a t the mud. A l t h o u g h g r a v i d females were found t h r o u g h most of the y e a r , r e p r o d u c t i o n o c c u r r e d m a i n l y i n w i n t e r . The Iona N o r t h p o p u l a t i o n showed s i g n s of r e c r u i t m e n t from o t h e r h a b i t a t s . The o t h e r E c t i n o s o m a t i d , Pseudobradya sp. , was a r e l a t i v e newcomer t o Iona N o r t h . I t i s v e r y s i m i l a r i n most of i t s known e c o l o g y t o H a l e c t inosoma sp. a l t h o u g h l a r g e r and more f e c u n d . T a c h i d i u s t r i a n g u l a r i s l i v e d . and repr o d u c e d t h r o u g h the year i n the mud of Iona N o r t h i n d i c a t i n g t h a t i t has broad p h y s i o l o g i c a l t o l e r a n c e s and can be c o n s i d e r e d an e s t u a r i n e s p e c i e s . H i g h e s t d e n s i t i e s o c c u r r e d i n summer when the water temperature was h i g h e s t . L i k e S c o t t o l a n a c a n a d e n s i s , T a c h i d i u s  t r i a n g u l a r i s s u c c e s s f u l l y i n v a d e d the sand h a b i t a t i n summer where i t e s t a b l i s h e d a l a r g e p o p u l a t i o n of b r e e d i n g f e m a l e s . C o p e p o d i t e s of t h i s s p e c i e s were r a r e l y found i n the sand and so (presumably) moved back t o the mud. I t s s u c c e s s i n the sand was undoubtedly due i n p a r t t o i t s a b i l i t y t o change f e e d i n g modes from r u b b l e s o r t i n g i n the mud t o sphere c l e a n i n g i n the sand. The e c o l o g y of t h i s s p e c i e s w i l l be c o n s i d e r e d f u r t h e r i n f u t u r e s e c t i o n s , p a r t i c u l a r l y i t s r e l a t i o n s h i p t o the p r e d a t o r s i n the t i d e p o o l s . 151 L e p t a s t a c u s c o n s t r i c t u s appeared t o be a s e a s o n a l , t r a n s i e n t a t Iona N o r t h , f o r m i n g a s m a l l p a r t of the s p r i n g and summer sand assemblage. I t i s c l o s e l y r e l a t e d t o a n o t h e r , l a r g e r C y l i n d r o p s y l l i d a t Iona N o r t h , P a r a l e p t a s t a c u s  s p i n i c a u d a . Both s p e c i e s are s e l e c t i v e e p i s t r a t e f e e d e r s . P a r a l e p t a s t a c u s s p i n i c a u d a was '. the most abundant i n t e r s t i t i a l s p e c i e s a t Iona N o r t h . A s i n g l e broad peak of b r e e d i n g a c t i v i t y was observed i n w i n t e r , accompanied by a l a r g e i n c r e a s e i n p o p u l a t i o n d e n s i t y . The p o p u l a t i o n c r a s h e d a b r u p t l y i n A p r i l . The cause of the c r a s h or the f a i l u r e of the p o p u l a t i o n t o r e c o v e r are not known. The e c o l o g y of t h i s s p e c i e s w i l l be c o n s i d e r e d i n more d e t a i l i n c h a p t e r V I I I . Huntemannia j a d e n s i s was much l e s s common at Iona N o r t h i n 1978 compared w i t h o t h e r P a c i f i c c o a s t a l h a b i t a t s . I t was m o s t l y r e s t r i c t e d t o the sand where i t produced two g e n e r a t i o n s i n 1978, the second of which m o s t l y f a i l e d t o mature. L i m n o c l e t o d e s b e h n i n q i was a major component of the mud h a r p a c t i c o i d fauna of Iona N o r t h . I t reproduced t h r o u g h most of 1978 a l t h o u g h h i g h e s t d e n s i t i e s of o v i g e r o u s females were c o l l e c t e d i n l a t e summer when te m p e r a t u r e s were h i g h and s a l i n i t i e s low. 152 V. FACTOR ANALYSIS OF IONA NORTH HARPACTICOID COMMUNITIES TEMPORAL PATTERNS "There i s no s e a r c h f o r t i m e l e s s , s p a c e l e s s , p o p u l a t i o n l e s s t r u t h i n f a c t o r a n a l y s i s ; r a t h e r , i t r e p r e s e n t s a s i m p l e , s t r a i g h t f o r e w a r d problem of d e s c r i p t i o n i n s e v e r a l d i m e n s i o n s of a d e f i n i t e group f u n c t i o n i n g i n d e f i n i t e manners, and he who assumes t o read more remote v e r i t i e s i n t o the f a c t o r i a l outcome i s c e r t a i n l y doomed t o d i s a p p o i n t m e n t . " T.L. K e l l e y (1940) A. I n t r o d u c t i o n P o p u l a t i o n s of m e i o b e n t h i c s p e c i e s are h e t e r o g e n e o u s l y d i s t r i b u t e d ' i n space and t h r o u g h t i m e . The a f f i n i t y of p a r t i c u l a r s p e c i e s f o r p a r t i c u l a r sediment regimes i s the p r i m a r y cause of s p a t i a l v a r i a b i l i t y (Por 1964; Noodt. 1971; F e n c h e l 1978). The d i f f e r e n t i a l response of i n d i v i d u a l s p e c i e s or s p e c i e s complexes t o s e a s o n a l c u e s , such as t h o s e d e s c r i b e d i n the p r e c e d i n g c h a p t e r , cause tempo r a l f l u c t u a t i o n s i n s p e c i e s c o m p o s i t i o n (Bodiou and Chardy 1973; C o u l l and Vernberg 1975; H e i p 1977,1980). Attempts t o i d e n t i f y m u l t i - s p e c i e s communities must ta k e both s p a t i a l and t e m p o r a l p a t t e r n s i n t o a c c o u n t . The o b j e c t i v e i d e n t i f i c a t i o n of assemblages (or communities) of marine s p e c i e s has been f a c i l i t a t e d by the i n t r o d u c t i o n of m u l t i v a r i a t e s t a t i s t i c a l t e c h n i q u e s ( C a s s i e 1963; W i l l i a m s o n 1963; Angel and Fasham 1973; E l e f t h e r i o u and N i c h o l s o n 1975; L e v i n g s 1975). The a d o p t i o n of t h e s e m u l t i v a r i a t e t e c h n i q u e s by m e i o b e n t h o l o g i s t s has been 1 53 v e r y r e c e n t ; s i n c e f i r s t a p p l i e d by Bodiou and Chardy (1973) they have been used m a i n l y t o r e s o l v e s p a t i a l p a t t e r n s . M u l t i v a r i a t e a n a l y s e s have r e c e n t l y been used t o c o n f i r m the prime r o l e of sediment v a r i a b l e s , p a r t i c u l a r l y median g r a i n d i a m e t e r and p e r c e n t s i l t - c l a y , i n d e t e r m i n i n g m e i o b e n t h i c community s t r u c t u r e : i n a South C a r o l i n a marsh cre e k system by m u l t i p l e - d i s c r i m i n a n t - c a n n o n i c a l c o r r e l a t i o n a n a l y s i s ( I v e s t e r 1975,1980), i n a Nova S c o t i a s a l t marsh by p r i n c i p a l c o m p o n e n t s - d i s c r i m i n a n t f u n c t i o n a n a l y s i s ( M a r c o t t e 1977a) and i n the I r i s h . S e a by p r i n c i p a l components a n a l y s i s (Moore 1979a and b ) . Both I v e s t e r (1980) and M a r c o t t e noted s e a s o n a l change i n community p a t t e r n s a l t h o u g h i n both s t u d i e s the sampling i n t e r v a l (2 and 3 months, r e s p e c t i v e l y ) was too l o n g t o a l l o w the f u l l r e s o l u t i o n of tempo r a l p a t t e r n s . F a c t o r a n a l y s i s p r o v i d e s a mechanism f o r the compact d e f i n i t i o n of p a t t e r n s of community change through time and f o r comparison of these p a t t e r n s a t sam p l i n g s i t e s w i t h d i f f e r e n t p h y s i c a l c h a r a c t e r i s t i c s . The major c o n t r i b u t i o n of f a c t o r a n a l y s i s t o e c o l o g i c a l s t u d i e s may be as as e x p l o r a t o r y t o o l -t o suggest hypotheses f o r f u t u r e t e s t i n g - and I w i l l use i t i n t h i s way i n t h i s t h e s i s t o uncover p a t t e r n s of community change i n two a d j a c e n t s i t e s which may be due t o b i o l o g i c a l p r o c e s s e s . In t h i s c h a p t e r I w i l l use f a c t o r a n a l y s i s t o i d e n t i f y the dominant p a t t e r n s of tempo r a l v a r i a b i l i t y i n the h a r p a c t i c o i d copepod community of Iona N o r t h . The a n a l y s i s w i l l be extended t o d etermine a l s o a) groups of s p e c i e s w i t h s i m i l a r h a b i t a t a f f i n i t i e s and s e a s o n a l p a t t e r n s and b) d i f f e r e n c e s i n p a t t e r n s 154 of community change t h r o u g h time a t two s i t e s w i t h d i f f e r e n t sediment p r o p e r t i e s . B. Methods For assessment of p a t t e r n s of abundance, f a u n a l samples were c o l l e c t e d at a p p r o x i m a t e l y b i - w e e k l y i n t e r v a l s from 4 Feb 1978 t o 22 Jan 1979. C o l l e c t i o n and treatment of samples were as d e s c r i b e d i n c h a p t e r I I . R e s u l t s from a t o t a l of 25 sampling t r i p s (='times') t o two s i t e s (sand and mud) were used i n the f a c t o r a n a l y s i s . D i v e r s i t y i n d i c e s were c a l c u l a t e d as d e s c r i b e d i n c h a p t e r V I . P r i o r t o d a t a m a n i p u l a t i o n , s p e c i e s c o u n t s were n o r m a l i z e d by a ln(x+1) t r a n s f o r m a t i o n ( E l l i o t 1971). A n a l y s e s were performed by computer programs from the S t a t i s t i c a l Package f o r the S o c i a l S c i e n c e s ( S P S S : v e r s i o n 8; Nie et a l . 1975; H u l l and Nie 1979). Two s e p a r a t e modes of f a c t o r a n a l y s i s were a p p l i e d t o the d a t a : R-mode which t r e a t e d the s p e c i e s as v a r i a b l e s and Q-mode which t r e a t e d the sa m p l i n g t r i p s as v a r i a b l e s . j _ . R-mode : Spec i e s as var i a b l e s E i g h t s p e c i e s of h a r p a c t i c o i d copepods were encountered r e g u l a r l y i n f a u n a l samples. These s p e c i e s were taken t o c o n s t i t u t e the community and were used i n the f a c t o r a n a l y s i s : H a l e c t i n o s o m a sp. (HAL) Huntemannia jadensis(HUN) L e p t a s t a c u s c o n s t r i c t u s ( L E P L i m n o c l e t o d e s b e h n i n g i ( L I M ) P a r a l e p t a s t a c u s s p i n i c a u d a ( P A R ) Pseudobradya sp. (PSE) S c o t t o l a n a canadensis(SCO) T a c h i d i u s t r i a n g u l a r i s ( T A C ) The m a t r i x of o b s e r v a t i o n s f o r the f a c t o r a n a l y s i s c o n s i s t e d of the means of t r a n s f o r m e d counts f o r each of the 1 56 i =• 1 to n species in k = 1 to 50 time/habitat samples (k = 1 to 25 and k = 26 to 50 were observations made on successive sampling t r i p s to the sand and mud habitats respectively). The matrix of observations ( y i k ) may be reexpressed in vector notation as Y i which is the vector of mean counts in each of the 50 samples of the i t h species. This vector notation w i l l be used in the remainder of the chapter. Factor analysis is a method of analysing the correlations among a set of n variables (each variable is a vector Y_^ ) which aims to resolve the linear relationships in the data in terms of a number of common factors. The method extracts m factors (m << n) which retain the underlying structure of the o r i g i n a l data. The factor analysis was ca r r i e d out in • four steps (Nie et a l . 1975): 1 ) An n x n correlation matrix of the o r i g i n a l variables ( i . e . vectors Y ) was calculated using product-moment corr e l a t i o n c o e f f i c i e n t s . This step replaces the o r i g i n a l variables with new variables (Z ) with means of 0 and unit j variances. 2) I n i t i a l factors were extracted by a p r i n c i p a l components analysis of the correlation matrix. Each factor is a vector which i s a linear combination of the n variable vectors and i s orthogonal (uncorrelated) to a l l other factors. Each variable may then be expressed as a l i n e a r combination of these 157 n f a c t o r s : (5) Z = " a F = a_ F i + a F2+...+a Fn j = 1 , 2 , . . . n i = l j i i j l j 2 j n The f a c t o r s a r e e x t r a c t e d s e q u e n t i a l l y s u c h t h a t e a c h a c c o u n t s f o r t h e maximum r e m a i n i n g v a r i a n c e i n t h e d a t a . The f a c t o r l o a d i n g s ^ a ^ ± ) a r e c o r r e l a t i o n s b e t ween t h e j t h v a r i a b l e and t h e i t h f a c t o r , s t a n d a r d i z e d so t h a t -1.0 < a . . < +1.0. The f i r s t few f a c t o r s ( F l , . . . r F m ; m < n) g e n e r a l l y a c c o u n t f o r a l a r g e p a r t o f t h e v a r i a n c e a n d a r e t h e o n l y o n e s r e t a i n e d f o r r o t a t i o n t o t h e t e r m i n a l s o l u t i o n . I n t h i s a n a l y s i s o n l y t h o s e f a c t o r s w i t h a s s o c i a t e d e i g e n v a l u e s g r e a t e r t h a n 1.0 ( i . e . . t h o s e f a c t o r s w h i c h a c c o u n t f o r more v a r i a n c e t h a n t h e o r i g i n a l v a r i a b l e s ) were c a r r i e d o v e r t o t h e f i n a l s t e p s . The p o s i t i o n o f s p e c i e s j r e l a t i v e t o t h e two a x e s r e p r e s e n t e d by F1 a n d F2 i s g i v e n by i t s f a c t o r l o a d i n g s . ( a ^ ) . 3) To s i m p l i f y t h e f a c t o r s t r u c t u r e and a i d i n i n t e r p r e t a t i o n , t h e f i r s t two f a c t o r s ( w h i c h t o g e t h e r a c c o u n t e d f o r 65.6% o f t h e v a r i a n c e ) were r o t a t e d u s i n g t h e VARIMAX c r i t e r i o n ( N i e e t a l . 1 9 7 5 ) . The v a r i a b l e s r e t a i n t h e i r p o s i t i o n s r e l a t i v e t o e a c h o t h e r f o l l o w i n g r o t a t i o n , b u t t h e i r a f f i n i t i e s f o r t h e r o t a t e d f a c t o r s a r e c l e a r e r t h a n f o r t h e u n r o t a t e d o n e s . F o r s i m p l i c i t y , o n l y p l o t s o f t h e v a r i a b l e s r e l a t i v e t o t h e r o t a t e d f a c t o r s w i l l be p r e s e n t e d . 158 4) The components of each f a c t o r v e c t o r ( t h a t i s , the v a l u e of each f a c t o r i n each sample - the s o - c a l l e d f a c t o r s c o r e s ) were p l o t t e d f o r f a c t o r 1 and f a c t o r 2. These p l o t s w i l l be r e f e r r e d t o as the f a c t o r s c o r e p l o t s . 2. Q-mode: Samples as v a r i a b l e s T h i s a n a l y s i s was c a r r i e d out t o compare p a t t e r n s of temporal changes i n community s t r u c t u r e of h a r p a c t i c o i d s at the sand and mud s i t e s . The o r i g i n a l d a t a m a t r i x was s p l i t i n t o two m a t r i c e s ; k = 1 t o 25 was the sand m a t r i x and k = 26 t o 50 the mud. These two m a t r i c e s were a n a l y s e d separately^. B e f o r e a n a l y s i s , the da t a m a t r i c e s were t r a n s p o s e d so t h a t the rows-were s p e c i e s and the columns ( v a r i a b l e s ) were samples. T h i s d i f f e r e n c e i n the form of the i n p u t m a t r i x i s the fundamental d i s t i n c t i o n between the two f a c t o r a n a l y s i s modes. Q-mode a n a l y s i s was performed on the s t e p s d e s c r i b e d above f o r the R-mode a n a l y s i s . The c o r r e l a t i o n m a t r i x (25 x 25) r e p r e s e n t e d c o r r e l a t i o n s between p a i r s of samples i n s t e a d of p a i r s of s p e c i e s . As i n the R-mode a n a l y s i s , two f a c t o r s were r e t a i n e d f o r t e r m i n a l r o t a t i o n . T o g ether, the f i r s t two f a c t o r s a c c o u n t e d f o r 67.9% and 92.0% of the sand and mud v a r i a n c e s , r e s p e c t i v e l y . The f a c t o r s c o r e s were c a l c u l a t e d and p l o t t e d as i n R-mode. 159 C. R e s u l t s j _ . R-mode f a c t o r a n a l y s i s a. I d e n t i f i c a t i o n of groups of s p e c i e s from f a c t o r l o a d i n g s The c l u s t e r i n g of s p e c i e s on the f i r s t two p r i n c i p a l f a c t o r s i s shown i n F i g . 28. F a c t o r 1 accounted f o r 46.0% of the v a r i a n c e , f a c t o r 2 f o r 19.0%. Both f a c t o r s are b i p o l a r and t o g e t h e r s e p a r a t e the e i g h t s p e c i e s i n t o t h r e e groups: a) Group 1 : V a r i a b l e s ( s p e c i e s ) w i t h p o s i t i v e l o a d i n g s on f a c t o r 2 and n e g a t i v e l o a d i n g s on f a c t o r 1. Group 1 c o n t a i n s 3 s p e c i e s , a l l i n t e r s t i t i a l i n h a b i t (see c h a p t e r I V ) : Huntemannia j a d e n s i s  L e p t a s t a c u s c o n s t r i c t u s  P a r a l e p t a s t a c u s s p i n i c a u d a b) Group 2 : V a r i a b l e s ( s p e c i e s ) w i t h h i g h p o s i t i v e l o a d i n g s on f a c t o r 1 and low l o a d i n g s ( p o s i t i v e and n e g a t i v e ) on f a c t o r 2. Group 2 i n c l u d e s 3 s p e c i e s , a l l e p i p e l i c / b u r r o w i n g i n h a b i t : L i m n o c l e t o d e s b e h n i n g i  S c o t t o l a n a c a n a d e n s i s T a c h i d i u s t r i a n g u l a r i s c) Group 3_ : V a r i a b l e s ( s p e c i e s ) w i t h h i g h l y n e g a t i v e l o a d i n g s 1 60 F i g u r e 28. H a r p a c t i c o i d s p e c i e s p l o t t e d i n the space d e f i n e d by the f i r s t two p r i n c i p a l f a c t o r s (R-mode) 1 6 1 GrOUp 1: INTERSTITIAL Huntemannia jadensis ( Hun ) Leptastacus constrictus ( Lep ) Paraleptastacus spinicauda (Par) Group 2 : EPIPELIC / BURROWING Limnocletodes behningi (Lim) Scottolana canadensis (Sco ) Tachidius triangularis ( Tac ) Group 3 : EPIPSAMMIC / BURROWING Halectinosoma sp. (Hal) Pseudobradya sp. (Pse J 162 o n - f a c t o r 2 and low l o a d i n g s ( n e g a t i v e and p o s i t i v e ) on f a c t o r 1. Group3 c o n s i s t s of 2 s p e c i e s , both E c t i n o s o m a t i d s , epipsammic and bu r r o w i n g i n h a b i t : H a l e c t i n o s o m a sp. Pseudobradya sp. b. I d e n t i f i c a t i o n of s e a s o n a l p a t t e r n s of groups from f a c t o r  s c o r e s P l o t s of f a c t o r s c o r e s w i t h time ( F i g . 29) have two p o s s i b l e i n t e r p r e t a t i o n s . The f i r s t comes from the way the f a c t o r s a r e d e f i n e d ; t h a t i s , as l i n e a r c o m b i n a t i o n s of v a r i a b l e s . Each f a c t o r has a v a l u e (the f a c t o r s c o r e ) f o r each sample. When these f a c t o r s c o r e s a re p l o t t e d i n sequence (as i n F i g . 2 9 ) , the r e s u l t i n g p l o t r e p r e s e n t s a p a t t e r n of v a r i a t i o n t h r o u g h time (and between s i t e s ) which i s shared by (or 'common t o ' ) two or more of the v a r i a b l e s (or s p e c i e s ) . The f a c t o r l o a d i n g s i n d i c a t e how s i m i l a r the s e a s o n a l abundance p a t t e r n of a p a r t i c u l a r s p e c i e s i s t o the 'common p a t t e r n ' r e p r e s e n t e d by t h a t f a c t o r . By combining the i n f o r m a t i o n i n F i g s . 28 and 29, t h e n , i t i s p o s s i b l e t o i d e n t i f y groups w i t h s i m i l a r p a t t e r n s of v a r i a t i o n ( i . e . , s p e c i e s w i t h s i m i l a r f a c t o r l o a d i n g s , F i g . 29) and t o i d e n t i f y the p a t t e r n which i s shared by t h a t group. Group 1, the i n t e r s t i t i a l s , i s a s s o c i a t e d ( h i g h f a c t o r l o a d i n g s ) w i t h f a c t o r 2 ( F i g . 2 8 ) . The s e a s o n a l p a t t e r n f o r the i n t e r s t i t i a l s as a group, t h e n , i s 163 F i g u r e 29. F a c t o r s c o r e s d e r i v e d from s e a s o n a l abundance data i n the sand and mud h a b i t a t s p l o t t e d a g a i n s t time (R-mode) F a c t o r s c o r e of 0 i n d i c a t e s average abundance. N e g a t i v e s c o r e s i n d i c a t e below average abundances. P o s i t i v e s c o r e s i n d i c a t e above average abundances. FACTOR SCORE FACTOR SCORE • • . . . . • • i 1 65 r e p r e s e n t e d by the f a c t o r s c o r e p l o t of f a c t o r 2 ( F i g . 29, bottom). These s p e c i e s occur m a i n l y i n the sand and have h i g h e r than average d e n s i t i e s i n the e a r l y p a r t of the year ( F e b r u a r y to J u l y ) . Group 2, the e p i p e l i c s , i s a s s o c i a t e d . w i t h f a c t o r 1 ( F i g . 28). The predominant s e a s o n a l p a t t e r n of t h i s group i s r e p r e s e n t e d by the f a c t o r s c o r e p l o t of f a c t o r 1 ( F i g . 29, t o p ) . These s p e c i e s occur m a i n l y i n the mud w i t h h i g h e r than average d e n s i t i e s t h r o u g h most of the y e a r , a broad peak of abundance i n e a r l y f a l l and lower than average abundance i n w i n t e r . Group 2 a l s o o c c u r s i n the sand, f o r a r e l a t i v e l y b r i e f p e r i o d i n mid-summer. Group 3 i s v e r y n e g a t i v e l y c o r r e l a t e d w i t h f a c t o r 2 ( F i g . 28). The s e a s o n a l p a t t e r n of group 3 t h e r e f o r e resembles t h e ' i n v e r s e of the f a c t o r s c o r e p l o t of f a c t o r 2 ( F i g . 29, bottom [ i n v e r t e d ] ) ; t h a t i s , h i g h e r than average abundances i n both h a b i t a t s i n t h e l a t t e r p a r t of the y e a r . The second i n t e r p r e t a t i o n of f a c t o r s c o r e p l o t s i s more s u b j e c t i v e . S i n c e each p l o t r e p r e s e n t s some p a t t e r n of v a r i a t i o n of s p e c i e s abundances t h r o u g h time i n the two h a b i t a t s , i t w i l l a l s o r e p r e s e n t the p a t t e r n of v a r i a t i o n of unknown p h y s i c a l f a c t o r s w i t h which the s p e c i e s may be c o r r e l a t e d ( a l t h o u g h I s h o u l d s t r e s s t h a t t h e s e p h y s i c a l 166 f a c t o r s were not e n t e r e d e x p l i c i t l y i n t o the a n a l y s i s ) . For the purpose of t h i s d i s c u s s i o n , I wi s h t o s t r e s s the p r e v i o u s i n t e r p r e t a t i o n of the f a c t o r s c o r e p l o t s . One p o s s i b l e c o n t r o l l i n g f a c t o r i s suggested by the p l o t s i n F i g . 29, however; the sand p o r t i o n of f a c t o r 1 c l o s e l y resembles the p a t t e r n of s e a s o n a l temperature v a r i a t i o n i n the h a b i t a t . I t i s i n t e r e s t i n g t h a t the s p e c i e s i n the h a b i t a t most exposed by the t i d e s appear most c l o s e l y t i e d t o the temperature v a r i a t i o n i n the h a b i t a t . 2. Q-mode f a c t o r a n a l y s i s : Sand The f a c t o r l o a d i n g s of samples on the f i r s t two p r i n c i p a l f a c t o r s ( a f t e r r o t a t i o n ) a r e p l o t t e d i n F i g . 30. To s i m p l i f y the f i g u r e , o n l y a few dates a re i d e n t i f i e d a l t h o u g h a l l a r e p l o t t e d . F a c t o r s I and I I accounted f o r 39.4% and 28.5% of the v a r i a n c e , r e s p e c t i v e l y . I n s t e a d of the more u s u a l r e p r e s e n t a t i o n of the v a r i a b l e s as c l u s t e r s of p o i n t s , I have p l o t t e d a t r a j e c t o r y through the p o i n t s which s i g n i f i e s the changing p a t t e r n of the h a r p a c t i c o i d copepod community t h r o u g h t i m e . In the Q-mode a n a l y s i s , the f a c t o r s c o r e s r e p r e s e n t r e l a t i v e abundances of the e i g h t s p e c i e s which c o n s t i t u t e the community. P o s i t i v e f a c t o r s c o r e s i n d i c a t e h i g h e r than average abundances of the s p e c i e s ; n e g a t i v e s c o r e s , lower than average abundances. The f a c t o r s c o r e h i s t o g r a m s r e p r e s e n t a copepod assemblage i n a h y p o t h e t i c a l sample w i t h a f a c t o r l o a d i n g of +1.0 on the f a c t o r w i t h which the h i s t o g r a m i s p l o t t e d . In F i g . 30 the f a c t o r s c o r e h i s t o g r a m s a re g i v e n w i t h t h e i r 1 67 F i g u r e 30. S e a s o n a l samples from sand p l o t t e d i n the space d e f i n e d by the f i r s t two p r i n c i p a l f a c t o r s (Q-mode) Samples are j o i n e d by a l i n e which r e p r e s e n t s a t r a j e c t o r y of community change through t i m e . H i s t o g r a m s i l l u s t r a t e the r e l a t i v e abundances of s p e c i e s i n the assemblage d e f i n e d by the f a c t o r w i t h which the h i s t o g r a m i s a s s o c i a t e d . 28.5% var. SUMMER-8.11 FALL Fl 2 6 . 6 S P E C I E S a S. canadens is b T. tr iangularis c L. behningi d Halect inosoma sp. e H. jadensis f Pseudobradya sp. g P. spinicauda h L. constr ic tus • 1 •2 L s m 39.4% var. g SAND 169 r e s p e c t i v e f a c t o r axes. From F i g . 30 i t i s e v i d e n t t h a t the sand community underwent l a r g e changes d u r i n g the c o u r s e of 1978. F u r t h e r , the p a t t e r n appears c y c l i c a l t h o u g h w i t h a d i f f e r e n t e n d - p o i n t i n 1979. Between 4 Feb and 28 A p r i l the community was dominated by P. s p i n i c a u d a and H . j a d e n s i s , two t y p i c a l ' i n t e r s t i t i a l ' s p e c i e s . In May, the community made an abrupt t r a n s i t i o n t o a new s t a t e dominated by two s p e c i e s , S. c a n a d e n s i s and T . t r i a n q u l a r i s , which are more c h a r a c t e r i s t i c of muddy h a b i t a t s . The community remained i n t h i s s t a t e u n t i l l a t e November when i t made another l a r g e change t o a s a n d i e r assemblage not w e l l c h a r a c t e r i s e d by e i t h e r of the f i r s t two f a c t o r s ( i n d i c a t e d by low f a c t o r l o a d i n g s ) but dominated by E c t i n o s o m a t i d s . S i n c e the f i r s t two f a c t o r s a ccounted f o r o n l y 67.9% of the v a r i a n c e , t h e r e may be g u i l d s of s p e c i e s a s s o c i a t e d w i t h f a c t o r s o t h e r than the f i r s t two which account f o r the r e m a i n i n g v a r i a n c e i n the d a t a . In summary, the p a t t e r n i n F i g . 30 i n d i c a t e s t h a t the sand h a r p a c t i c o i d copepod community underwent a marked s e a s o n a l s u c c e s s i o n i n 1978 i n which a number of g u i l d s or s i n g l e s p e c i e s each dominated the assemblage f o r a b r i e f p e r i o d . 3_. Q-mode f a c t o r a n a l y s i s ; Mud The f a c t o r l o a d i n g s of samples on the f i r s t two p r i n c i p a l f a c t o r s a re p l o t t e d i n F i g . 31. F a c t o r I ac c o u n t e d f o r 76.7% of the v a r i a n c e ; F a c t o r I I f o r 15.4%, f o r a- t o t a l of 92.1%. The p a t t e r n of community change i n the mud i s not a t a l l l i k e t h a t 1 70 F i g u r e 31. S e a s o n a l samples from mud p l o t t e d i n the space d e f i n e d by the f i r s t two p r i n c i p a l f a c t o r s (Q-mode) Samples a r e j o i n e d by a l i n e which r e p r e s e n t s a t r a j e c t o r y of community change through, t i m e . Histograms i l l u s t r a t e the r e l a t i v e abundances of s p e c i e s i n the assemblage d e f i n e d by the f a c t o r w i t h which the h i s t o g r a m i s a s s o c i a t e d . MUD S P E C I E S a S. canadensis b T. triangularis c L. behningi d Ha lec t inosoma sp. e H. jadensis f Pseudobradya sp. g P. spinicauda h L. constr ictus 172 i n the sand. S i n c e the f i r s t two f a c t o r s account f o r such a l a r g e p a r t of the v a r i a n c e , and s i n c e a l l samples throughout the year l o a d e d h i g h on one of the two f a c t o r s , we can co n c l u d e t h a t the mud community i n 1978 e x i s t e d i n one of two s t a t e s . For a b r i e f p a r t of the w i n t e r , H a l e c t i n o s o m a sp. and. T. t r i a n g u l a r i s dominated (samples w i t h h i g h f a c t o r l o a d i n g s on f a c t o r I I ) . For most of the year the S. c a n a d e n s i s - L . b e h n i n g i g u i l d dominated ( m a j o r i t y of samples have a h i g h l o a d i n g on f a c t o r I ) . • . . The i d e a l i z e d p a t t e r n of community c o m p o s i t i o n r e v e a l e d by the f a c t o r a n a l y s e s can be compared w i t h the a c t u a l p a t t e r n s of tempora l v a r i a t i o n s of h a r p a c t i c o i d s p e c i e s observed i n 1978 ( F i g . 3 2 ) . As i n f e r r e d from the f a c t o r a n a l y s i s the sand s p e c i e s have much s h a r p e r peaks of abundance than the mud s p e c i e s and p e r s i s t f o r a r e l a t i v e l y s h o r t time i n the h a b i t a t ; sand s p e c i e s a l s o appear t o r e p l a c e ' one another t h r o u g h t i m e . Mud s p e c i e s p e r s i s t i n the mud h a b i t a t f o r a l o n g e r time and have broader abundance peaks than s p e c i e s i n the sand. One mud s p e c i e s , T. t r i a n g u l a r i s , showed no d i s t i n c t s e a s o n a l p a t t e r n i n the mud ( F i g . 32). A l t h o u g h h i g h e r d e n s i t i e s were observed i n the mud than i n the sand, the two communities were e q u a l l y d i v e r s e i n 1978 ( F i g . 33, and see next c h a p t e r ) , a l t h o u g h the p a t t e r n of d i v e r s i t y was d i f f e r e n t i n the two h a b i t a t s . Two mud s p e c i e s , S. c a n a d e n s i s and T. t r i a n g u l a r i s , appeared i n the sand i n summer ( F i g . 32 and p r e v i o u s c h a p t e r ) . T a c h i d i u s . t r i a n g u l a r i s , which showed no p a r t i c u l a r s e a s o n a l i t y i n the mud, had a ve r y sharp June peak and a s m a l l September 1 73 F i g u r e 32. P a t t e r n s of s e a s o n a l change of abundance of the h a r p a c t i c o i d s of Iona N o r t h . , Abundances are p l o t t e d t o d i f f e r e n t s c a l e s f o r each s p e c i e s f o r comparison of s e a s o n a l p a t t e r n s o f • c h a n g i n g d e n s i t y o n l y . 174 30Nvai\inav 175 F i g u r e 33. S e a s o n a l p a t t e r n s of s p e c i e s d i v e r s i t y (top) and t o t a l abundance o f • h a r p a c t i c o i d s (bottom) i n the sand and mud h a b i t a t s t h rough 1978. D I V E R S I T Y ( B I T S ) o -» -» ro M GO o u i b cn b 01 b 177 peak i n the sand. S c o t t o l a n a c a n a d e n s i s a l s o had a t e m p o r a l l y more r e s t r i c t e d peak i n the sand than i n the mud. I t seems, t h e r e f o r e , t h a t when 'mud-type' s p e c i e s m i g r a t e i n t o the sand they take on a more t y p i c a l 'sand-type' s e a s o n a l p a t t e r n . 178 D. D i s c u s s i o n J_. C l u s t e r i n q of s p e c i e s (R-mode a n a l y s i s ) When a l l d a t a from both s i t e s were c o n s i d e r e d t o g e t h e r , the s p e c i e s were d i v i d e d i n t o t h r e e groups by the f i r s t two f a c t o r s e x t r a c t e d . The c l u s t e r i n g of s p e c i e s was the same as might a r i s e from a more c o n v e n t i o n a l (and more s u b j e c t i v e ) c o n s i d e r a t i o n of f u n c t i o n a l morphology, b e h a v i o r and taxonomic r e l a t i o n s h i p s (see p r e v i o u s c h a p t e r ) . The o n l y c r i t e r i a used i n the f a c t o r a n a l y s i s were the dichotomous c l a s s i f i c a t i o n of h a b i t a t a f f i n i t i e s (sand v e r s u s mud) and s e a s o n a l v a r i a t i o n s i n abundance. S i m i l a r c l u s t e r i n g of h a r p a c t i c o i d s p e c i e s i n t o g u i l d s c o r r e s p o n d i n g t o d i s t i n c t sediment regimes was performed by Bodiou and Chardy (1973), M a r c o t t e (1977a), Moore (1979a and b) and I v e s t e r (1980). The a f f i n i t i e s of s p e c i e s - i n the t h r e e c l u s t e r s a r i s e from s i m i l a r i t i e s i n e i t h e r sediment use or s e a s o n a l p a t t e r n s or bo t h . The group which l o a d s h i g h on f a c t o r 1, the e p i p e l s , a re m o s t l y mud-dwelling w i t h l a r g e s t p o p u l a t i o n s i n l a t e summer/early f a l l . The t h r e e e p i p e l i c s p e c i e s have broad, synchronous peaks i n the mud. The e p i p e l s dominate the Iona N o r t h community; f a c t o r 1 w i t h which they a re c o r r e l a t e d , a c c o u n t s f o r 46.0% of the v a r i a n c e i n the d a t a . The s u c c e s s of the e p i p e l i c s p e c i e s i n the l a t e summer/early f a l l may be due to t h e i r a b i l i t y t o s t a y above the s h a l l o w RPD i n the mud a t t h a t time ( F e n c h e l 1969; C o u l l 1973). In a d d i t i o n t o i t s swimming a b i l i t y , one e p i p e l i c s p e c i e s , S. c a n a d e n s i s i s 179 r e l a t i v e l y t o l e r a n t of a n o x i a (Vernberg and C o u l l 1975). The i n t e r s t i t i a l s p e c i e s were c o r r e l a t e d w i t h f a c t o r 2 which a c c o u n t e d f o r o n l y 19.5% of the v a r i a n c e i n the d a t a . As a group, the i n t e r s t i t i a l s predominated at the sand s i t e i n s p r i n g and e a r l y summer. A l l t h r e e s p e c i e s showed t e m p o r a l l y r e s t r i c t e d peaks ( e s p e c i a l l y P. s p i n i c a u d a ) , u n l i k e the i n t e r s t i t i a l s p e c i e s d e s c r i b e d by C o u l l and V e r n b e r g (1975). The i n t e r s t i t i a l h a r p a c t i c o i d s on a sandy beach i n England reproduced m a i n l y i n the warm summer months and had broad peaks of abundance ( H a r r i s 1972a). There does not seem t o be a ' t y p i c a l ' s e a s o n a l p a t t e r n f o r temperate i n t e r s t i t i a l copepod s p e c i e s . The s e a s o n a l p a t t e r n of the epipsammic s p e c i e s was e s s e n t i a l l y the i n v e r s e of the p a t t e r n shown by the i n t e r s t i t i a l s p e c i e s , w i t h peak abundances i n e a r l y w i n t e r i n both h a b i t a t s f o r Pseudobradya sp. (a newcomer t o Iona N o r t h i n l a t e 1978) and h i g h abundances from September t o A p r i l i n the mud f o r H a l e c t i n o s o m a sp. ( F i g . 3 2 ) . These s p e c i e s d i d not show the e x p e c t e d temporal s e g r e g a t i o n d e s c r i b e d f o r two o t h e r but s i m i l a r s p e c i e s of E c t i n o s o m a t i d s by C o u l l e t a l . (1979). A l t h o u g h H a l e c t i n o s o m a sp. and Pseudobradya sp. are m o r p h o l o g i c a l l y almost i d e n t i c a l , the l a r g e d i f f e r e n c e s i n t h e i r body s i z e s i s p r o b a b l y s u f f i c i e n t t o e l i m i n a t e c o m p e t i t i o n between them (see c h a p t e r V I I I ) . 180 2. S e a s o n a l p a t t e r n s of community change (Q-mode a n a l y s i s ) Through the course of 1978 comparable numbers of s p e c i e s were i d e n t i f i e d from the sand and mud h a b i t a t s . A l t h o u g h the p a t t e r n s of d i v e r s i t y changes w i t h time were d i f f e r e n t i n the two h a b i t a t s ( F i g . 33 t o p ) , over the whole year the communities were s i m i l a r l y d i v e r s e , a l t h o u g h . the t o t a l abundance of copepods was g r e a t e r i n the mud than i n the sand ( F i g . 33 bottom). The communities a t the two s i t e s showed v e r y d i s s i m i l a r b e h a v i o r through the y e a r , i n s p i t e of the s i m i l a r i t y i n t h e i r d i v e r s i t i e s . The s p e c i e s i n the sand community underwent a d i s t i n c t s e a s o n a l s u c c e s s i o n ( F i g . 30) from w i n t e r / s p r i n g dominance by two of the i n t e r s t i t i a l s p e c i e s (P. s p i n i c a u d a - H . j a d e n s i s ) t o s u m m e r / f a l l dominance by the e p i p e l i c s p e c i e s (T. t r i a n g u l a r i s - S ' . c a n a d e n s i s ) t o w i n t e r dominance by the b u r r o w i n g E c t i n o s o m a t i d s (Pseudobradya sp. - H a l e c t i n o s o m a sp. ). The s t r e n g t h of t h i s p a t t e r n i s due t o t e m p o r a l s e g r e g a t i o n of s p e c i e s w i t h abrupt s e a s o n a l peaks ( F i g . 32). By c o n t r a s t , the mud community was much more homogeneous through most of the y e a r , w i t h s t r o n g dominance by the e p i p e l i c s p e c i e s (S. c a n a d e n s i s - L . b e h n i n g i ) except f o r the b r i e f w i n t e r dominance by H a l e c t inosoma sp. . I n d i v i d u a l mud s p e c i e s showed l i t t l e i n d i c a t i o n of t e m p o r a l s e g r e g a t i o n compared w i t h the sand s p e c i e s ( F i g . 3 2 ) . The u s u a l e x p l a n a t i o n f o r changing dominance by h a r p a c t i c o i d f u n c t i o n a l groups i s a s e a s o n a l change i n sediment p r o p e r t i e s . For s e v e r a l r e a s o n s , t h i s h y p o t h e s i s can o n l y p a r t l y account f o r the p a t t e r n s d e s c r i b e d above. F i r s t , the 181 s u c c e s s i o n from i n t e r s t i t i a l s p e c i e s to e p i p e l i c s p e c i e s t o epipsammic s p e c i e s i n the sand s h o u l d s i g n a l s i g n i f i c a n t g e o chemical changes i n the h a b i t a t ; such changes were not o b s e r v e d . The h a b i t a t d i d not i n c r e a s e i n s i l t i n e s s t h r o u g h 1978 ( F i g . 9 ) ; n e i t h e r d i d the RPD r i s e t o the s u r f a c e ( F i g . 8a) (a change which would e l i m i n a t e the s t r i c t l y i n b e n t h i c , i n t e r s t i t i a l s p e c i e s ) . Narrow o p t i m a l ranges f o r temperature and s a l i n i t y (or some oth e r p h y s i c a l f a c t o r s or c o m b i n a t i o n of f a c t o r s ) of i n d i v i d u a l s p e c i e s may account f o r such sharp s e a s o n a l peaks, but T. t r i a n g u l a r i s and S. c a n a d e n s i s which have sharp peaks i n the sand have v e r y broad peaks i n the mud where the t e m p e r a t u r e / s a l i n i t y regime i s the same as i n the sand. H a l e c t i n o s o m a sp. does show e v i d e n c e of c o n t r o l by p h y s i c a l f a c t o r s . I t s mid-summer low i n the sand may be caused by low s a l i n i t i e s ; i t s m i d w i n t e r peak may be c o r r e l a t e d w i t h the i n c r e a s e d sand c o n t e n t of the mud s i t e i n w i n t e r ( F i g . 9) ( H a l e c t i n o s o m a sp. feeds by a b r a d i n g food from the s u r f a c e of sand g r a i n s ) . C o n s i d e r a t i o n of t h e s e i d e a s i n d i c a t e s t h a t we must l o o k beyond p h y s i c a l f a c t o r s as the s o l e c o n t r o l l i n g mechanism i n t h e s e two communities. In terms of n i c h e t h e o r y , the sand s p e c i e s a r e c l e a r l y s e g r e g a t e d i n t i m e ; the mud s p e c i e s , w i t h the e x c e p t i o n of H a l e c t i n o s o m a sp. a r e b o t h s y m p a t r i c and s y n c h r o n i c . By what o t h e r mechanisms, i f any, a r e the n i c h e s of the mud and sand s p e c i e s s e p a r a t e d ? The o t h e r main n i c h e axes ( C h r i s t i a n s e n and F e n c h e l 1977) a l o n g which e f f i c i e n t s e p a r a t i o n might occur w i t h i n a s i n g l e h a b i t a t a r e the s p a t i a l 1 82 d i m e n s i o n ( m i c r o h a b i t a t s e g r e g a t i o n ) and s i z e - r e l a t e d d i e t d i f f e r e n c e s ( c h a r a c t e r d i s p l a c e m e n t ) among t h e s p e c i e s . S p a t i a l p a t t e r n s w i l l be c o n s i d e r e d i n t h e f o l l o w i n g c h a p t e r ; , s i z e w i l l be t h e s u b j e c t of c h a p t e r V I I I . . 183 V I . SPATIAL PATTERNS A. I n t r o d u c t i o n "Thus i t may w e l l be t h a t m i c r o h a b i t a t s w i t h i n a more g e n e r a l h a b i t a t w i l l o f t e n be o c c u p i e d by c l o s e l y • r e l a t e d s p e c i e s , o r , c o n v e r s e l y , i f c l o s e l y r e l a t e d s p e c i e s are found w i t h i n one w e l l - d e f i n e d h a b i t a t , the s e g r e g a t i o n of the h a b i t a t s i n t o m i c r o h a b i t a t s i s i n d i c a t e d . " w. Wieser (1960) The f a c t o r s r e s p o n s i b l e f o r the l a r g e - s c a l e s p a t i a l h e t e r o g e n e i t y of m e i o b e n t h i c t a x a have been the s u b j e c t of numerous i n v e s t i g a t i o n s ( r e v i e w e d by M c l n t y r e 1971; Fe n c h e l * 1978; C o u l l and B e l l 1979). S m a l l - s c a l e h e t e r o g e n e i t y has r e c e i v e d much l e s s a t t e n t i o n and i s o f t e n regarded as a sampling problem (e.g. Gray 1971; Ranta and S a r v a l a 1978; F i n d l a y 1978). S e v e r a l p r o c e s s e s have been h y p o t h e s i z e d t o account f o r the clumped d i s t r i b u t i o n of meiofauna ( C o u l l and B e l l 1979; F i n d l a y 1981): a) a t t r a c t i o n t o decomposing c a r c a s s e s (Bush 1966; G e r l a c h 1977b) or eggs of macrofauna (Hummon et a l . 1976), b) a t t r a c t i o n t o p a t c h i l y d i s t r i b u t e d food ( m i c r o f l o r a ) (Gray 1968; Gray and Johnson 1970; G i e r e 1975; Lee e t a l . 1977), c) r e a c t i o n t o b i o g e n i c s t r u c t u r e s such as p o l y c h a e t e t u b e s (Lee e t a l . 1977; T h i s t l e 1979; B e l l and Coen 1980), mounds of f e c a l m a t e r i a l ( T h i s t l e 1980) or macrophytes ( T e a l and Wieser 1966; B e l l e t a l . 1978), d) a g g r e g a t i o n f o r r e p r o d u c t i o n (Heip and E n g e l s 1977; H i c k s 184 1979), e) . l o c a l i z e d , s e l e c t i v e p r e d a t i o n ( C o u l l and B e l l 1979) and f ) h a b i t a t p a r t i t i o n i n g ( I v e s t e r 1975; C o u l l and F l e e g e r 1977; H a r r i s o n 1977; Heip . and E n g e l s 1977; H i c k s 1980). T h i s l a s t c l a s s of p r o c e s s e s c a u s i n g s m a l l - s c a l e h e t e r o g e n e i t y w i l l be the s u b j e c t of t h i s c h a p t e r . . M i c r o h a b i t a t p a r t i t i o n i n g i s a community p r o p e r t y of c o n s i d e r a b l e i n t e r e s t . P a r t i t i o n i n g may have s e v e r a l causes: c o m p e t i t i v e d i s p l a c e m e n t , d i f f e r e n t i a l p r e d a t i o n or exogenous, p h y s i c a l p r o c e s s e s . Because of the c o m p l e x i t y of these p r o c e s s e s and p o s s i b l e i n t e r a c t i o n s among them, i t i s not p o s s i b l e t o i d e n t i f y a p o s t e r i o r i a unique p r o c e s s f o r each observed p a t t e r n ( P i e l o u 1974). N o n e t h e l e s s , when combined w i t h o t h e r i n f o r m a t i o n on the b e h a v i o r of a s p e c i e s (the temporal p a t t e r n s d i s c u s s e d i n the p r e v i o u s s e c t i o n , f o r example) p a t t e r n s of h a b i t a t s e g r e g a t i o n may p r o v i d e i n s i g h t s which w i l l a i d i n the i n t e r p r e t a t i o n of observed p a t t e r n s of community change. One d i f f i c u l t y i n the st u d y of s m a l l - s c a l e s p a t i a l p a t t e r n s i s t h a t the fauna as a whole may or may not respond t o h a b i t a t h e t e r o g e n e i t y . For example, i n a p r e l i m i n a r y survey of sand r i p p l e meiofauna ( H a r r i s o n 1977), nematodes as a group were s i g n i f i c a n t l y more abundant i n r i p p l e t r o u g h s . The h a r p a c t i c o i d fauna- as a whole was e q u a l l y abundant i n c r e s t s and t r o u g h s , but i n d i v i d u a l s p e c i e s w i t h i n the complex showed n o n - o v e r l a p p i n g d i s t r i b u t i o n s . A second d i f f i c u l t y i s t h a t i t may not be p o s s i b l e t o i d e n t i f y s p a t i a l h e t e r o g e n e i t y t o which 185 organisms as s m a l l as the meiobenthos may respond. H e t e r o g e n e i t y c h i - s q u a r e (HCS) ( S o k a l and R o h l f 1969; Jumars 1975) i s an index of h e t e r o g e n e i t y which p e r m i t s d e t e c t i o n of i n t e r s p e c i f i c s p a t i a l s e g r e g a t i o n a t chosen s p a t i a l s c a l e s i n communities such as the meiobenthos where the ' h a b i t a t s ' a p p r e c i a t e d by the fauna may not be known a p r i o r i . H e t e r o g e n e i t y c h i - s q u a r e a n a l y s i s has been p r e v i o u s l y a p p l i e d t o h a r p a c t i c o i d communities by F l e e g e r (1977), T h i s t l e (1978) and B e l l (1979a). In t h i s c h a p t e r I w i l l i n v e s t i g a t e s m a l l - s c a l e s p a t i a l p a t t e r n s i n the Iona N o r t h meiofauna i n two ways. In the f i r s t p a r t I w i l l assume t h a t u n s p e c i f i e d s p a t i a l h e t e r o g e n e i t y e x i s t s a t a s m a l l s p a t i a l s c a l e ( w i t h i n 0.25 m 2) a t both the sand and mud s i t e s . U s i n g h e t e r o g e n e i t y c h i - s q u a r e , I w i l l compare the p a t t e r n s of s p a t i a l s e g r e g a t i o n ( i f any) among the h a r p a c t i c o i d s p e c i e s a t the two s i t e s a t monthly i n t e r v a l s t h r ough 1978. I w i l l a l s o 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 h e t e r o g e n e i t y c h i - s q u a r e and p o o l e d c h i - s q u a r e ( d i s p e r s i o n of the t o t a l h a r p a c t i c o i d assemblage) to season, s p e c i e s c o m p o s i t i o n and d i v e r s i t y , and h a r p a c t i c o i d abundance p a t t e r n s . In the second p a r t of the c h a p t e r , I w i l l i n v e s t i g a t e the response of the meiobenthos t o the m i c r o t o p o g r a p h y caused by sand r i p p l e s (wave- and c u r r e n t - g e n e r a t e d h y d r a u l i c b edforms). In t h i s c a s e , the source of s p a t i a l h e t e r o g e n e i t y i s s p e c i f i e d a p r i o r i and sampled d i r e c t l y . The methods and r e s u l t s of the two p a r t s of the c h a p t e r w i l l be p r e s e n t e d s e p a r a t e l y . D i s c u s s i o n of r e s u l t s from both p a r t s of the c h a p t e r w i l l be combined a t the end. 187 B. H e t e r o g e n e i t y Chi-Square A n a l y s i s ( M i c r o h a b i t a t s U n s p e c i f i e d ) 1. Methods Samples used i n t h i s a n a l y s i s ( d e s i g n a t e d 'random samples') were c o l l e c t e d a t a p p r o x i m a t e l y monthly i n t e r v a l s from 4 Feb 1978 t o 10 Jan 1979 a t the two Iona N o r t h s i t e s : sand and mud. At each s i t e , 12 c o r e s (each sampling a s u r f a c e area of 1.65 cm 2) were taken a t randomized l o c a t i o n s w i t h i n a 0.25 m2 g r i d (see c h a p t e r I I ) . S i n c e I am i n t e r e s t e d here i n l a t e r a l p a r t i t i o n i n g o n l y , c o u n t s from s u r f a c e and s u b s u r f a c e c o r e f r a c t i o n s were added. The d a t a comprised an i by j m a t r i x where i i s the number of s p e c i e s (i=1,N) and j i s the number of c o r e s (j=1,n; n=12). The m a t r i x e n t r i e s C ( i , j ) were the un t r a n s f o r m e d c o u n t s of s p e c i e s i i n c o r e j ( a d u l t s and c o p e p o d i t e s combined). The t o t a l d i s p e r s i o n c h i - s q u a r e (TCS) was c a l c u l a t e d as f o l l o w s (Jumars 1975) : (6) N TCS = X 2 {N[n-1]} = • Z [ s 2 , / x. {n-1} '] 1=1 where s ^ / x^ ^ i s the variance/mean index of d i s p e r s i o n f o r s p e c i e s i . 188 The p o o l e d c h i - s q u a r e , o r d i s p e r s i o n o f t h e h a r p a c t i c o i d a s s e m b l a g e t r e a t e d a s a u n i t , was: ' (7) PCS = X 2 {n-1 } = s 2 T / x T (n-1 ) N where T i s £ C ( i , j ) . The h e t e r o g e n e i t y c h i - s q u a r e was t h e n : 1=1 (8) HCS = TCS -PCS = X 2 [ N ( n - 1 ) - ( n - 1 ) ] The c a l c u l a t e d h e t e r o g e n e i t y c h i - s q u a r e was c o m p a r e d w i t h t h e t a b u l a t e d c h i - s q u a r e f o r N ( n - l ) - ( n - 1 ) d e g r e e s o f f r e e d o m u n d e r t h e n u l l h y p o t h e s i s t h a t t h e r e l a t i v e c o m p o s i t i o n o f the, community r e m a i n e d c o n s t a n t among c o r e s ( i . e . among m i c r o h a b i t a t s ) . A s i g n i f i c a n t l y h i g h e r t h a n t a b u l a t e d h e t e r o g e n e i t y c h i - s q u a r e was t a k e n a s r e j e c t i o n o f t h e n u l l h y p o t h e s i s , o f no m i c r o h a b i t a t p a r t i t i o n i n g . . The s p e c i e s d i v e r s i t y a t e a c h s i t e on e a c h s a m p l i n g o c c a s i o n was c a l c u l a t e d f r o m t h e S h a n n o n - W i e n e r i n d e x ( P i e l o u 1 9 7 4 ) : (9) N H' = - I p. log„ p . i = 1,2,...,S . , i 2 l i = l where p ^ i s t h e p r o p o r t i o n o f t h e t o t a l number o f c o p e p o d s c o l l e c t e d t h a t b e l o n g e d t o s p e c i e s i and S i s t h e t o t a l number o f s p e c i e s i n t h e c o l l e c t i o n . C o m p l e t e t a b l e s o f t h e d a t a u s e d i n t h e a n a l y s i s and t h e r e s u l t s o b t a i n e d a r e g i v e n i n A p p e n d i x 5. 189 2. R e s u l t s D i s t i n c t h a r p a c t i c o i d assemblages i n h a b i t e d the sand and mud s i t e s a t Iona N o r t h . The p r i n c i p a l d i f f e r e n c e was i n s p e c i e s c o m p o s i t i o n . The sand s i t e was dominated i n w i n t e r and e a r l y s p r i n g by P a r a l e p t a s t a c u s s p i n i c a u d a and Huntemannia  j a d e n s i s , both s a n d - d w e l l i n g s p e c i e s . There was a d i s t i n c t p a t t e r n of s e a s o n a l d i s p l a c e m e n t of s p e c i e s u n t i l summer when the community was dominated by two e p i p e l i c i m migrants, T a c h i d i u s t r i a n g u l a r i s and S c o t t o l a n a c a n a d e n s i s (see p r e v i o u s c h a p t e r ) . The mud community was dominated by S. c a n a d e n s i s i n the warm months and H a l e c t i n o s o m a sp. i n the w i n t e r . A l t h o u g h some s p e c i e s appeared i n both h a b i t a t s f o r a t l e a s t p a r t of .1978, t h e i r apparent s e a s o n a l i t y was d i f f e r e n t between the two h a b i t a t s (see c h a p t e r s IV and V ) . In 1978, . h a r p a c t i c o i d s reached s i g n i f i c a n t l y h i g h e r d e n s i t i e s i n the mud than i n the sand ( W i l c o x o n ' s s i g n e d - r a n k s t e s t ; T = 6; P<0.01; t w o - t a i l e d t e s t ) . Maximum d e n s i t i e s o c c u r r e d i n ' A p r i l and June i n the sand and l a t e September i n the mud ( F i g . 34a). D i s t i n c t s e a s o n a l p a t t e r n s of d i v e r s i t y were observed i n the two communities i n 1978 ( F i g . 34b). In the mud, d i v e r s i t y was h i g h i n w i n t e r and low from May through O c t o b e r ; i n the sand, d i v e r s i t y was v e r y low i n e a r l y s p r i n g and h i g h but v a r i a b l e t h r o u g h the r e s t of the year w i t h the n o t a b l e e x c e p t i o n of June ( h i g h dominance by T. t r i a n g u l a r i s ) . H a r p a c t i c o i d s p e c i e s d i v e r s i t y was n e g a t i v e l y c o r r e l a t e d w i t h the t o t a l d e n s i t y of copepods i n the sand ( r = -0.79; n = 13; 190 F i g u r e 34. S e a s o n a l v a r i a t i o n i n (a) d e n s i t y and (b) s p e c i e s d i v e r s i t y of h a r p a c t i c o i d copepods a t the two s i t e s i n 1978. Comparison of the r e l a t i o n s h i p between d e n s i t y and s p e c i e s d i v e r s i t y i n the (c) sand and (d) mud communities. 191 a. (D o o 2501 V) Q o CL HI 0 . O O —I < H O 200 150 100 50 mud , .o-c5 o /» o \ / \ / /o\ sand \ n j ; i Z—i i i »-Q M J S 1978 N J '79 b . 2.5 2.0 H'l.5 1.0 0.5 0 o ~ • sand '°x / \ \ o''m mud J_ F A M J S 1978 N J '79 H c. sand _L _L 20 40 60 80 100 120 TOTAL DENSITY d. 8 o o o o o C O mud o J_ _L J . 50 100 150 200 250 300 TOTAL DENSITY 192 P<0.01) ( F i g . 3 4 c ) . D i v e r s i t y was n e g a t i v e l y r e l a t e d t o d e n s i t y ' i n the mud, as w e l l , ( F i g . 34d) a l t h o u g h the c o r r e l a t i o n was not s t a t i s t i c a l l y s i g n i f i c a n t ( r = -0,44;. n = 13; P>0.10). In s p i t e of s u b s t a n t i a l d i f f e r e n c e s i n s p e c i e s c o m p o s i t i o n and s e a s o n a l p a t t e r n s of d e n s i t y and d i v e r s i t y between the two s i t e s , the data do not i n d i c a t e r e j e c t i o n of the n u l l h y p o t h e s i s of eq u a l d i v e r s i t i e s a t the two s i t e s (Mann-Whitney U - t e s t ; U = 77; P>0.10 . / p a i r e d t - t e s t ; t = -0.15; n = 13; P>0.50). The t o t a l d i s p e r s i o n of h a r p a c t i c o i d s among the t w e l v e r e p l i c a t e c o r e s (TCS) from each s i t e monthly through 1978 i s g i v e n i n Ta b l e *6. H i g h l y s i g n i f i c a n t t o t a l c h i - s q u a r e s were c a l c u l a t e d f o r each month except Jan 1979 ( s a n d ) . S i g n i f i c a n t v a l u e s of TCS i n d i c a t e r e j e c t i o n of the n u l l h y p o t h e s i s t h a t the c o u n t s per core of each s p e c i e s a re random v a r i a b l e s ( T h i s t l e 1978). For a l l months except Jan 1979 the h a r p a c t i c o i d s p e c i e s of the two s i t e s were non-randomly d i s t r i b u t e d among c o r e s . U s i n g Jumars'(1975) methods, the t o t a l c h i - s q u a r e was p a r t i t i o n e d i n t o a component due t o d i s p e r s i o n of the h a r p a c t i c o i d taxon as a whole ( p o o l e d c h i - s q u a r e ) and d i s p e r s i o n due t o d i f f e r e n t i a l d i s t r i b u t i o n of s p e c i e s among c o r e s ( h e t e r o g e n e i t y c h i - s q u a r e ) . The s e a s o n a l p a t t e r n s of p o o l e d c h i - s q u a r e f o r the two s i t e s a r e g i v e n i n F i g . 35a. The mud h a r p a c t i c o i d s as a group were s i g n i f i c a n t l y a g g r e g a t e d (P<0.005) i n a l l months, w i t h h i g h e s t a g g r e g a t i o n s i n l a t e f a l l . The sand h a r p a c t i c o i d s were s i m i l a r l y s i g n i f i c a n t l y a g g r e g a t e d i n a l l but 3 months ( c i r c l e d 1 93 F i g u r e 35. (a) Seasonal v a r i a t i o n i n p o o l e d c h i - s q u a r e (PCS) at the two s i t e s t h r ough 1978. The r e l a t i o n s h i p s between PCS and h a r p a c t i c o i d d e n s i t y i n the (b) sand and (c) mud communities and between PCS and s p e c i e s d i v e r s i t y i n the (d) sand and (e) mud communities. 194 b . sand x X X J_ 40 60 80 100 TOTAL DENSITY 120 300 r O 250 -200 -100-° 50h 0 C. o o o o o X mud o 50 100 150 200 250 300 TOTAL DENSITY 300 r 250 200 CO " 1 5 0 CL 100 50 0 x d. sand 9 9 X x 0.5 1.0 1.5 2.0 2.5 3.0 H' 300" 250 -200 -CO 2 150-100 -50-0 L e. o o o o o o o o o o o mud 0.5 1.0 1.5 2.0 2.5 3.0 H 196 Table 6. Se a s o n a l v a r i a t i o n i n T o t a l C h i - s q u a r e (TCS) of h a r p a c t i c o i d copepods c a l c u l a t e d from monthly random samples from the two study s i t e s t h r o u g h 1978. DATE SAND MUD TCS . df P TCS df P 4 Feb 78 66.00 33 <.005 . . 427,74 55 <.005 4 Mar 88.63 33 <.005 272.26 66 <.005 1 Apr 199.11 55 <.005 176.88 44 <.005 28 Apr 13 5.36 55 <.005 205.28 55 <.005 2 5 May 197.80 66 <.005 159.35 55 <.005 8 June 308.99 66 <.005 97.15 55 <.005 11 J u l y 174.19 66 <.005 207.13 55 <.005 4 Aug 216.40 77 <.005 240.22 44 <.005 1 Sept 117.51 66 <.005 296.35 44 <.005 29 Sept 94.92 55 <.005 168.21 44 <.005 8 Nov 94.54 66 <.005 549.27 66 <.005 8 Dec 64. 1 3 44 < . 0 1 0 654.41 77 <.005 10 Jan 79 94. 1 0 88 >.050 309.39 77 <.005 p o i n t s i n F i g . 35a). Sand and mud PCS were s i g n i f i c a n t l y n e g a t i v e l y c o r r e l a t e d ( r = -0.62; df = 11; P<0.05). The r e l a t i o n s h i p s between p o o l e d c h i - s q u a r e and two o t h e r community p r o p e r t i e s ( s p e c i e s d i v e r s i t y and t o t a l d e n s i t y of h a r p a c t i c o i d s ) a re shown i n F i g s . 35b t o e. In sand the po o l e d c h i - s q u a r e was p o s i t i v e l y c o r r e l a t e d w i t h the t o t a l number of copepods ( r = +0.92; P<0.001) ( F i g . 35b) and 1 97 n e g a t i v e l y c o r r e l a t e d w i t h s p e c i e s d i v e r s i t y (r = -0.64; P<0.02) ( F i g . 35d). As the d e n s i t y of the h a r p a c t i c o i d community i n the sand i n c r e a s e d (and the d i v e r s i t y d e c r e a s e d ) , the copepods as a group became s i g n i f i c a n t l y more aggregated (PCS i n c r e a s e d ) . No s i g n i f i c a n t r e l a t i o n s h i p s were found among thes e measures i n the mud. P o o l e d c h i - s q u a r e was n e g a t i v e l y r e l a t e d t o the t o t a l abundance of copepods ( F i g . 35c) but the r e l a t i o n s h i p was not s t a t i s t i c a l l y s i g n i f i c a n t (r = -0.16; P>0. 10). P o o l e d c h i - s q u a r e was p o s i t i v e l y r e l a t e d t o s p e c i e s d i v e r s i t y i n the mud ( F i g . 35e) a l t h o u g h , again,' the r e l a t i o n s h i p was not s t a t i s t i c a l l y s i g n i f i c a n t (r = +0.34; P>0.10). We may c o n c l u d e , t h e n , t h a t p o o l e d c h i - s q u a r e , d e n s i t y and s p e c i e s d i v e r s i t y were s i g n i f i c a n t l y i n t e r r e l a t e d i n the sand but not i n the mud community. The o t h e r component of TCS i s the d i s p e r s i o n due t o changes i n the r e l a t i v e abundance of i n d i v i d u a l s p e c i e s among c o r e s , the h e t e r o g e n e i t y c h i - s q u a r e . I f HCS i s s i g n i f i c a n t , we may r e j e c t the n u l l h y p o t h e s i s t h a t the r e l a t i v e c o m p o s i t i o n of the community i s c o n s t a n t ( w i t h i n the l i m i t s of chance v a r i a t i o n ) from c o r e t o c o r e (Jumars 1975). A s i g n i f i c a n t HCS, t h e r e f o r e , i s s t r o n g e v i d e n c e f o r h a b i t a t p a r t i t i o n i n g among s p e c i e s a t the s p a t i a l s c a l e sampled. In a l l but 3 months i n the sand (F e b r u a r y t o A p r i l ) and one i n the mud ( J u n e ) , h e t e r o g e n e i t y c h i - s q u a r e was s i g n i f i c a n t l y g r e a t e r than e x p e c t e d under the n u l l h y p o t h e s i s (P<0.05) ( F i g . 36a). T h i s o b s e r v a t i o n i n d i c a t e s t h a t , on av e r a g e , the s i g n i f i c a n t t o t a l h e t e r o g e n e i t y c a l c u l a t e d (TCS) 198 F i g u r e 36. S e a s o n a l v a r i a t i o n i n (a) h e t e r o g e n e i t y c h i -square (HCS) and (b) HCS/df at the two s i t e s t h r ough 1978 and -the r e l a t i o n s h i p between HCS/df and s p e c i e s d i v e r s i t y i n the (c) sand and (d) mud. HCS/DF o >o ^ . o co o ro l 1 1 1 1 1 i o O C O o o O 0 ° o u o 3 c Q. CO b HCS _. —i hO to CO Cn O Oi O Cn O O O O O O O O <o C. 00 CO co S T T T i r , -o o / p jo ; 3 I O- _ . D3 3 c a. o HCS/DF o r~ -O CO o to 3 c a c r 2 0 0 was due t o d i f f e r e n t i a l use of the s p a t i a l r e s o u r c e by d i f f e r e n t h a r p a c t i c o i d s p e c i e s ( i . e . m i c r o h a b i t a t p a r t i t i o n i n g ) as w e l l as the whole assemblage ( s i g n i f i c a n t PCS). As w i t h PCS, HCS v a r i e d s e a s o n a l l y a t both s i t e s ( F i g . 36a). I t was lowe s t i n w i n t e r and h i g h from May t o September at the sand s i t e and low e s t i n summer and h i g h i n w i n t e r i n the mud. To s t a n d a r d i z e f o r v a r i a t i o n s i n the number of s p e c i e s p r e s e n t t h rough the y e a r , HCS was d i v i d e d by degrees of freedom ( F i g . 36b). The exp e c t e d v a l u e of r e l a t i v e m i c r o h a b i t a t p a r t i t i o n i n g (HCS/df) i f Ho i s t r u e i s then 1.0. The mud HCS m a i n t a i n e d the same s e a s o n a l p a t t e r n f o l l o w i n g t h i s t r a n s f o r m a t i o n but the sand s e a s o n a l i t y was g r e a t l y reduced. In the sand, r e l a t i v e m i c r o h a b i t a t p a r t i t i o n i n g was s i g n i f i c a n t and f a i r l y c o n s t a n t a f t e r A p r i l 1978. F u r t h e r , r e l a t i v e m i c r o h a b i t a t p a r t i t i o n i n g , a t the s m a l l s c a l e s t u d i e d , was s i g n i f i c a n t l y s t r o n g e r i n the mud than i n the sand community (Wi l c o x o n ' s s i g n e d ranks t e s t ; T = 6; P<0.01). R e l a t i v e m i c r o h a b i t a t p a r t i t i o n i n g was u n c o r r e l a t e d w i t h d i v e r s i t y i n both sand (r = +0.20; P>0.10) ( F i g . 36c) and mud (r = +0.36; P>0.10) ( F i g . 36d). R e l a t i v e m i c r o h a b i t a t p a r t i t i o n i n g was s i m i l a r l y u n c o r r e l a t e d w i t h t o t a l copepod d e n s i t y i n the sand ( r = -0.10; P>0.10) and i n the mud (r = +0.11; P>0.10). 201 C. Sand R i p p l e A n a l y s i s ( M i c r o h a b i t a t s S p e c i f i e d ) J _ . I n t r o d u c t i o n R i p p l e d bedforms are a.common m i c r o t o p o g r a p h i c f e a t u r e of i n t e r t i d a l sand f l a t s . Sand r i p p l e s a r e formed by c u r r e n t - and wave-induced t r a n s p o r t of sandy sediment (Shepard 1973). The r i p p l e s a t Iona N o r t h form on the f l o o d t i d e , p e r s i s t t h rough the p e r i o d of emergence and are o b l i t e r a t e d by the i n i t i a l i n u n d a t i o n of the s u c c e e d i n g f l o o d t i d e ( p e r s o n a l o b s e r v a t i o n s ) . The p a t t e r n s of water f l o w t h r o u g h submerged r i p p l e systems are h i g h l y complex and cause c o n s i d e r a b l e h e t e r o g e n e i t y i n sediment p r o p e r t i e s known t o be e c o l o g i c a l l y s i g n i f i c a n t t o the meiobenthos, w i t h o u t c a u s i n g a s i g n i f i c a n t s h i f t i n sediment g r a i n s i z e (Webb and Theodor 1972). I t i s v e r y l i k e l y , t h e r e f o r e , t h a t the meiobenthos i s c a p a b l e of d e t e c t i n g and r e s p o n d i n g t o t h i s s ource of s m a l l - s c a l e h e t e r o g e n e i t y . In the f i r s t p a r t of t h i s c h a p t e r I demonstrated t h a t h a r p a c t i c o i d copepod s p e c i e s a r e s e g r e g a t e d a t s m a l l s p a t i a l s c a l e s . I f h a r p a c t i c o i d s p e c i e s d i f f e r e n t i a l l y p o p u l a t e p a r t s of the sand r i p p l e system, t h i s m i c r o h a b i t a t d i s p l a c e m e n t c o u l d account f o r some of the h e t e r o g e n e i t y observed and p e r m i t the c o e x i s t e n c e of s i m i l a r s p e c i e s . I n t h i s s e c t i o n I w i l l show t h a t h a r p a c t i c o i d s p e c i e s do make d i f f e r e n t i a l use of r i p p l e c r e s t s and t r o u g h s and t h a t some of t h i s p a t t e r n may be due t o 202 c o m p e t i t i v e m i c r o h a b i t a t d i s p l a c e m e n t . 2. Methods Sand r i p p l e samples were c o l l e c t e d and t r e a t e d as d e s c r i b e d i n c h a p t e r I I except t h a t on 22 Jan 1977 the 'Across' t r a n s e c t d i d not i n t e r s e c t the ' C r e s t ' and. 'Trough' t r a n s e c t s as shown i n F i g . 3. On t h a t d a t e , t h e r e f o r e , a t o t a l of 24 c o r e s were c o l l e c t e d . . The r e s u l t s of the monthly- r i p p l e samples w i l l be p r e s e n t e d i n c h a p t e r V I I I . The p r e s e n t a n a l y s i s was r e s t r i c t e d t o two s e t s of r i p p l e samples, one r e p r e s e n t i n g mid-w i n t e r (22 Jan 1977) and the o t h e r , mid-summer (21 J u l y 1978). As w e l l as f a u n a l samples, d u p l i c a t e c o r e s ( t o 5. cm) from a r i p p l e c r e s t and the a d j a c e n t t r o u g h were c o l l e c t e d i n January 1977 f o r sediment g r a i n s i z e a n a l y s i s . For comparison of abundance of major t a x a (nematodes and h a r p a c t i c o i d copepods) i n c r e s t and t r o u g h samples, counts of the s u r f a c e and s u b s u r f a c e f r a c t i o n s were added. The mean cou n t s f o r each taxon a l o n g the c r e s t t r a n s e c t (xc) and t r o u g h t r a n s e c t ( x t ) were assumed t o be independent e s t i m a t e s of the t r u e p o p u l a t i o n mean f o r t h a t t a x o n . The s i g n i f i c a n c e of the d i f f e r e n c e s between p a i r s of means were t e s t e d w i t h a t - t e s t ( B r u n i n g and K i n t z 1968). The d a t a were n o r m a l i z e d w i t h a ln(x+1) t r a n s f o r m a t i o n ( E l l i o t 1971) p r i o r t o t h e t e s t s . At l e a s t f o u r s e p a r a t e m i c r o h a b i t a t s a p p r e c i a b l e t o the i n v e s t i g a t o r e x i s t f o r the sand r i p p l e meiobenthos ( H a r r i s o n 1977): c r e s t s u r f a c e , 0-1 cm ( C a ) , c r e s t s u b s u r f a c e , 1-5 cm ( C b ) , t r o u g h s u r f a c e , 0-1 cm (Ta) and t r o u g h s u b s u r f a c e , 1-5 cm 203 (Tb). The t o t a l number of i n d i v i d u a l s of s p e c i e s i counted i n the e i g h t samples c o l l e c t e d i n a g i v e n m i c r o h a b i t a t h, d , was used as an e s t i m a t e of the e x p l o i t a t i o n of m i c r o h a b i t a t h by s p e c i e s i . The r e l a t i v e f r e q u e n c y of m i c r o h a b i t a t use was 4 t h e n , d ../ E d M . In o r d e r t o t e s t the s i g n i f i c a n c e of the in , , in h=l o bserved m i c r o h a b i t a t s e l e c t i o n , I w i l l assume t h a t the number of i n d i v i d u a l s i n each m i c r o h a b i t a t sampled i s a s i m p l e f u n c t i o n of the volume of sediment sampled. Equal numbers (n = 8) of samples were taken from each m i c r o h a b i t a t . Each s u b s u r f a c e sample was f o u r times the sediment volume of a s u r f a c e sample. The e x p e c t e d r a t i o of numbers i n the 4 m i c r o h a b i t a t s i s , then Ca:Cb:Ta:Tb = 1:4:1:4 under the n u l l h y p o t h e s i s of no m i c r o h a b i t a t s e l e c t i o n ( i . e . assuming t h a t copepod d e n s i t y i s a f u n c t i o n of the amount of l i v i n g space, o n l y ) . Observed f r e q u e n c i e s were t e s t e d a g a i n s t the n u l l h y p o t h e s i s w i t h a C h i - s q u a r e goodness of f i t t e s t ( S o k a l and R o h l f 1969). C a l c u l a t e d c h i - s q u a r e s e x c e e d i n g 7.8 i n d i c a t e d r e j e c t i o n of the n u l l h y p o t h e s i s of no m i c r o h a b i t a t s e l e c t i o n (p<0.05; df = 3 ) . The f a u n a l a f f i n i t i e s among w i n t e r samples c o l l e c t e d w i t h i n a p a r t i c u l a r m i c r o h a b i t a t . and among samples from d i f f e r e n t m i c r o h a b i t a t s were c a l c u l a t e d u s i n g the p e r c e n t s i m i l a r i t y i n d e x : (10) PS = 200 • E .min(X /Z,Y /Z) , 0 < PS < 100% j j j where Z = the t o t a l number of a l l h a r p a c t i c o i d s i n c o r e s X and 204 Y and X ^  and Y are the d e n s i t y of s p e c i e s j i n the two c o r e s ( P i e l o u 1974). The s u r f a c e and s u b s u r f a c e c o u n t s were summed f o r t h i s a n a l y s i s . The r e s u l t s were d i s p l a y e d i n a t r e l l i s diagram (Sanders 1960). A p o s s i b l e mechanism f o r d i f f e r e n t i a l m i c r o h a b i t a t use by r e l a t e d s p e c i e s i s c o m p e t i t i v e d i s p l a c e m e n t . Two s p e c i e s , H a l e c t inosoma sp. and P a r a l e p t a s t a c u s s p i n i c a u d a , appeared, t o have d i s c o r d a n t s p a t i a l d i s t r i b u t i o n s i n January 1977 ( H a r r i s o n 1977). The s t a t i s t i c a l s i g n i f i c a n c e of t h i s a s s o c i a t i o n was t e s t e d , w i t h a s t a n d a r d C h i - s q u a r e t e s t f o r independence i n a 2 x 2 t a b l e f o r which the t e s t c r i t e r i o n i s (12) X 2 c = [ ( | a d - b c | - N / 2 ) 2 N ] / [ ( a + b ) ( c + d ) ( a + c ) ( b + d ) ] where a i s the number of samples w i t h both s p e c i e s p r e s e n t , d i s the number of samples w i t h both s p e c i e s a b s e n t , b the number of samples w i t h P. s p i n i c a u d a o n l y , c the number of samples w i t h H a l e c t i n o s o m a sp. o n l y , and N the t o t a l number of samples (N = a+b+c+d) ( P i e l o u 1974). T h i s t e s t was performed on N = 3 2 samples ( c r e s t and t r o u g h o n l y ; s u r f a c e and s u b s u r f a c e f r a c t i o n s c o n s i d e r e d s e p a r a t e l y ) and N = 48 samples ( a c r o s s s e r i e s i n c l u d e d ) . The p r o b a b i l i t y of a v a l u e as l a r g e as the c a l c u l a t e d X 2 c , i f the n u l l h y p o t h e s i s of independence i s c o r r e c t , i s g i v e n by a X 2 t a b l e w i t h 1 degree of freedom (p<0.05 f o r X 2 c >3.8). 205 3_. R e s u l t s a. Sand r i . p p l e s Sand r i p p l e s were a permanent f e a t u r e of the exposed sand s i t e a t Iona N o r t h and were o c c a s i o n a l l y observed i n w i n t e r a t the mud s i t e . The wavelength and h e i g h t ( t r o u g h t o c r e s t ) of the r i p p l e s v a r i e d w i t h no d i s c e r n i b l e p a t t e r n t h r o u g h the y e a r but were g e n e r a l l y 6 t o 10 cm (mode = 7cm) and 0.5 t o 3 cm (mode = 0.8cm), r e s p e c t i v e l y . On some o c c a s i o n s s m a l l a c c u m u l a t i o n s of p l a n t d e t r i t u s and/or s i l t were v i s i b l e on the s u r f a c e of the t r o u g h s . No l a r g e d i f f e r e n c e s i n sediment g r a i n s i z e p r o p e r t i e s were obse r v e d between c r e s t and t r o u g h samples c o l l e c t e d i n January 1977 (Table 7 ) . The major d i f f e r e n c e between samples was the p e r c e n t of m a t e r i a l r e t a i n e d on the 0.355 and 0.177 mm s c r e e n s . D e v i a t i o n s of up t o 4% i n the weight of m a t e r i a l r e t a i n e d on a s c r e e n i n r e p e a t e d s i e v i n g s of the same sample have been r e p o r t e d (Webb 1969); t h e r e f o r e , the observed d i f f e r e n c e s i n T able 7 a r e not l i k e l y t o be r e a l . The measured median d i a m e t e r of a d j a c e n t c r e s t and t r o u g h samples d i f f e r e d by o n l y 20 t o 30 um. The sediment a t the s i t e was w e l l - s o r t e d medium sand (Md = 0.34 t o 0.37 mm) w i t h s l i g h t skewness. 206 T a b l e 7. Summary of g r a i n - s i z e c h a r a c t e r i s t i c s of d u p l i c a t e , 5 cm c o r e s taken from sand r i p p l e c r e s t s and t r o u g h s on 22 Jan 1977. V a l u e s i n upper p a r t of t a b l e are p e r c e n t (by-dry wt.) of m a t e r i a l r e t a i n e d on each mesh; v a l u e s i n lower p a r t of t a b l e are c h a r a c t e r i s t i c s of s i z e f r e q u e n c y d i s t r i b u t i o n s f o r each c o r e . - 0 • MESH SIZE (mm) Crest#1 Trough#1 Crest=2 Trough#2 0 1 .000 2.76 2.73 2.08 3.17 + 1 .0 0.590 7.28 9.54 10.13 8.17 + 1 .5 0.355 40.17 41 .58 34.34 41 .22 + 2.5 0.177 37.16 29.69 40. 52 30.80 + 3.5 0.074 1 1 .48 15.75 12.52 15.40 + 4.0 0.053 0.13 0.35 0.29 0.41 >+4. 0 <0.053 1 . 3 3 0.36 0.12 0.68 Md p [ mm ] 1 .50 [0.35] 1 .44 [0.37] 1 .57 [0.34] 1 .44 [0.37] Q10 1 .20 1.25 1 .20 1 .24 Q30 2.10 2.14 2.10 2.13 QD0 0.45 0.45 0.45 0.45 Skq0 + 0.15 + 0.25 +0.08 ' + 0.25 b. W i n t e r f a u n a l samples [ J a n u a r y 1977] Nematodes and h a r p a c t i c o i d copepods ( a l l s t a g e s combined) t o g e t h e r c o m p rised 93.9% of the w i n t e r meiobenthos (Table 8 ) ; 26% of the i n d i v i d u a l s c o l l e c t e d were a d u l t and c o p e p o d i t e h a r p a c t i c o i d s . The r e l a t i v e abundance of nematodes and h a r p a c t i c o i d s i n t r a n s e c t s t h r o u g h the r i p p l e system a r e shown 207 i n F i g . 37. Nematodes were more abundant i n samples from the Table 8. The s t r u c t u r e of the m e i o b e n t h i c assemblage of the sand r i p p l e s i n w i n t e r and summer c o l l e c t i o n s . T a b u l a t e d v a l u e s a r e the p e r c e n t c o n t r i b u t i o n s (by number) of major t a x a t o the t o t a l meiobenthos c o l l e c t e d on t h a t d a t e . TAXON PERCENTAGE OF TOTAL MEIOBENTHOS 22 Jan 1977 21 J u l y 1978 Nematodes 35.8 27.4 Harpact i c o i d s 26.0 3.4 N a u p l i i 32.1 67.8 O l i g o c h a e t e s 1 .4 0.3 T u r b e l l a r i a 4.7 0.9 t r o u g h (41.13 ± 2.98 c o r e " 1 ; n = 8) than i n the c r e s t (20.0 + 2.38 c o r e " 1 ) and the d i f f e r e n c e was s t a t i s t i c a l l y s i g n i f i c a n t ( t = 5.2; df = 1 4 ; p<0.00V). T h i s d i f f e r e n c e i n c r e s t / t r o u g h d e n s i t y of nematodes was r e f l e c t e d i n the nematode c o u n t s a c r o s s the r i p p l e s ( F i g . 37). H a r p a c t i c o i d s were e q u a l l y abundant i n c r e s t (27.5 ± 2.91 c o r e ' 1 ) and t r o u g h (23.75 ± 2.08 c o r e " 1 ) samples ( t = 0.96; P > 0 . 1 0 ) . A l t h o u g h the h a r p a c t i c o i d fauna as a whole d i d not appear t o respond t o the m i c r o t o p o g r a p h y , i n d i v i d u a l s p e c i e s were not e q u a l l y d i s t r i b u t e d t h r o u g h the r i p p l e system ( F i g . 3 8 ) . The m i c r o h a b i t a t d i s t r i b u t i o n s of a l l 5 s p e c i e s c o l l e c t e d i n January 1977 were s i g n i f i c a n t l y d i f f e r e n t (P<0.001) from 208 F i g u r e 37. Counts of nematodes and h a r p a c t i c o i d s i n t r a n s e c t s t h r o u g h r i p p l e s 22 Jan 1977. The dashed l i n e r e p r e s e n t s a p r o f i l e t h r ough the sand r i p p l e . NEMATODES s o 6 0 h 4 0 s o « ACROSS 111 Lt • u a. m a CREST 3 4 5 6 7 8 1 2 3 4 5 6 7 8 HARPACTICOIDS C R E S T TROUGH 1 2 3 4 5 6 7 8 TROUGH 210 F i g u r e 38. M i c r o h a b i t a t d i s t r i b u t i o n s of h a r p a c t i c o i d s p e c i e s on 22 Jan 1977. Histograms i n d i c a t e f r e q u e n c y of m i c r o h a b i t a t use ( r e l a t i v e abundance of i n d i v i d u a l s found i n each m i c r o h a b i t a t ) . Numbers above bars g i v e t o t a l number of i n d i v i d u a l s i n 8 samples from m i c r o h a b i t a t . Ca = c r e s t s u r f a c e (0-1 cm) Cb = c r e s t s u b s u r f a c e (1-5 cm) Ta = t r o u g h s u r f a c e (0-1 cm) Tb = t r o u g h s u b s u r f a c e (1-5 cm) 2 1 1 Ca Cb Ta T b Ca Cb Ta T b C a C b T a T b Ca C b T a T b MICROHABITAT 22.1.77 212 expected under the n u l l h y p o t h e s i s t h a t the number of i n d i v i d u a l s p r e s e n t i n a g i v e n h a b i t a t was a s i m p l e f u n c t i o n of sediment volume (Table 9 ) . C l e a r d i f f e r e n c e s i n m i c r o h a b i t a t Table 9. . M i c r o h a b i t a t s e l e c t i o n . b y sand r i p p l e h a r p a c t i c o i d . s p e c i e s . A c h i - s q u a r e d comparison of the number of each s p e c i e s c o l l e c t e d and the number e x p e c t e d a i n each of the 4 r i p p l e m i c r o h a b i t a t s . _ _ _ _ _ _ _ SPECIES Xc 22 Jan 1977 21 J u l y 1978 P. s p i n i c a u d a . 54.92 .* H. j a d e n s i s 41.52 72.63 H a l e c t inosoma sp. 324.67 * L. c o n s t r i c t u s * 83.84 T. t r i a n g u l a r i s 32.00 251.30 S. c a n a d e n s i s 63.00 312.05 a e x p e c t e d number' assumed t o be p r o p o r t i o n a l t o the volume of sediment c o l l e c t e d from each m i c r o h a b i t a t b p<0.00l i n a l l cases * too few o b s e r v a t i o n s t o t e s t p r e f e r e n c e s s e p a r a t e d many of the s p e c i e s s p a t i a l l y . For example, a l l 7 S c o t t o l a n a c a n a d e n s i s o c c u r r e d i n the t r o u g h s u r f a c e samples w h i l e o n l y 2 P a r a l e p t a s t a c u s s p i n i c a u d a (0.8%) o c c u r r e d i n t h a t h a b i t a t . The p r e f e r e n c e of i n d i v i d u a l s p e c i e s f o r d i f f e r e n t p a r t s of the r i p p l e system r e s u l t e d i n e q u a l d e n s i t i e s of copepods o c c u r i n g i n c r e s t s and t r o u g h s . The r e l a t i v e s i m i l a r i t i e s of the copepod fauna (by % 213 s p e c i e s c o m p o s i t i o n ) between p a i r s , of c o r e s from w i t h i n a m i c r o h a b i t a t and between m i c r o h a b i t a t s a re shown i n F i g . ; 39 and summarized i n T a b l e 10. C r e s t samples were the most homogeneous f o r the h a r p a c t i c o i d s ; a c r o s s samples were the l e a s t . C r e s t and t r o u g h samples sh a r e d , on average , o n l y about 50% of t h e i r f aunas. A l t h o u g h the c r e s t and t r o u g h samples were not c o m p l e t e l y homogeneous, they were, on average, more s i m i l a r t o o t h e r samples from the same m i c r o h a b i t a t than t o samples c l o s e r i n space but from a d i f f e r e n t m i c r o h a b i t a t . For example, T1 shared 67% of i t s copepod fauna w i t h sample T8, 8.4 cm away, but o n l y 32% of i t s fauna w i t h C1, o n l y 2.8 cm away. Table 10. Summary of f a u n a l a f f i n i t y a n a l y s i s f o r samples c o l l e c t e d on. 22 Jan 1977. T a b u l a t e d v a l u e s are mean P e r c e n t S i m i l a r i t y (±1SE) of h a r p a c t i c o i d s c a l c u l a t e d between p a i r s of c o r e s from the same m i c r o h a b i t a t and from d i f f e r e n t m i c r o h a b i t a t s (n=28 f o r each w i t h i n - h a b i t a t comparison; n=64 f o r each b e t w e e n - h a b i t a t c o m p a r i s o n ) . MICROHABITAT CREST TROUGH ACROSS CREST 77.2±1.93 50.98±1.99 50.05±2.29 TROUGH 66.68±2.51 43.95±2.09 ACROSS 43.64±3.80 214 F i g u r e 39. T r e l l i s diagram f o r the 24 sand r i p p l e samples c o l l e c t e d on 22 Jan 1977 showing the p e r c e n t s i m i l a r i t y of h a r p a c t i c o i d fauna between p a i r s of c o r e s . 215 CREST TROUGH CACROSS 1 2 3 4 5 6 7 8 1 75 < 100% 216 c. Summer f a u n a l samples [ J u l y 1978] In J u l y 1978 h a r p a c t i c o i d copepods were s t i l l the most abundant taxon p r e s e n t i n the sand r i p p l e s , a l t h o u g h most were n a u p l i i ; o n l y 8.64 ± 1.13 c o r e " 1 or 3.4% of the t o t a l meiobenthos were a d u l t s and c o p e p o d i t e s . Nematodes were more than t w i c e as abundant as i n January 1977 (69.27 ± 6.34 c o r e " 1 ) but c o m p r i s e d a s l i g h t l y s m a l l e r p o r t i o n of the t o t a l meiobenthos (Table 8 ) . The r e l a t i v e abundances of h a r p a c t i c o i d s and nematodes i n t r a n s e c t s t h r o u g h d i f f e r e n t r i p p l e m i c r o h a b i t a t s i n J u l y are shown i n F i g . 40. Nematodes were more abundant i n t r o u g h samples (85.1 ± 14.38 c o r e " 1 ) than i n c r e s t samples (56.0 ±7.13 c o r e " 1 ) and a l t h o u g h t h i s d e n s i t y d i f f e r e n c e was s t a t i s t i c a l l y s i g n i f i c a n t ( t = 2.35; P<0.05) i t was l e s s marked than i n J a n u a r y ; a l s o , the a c r o s s t r a n s e c t d i d not show a p a r t i c u l a r p a t t e r n . The h a r p a c t i c o i d fauna as a whole was u n e q u a l l y d i s t r i b u t e d t h r o u g h the r i p p l e m i c r o h a b i t a t s i n summer; 72% of the copepods were c o l l e c t e d from the t r o u g h samples (13.9 ± 1.39 c o r e " 1 ) . There were s i g n i f i c a n t l y fewer copepods i n the c r e s t samples (5.38 ± 0.92 c o r e " 1 ) ( t = 5.01; P<0.001). Copepods were a l s o s t r o n g l y a g g r e g a t e d a t the s u r f a c e i n summer (96.7% of a l l copepods c o l l e c t e d o c c u r r e d i n the 0-1 cm l a y e r ) . I n d i v i d u a l h a r p a c t i c o i d s p e c i e s were u n e q u a l l y d i s t r i b u t e d among h a b i t a t s i n J u l y ; a l l s i x s p e c i e s p r e s e n t were most abundant i n t r o u g h s u r f a c e samples ( F i g . 4 1 ) . The w i n t e r dominants, P. s p i n i c a u d a and H a l e c t i n o s o m a sp. were r e p l a c e d 217 F i g u r e 40. Counts of nematodes and h a r p a c t i c o i d s i n t r a n s e c t s t h r o u g h sand r i p p l e s 21 J u l y 1978. The dashed l i n e r e p r e s e n t s ' a p r o f i l e t hrough the sand r i p p l e . NEMATODES I S 3 4 5 6 7 8 1 2 3 a 5 B 7 a HARPACTICOIDS C R E S T 1 2 3 4 5 6 7 S C O R E T R O U G H 1 S 3 4 5 6 7 8 2 1 9 F i g u r e 41. M i c r o h a b i t a t d i s t r i b u t i o n s of h a r p a c t i c o i d s p e c i e s on 21 J u l y 1978. Histograms i n d i c a t e r e l a t i v e abundance of i n d i v i d u a l s i n each m i c r o h a b i t a t . Numbers above ba r s g i v e t o t a l number of i n d i v i d u a l s i n 8 samples from m i c r o h a b i t a t . Ca = c r e s t s u r f a c e (0-1 cm) Cb = c r e s t s u b s u r f a c e (1-5 cm) .Ta = t r o u g h s u r f a c e (0-1 cm) Tb = t r o u g h s u b s u r f a c e (1-5 cm) 220 R spinicauda 1.0 .75 .50 .25 1.0 i (J .751 UJ S .501 O E E - 2 5 Ca Cb Ta T b Halectinosoma sp. 4 Ca Cb T a T b 1.0, .75 .50 .25 T. triangularis 31 1.0 .75 .50 .25 H. jadensis 8 1 11 1.0 .75 .50 .25 C a Cb T a T b L. constrictus 12 1.0 75 .50 .25 Ca Cb Ta Tb S. canadensis 48 28 2 Ca Cb T a T b Ca Cb Ta T b MICROHABITAT 21.7.78 221 by . two immigrants from the mud, S. 'canadensis and T. t r i a n g u l a r i s . A second C y l i n d r o p s y l l i d , L. c o n s t r i c t u s , had l a r g e l y r e p l a c e d P. s p i n i c a u d a . There was l i t t l e e v i d e n c e of m i c r o s p a t i a l s e g r e g a t i o n among s p e c i e s i n summer, w i t h the e x c e p t i o n of the dominants; 35.4% of S. c a n a d e n s i s i n d i v i d u a l s were c o l l e c t e d from C r e s t s u r f a c e samples w h i l e o n l y 8.8% of i n d i v i d u a l s of T. t r i a n g u l a r i s were found i n t h a t m i c r o h a b i t a t . d. M i c r o h a b i t a t d i s p l a c e m e n t The o v e r a l l h a b i t a t use p a t t e r n of the h a r p a c t i c o i d s i n January 1977 was m o s t l y d e t e r m i n e d by the p a t t e r n s of two s p e c i e s , P. s p i n i c a u d a and H a l e c t inosoma sp. which t o g e t h e r c o m p r i sed 91.7% of the copepod community. These two s p e c i e s were most abundant i n s e p a r a t e m i c r o h a b i t a t s ; 59.5% of P. s p i n i c a u d a were found i n C r e s t s u b s u r f a c e , 0.8% i n Trough s u r f a c e . H a l e c t inosoma sp. showed the r e v e r s e • s p e c i a l i z a t i o n w i t h 1.5% found i n C r e s t s u b s u r f a c e and 52.6% i n Trough s u r f a c e . On an even s m a l l e r s c a l e ( i n d i v i d u a l s a m p l e s ) , the two s p e c i e s were s i g n i f i c a n t l y n e g a t i v e l y a s s o c i a t e d ( X 2 c = 3.85; P<0.05 i f o n l y c r e s t and t r o u g h samples a r e c o n s i d e r e d ; X 2 c = 8.84; P<0.01 i f a l l samples a r e c o n s i d e r e d ) ( T a b l e 11). In o t h e r words, more samples c o n t a i n e d o n l y one of the two s p e c i e s than e x p e c t e d by chance a l o n e i f the two s p e c i e s were i n d e p e n d e n t l y d i s t r i b u t e d . 222 T a b l e 11. P a r a l e p t a s t a c u s s p i n i c a u d a and H a l e c t i n o s o m a sp. . C h i - s q u a r e t e s t f o r independence based on sand r i p p l e samples c o l l e c t e d on 22 Jan 1977. (top ) Only C r e s t and Trough samples i n c l u d e d i n - a n a l y s i s (bottom) C r e s t , Trough and A c r o s s samples i n c l u d e d i n a n a l y s i s . Halectinosoma sp. PRESENT A B S E N T T O T A L S PRESENT 13 1Q S3 ABSENT S O S TOTALS SS IO 3S Xc = 3.85* b . Halectinosoma sp. PRESENT ABSENT TOTALS PRESENT 17 15 3 2 ABSENT 16 • i g TOTALS 33 15 2 X c = 8.84** 4 8 224 D. D i s c u s s i o n These r e s u l t s support the c o n c l u s i o n reached i n e a r l i e r s e c t i o n s t h a t the mud and sand s i t e s h a r b o r e d d i s t i n c t h a r p a c t i c o i d communities w i t h d i s t i n c t dynamics. The s t r o n g n e g a t i v e c o r r e l a t i o n between s p e c i e s d i v e r s i t y and d e n s i t y i n the sand assemblage ( F i g . 34c) i s c o n s i s t e n t w i t h the te m p o r a l p a t t e r n s of sand s p e c i e s d i s c u s s e d i n the p r e v i o u s s e c t i o n : the c y c l i n g of dominant s p e c i e s which a t t a i n , h i g h abundances f o r b r i e f p e r i o d s and are asynchronous w i t h peaks of the o t h e r s p e c i e s i n the community. The n o n - s i g n i f i c a n t c o r r e l a t i o n between d e n s i t y and d i v e r s i t y i n the mud community i s c o n s i s t e n t w i t h the tempor a l p a t t e r n s of i t s s p e c i e s ; t h a t i s , h i g h t e m p o r a l o v e r l a p and l e s s d i s t i n c t s e a s o n a l i t y among the dominant s p e c i e s . S i m i l a r r e l a t i o n s h i p s between d e n s i t y and d i v e r s i t y i n a sand and mud community were r e p o r t e d by C o u l l and F l e e g e r (1977) who p o s t u l a t e d t h a t the sand p a t t e r n was caused by o p p o r t u n i s t i c blooms of i n t e r s t i t i a l s p e c i e s . W h i l e my r e s u l t s support t h i s h y p o t h e s i s , i t s h o u l d be noted t h a t some e p i p e l i c s p e c i e s a re a l s o c a p a b l e of the o p p o r t u n i s t i c e x p l o i t a t i o n of the sand h a b i t a t . H a r p a c t i c o i d s were h e t e r o g e n e o u s l y d i s t r i b u t e d a t s m a l l s p a t i a l s c a l e s a t both s i t e s (TCS s i g n i f i c a n t ) which agrees w i t h H e i p ' s (1975) a s s e r t i o n t h a t a g g r e g a t e d p a t t e r n s a r e the r u l e among m e i o b e n t h i c s p e c i e s . The h a r p a c t i c o i d s as a group were s i g n i f i c a n t l y a g g r e g a t e d a t both s i t e s on most d a t e s (PCS s i g n i f i c a n t ) . In o t h e r words some of the c o r e s sampled ' m i c r o h a b i t a t s ' which were more f a v o r a b l e t o h a r p a c t i c o i d s i n 225 g e n e r a l . S i m i l a r a g g r e g a t i o n s of the t o t a l h a r p a c t i c o i d assemblage have been r e p o r t e d from a v a r i e t y of h a b i t a t s ( V i t i e l l o 1968; Gray and R i e g e r 1971; A r l t 1973; O l s s o n and E r i k s o n 1974; H e ip 1975; T h i s t l e 1978). I n d i v i d u a l s p e c i e s a t Iona N o r t h were, on average, aggregated at s m a l l s p a t i a l s c a l e s ( s i g n i f i c a n t TCS, T a b l e 6; s i g n i f i c a n t i n d i v i d u a l i n d i c e s of d i s p e r s i o n ; Appendix 5 ) , and, through most of the y e a r , s p e c i e s ' a g g r e g a t i o n s were, on average, d i s j u n c t ( s i g n i f i c a n t HCS; F i g . 36a). In the sand, p a t c h i n e s s of h a r p a c t i c o i d s was p r o p o r t i o n a l t o , d e n s i t y and i n v e r s e l y p r o p o r t i o n a l t o d i v e r s i t y . In o t h e r words, the sand h a r p a c t i c o i d s were p a t c h i e s t a t the t i m e s of the l a r g e , s i n g l e - s p e c i e s blooms (of P a r a l e p t a s t a c u s s p i n i c a u d a i n A p r i l and T a c h i d i u s t r i a n g u l a r i s i n June) and so may have been r e l a t e d t o a g g r e g a t i o n f o r r e p r o d u c t i o n . No s i g n i f i c a n t changes i n h a b i t a t h e t e r o g e n e i t y were noted at these t i m e s and so response t o c hanging h a b i t a t s t r u c t u r e seems u n l i k e l y t o have caused the l a r g e i n c r e a s e s i n a g g r e g a t i o n o b s e r v e d . In f a c t , most of the d i s p e r s i o n on both d a t e s i s a ccounted f o r by the h i g h l y s i g n i f i c a n t i n d i c e s of d i s p e r s i o n s of the dominant s p e c i e s (153.77 f o r P. s p i n i c a u d a and 241.05 f o r T. t r i a n g u l a r i s , see Appendix 5 ) . S i m i l a r i n t r a s p e c i f i c a g g r e g a t i o n s of h a r p a c t i c o i d s p e c i e s r e l a t e d t o r e p r o d u c t i v e a c t i v i t y were r e p o r t e d by H e i p and E n g e l s (1977) and H i c k s (1979). A g g r e g a t i o n of the t o t a l h a r p a c t i c o i d s of the mud was not s i g n i f i c a n t l y c o r r e l a t e d w i t h e i t h e r d e n s i t y or d i v e r s i t y . L arge changes i n sediment p r o p e r t i e s ( i . e . the s t r u c t u r e of the 226 h a b i t a t ) d i d occur i n the mud th r o u g h 1978 and i t i s p o s s i b l e t h a t they caused the tempora l f l u c t u a t i o n s i n a g g r e g a t i o n s t r e n g t h . S e v e r a l p r o c e s s e s a r e l i k e l y t o o p e r a t e on the community and w i t h o u t e x p e r i m e n t a l e v i d e n c e I can o n l y s p e c u l a t e on t h e i r l i k e l y e f f e c t s . Sediment t e x t u r e was heterogeneous i n w i n t e r when sand was d e p o s i t e d a t the mud s i t e c r e a t i n g temporary p a t c h e s of d i s t i n c t m i c r o h a b i t a t s ( F i g . 9 ) . The i n c r e a s e d s p a t i a l h e t e r o g e n e i t y , c o u p l e d w i t h h i g h l e v e l s of p h y s i c a l d i s t u r b a n c e may have i n c r e a s e d the p a t c h i n e s s of h a r p a c t i c o i d s from November t h r o u g h March s i n c e d i f f e r e n t i a l c o l o n i z a t i o n of newly opened m i c r o h a b i t a t s may r e s u l t from i n t e r s p e c i f i c d i f f e r e n c e s i n copepod b e h a v i o r ( T h i s t l e 1980). The monotonic i n c r e a s e i n PCS observ e d between June and August may have r e s u l t e d from i n c r e a s e d b i o g e n i c h e t e r o g e n e i t y of the h a b i t a t t h r o u g h the summer. T u b i c o l o u s o l i g o c h a e t e s and p o l y c h a e t e s i n c r e a s e d i n d e n s i t y through the summer , t h e i r tubes c r e a t i n g an i m p o r t a n t s o u r c e of s p a t i a l h e t e r o g e n e i t y i n an o t h e r w i s e f e a t u r e l e s s h a b i t a t . Analagous responses of meiofauna t o "tube m i c r o t o p o g r a p h y " have been r e p o r t e d by Jensen (1977), T h i s t l e (1978) and Eckman (1979). D i s t u r b a n c e from f e e d i n g a c t i v i t y of the p o l y c h a e t e s and/or d i r e c t p r e d a t i o n by s m a l l f i s h have a l s o been suggested as causes of h o r i z o n t a l p a t c h i n e s s of mud-dwelling h a r p a c t i c o i d s ( B e l l 1980; F l e e g e r 1980). I w i l l p r e s e n t e v i d e n c e i n c h a p t e r V I I t h a t a s m a l l goby, C l e v e l a n d i a i o s i s a v e r y a c t i v e p r e d a t o r i n the t i d e p o o l s i n summer and i t s s e d i m e n t - b i t i n g b e h a v i o r may w e l l c r e a t e s m a l l d e f a u n a t e d p a t c h e s of h a b i t a t . From t h i s 227 d i s c u s s i o n I would suggest t h a t the mechanisms c o n t r o l l i n g p a t c h i n e s s i n the mud h a r p a c t i c o i d s as a group (PCS) may be p r i m a r i l y b i o l o g i c a l i n summer and p h y s i c a l i n w i n t e r . I n t e r s p e c i f i c m i c r o h a b i t a t p a r t i t i o n i n g was s i g n i f i c a n t i n both assemblages i n 1978. P a r t i t i o n i n g was a c o n s e r v a t i v e p r o p e r t y of the sand community, r e m a i n i n g e s s e n t i a l l y c o n s t a n t over a broad range of d e n s i t y and s p e c i e s d i v e r s i t y ( F i g . 36b). T h i s i s perhaps not too s u r p r i s i n g , c o n s i d e r i n g the c o n s t a n c y of sediment p r o p e r t i e s a t the s i t e i n 1978. F u r t h e r , the major sou r c e of s m a l l - s c a l e h e t e r o g e n e i t y , the sand r i p p l e m i c r o t o p o g r a p h y , was a h i g h l y p r e d i c t a b l e f e a t u r e of the environment. H a r p a c t i c o i d s p e c i e s p a r t i t i o n e d the m i c r o h a b i t a t s i n the sand, a l t h o u g h d e t a i l s of the p a r t i t i o n i n g p a t t e r n changed t h r o u g h the seasons ( F i g s . 38 and 41). The sand copepods s e g r e g a t e d the h a b i t a t v e r t i c a l l y as w e l l as h o r i z o n t a l l y e s p e c i a l l y i n w i n t e r ( F i g s . 38 and 41). S i m i l a r v e r t i c a l s e g r e g a t i o n of sand h a b i t a t s has been p r e v i o u s l y d e s c r i b e d ; f o r example, f o r h a r p a c t i c o i d s ( H a r r i s 1972b) and f o r g a s t r o t r i c h s (Hogue 1978). D u r i n g the 3 months when h o r i z o n t a l h a b i t a t p a r t i t i o n i n g was not s i g n i f i c a n t ( F e b r u a r y , March, A p r i l ) a s i g n i f i c a n t p r o p o r t i o n of the sand h a r p a c t i c o i d s were found i n the s u b s u r f a c e sediments ( F i g . 4 2 ) , a l l o w i n g f o r the o b s e r v e d v e r t i c a l s e g r e g a t i o n of s p e c i e s . A f t e r m i d - A p r i l more than 95% of the sand h a r p a c t i c o i d s were found a t the s u r f a c e and h o r i z o n t a l p a r t i t i o n i n g c o u p l e d w i t h t e m p o r a l p a r t i t i o n i n g ( c h a p t e r V) became the predominant i n t e r s p e c i f i c s e g r e g a t i n g mechanisms. 228 F i g u r e 42. S e a s o n a l change i n v e r t i c a l d i s t r i b u t i o n of sand r i p p l e h a r p a c t i c o i d s t h r o u g h 1978. Note s m a l l p e r c e n t a g e of i n d i v i d u a l s c o l l e c t e d below 1 cm from May t o October. 229 100 1978 •79 230 M i c r o h a b i t a t p a r t i t i o n i n g was an i m p o r t a n t component of mud community o r g a n i z a t i o n i n 1978 and was s t r o n g e r than i n the sand p a r t l y because the a l t e r n a t e s e g r e g a t i n g mechanisms were c o n s i d e r a b l y weaker i n the mud. The mud h a r p a c t i c o i d s a r e p h y s i c a l l y and b e h a v i o r l y l i m i t e d t o the s u r f a c e l a y e r and so v e r t i c a l s e g r e g a t i o n i s u n l i k e l y and t e m p o r a l o v e r l a p r a t h e r than t e m p o r a l s e g r e g a t i o n was observed ( c h a p t e r V)..Mud h a b i t a t p a r t i t i o n i n g v a r i e d s e a s o n a l l y but was u n c o r r e l a t e d w i t h e i t h e r s p e c i e s d i v e r s i t y or d e n s i t y . P a r t i t i o n i n g (HCS/df) was s i g n i f i c a n t l y c o r r e l a t e d w i t h PCS i n the mud s u g g e s t i n g t h a t i t may be s i m i l a r l y r e l a t e d t o s e a s o n a l v a r i a t i o n i n h a b i t a t h e t e r o g e n e i t y . The two measures were u n c o r r e l a t e d i n the sand. The p a t t e r n of h a r p a c t i c o i d s p e c i e s ' o c c u r r e n c e s i n the sand r i p p l e s p r o v i d e s independent e v i d e n c e t h a t m i c r o s p a t i a l p a r t i t i o n i n g o c c u r s w i t h i n the h a r p a c t i c o i d community and, a l s o , e v i d e n c e to suggest t h a t the p a r t i t i o n i n g o b s e r v e d may be due i n p a r t t o i n t e r s p e c i f i c c o m p e t i t i o n . A l t h o u g h c r e s t s and t r o u g h s of the sand r i p p l e s were s i m i l a r s e d i m e n t o l o g i c a l l y , t h e i r topography a l t e r s water f l o w p a t t e r n s over the bed and causes i n h o m o g e n e i t i e s i n s e v e r a l b i o l o g i c a l l y s i g n i f i c a n t p r o p e r t i e s (Webb and Theodor 1972), i n c l u d i n g the d i s t r i b u t i o n of m i c r o b i a l f i l m s t o which meiofauna are known t o respond (e. g . Gray 1968). I t i s not s u r p r i s i n g , t h e n , t h a t a l l h a r p a c t i c o i d s p e c i e s p r e s e n t i n w i n t e r samples s e l e c t i v e l y p o p u l a t e d the r i p p l e m i c r o h a b i t a t s . P a r t of the h a b i t a t s e l e c t i o n o b s e r v e d might be e x p l a i n e d i n terms of the b e h a v i o r of the copepods c o u p l e d w i t h the 231 l i k e l y f l o w p a t t e r n s over the bed. Eckman (1978) argued t h a t a n i m a l s t r a n s p o r t e d over a r i p p l e d bed s h o u l d be d e p o s i t e d i n the t r o u g h s . S c o t t o l a n a c a n a d e n s i s swims a c t i v e l y above the sediment and was, i n d e e d , found o n l y i n Trough s u r f a c e samples i n w i n t e r ( F i g . 38). In summer, most copepod s p e c i e s were found i n the t r o u g h s ( F i g s . 40 and 4 1 ) . Nematodes were c o n c e n t r a t e d i n the t r o u g h s i n both seasons ( F i g s . 37 and 4 0 ) , a g a i n s u p p o r t i n g Eckman's (1978) h y p o t h e s i s . P a s s i v e t r a n s p o r t can o n l y p a r t l y e x p l a i n the observed d i s t r i b u t i o n p a t t e r n s . In w i n t e r , an e q u a l number of h a r p a c t i c o i d s were found i n r i p p l e c r e s t s and t r o u g h s and one s p e c i e s , P. s p i n i c a u d a , c l e a r l y ' p r e f e r r e d ' c r e s t s over t r o u g h s . An a c t i v e mechanism f o r h a b i t a t s e l e c t i o n must be i n v o l v e d as w e l l . One p o s s i b i l i t y may be the a g g r e g a t i o n of h a r p a c t i c o i d s around m i c r o b i a l food d i f f e r e n t i a l l y d i s t r i b u t e d i n c r e s t s and t r o u g h s . W h i l e meiofauna do respond t o food p a t c h i n e s s (e.g. Lee et a l . 1977) I know of no study which r e p o r t s d i f f e r e n t i a l p o p u l a t i o n of u n s t a b l e bedforms by m i c r o f l o r a . A second h y p o t h e s i s i s t h a t the observed p a t t e r n s were a t l e a s t p a r t l y due t o i n t e r s p e c i f i c c o m p e t i t i o n . T h i s h y p o t h e s i s w i l l be more f u l l y e x p l o r e d i n c h a p t e r V I I I a l t h o u g h s e v e r a l p o i n t s s h o u l d be made h e r e . A l l h a r p a c t i c o i d s p e c i e s s t u d i e d were s e n s i t i v e t o the t o u c h of an i n d i v i d u a l of another s p e c i e s and i n the l a b o r a t o r y they were c o n s i s t e n t l y observed t o r e a c t t o i n t e r s p e c i f i c e n c o u n t e r s by d a r t i n g away. T h i s i n t e r f e r e n c e b e h a v i o r i s , I t h i n k , i m p o r t a n t i n the e s t a b l i s h m e n t of the d i s c o r d a n t 232 abundance p a t t e r n s o b s e r v e d a t s m a l l s p a t i a l s c a l e s by both t y p e s of a n a l y s i s used i n t h i s c h a p t e r . Many examples of d i s c o r d a n t d i s t r i b u t i o n s of s p e c i e s p a i r s , p a r t i c u l a r l y among the more abundant s p e c i e s , a r e e v i d e n t i n F i g s . 38 and 41. The n e g a t i v e a s s o c i a t i o n between P. s p i n i c a u d a and H a l e c t inosoma sp. on a per c o r e comparison f u r t h e r s u g g e s t s c o m p e t i t i v e i n t e r a c t i o n s . E. Summary The Iona N o r t h h a r p a c t i c o i d s were h e t e r o g e n e o u s l y d i s t r i b u t e d a t s m a l l s p a t i a l s c a l e s . P a r t of t h i s h e t e r o g e n e i t y was caused by s p e c i e s - s p e c i f i c m i c r o h a b i t a t s e l e c t i o n . In the sand the p r i m a r y s o u r c e of s p a t i a l h e t e r o g e n e i t y was the p h y s i c a l l y - p r o d u c e d r i p p l e m i c r o t o p o g r a p h y . In the mud, h o r i z o n t a l m i c r o h a b i t a t p a r t i t i o n i n g was a l s o i n t e n s e ; i n d i r e c t e v i d e n c e suggests t h a t the m i c r o h a b i t a t s p e r c e i v e d by the fauna were b i o g e n i c (worm-tubes and p r e d a t o r / d e p o s i t f e e d e r - d i s t u r b e d sediments) i n summer and p h y s i c a l l y produced i n w i n t e r (mosaic of mud and sand). I t i s becoming i n c r e a s i n g l y c l e a r t h a t an u n d e r s t a n d i n g of m e i o b e n t h i c community dynamics must ta k e s m a l l - s c a l e p a t t e r n s and the p r o c e s s e s which g e n e r a t e them i n t o account ( C o u l l and F l e e g e r 1977; Heip and E n g e l s 1977; B e l l e t a l . 1978; Hogue 1978; T h i s t l e 1978,1980; B e l l 1980; F l e e g e r 1980). As p o i n t e d out by C o u l l and F l e e g e r (1977) and c o n f i r m e d i n the p r e s e n t s t u d y , two communities may have the same s p e c i e s d i v e r s i t i e s , even share some of the same s p e c i e s , and y e t be o r g a n i z e d v e r y 233 d i f f e r e n t l y . My study does not support t h e i r h y p o t h e s i s t h a t sand i n t r i n s i c a l l y has more v a r i e d m i c r o h a b i t a t s than mud, e s p e c i a l l y i f the mud i s p o p u l a t e d w i t h t u b i c o l o u s or b u r r o w i n g s p e c i e s which may p r o v i d e a w e a l t h of b i o g e n i c h e t e r o g e n e i t y . I concur w i t h Elmgren (1S78) and B e l l (1980) t h a t the macrofauna-meiofauna i n t e r a c t i o n s on s o f t bottoms may be a dominant f o r c e c o n t r o l l i n g meiofauna community s t r u c t u r e and c e r t a i n l y a s u b j e c t worthy of f u r t h e r s t u d y . 2 3 4 V I I . PREDATION BY SMALL TIDEPOOL FISH A. I n t r o d u c t i o n E c o l o g i c a l s t u d i e s on the marine meiobenthos t r a d i t i o n a l l y have c o n c e n t r a t e d on the d i f f e r e n t i a l r esponses of s p e c i e s t o g r a d i e n t s and patc h e s of e n v i r o n m e n t a l c o n d i t i o n s ( P o l l o c k 1971; F e n c h e l 1978). T h i s ' e c o p h y s i o l o g i c a l ' a pproach, a l t h o u g h p r o d u c i n g v a l u a b l e i n f o r m a t i o n . c o n c e r n i n g the fundamental n i c h e (sensu H u t c h i n s o n 1957) of the s p e c i e s i n q u e s t i o n , may l e a d t o the t r i v i a l c o n c l u s i o n t h a t "...by v i r t u e of i t s m o r p h o l o g i c a l and p h y s i o l o g i c a l s p e c i a l i z a t i o n s , a p a r t i c u l a r s p e c i e s or p a r t i c u l a r p o p u l a t i o n i s c a p a b l e of l i v i n g where, i n d e e d , i t l i v e s . " (Wieser 1975). P o p u l a t i o n s may be l i m i t e d t o a s m a l l e r range of environments (the r e a l i z e d n i c h e of H u t c h i n s o n 1957) or may be h e l d a t d e n s i t i e s below those e x p e c t e d f o r the p r e v a i l i n g c o n d i t i o n s by a number of p r o c e s s e s c o l l e c t i v e l y termed ' b i o l o g i c a l i n t e r a c t i o n s ' . The i n f l u e n c e of t h e s e b i o l o g i c a l i n t e r a c t i o n s on m e i o b e n t h i c community s t r u c t u r e i s p o o r l y u n d e r s t o o d ( C o u l l and B e l l 1979). The two b i o l o g i c a l i n t e r a c t i o n s I w i l l c o n s i d e r i n t h i s t h e s i s a r e p r e d a t i o n ( i n t e r a c t i o n s w i t h s p e c i e s from a h i g h e r t r o p h i c l e v e l ) and c o m p e t i t i o n ( i n t e r a c t i o n s w i t h s p e c i e s from the same t r o p h i c l e v e l ) . C o m p e t i t i o n i s the s u b j e c t of the next 235 c h a p t e r . P r e d a t i o n has been p a r t i c u l a r l y n e g l e c t e d i n m e i o b e n t h i c s t u d i e s , due i n p a r t t o the w i d e s p r e a d b e l i e f t h a t the meiobenthos i s not preyed upon s i g n i f i c a n t l y by e i t h e r the macrobenthos or f i s h ( M c l n t y r e 1969; G e r l a c h 1971; G i e r e 1975; F e n c h e l 1978; Banse and Mosher 1980) and so i s an independent food web w i t h i t s own 'meiobenthic' p r e d a t o r s (e.g. P r o t o h y d r a  l e u c k a r t i , H e i p and Smol 1976b). Not a l l r e s e a r c h e r s on meiofauna have r e p o r t e d ' i n s i g n i f i c a n t ' l e v e l s of p r e d a t i o n from o u t s i d e the meiobenthos. H a r p a c t i c o i d copepods, i n p a r t i c u l a r , a r e an i m p o r t a n t food f o r j u v e n i l e s of some commercial f i s h s p e c i e s , n o t a b l y f l a t f i s h (Smidt 1951; B r e g n b a l l e 1961; Muus 1967; Toole 1980) and s a l m o n i d s ( K a c z y n s k i et a l . 1973; S i b e r t et a l . 1977; Levy et a l . 1979). B r e g n b a l l e (1961) e s t i m a t e d t h a t j u v e n i l e p l a i c e (about 12-40 mm l o n g ) f e e d i n g on a s h a l l o w (<1.5 m) sand bar a t the mouth of K y s i n g F j o r d , an e s t u a r y on the e a s t c o a s t of J u t l a n d , Denmark consumed 1.2% of the s t a n d i n g c r o p of h a r p a c t i c o i d s per day (based on a s t a n d i n g c r o p of 86,000 copepods m~2, maximum d a i l y i n t a k e of 500 copepods p l a i c e " ' and 2 f i s h m" 2). A l t h o u g h the p e r i o d i n which these j u v e n i l e s e x p l o i t the meiobenthos may be b r i e f , t hey may s t i l l decimate the p o p u l a t i o n of t h e i r p r e f e r r e d prey s p e c i e s ( S i b e r t 1979). For example, a s i n g l e , s m a l l (<45 mm l o n g ) t i d e p o o l s c u l p i n , 0 1 i q o c o t t u s maculosus , can consume over 1000 copepods day" 1 and thus e l i m i n a t e the h a r p a c t i c o i d T i g r i o p u s c a l i f o r n i c u s from a h i g h s p l a s h p o o l (<5 1 volume) i n 24 hours ( D e t h i e r 1980). O l i g o c o t t u s maculosus i s o n l y one of a l a r g e number of.. 2 3 6 f i s h s p e c i e s w h i c h a r e p h y s i o l o g i c a l l y and m o r p h o l o g i c a l l y ( i n c l u d i n g b e i n g s m a l l ) a d a p t e d t o l i f e i n t h e m a r i n e i n t e r t i d a l zone ( G i b s o n 1969). A l t h o u g h t h e s e f i s h may be v e r y a b u n d a n t , t h e y a r e g e n e r a l l y n e g l e c t e d i n e c o l o g i c a l s t u d i e s of m a r i n e b e n t h i c c o m m u n i t i e s b e c a u s e t h e y a r e d i f f i c u l t t o c a p t u r e w i t h c o n v e n t i o n a l s a m p l i n g gear ( G i b s o n 1969; Grossman e t a l . 1980) and a r e of no d i r e c t c o m m e r c i a l i m p o r t a n c e . Many of t h e s e s p e c i e s a r e c a r n i v o r o u s and, s i n c e t h e y r e m a i n s m a l l t h r o u g h t h e i r l i f e h i s t o r y , a r e p o t e n t i a l l y i m p o r t a n t p r e d a t o r s on t h e i n t e r t i d a l m e i o b e n t h o s . A s t u d y o f t h e e f f e c t of t h e s e p r e d a t o r s on t h e m e i o b e n t h o s must be more t h a n a l i s t i n g of f i s h s p e c i e s w i t h m e i o b e n t h i c r e m a i n s i n t h e i r g u t s . The p o t e n t i a l e f f e c t s of p r e d a t i o n o f t h e p r e y community a r e many and v a r i e d , P r e d a t i o n may i n t e r a c t w i t h p h y s i c a l f a c t o r s of t h e e n v i r o n m e n t t o s e t t h e i n t e r t i d a l z o n a t i o n p a t t e r n of a p r e y s p e c i e s ( D e t h i e r 1980). More i m p o r t a n t l y , p r e d a t i o n may c o n t r o l t h e r e l a t i v e a b u n d a n c e s of p r e y s p e c i e s and t h e r e b y a f f e c t community s t r u c t u r e and d y n a m i c s . G r a s s s h r i m p , P a l a e m o n e t e s p u g i o , f o r example, a l t e r t h e c o m p o s i t i o n of s a l t marsh m e i o b e n t h i c a s s e m b l a g e s by s e l e c t i v e l y e l i m i n a t i n g t h e p o l y c h a e t e s , o l i g o c h a e t e s and nematodes ( B e l l and C o u l l 1978; B e l l 1979a). A l t h o u g h t h e g r a s s s h r i m p d e c r e a s e d t h e t o t a l d e n s i t y o f nematodes, t h e y had no a p p a r e n t e f f e c t on w i t h i n - c o m m u n i t y s t r u c t u r e i n e x p e r i m e n t a l e n c l o s u r e s ; d i v e r s i t y , dominance and s p e c i e s c o m p o s i t i o n were t h e same i n t a n k s where s h r i m p had f e d f o r 12 weeks as i n the c o n t r o l t a n k s f r o m w h i c h p r e d a t o r s were 237 e x c l u d e d ( B e l l and C o u l l 1978). The g r a s s shrimp d i d n o t , t h e r e f o r e , appear t o feed s e l e c t i v e l y on p a r t i c u l a r nematode s p e c i e s . S p e c i e s - s e l e c t i v e p r e d a t i o n has o f t e n been p o s t u l a t e d t o e x p l a i n o b s e r v e d changes i n s t r u c t u r e of h a r p a c t i c o i d communities w i t h time (eg. Brickman 1972; M a r c o t t e 1977a; C o u l l et a l . 1979; F l e e g e r 1979,1980). R e l e a s e from s p e c i e s - s p e c i f i c p r e d a t i o n by a goby, P o m a t o s c h i s t u s m i c r o p s , was a l s o i m p l i c a t e d as the cause of i n c r e a s e s i n d e n s i t y of some h a r p a c t i c o i d s p e c i e s i n s i d e p r e d a t o r e x c l o s u r e s on a m u d f l a t i n the Lynher E s t u a r y , UK (Warwick 1980b and p e r s o n a l communication). I t i s . apparent t h a t e c o l o g i c a l s t u d i e s on i n t e r t i d a l m e i o b e n t h i c communities can no l o n g e r be based on the assumption t h a t t h e r e i s no s i g n i f i c a n t p r e d a t o r y m o r t a l i t y from o u t s i d e the meiobenthos. For t h i s r e a s o n , i n the summers of 1979 and 1980 I conducted a f i e l d survey of the f e e d i n g of two s m a l l i n t e r t i d a l f i s h , t he arrow goby, C l e v e l a n d i a i o s Jordan and G i l b e r t 1882, and j u v e n i l e s of the P a c i f i c s t a g h o r n s c u l p i n , L e p t o c o t t u s armatus G i r a r d 1854, which f r e q u e n t the Iona N o r t h t i d e p o o l s ( F i g . 4 3 ) . C l e v e l a n d i a i o s , a common r e s i d e n t of t i d e p o o l s from s o u t h e r n C a l i f o r n i a t o s o u t h e r n B r i t i s h C o l u m b i a , feeds on a l g a e or s m a l l C r u s t a c e a (Hart 1973; M a c G i n i t i e 1935). On m u d f l a t s i n C a l i f o r n i a h a r p a c t i c o i d copepods a r e i t s p r e f e r r e d prey ( B r o t h e r s 1975). A l t h o u g h not r e s t r i c t e d t o the l i t t o r a l zone, L e p t o c o t t u s armatus i s a common r e s i d e n t of t i d e p o o l s from n o r t h e r n C a l i f o r n i a t o the 238 F i g u r e 43. P o t e n t i a l p r e d a t o r s on h a p a c t i c o i d s i n Iona N o r t h t i d e p o o l s (top) Photograph of 3. f i s h s p e c i e s i n c l u d e d i n the gut a n a l y s i s . Shrimp r e p r e s e n t s p o t e n t i a l i n v e r t e b r a t e p r e d a t o r s not s t u d i e d . (bottom) Range of s i z e s of C l e v e l a n d i a i o s used i n the e l e c t i v i t y a n a l y s e s . 240 G u l f of A l a s k a . L i k e most s c u l p i n s , L. armatus i s a v o r a c i o u s p r e d a t o r on a v a r i e t y of i n v e r t e b r a t e s (Clemens and W i l b y 1961; Hart 1973). S e v e r a l o t h e r f i s h s p e c i e s , i n c l u d i n g j u v e n i l e s a l m o n i d s , have been r e c o r d e d from the i n t e r c a u s e w a y a r e a t o the west of Iona N o r t h (Greer e t a l . 1980) and may a l s o prey on h a r p a c t i c o i d s . I n v e s t i g a t i o n s of the f e e d i n g b e h a v i o r of t h e s e f i s h a re i n p r o g r e s s ( C D . L e v i n g s , p e r s . comm.). One u l t i m a t e aim of s t u d i e s on the p r e d a t o r s of m e i o b e n t h i c communities i s t o r e s o l v e the r o l e of p r e d a t i o n as a s e l e c t i v e agent which d e t e r m i n e s community c o m p o s i t i o n . B e f o r e the r o l e of p r e d a t i o n by the s m a l l t i d e p o o l f i s h a t Iona N o r t h may be a s s e s s e d i t i s n e c e s s a r y t o determine 1) the number of h a r p a c t i c o i d s eaten by i n d i v i d u a l f i s h of each s p e c i e s and d i f f e r e n t s i z e c l a s s e s w i t h i n each s p e c i e s and 2) which h a r p a c t i c o i d s p e c i e s are eaten and i n what r e l a t i v e p r o p o r t i o n s . These are the p r i m a r y aims of the s t u d y t o be r e p o r t e d i n t h i s c h a p t e r . B. Methods Arrow g o b i e s ( C l e v e l a n d i a i o s J o r d a n and G i l b e r t 1882) and j u v e n i l e P a c i f i c s t a g h o r n s c u l p i n s ( L e p t o c o t t u s armatus G i r a r d 1854) were c o l l e c t e d from the t i d e p o o l s of Iona N o r t h on f o u r o c c a s i o n s i n 1979: 25 May, 25 June, 25 J u l y and 23 August and t w i c e i n 1980: 25 A p r i l and 26 June. F i s h were c a p t u r e d by d i p - n e t 2 t o 3 hours a f t e r exposure of the p o o l s by the 241 r e c e d i n g t i d e , and i m m e d i a t e l y f i x e d i n a 4% ( v / v ) s o l u t i o n of b u f f e r e d f o r m a l i n i n s e a w a t e r . In June and A u g u s t 1979 and June 1980 m e i o f a u n a were c o l l e c t e d a t t h e same t i m e and from t h e same p a r t of t h e p o o l as t h e f i s h samples by s c o o p i n g up a b o u t 100 ml of s u r f i c i a l s e d i m e n t and p r e s e r v i n g t h e sample i n 4% f o r m a l i n i n s e a w a t e r t o w h i c h Rose B e n g a l had been a d d e d . j _ . D e s c r i p t i o n of d i e t s of t i d e p o o l f i s h W i t h i n a week of c o l l e c t i o n , e a c h f i s h was i d e n t i f i e d t o s p e c i e s , numbered, i t s s t a n d a r d l e n g t h ( t o t h e n e a r e s t mm) r e c o r d e d and i t s gut d i s s e c t e d . B e f o r e r e m o v a l of t h e g u t s , t h e wet w e i g h t ( a f t e r e x c e s s water was removed by b l o t t i n g ) of a s e l e c t e d sample of f i s h was a l s o r e c o r d e d . Due t o d i f f e r e n c e s i n gut m o r p h o l o g y , t h e e n t i r e a l i m e n t a r y c a n a l of t h e g o b i e s was u s e d , w h i l e o n l y t h e stomach of t h e s c u l p i n s was examined. B o t h w i l l be r e f e r r e d t o i n t h e r e m a i n d e r o f t h i s c h a p t e r a s ' g u t ' . The c o n t e n t s of each, gut were examined under a d i s s e c t i n g m i c r o s c o p e a t m a g n i f i c a t i o n s of X 1 6 and x40. E a c h r e c o g n i z a b l e f o o d i t e m was a s s i g n e d t o one of t h e f o l l o w i n g c a t e g o r i e s : h a r p a c t i c o i d c o p e p o d s , o l i g o c h a e t e s , p o l y c h a e t e s , amphipods, m o l l u s c s i p h o n s , m y s i d s , o r g a n i c d e t r i t u s , s e d i m e n t , and a l g a e . The a p p r o x i m a t e c o n t r i b u t i o n of e a c h c a t e g o r y t o t h e t o t a l volume o f m a t e r i a l i n t h e g u t was e s t i m a t e d v i s u a l l y . A l l h a r p a c t i c o i d s were p i c k e d out and p r e s e r v e d f o r more d e t a i l e d a n a l y s i s . The c o n t r i b u t i o n s o f e a c h f o o d c a t e g o r y t o t h e " d i e t " o f a p a r t i c u l a r g r o u p of f i s h ( e . g . l a r g e g o b i e s ) was c a l c u l a t e d 2 4 2 from the d a t a on the volume of m a t e r i a l i n the g u t s as f o l l o w s : The t o t a l volume of m a t e r i a l i n each gut was t a k e n as 1 0 0 % . The p e r c e n t volume c o n t r i b u t i o n of each food c a t e g o r y , X, t o t h a t i n d i v i d u a l f i s h ' s d i e t i s , then ( 1 2 ) % X = ( v o l / E v o l ) 1 0 0 % X X X and the p e r c e n t c o n t r i b u t i o n of t h a t food c a t e g o r y t o the o v e r a l l d i e t of the group of n f i s h t o which t h a t f i s h belongs i s ( 1 3 ) % V = E (% X ) / 1 0 0 n % , j - 1 ,n A . j These measures of c o n t r i b u t i o n of food t y p e s t o d i e t are e x t r e m e l y c o a r s e , and s h o u l d be used w i t h an awareness of s e v e r a l s o u r c e s of e r r o r , the most s e r i o u s of which a r e : the o v e r - e s t i m a t i o n of the importance of h a r d - b o d i e d t o s o f t - b o d i e d forms, unequal gut passage t i m e s of d i f f e r e n t food t y p e s , the d i f f i c u l t y of e s t i m a t i n g 'volume' and the l a c k of i n f o r m a t i o n on the r e l a t i v e n u t r i t i o n a l v a l u e of d i f f e r e n t f o o d s . They do s u f f i c e f o r the purposes of t h i s c h a p t e r , which a r e t o examine i n t e r s p e c i f i c d i f f e r e n c e s i n p a t t e r n s of p r e d a t i o n on h a r p a c t i c o i d s among the t i d e p o o l f i s h e s and t o determine d i f f e r e n c e s i n p r e d a t i o n by d i f f e r e n t s i z e c l a s s e s w i t h i n a s p e c i e s . 243 2. E l e c t i v i t y Q u a l i t a t i v e s e d i m e n t s a m p l e s were c o l l e c t e d on 25 June and 23' Aug 1979 and 26 June 1980. H a r p a c t i c o i d s were s e p a r a t e d from t h e s e d i m e n t and i d e n t i f i e d as d e s c r i b e d i n c h a p t e r I I . The l e n g t h of e a c h c o p e p o d ( f r o m t h e base of t h e r o s t r u m t o t h e i n s e r t i o n of t h e c a u d a l r a m i ) , o r a subsample of a p p r o x i m a t e l y 100 i n d i v i d u a l s of e a c h s p e c i e s i n t h e c a s e of v e r y dense s a m p l e s , was measured w i t h an o c u l a r m i c r o m e t e r a t x40 m a g n i f i c a t i o n . F o r c a l c u l a t i o n o f e l e c t i v i t y i n d i c e s t h e p r o p o r t i o n o f s p e c i e s i i n t h e q u a l i t a t i v e sample was c a l c u l a t e d as a a p p r o x i m a t i o n o f t h e p r o p o r t i o n of t h a t s p e c i e s i n t h e ' a v a i l a b l e ' p r e y : (14) s p . =N . / £ N . 1 1 J - l 2 where N.^  i s t h e number o f i n d i v i d u a l s o f s p e c i e s i i n t h e c o l l e c t i o n , N ^ i s t h e t o t a l number of i n d i v i d u a l s of s p e c i e s j i n the. c o l l e c t i o n , and s i s t h e t o t a l number of s p e c i e s c o l l e c t e d from t h e s e d i m e n t sample. A l l h a r p a c t i c o i d s p e c i e s f o u n d i n t h e s e d i m e n t samples were i n c l u d e d i n t h i s c a l c u l a t i o n r e g a r d l e s s o f whether t h e y o c c u r r e d i n t h e f i s h g u t s sampled on t h a t d a t e . I t may be a r g u e d t h a t i f a s p e c i e s i s n e v e r e a t e n by t h e f i s h , i t i s n o t ' a v a i l a b l e ' t o t h e p r e d a t o r . T h i s argument i s v a l i d b u t i r r e l e v a n t t o t h e p r e s e n t p u r p o s e . The aim o f t h i s s t u d y i s t o d e t e r m i n e t h e s e l e c t i v e r e m o v a l o f s p e c i e s f r o m t h e t o t a l h a r p a c t i c o i d c o p e p o d community; hence t h e i n c l u s i o n of a l l s p e c i e s i n t h e community i n t h e c a l c u l a t i o n s of e l e c t i v i t y 244 i s v a l i d . For reasons which w i l l be d i s c u s s e d below, o n l y C l e v e l a n d i a i o s which c o n t a i n e d h a r p a c t i c o i d s were used i n the e l e c t i v i t y a n a l y s i s . Copepods were always swallowed whole by the f i s h and g e n e r a l l y showed l i t t l e m a s t i c a t o r y damage. F u r t h e r , the r e l a t i v e l y hard e x o s k e l e t o n of the copepods g e n e r a l l y remained i n t a c t , even i n t o the f e c a l p e l l e t of the f i s h , and so h a r p a c t i c o i d s were e a s i l y i d e n t i f i e d t o s p e c i e s i n the gut c o n t e n t s . Both the i d e n t i t y and l e n g t h of each specimen from the g u t s were noted and the s p e c i e s c o m p o s i t i o n . o f the h a r p a c t i c o i d f r a c t i o n of the food c a l c u l a t e d from (15). s r . - n . / s n . where r i s the p r o p o r t i o n of s p e c i e s i i n the r a t i o n , n i i s i t he number of i n d i v i d u a l s of s p e c i e s i i n the g u t , n i s the i t o t a l number of i n d i v i d u a l s of s p e c i e s j i n the gut and S i s the t o t a l number of s p e c i e s i n the gut. In the s t r i c t sense, ' r a t i o n ' r e f e r s t o the t o t a l q u a n t i t y of food consumed i n a g i v e n time ( I v l e v 1961). The e x a c t time each f i s h i n t h i s study had f e d i s not known; t h e r e f o r e ' r a t i o n ' here r e f e r s t o the q u a n t i t y of fo o d , s p e c i f i c a l l y the t o t a l number of h a r p a c t i c o i d s , i n the gut c o n t e n t s of each f i s h . ' E l e c t i v i t y ' ( I v l e v 1961) was c a l c u l a t e d as a measure of the d i f f e r e n t i a l removal of prey t y p e s ( s p e c i e s or s i z e c l a s s e s ) from the h a r p a c t i c o i d copepod community. No c o r r e c t i o n was made i f h a r p a c t i c o i d s were l e s s than 100% of the t o t a l gut 245 c o n t e n t s . E l e c t i v i t y i n d i c e s were c a l c u l a t e d f o r the two most abundant prey s p e c i e s , S c o t t o l a n a c a n a d e n s i s and T a c h i d i u s  t r i a n q u l a r i s , from I v l e v ' s (1961) e q u a t i o n : (16) K i = ( r i " P i ) / / ( r i + P i ) / ' - 1 . 0 - K < +1 .0 where K.^  i s e l e c t i v i t y on prey s p e c i e s i . Analagous e l e c t i v i t i e s were c a l c u l a t e d on two s i z e c a t e g o r i e s of h a r p a c t i c o i d s ( r e g a r d l e s s of s p e c i e s ) : l a r g e prey ( l e n g t h > 0.5 mm) and s m a l l prey ( l e n g t h < 0.5 mm). 3 246 C. R e s u l t s and d i s c u s s i o n J _ . C l e v e l a n d i a i o s The numbers and s i z e s of C l e v e l a n d i a i o s c a p t u r e d i n Iona N o r t h t i d e p o o l s a re summarized i n Table 12. A t o t a l of 61 g o b i e s r a n g i n g from 11 mm j u v e n i l e s t o 39 mm a d u l t s were d i s s e c t e d . The guts of these f i s h c o n t a i n e d a t o t a l of 4746 h a r p a c t i c o i d copepods. The l e n g t h of each f i s h and the Tab l e 12. C l e v e l a n d i a i o s . Mean l e n g t h , 1 S.E. and range of i n d i v i d u a l s from Iona N o r t h t i d e p o o l s used i n the a n a l y s e s and the t o t a l number of h a r p a c t i c o i d copepods c o n t a i n e d i n t h e i r guts on each sampling d a t e . DATE LENGTH (mm) X S.E. range n TOTAL PREY 1 979 25 May 34.0 1 29 25 June 35.7 0.7 27-39 1 4 703 25 J u l y 17.5 0.8 1 4-23 1 3 918 23 Aug 13.9 0.6 11-18 1 4 661 1980 26 June 21 .5 1.8 15-39 19 2435 f r a c t i o n a l c o m p o s i t i o n of the copepods i n i t s gut c o n t e n t s a r e g i v e n f o r each date i n Appendix 6. The p e r c e n t a g e c o n t r i b u t i o n of r e c o g n i z a b l e food items t o the d i e t s of C. i o s a r e g i v e n i n T a b l e 13. C l e v e l a n d i a i o s a t 247 Iona N o r t h i s c l e a r l y a p r e d a t o r on the meiobenthos; i n terms of b oth volume and numbers, h a r p a c t i c o i d copepods were the dominant prey of f i s h of a l l s i z e s . The o b s e r v a t i o n s , p r e s e n t e d i n T able 13 a l s o i n d i c a t e some d i f f e r e n c e s i n d i e t between j u v e n i l e and a d u l t f i s h . H a r p a c t i c o i d s made up >75% by volume of the d i e t of s m a l l (<30mm s t a n d a r d l e n g t h ) g o b i e s (Table 13). S m a l l macrofauna, p a r t i c u l a r l y the t i p s of the s i p h o n s of b i v a l v e s (Macoma  b a l t h i c a ) and ( i n f r e q u e n t l y ) amphipods (Corophium s p . ) , p o l y c h a e t e s and o l i g o c h a e t e s were a l s o e a t e n , a l t h o u g h they were a minor component of the d i e t ( T a b l e s 13 and 14) compared w i t h h a r p a c t i c o i d s . ' D e t r i t u s ' , which i n c l u d e d p l a n t fragments, amorphous m a t e r i a l and a s m a l l q u a n t i t y of sediment, was commonly enc o u n t e r e d i n the g u t s a l t h o u g h i t was l e s s than 20% of the d i e t by volume. A d u l t g o b i e s (>30 mm s t a n d a r d l e n g t h ) o c c u r r e d i n the p o o l s i n May and June. A l t h o u g h h a r p a c t i c o i d s remained the dominant p r e y , macrofauna and d e t r i t u s were q u a n t i t a t i v e l y more imp o r t a n t i n the d i e t of l a r g e r f i s h and e q u a l l e d the c o n t r i b u t i o n of m e i o b e n t h i c prey i n June 1979 ( T a b l e s 13 and 14). D e t r i t u s and s i p h o n s both c o n t r i b u t e d t h r e e t i m e s the volume i n l a r g e f i s h compared w i t h s m a l l f i s h but the l a r g e s t d i s t i n c t i o n was i n o l i g o c h a e t e s ( n e g l i g i b l e i n the d i e t of s m a l l f i s h but 12% i n l a r g e f i s h ) . The gut c o n t e n t s of the f o u r l a r g e s t g o b i e s c a p t u r e d i n June 1980 were markedly d i f f e r e n t from those d e s c r i b e d above. A l t h o u g h t h e s e f i s h had consumed a s m a l l e r p r o p o r t i o n of T a b l e 14.Leptocottus armatus and Clevelandia ios. C o n t r i b u t i o n s o f m a j o r d i e t components t o t h e t o t a l volume o f m a t e r i a l i n the g u t s (by %). Component C o n t r i b u t i o n t o d i e t (%) A p r ' 8 0 May '79 J u n ' 7 9 J u n ' 8 0 J u l ' 7 9 A u g ' 7 9 -_——____-___ - — •________________________________ 0 ___________ S S S G S G,_ G r G G b s M e i o b e n t h o s 32.7 22 .7 0 .2 33 .3 8 .9 77 .3 93 .4 8 0 . 9 77.1 M a c r o b e n t h o s 29.7 35 .7 69 .3 33 .5 4 6 . 7 9 .0 0 .7 8 .8 6 .5 ' D e t r i t u s ' 37 .6 3 8 . 2 26 .3 33 .2 4 3 . 5 13 .7 5 . 9 1 0 . 3 16 .4 G = g o b i e s G g = g o b i e s l e s s t h a n 30 mm l o n g G^ = g o b i e s l o n g e r than 30 mm S = s c u l p i n s 249 Table 13. C l e v e l a n d i a i o s . S e m i - q u a n t i t a t i v e a n a l y s i s of the d i e t of f i s h c a p t u r e d i n Iona N o r t h t i d e p o o l s . T a b u l a t e d v a l u e s a r e e s t i m a t e d v o l u m e t r i c c o n t r i b u t i o n of each food c a t e g o r y t o the t o t a l volume of food consumed by a l l g o b i e s c a p t u r e d on each d a t e . PREY CATEGORY CONTRIBUTION TO DIET (% TOTAL VOLUME) Jun 79' ' J u l 79' Aug 79' Jun 80' Jun 80' ' Harpact i c o i d s 33.3 80.9 77. 1 93.4 77 .25 D e t r i t u s 33.2 10.3 16.4 . 5.9 1 3 .75 O l i g o c h a e t e s 12.1- 0.4 0.4 0.7 0 .50 P o l y c h a e t e s 1 . 1 Amphipods 1.9 6 .25 M o l l u s c s i p h o n s 18.2 6.5 5.0 0 .50 Mysids 1 . 1 Sediment 1 .50 Algae 0 .25 ' s m a l l f i s h ' ' l a r g e f i s h (< 30 mm (> 30 mm lon g ) l o n g ) h a r p a c t i c o i d s than the s m a l l f i s h . c a p t u r e d a t the same time (Table 13), they consumed more than t w i c e the p r o p o r t i o n of h a r p a c t i c o i d s as the l a r g e f i s h caught i n 1979. O l i g o c h a e t e s and m o l l u s c s i p h o n s , which t o g e t h e r c o m p r i s e d 1/3 of the d i e t volume of l a r g e f i s h i n 1979, were a n e g l i g i b l e component i n 1980. The l a r g e f i s h caught i n 1980 showed a s u b s t a n t i a l i n c r e a s e i n f e e d i n g on o n l y one macrobenthic c a t e g o r y , s m a l l (2 t o 5 mm) amphipods (Corophium s p p . ) . 250 The f e e d i n g of C. i o s on m u d f l a t s i n C a l i f o r n i a (near the so u t h e r n l i m i t s of the range of the s p e c i e s ) was i n c l u d e d i n a co m p a r a t i v e study of t h r e e s p e c i e s of g o b i e s by B r o t h e r s (1975). B r o t h e r s examined the guts of f i s h between 13.7 and 38 mm s t a n d a r d l e n g t h from s e v e r a l s i t e s . Of 118 i n d i v i d u a l s examined, 88% c o n t a i n e d h a r p a c t i c o i d copepods. Depending on the h a b i t a t i n which the f i s h were f e e d i n g , h a r p a c t i c o i d s made up 8-75% of the gut c o n t e n t s by volume and 16-90% by numbers. In g e n e r a l , the C a l i f o r n i a f i s h f e d i n much the same way as the Iona N o r t h i n d i v i d u a l s . O s t r a c o d s , i m p o r t a n t prey f o r the g o b i e s i n some h a b i t a t s i n B r o t h e r ' s s t u d y , were not eaten by the g o b i e s of Iona N o r t h , perhaps because they o c c u r r e d i n v e r y low numbers i n summer ( F i g . 15). 2. L e p t o c o t t u s armatus The numbers and s i z e s of L e p t o c o t t u s armatus examined are summarized i n Table 15. F o r t y f i s h from 13 t o 47 mm s t a n d a r d l e n g t h were examined. T h e i r g u t s c o n t a i n e d a t o t a l of 450 h a r p a c t i c o i d copepods. H a r p a c t i c o i d copepods were a s m a l l e r component of the d i e t s of s c u l p i n s than of the g o b i e s (Table 16). The gut s of s m a l l s c u l p i n s c a p t u r e d i n May 1 9 7 9 c o n t a i n e d a s u b s t a n t i a l p r o p o r t i o n (22 . 7 % ) of h a r p a c t i c o i d s . One month l a t e r , of the s i x guts examined, o n l y one c o n t a i n e d a s i n g l e h a r p a c t i c o i d . A s i m i l a r l y s harp drop i n the d i e t a r y c o n t r i b u t i o n of h a r p a c t i c o i d s t o l a r g e s c u l p i n s was observed i n 1980, a l t h o u g h , 251 Table 15. L e p t o c o t t u s armatus. Mean l e n g t h , .1 S.E. and range of i n d i v i d u a l s from Iona N o r t h t i d e p o o l s used i n the a n a l y s e s and the t o t a l number of h a r p a c t i c o i d copepods c o n t a i n e d i n t h e i r guts, on each samp l i n g d a t e . DATE LENGTH (mm) X S.E. range n TOTAL PREY 1.979 2 5 May 21.4 1.5 1 3-35 1 6 226 25 June 34.2 3.9 18-47 6 1 . 1 980 17 A p r i l 22.0 0.6 19-25 8 119 26 June 28.9 1.9 17-40 10 1 04 as observed w i t h the g o b i e s , l a r g e r s c u l p i n s a t e a g r e a t e r number of h a r p a c t i c o i d s i n 1980 than i n 1979. The most impo r t a n t component of the s c u l p i n s ' d i e t was the s m a l l macrobenthos, p a r t i c u l a r l y amphipods, m o l l u s c s i p h o n s , p o l y c h a e t e s and mysids. L e p t o c o t t u s armatus i s an ambush p r e d a t o r . I t r e s t s near the sediment s u r f a c e and a t t a c k s i n d i v i d u a l , moving p r e y . Of the h a r p a c t i c o i d s eaten by s c u l p i n s i n May 1979, 98% belonged t o the two e p i p e l i c s p e c i e s , S c o t t o l a n a c a n a d e n s i s and T a c h i d i u s t r i a n g u l a r i s (T. t r i a n g u l a r i s was p a r t i c u l a r l y abundant i n the guts of the s m a l l e r f i s h ) . The predominance of these two s p e c i e s i n the gut c o n t e n t s of s c u l p i n s may be l i n k e d t o the i n t e r h a b i t a t m i g r a t i o n d e s c r i b e d i n c h a p t e r •IV. I f the proposed model ( F i g . 27) i s c o r r e c t , s u b s t a n t i a l d e n s i t i e s of the two s p e c i e s , ( p a r t i c u l a r l y T. t r i a n g u l a r i s ) must e n t e r the b e n t h i c boundary l a y e r i n May ( F i g s . 17 and 21) and thus would 252 T a b l e 16. L e p t o c o t t u s armatus. S e m i - q u a n t i t a t i v e a n a l y s i s of the d i e t of f i s h c a p t u r e d i n Iona N o r t h t i d e p o o l s . T a b u l a t e d v a l u e s a re e s t i m a t e d v o l u m e t r i c c o n t r i b u t i o n of each food c a t e g o r y t o the t o t a l volume of food consumed by a l l s c u l p i n s c a p t u r e d on each d a t e . PREY CATEGORY CONTRIBUTION TO DIET (% TOTAL VOLUME) May 7 9 Jun. 7 9 Apr 80 Jun 80 Harpact i c o i d s 22.7 0.2 32.7 8.9 Amphipods 4.8 30.8 17.8 36.7 Isopods 5.0 M y s i d s / s h r i m p 1 .5 13.5 I n s e c t s .3 .4 0.8 P o l y c h a e t e s 8 . 8 •15.8 •8.1 6.0 M o l l u s c s i p h o n s 19.1 4.2 4.0 Trematodes + 3.3 + + ' D e t r i t u s ' 38.2 26.3 37.6 43.5 O l i g o c h a e t e s 1 .5 2.5 Cumacea 1.3 Al g a e 0. 1 Sediment 0.8 become v u l n e r a b l e t o a t t a c k from a p r e d a t o r such as L. armatus. In A p r i l 1980, a p p a r e n t l y b e f o r e the " m i g r a t i o n s " b e g i n , the s c u l p i n s examined, w i t h the e x c e p t i o n of f i s h #6 (23 mm lo n g ) and f i s h #8 ( 1 9 mm lo n g ) d i d not c o n t a i n S. c a n a d e n s i s and T. t r i a n g u l a r i s . I n s t e a d , seven of the e i g h t f i s h examined had consumed H a r p a c t i c u s u n i r e m i s , a l a r g e h a r p a c t i c o i d copepod 253 which a t Iona N o r t h does not l i v e i n the sediment but c l i n g s by i t s g r a p p l i n g - h o o k shaped P.1 t o the f i l a m e n t s of a c o l o n i a l n a v i c u l o i d d iatom ( F i g . 4 e ) . In terms of broader c a t e g o r i e s , s m a l l s c u l p i n s , l i k e l a r g e g o b i e s , f e d almost e q u a l l y on the meiobenthos, macrobenthos and d e t r i t u s ; however, w i t h growth, they s p e c i a l i z e d much more h e a v i l y on the macrobenthos (Table 14). S c u l p i n s f e d on a broad range of the s m a l l e r macrobenthos (Table 16). The p a r t i c u l a r prey c o n c e n t r a t e d upon was h i g h l y v a r i a b l e and p r o b a b l y r e l a t e d t o c hanging r e l a t i v e abundances (and a c t i v i t y ) i n the environment, a l t h o u g h I have no d a t a on the a v a i l a b i l i t y of macrobenthic p r e y . The p r e d a t i o n p a t t e r n of L. armatus i n f e r r e d from i t s gut c o n t e n t s i s c o n s i s t e n t w i t h what would'be e x p e c t e d of an e p i -b e n t h i c p r e d a t o r which l o c a t e s i t s prey p r i m a r i l y v i s u a l l y . S c u l p i n s a t e r e l a t i v e l y s m a l l numbers of h a r p a c t i c o i d s (max 101, o t h e r w i s e fewer than 50 copepods per g u t ) ; a t e the l a r g e s t s p e c i e s a v a i l a b l e (e.g. H a r p a c t i c u s u n i r e m i s ) w i t h s i z e of p r e y i n c r e a s i n g r a p i d l y w i t h i n c r e a s i n g s i z e of p r e d a t o r ; and s w i t c h e d from h a r p a c t i c o i d s t o l a r g e r prey when the f i s h were r e l a t i v e l y s m a l l (about 20 mm)(Tables 15 and 16). The h a r p a c t i c o i d s p e c i e s eaten by t h i s ' v i s u a l ' p r e d a t o r were e p i b e n t h i c and v i s i b l e (H. u n i r e m i s ) , l a r g e (H. j a d e n s i s ) and/or e p i p e l i c s p e c i e s which swim some of the time above the sediment s u r f a c e (S. c a n a d e n s i s and T. t r i a n g u l a r i s ) . 254 3. S e l e c t i v e p r e d a t i o n by C l e v e l a n d i a i o s The s p e c i e s c o m p o s i t i o n of the h a r p a c t i c o i d copepod community i n the t i d e p o o l s sampled on the same da t e s when f i s h were c a p t u r e d i s g i v e n i n Ta b l e 17. The prey community was both T a b l e 17. The p r o p o r t i o n a l c o m p o s i t i o n ( P i ) of the t i d e p o o l h a r p a c t i c o i d communities, e s t i m a t e d from q u a l i t a t i v e sediment samples c o l l e c t e d a t the same time as f i s h samples. S p e c i e s are ranked i n o r d e r of i n c r e a s i n g s i z e . SPECIES June 1979 Aug 1979 June 1980 SP* SP NP SP NP P. s p i n i c a u d a 0 . 344 0. 132 0 0 0 Ha l e c t i n o s o m a sp. 0 0. 1 60 0 .048 0 0.016 L. b e h n i n g i 0 .082 0. 226 0 .095 0 .022 0. 1 36 T. t r i a n g u l a r i s 0 .482 0. 387 0 .095 0 .227 0.119 L. vaga 0 0 0 0 .016 0.001 H. j a d e n s i s 0 .004 0 0 0 0.005 S. c a n a d e n s i s 0 .088 0. 095 0 .762 0 .735 0.723 * SP i s the so u t h p o o l ; NP i s the n o r t h p o o l s p a t i a l l y . ( b e t w e e n p o o l s ) and t e m p o r a l l y ( w i t h i n and between •years) v a r i a b l e i n the r e l a t i v e abundance of s p e c i e s . F i v e of the seven s p e c i e s i d e n t i f i e d from the sediment samples were t h e ex p e c t e d e p i - and e n d o - p e l i c forms ( P a r a l e p t a s t a c u s s p i n i c a u d a and Huntemannia j a d e n s i s a r e i n t e r s t i t i a l forms u s u a l l y found 255 i n sandy h a b i t a t s ) . Of t h e s e seven " a v a i l a b l e " s p e c i e s , two, P. s p i n i c a u d a and H a l e c t i n o s o m a sp. , were never found i n f i s h gut samples and one, L i m n o c l e t o d e s b e h n i n g i was seldom found. The s p e c i e s which o c c u r r e d w i t h g r e a t e s t f r e q u e n c y i n f i s h gut samples, S. c a n a d e n s i s and T. t r i a n g u l a r i s , were a l s o ( g e n e r a l l y ) the most abundant h a r p a c t i c o i d s i n the sediment (Table 1 7 ) . To determine the r e l a t i v e degree of " s e l e c t i v e removal" of these two s p e c i e s from the h a r p a c t i c o i d community by g o b i e s of d i f f e r e n t s i z e s , I v l e v ' s (1961) e l e c t i v i t y index was c a l c u l a t e d from d a t a o b t a i n e d i n June and August 1979 and June 1980. One of the p r i n c i p a l d i f f i c u l t i e s i n d e t e r m i n i n g f e e d i n g s e l e c t i v i t y i s the d e t e r m i n a t i o n of which prey a r e " a v a i l a b l e " t o the f i s h (Berg 1979). For f i s h such as L. armatus or j u v e n i l e s a l m o n i d s , f o r example, which prey on i n d i v i d u a l s emerging from the sediment, t h i s i s p a r t i c u l a r l y d i f f i c u l t ( S i b e r t 1979) s i n c e i t would be n e c e s s a r y t o q u a n t i f y r e l a t i v e numbers and r a t e s of emergence of prey s p e c i e s as w e l l as t h e i r r e l a t i v e v i s i b i l i t y t o the p r e d a t o r . These d a t a a r e not y e t a v a i l a b l e f o r the Iona N o r t h h a r p a c t i c o i d s , hence I w i l l not attempt t o c a l c u l a t e e l e c t i v i t i e s f o r L. armatus. The b e h a v i o r of C. i o s d u r i n g f e e d i n g j u s t i f i e s the use of sediment d e n s i t i e s of h a r p a c t i c o i d s i n the e s t i m a t i o n of r e l a t i v e " a v a i l a b i l i t y " of prey s p e c i e s . C l e v e l a n d i a i o s f e e d s on s m a l l , b e n t h i c p r e y by "sediment-b i t i n g " ( B r o t h e r s 1975 and my own o b s e r v a t i o n s ) . The f i s h opens i t s jaws, t h r u s t s i t s head 3-4 mm i n t o the sediment, c l o s e s i t s 256 jaws and churns the i n g e s t e d sediment i n i t s mouth. Prey items are thus s o r t e d from the f i n e sediment which i s e x p e l l e d i n s e v e r a l p u f f s t h rough the o p e r c u l a . By f e e d i n g i n t h i s way, the go b i e s i n the Iona N o r t h t i d e p o o l s had a v a i l a b l e t o them the same spectrum of h a r p a c t i c o i d s p r e s e n t e d i n Ta b l e 17. In 1979 a d u l t g o b i e s were c a u g h t , i n the upper i n t e r t i d a l i n June (one e a r l y a r r i v a l was caught i n May) (Table 12). At t h i s time 1/3 of t h e i r d i e t , was h a r p a c t i c o i d copepods (Table 13) and S c o t t o l a n a c a n a d e n s i s , a l t h o u g h o n l y 8.8% of the h a r p a c t i c o i d copepod community, was the f a v o r e d p r e y . F i s h l o n g e r than 34 mm had a v e r y h i g h p o s i t i v e e l e c t i v i t y f o r t h i s r e l a t i v e l y l a r g e prey s p e c i e s ( F i g . 44a) but a v e r y low e l e c t i v i t y f o r the more abundant, but s m a l l e r , T. t r i a n g u l a r i s ( F i g . 44b). More than 75% (by volume) of the prey of j u v e n i l e g o b i e s c o l l e c t e d i n 1979 were h a r p a c t i c o i d copepods (Table 13). These s m a l l f i s h , l e s s than 20 mm s t a n d a r d l e n g t h , had eaten the same two s p e c i e s of h a r p a c t i c o i d copepods as the a d u l t s but the s m a l l g o b i e s showed a h i g h e r e l e c t i v i t y f o r T. t r i a n g u l a r i s than f o r S. c a n a d e n s i s ( F i g . 4 4 ) . From the 1979 r e s u l t s , i t i s c l e a r t h a t l a r g e g o b i e s p r e f e r e n t i a l l y consumed a l a r g e h a r p a c t i c o i d s p e c i e s and s m a l l g o b i e s p r e f e r e n t i a l l y consumed a s m a l l e r s p e c i e s . I n t e r p r e t a t i o n of t h i s apparent dichotomy i n f e e d i n g p r e f e r e n c e s i s c o m p l i c a t e d by the f a c t t h a t the two s i z e c l a s s e s of f i s h d i d not c o - o c c u r i n 1979. As a t e s t of the h y p o t h e s i s t h a t the apparent o n t o g e n e t i c s h i f t i n f e e d i n g p r e f e r e n c e s o b s e r v e d i n 1979 was an a r t i f a c t of the t e m p o r a l 257 F i g u r e 44. C l e v e l a n d i a i o s . R e l a t i o n s h i p between f i s h l e n g t h and e l e c t i v i t y . c a l c u l a t e d f o r (a) S c o t t o l a n a c a n a d e n s i s and (b) T a c h i d i u s t r i a n g u l a r i s . S m a l l f i s h (<20mm long) were c o l l e c t e d from the south p o o l on 25 June 1979; l a r g e f i s h (>30mm long) were c o l l e c t e d from.both t i d e p o o l s on 23 Aug 1979. 259 s e g r e g a t i o n of f e e d i n g a c t i v i t y by the two s i z e c l a s s e s , the a n a l y s i s was r e p e a t e d i n June 1980 when l a r g e and s m a l l f i s h were f e e d i n g t o g e t h e r i n the Iona N o r t h t i d e p o o l s . The p l o t s of e l e c t i v i t y f o r T. t r i a n g u l a r i s and S. c a n a d e n s i s a re g i v e n i n F i g . 45 f o r g o b i e s of d i f f e r e n t s i z e s . The e l e c t i v i t y p a t t e r n r e l a t i v e t o the s i z e of the p r e d a t o r conforms t o t h a t d e s c r i b e d i n 1979. S m a l l f i s h had a h i g h e r e l e c t i v i t y on T. t r i a n g u l a r i s than on S. c a n a d e n s i s w h i l e l a r g e f i s h showed the r e v e r s e p a t t e r n , a l t h o u g h the d i s t i n c t i o n was not as c l e a r i n 1980 as i n 1979. There was no c l e a r between-pool d i f f e r e n c e i n e l e c t i v i t i e s f o r s m a l l f i s h . There was some i n d i c a t i o n i n the d a t a t h a t l a r g e f i s h which had fe d i n the n o r t h p o o l had eaten p r o p o r t i o n a t e l y more T. t r i a n g u l a r i s than l a r g e f i s h which had f e d i n the south p o o l . The sample s i z e i s too s m a l l t o determine i f t h i s i s a r e a l d i f f e r e n c e . From t h i s d i s c u s s i o n we may c o n c l u d e t h a t the p a t t e r n s of e l e c t i v i t y by d i f f e r e n t s i z e d p r e d a t o r s observed i n 1979 were r e a l o n t o g e n e t i c d i f f e r e n c e s and not an a r t i f a c t of t i m e . The d a t a from 1979 were r e e v a l u a t e d i n terms of the s i z e of each h a r p a c t i c o i d prey i t e m i r r e s p e c t i v e of s p e c i e s . The h a r p a c t i c o i d copepods were a r b i t r a r i l y d i v i d e d i n t o two s i z e c l a s s e s , >0.5 mm and <0.5 mm. The e l e c t i v i t y index was r e c a l c u l a t e d f o r each f i s h on the newly coded d a t a . A d u l t g o b i e s , as e x p e c t e d , showed a h i g h e l e c t i v i t y on l a r g e prey ( F i g . 46a) and a low e l e c t i v i t y on s m a l l prey ( F i g . 46b). J u v e n i l e f i s h showed the r e v e r s e p a t t e r n , a p p a r e n t l y p r e f e r r i n g 260 F i g u r e 45. C l e v e l a n d i a i o s . R e l a t i o n s h i p between f i s h l e n g t h and e l e c t i v i t y c a l c u l a t e d f o r (a) S c o t t o l a n a c a n a d e n s i s and (b) T a c h i d i u s t r i a n g u l a r i s . F i s h were c o l l e c t e d on 26 June 1980. S o l i d symbols r e p r e s e n t f i s h from the south p o o l ; open symbols r e p r e s e n t f i s h from the n o r t h p o o l . 2 6 1 b. + 1.0 > +0.5 > i= o o ^ -0.5 -1.0 -A * A A A A - T. triangularis _ i i i i i 1 • 1 1 1 1 1 1 I I ' ' I I 0 5 10 15 20 25 30 35 40 FISH LENGTH fmm) 262 F i g u r e 46. C l e v e l a n d i a i o s . R e l a t i o n s h i p between f i s h l e n g t h and e l e c t i v i t y c a l c u l a t e d f o r (a) l a r g e (>0.5mm) and (b) s m a l l 0.5mm) h a r p a c t i c o i d s . S m a l l f i s h were c o l l e c t e d from the s o uth p o o l on 25 June 1979; l a r g e f i s h were c o l l e c t e d from both p o o l s on 23 August 1979. 1 0 15 2 0 2 5 3 0 3 5 4 0 F I S H L E N G T H ( m m ) b 1.0 0.5 0 0.5 1.0 P R E Y S 0.5 mm ° e - @% °co oo° w o . -I I 1 I 1 1 o 0 5 10 15 2 0 2 5 3 0 3 5 4 0 F I S H L E N G T H ( m m ) 264 s m a l l ( F i g . 46b) t o l a r g e ( F i g . 46a) p r e y . S i z e , t h e r e f o r e , seemed t o be p a r t of the c r i t e r i o n of prey s e l e c t i o n by j u v e n i l e and a d u l t g o b i e s . I s h o u l d s t r e s s a t t h i s p o i n t t h a t none of the h a r p a c t i c o i d s i s too l a r g e f o r a s m a l l goby t o i n g e s t . The gape of the f i s h i s not d e t e r m i n i n g the s i z e of h a r p a c t i c o i d s e a t e n . 4. Comparison of the two p r e d a t o r s The d a t a which I have p r e s e n t e d on the gut c o n t e n t s of the two p r e d a t o r s l e a d me t o p o s t u l a t e t h a t at Iona N o r t h m o r t a l i t y of s e d i m e n t - d w e l l i n g h a r p a c t i c o i d s due t o p r e d a t i o n by e p i b e n t h i c , v i s u a l p r e d a t o r s ( s c u l p i n s ) i s - much lower than m o r t a l i t y due t o p r e d a t i o n by ' i n b e n t h i c ' , t a c t i l e ( t a c t i l e , because p r e y • s e l e c t i o n o c c u r s p r i m a r i l y i n the mouth) p r e d a t o r s ( g o b i e s ) . The c o n t r i b u t i o n s of h a r p a c t i c o i d copepods t o the d i e t (by volume i n g e s t e d ) of the two p r e d a t o r s a r e compared i n F i g . 47. H a r p a c t i c o i d s were a minor component of the s c u l p i n s ' d i e t except i n A p r i l 1980 when the f i s h were f e e d i n g on the p h y t a l - d w e l l i n g H a r p a c t i c u s u n i r e m i s . A l t h o u g h t h e s e a n i m a l s a r e l a r g e f o r h a r p a c t i c o i d s , they made up o n l y 32.7% of the d i e t of the s c u l p i n s on t h a t d a t e . In c o n t r a s t , h a r p a c t i c o i d copepods were the dominant p r e y of g o b i e s of a l l s i z e c l a s s e s ( T a b l e 13). They were l e a s t i m p o r t a n t t o the l a r g e g o b i e s c a p t u r e d i n June 1979, y e t on t h a t date the h a r p a c t i c o i d f r a c t i o n (33.3%) was e q u a l t o the maximum obser v e d f o r s c u l p i n s ( 3 2 . 7 % ) . In o t h e r words, h a r p a c t i c o i d copepods were the p r e f e r r e d f o o d of the g o b i e s w h i l e they were a s i g n i f i c a n t , but 2 6 5 F i g u r e 47. R e l a t i o n s h i p between p r e d a t o r l e n g t h and c o n t r i b u t i o n of h a r p a c t i c o i d copepods (by % of t o t a l volume m a t e r i a l i n gut) t o p r e d a t o r ' s d i e t f o r (a) L e p t o c o t t u s armatus and (b) C l e v e l a n d i a i o s c o l l e c t e d on a l l d a t e s i n 1979 and 1980. 266 1 0 0 1 0 2 0 3 0 FISH LENGTH (mm) 4 0 5 0 1 0 0 % 8 0 _> —I O > w 6 0 Q u_ O S 4 0 < O CC w 2 0 • « * * • • • • • • — • • * • • • — • • • • * — • • • • • Clevelandia Ios • • I 1 I • 1 •1 *3 1 0 2 0 3 0 FISH LENGTH (mm) 4 0 5 0 267 c o m p a r a t i v e l y minor component of the d i e t of s c u l p i n s . To p r o p e r l y a s s e s s r e l a t i v e m o r t a l i t y r a t e s from the two p r e d a t o r s , i t w i l l be n e c e s s a r y t o c o l l e c t d a t a on p r e d a t o r d e n s i t i e s and r a t e s of f e e d i n g on h a r p a c t i c o i d s . The Iona N o r t h gut d a t a do g i v e some i n d i c a t i o n t h a t u n l e s s s c u l p i n d e n s i t i e s and f e e d i n g r a t e s a re much h i g h e r than those of the g o b i e s , the l a t t e r a re l i k e l y t o be a more s i g n i f i c a n t source of m o r t a l i t y t o the t i d e p o o l h a r p a c t i c o i d s . F i g u r e 48 compares ' the numbers of h a r p a c t i c o i d s found i n the gu t s of the two p r e d a t o r s . W ith the e x c e p t i o n of a s i n g l e f i s h , a l l s c u l p i n s c o n t a i n e d fewer than 50 i n d i v i d u a l s . W ith the e x c e p t i o n of t h a t one f i s h , maximum numbers of prey were found i n f i s h between 17 and 27 mm l o n g . F i s h l o n g e r than 27 mm • a t e a n e g l i g i b l e number of h a r p a c t i c o i d s . G o b i e s , on the o t h e r hand, c o n s i s t e n t l y c a p t u r e d l a r g e r numbers of h a r p a c t i c o i d s than s c u l p i n s of the same s i z e ( F i g . 4 8 ) . The number of h a r p a c t i c o i d s i n the gu t s of the g o b i e s was s i g n i f i c a n t l y c o r r e l a t e d w i t h the s i z e of the p r e d a t o r i n f i s h between 11 and 23 mm l o n g ( r = +0.67; n = 42; P<0.001). The two v a r i a b l e s were u n c o r r e l a t e d f o r the s m a l l s c u l p i n s ( F i g . 48a). Gobies l o n g e r than 30 mm i n 1979 took v a r i a b l e numbers of h a r p a c t i c o i d s per gut f i l l but showed a weak tendency t o s w i t c h t o o t h e r prey w i t h i n c r e a s i n g p r e d a t o r s i z e ( F i g . 48b). The da t a from 1980 g e n e r a l l y agree w i t h those from 1979 f o r s m a l l f i s h , but the l a r g e r g o b i e s c a p t u r e d e x t r e m e l y l a r g e numbers of h a r p a c t i c o i d s compared w i t h s i m i l a r -s i z e d f i s h i n 1979. G o b i e s , t h e n , consume from 2 t o 100 ti m e s the number of h a r p a c t i c o i d s compared w i t h s c u l p i n s of the same 268 F i g u r e 48. R e l a t i o n s h i p between l e n g t h of each p r e d a t o r and the t o t a l number of h a r p a c t i c o i d s i d e n t i f i e d from i t s gut c o n t e n t s f o r (a) L e p t o c o t t u s armatus and (b) C l e v e l a n d i a i o s . Open symbols r e p r e s e n t o b s e r v a t i o n s from f i s h c a p t u r e d i n 1979. C l o s e d symbols r e p r e s e n t o b s e r v a t i o n s from 1980. 269 10 15 20 25 30 35 40 45 50 FISH LENGTH (mm) 500 10 15 20 25 3 0 35 40 FISH LENGTH (mm) 270 s i z e . These major d i s t i n c t i o n s i n the d i e t s of the two p r e d a t o r s a r e the d i r e c t r e s u l t of the d i f f e r e n c e s i n f e e d i n g b e h a v i o r which they e x h i b i t . V i s u a l p r e d a t o r s , such as L. armatus, must p e r c e i v e , pursue and a t t a c k i n d i v i d u a l prey which emerge from the sediment. For such p r e d a t o r s , not a l l a t t a c k s w i l l be s u c c e s s f u l ; the s i z e of t h e prey i s one c r i t i c a l f a c t o r d e t e r m i n i n g p r o b a b i l i t y of c a p t u r e (Thompson 1975). As the s i z e of the p r e d a t o r i n c r e a s e s r e l a t i v e t o the s i z e of the p r e y , s m a l l prey become p r o g r e s s i v e l y l e s s p r o f i t a b l e u n t i l they are no l o n g e r a t t a c k e d and the f i s h s w i t c h t o r e l a t i v e l y l a r g e r " t a r g e t s . T h i s b e h a v i o r l e a d s t o the r e l a t i o n s h i p s shown i n F i g s . 45a and 46a. As the s c u l p i n s grew they s w i t c h e d t o l a r g e r h a r p a c t i c o i d s p e c i e s (from T. t r i a n g u l a r i s t o H. j a d e n s i s t o S. c a n a d e n s i s t o H. u n i r e m i s ) (Appendix 6) and f i n a l l y s w i t c h e d from h a r p a c t i c o i d s t o l a r g e r food i t e m s . These complex r e l a t i o n s h i p s between prey and p r e d a t o r s i z e , and p r e d a t o r s i z e and p r e f e r e n c e f o r h a r p a c t i c o i d copepods l e a d t o the ' p l a t e a u ' of numbers of h a r p a c t i c o i d s i n the guts of s c u l p i n s between 13 and 27 mm l o n g and the r a p i d d e c l i n e i n both the number of h a r p a c t i c o i d s i n the g u t s and the p e r c e n t a g e c o n t r i b u t i o n of h a r p a c t i c o i d s t o the d i e t of f i s h g r e a t e r than 27 mm l o n g ( F i g s . 45 and 4 6 ) . The s i z e of prey r e t a i n e d by s e d i m e n t - b i t i n g f i s h such as C. i o s depends upon the morphometries of the p r e d a t o r (see b e l o w ) . The number of p r e y o b t a i n e d by a s e d i m e n t - b i t i n g f i s h i s a f u n c t i o n of the d e n s i t y and d i s t r i b u t i o n of prey i n the 271 sediment (which i s independent of p r e d a t o r s i z e ) and the q u a n t i t y of sediment i n g e s t e d i n a s i n g l e b i t e (which i s p r o p o r t i o n a l t o the s i z e of the p r e d a t o r ) . From t h i s we have the p o s i t i v e c o r r e l a t i o n between number of prey i n the gut and l e n g t h of the p r e d a t o r i n f i s h l e s s than 23 mm l o n g ( F i g . 48b). Large f i s h do not n e c e s s a r i l y f i t t h i s r e l a t i o n s h i p s i n c e they spend more time, s i g h t - f e e d i n g on l a r g e r p r e y , such as amphipods and m o l l u s c s i p h o n s . The number of h a r p a c t i c o i d prey i n the gut s of l a r g e g o b i e s may c o n t i n u e t o i n c r e a s e w i t h i n c r e a s i n g f i s h s i z e a s . i t d i d i n 1980 i f the f i s h c o n t i n u e t o sediment-f e e d or d e c r e a s e as i t d i d i n 1979 i f the f i s h spend more time f e e d i n g on l a r g e r prey i t e m s . ' S e d i m e n t - b i t i n g ' may o n l y work i n h a b i t a t s where the prey are c o n s i d e r a b l y l a r g e r than the sediment g r a i n s . I t i s p r o b a b l y an i n e f f e c t i v e means of s e p a r a t i n g h a r p a c t i c o i d s from c o a r s e r , sandy sediments. E l e c t i v i t i e s f o r d i f f e r e n t s p e c i e s (and s i z e s ) of h a r p a c t i c o i d s were a f u n c t i o n of the s i z e of the g o b i e s ( F i g s . 44-46). The s i z e of prey r e t a i n e d depends on the s i z e of the m o r p h o l o g i c a l s o r t i n g mechanism of the p r e d a t o r (e.g. g i l l -r a k e r s p a c i n g ) which presumably i n c r e a s e s as the f i s h grow (Grossman 1980). C l e v e l a n d i a i o s does not have n a r r o w l y - s p a c e d g i l l - r a k e r s and y e t s m a l l prey were o f t e n i m p o r t a n t i n i t s d i e t on m u d f l a t s i n M i s s i o n Bay, San Diego ( B r o t h e r s 1975). I n d i s s e c t e d specimens from Iona N o r t h , prey were o f t e n found caught i n the f r o n t a l p i t beneath the a n t e r i o r p a r t of the tongue of the g o b i e s . F i g u r e 49 shows the morphology of t h i s p i t , from an SEM photograph and a s k e t c h of the lower jaw of 272 the f i s h from the l i g h t m i c r o s c o p e . The w i d t h of the f r o n t a l p i t s of 25 p r e s e r v e d specimens (12-39 mm l o n g ) from the gut a n a l y s i s were measured. The r e l a t i o n s h i p between p i t w i d t h and f i s h l e n g t h i s shown i n F i g . 50 a l o n g w i t h composite s i z e -f r equency d i s t r i b u t i o n s of the two dominant h a r p a c t i c o i d prey s p e c i e s . P i t w i d t h (PW) i n c r e a s e d l i n e a r l y w i t h i n c r e a s i n g f i s h l e n g t h (FL) (PW(mm) = 0.03(FLmm)-0.01; r 2 = 0.88; n = 25). O n t o g e n e t i c v a r i a t i o n i n the morphometry of the f r o n t a l p i t of C. i o s may account f o r the observed d i f f e r e n c e s i n prey s e l e c t i v i t y between s m a l l and l a r g e f i s h ( F i g s . 44-46), w i t h s m a l l f i s h r e t a i n i n g a d i s p r o p o r t i o n a t e l y l a r g e number of s m a l l prey (T. t r i a n g u l a r i s ) and l a r g e f i s h r e t a i n i n g a d i s p r o p o r t i o n a t e l y l a r g e number of l a r g e prey (S. c a n a d e n s i s ) . Whatever the mechanism of prey r e t e n t i o n , from a comparison of the number of prey c a p t u r e d by the two t y p e s of p r e d a t o r s ( F i g . 4 8 ) , t a c t i l e p r e d a t i o n ( s e d i m e n t - b i t i n g ) i s a more e f f e c t i v e means of s p e c i a l i z i n g on these t i n y , a l t h o u g h v e r y abundant, p r e y . 5. S i g n i f i c a n c e of p r e d a t i o n by l i t t o r a l f i s h In T a b l e 18 I have c o m p i l e d a l i s t of r e p o r t s of p r e d a t i o n on h a r p a c t i c o i d s by i n t e r t i d a l or s h a l l o w s u b t i d a l f i s h e s . T h i s l i s t i s not e x h a u s t i v e but s h o u l d i n d i c a t e t h a t s h a l l o w - w a t e r h a r p a c t i c o i d communities i n g e n e r a l have a v a r i e t y of f i s h p r e d a t o r s . A l t h o u g h i t i s d i f f i c u l t t o compare r e p o r t s s i n c e methods v a r i e d w i d e l y among a u t h o r s , i t i s c l e a r t h a t h a r p a c t i c o i d s a r e an i m p o r t a n t prey f o r many s p e c i e s , 273 F i g u r e 49. C l e v e l a n d i a i o s . O r a l morphology ( r i g h t ) SEM photograph of lower jaw ( f i s h number 20, 39mm l o n g c a p t u r e d on 26 Jun 1980). ( l e f t ) I n t e r p r e t i v e diagram from l i g h t m i c r o s c o p e . S c a l e 0.5mm. 0.5 mm f r o n t a l p i t t e e t h tongue papil lae la tera l pit T. triangularis lower jaw C. ios 26.6.80 #21; 19 mm 275 F i g u r e 50. R e l a t i o n s h i p between o n t o g e n e t i c v a r i a t i o n i n f r o n t a l p i t w i d t h and s i z e of dominant p r e y . SCO = S c o t t o l a n a c a n a d e n s i s TAC = T a c h i d i u s t r i a n g u l a r i s PW = w i d t h (mm) of f r o n t a l p i t FL = l e n g t h (mm) of f i s h 277 p a r t i c u l a r l y when the f i s h a r e l e s s than about 50 mm l o n g . For some s p e c i e s , p a r t i c u l a r l y the s m a l l G o b i i d a e (Table 18, p a r t 1), h a r p a c t i c o i d s remained the c h i e f food throughout the l i f e h i s t o r y . For o t h e r s p e c i e s , n o t a b l y the Salmonidae (Table 18, p a r t 3) and f l a t f i s h (Table 18, p a r t 4 ) , h a r p a c t i c o i d s were an i m p o r t a n t food used e a r l y i n the l i f e h i s t o r y of the f i s h . P r e d a t i o n by f i s h f e e d i n g on s h a l l o w , s o f t bottoms r e s u l t s i n the l a r g e s t numbers of h a r p a c t i c o i d copepods b e i n g consumed by i n d i v i d u a l p r e d a t o r s (Smidt 1951; B r e g n b a l l e 1961; Fonds 1973; F e l l e r and K a c z y n s k i 1975; S i b e r t et a l . 1977; Healey 1979). C o n s i d e r a b l y fewer prey may be consumed by i n d i v i d u a l s f e e d i n g on c o a r s e r bottoms (Monroe and L o t s p e i c h 1979), i n the water column (Berg 1979), or i n the p h y t a l (Roland 1978 and L. armatus i n t h i s c h a p t e r ) . From the p o i n t of view of the p r e y , p r e d a t i o n by these s m a l l f i s h s h o u l d be an i m p o r t a n t s e l e c t i o n p r e s s u r e i n a v a r i e t y of h a b i t a t s , most n o t a b l y s h a l l o w s o f t bottoms. D. Summary The t i d e p o o l h a r p a c t i c o i d s of Iona N o r t h were s u b j e c t t o p r e d a t i o n from two s p e c i e s of f i s h , C l e v e l a n d i a i o s and L e p t o c o t t u s armatus. Gobies of a l l s i z e s between 11 and 39 mm l o n g consumed l a r g e ..numbers of h a r p a c t i c o i d s . P r e d a t i o n was b o t h s p e c i e s - and s i z e - s e l e c t i v e . For s c u l p i n s , h a r p a c t i c o i d s were o n l y a minor f o o d , seldom eaten by f i s h l o n g e r than 30 mm. The d i f f e r e n c e i n importance of h a r p a c t i c o i d s t o the d i e t s of the two p r e d a t o r s was p a r t l y a c c o u n t e d f o r by d i f f e r e n c e s i n T a b l e 18 . L i t e r a t u r e r e p o r t s o f f i s h f e e d i n g on h a r p a c t i c o i d c o p e p o d s . P a r t 1: G o b i i d a e S p e c i e s Length (mm) %Vol. ( N o / f i s h ) L o c a t i o n S o u r c e Gobius minutus Lebetus orca Microgobius gulosus Pomatoschistus minutus minutus P. minutus lozanoi Deltentosteus quadrimaculatus Gobiusculus flavesoens Gobiosoma ginsbevgi Pomatoschistus pictus P. mi crops Lepidogobius lepidus < 50 > 50 < 39 18 - 32 ; x = 59 .7 x = 4 8 . 7 x = 22 .5 (12-38) x = 28.6 18 - 42 26 - 30 27 - 50 < 50 > 50 100 (.-< 50-100) ' p r e d o m i n a n t ' 4 . 4 21 (10-100;, o c c a s i o n -a l l y 150-300) (67.8%) (10%=pelagic Micro-setella elegans) (88%;x = 9 . 5 / f i s h ; Longepedia,Laophon-tidae) (39%) (36%) 31; max.=53% 15; max.=26% D a n i s h Waddensea Smidt (1951) I s l e o f Man (18-51m) M i l l e r (1963) F l a . (mangroves) ,0dum § H e a l d (1972) Dutch Waddensea B a n y u l s , F r a n c e (5-20m) H e l g o l a n d (3-4m) Sakonnet R i v e r , R . I H e l g o l a n d (2 m) Denmark ( to 12 m) Mor ro B a y , C a l i f , ( i n t e r t i d a l ) Fonds (1973) B o d i o u § V i l l i e r s (1978-1979) B e r g (1979) Munroe § L o t s p e i c h (1979) Zander (1979a) Zander (1979b) Grossman e t a l . (1980) T a b l e 18 . P a r t 2. C o t t i d a e . S p e c i e s Length (mm) %Vol ( N o . / f i s h ) L o c a t i o n S o u r c e Oligoaottus snyderi 33 - 66 (x = 3 4 . 0 / f i s h ) C a l i f o r n i a ( i n t e r t i d a l ) J o h n s t o n (1954) Clinocottus analis Clinooottus reaalvus Aoanthooottus hubalis Oligoaottus maculosus 31 - 120 24 - 58 < 50 30 - 90 (x = 5 4 . 7 / f i s h ) (x = ' 1 9 . 9 / f i s h ; Tisbe fuvoatd) 5% o v e r a l l ; 16% i n A p r i l - June Tigriopus califov-nious) I s l e o f Man ( i n t e r t i d a l R i c e (1962) f, s u b t i d a l ) ( to 1 0 0 0 / f i s h / d a y ; San J u a n I s l . D e t h i e r (1980) Wash, ( h i g h i n t e r t i d a l s p l a s h p o o l ) T a b l e 18. P a r t 3. S a l m o n i d a e . S p e c i e s L e n g t h (mm) % V o l . ( N o . / f i s h ) L o c a t i o n S o u r c e Oncorhynchus keta ' f r y ' 50 (62% by n o ; to Nanaimo e s t u a r y S i b e r t e t a l . (1977) 1000 p e r g u t ; Earpacticus ( m u d f l a t ) H e a l e y (1979) uniremis3 Huntemannia jadensis,Tisbe furcata) 0. keta x = 38.1 1 (83.6%; x = 1 6 1 . 5 / f i s h ) Dabob B a y , Wash. F e l l e r <5 K a c z -(33- -48.5) ( i n t e r t i d a l ) y n s k i (1975) 0. keta x = 4 3 . 5 1 (85.3%; x = 4 5 6 . 6 / f i s h ) A n d e r s o n I s l . , W a s h . (36- -52 .5 ) ( i n t e r t i d a l ) 0. keta x = 4 2 . 6 11 F r a s e r R i v e r S o u t h Levy e t a l . (1979) Arm marshes 0. nerka x = 5 4 . 3 0 .29 0. tschawytscha x = 4 9 . 2 0.02 0. gorbuscha X = 33 .5 49 .8 0. gorbuscha x = 39 36 .0 Puget Sound K a c z y n s k i e t a l . (33 - 55) ( i n t e r t i d a l ) (1973) F o r k l e n g t h ro oo o T a b l e 18. P a r t 4 . J u v e n i l e f l a t f i s h . S p e c i e s L e n g t h (mm) % V o l . ( N o . / f i s h ) L o c a t i o n S o u r c e Pleuvoneatus platessa < 50 " m a i n . . . i n many c a s e s o n l y f o o d " D a n i s h Waddensea S m i d t (1951) Limanda limanda < 50 main f o o d ( c . 10-100) Pleuroneotes platessa x = 25 .2 c h i e f p r e y (x = 3 1 . 2 / g u t ; m o s t l y Laophontidae) K y s i n g F j o r d , D k . B r e g n b a l l e (1961) P. flesus 9 - 1 1 12 - 14 15 - 17 18 - 22 (x = 65 176 307 223) P. flesus s m a l l 0-group i m p o r t a n t Denmark ( s h a l l o w ) Muus (1967) Parophrys vetulus < 50 (86-99%) Humboldt B a y , C a l i f . T o o l e (1980) 50 - 65 (38-80%) ( i n t e r t i d a l s a n d f l a t ) > 65 ( 0-3% ) T a b l e 18. P a r t 5 . M i s c e l l a n e u s s p e c i e s . S p e c i e s Length (mm) % V o l . ( N o . / F i s h ) L o c a t i o n S o u r c e Girella nigricans Xerepes fucorum Atherinops affinis Xerepes fucorum Gobiesox maendricus Gibbonsia rnetzi Heterandria formosa Eucinostonrus gula Menidia b e r y l l i n a Rimicola muscarum Blennius rouxi 50 78 58 51 - 70 85 131 75 77 - 125 46 36 11 19 35 -25 -< 78 82 78 18 45 65 34 40 10 - 20 C a l i f o r n i a ( i n t e r t i d a l ) M i t c h e l l (1953) 80 ; Zaus & Porcellidium 5 - 1 0 (x=54 Peltidiidae C a l i f o r n i a 3.5 Tisbe furcata ( i n t e r t i d a l ) 101 Tigriopus spp.) (x = 71.7) (x = 2) 20 33 42 F l o r i d a Mangroves (x = 1 5 . 8 ; 90% o f t o t a l p r e y ) 13 17 B a m f i e l d , B . C . (on Macrocystus integ-r i f o l i a ) B a n y u l s (2-6m) (20-36m) J o h n s t o n (1954). Odum S H e a l d (1972) R o l a n d (1978) Heymer § Z a n d e r (1975) OO ro 283 t h e i r modes of f e e d i n g . C l e v e l a n d i a i o s i s a ' t a c t i l e ' p r e d a t o r , f e e d i n g d i r e c t l y on copepods i n the sediment. L e p t o c o t t u s armatus i s a h i g h l y o p p o r t u n i s t i c ' v i s u a l ' p r e d a t o r and feeds on copepods which l e a v e the sediment ( S c o t t o l a n a  c a n a d e n s i s and T a c h i d i u s t r i a n g u l a r i s ) and on a l a r g e a l g a l -d w e l l i n g s p e c i e s ( H a r p a c t i c u s u n i r e m i s ) . The d i f f e r e n c e s i n the b e h a v i o r of the two p r e d a t o r s d e s c r i b e d i n t h i s c h a p t e r reduce t h e i r t r o p h i c o v e r l a p and thus enhance t h e i r c o e x i s t e n c e on the Iona I s l a n d m u d f l a t . 284 V I I I . INTERSPECIFIC COMPETITION AND COMMUNITY STRUCTURE A. I n t r o d u c t i o n The t h r e e p r i n c i p a l d i m e n s i o n s of the n i c h e as d e f i n e d by H u t c h i n s o n (1957) a r e space, time and food (Shoener 1974; C h r i s t i a n s e n and F e n c h e l 1977); the p a t t e r n s of o c c u r r e n c e of. s p e c i e s r e l a t i v e t o these d i m e n s i o n s c o n s t i t u t e the s t r u c t u r e of the community (Cody and Diamond 1975). T h i s s t r u c t u r e i s d e t e r m i n e d i n p a r t by the d i f f e r e n t i a l responses of s p e c i e s t o the a b i o t i c ( p h y s i c a l ) environment and i n p a r t by responses of s p e c i e s t o t h e i r b i o t i c environment ( c o m p e t i t o r s and p r e d a t o r s ) . The s p a t i a l and t e m p o r a l p a t t e r n s of Iona N o r t h h a r p a c t i c o i d copepods ( t h e i r r e l a t i o n s h i p t o the a b i o t i c environment) were d i s c u s s e d i n c h a p t e r s VI and V; p r e d a t i o n as a s e l e c t i o n p r e s s u r e was the s u b j e c t of c h a p t e r V I I . The purpose of the p r e s e n t c h a p t e r i s t o c o n s i d e r the a c t i o n of i n t e r s p e c i f i c c o m p e t i t i o n i n the sand assemblage and f u r t h e r t o r e f i n e the d e s c r i p t i o n of the s t r u c t u r e and dynamics of the two communities p r e s e n t e d i n p r e c e d i n g c h a p t e r s . E c o l o g i c a l l y s i m i l a r s p e c i e s c o - o c c u r r i n g w i t h i n a l o c a l environment ( i . e . s y m p a t r i c s p e c i e s , sensu Mayr 1970) are o f t e n s e r i a l l y a r r a y e d a l o n g one or more n i c h e d i m e n s i o n s i n what has been c a l l e d a d i s p l a c e m e n t p a t t e r n ( L e v i n s 1968; Cody 1974). The d e m o n s t r a t i o n of such a p a t t e r n w i t h i n a community i s c i r c u m s t a n t i a l e v i d e n c e t h a t c o m p e t i t i o n has h e l p e d t o s t r u c t u r e t h a t community. The body s i z e s of s y m p a t r i c s p e c i e s which p a r t i t i o n t h e i r r e s o u r c e s p r i m a r i l y by f e e d i n g on 285 d i f f e r e n t s i z e s of food o f t e n e x h i b i t a c l e a r d i s p l a c e m e n t p a t t e r n . Among the many examples are Brown's (1975) h e t e r o m y i d r o d e n t s (kangaroo r a t s and pocket m i c e ) ; Diamond's (1975) New Guinea f r u i t p i g e o n s ; F e n c h e l ' s (1975b) h y d r o b i i d mud s n a i l s ; D a vidson's (1977) d e s e r t s e e d - e a t i n g a n t s and Emmon's (1980) A f r i c a n r a i n f o r e s t s q u i r r e l s . The body s i z e spectrum- of the e i g h t . h a r p a c t i c o i d s p e c i e s i n the sand community i n Jan 1980 ( F i g . 51) resembles the f a m i l i a r d i s p l a c e m e n t p a t t e r n . From a c r i t i c a l r e e v a l u a t i o n of much of the e x i s t i n g d ata p u r p o r t i n g t o show m o r p h o l o g i c a l c h a r a c t e r d i s p l a c e m e n t (Grant 1972) has come s k e p t i c i s m r e g a r d i n g the i n f e r e n c e of c o m p e t i t i o n from morphometric d i s p l a c e m e n t p a t t e r n s a l o n e (e.*g. Dunham et a l . 1978; S t r o n g et al' . 1979). P r o c e s s e s u n r e l a t e d t o i n t e r s p e c i f i c c o m p e t i t i o n , e.g. s i z e - s e l e c t i v e p r e d a t i o n , may cause body s i z e d i s p l a c e m e n t i n the absence of c o m p e t i t i v e i n t e r a c t i o n s . Thus, w h i l e the body s i z e s t r u c t u r e of the Iona N o r t h h a r p a c t i c o i d copepod community suggests t h a t c o m p e t i t i o n may be im p o r t a n t i n the community, i t c e r t a i n l y does not prove i t . To i n v e s t i g a t e the b i o l o g i c a l s t r u c t u r i n g mechanisms i n a n a t u r a l community, t h r e e approaches may be used ( C o n n e l l 1975): 1) d e s c r i p t i o n of s t a t i c p a t t e r n s w i t h i n the community which are compared w i t h model p r e d i c t i o n s 2) c o n t r o l l e d f i e l d e x p e r i m e n t s d e s i g n e d t o t e s t s p e c i f i c hypotheses and 3) " n a t u r a l e x p e r i m e n t s " which make use of n a t u r a l l y o c c u r r i n g f l u c t u a t i o n s i n the b i o t i c and/or a b i o t i c 286 F i g u r e 51. Length f r e q u e n c y d i s t r i b u t i o n s of the 8 h a r p a c t i c o i d s p e c i e s c o l l e c t e d from the sand on 22 Jan 1980. A l l i n d i v i d u a l s ( e x c l u d i n g n a u p l i i ) from f a u n a l samples were measured. 287 7~ rrr L. constrictus 10 AM. BJL R spinicauda 10 5 1 Schizopera sp. M E l l . Halectinosoma sp. J__ T. triangularis 25 20 15 10 M m J _ _ Pseudobradya sp. _JL__3_[_J_ H. jadensis JU i m Fl ra oLv J ELL S . canadensis l m I E L .2 .4 .5 .6 Body length (mm) .8 288 e n v i r o n m e n t t o t e s t h y p o t h e s e s . The f i r s t a p p r o a c h i s commonly t a k e n and a l t h o u g h i t p r o v i d e s o n l y c i r c u m s t a n t i a l e v i d e n c e i t i s a u s e f u l e x p l o r a t o r y t o o l w h i c h s u g g e s t s h y p o t h e s e s f o r t e s t i n g . I t i s p a r t i c u l a r l y u s e f u l f o r s t u d y i n g s y s t e m s w h i c h a r e i n a p p r o p r i a t e f o r an e x p e r i m e n t a l a p p r o a c h , f o r e x a m p l e , t h e b i o t a s o f e n t i r e c o n t i n e n t s (Cody 1974; P i a n k a 1 9 7 5 ) . . C a r e f u l l y c o n t r o l l e d f i e l d e x p e r i m e n t s p r o v i d e d i r e c t e v i d e n c e f o r t h e i m p o r t a n c e o f t h e p r o c e s s i n q u e s t i o n and so a r e c l e a r l y t h e s u p e r i o r a p p r o a c h i n s t u d y i n g t h e d y n a m i c s i n c e r t a i n t y p e s o f s y s t e m s , n o t a b l y t e r r e s t r i a l h a b i t a t s and t h e r o c k y i n t e r t i d a l ( C o n n e l l 1 9 7 5 ) . M a n i p u l a t i o n s o f p r e d a t o r d e n s i t i e s h a v e been u s e d t o s t u d y t h e e f f e c t s o f p r e d a t i o n on m e i o b e n t h i c c o m m u n i t i e s ( B e l l 1 9 79a,1980; D e t h i e r 1980; W a r w i c k 1980b) b u t t h e r e i s no e f f e c t i v e way o f m a n i p u l a t i n g d e n s i t i e s o f f i e l d p o p u l a t i o n s o f c o m p e t i n g m e i o b e n t h i c h a r p a c t i c o i d s p e c i e s . I n f a c t , c a g i n g e x p e r i m e n t s t o d e t e r m i n e t h e e f f e c t s o f p r e d a t i o n on t h e m e i o b e n t h o s must be c a r e f u l l y c o n t r o l l e d a n d r e s u l t s v i e w e d w i t h some c a u t i o n i f t h e h a r p a c t i c o i d m i g r a t i o n s d e s c r i b e d i n t h e p r e c e d i n g c h a p t e r a r e a common phenomenon. I n s p i t e o f t h e f a c t t h a t ' n a t u r a l e x p e r i m e n t s ' c a n n o t be c o n t r o l l e d , t h e r i g h t c o m b i n a t i o n o f c h a n c e e v e n t s may m i m i c f i e l d m a n i p u l a t i o n s and p r o v i d e v e r y s t r o n g e v i d e n c e t h a t a p a r t i c u l a r p r o c e s s i s o c c u r r i n g w i t h i n a c o m m u n i t y . A n a t u r a l e x p e r i m e n t a l s o h a s t h e a d v a n t a g e o f r e a l i s m s i n c e , by d e f i n i t i o n , i t d o e s n o t e x c e e d t h e bounds o f n a t u r a l f l u c t u a t i o n s e x p e r i e n c e d by t h e c o m m u n i t y . 2 8 9 I n t h i s c h a p t e r I w i l l p r e s e n t o b s e r v a t i o n s made on t h e s a n d c o m m u n i t y of I o n a N o r t h b e t w e e n J a n u a r y 1977 and J a n u a r y 1980 w h i c h s u g g e s t t h a t i n t e r s p e c i f i c c o m p e t i t i o n was an i m p o r t a n t d e t e r m i n a n t o f t h e c o m m u n i t y ' s s t r u c t u r e i n t h a t p e r i o d . 290 B. Methods _V. D e t e c t i o n of . v a r i a t i o n between y e a r s V a r i a t i o n between y e a r s i n the s t r u c t u r e of the sand h a r p a c t i c o i d copepod community was determined by sampling each January f r o m . 1977 t o 1980. M i d - w i n t e r i s a time of r e l a t i v e s h o r t a g e of r e s o u r c e s ( F i g . 11) as w e l l as a time when those r e s o u r c e s are q u a l i t a t i v e l y l e a s t d i v e r s e ( m i c r o a l g a e a r e almost e n t i r e l y pennate d i a t o m s ) . In s p i t e of these f a c t o r s , m i d - w i n t e r i s a l s o a time of h i g h copepod s p e c i e s d i v e r s i t y ( F i g . 33) and a time when many of the s p e c i e s a r e r e p r o d u c t i v e l y - a c t i v e (see c h a p t e r I V ) . T h i s c o m b i n a t i o n of f a c t o r s s h o u l d make c o m p e t i t i o n most severe and r e s o u r c e a l l o c a t i o n p a t t e r n s most e a s i l y d e t e c t e d i n m i d - w i n t e r . The s t r u c t u r e of the h a r p a c t i c o i d community i n January was det e r m i n e d from ' r i p p l e samples'. For d e t a i l s of s a m p l i n g d e s i g n and sample treatment see c h a p t e r I I . S p a t i a l p a t t e r n s of the s p e c i e s were d e t e r m i n e d as d e s c r i b e d i n c h a p t e r V I . Community s t r u c t u r e was d e f i n e d by a 'Theory of the Nich e A n a l y s i s ' ( L e v i n s 1968) as d e s c r i b e d below. 2. Q u a n t i f i c a t i o n of morphometric and t r o p h i c r e l a t i o n s h i p s The t r o p h i c s t r u c t u r e of the h a r p a c t i c o i d community was d e s c r i b e d by s e v e r a l methods. Where p o s s i b l e , the f e e d i n g b e h a v i o r of each s p e c i e s was observed d i r e c t l y i n the l a b o r a t o r y . These b e h a v i o r s a r e d e s c r i b e d i n c h a p t e r IV. O r a l 291 morphology was observed by s c a n n i n g e l e c t r o n m i c r o s c o p y of whole i n d i v i d u a l s ; the s t r u c t u r e of i n d i v i d u a l appendages was observed by l i g h t m i c r o s c o p y of d i s s e c t i o n s . Each s p e c i e s was then a s s i g n e d t o one of M a r c o t t e ' s (I977a,b) f e e d i n g groups based on a c o m b i n a t i o n of m o r p h o l o g i c a l and b e h a v i o r a l c r i t e r i a (see c h a p t e r I V ) . The s i z e of food items eaten i s c o r r e l a t e d w i t h body s i z e and/or s i z e of t r o p h i c a p p a r a t u s f o r a v a r i e t y of an i m a l s p e c i e s (e.g. F e n c h e l 1968, 1975b; Brown 1975; Diamond 1975; Davidson 1977; T i e t j e n 1980; and c h a p t e r V I I of the p r e s e n t work). Body s i z e s ( l e n g t h s ) of c o - o c c u r r i n g h a r p a c t i c o i d s p e c i e s were measured and used as an i n d i c a t i o n of which s p e c i e s might o v e r l a p i n food r e q u i r e m e n t s . In 1977 and 1978 the f i r s t 45 t o 60 i n d i v i d u a l s of each s p e c i e s ( i f t h e r e were t h a t many c o l l e c t e d ) e n c ountered w h i l e s o r t i n g the q u a n t i t a t i v e samples were measured and l e n g t h s r e c o r d e d t o the n e a r e s t 0.01 mm. In 1979 and 1980 a l l i n d i v i d u a l s i n the c o l l e c t i o n s were measured and l e n g t h s r e c o r d e d t o the n e a r e s t 0.001 mm. 'Body l e n g t h ' here r e f e r s t o prosome + urosome l e n g t h s measured from the base of the r o s t r u m ( i f any) t o the base of the c a u d a l rami ( C o u l l 1977). A f t e r measurements were made, a n i m a l s , except t h o s e used f o r gut a n a l y s i s , were s t o r e d i n a 5% s o l u t i o n (v/v) of formaldehyde i n seawater. Summary s t a t i s t i c s of the l e n g t h f r e q u e n c y d a t a were c a l c u l a t e d w i t h programs from the S t a t i s t i c a l Package f o r the S o c i a l S c i e n c e s ( N i e e t a l . 1975). To t e s t the h y p o t h e s i s t h a t body s i z e d i f f e r e n c e s between 292 h a r p a c t i c o i d s p e c i e s might a l l o w r e s o u r c e a l l o c a t i o n based on s i z e of food p a r t i c l e s e a t e n , the gut c o n t e n t s of 66 i n d i v i d u a l s r e p r e s e n t i n g the 8 s p e c i e s i n the 1980 c o l l e c t i o n were compared. Whole copepods were measured and then mounted i n d i v i d u a l l y i n Hoyer's medium ( C o u l l 1977). These permanent mounts were examined a t X100 and x400 (phase c o n t r a s t ) w i t h a L e i t z D i a l u x m i c r o s c o p e . The s i l i c e o u s f r u s t u l e s of diatoms were e a s i l y r e c o g n i z e d i n the g u t s . The l e n g t h of the a p i c a l a x i s of each di a t o m found i n t a c t was r e c o r d e d t o the n e a r e s t 0.001 mm. Broken f r u s t u l e s were i n c l u d e d i f the a p i c a l a x i s was unbroken. One c e n t r i c diatom was found ( i n the gut of a female Pseudobradya sp. . ) ; i t s diameter was r e c o r d e d . 3_. A n a l y s i s of community s t r u c t u r e The s t r u c t u r e of the sand r i p p l e h a r p a c t i c o i d community was d e f i n e d from monthly o b s e r v a t i o n s i n 1978 and Ja n u a r y o b s e r v a t i o n s from 1977, 1979 and 1980 u s i n g a s u i t e of parameters from the 'Theory of the N i c h e ' a n a l y s i s ( L e v i n s 1968; Lane 1975). In the format which f o l l o w s , the a n a l y s i s i s a p p r o p r i a t e o n l y f o r s p e c i e s which p a r t i t i o n r e s o u r c e s p r i m a r i l y by h a b i t a t s e l e c t i o n . H e t e r o g e n e i t y c h i -square a n a l y s i s ( c h a p t e r VI.B.) showed t h a t the Iona N o r t h h a r p a c t i c o i d copepod community s a t i s f i e s t h i s c r i t i c a l a s s umption. The ' h a b i t a t s ' used i n the n i c h e a n a l y s i s a r e the same f o u r which were i d e n t i f i e d i n c h a p t e r VI.C: C r e s t s u r f a c e ( C a ) , C r e s t s u b s u r f a c e ( C b ) , Trough s u r f a c e (Ta) and Trough s u b s u r f a c e ( T b ) . The t o t a l number of i n d i v i d u a l s of 2 9 3 s p e c i e s i ( i = 1 , 2 , . . . , N , where N i s t h e t o t a l number of s p e c i e s i n t h e community) c o l l e c t e d from h a b i t a t h i s a measure of t h e h a b i t a t - S D e c i f i c d e n s i t y of s p e c i e s i , d (h = 1,2,...,E, ih where E = t h e t o t a l number o f h a b i t a t s = 4 ) . The a v e r a g e d e n s i t y of s p e c i e s i p e r h a b i t a t i s (17) E D . = ( I d,, ) / E 1 h=l l h The p r o p o r t i o n of t h e t o t a l number of s p e c i e s i i n t h e community w h i c h o c c u r s i n h a b i t a t h i s (18) E P ± h » a i h / E / d i h 0 - p i h * h=l The m i c r o h a b i t a t n i c h e b r e a d t h o f s p e c i e s i , a measure of g e n e r a l i z a t i o n o f h a b i t a t use by s p e c i e s i , i s t h e n (19) E 2 B i = 1 / E P i h 0< B- < E h-1 A n a l a g o u s measures were c a l c u l a t e d f o r t h e h a r p a c t i c o i d c o p e p o d community as a whole: t h e p r o p o r t i o n of t h e community i n h a b i t a t h i s (20) N N E P = E d / Z Z d 1=1 1=1 h=l and t h e m i c r o h a b i t a t n i c h e b r e a d t h o f t h e community i s (21) 2 9 4 The r e l a t i v e niche breadth of each species, that i s , the proportion of t o t a l habitats used by copepods which are used by an individual species is B i / B*. The re l a t i v e community niche breadth, or the proportion of available microhabitats used by a l l copepods i s B*/E. Assuming that two species which occur in the same . habitat are more l i k e l y to come into c o n f l i c t over the same resources, then the sp a t i a l overlap of species j on species i , the 'probability of co-occurrence alpha', (22) E E a i i = 1 P i h P i h 7 r P i h ; N i # j 3 h=l 3 h=l i s , in a sense, a measure of the li k e l i h o o d that species i and j are p o t e n t i a l l y in c o n f l i c t over the same resources. The mean microhabitat overlap in the community is (23) N a = ! / N(N-1 ). z a . . The maximum population of species i , i t s carrying capacity, expected in the absence of competitive l i m i t a t i o n s on i t s density (assuming no change on the l i m i t a t i o n of the population by physical factors) can be estimated from the alpha matrix and the vector of species' densities (Dj): (24) N K± = E a. . Dj If 'environmental resistance' to the increase of species i is a l l e v i a t e d , as well as competition, then the carrying capacity 295 i s K ./(B ./B*) . 1 x 296 C. R e s u l t s and D i s c u s s i o n E i g h t s p e c i e s of h a r p a c t i c o i d copepods were i d e n t i f i e d from the m i d - w i n t e r sand c o l l e c t i o n s between 1977 and 1980: S c o t t o l a n a c a n a d e n s i s H a l e c t i n o s o m a sp. Pseudobradya sp. T a c h i d i u s t r i a n g u l a r i s L e p t a s t a c u s c o n s t r i c t u s P a r a l e p t a s t a c u s s p i n i c a u d a Huntemannia j a d e n s i s S c h i z o p e r a sp. The f e e d i n g b e h a v i o r , m a c r o h a b i t a t use and month ( i n 1978) of maximum p o p u l a t i o n d e n s i t y of each s p e c i e s (except S c h i z o p e r a sp. ) are d i s c u s s e d i n d e t a i l i n c h a p t e r IV and summarized i n Table 19. J _ . Body s i z e and t r o p h i c r e l a t i o n s h i p s The e i g h t h a r p a c t i c o i d s p e c i e s may be s e p a r a t e d i n t o f o u r t r o p h i c groups on the b a s i s of mouthpart morphology and f e e d i n g b e h a v i o r : 'sand f i l e r s ' (two s p e c i e s ) , ' s e l e c t i v e e p i s t r a t e p i c k e r s ' ( t h r e e s p e c i e s ) , 'sphere c l e a n e r s ' (two s p e c i e s ) and a mixed f e e d e r ( T a b l e 19). The g r o s s morphology and r e l a t i v e s i z e s of members of the sand community are shown i n F i g . 52. S p e c i e s which f e e d by the same mechanism and/or a r e m o r p h o l o g i c a l l y s i m i l a r d i v e r g e d i n s i z e . T h i s s i z e d i f f e r e n c e was p a r t i c u l a r l y marked i n the sand f i l e r s which have e x t r e m e l y s i m i l a r o r a l morphology ( F i g s . 1 8 and 20) and f e e d i n g b e h a v i o r ( s e c t i o n I V ) . The mean l e n g t h of i n d i v i d u a l s of Pseudobradya sp. c o l l e c t e d i n Jan 1980 was 1.49 tim e s the mean l e n g t h of H a l e c t i n o s o m a sp. c o l l e c t e d a t the same time T a b l e 19. Summary o f t h e . - s a l i e n t f e a t u r e s o f the a u t e c o l o g y o f h a r p a c t i c o i d s p e c i e s w h i c h o c c u r i n the sand i n m i d - w i n t e r . S p e c i e s M a c r o h a b i t a t 1 F e e d i n g c l a s s ^ Month o f peak d e n s i t y R e p r o d u c t i v e p e r i o d i c i t y 3 1. Pseudobradya sp. 2. Halectinosoma sp. 3. P. spinicauda 4. T. triangularis 5. H. jadensis 6. S. canadensis 7. Schizopera sp. 8. L. constrictus sand sandy mud / sand sand mud sand sand mud sand sand Sand f i l e r Sand f i l e r S e l e c t i v e e p i -s t r a t e p i c k e r Rubb le s o r t e r Sphere c l e a n e r Sphere c l e a n e r Mixed S e l e c t i v e e p i -s t r a t e p i c k e r S e l e c t i v e e p i -s t r a t e p i c k e r w i n t e r ? November A p r i l November June A p r / M a y September A u g u s t A p r i l (?) w i n t e r . (c) max. i n w i n t e r (s) w i n t e r , max. i n (c) max. s u m m e r / f a l l (s) A p r - O c t . (s) F e b / M a y ; J u l y (s) A p r - O c t . (s) Mar ; A p r . 1 h a b i t a t i n which most commonly found l i s t e d f i r s t 2 b a s e d on M a r c o t t e (1977a,b) 3 s = s e a s o n a l c = ' c o n t i n u o u s ' ( g r a v i d fema les p r e s e n t t h r o u g h most o f the y e a r ) ro <_> 298 F i g u r e 52. H a b i t u s drawings of the 8 s p e c i e s which o c c u r r e d at the sand i n m i d - w i n t e r . For comparison of r e l a t i v e s i z e as w e l l as body form of s p e c i e s i n each t r o p h i c c a t e g o r y , a l l i n d i v i d u a l s a re a d u l t females and a l l are drawn t o the same s c a l e . T r o p h i c c a t e g o r i e s a r e t h o s e of M a r c o t t e ( 1 9 7 7 a ) : SF = sand f i l e r E = s e l e c t i v e e p i s t r a t e feeder SC = sphere c l e a n e r M = mixed f e e d e r . S c a l e 0.10 mm. ' 299 300 (0.62 ± 0.120 mm, n = 79 and 0.42 ± 0.007 mm, n = 13 r e s p e c t i v e l y ) . S i m i l a r s i z e s e g r e g a t i o n was observed between the two sphere c l e a n e r s ; Huntemannia j a d e n s i s (0.70 ± 0.025 mm, n = 12) was 1.44 times as l o n g as T a c h i d i u s t r i a n g u l a r i s (0.49 ± 0.009 mm, n = 11). The t h r e e s e l e c t i v e e p i s t r a t e f e e d e r s were more s i m i l a r i n s i z e : P a r a l e p t a s t a c u s s p i n i c a u d a (0.33 ± 0.006 mm, n = 29) was 1.36 tim e s as l o n g as L e p t a s t a c u s  c o n s t r i c t u s (0.24 ± 0.004 mm, n = 4) and o n l y 1.02 times as l o n g as S c h i z o p e r a sp. (0.32 ± 0.012 mm, n = 46). The l e n g t h f r e q u e n c y d i s t r i b u t i o n s ' of pennate diatoms i n g e s t e d by the f i v e most abundant h a r p a c t i c o i d s p e c i e s sampled i n