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Functional morphology of egg capsules in a marine gastropod Nucella emarginata Rawlings, Timothy Alexander 1989

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FUNCTIONAL MORPHOLOGY OF EGG CAPSULES IN A MARINE GASTROPOD NUCELLA EMARGINATA By Timothy A l e x a n d e r R a w l i n g s B.Sc. (Hons.)/ U n i v e r s i t y o f B r i t i s h Columbia, 1986 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (ZOOLOGY) We a c c e p t t h i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA August 1989 Timothy A l e x a n d e r R a w l i n g s , 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Z o o l The University of British Columbia Vancouver, Canada DE-6 (2/88) i i ABSTRACT Egg c a p s u l e s o f t h e marine whelk N u c e l l a e m a r q i n a t a were examined w i t h r e s p e c t t o i n t r a s p e c i f i c v a r i a t i o n i n c a p s u l e morphology and r e s i s t a n c e t o i n t e r t i d a l p r e d a t o r s . C a p s u l e s were c o l l e c t e d from t h r e e i n t e r t i d a l p o p u l a t i o n s s e p a r a t e d a l o n g a wave-exposure g r a d i e n t . W a l l t h i c k n e s s , d r y we i g h t , and p r o t e c t i v e q u a l i t y o f c a p s u l e s d i f f e r e d e x t e n s i v e l y among t h e s e p o p u l a t i o n s ; however, t h e s e c a p s u l a r p r o p e r t i e s d i d not r e f l e c t d i f f e r e n c e s i n wave-exposure l e v e l s . C a p s u l e s i z e was found t o i n c r e a s e from wave-exposed t o w a v e - s h e l t e r e d s h o r e s and p a r a l l e l e d d i f f e r e n c e s i n s n a i l s i z e among s i t e s . L a b o r a t o r y e x p e r i m e n t s , and f i e l d t e s t s i n c o r p o r a t i n g p r e d a t o r - e x c l u s i o n cages, were used t o dete r m i n e t h e e x t e n t o f p r e d a t i o n on N u c e l l a e m a r q i n a t a c a p s u l e s and t o i d e n t i f y c a p s u l e p r e d a t o r s . C a p s u l e cases were r e g u l a r l y e a t e n by i n t e r t i d a l p r e d a t o r s such as shore c r a b s , Hemiqrapsus spp., and i s o p o d s , I d o t e a w o s n e s e n s k i i . These i n v e r t e b r a t e s were r e s p o n s i b l e f o r opening a maximum o f 32% o f c a p s u l e s p r e s e n t a t two s t u d y s i t e s . D e s p i t e d i f f e r e n c e s i n t h i c k n e s s and s t r e n g t h o f c a p s u l e s among p o p u l a t i o n s , no c a p s u l e s were c o m p l e t e l y r e s i s t a n t t o t h e s e p r e d a t o r s ; however, t h i c k c a p s u l e w a l l s d i d appear t o convey some p r o t e c t i v e advantage. P r e l i m i n a r y l a b o r a t o r y t e s t s i n d i c a t e d t h a t t h i n - w a l l e d c a p s u l e s were p r e f e r e n t i a l l y opened by I d o t e a w o s n e s e n s k i i . i i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS x GENERAL INTRODUCTION 1 CHAPTER 1. INTRASPECIFIC VARIATION IN CAPSULE MORPHOLOGY INTRODUCTION 3 STUDY SITE DESCRIPTIONS 7 MATERIALS AND METHODS 12 I . D i f f e r e n c e s i n s n a i l morphology among s i t e s . . . 12 I I . C a p s u l e morphology 12 1. R e l a t i o n s h i p between s n a i l s i z e and c a p s u l e s i z e 12 2. Micromorphology o f L . em a r g i n a t a egg c a p s u l e s 15 3. I n t r a c a p s u l a r v a r i a t i o n i n w a l l t h i c k n e s s 15 4. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s among p o p u l a t i o n s 16 5. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n and among c l u t c h e s 17 6. V a r i a t i o n i n d r y weight o f c a p s u l e s 17 I I I . VARIATION IN CAPSULE CONTENTS AMONG SITES... 18 1. Egg number and volume 18 2. Number and s i z e o f h a t c h i n g s n a i l s 19 IV. CAPSULE STRENGTH 19 . 1. R e s i s t a n c e t o p u n c t u r i n g 19 i v Page 2. R e s i s t a n c e t o s q u e e z i n g 20 RESULTS 22 I . D i f f e r e n c e s i n s n a i l morphology among s i t e s . . . 22 I I . C a p s u l e morphology 22 1. R e l a t i o n s h i p between s n a i l s i z e and c a p s u l e s i z e 22 2. Micromorphology o f tL_ e m a r q i n a t a egg c a p s u l e s 27 3. I n t r a c a p s u l a r v a r i a t i o n i n w a l l t h i c k n e s s 27 4. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s among p o p u l a t i o n s 30 5. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n and among c l u t c h e s l a i d by d i f f e r e n t s n a i l s 33 6. V a r i a t i o n i n d r y w e i ght o f c a p s u l e s 35 I I I . VARIATION IN CAPSULE CONTENTS AMONG SITES... 37 1. Egg number and volume 37 2. Number and s i z e o f h a t c h i n g s n a i l s 39 IV. CAPSULE STRENGTH 41 1. R e s i s t a n c e t o p u n c t u r i n g 41 2. R e s i s t a n c e t o s q u e e z i n g 41 DISCUSSION 43 Advantages o f t h i c k , s t r o n g c a p s u l e w a l l s 43 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 c a p s u l a r s t r u c t u r e . . 44 E f f e c t s o f e n v i r o n m e n t a l s t r e s s e s on embryos 47 T r a d e o f f s i n c a p s u l e s t r u c t u r e 48 E f f e c t s o f e n v i r o n m e n t a l s t r e s s e s on a d u l t s n a i l s 49 REFERENCES 51 V Page CHAPTER 2. LABORATORY AND FIELD TESTS OF PREDATION INTRODUCTION . 55 MATERIALS AND METHODS 58 I . LABORATORY EXPERIMENTS.... 58 I I . FIELD CENSUSES OF PREDATION 59 1. G r a p p l e r I n l e t 59 2. Ross I s l e t s 60 3. Seppings I s l a n d 61 I I I . FIELD EXPERIMENTS 61 1. G r a p p l e r I n l e t 63 2. Ross I s l e t s . . . . . 64 IV. SUSCEPTIBILITY OF CAPSULES TO PREDATORS 65 RESULTS 67 I . LABORATORY EXPERIMENTS . 67 I I . FIELD CENSUSES OF PREDATION 73 1. G r a p p l e r I n l e t 73 2. Ross I s l e t s 78 3. Seppings I s l a n d 79 I I I . FIELD PREDATION EXPERIMENTS 80 1. G r a p p l e r I n l e t 80 a) P i l o t e x p e r i m e n t s 80 • b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s 82 2. Ross I s l e t s 82 a) P i l o t E x p e r i m e n t s 82 b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s 85 IV. SUSCEPTIBILITY OF CAPSULES TO PREDATORS 87 v i Page DISCUSSION 89 R e s i s t a n c e o f i n t a c t c a p s u l e s t o p r e d a t o r s 89 D i g e s t i b i l i t y and p a l a t a b i l i t y o f c a p s u l e w a l l s . . 91 P r e d a t i o n on egg c a p s u l e s i n t h e f i e l d 92 S u s c e p t i b i l i t y o f t h i c k - and t h i n - w a l l e d c a p s u l e s t o p r e d a t o r s 94 REFERENCES 97 GENERAL CONCLUSIONS 100 v i i LIST OF TABLES Page CHAPTER 2 I. Summary o f t h e s p e c i e s t e s t e d f o r p r e d a t o r y a c t i v i t y on N u c e l l a e m a r g i n a t a egg c a p s u l e s i n t h e l a b o r a t o r y . . 68 I I . D e n s i t y o f N u c e l l a e m a r g i n a t a , t h e i r egg c a p s u l e s , and c a p s u l e p r e d a t o r s a t s t u d y s i t e s i n G r a p p l e r I n l e t and Ross I s l e t s 74 I I I . Summary o f egg c a p s u l e s censused a t G r a p p l e r I n l e t and Ross I s l e t s t u d y s i t e s 76 IV. Summary o f N u c e l l a e m a r g i n a t a egg c a p s u l e s opened by p r e d a t o r s i n p i l o t e x p e r i m e n t s a t G r a p p l e r I n l e t , June 1988 81 v i i i LIST OF FIGURES Page CHAPTER 1 1. L o c a t i o n o f s t u d y s i t e s a l o n g t h e s o u t h e r n s h o r e s o f B a r k l e y Sound on t h e west c o a s t o f Vancouver I s l a n d , B.C 8 2. N u c e l l a e m a r g i n a t a egg c a p s u l e , i l l u s t r a t i n g t h e t h r e e measurements t a k e n f o r each c a p s u l e 14 3. Techniques used t o compare t h e s t r e n g t h o f egg c a p s u l e s 21 4. S i z e - f r e q u e n c y h i s t o g r a m s o f 50 s n a i l s c o l l e c t e d from each s t u d y s i t e 23 5 . R e l a t i o n s h i p between c a p s u l e body l e n g t h and s n a i l l e n g t h f o r l a b o r a t o r y l a i d c a p s u l e s f o r each s t u d y s i t e 24 6 . R e l a t i o n s h i p between capsule-chamber volume and s n a i l l e n g t h f o r l a b o r a t o r y p o p u l a t i o n s 26 7. M i c r o s t r u c t u r e o f N u c e l l a e m a r g i n a t a egg c a p s u l e s 28 8. V a r i a t i o n i n w a l l t h i c k n e s s a l o n g t h e c a p s u l e chamber o f f i e l d - c o l l e c t e d N u c e l l a e m a r g i n a t a c a p s u l e s 29 9. V a r i a t i o n i n w a l l t h i c k n e s s and c a p s u l e w i d t h w i t h i n one N u c e l l a e m a r g i n a t a c a p s u l e from G r a p p l e r I n l e t . . . . 31 10 V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h c a p s u l e body l e n g t h f o r 30 N u c e l l a e m a r g i n a t a c a p s u l e s from e a ch l a b o r a t o r y p o p u l a t i o n 32 11. V a r i a t i o n i n w a l l t h i c k n e s s w i t h i n and between c l u t c h e s o f N u c e l l a e m a r g i n a t a c a p s u l e s 34 12. Dry weight o f empty c a p s u l a r cases as a f u n c t i o n o f c a p s u l e body l e n g t h f o r each l a b o r a t o r y p o p u l a t i o n . . . . 36 13. R e l a t i o n s h i p between t h e number o f eggs p e r c a p s u l e . . . 38 and t h e volume o f t h e capsule-chamber f o r Seppings, Ross I s l e t s , and G r a p p l e r c a p s u l e s . 14. Mean h a t c h i n g s i z e o f embryos as a f u n c t i o n o f t h e number o f embryos c o n t a i n e d w i t h i n each c a p s u l e f o r Seppings, Ross I s l e t s and G r a p p l e r p o p u l a t i o n s 40 i x Page CHAPTER 2 1. P r e d a t o r e x c l u s i o n cages, i l u s t r a t i n g : a) t h e cage base and d e t a c h a b l e frame, and b) t h e f i v e cage t y p e s u sed t o e x c l u d e v a r i o u s s i z e - c l a s s e s o f p r e d a t o r s 62 2. Mean number o f N u c e l l a e m a r g i n a t a egg c a p s u l e s r e m a i n i n g i n t a c t a f t e r 5 days exposure t o : a) i s o p o d s , I d o t e a w o s n e s e n s k i i (n = 11) and b) t h r e e s i z e - c l a s s e s o f Hemigrapsus nudus 69 3. C h a r a c t e r i s t i c s o f s p e c i e s - s p e c i f i c p r e d a t i o n on N u c e l l a e m a r g i n a t a c a p s u l e s by: I d o t e a w o s e n e s e n s k i i  Hemigrapsus spp., M o p a l i a spp., and an unknown p r e d a t o r 71 4. R e s u l t s o f t h e p r e d a t o r - e x c l u s i o n e x p e r i m e n t s i n G r a p p l e r I n l e t , J u l y 1988 83 5 . R e s u l t s o f t h e p r e d a t o r - e x c l u s i o n e x p e r i m e n t s i n Ross I s l e t s , September 1988 86 6 . Mean number o f t h e f i r s t f i v e c a p s u l e s opened by I d o t e a w o s n e s e n s k i i when g i v e n a c h o i c e o f f e e d i n g on c a p s u l e s from two d i f f e r e n t s t u d y s i t e s . 88 X ACKNOWLEDGEMENTS F i r s t , I would l i k e t o thank my s u p e r v i s o r Dr. Thomas C a r e f o o t f o r h i s a d v i c e and h e l p d u r i n g t h e c o u r s e o f t h i s s t u d y . I would a l s o l i k e t o thank my committee members, Dr. Jamie Smith and Dr. John G o s l i n e , f o r t h e i r i n p u t i n t o t h i s p r o j e c t . Much c r e d i t i s due a l s o t o Gle n y s G i b s o n f o r th e many hours she spent showing me how t o d e v e l o p photographs and a l s o f o r her mor a l s u p p o r t d u r i n g t h i s l o n g - w i n d e d w r i t e -up. L o i s H o l l e t t and E l i z a b e t h C a r e f o o t d e s e r v e a s p e c i a l m ention f o r t h e i r h e l p i n p r o d u c i n g t h e f i g u r e s . I am a l s o i n d e b t e d t o Dr. John Steeves f o r a l l o w i n g me t o use h i s m i c r o s c o p e and camera system t o photograph my c a p s u l e w a l l s e c t i o n s . F i n a l l y , I would l i k e t o acknowledge t h e d i r e c t o r and s t a f f o f B a m f i e l d M a r i n e S t a t i o n who made my s t a y an e x t r e m e l y e n j o y a b l e and r e w a r d i n g e x p e r i e n c e . 1 GENERAL INTRODUCTION M a r i n e g a s t r o p o d s e x h i b i t a v a r i e t y o f r e p r o d u c t i v e and de v e l o p m e n t a l p a t t e r n s (Webber, 1977). An i m p o r t a n t advance i n t h e r e p r o d u c t i v e e c o l o g y o f t h e s e organisms has been t h e e v o l u t i o n o f i n t e r n a l f e r t i l i z a t i o n i n t h e Meso- and Neogastropoda ( G a l l a r d o and P e r r o n , 1982). I n t e r n a l f e r t i l i z a t i o n has a l l o w e d f o r t h e development o f new r e p r o d u c t i v e p a t t e r n s a s s o c i a t e d w i t h a n o n - p e l a g i c l a r v a l s t a g e , such as t h e d e p o s i t i o n o f eggs i n t o p r o t e c t i v e g e l a t i n o u s e n v e l o p e s o r i n t o e l a b o r a t e egg c a p s u l e s . I n many meso- and neogastropods embryos a re c o n f i n e d w i t h i n b e n t h i c egg c a p s u l e s f o r some, i f not a l l , o f t h e i r d e v e l o p m e n t a l p e r i o d . The a d a p t i v e s i g n i f i c a n c e o f such s t r u c t u r e s i s g e n e r a l l y t hought t o be a s s o c i a t e d w i t h a r e d u c t i o n i n t h e development t i m e o f embryos w i t h i n t h e p l a n k t o n and, c o n s e q u e n t l y , an i n c r e a s e i n t h e s u r v i v o r s h i p o f embryos (Pechenik, 1979) . The confinement o f embryos w i t h i n b e n t h i c egg c a p s u l e s , however, has i t s own r i s k s . Embryos f r e e o f m o r t a l i t y a s s o c i a t e d w i t h a p l a n k t o n i c e x i s t e n c e a r e exposed t o a v a r i e t y o f new e n v i r o n m e n t a l s t r e s s e s w i t h i n t h e b e n t h i c marine environment. L i t t l e i s known about t h e importance o f t h e s e s t r e s s e s on t h e s u r v i v o r s h i p o f e n c a p s u l a t e d embryos. Recent s t u d i e s , however, have shown t h a t t h e w a l l s t r e n g t h o f many n e o g a s t r o p o d egg c a p s u l e s i s r e l a t e d t o t h e development t i m e o f e n c a p s u l a t e d embryos ( P e r r o n , 1981). These r e s u l t s 2 suggest t h a t l o n g e r development t i m e s may be a s s o c i a t e d w i t h a g r e a t e r r i s k o f embryonic m o r t a l i t y and, hence, d i f f e r e n c e s i n c a p s u l a r s t r u c t u r e may a l s o be c o r r e l a t e d w i t h d i f f e r e n c e s i n t h e l e v e l s o f s p e c i f i c e n v i r o n m e n t a l s t r e s s e s . The g o a l s o f t h e p r e s e n t s t u d y were: 1) t o examine v a r i a t i o n i n t h e morphology o f egg c a p s u l e s among p o p u l a t i o n s o f t h e i n t e r t i d a l s n a i l N u c e l l a e m a r g i n a t a , and 2) t o det e r m i n e t h e e f f e c t i v e n e s s o f t h e s e s t r u c t u r e s i n p r o t e c t i n g d e v e l o p i n g embryos from p r e d a t o r s . T h i s t h e s i s i s d i v i d e d i n t o two c h a p t e r s . C h a p t e r 1 p r e s e n t s d a t a on t h e morphology o f N u c e l l a e m a r g i n a t a egg c a p s u l e s c o l l e c t e d from t h r e e s i t e s a l o n g a wave-exposure g r a d i e n t . D i f f e r e n c e s i n egg c a p s u l e w a l l t h i c k n e s s a re examined w i t h i n and among s i t e s and c o r r e l a t e d w i t h measurements o f c a p s u l e s t r e n g t h . The i m p l i c a t i o n s o f i n t r a -and 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 c a p s u l e w a l l t h i c k n e s s a r e d i s c u s s e d w i t h r e f e r e n c e t o t h e p o s s i b l e f u n c t i o n ( s ) o f such e x t r a - e m b r y o n i c s t r u c t u r e s . Chapter 2 i n v e s t i g a t e s t h e e x t e n t o f p r e d a t i o n on i n t e r t i d a l N u c e l l a e m a r g i n a t a egg c a p s u l e s . P o t e n t i a l i n t e r t i d a l p r e d a t o r s a re i d e n t i f i e d t h r o u g h a c o m b i n a t i o n o f f i e l d and l a b o r a t o r y s t u d i e s , and e v i d e n c e o f s p e c i e s - s p e c i f i c p r e d a t i o n i n t h e f i e l d i s d e s c r i b e d . A l s o , p r e d a t o r p r e f e r e n c e s f o r t h i c k - o r t h i n - w a l l e d egg c a p s u l e s a r e examined. The e x t e n t o f f i e l d p r e d a t i o n on N u c e l l a  e m a r g i n a t a egg c a p s u l e s i s d i s c u s s e d i n terms o f t h e r o l e t h a t p r e d a t i o n may have p l a y e d i n t h e e v o l u t i o n o f c a p s u l e morphology. 3 CHAPTER 1 FUNCTIONAL MORPHOLOGY OF MARINE GASTROPOD EGG CAPSULES: INTRASPECIFIC VARIATION IN SIZE, WALL THICKNESS AND STRENGTH OF NUCELLA EMARGINATA EGG CAPSULES INTRODUCTION The confinement o f d e v e l o p i n g embryos w i t h i n egg c a p s u l e s i s a common phenomenon among marine i n v e r t e b r a t e s . N e ogastropod m o l l u s c s e n c l o s e t h e i r embryos w i t h i n s t r u c t u r a l l y complex p r o t e i n a c e o u s c a p s u l e s , and embryos d e v e l o p w i t h i n t h e s e c a p s u l e s f o r a t l e a s t some, i f not a l l , o f t h e i r l a r v a l l i f e . G a s t r o p o d egg c a p s u l e s are f r e q u e n t l y c o n s i d e r e d t o be " p r o t e c t i v e " (Pechenik, 1979; P e r r o n , 1981; P e r r o n and Corpuz, 1982), but what t h e y p r o t e c t embryos a g a i n s t i s u n c l e a r . Commonly, t h e egg c a p s u l e s have been tho u g h t t o reduce such e n v i r o n m e n t a l s t r e s s e s as: p r e d a t i o n (Pechenik, 1979; P e r r o n , 1981), b a c t e r i a l a t t a c k ( L o r d , 1986), o s m o t i c changes (Pechenik, 1982; 1983, Hawkins and H u t c h i n s o n , 1988), d e s i c c a t i o n ( S p i g h t , 1977; P e c h e n i k , 1978), t e m p e r a t u r e shock ( S p i g h t , 1977; P e c h e n i k , 1986), and wave a c t i o n ( P e r r o n , 1981). However, o n l y a few s t u d i e s have s p e c i f i c a l l y examined t h e r e s i s t a n c e o f e n c a p s u l a t e d embryos t o t h e s e f a c t o r s ( S p i g h t , 1977; P e c h e n i k , 1978; 1982; 1983; B r e n c h l e y , 1982; D a v i e s , 1984; L o r d , 1986; Hawkins and H u t c h i n s o n , 1988) and l i t t l e i s known about t h e s u r v i v o r s h i p o f e n c a p s u l a t e d embryos i n a c t u a l f i e l d s i t u a t i o n s . 4 An e x a m i n a t i o n o f i n t r a - and i n t e r s p e c i f i c v a r i a t i o n i n t h e s t r u c t u r e o f egg c a p s u l e w a l l s may be u s e f u l i n a s s e s s i n g t h e r o l e t h a t c a p s u l e s p l a y i n g a s t r o p o d l i f e - h i s t o r i e s . V a r i a t i o n i n c a p s u l e w a l l s t r e n g t h and t h e energy i n v e s t e d i n c a p s u l a r c a s e s among s p e c i e s w i t h i n t h e genus Conus has been found t o be p o s i t i v e l y c o r r e l a t e d w i t h embryonic d e v e l o p m e n t a l t i m e ( P e r r o n , 1981). F u r t h e r m o r e , c a p s u l e w a l l s a r e known t o be t h i c k e r i n Conus s p e c i e s w i t h l o n g e n c a p s u l a t e d development (P e r r o n and Corpuz, 1982). As i n some s p e c i e s c a p s u l a r c ases can account f o r almost 50% o f t h e energy i n v e s t e d i n i n t a c t c a p s u l e s ( P e r r o n , 1981), s t r o n g , t h i c k - w a l l e d c a p s u l e s may have e v o l v e d f o r i n c r e a s e d p r o t e c t i o n o f e n c a p s u l a t e d embryos w i t h l o n g - t e r m exposure t o e n v i r o n m e n t a l s t r e s s e s ( P e r r o n , 1981; P e r r o n and Corpuz, 1982). I f s e l e c t i o n has a l s o responded t o i n t e n s i t y o f t h e s e e n v i r o n m e n t a l f a c t o r s , t h e n i n t r a s p e c i f i c comparisons o f c a p s u l a r s t r u c t u r e a c r o s s a v a r i e t y o f h a b i t a t s c o u l d r e v e a l d i f f e r e n c e s a s s o c i a t e d w i t h s p e c i f i c s o u r c e s o f m o r t a l i t y . As y e t , no s t u d i e s have s p e c i f i c a l l y examined i n t r a - o r i n t e r s p e c i f i c v a r i a t i o n i n t h e s t r u c t u r e o f g a s t r o p o d c a p s u l e s among d i f f e r e n t h a b i t a t s . D i f f e r e n c e s i n t h e s t r u c t u r e o f egg c a p s u l e s w i t h i n a s p e c i e s may be most apparent among p o p u l a t i o n s s e p a r a t e d a l o n g s h a r p e n v i r o n m e n t a l g r a d i e n t s , such as wave-exposure. S t r e s s e s imposed on i n t e r t i d a l organisms a r e known t o d i f f e r g r e a t l y a l o n g wave-exposure g r a d i e n t s (Menge, 1978a; 1978b; Menge and S u t h e r l a n d , 1987). S t u d i e s have shown t h a t i n c r e a s e s i n wave-exposure a r e matched by: 1) d e c r e a s e s i n p r e d a t i o n i n t e n s i t y , as wave a c t i o n g e n e r a l l y t e n d s t o d i s r u p t 5 p r e d a t o r f o r a g i n g a c t i v i t i e s ( K i t c h i n g e t a l . , 1959; Menge, 1978a; 1978b; R o b l e s , 1987), and 2) d e c r e a s e s i n d e s i c c a t i o n s t r e s s , as a r e a s s p l a s h e d by waves s u f f e r l e s s d r y i n g (Dayton, 1971; Menge, 1978a). Wave-action i t s e l f i s known t o impose s e v e r e p h y s i c a l s t r e s s e s upon i n t e r t i d a l organisms due t o d i s l o d g e m e n t (Denny, 1985, Denny e t a l . , 1985; E t t e r , 1987), a b r a s i o n ( C r a i k , 1980), and w a t e r - b o r n r o c k s (Shanks and W r i g h t , 1986). Assuming t h a t b e n t h i c egg c a p s u l e s a r e exposed t o e n v i r o n m e n t a l s t r e s s e s s i m i l a r t o s e s s i l e i n t e r t i d a l o rganisms, a wave-exposure g r a d i e n t may p r o v i d e a c o n v e n i e n t means o f comparing c a p s u l e s t r u c t u r e a c r o s s a range o f e n v i r o n m e n t a l c o n d i t i o n s . In o r d e r t h a t 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 c a p s u l e s t r u c t u r e can be i n t e r p r e t e d , i t i s e s s e n t i a l t o u n d e r s t a n d c e r t a i n c o n s t r a i n t s imposed on t h e morphology o f g a s t r o p o d egg c a p s u l e s . F o r i n s t a n c e , i t i s known from t h e work o f S p i g h t e t a l . (1974), S p i g h t and Emlen (1976) and P e r r o n and Corpuz (1982) t h a t t h e l e n g t h , volume and w a l l t h i c k n e s s o f g a s t r o p o d egg c a p s u l e s i s r e l a t e d t o female s i z e . C o n s t r a i n t s may a l s o be p l a c e d on c a p s u l e s t r u c t u r e by t h e r e q u i r e m e n t s o f d e v e l o p i n g embryos (Strathmann and C h a f f e e , 1984). F o r i n s t a n c e , t h i c k c a p s u l e w a l l s o r c a p s u l e shapes w i t h low s u r f a c e a r e a t o volume r a t i o s may r e s t r i c t t h e d i f f u s i o n o f oxygen or waste p r o d u c t s and t h u s reduce embryo s u r v i v o r s h i p . Hence, t h e r e may be t r a d e o f f s i n c a p s u l e d e s i g n , such t h a t t h i c k - w a l l e d c a p s u l e s p r o t e c t embryos b e t t e r from p r e d a t i o n or p h y s i c a l s t r e s s , but may l i m i t t h e number o f embryos s u r v i v i n g . T h e r e f o r e , a s t u d y o f c a p s u l e f u n c t i o n must 6 i n v o l v e a knowledge o f t h e i n t e r r e l a t i o n s h i p s between c a p s u l e morphology, c a p s u l e w a l l t h i c k n e s s , and t h e p a c k a g i n g o f embryos w i t h i n c a p s u l e s . The marine i n t e r t i d a l s n a i l , N u c e l l a e m a r g i n a t a , i s a common i n h a b i t a n t o f r o c k y s h o r e s from C a l i f o r n i a t o A l a s k a and ranges a c r o s s wide extremes i n wave-exposure. These s n a i l s d e p o s i t eggs w i t h i n 6-10 mm-long vase-shaped c a p s u l e s , w h i c h t h e y a t t a c h d i r e c t l y t o t h e s u b s t r a t u m . Three t o 35 embryos a r e e n c l o s e d w i t h hundreds o f nu r s e eggs, used as f o o d by t h e d e v e l o p i n g l a r v a e . A f t e r a p p r o x i m a t e l y 80 days (Emlen, 1966), embryos emerge from t h e egg c a p s u l e s as j u v e n i l e s n a i l s . I n t h i s s t u d y , I examined i n t r a s p e c i f i c v a r i a t i o n i n c a p s u l e morphology w i t h i n and among p o p u l a t i o n s o f N u c e l l a  e m a r g i n a t a . P o p u l a t i o n s were chosen from t h r e e s i t e s s e p a r a t e d a l o n g a g r a d i e n t o f wave-exposure. Data were c o l l e c t e d on: 1) t h e s i z e and shape o f s n a i l s w i t h i n and among p o p u l a t i o n s , 2) 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 c a p s u l e s i z e and w a l l t h i c k n e s s , 3) v a r i a t i o n i n t h e p a c k a g i n g o f eggs and embryos w i t h i n c a p s u l e s , and 4) t h e r e l a t i o n s h i p between c a p s u l e w a l l t h i c k n e s s and c a p s u l e s t r e n g t h , f o r each s i t e . 7 STUDY SITE DESCRIPTIONS T h i s p r o j e c t was conducted a t t h e B a m f i e l d M a r i n e S t a t i o n on t h e west c o a s t o f Vancouver I s l a n d (125°10'N, 48°50'W; F i g . l ) . Study s i t e s were e s t a b l i s h e d i n B a r k l e y Sound f o r t h e purpose o f c o l l e c t i n g N u c e l l a e m a r q i n a t a a d u l t s and t h e i r egg c a p s u l e s . Three l o c a t i o n s were chosen t o r e p r e s e n t a g r a d i e n t o f wave-exposure from s h e l t e r e d t o exposed: G r a p p l e r I n l e t , Ross I s l e t s , and Seppings I s l a n d . A l t h o u g h no e m p i r i c a l s t u d i e s have r a n k e d t h e s e a r e a s i n B a r k l e y Sound w i t h r e s p e c t t o wave-exposure, my r a t i n g system, based on v i s u a l o b s e r v a t i o n s , c o r r e s p o n d e d w i t h s u b j e c t i v e exposure s c a l e s employed by o t h e r s i n t h e same g e o g r a p h i c r e g i o n ( A u s t i n , D r u e h l , and Haven, 1971; K i t c h i n g , 1976; C r o t h e r s , 1984). 1. G r a p p l e r I n l e t The G r a p p l e r I n l e t s i t e r e p r e s e n t e d t h e l e a s t wave-exposed s t u d y a r e a ( F i g . 1 ) . A l t h o u g h t h e a c t u a l s i t e was t o o f a r up t h e i n l e t t o r e c e i v e o c e a n i c s w e l l , i t was s u b j e c t t o a c o n s i d e r a b l e t i d a l c u r r e n t due t o t h e c o n s t r i c t e d w i d t h o f t h e c h a n n e l and l a r g e volume o f t i d a l exchange. T h i s s i t e r e p r e s e n t e d an extreme d i s t r i b u t i o n a l l i m i t f o r N u c e l l a e m a r q i n a t a , w h i c h a r e n o r m a l l y absent from p r o t e c t e d i n l e t s ( C r o t h e r s , 1984). A g e n e r a l s e a r c h f o r N. e m a r q i n a t a a l o n g G r a p p l e r I n l e t r e v e a l e d t h a t t h e y were p r e s e n t o n l y i n two a r e a s : a t my st u d y l o c a t i o n and on r o c k y beaches around t h e mouth o f t h e i n l e t . The s i t e was l o c a t e d i n an i n t e r t i d a l c h a n n e l , 1.6m above z e r o c h a r t datum, c o n n e c t i n g t h e m a i n l a n d and a s m a l l 8 FIGURE 1. The l o c a t i o n of study s i t e s along the southern shores of Barkley Sound on the west coast of Vancouver Island, B.C. Study locations were chosen along a wave-exposure gradient. Wave-exposure l e v e l s were predicted to be lowest at Grappler Inlet, highest at Seppings Island, and intermediate at the Ross I s l e t s s i t e . 9 p i e c e o f l a n d i s o l a t e d a t h i g h t i d e . The i n t e r t i d a l s u b s t r a t e c o n s i s t e d o f f i n e s i l t y mud o v e r l a i d by clam s h e l l s and a meshwork o f m u s s e l - and b a r n a c l e - c o v e r e d r o c k s ( M y t i l u s  e d u l i s , B a lanus q l a n d u l a and Semibalanus c a r i o s u s ) . N u c e l l a  e m a r q i n a t a were p r e s e n t t h r o u g h o u t t h e c h a n n e l and ranged t o a t i d a l h e i g h t o f a p p r o x i m a t e l y 2.6m above z e r o c h a r t datum. Other g a s t r o p o d s p r e s e n t were N u c e l l a l a m e l l o s a , S e a r l e s i a d i r a , O n c h i d e l l a b o r e a l i s , and v a r i o u s l i m p e t s p e c i e s . The c h i t o n s M o p a l i a spp. were a l s o abundant t h r o u g h o u t t h e c h a n n e l . The p o l y c h a e t e s , N e r e i s v e x i l l o s a and s e v e r a l s p e c i e s o f s c a l e worms were a s s o c i a t e d w i t h t h e m u s s e l - and b a r n a c l e - c o v e r e d r o c k s , w h i l e s e v e r a l nemertean s p e c i e s were u b i q u i t o u s . Three i s o p o d s p e c i e s were p r e s e n t : Gnorimosphaeroma oreqonense, C i r o l a n a h a r f o r d i , and I d o t e a  w o s n e s e n s k i i . Hemigrapsus o r e g o n e n s i s burrows were e v i d e n t i n t h e compact mud found i n h i g h e r i n t e r t i d a l r e g i o n s ; however, H. nudus were r a r e l y seen. Hermit c r a b s (Pagurus spp.) c o u l d be found i n amongst t h e meshwork o f mu s s e l s , b a r n a c l e s and r o c k s . Fucus and U l v a were t h e predominant i n t e r t i d a l a l g a e . 2. Ross I s l e t s T h i s s i t e was chosen t o r e p r e s e n t a r e g i o n w i t h i n t e r m e d i a t e wave-exposure ( F i g . 1 ) . The c o l l e c t i n g areas were l o c a t e d on b o t h s i d e s o f a w a v e - p r o t e c t e d c h a n n e l . N o r m a l l y t h e s e s i t e s r e c e i v e d o n l y s m a l l s w e l l s r e s u l t i n g from waves b r e a k i n g on t h e s o u t h - f a c i n g s h o r e s o f t h e i s l e t s and on a r e e f between two n e i g h b o u r i n g i s l a n d s . The i n t e r t i d a l s u b s t r a t e i n t h i s r e g i o n c o n s i s t e d o f g r a n i t e bedrock, w i t h a b o u l d e r beach c o v e r i n g some o f t h e 10 l o w e r r e g i o n s . Three b a r n a c l e s p e c i e s were p r e s e n t i n t e r t i d a l l y : B a l a n u s g l a n d u l a , Semibalanus c a r i o s u s and Chthamalus d a l l i . M y t i l u s c a l i f o r n i a n u s were p r e s e n t i n p a t c h y clumps. N u c e l l a e m a r g i n a t a were found i n t h e mid- t o h i g h - i n t e r t i d a l zones between 1.8 - 3.1 m above z e r o c h a r t datum, and were p r e s e n t o c c a s i o n a l l y i n t h e lower b o u l d e r beach r e g i o n . Other l i t t o r a l g a s t r o p o d s p r e s e n t were N u c e l l a  l a m e l l o s a , T e g u l a f u n e b r a l i s , S e a r l e s i a d i r a and v a r i o u s l i m p e t s p e c i e s . The c h i t o n s , M o p a l i a spp., were seen o c c a s i o n a l l y on g r a n i t e p r o m o n t o r i e s . I n t e r t i d a l p o l y c h a e t e s and nemerteans were s p a r s e , w i t h N e r e i s v e x i l l o s a and Emplectonema g r a c i l e b e i n g t h e o n l y o b v i o u s r e p r e s e n t a t i v e s o f t h e s e groups. The p u r p l e shore c r a b s , Hemigrapsus nudus, and p o r c e l a i n c r a b s , P e t r o l i s t h e s spp. were abundant under r o c k s i n t h e b o u l d e r beaches and i n some h i g h e r i n t e r t i d a l c r e v i c e s . S t a r f i s h , P i s a s t e r - o c h r a c e u s , were a l s o common i n t h e b o u l d e r beach a r e a . The predominant h i g h i n t e r t i d a l a l g a was Fucus  d i s t i c h u s , d i s t r i b u t e d i n a d i s t i n c t v e r t i c a l band at a t i d e h e i g h t o f a p p r o x i m a t e l y 2.6 - 2.9 m above z e r o c h a r t datum. 3. Seppings I s l a n d T h i s was t h e most wave-exposed s i t e ( F i g . 1 ) . The c o l l e c t i n g a r e a was l o c a t e d i n a l a r g e b o u l d e r - l i n e d c h a n n e l , 10 m wide, f a c i n g a r e l a t i v e l y u n o b s t r u c t e d o c e a n i c s w e l l . The c h a n n e l was b o r d e r e d on one s i d e by a h i g h g r a n i t e w a l l and on t h e o t h e r by a l a r g e r o c k y promontory c o v e r e d w i t h M y t i l u s c a l i f o r n i a n u s . B o u l d e r s i n t h e c h a n n e l ranged i n s i z e from 0.3 - 2.0 m d i a m e t e r . D u r i n g w i n t e r storms, b o u l d e r s o f t e n were r e d i s t r i b u t e d t h r o u g h o u t t h e i n t e r t i d a l a r e a by 11 wave a c t i o n . The c o l l e c t i n g c h a n n e l was c h a r a c t e r i z e d by a v a r i e t y o f b a r n a c l e s (Balanus g l a n d u l a , Semibalanus c a r i o s u s , Cthamalus  d a l l i , and P o l i c i p e s p o l y m e r u s ) , whelks ( N u c e l l a e m a r g i n a t a , N. c a n a l i c u l a t a , and Ceratostoma f o l i a t u m ) and o t h e r g a s t r o p o d s (Ocenebra l u r i d a , T e g u l a f u n e b r a l i s , C a l l i o s t o m a  l i g a t u m and v a r i o u s l i m p e t s p e c i e s ) . I d o t e a w o s n e s e n s k i i were t h e o n l y i n t e r t i d a l i s o p o d s p r e s e n t . Hemigrapsus nudus were p r e s e n t i n l a r g e numbers u n d e r n e a t h t h e r o c k y b o u l d e r s , as were s m a l l h e r m i t c r a b s (Pagurus spp.) and p o r c e l a i n c r a b s ( P e t r o l i s t h e s c i n c t i p e s ) . A l g a e c o n s i s t e d o f L a m i n a r i a and I r i d a e a s p e c i e s i n t h e low i n t e r t i d a l a r e a , and P e l v e t i o p s i s  l i m i t a t a i n t h e h i g h i n t e r t i d a l r e g i o n s . 12 MATERIALS AND METHODS I . DIFFERENCES IN SNAIL MORPHOLOGY AMONG SITES S h e l l - l e n g t h t o a p e r t u r e - l e n g t h r a t i o s were used t o compare s h e l l morphology among s i t e s , as t h e s e . r a t i o s a r e t h e q u i c k e s t and s i m p l e s t method o f d e t e r m i n i n g s h e l l - s h a p e v a r i a t i o n i n t h e genus N u c e l l a ( C r o t h e r s , 1984). F i f t y s n a i l s were c o l l e c t e d from each s t u d y a r e a i n t h e s p r i n g o f 1988. C o l l e c t i o n s were made by removing a l l l i v i n g N u c e l l a  e m a r q i n a t a from a g i v e n a r e a t o a v o i d any b i a s e s f o r s h e l l c o l o u r , s i z e , o r shape. S n a i l s c o n s i d e r e d t o be j u v e n i l e s ( l e s s t h a n 10 mm i n l e n g t h ) were r e p l a c e d , as c o n s i d e r a b l e v a r i a t i o n i n s h e l l shape i s known t o o c c u r d u r i n g e a r l y j u v e n i l e development ( C r o t h e r s , 1984). S h e l l and a p e r t u r e -l e n g t h s were measured t o t h e n e a r e s t 0.1mm w i t h v e r n i e r c a l i p e r s . S h e l l - l e n g t h was d e f i n e d as t h e maximum l e n g t h between t h e s h e l l apex and a n t e r i o r t i p o f t h e s i p h o n a l c a n a l , w h i l e a p e r t u r e - l e n g t h was t h e maximum d i s t a n c e between t h e p o s t e r i o r c o r n e r o f t h e a p e r t u r e l i p and a n t e r i o r t i p o f t h e s i p h o n a l c a n a l . I I . CAPSULE MORPHOLOGY 1. R e l a t i o n s h i p between s n a i l s i z e and c a p s u l e s i z e I n o r d e r t o compare t h e s i z e o f egg c a p s u l e s l a i d by s n a i l s from each s i t e , a p p r o x i m a t e l y 50-100 s n a i l s were c o l l e c t e d from each s t u d y a r e a . S n a i l s were brought i n t o t h e l a b o r a t o r y , t a g g e d f o r i d e n t i f i c a t i o n , and a s s i g n e d t o s i t e -s p e c i f i c p l a s t i c c o n t a i n e r s (32x26x12cm, w i t h 20x8cm lmm-pore 13 mesh windows i n each o f t h e f o u r s i d e s ) . A p p r o x i m a t e l y 40-50 s n a i l s were h e l d i n each c o n t a i n e r and were p r o v i d e d w i t h b a r n a c l e s f o r f o o d . C o n t a i n e r s were kept submerged i n l a b o r a t o r y seawater t a b l e s and s u p p l i e d w i t h a c o n t i n u o u s f l o w o f f r e s h seawater. Each l a b o r a t o r y p o p u l a t i o n was checked e v e r y two days over a six-week p e r i o d t o i d e n t i f y s n a i l s l a y i n g egg c a p s u l e s . A s n a i l was r e c o g n i z e d t o be l a y i n g an egg c a p s u l e o n l y i f i t was found a c t u a l l y m o l d i n g a new c a p s u l e w i t h i t s v e n t r a l p e d a l g l a n d . Such c a p s u l e s c o u l d be i d e n t i f i e d r e a d i l y by t h e i r s o f t w a l l s and m i l k y - y e l l o w appearance. Other c a p s u l e s were c o l l e c t e d w i t h t h e n e w l y - l a i d ones o n l y i f t h e y were c o n s i d e r e d t o be p a r t o f t h e same c l u t c h . A c l u t c h was d e f i n e d t o be any number o f c a p s u l e s l a i d i n w i t h i n a few mm o f one a n o t h e r t h a t were s i m i l a r i n shape and o r i e n t a t i o n ( G a l l a r d o , 1979). A maximum o f 5 c a p s u l e s was c o l l e c t e d from each female a t any spawning check. C a p s u l e - l a y i n g females were measured f o r s h e l l l e n g t h and r e t u r n e d t o t h e i r c o n t a i n e r s . C a p s u l e s were p r e s e r v e d i n 5% f o r m a l i n f o r subsequent measurement. Three measurements were t a k e n f o r each c a p s u l e ( F i g . 2 ) : 1 ) " c a p s u l e body l e n g t h " , w h i c h e x c l u d e d t h e stem l e n g t h as t h i s was known t o be e x t r e m e l y v a r i a b l e ( S p i g h t and Emlen, 1976); 2 ) " c a p s u l e chamber l e n g t h " , r e p r e s e n t i n g t h e l e n g t h o f chamber h o u s i n g t h e embryos and nurse eggs; and, 3) t h e "maximum c a p s u l e w i d t h " , w h i c h was t h e maximum w i d t h o f t h e capsule-chamber. The " c a p s u l e chamber volume" was e s t i m a t e d u s i n g t h e f o r m u l a f o r a p r o l a t e e l l i p s o i d , V=4/37T(a/2) (b/2)2, where a = t h e c a p s u l e chamber l e n g t h and b = t h e maximum 14 Capsule Body Length Capsular H u g Capsule Chamber Length Stem Maximum Capsular Width 1 2mm Scale FIGURE 2. Nucella emarginata egg capsule, i l l u s t r a t i n g the three measurements taken f or each capsule: capsule-body length, capsule-chamber length, and maximum capsule width. The capsular-plug region and the stem are also indicated. 15 c a p s u l e w i d t h (Pechenik, 1982). 2. Micro-morphology o f N u c e l l a e m a r g i n a t a egg c a p s u l e s R e p r e s e n t a t i v e egg c a p s u l e s o f N u c e l l a e m a r g i n a t a were s e c t i o n e d u s i n g a f r e e z e microtome. The w a l l m i c r o s t r u c t u r e o f each c a p s u l e was examined u s i n g a compound l i g h t m i c r o s c o p e and i n t e r p r e t e d w i t h r e s p e c t t o p r e v i o u s h i s t o l o g i c a l s t u d i e s on t h e egg c a p s u l e s o f N. l a p i l l u s and o t h e r m u r i c i d s (Bayne, 1968; S u l l i v a n and Maugel, 1984; D'Asaro, 1988). 3. I n t r a c a p s u l a r v a r i a t i o n i n w a l l t h i c k n e s s I n t r a c a p s u l a r v a r i a t i o n i n t h e w a l l t h i c k n e s s o f N u c e l l a e m a r g i n a t a c a p s u l e s was examined f o r each s i t e . C a p s u l e s were c o l l e c t e d from d i f f e r e n t c l u t c h e s w i t h i n a s i t e t o m i n i m i z e t h e chance o f o b t a i n i n g c a p s u l e s from any one f e m a l e . In t h e l a b o r a t o r y , t h e s e were t h e n p l a c e d i n c y l i n d r i c a l v i a l s (3.5x3.5x6cm w i t h two 2.0x2.5cm lmm-pore mesh p a n e l s ) and m a i n t a i n e d i n f l o w i n g seawater. C a p s u l e s were measured as b e f o r e , e m p t i e d o f a l l c o n t e n t s by removing t h e c a p s u l a r p l u g , and t h e n i n d i v i d u a l l y f r o z e n on a f r e e z e microtome. S e c t i o n s , each 10-12yum t h i c k , were t a k e n a t 10 p e r c e n t i l e i n t e r v a l s a l o n g t h e l e n g t h o f t h e c a p s u l e chamber. The f i r s t s e c t i o n s (0%) were t a k e n a t t h e o p ening o f t h e p l u g r e g i o n i n t o t h e capsule-chamber. The l a s t s e c t i o n (100%) was t a k e n c l o s e t o t h e j u n c t i o n between t h e capsule-chamber and stem. S e c t i o n s were mounted i n a s e a w a t e r - s o l u b l e mounting medium and measurements t a k e n u s i n g a compound m i c r o s c o p e w i t h c a l i b r a t e d o c u l a r m i c r o m e t e r . E i g h t measurements o f w a l l t h i c k n e s s were 16 t a k e n a t a p p r o x i m a t e l y e q u a l i n t e r v a l s around each c a p s u l e s e c t i o n . The average w a l l t h i c k n e s s w i t h i n each s e c t i o n was used i n a l l subsequent d a t a a n a l y s e s . 4. V a r i a t i o n i n c a p s u l e w a l l - t h i c k n e s s among p o p u l a t i o n s . I n o r d e r t o examine w a l l t h i c k n e s s d i f f e r e n c e s among a l a r g e number o f egg c a p s u l e s , a l a b o r a t o r y p o p u l a t i o n o f 60 s n a i l s was e s t a b l i s h e d from each s i t e . S n a i l s were sexed by a l l o w i n g each a n i m a l t o a t t a c h t o a r o c k s u r f a c e and t h e n g e n t l y p u l l i n g t h e s h e l l away from t h e body mass. A male c o u l d be i d e n t i f e d by t h e p r e s e n c e o f a p e n i s l a r g e r t h a n i t s r i g h t t e n t a c l e ( r a t h e r t h a n t h e s m a l l e r p e n i s o f t h e female; Palmer, 1984). F i v e male and f i v e female s n a i l s from each s i t e were a l l o c a t e d t o each o f s i x r e p l i c a t e cages (26x16.5x13cm, w i t h 8x16cm lmm-pore mesh p a n e l s i n each s i d e ) and were s u p p l i e d w i t h b a r n a c l e s f o r f o o d . Female s n a i l s were s e l e c t e d so t h a t each r e p l i c a t e cage had a s i m i l a r mean s n a i l s i z e ( G r a p p l e r : X=3.0 cm; Ross I s l e t s : X=2.3 cm; Seppings: X=2.0 cm). A l l cages were kept c o m p l e t e l y . i m m e r s e d i n f l o w i n g s eawater. E v e r y two weeks f r e s h l y l a i d c a p s u l e s were c o l l e c t e d and p l a c e d i n s m a l l m e s h - p a n e l l e d v i a l s . V i a l s were l a b e l l e d , d a t e d , and immersed i n f l o w i n g seawater u n t i l c a p s u l e s were needed. C a p s u l e s c o n t a i n e d i n t h e s e " c a p s u l e v i a l s " were used i n s e v e r a l e x p e r i m e n t s as f o l l o w s . To examine v a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n and among p o p u l a t i o n s , f i v e c a p s u l e s were s e l e c t e d randomly from each r e p l i c a t e v i a l (n=30 c a p s u l e s / s i t e ) . C a p s u l e s were 17 measured i n d i v i d u a l l y and marked a t a p o i n t 70% a l o n g t h e l e n g t h o f t h e c a p s u l e chamber w i t h a f i n e S t a e d t l e r Lumocolour pen. P r e v i o u s d a t a on w a l l t h i c k n e s s v a r i a t i o n w i t h i n a c a p s u l e i n d i c a t e d t h a t c a p s u l e s were t h i n n e s t and w a l l t h i c k n e s s l e a s t v a r i a b l e i n t h i s r e g i o n . C a p s u l e s were emp t i e d by removing t h e p l u g and t h e n s e c t i o n e d on t h e f r e e z e -microtome. S e c t i o n s were c o l l e c t e d o n l y when t h e b l a d e r e a c h e d t h e p o r t i o n o f t h e c a p s u l e chamber marked w i t h i n k . F i v e s e c t i o n s , each 10-12yum t h i c k , were t a k e n f o r each c a p s u l e and one s e c t i o n was chosen f o r measurement. 5. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n and among  c l u t c h e s l a i d by d i f f e r e n t females I n t r a - and i n t e r c l u t c h v a r i a b i l i t y i n w a l l t h i c k n e s s was examined t o d e t e r m i n e i f females w i t h i n a p o p u l a t i o n l a i d c a p s u l e s o f d i f f e r e n t w a l l t h i c k n e s s e s . One c l u t c h o f egg c a p s u l e s was c o l l e c t e d from each o f f i v e r e p l i c a t e cages f o r each o f t h e t h r e e s i t e s t o ensure t h a t a l l c l u t c h e s were l a i d by d i f f e r e n t f e m a l e s . Each c l u t c h was c o l l e c t e d and kept i n i t s own l a b e l l e d m e s h - p a n e l l e d c o n t a i n e r u n t i l c a p s u l e s were needed f o r s e c t i o n i n g . R e p r e s e n t a t i v e c a p s u l e s were s e l e c t e d randomly from each c l u t c h , measured under a d i s s e c t i n g m i c r o s c o p e , and t h e n s e c t i o n e d a t a p o i n t 70 % a l o n g t h e l e n g t h o f t h e c a p s u l e chamber. W a l l t h i c k n e s s measurements were made as d e s c r i b e d p r e v i o u s l y . 6. V a r i a t i o n i n d r y weight o f c a p s u l e s among p o p u l a t i o n s . Dry w e i g ht measurements o f c a p s u l e s were t a k e n f o r each 18 p o p u l a t i o n t o d e t e r m i n e i f d i f f e r e n c e s among s i t e s c o r r e s p o n d e d t o d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s . F o r each p o p u l a t i o n , r e p r e s e n t a t i v e c a p s u l e s were c o l l e c t e d from each o f s i x r e p l i c a t e c a p s u l e v i a l s . C a p s u l e s were measured and t h e n opened t o remove a l l c o n t e n t s . Stems were removed from c a p s u l e s t o m i n i m i z e v a r i a b i l i t y i n weight among c a p s u l e s . C a p s u l e s were r i n s e d t w i c e i n d i s t i l l e d water and t h e n d r i e d f o r 48 h r s a t 75°C. A f t e r d r y i n g , c a p s u l e s were weighed t o O.Olmg. I I I . VARIATION IN CAPSULE CONTENTS AMONG SITES 1. Egg number and volume Egg c a p s u l e c o n t e n t s were examined t o d e t e r m i n e i f t h e number o r s i z e o f eggs p e r c a p s u l e d i f f e r e d w i t h p o p u l a t i o n d i f f e r e n c e s i n c a p s u l e s t r u c t u r e . Three newly l a i d c a p s u l e s were c o l l e c t e d from each o f s i x r e p l i c a t e c a p s u l e v i a l s f o r each s i t e (18 c a p s u l e s / s i t e ) . C a p s u l e s were measured, s l i c e d open, and t h e i r c o n t e n t s washed w i t h f i l t e r e d seawater i n t o a s m a l l p e t r i d i s h . As n u r s e eggs t e n d e d t o clump t o g e t h e r , eggs were g e n t l y a g i t a t e d a p a r t w i t h a p i p e t t e . A l l n u r s e eggs and embryos w i t h i n a c a p s u l e were counted. B e f o r e t h e s e c o u n t s were made, however, embryos were examined t o ensure t h a t t h e y had not advanced p a s t t h e second v e l i g e r s t a g e . LeBoeuf (1971) and Lyons and S p i g h t (1973) have n o t e d t h a t once p a s t t h i s d e v e l o p m e n t a l s t a g e , embryos become c a p a b l e o f f e e d i n g on e n c a p s u l a t e d n u r s e eggs. As egg s i z e w i t h i n a c a p s u l e was r e l a t i v e l y c o n s t a n t , o n l y f i v e eggs were sampled from each c a p s u l e . Length and 19 w i d t h measurements were t a k e n f o r each egg. Egg volume was e s t i m a t e d by u s i n g t h e f o r m u l a f o r a p r o l a t e e l l i p s o i d as d e s c r i b e d p r e v i o u s l y . 2. Number and s i z e o f h a t c h i n g s n a i l s . To de t e r m i n e i f t h e r e was a d i f f e r e n c e i n t h e number o f embryos p e r c a p s u l e from each s i t e , embryos were a l l o w e d t o h a t c h i n t h e l a b o r a t o r y . E n c a p s u l a t e d l a r v a e d e v e l o p e d w i t h i n t h e i r c a p s u l e v i a l s u n t i l development n e a r e d c o m p l e t i o n . At t h i s p o i n t , i n d i v i d u a l c a p s u l e s from each s i t e were p l a c e d i n t h e i r own m e s h - p a n e l l e d v i a l s (600 yUm mesh pore) and submerged i n seawater u n t i l t h e embryos h a t c h e d . C a p s u l e s were checked e v e r y two days and as soon as an embryo had emerged, t h e c a p s u l e was measured and emptied o f a l l r e m a i n i n g embryos. A l l l i v e embryos were cou n t e d and t h e i r s h e l l - l e n g t h s measured. IV. CAPSULE STRENGTH MEASUREMENTS 1. R e s i s t a n c e t o p u n c t u r i n g T h i s i n d e x d e t e r m i n e d t h e r e s i s t a n c e o f c a p s u l e w a l l s t o p u n c t u r i n g and was based on P e r r o n ' s (1981) p r o c e d u r e f o r Conus egg c a p s u l e s . Newly l a i d N u c e l l a e m a r g i n a t a c a p s u l e s were t a k e n from t h e i r r e s p e c t i v e c a p s u l e v i a l s , measured, and t h e n marked a t a p o i n t 70% a l o n g t h e l e n g t h o f t h e c a p s u l e chamber. C a p s u l e s were t h e n b i s e c t e d by c u t t i n g a l o n g t h e two seams o f t h e c a p s u l e chamber and t h e i r c o n t e n t s d i s c a r d e d . Each c a p s u l e h a l f was mounted i n d i v i d u a l l y between two p i e c e s o f p l e x i g l a s s (8.5x5cm) and o r i e n t a t e d such t h a t a 1mm d i a . 20 h o l e i n each p i e c e o f p l e x i g l a s s was p o s i t i o n e d d i r e c t l y over t h e marked r e g i o n o f t h e c a p s u l e chamber ( F i g . 3 a ) . Care was t a k e n t o i n s u r e t h a t t h e r e were no f o l d s o r c r e a s e s i n t h e c a p s u l e s e c t i o n and t h a t i t remained m o i s t . A p u n c t u r i n g d e v i c e , c o n s i s t i n g o f a b l u n t - e n d e d n e e d l e (0.36 mm^  area) mounted beneath a f l a t w e i g h i n g pan, was p o s i t i o n e d over t h e p l e x i g l a s s such t h a t t h e n e e d l e r e s t e d a t r i g h t a n g l e s t o t h e exposed c a p s u l e w a l l . F i v e - g r a m w e i g h t s were added t o t h e w e i g h i n g pan u n t i l t h e n e e d l e p u n c t u r e d t h e c a p s u l e w a l l . Each c a p s u l e p i e c e was o n l y p u n c t u r e d once. 2. R e s i s t a n c e t o s q u e e z i n g T h i s i n d e x o f c a p s u l e s t r e n g t h measured t h e f o r c e needed t o squeeze t h e p l u g out o f i n t a c t c a p s u l e s . Shore c r a b s were o f t e n seen t o r u p t u r e N u c e l l a e m a r g i n a t a egg c a p s u l e s by s q u e e z i n g them i n t h e i r c h e l a e . L a b o r a t o r y c a p s u l e s were c o l l e c t e d from r e p l i c a t e c a p s u l e v i a l s and measured. I n d i v i d u a l c a p s u l e s were mounted w i t h " S u p e r g l u e " onto a m e t a l p l a t e , w h i c h was t h e n b o l t e d t o a v e r t i c a l p i e c e o f p l e x i g l a s s ( F i g . 3 b ). S t r a i n gauges, g l u e d t o t h e p l e x i g l a s s , were c o n n e c t e d t o an a m p l i f i e r and c h a r t r e c o r d e r . A second m e t a l p l a t e was a t t a c h e d t o a s p i n d l e so t h a t t h i s p l a t e c o u l d be hand-cranked towards t h e mounted c a p s u l e . A c h a r t r e c o r d e r p r o v i d e d a r e c o r d o f t h e f o r c e r e q u i r e d t o r u p t u r e t h e egg c a p s u l e . T h i s system was c a l i b r a t e d w i t h known w e i g h t s . 21 a) Weights Plexiglass Plates Piece of Capsule Wall Loading Pan Stand Blunt Pin Clamp b ) Capsule Metal Plate Plexiglass with Strain Gauge Metal Plate immmmimmmn. Hand Crank I'i-x-l'i-iji-i-x-w Metal Spindle FIGURE 3. Techniques used to compare the strength of egg capsules: a) puncturing method used to cal c u l a t e the force required to pierce capsule walls, and b) squeezing method used to determine the resistance of in t a c t capsules to squeezing forces. 22 RESULTS. I . DIFFERENCES IN SNAIL MORPHOLOGY AMONG SITES The s i z e and shape o f s n a i l s d i f f e r e d e x t e n s i v e l y among st u d y s i t e s ( F i g . 4 ) . N u c e l l a e m a r g i n a t a from Seppings I s l a n d , t h e most wave-exposed a r e a , had t h e s m a l l e s t mean s i z e (X=1.9cm) and t h e l o w e s t l e n g t h / a p e r t u r e r a t i o (X L/ A+S.D.=1.42+0.05). S n a i l s c o l l e c t e d from t h e l e s s exposed Ross I s l e t s s i t e had a g r e a t e r range o f s h e l l l e n g t h s , a l a r g e r mean s i z e , (X=2.1cm), and p r o p o r t i o n a l l y l a r g e r l e n g t h / a p e r t u r e r a t i o s t h a n s n a i l s from Seppings (X L/ A+S.D.=l.53+0.07). W a v e - s h e l t e r e d s n a i l s from G r a p p l e r I n l e t were i n t e r m e d i a t e i n body shape between Seppings and Ross I s l e t s s n a i l s (X L/ A+S.D.=1.49+0.06), but had t h e l a r g e s t s h e l l l e n g t h s o f a l l t h r e e p o p u l a t i o n s (X=2.7cm). These d i f f e r e n c e s i n t h e average s h e l l l e n g t h o f s n a i l s showed an ob v i o u s r e l a t i o n s h i p w i t h wave-exposure, w i t h s h e l l s i z e i n c r e a s i n g from wave-exposed t o w a v e - s h e l t e r e d s h o r e s . Changes i n l e n g t h / a p e r t u r e r a t i o s among s i t e s d i d not appear t o r e f l e c t changes i n wave-exposure, as G r a p p l e r s n a i l s d i d not f o l l o w t h e same t r e n d i n body shape as Seppings and Ross I s l e t s n a i l s . I I . CAPSULE MORPHOLOGY 1• R e l a t i o n s h i p between s n a i l s i z e and c a p s u l e s i z e F i g u r e 5 shows t h e r e l a t i o n s h i p between c a p s u l e s i z e and s n a i l s h e l l - l e n g t h w i t h i n and among p o p u l a t i o n s . W i t h i n each p o p u l a t i o n l a r g e r females produced s i g n i f i c a n t l y l o n g e r egg 23 16-1 2 -8-4-12-> Z3 o LL) SEPPINGS ISLAND ROSS ISLETS h n GRAPPLER INLET 1 2 -4-m h 1.0 1.5 2.0 2.5 3.0 3.5 SNAIL LENGTH (cm) 4.0 FIGURE 4. Size-frequency histograms of 50 s n a i l s c o l l e c t e d from each study s i t e i n March, 1988. Snails smaller than 10 mm i n s h e l l length were not included. Wave-exposure l e v e l s increased from Grappler Inlet to Seppings Island. The mean s h e l l lengths of s n a i l s were: 1.9, 2.1 and 2.7 cm for Seppings, Ross I s l e t s , and Grappler Inlet s n a i l s , r e s p e c t i v e l y . 24 SNAIL LENGTH ( c m ) FIGURE 5. Relationship between capsule body length and s n a i l length f o r laboratory l a i d capsules f o r each study s i t e . Snails smaller than 1.7, 2.1 and 2.7 cm from Seppings, Ross I s l e t s and Grappler populations d i d not spawn i n the laboratory. Regression equations f o r each s i t e are: Seppings: Y = 3.185X - 0.111, r =0.740, n = 23; Ross I s l e t s : Y = 3.139X - 1.232, r = 0.867, n = 23; Grappler I n l e t : Y = 2.206 + 1.481, r = 0.650, n = 20. 25 c a p s u l e s t h a n s m a l l e r f e m a l e s . The s l o p e s o f t h e s e r e l a t i o n s h i p s d i d not v a r y s i g n i f i c a n t l y among s i t e s (ANCOVA f o r s l o p e s ; F=1.20, p>0.25), however, s l o p e e l e v a t i o n s d i f f e r e d s i g n i f i c a n t l y between t h e Seppings and Ross I s l e t s p o p u l a t i o n s (ANCOVA f o r e l e v a t i o n s ; F=14.84, p<0.001), w i t h Seppings s n a i l s p r o d u c i n g d i s p r o p o r t i o n a t e l y l a r g e c a p s u l e s . S u b s t a n t i a l d i f f e r e n c e s were a l s o e v i d e n t i n t h e s i z e o f spawning s n a i l s from each l a b o r a t o r y p o p u l a t i o n , as shown i n F i g u r e 5. A l t h o u g h l a b o r a t o r y s n a i l p o p u l a t i o n s g r e a t l y o v e r l a p p e d i n s i z e range (Seppings: 1.4-2.2cm; Ross I s l e t s : 1.4-2.9cm; G r a p p l e r : 1.8-3.5cm), t h e range i n s i z e o f spawning females from each p o p u l a t i o n b a r e l y c o i n c i d e d . The s m a l l e s t s n a i l s t o spawn i n t h e l a b o r a t o r y were 1.7, 2.1, and 2.7 cm i n s h e l l l e n g t h f o r Seppings, Ross I s l e t s , and G r a p p l e r p o p u l a t i o n s , r e s p e c t i v e l y . T h i s s u g g e s t s t h a t t h e onset o f r e p r o d u c t i v e m a t u r i t y v a r i e d among s i t e s , w i t h wave-exposed s n a i l s m a t u r i n g a t a much s m a l l e r s i z e t h a n w a v e - s h e l t e r e d s n a i l s . S n a i l s i z e was a l s o r e f l e c t e d i n o t h e r c a p s u l a r d i m e n s i o n s , as l a r g e r s n a i l s p roduced c a p s u l e s w i t h g r e a t e r chamber volumes t h a n s m a l l e r s n a i l s ( F i g . 6 ) . Comparisons among s i t e s showed t h a t , a l t h o u g h t h e s l o p e s o f t h e s e r e l a t i o n s h i p s d i d not d i f f e r s i g n i f i c a n t l y (ANCOVA f o r s l o p e s ; F=0.57, p>0.25), Seppings and Ross I s l e t s s n a i l s l a i d c a p s u l e s w i t h l a r g e r chamber volumes t h a n s i m i l a r - s i z e d s n a i l s from G r a p p l e r I n l e t (ANCOVA; F=5.56, p<0.01). As chamber volumes are known t o r e f l e c t t h e number o f eggs c o n t a i n e d w i t h i n t h e c a p s u l e s ( S p i g h t and Emlen, 1976), such d i f f e r e n c e s i n c a p s u l e 26 SNAIL LENGTH ( c m ) FIGURE 6. Relationship between capsule-chamber volume and s n a i l length f o r laboratory populations established from each study s i t e . Regression equations f o r each s i t e are: Seppings: Y = 18.245X - 15.257, r = 0.628, n = 23; Ross I s l e t s : Y = 28.193X - 41.722, r = 0.749, n = 23; Grappler, Y = 24.006X - 37.710, r = 0.690, n = 20. 27 s i z e can a l s o i n d i c a t e i m p o r t a n t d i f f e r e n c e s i n t h e f e c u n d i t y o f t h e s e p o p u l a t i o n s . 2. Micromorphology o f N u c e l l a e m a r g i n a t a egg c a p s u l e s The m i c r o s t r u c t u r e o f IsL. e m a r g i n a t a egg c a p s u l e s i s shown i n F i g u r e 7. C a p s u l e w a l l s o f N. e m a r g i n a t a c o n s i s t e d o f t h r e e d i s c r e t e laminae (L^, L 2 and L 3 ) and were s i m i l a r i n s t r u c t u r e t o t h e c a p s u l e w a l l s o f o t h e r m u r i c i d s ( S u l l i v a n and Maugel, 1984; D'Asaro, 1988; F i g . 7A,B). A l l measurements o f c a p s u l e w a l l t h i c k n e s s were t a k e n s o l e l y from t h e m i d d l e l a m i n a ( L 2 )/ as t h i s was t h e t h i c k e s t p a r t o f t h e c a p s u l e w a l l . T h i s l a m i n a c o n s i s t e d a dense, f i b r o u s m i d d l e l a y e r ( L 2 b ) , w h i c h was sandwiched by two t r a n s p a r e n t , homogeneous l a y e r s {l>2a a n c * L 2 c ^ • T ^ e innermost c a p s u l e l a m i n a (L3) l i n e d t h e c a p s u l e chamber and e n c l o s e d d e v e l o p i n g embryos, n u r s e eggs, and i n t r a c a p s u l a r f l u i d . S e c t i o n s i n t h e a p i c a l r e g i o n o f t h e c a p s u l e i n d i c a t e d t h a t t h i s l a m i n a was a c t u a l l y c o n n e c t e d t o t h e c a p s u l e p l u g and appeared t o be composed o f a s i m i l a r m a t e r i a l ( F i g . 7D). The s t r u c t u r e o f t h e s e c a p s u l e w a l l s was not homogeneous t h r o u g h o u t t h e c a p s u l e , as i s shown by l o n g i t u d i n a l s e c t i o n s t h r o u g h t h e stem and c a p s u l a r - p l u g r e g i o n s ( F i g . 7C,D). 3. I n t r a c a p s u l a r v a r i a t i o n i n w a l l t h i c k n e s s . S e r i a l s e c t i o n s a l o n g t h e c a p s u l e chamber o f N u c e l l a  e m a r g i n a t a showed c o n s i d e r a b l e v a r i a t i o n i n w a l l t h i c k n e s s ( F i g . 8 ) . W i t h i n i n d i v i d u a l c a p s u l e s , w a l l s t e n d e d t o be t h i c k e s t i n t h e p l u g and stem r e g i o n s and t h i n n e s t about 75% FIGURE 7. Microstructure of Nucella emarginata egg capsules: a) transverse section 70 % along the chamber of a capsule from Ross I s l e t s (mean thickness = 60juun), b) transverse section 70% along the chamber of a capsule from Grappler Inlet (mean thickness = 90^wm), c) l o n g i t u d i n a l section through the stem region of a N^ . emarginata capsule, d) l o n g i t u d i n a l section th r o u g h t h e plug r e g i o n of a emarginata c a p s u l e . Outer ( L ^ ) , middle (I^) and inner ( L 3 ) capsule wall laminae are indicated, as are the three component layers (l>2a, L 2 b , L 2 c ^ °^ t h e n^-ddle lamina. The capsule plug (P) and stem (St) are also shown. 29 180 40 -I 1 1 1 1 1 1 — 1 — i 1 1 0 10 20 30 40 50 60 70 80 90 100 POSITION ALONG C A P S U L E CHAMBER {%) FIGURE 8. V a r i a t i o n i n wall thickness along the capsule chamber of f i e l d -c o l l e c t e d Nucella emarginata capsules from Grappler I n l e t , Ross I s l e t s , and Seppings Island. Values are expressed as X + 1 S.E. f o r n = 8 capsules from each population. 30 a l o n g t h e c a p s u l e chamber. A l t h o u g h changes i n c a p s u l e w i d t h a l s o o c c u r r e d a l o n g t h e l e n g t h o f t h e chamber, t h e s e d i d not appear t o c o r r e s p o n d w i t h v a r i a t i o n i n w a l l t h i c k n e s s ( F i g . 9 ) . S e c t i o n s t h r o u g h t h e w a l l s o f f i e l d - c o l l e c t e d N u c e l l a  e m a r g i n a t a c a p s u l e s r e v e a l e d o b v i o u s d i f f e r e n c e s i n t h i c k n e s s among t h e G r a p p l e r I n l e t , Ross I s l e t s , and Seppings I s l a n d p o p u l a t i o n s . Comparisons o f w a l l t h i c k n e s s d a t a from a p o i n t 70% a l o n g t h e chamber chamber i n d i c a t e d t h a t c a p s u l e s from Ross I s l e t s were s i g n i f i c a n t l y t h i n n e r t h a n c a p s u l e s from Seppings and G r a p p l e r (means o f 61, 80 and 81pm, r e s p e c t i v e l y ; ANOVA: F=29.9, p<0.001; F i g . 7A,B). C a p s u l e s c o l l e c t e d from G r a p p l e r and Seppings d i d not show any s i g n i f i c a n t d i f f e r e n c e s i n w a l l t h i c k n e s s . T h e r e f o r e , w a l l - t h i c k n e s s v a r i a t i o n among s i t e s d i d not appear t o r e f l e c t d i f f e r e n c e s i n wave-exposure, as c a p s u l e w a l l s were most s i m i l a r between w a v e - s h e l t e r e d and wave-exposed p o p u l a t i o n s . 4. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s among l a b o r a t o r y  p o p u l a t i o n s C a p s u l e w a l l t h i c k n e s s a l s o v a r i e d among l a b o r a t o r y p o p u l a t i o n s w i t h Ross I s l e t c a p s u l e s b e i n g t h e t h i n n e s t , and Seppings and G r a p p l e r I n l e t c a p s u l e s t h e t h i c k e s t (X=60, 78, and 83^um, f o r Ross, Seppings, and G r a p p l e r , r e s p e c t i v e l y ; F i g . 1 0 ) . These d i f f e r e n c e s were s i g n i f i c a n t among a l l t h r e e l a b o r a t o r y p o p u l a t i o n s (ANOVA; F=81.32, p<0.001) and c o r r e s p o n d e d w e l l w i t h p r e v i o u s r e s u l t s f o r f i e l d - c o l l e c t e d c a p s u l e s . Hence, t h e r e was no a p o s t e r i o r i r e a s o n t o s u s p e c t t h a t s n a i l s p r o d u c e d d i f f e r e n t t h i c k n e s s e s o f c a p s u l e s i n t h e POSITION ALONG CAPSULE CHAMBER {%) FIGURE 9. V a r i a t i o n i n wall thickness and capsule width within one Nucella  emarginata capsule from Grappler I n l e t . Wall thickness values are the mean + 1 S.E. of 8 measurements taken from within each section. Capsule width values represent the maximum width at each section along the capsule chamber. 32 E CO to U J o X LxJ _ J Z ) CO Q . < 1 1 0 100 90-\ 8 0 7 0 6 0 5 0 4 0 G R A P P L E R * R O S S • S E P P I N G S o O \7 o o o o o * o o o o o « o . • • • ! • 4 .0 5.0 6.0 7.0 8.0 C A P S U L E BODY LENGTH ( m m ) FIGURE 10 V a r i a t i o n i n capsule wall thickness with capsule body length f o r 30 Nucella emarginata capsules from each laboratory population. Each value represents a mean of 8 measurements taken from one representative section at a point 70% along the capsule-chamber. 33 l a b o r a t o r y as compared w i t h t h e f i e l d . I n f a c t , s n a i l s s t i l l c o n t i n u e d t o produce t h e i r t h i c k - or t h i n - w a l l e d c a p s u l e s even a f t e r 5 months i n t h e l a b o r a t o r y . These d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s appeared t o r e s u l t from v a r i a t i o n i n t h e t h i c k n e s s o f a l l t h r e e component l a y e r s o f t h e m i d d l e l a m i n a , r a t h e r t h a n i n one component a l o n e . Component l a y e r s v a r i e d i n t h e p r o p o r t i o n o f 2:7:1 f o r L 2 a , l>2b a n c * L 2 c r e s p e c t i v e l y , r e g a r d l e s s o f t h e a b s o l u t e t h i c k n e s s o f c a p s u l e w a l l s . No r e l a t i o n s h i p was e v i d e n t between w a l l t h i c k n e s s and c a p s u l e l e n g t h w i t h i n each p o p u l a t i o n ( F i g . 1 0 ) . S i n c e c a p s u l e l e n g t h was r e l a t e d t o female s h e l l l e n g t h ( F i g . 5 ) , d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s w i t h i n each p o p u l a t i o n were p r o b a b l y not r e l a t e d t o female s i z e . S i t e d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s a l s o d i d not appear t o r e f l e c t v a r i a t i o n i n s n a i l s i z e , as s m a l l Seppings s n a i l s (X=1.9 cm) and l a r g e G r a p p l e r s n a i l s (X=2.7cm)' b o t h produced t h i c k - w a l l e d c a p s u l e s . 5. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n and between  c l u t c h e s l a i d by d i f f e r e n t females F i g u r e 11 shows t h e v a r i a t i o n i n w a l l t h i c k n e s s w i t h i n and among c l u t c h e s f o r each l a b o r a t o r y p o p u l a t i o n . C a psule w a l l t h i c k n e s s was found t o v a r y s i g n i f i c a n t l y among c l u t c h e s w i t h i n each p o p u l a t i o n (ANOVA; G r a p p l e r , F=3.44, P=0.02; Seppings, F=47.52, P<0.001; Ross, F=32.05, P<0.001). V a r i a b i l i t y i n c a p s u l e w a l l t h i c k n e s s among c l u t c h e s , however, d i d not obscure t h e s i t e d i f f e r e n c e s i n w a l l t h i c k n e s s found 34 105 E 3 CO CO o < LlJ CO < o S E P P I N G S R O S S ISLETS G R A P P L E R FIGURE 11. V a r i a t i o n i n wall thickness within and between clutches of Nucella emarginata capsules. Five clutches were sampled from each laboratory population with n = 6 capsules/clutch, n = 4 capsules/clutch, and n = 6 capsules/clutch for Seppings, Ross I s l e t s , and Grappler populations, r e s p e c t i v e l y . Each data point represents the mean of 8 measurements taken from one representative section at a point 70 % along the capsule chamber. Each v e r t i c a l group of points represents one c l u t c h of capsules. 35 p r e v i o u s l y . Ross I s l e t c a p s u l e s ranged i n w a l l t h i c k n e s s from 5 0 - 7 6 ^ , w h i l e Seppings and G r a p p l e r c a p s u l e s ranged from 71-92jum and 72-102yum, r e s p e c t i v e l y . 6. V a r i a t i o n i n d r y weight o f c a p s u l e s among; s i t e s A s i g n i f i c a n t r e l a t i o n s h i p was found between d r y weight o f t h e c a p s u l a r case and c a p s u l e body l e n g t h f o r each l a b o r a t o r y p o p u l a t i o n o f s n a i l s ( F i g . 1 2 ) . The s l o p e s o f t h e s e r e l a t i o n s h i p s were not s i g n i f i c a n t l y d i f f e r e n t (ANCOVA f o r s l o p e s ; F=1.20, p>0.25), but t h e e l e v a t i o n s d i d v a r y s i g n i f i c a n t l y (ANCOVA f o r e l e v a t i o n s ; F=50.52; p<0.001). These d a t a c o r r e s p o n d e d w e l l w i t h t h e a l r e a d y known d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s e s among p o p u l a t i o n s , as t h i n - w a l l e d Ross I s l e t c a p s u l e s were found t o weigh s i g n i f i c a n t l y l e s s t h a n t h i c k e r - w a l l e d c a p s u l e s from t h e o t h e r two s i t e s . F o r example, a 6.5 mm-long egg c a p s u l e from t h e Ross I s l e t s weighed 24% l e s s t h a n a c a p s u l e o f t h e same l e n g t h from G r a p p l e r I n l e t and 16% l e s s t h a n one from Seppings ( F i g . 1 2 ) . G r a p p l e r c a p s u l e s were a l s o found t o be s i g n i f i c a n t l y h e a v i e r t h a n Seppings c a p s u l e s , w h i c h a g a i n r e f l e c t e d t h e d i f f e r e n c e s found p r e v i o u s l y i n c a p s u l e w a l l t h i c k n e s s between t h e s e p o p u l a t i o n s . I n summary, t h e r e were o b v i o u s d i f f e r e n c e s i n t h e s i z e and w a l l s t r u c t u r e o f c a p s u l e s among t h e t h r e e p o p u l a t i o n s o f N u c e l l a e m a r g i n a t a . V a r i a t i o n i n c a p s u l a r s i z e was l a r g e 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 s n a i l s h e l l l e n g t h , a l t h o u g h , s n a i l s from Seppings I s l a n d were found t o produce p r o p o r t i o n a l l y l a r g e r c a p s u l e s p e r u n i t s h e l l l e n g t h t h a n 36 Q 1.0-1 I : 1 1 1 1 1 1 1 4 .5 5 .0 5 .5 6.0 6 .5 7.0 7 .5 8 .0 8 .5 9 .0 C A P S U L E BODY LENGTH ( m m ) FIGURE 12. Dry weight of empty capsular cases as a function of capsule body length f o r each laboratory population. Each data point represents one capsule. Regression equations f o r each s i t e are: Seppings: Y = 0.569X -1.429, r = 0.837, n = 27; Ross I s l e t s , Y = 0.414X - 0.792, r = 0.723, n = 33; Grappler In l e t , Y = 0.539X - 1.007, r = 0.860, n = 28. 37 s n a i l s from G r a p p l e r I n l e t o r Ross I s l e t s . The s t r u c t u r e o f c a p s u l e w a l l s a l s o d i f f e r e d among s i t e s , w i t h Ross I s l e t s s n a i l s p r o d u c i n g s i g n i f i c a n t l y t h i n n e r - w a l l e d c a p s u l e s t h a n G r a p p l e r and Seppings s n a i l s . V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s d i d not appear t o r e f l e c t d i f f e r e n c e s i n c a p s u l e s i z e , female s i z e , o r i n c r e a s i n g wave-exposure l e v e l s . However, t h e d r y weight o f c a p s u l a r cases d i f f e r e d among p o p u l a t i o n s and c o r r e s p o n d e d w i t h d i f f e r e n c e s i n w a l l t h i c k n e s s . Hence, f o r a g i v e n c a p s u l e s i z e , s n a i l s from Ross I s l e t s a l l o c a t e d s i g n i f i c a n t l y l e s s m a t e r i a l t o t h e i r egg c a p s u l e s t h a n d i d s n a i l s from Seppings I s l a n d o r G r a p p l e r I n l e t . I I I . VARIATION IN CAPSULE CONTENTS AMONG SITES 1. Egg number and egg volume The r e l a t i o n s h i p between egg number ( i n c l u d i n g b o t h n u r s e eggs and embryos) p e r c a p s u l e and c a p s u l e volume i s shown f o r each p o p u l a t i o n i n F i g u r e 13. Comparisons among s i t e s i n d i c a t e d t h a t t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n t h e t o t a l number o f eggs a l l o c a t e d t o Seppings, Ross, and G r a p p l e r c a p s u l e s . N e i t h e r t h e s l o p e s (ANCOVA f o r s l o p e s : F=0.65, p>0.50) nor e l e v a t i o n s (ANCOVA f o r e l e v a t i o n s : F=0.36; p>0.50) o f t h e s e r e l a t i o n s h i p s d i f f e r e d s i g n i f i c a n t l y among p o p u l a t i o n s . The s i z e o f eggs d i d not d i f f e r s i g n i f i c a n t l y among s i t e s e i t h e r . A l t h o u g h Ross I s l e t c a p s u l e s c o n t a i n e d s l i g h t l y l a r g e r eggs t h a n G r a p p l e r or Seppings c a p s u l e s (X egg volume =40.5xl0" 4mm 3, 39.6xl0" 4mm 3, and 3 8 . 1 x l 0 - 4 mm3, r e s p e c t i v e l y ) , 38 C A P S U L E V O L U M E (/xl) FIGURE 13. Relationship between the number of eggs per capsule and the volume of the capsule-chamber f o r Seppings, Ross I s l e t s , and Grappler capsules. Counts of eggs include both developing embryos and non-developing nurse eggs. Regression equations f o r each population are: Seppings: Log Y = 0.676 Log X + 1.954, r = 0.742, n = 18; Ross I s l e t s : Log Y = 0.669 Log X + 1.962, r = 0.583, n = 18; Grappler: Log Y = 0.492 Log X + 2.192, r = 0.640, n = 18. 39 t h e s e d i f f e r e n c e s were not s i g n i f i c a n t (ANOVA: F=1.55, P>0.22). T h e r e f o r e , t h e r e was no e v i d e n c e o f independent s e l e c t i o n f o r egg number or egg s i z e i n t h e s e p o p u l a t i o n s . 2. Number and s i z e o f hatching- s n a i l s G r a p p l e r I n l e t c a p s u l e s were found t o c o n t a i n s l i g h t l y fewer embryos p e r u n i t volume t h a n s i m i l a r - s i z e d c a p s u l e s from Seppings I s l a n d and Ross I s l e t s (means o f 14, 17 and 19 embryos f o r a 30jul c a p s u l e from G r a p p l e r , Seppings and Ross I s l e t s , r e s p e c t i v e l y ) . However, t h e r e l a t i o n s h i p s between embryo number and c a p s u l e volume d i d not d i f f e r s i g n i f i c a n t l y among s i t e s (ANCOVA f o r s l o p e s , F=0.76, p>0.25; and f o r e l e v a t i o n s , F=0.82, p>0.25). The mean s i z e o f j u v e n i l e s h a t c h i n g from c a p s u l e s was i n v e r s e l y p r o p o r t i o n a l t o t h e number o f embryos c o n t a i n e d w i t h i n each c a p s u l e ( F i g . 14). Thus, l a r g e j u v e n i l e s emerged from c a p s u l e s c o n t a i n i n g r e l a t i v e l y few embryos, w h i l e s m a l l j u v e n i l e s emerged from c a p s u l e s c o n t a i n i n g many embryos. Because embryos a r e known t o compete f o r n u r s e eggs d u r i n g t h e i r development ( S p i g h t , 1976; R i v e s t , 1983), d i f f e r e n c e s i n t h e s e r e l a t i o n s h i p s among p o p u l a t i o n s c o u l d i n d i c a t e v a r i a t i o n i n e i t h e r : 1) t h e number o f n u r s e eggs a p p o r t i o n e d t o embryos w i t h i n c a p s u l e s , o r 2) t h e number o f embryos a l l o c a t e d t o each c a p s u l e ( E t t e r , 1987). However, such d i f f e r e n c e s were not found (comparisons among p o p u l a t i o n s i n d i c a t e d t h a t s l o p e s (ANCOVA f o r s l o p e s : F=0.93, P>0.5) and e l e v a t i o n s (ANCOVA f o r e l e v a t i o n s : F=3.2, P=0.01) were not s i g n i f i c a n t l y d i f f e r e n t ) . I n summary, t h e r e f o r e , t h e number o f eggs and embryos p e r u n i t 40 N U M B E R OF E M B R Y O S P E R C A P S U L E FIGURE 14. Mean hatching s i z e of embryos as a function of the number of embryos contained within each capsule f o r Seppings, Ross I s l e t s and Grappler populations. Regression equations f o r each population are: Seppings: Log Y = -0.199 Log X + 0.321, r=0.636, n=19; Ross I s l e t s : Log Y = -0.228 Log X + 0.322, r=0.895, n=16; Grappler I n l e t : Log Y = -0.134 Log X + 0.248, r=0.614, n=18. 41 volume d i d not v a r y among c a p s u l e s from Seppings I s l a n d , Ross I s l e t s and G r a p p l e r I n l e t . IV. CAPSULE STRENGTH MEASUREMENTS 1. R e s i s t a n c e t o p u n c t u r i n g The f o r c e r e q u i r e d t o p u n c t u r e c a p s u l e s d i f f e r e d among t h e t h r e e l a b o r a t o r y p o p u l a t i o n s (X+S.D.=6.18+0.66 Mega Newtons/m 2 (n=10), 5.17+0.70 MN/m2 (n=15), and 4.92+0.46 MN/m: (n=10), f o r G r a p p l e r I n l e t , Ross I s l e t and Seppings c a p s u l e s , r e s p e c t i v e l y ) . G r a p p l e r I n l e t c a p s u l e w a l l s appeared t o be th e s t r o n g e s t , as t h e y r e q u i r e d s i g n i f i c a n t l y g r e a t e r p u n c t u r i n g f o r c e s t h a n d i d Ross I s l e t o r Seppings c a p s u l e s (ANOVA, F=11.77, P<0.001; p<0.05, Tukey M u l t i p l e Comparison T e s t ) . However, Ross I s l e t and Seppings c a p s u l e s d i d not d i f f e r s i g n i f i c a n t l y i n p u n c t u r i n g r e s i s t a n c e (p>0.05, Tukey M.C.T.). Hence, t h i c k - w a l l e d G r a p p l e r I n l e t c a p s u l e s were s t r o n g e r t h a n b o t h t h i c k - w a l l e d Seppings c a p s u l e s and t h i n -w a l l e d Ross I s l e t c a p s u l e s . 2. R e s i s t a n c e t o s q u e e z i n g The f o r c e needed t o r u p t u r e c a p s u l e s by s q u e e z i n g a l s o d i f f e r e d among l a b o r a t o r y p o p u l a t i o n s and f o l l o w e d a t r e n d s i m i l a r t o t h e p r e v i o u s r e s u l t s (X+S.D.= 14.5+4.3 N (n=19), 7.5+2.7 N (n=21), and 9.7+3.9 N (n=15), f o r G r a p p l e r , Ross I s l e t s and Seppings c a p s u l e s , r e s p e c t i v e l y ) . G r a p p l e r c a p s u l e s r e q u i r e d s i g n i f i c a n t l y l a r g e r f o r c e s t o r u p t u r e t h e c a p s u l a r p l u g t h a n d i d Ross I s l e t and Seppings c a p s u l e s (ANOVA, F=18.67, P<0.001; p<0.05, Tukey M.C.T.). A l t h o u g h 42 Seppings c a p s u l e s were s l i g h t l y more r e s i s t a n t t o s q u e e z i n g t h a n Ross I s l e t c a p s u l e s , t h i s d i f f e r e n c e was not s i g n i f i c a n t (p>0.05, Tukey M.C.T.). In summary, G r a p p l e r I n l e t c a p s u l e s were s i g n i f i c a n t l y more r e s i s t a n t t o p u n c t u r i n g and s q u e e z i n g f o r c e s t h a n c a p s u l e s from Seppings I s l a n d and Ross I s l e t s . T h i s c o r r e s p o n d e d t o t h e f a c t t h a t G r a p p l e r c a p s u l e s a l s o had t h e t h i c k e s t c a p s u l e w a l l s . Seppings c a p s u l e s , however, which were a l s o t h i c k - w a l l e d , were not s i g n i f i c a n t l y more r e s i s t a n t t o p u n c t u r i n g o r s q u e e z i n g f o r c e s t h a n were t h i n - w a l l e d Ross I s l e t c a p s u l e s . 43 DISCUSSION Advantages o f t h i c k , s t r o n g c a p s u l e w a l l s A l t h o u g h numerous s t u d i e s have documented 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 t h e t h i c k n e s s and s t r e n g t h o f c a p s u l e w a l l s i n g a s t r o p o d s ( P e r r o n , 1981; P e r r o n and Corpuz, 1982; P e c h e n i k , 1983), as y e t t h e r e i s l i t t l e e v i d e n c e t o i n d i c a t e t h a t t h i c k -w a l l e d c a p s u l e s a c t u a l l y p r o t e c t d e v e l o p i n g embryos b e t t e r t h a n t h i n - w a l l e d c a p s u l e s . I n f a c t , P e c h e n i k (1983) found t h a t r a t e o f s a l t movement a c r o s s t h e w a l l s o f N u c e l l a  l a m e l l o s a , N. l a p i l l u s and N. l i m a c a p s u l e s d i d not d i f f e r i n accordance w i t h c a p s u l e w a l l t h i c k n e s s . Thus, t h e s e r e s u l t s suggest t h a t r a t e o f o s m o t i c change and d e s i c c a t i o n might not d i f f e r among t h i c k - o r t h i n - w a l l e d c a p s u l a r s t r u c t u r e s i n t h e r e l a t e d s p e c i e s N u c e l l a e m a r g i n a t a . The o n l y e v i d e n c e t o s u p p o r t t h e h y p o t h e s i s t h a t t h i c k -w a l l e d c a p s u l e s a re more p r o t e c t i v e t h a n t h i n - w a l l e d c a p s u l e s comes from p o s i t i v e c o r r e l a t i o n s found between c a p s u l e s t r e n g t h (as measured by t h e p u n c t u r e - r e s i s t a n c e o f c a p s u l e w a l l s ) , c a p s u l e w a l l t h i c k n e s s , and d e v e l o p m e n t a l t i m e o f e n c a p s u l a t e d embryos among Conus s p e c i e s ( P e r r o n , 1981; P e r r o n and Corpuz, 1982). P e r r o n (1981) a l s o found t h a t t h e p r o p o r t i o n o f r e p r o d u c t i v e energy i n v e s t e d i n c a p s u l e w a l l s i n c r e a s e d from 20 t o 47% w i t h an i n c r e a s e i n e n c a p s u l a t e d development t i m e from 11 t o 2 6 days i n Conus s p e c i e s . These s t u d i e s by P e r r o n (1981) and P e r r o n and Corpuz (1982) have p r o v i d e d a t l e a s t some d a t a t o suggest t h a t s t r o n g , t h i c k -44 w a l l e d c a p s u l e s may r e f l e c t s e l e c t i o n f o r i n c r e a s e d p r o t e c t i o n o f embryos when exposure t o e n v i r o n m e n t a l s t r e s s e s i s l o n g . The r e l a t i o n s h i p between c a p s u l e s t r e n g t h and embryonic development t i m e found by P e r r o n (1981) may be g e n e r a l f o r a l l marine g a s t r o p o d s . I f so, t h e n P e r r o n ' s d a t a on p u n c t u r e r e s i s t a n c e i n Conus spp. can be e x t r a p o l a t e d t o N u c e l l a  e m a r q i n a t a . C a p s u l e s c o n t a i n i n g embryos w i t h an 80 day development p e r i o d , such as N. e m a r q i n a t a (Emlen, 1966), s h o u l d r e q u i r e 6.11 MN/m^ o f f o r c e t o p u n c t u r e t h e i r w a l l s . I n t h e p r e s e n t s t u d y , t h e mean f o r c e needed t o p u n c t u r e N u c e l l a e m a r q i n a t a c a p s u l e s w a l l s ranged from 4.92-6.18 MN/m^, th u s c l o s e l y a p p r o x i m a t i n g P e r r o n ' s (1981) p r e d i c t i o n s . 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 c a p s u l e s t r u c t u r e A l t h o u g h d i f f e r e n c e s i n c a p s u l a r s t r u c t u r e may be more apparent between s p e c i e s , s t u d i e s o f v a r i a t i o n w i t h i n a s p e c i e s a r e l i k e l y t o be more u s e f u l i n e l u c i d a t i n g t h e i m p o r t a n c e o f 1) p h y s i c a l c o n s t r a i n t s o f body s i z e , 2) p h e n o t y p i c r e s p o n s e s t o v a r i a t i o n i n e n v i r o n m e n t a l p a r a m e t e r s , and 3) g e n e t i c d i v e r g e n c e r e s u l t i n g from s e l e c t i o n , i n a c c o u n t i n g f o r d i f f e r e n c e s i n c a p s u l a r s t r u c t u r e (Brown, 1983). S u r p r i s i n g l y , no p r e v i o u s s t u d i e s on g a s t r o p o d s have examined i n t r a s p e c i f i c v a r i a t i o n i n c a p s u l e w a l l s t r u c t u r e among p o p u l a t i o n s . I n t h e p r e s e n t s t u d y , such comparisons i n d i c a t e d t h a t t h e t h i c k n e s s and s t r e n g t h o f c a p s u l e w a l l s v a r i e d among i n t e r t i d a l l o c a t i o n s . C a p s u l e s c o l l e c t e d from G r a p p l e r I n l e t had t h e t h i c k e s t w a l l s and were most r e s i s t a n t 45 t o p u n c t u r e and s q u e e z i n g t e s t s , whereas c a p s u l e s from Seppings I s l a n d were a l s o t h i c k - w a l l e d , but were s i g n i f i c a n t l y l e s s r e s i s t a n t t o t h e s e t e s t s . Ross I s l e t s n a i l s p roduced c o m p a r a t i v e l y weak t h i n - w a l l e d c a p s u l e s . What i s t h e cause o f 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 c a p s u l a r s t r u c t u r e among t h e s e p o p u l a t i o n s ? D i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s among p o p u l a t i o n s c o u l d s i m p l y r e f l e c t c o n s t r a i n t s a s s o c i a t e d w i t h female s i z e . A l t h o u g h t h e morphology o f n e o g a s t r o p o d egg c a p s u l e s i s governed by t h e s i z e o f t h e c a p s u l e g l a n d w h ich, i n t u r n , i s r e s t r i c t e d by female s h e l l - l e n g t h ( S p i g h t e t a l . , 1974; S p i g h t and Emlen, 1976; P e r r o n and Corpuz, 1982; p r e s e n t s t u d y ) , l i t t l e i s known about t h e e f f e c t o f female s i z e on c a p s u l e w a l l t h i c k n e s s . P r e v i o u s l y , P e r r o n and Corpuz (1982) r e p o r t e d t h a t w a l l t h i c k n e s s and s t r e n g t h o f Conus pennaceus c a p s u l e s i n c r e a s e d w i t h c a p s u l e s i z e and s n a i l s h e l l - l e n g t h . T h e i r r e s u l t s suggest t h a t t h e s t r u c t u r e o f c a p s u l e w a l l s may be l i m i t e d by t h e s i z e o f t h e c a p s u l e g l a n d . I n t h e p r e s e n t s t u d y , c a p s u l e s i z e and s n a i l s h e l l - l e n g t h v a r i e d markedly w i t h i n and among t h e G r a p p l e r , Ross I s l e t s and Seppings p o p u l a t i o n s . However, t h e t h i c k n e s s and s t r e n g t h o f c a p s u l e w a l l s d i d not v a r y as p r e d i c t e d w i t h c a p s u l e l e n g t h o r s n a i l s h e l l - l e n g t h . Hence, i n t r a s p e c i f i c v a r i a t i o n i n t h e s t r u c t u r e o f c a p s u l e w a l l s among N u c e l l a e m a r g i n a t a p o p u l a t i o n s d i d not r e f l e c t a l l o m e t r i c c o n t r a i n t s a s s o c i a t e d w i t h female s i z e . V a r i a t i o n i n t h e s t r u c t u r e o f N u c e l l a e m a r g i n a t a c a p s u l e w a l l s was not p h e n o t y p i c a l l y p l a s t i c . T h i s was i n d i c a t e d by 46 two d i f f e r e n t r e s u l t s . F i r s t , v a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n a c l u t c h was low compared t o v a r i a t i o n among c l u t c h e s produced by d i f f e r e n t i n d i v i d u a l s . Hence, i n d i v i d u a l s n a i l s appeared t o be r e s t r i c t e d i n t h e t h i c k n e s s o f c a p s u l e w a l l s t h e y produced. Second, s n a i l s from each s i t e c o n t i n u e d t o produce t h e i r r e s p e c t i v e t h i c k - o r t h i n - w a l l e d c a p s u l e s even a f t e r 5 months i n t h e l a b o r a t o r y d u r i n g w h i c h a l l s n a i l s were kept under s i m i l a r e n v i r o n m e n t a l c o n d i t i o n s . T h i s i n d i c a t e d t h a t d i f f e r e n c e s i n t h e s t r u c t u r e o f egg c a p s u l e s were not p h e n o t y p i c r e s p o n s e s t o s i t e d i f f e r e n c e s i n d i e t , f o o d abundance, o r l e v e l s o f e n v i r o n m e n t a l s t r e s s . The p r o d u c t i o n o f t h i c k c a p s u l e w a l l s must have a d a p t i v e v a l u e , as t h i c k - w a l l e d c a p s u l e s i n c u r a g r e a t e r e n e r g e t i c c o s t t h a n t h i n - w a l l e d c a p s u l e s . F o r i n s t a n c e , t h i n - w a l l e d c a p s u l a r c a ses from t h e Ross I s l e t s (6.5 mm i n l e n g t h ) weighed 24 % l e s s t h a n t h i c k - w a l l e d c a p s u l e s from G r a p p l e r I n l e t , and 16% l e s s t h a n t h i c k - w a l l e d c a p s u l e s from Seppings I s l a n d . As c a p s u l a r c a s e s can account f o r more t h a n 50% o f t h e d r y w e i g ht o f i n t a c t c a p s u l e s ( i e . , i n c l u d i n g t h e eggs; t h i s s t u d y ; R o l l e r and S t i c k l e , 1988) and as N u c e l l a e m a r g i n a t a c a p s u l a r m a t e r i a l has a lmost t h e same energy c o n t e n t p e r u n i t w e i g ht as t h e eggs (22.6 K J p e r a s h - f r e e g - 1 compared t o 25.1 K J p e r a s h - f r e e g - 1 o f embryos; D a v i e s , 1984), t h e energy spent i n p r o d u c i n g t h i c k e r c a p s u l e w a l l s must r e p r e s e n t e i t h e r a s u b s t a n t i a l d e c r e a s e i n t h e energy a v a i l a b l e f o r egg p r o d u c t i o n or an i n c r e a s e i n t h e r e p r o d u c t i v e e f f o r t o f an i n d i v i d u a l . 47 P e r r o n (1982) found t h a t t h e p r o d u c t i o n o f p u n c t u r e -r e s i s t a n t , t h i c k c a p s u l e w a l l s among Conus spp. was a s s o c i a t e d w i t h a h i g h e r a n n u a l r e p r o d u c t i v e e f f o r t t h a n t h e p r o d u c t i o n o f weak, t h i n - w a l l e d c a p s u l e s . The r e p r o d u c t i v e e f f o r t o f s n a i l s was not compared among p o p u l a t i o n s i n t h e p r e s e n t s t u d y . However, t h e p r o d u c t i o n o f t h i c k - w a l l e d c a p s u l e s d i d not r e s u l t i n a r e d u c t i o n o f t h e number o f eggs c o n t a i n e d p e r u n i t c a p s u l e volume. Hence, on a p e r c a p s u l e b a s i s , t h e r e was no e v i d e n c e o f a t r a d e o f f between t h e amount o f energy i n v e s t e d i n e x t r a e m b r y o n i c p r o d u c t s v e r s u s eggs. E f f e c t s o f e n v i r o n m e n t a l s t r e s s e s on e n c a p s u l a t e d embryos I t seems l i k e l y t h a t t h e t h i c k n e s s o f c a p s u l e w a l l s r e f l e c t s s e l e c t i o n f o r i n c r e a s e d p r o t e c t i o n o f embryos a g a i n s t i n t e n s e e n v i r o n m e n t a l s t r e s s e s . D e s i c c a t i o n (Feare, 1970; S p i g h t , 1977; P e c h e n i k , 1978), o s m o t i c s t r e s s (Pechenik, 1982; 1983), w a v e - a c t i o n ( P e r r o n , 1981), b a c t e r i a l a t t a c k ( L o r d , 1986), p r e d a t i o n ( S p i g h t , 1977; P e r r o n , 1981; B r e n c h l e y , 1982), and t h e r m a l s t r e s s ( S p i g h t , 1977) a r e a l l p o t e n t i a l l y i m p o r t a n t s o u r c e s o f m o r t a l i t y f o r e n c a p s u l a t e d embryos. In t h e p r e s e n t s t u d y , a l t h o u g h t h e s t r u c t u r e o f c a p s u l e s was compared among s i t e s s e p a r a t e d a l o n g a g r a d i e n t o f wave- / e x p o s u r e , t h e t h i c k n e s s o f c a p s u l e w a l l s d i d not v a r y as p r e d i c t e d by t h i s g r a d i e n t . The t h i c k n e s s o f c a p s u l e w a l l s may be s e l e c t e d f o r by more t h a n one f a c t o r . F o r example, c a p s u l e w a l l s were t h i c k a t t h e wave-exposed s i t e , where w a v e - a c t i o n and a s s o c i a t e d a b r a s i o n 48 would be p r e d i c t e d t o be most extreme and were a l s o t h i c k a t t h e w a v e - s h e l t e r e d s i t e , where d e s i c c a t i o n , p r e d a t i o n , and o s m o t i c s t r e s s e s s h o u l d be most i n t e n s e . I n t h i s way, c a p s u l e w a l l t h i c k n e s s might be a good b i o l o g i c a l i n d i c a t o r o f t h e i n t e n s i t y o f e n v i r o n m e n t a l s t r e s s e s a c t i n g upon d e v e l o p i n g embryos i n v a r i o u s i n t e r t i d a l l o c a l i t i e s . F u r t h e r m o r e , d i f f e r e n t e n v i r o n m e n t a l s t r e s s e s may have s e l e c t e d i n d e p e n d e n t l y f o r c a p s u l e w a l l t h i c k n e s s and c a p s u l e s t r e n g t h , as t h e s t r e n g t h o f c a p s u l e s from G r a p p l e r I n l e t , Seppings I s l a n d , and Ross I s l e t s d i d not c o r r e s p o n d t o d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s among t h e s e s i t e s . Hence, an e x a m i n a t i o n o f b o t h components o f c a p s u l e s t r u c t u r e i n f u t u r e s t u d i e s might be n e c e s s a r y t o d i f f e r e n t i a t e between s e l e c t i v e p r e s s u r e s a c t i n g upon g a s t r o p o d egg c a p s u l e s . T r a d e o f f s i n c a p s u l e s t r u c t u r e T h i c k c a p s u l e w a l l s may i n c r e a s e t h e s u r v i v o r s h i p o f d e v e l o p i n g embryos exposed t o s e v e r e e n v i r o n m e n t a l s t r e s s e s , but such s t r u c t u r e s c o u l d a l s o a c t t o l i m i t embryo s u r v i v o r s h i p by r e s t r i c t i n g t h e d i f f u s i o n o f oxygen and n i t r o g e n o u s wastes a c r o s s c a p s u l e w a l l s . I n t h i s r e g a r d , P e r r o n and Corpuz (1982) found t h a t l a r g e , t h i c k - w a l l e d Conus  pennaceus c a p s u l e s c o n t a i n e d fewer eggs p e r u n i t volume t h a n d i d s m a l l , t h i n - w a l l e d c a p s u l e s . In c o n t r a s t , t h e w a l l t h i c k n e s s o f N u c e l l a e m a r g i n a t a c a p s u l e s d i d not appear t o a f f e c t t h e number o f eggs and embryos a l l o c a t e d t o c a p s u l e -chambers i n t h e p r e s e n t s t u d y . F o r i n s t a n c e , t h e d e n s i t y o f 49 eggs and embryos c o n t a i n e d w i t h i n G r a p p l e r I n l e t c a p s u l e s , w h i c h had t h e t h i c k e s t c a p s u l e w a l l s and l o w e s t s u r f a c e a r e a t o volume r a t i o s o f c a p s u l e s from a l l t h r e e s t u d y s i t e s , was not s i g n i f i c a n t l y d i f f e r e n t from t h e d e n s i t y i n Seppings and Ross c a p s u l e s . A l t h o u g h l a r g e - v o l u m e d N u c e l l a e m a r q i n a t a c a p s u l e s d i d c o n t a i n l o w e r d e n s i t i e s o f eggs t h a n s m a l l e r -volumed c a p s u l e s ( c f . Conus pennaceus; P e r r o n and Corpuz, 1982), l a r g e r c a p s u l e s were not found t o be t h i c k e r - w a l l e d t h a n s m a l l e r c a p s u l e s . Hence, egg and embryo d e n s i t y d i d not r e f l e c t d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s . E f f e c t s o f e n v i r o n m e n t a l s t r e s s e s a c t i n g upon a d u l t s n a i l s D i f f e r e n c e s i n t h e i n t e n s i t y o f e n v i r o n m e n t a l s t r e s s e s a c t i n g upon t h e a d u l t s n a i l s a t d i f f e r e n t s i t e s may.make i n t e r p r e t a t i o n s o f s i t e d i f f e r e n c e s i n c a p s u l e w a l l s t r u c t u r e even more d i f f i c u l t . E n v i r o n m e n t a l s t r e s s e s such as wave-exposure a r e known t o a f f e c t t h e r e p r o d u c t i v e e f f o r t o f g a s t r o p o d s p r o f o u n d l y . F o r i n s t a n c e , wave-exposed s n a i l s t y p i c a l l y mature a t s m a l l e r s i z e s and e x h i b i t h i g h e r r e p r o d u c t i v e e f f o r t s o v er s h o r t e r l i f e s p a n s t h a n l o n g e r - l i v e d w a v e - s h e l t e r e d s n a i l s (Lvmnaea p e r e g r a , Calow, 1981; L i t t o r i n a r u d i s , R o b e r t s and Hughes, 1980; N u c e l l a l a p i l l u s , E t t e r , 1987). There was some e v i d e n c e f o r t h i s i n t h e p r e s e n t s t u d y , as Seppings s n a i l s matured at s m a l l e r s i z e s and p r o d u c e d p r o p o r t i o n a l l y l a r g e r c a p s u l e s t h a n G r a p p l e r I n l e t s n a i l s . I t i s not known how such d i f f e r e n c e s i n r e p r o d u c t i v e e f f o r t might be r e f l e c t e d i n t h e p a r t i t i o n i n g o f energy 50 between eggs and e x t r a e m b r y o n i c p r o d u c t s . S n a i l p o p u l a t i o n s expending a low r e p r o d u c t i v e e f f o r t might a l l o c a t e p r o p o r t i o n a l l y more energy i n t o p r o t e c t i v e c a p s u l a r cases v e r s u s eggs t h a n s n a i l s e x h i b i t i n g a h i g h r e p r o d u c t i v e e f f o r t . The e x p l a n a t i o n f o r t h i s i s t h a t w i t h l e s s energy t o expend, s n a i l s s h o u l d adopt a " b e t - h e d g i n g " s t r a t e g y - one o f e n s u r i n g maximal p r o t e c t i o n f o r a few eggs r a t h e r t h a n m i n i m a l p r o t e c t i o n f o r many. T h e r e f o r e , a l t h o u g h t h e t h i c k n e s s and s t r e n g t h o f c a p s u l e w a l l s u n d o u b t e d l y must r e f l e c t t h e p r i m a r y e f f e c t s o f s t r e s s e s a c t i n g upon e n c a p s u l a t e d embryos, secondary e f f e c t s a c t i n g upon a d u l t s n a i l s might a l s o i n f l u e n c e t h e t h i c k n e s s and s t r e n g t h o f c a p s u l e w a l l s produced. The r e s u l t s o f t h e p r e s e n t s t u d y have shown t h e f i r s t e v i d e n c e o f i n t r a s p e c i f i c v a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s and s t r e n g t h among p o p u l a t i o n s o f a marine g a s t r o p o d . These f i n d i n g s a r e a n e c e s s a r y b a s i s f o r f u r t h e r i n v e s t i g a t i o n i n t o t h e i n t e n s i t y o f s p e c i f i c e n v i r o n m e n t a l s t r e s s e s a c t i n g upon egg c a p s u l e s i n s i t u , such as d e s i c c a t i o n ( S p i g h t , 1977; P e c h e n i k , 1978), p r e d a t i o n ( S p i g h t , 1977; P e r r o n , 1981; B r e n c h l e y , 1982) and o s m o t i c s t r e s s (Pechenik, 1982; 1983). The second c h a p t e r o f t h i s t h e s i s w i l l examine t h e e f f e c t o f one o f t h e s e s t r e s s e s , p r e d a t i o n , on s u r v i v a l o f e n c a p s u l a t e d embryos o f N u c e l l a e m a r g i n a t a . 51 R E F E R E N C E S A u s t i n , W.C., L.C. D r u e h l and S.B. Haven. 1971. B a m f i e l d Survey: marine h a b i t a t s and b i o t a . B a m f i e l d Survey R e p o r t 2: 1-30. Bayne, C.J. 1968. H i s t o c h e m i c a l s t u d i e s on t h e egg c a p s u l e s o f e i g h t g a s t r o p o d M o l l u s c s . P r o c . M a l a c . Soc. Lond. 38: 199-212. B r e n c h l e y , G.A. 1982. P r e d a t i o n on e n c a p s u l a t e d l a r v a e by a d u l t s : e f f e c t s o f i n t r o d u c e d s p e c i e s on t h e g a s t r o p o d I l y a n a s s a o b s o l e t a . Mar. E c o l . P r o g . Ser. 9: 255-62. Brown, K.M. 1983. Do l i f e h i s t o r y t a c t i c s e x i s t a t t h e i n t r a s p e c i f i c l e v e l ? Example from a f r e s h w a t e r s n a i l . Am. Nat. 121: 871-9. Calow, P. 1981. A d a p t a t i o n a l a s p e c t s o f growth and r e p r o d u c t i o n i n Lymnaea p e r e g r a (Gastropoda: Pulmonata) from exposed and s h e l t e r e d a q u a t i c h a b i t a t s . M a l a c o l o g i a 21: 5-13. C r a i k , G.J. 1980. Simple method f o r measuring t h e r e l a t i v e s c o u r i n g o f i n t e r t i d a l a r e a s . Mar. B i o l . 59: 257-260. C r o t h e r s , J.H. 1984. Some o b s e r v a t i o n s on s h e l l shape v a r i a t i o n i n P a c i f i c N u c e l l a . B i o l . J . L i n n . Soc. 21: 259-281. D'Asaro, C.N. 1988. Micromorphology o f n e o g a s t r o p o d egg c a p s u l e s . N a u t i l u s 102: 134-148. D a v i e s , J . 1984. A s p e c t s o f t h e r e p r o d u c t i v e e c o l o g y and e n e r g e t i c s o f T h a i s l a m e l l o s a , T h a i s c a n a l i c u l a t a and T h a i s e m a r g i n a t a . L a r v a l E c o l o g y P r o j e c t . F r i d a y Harbor L a b o r a t o r i e s . Dayton, P.K. 1971. C o m p e t i t i o n , d i s t u r b a n c e and community o r g a n i z a t i o n : t h e p r o v i s i o n and subsequent u t i l i z a t i o n o f space i n a r o c k y i n t e r t i d a l community. E c o l . Monog. 41: 351-89. Denny, M.W. 1985. Wave f o r c e s on i n t e r t i d a l o r g a nisms: a case s t u d y . L i m n o l . Oceanog. 30: 1171-87. Denny, M.W., T.L. D a n i e l and M.A.R. K o e h l . 1985. M e c h a n i c a l l i m i t s t o s i z e i n wave swept organisms. E c o l . Monog. 55: 69-102. Emlen, J . 1966. Time, energy and r i s k i n two s p e c i e s o f c a r n i v o r o u s g a s t r o p o d s . Ph.D. t h e s i s . U n i v e r s i t y o f Washington. 52 E t t e r , R.J. 1987. The e f f e c t o f w a v e - a c t i o n on t h e b i o l o g y o f t h e i n t e r t i d a l s n a i l N u c e l l a l a p i l l u s . Ph.D. t h e s i s . H a r v a r d U n i v e r s i t y . F e a r e , C.J. 1970. A s p e c t s o f t h e e c o l o g y o f an exposed shore p o p u l a t i o n o f dogwhelks N u c e l l a l a p i l l u s ( L . ) . O e c o l o g i a 5: 1-18. G a l l a r d o , C.S. 1979. Development p a t t e r n and a d a p t a t i o n s f o r r e p r o d u c t i o n i n N u c e l l a c r a s s i l a b r u m and o t h e r m u r i c a c e a n G a s t r o p o d s . B i o l . B u l l . 157: 453-63. G a l l a r d o , C.S. and F . E . P e r r o n . 1982. E v o l u t i o n a r y e c o l o g y o f r e p r o d u c t i o n i n marine b e n t h i c m o l l u s k s . ( P r o c . Seventh I n t . Ma l a c . C o n g r e s s ) . M a l a c o l o g i a 22: 109-114. Hawkins, L.E. and S. H u t c h i n s o n . 1988. Egg c a p s u l e s t r u c t u r e and h a t c h i n g mechanism o f Ocenebra e r i n a c e a (L.) ( P r o s o b r a n c h i a : M u r i c i d a e ) . J . Exp. Mar. B i o l . E c o l . 119: 269-283. K i t c h i n g , J.A. 1976. D i s t r i b u t i o n and changes i n s h e l l form o f T h a i s spp. (Gastropoda) near B a m f i e l d , B.C. J . Exp. Mar. B i o l . E c o l . 23: 109-126. K i t c h i n g , J.A., J.F. Sloane and F . J . E b l i n g . 1959. The e c o l o g y o f Lough Ine. V I I I . M u s s e l s and t h e i r p r e d a t o r s . J . Anim. E c o l . 28: 331-41. LeBoeuf, R. 1971. T h a i s e m a r q i n a t a . D e s c r i p t i o n o f t h e v e l i g e r and egg c a p s u l e . V e l i g e r 14: 205-10. L o r d , A. 1986. Are t h e c o n t e n t s o f egg c a p s u l e s o f t h e marine g a s t r o p o d N u c e l l a l a p i l l u s (L.) a x e n i c ? Amer. Mala c . B u l l . 4: 201-203. Lyons, A. and T.M. S p i g h t . 1973 D i v e r s i t y o f f e e d i n g mechanisms among embryos o f P a c i f i c Northwest T h a i s . V e l i g e r 16: 189-194. Menge, B.A. 1978a. P r e d a t i o n i n t e n s i t y i n a r o c k y i n t e r t i d a l community: r e l a t i o n between p r e d a t o r f o r a g i n g a c t i v i t y and e n v i r o n m e n t a l h a r s h n e s s . O e c o l o g i a 34: 1-16. Menge, B.A. 1978b. P r e d a t i o n i n t e n s i t y i n a r o c k y i n t e r t i d a l community: E f f e c t o f a l g a l canopy, wave a c t i o n and d e s i c c a t i o n on p r e d a t o r f e e d i n g r a t e s . O e c o l o g i a 34: 17-35. 53 Menge,B.A. and J.P. S u t h e r l a n d . 1987. Community r e g u l a t i o n : v a r i a t i o n i n d i s t u r b a n c e c o m p e t i t i o n , and p r e d a t i o n i n r e l a t i o n t o e n v i r o n m e n t a l s t r e s s and r e c r u i t m e n t . Am. Nat. 130: 730-57. Palmer, A.R. 1984. S p e c i e s c o h e s i v e n e s s and g e n e t i c c o n t r o l o f s h e l l c o l o r and form i n T h a i s e m a r q i n a t a ( P r o s o b r a n c h i a , M u r i c a c e a ) : p r e l i m i n a r y r e s u l t s . M a l a c o l o g i a 25: 477-491. P e c h e n i k , J.A. 1978. A d a p t a t i o n s t o i n t e r t i d a l development: S t u d i e s on N a s s a r i u s o b s o l e t u s . B i o l . B u l l . 154: 282-291. P e c h e n i k , J.A. 1979. R o l e o f e n c a p s u l a t i o n i n i n v e r t e b r a t e l i f e h i s t o r i e s . Am. Nat. 114: 859-870. P e c h e n i k , J.A. 1982. A b i l i t y o f some g a s t r o p o d egg c a p s u l e s t o p r o t e c t a g a i n s t l o w - s a l i n i t y s t r e s s . J . Exp. Mar. B i o l . E c o l . 63: 195-208. P e c h e n i k , J.A. 1983. Egg c a p s u l e s o f N u c e l l a l a p i l l u s (L.) p r o t e c t a g a i n s t l o w - s a l i n i t y s t r e s s . J . Exp. Mar. B i o l . E c o l . 71: 165-179. P e c h e n i k , J.A. 1986. The e n c a p s u l a t i o n o f eggs and embryos-by m o l l u s k s : an o v e r v i e w . American Ma l a c . B u l l . 4: 165-72. P e r r o n , F.E. 1981. The p a r t i t i o n i n g o f r e p r o d u c t i v e energy between ova and p r o t e c t i v e c a p s u l e s i n marine g a s t r o p o d s o f t h e genus Conus. Am. Nat. 118: 110-118. P e r r o n , F.E. 1982. I n t e r - and i n t r a s p e c i f i c p a t t e r n s o f r e p r o d u c t i v e e f f o r t i n f o u r s p e c i e s o f cone s h e l l s (Conus spp.) Mar. B i o l . 68: 161-167. P e r r o n , F.E. and G.C. Corpuz. 1982. Cost o f p a r e n t a l c a r e i n t h e g a s t r o p o d Conus pennaceus: Age s p e c i f i c changes and p h y s i c a l c o n s t r a i n t s . O e c o l o g i a 55: 319-324. R i v e s t , B.R. 1983. Development and t h e i n f l u e n c e o f nurse egg a l l o t m e n t on h a t c h i n g s i z e i n S e a r l e s i a d i r a (Reeve, 1846) ( P r o s o b r a n c h i a : B u c c i n i d a e ) . J . Exp. Mar. B i o l . E c o l . 69: 217-241. R o b e r t s , D.J. and R.N. Hughes. 1980. Growth and r e p r o d u c t i v e r a t e s o f L i t t o r i n a r u d i s from t h r e e c o n t r a s t e d shores i n N o r t h Wales, U.K. Mar. B i o l . 58: 47-54. R o b l e s , C. 1987. P r e d a t o r f o r a g i n g c h a r a c t e r i s t i c and p r e y p o p u l a t i o n s t r u c t u r e on a s h e l t e r e d s h o r e . E c o l o g y 68: 1502-1514. R o l l e r , R. A. and W.B. S t i c k l e . 1988. I n t r a c a p s u l a r development o f T h a i s haemostoma c a n a l i c u l a t a (Gray) ( P r o s o b r a n c h i a : M u r i c i d a e ) under l a b o r a t o r y c o n d i t i o n s Am. M a l a c . B u l l . 6: 189-98. Shanks, A.L. and W.G. W r i g h t . 1986. A d d i n g t e e t h t o wave-a c t i o n : t h e e f f e c t s o f water-borne r o c k s on i n t e r t i d a l o r g a n i s m s . O e c o l o g i a 69: 420-428. S p i g h t , T.M. 1976. H a t c h i n g s i z e and t h e d i s t r i b u t i o n o f n u r s e eggs among p r o s o b r a n c h embryos. B i o l . B u l l . 150 491-99. S p i g h t , T.M. 1977 Do i n t e r t i d a l s n a i l s spawn i n t h e r i g h t p l a c e s ? E v o l u t i o n 31: 682-691. S p i g h t , T.M., C. B i r k e l a n d , and A. Lyons. 1974. L i f e h i s t o r i e s o f l a r g e and s m a l l Murexes ( P r o s o b r a n c h i a : M u r i c i d a e ) . Mar. B i o l . 24: 229-242. S p i g h t , T.M. and J . Emlen. 1976 C l u t c h s i z e s o f two marine s n a i l s w i t h a c h a n g i n g f o o d s u p p l y . E c o l o g y 57: 1162-1178. Strathmann, R.R and C. C h a f f e e . 1984. C o n s t r a i n t s on egg masses. I I : E f f e c t o f s p a c i n g , s i z e and number o f eggs on v e n t i l a t i o n o f masses o f embryos i n j e l l y , adherent groups, or t h i n w a l l e d c a p s u l e s . J . Exp. Mar. B i o l . E c o l . 84: 85-93. S u l l i v a n , C.H. and T.K. Maugel. 1984. F o r m a t i o n , o r g a n i z a t i o n and c o m p o s i t i o n o f t h e egg c a p s u l e o f t h e marine g a s t r o p o d , I l y a n a s s a o b s o l e t a . B i o l . B u l l . 167 378-389. Webber, H.H. 1977. G a s t r o p o d a : P r o s o b r a n c h i a . I n : R e p r o d u c t i o n o f M a r i n e I n v e r t e b r a t e s , Volume IV. A.C. G i e s e and J.S P e a r s e , eds., pp. 291-336. Academic P r e s s , New York. 55 CHAPTER 2 FUNCTIONAL MORPHOLOGY OF MARINE GASTROPOD EGG CAPSULES: LABORATORY AND FIELD TESTS OF PREDATION INTRODUCTION D e s p i t e f r e q u e n t s p e c u l a t i o n about t h e " p r o t e c t i v e " r o l e t h a t egg c a p s u l e s p l a y i n g a s t r o p o d l i f e - h i s t o r i e s (Pechenik, 1979; P e r r o n , 1981; P e c h e n i k , 1986), l i t t l e i s known about t h e s u r v i v o r s h i p o f e n c a p s u l a t e d embryos i n t h e marine environment. G a s t r o p o d embryos may spend from a few days ( P e r r o n , 1981) t o more t h a n 6 months w i t h i n b e n t h i c egg c a s p u l e s (West, 1973) b e f o r e emerging as l a r v a e o r j u v e n i l e s n a i l s . D u r i n g t h i s p e r i o d o f e n c a p s u l a t i o n embryos are s u s c e p t i b l e t o : p r e d a t i o n ( S p i g h t , 1977; B r e n c h l e y , 1982, Abe, 1983), b a c t e r i a l a t t a c k ( L o r d , 1986), d e s i c c a t i o n (Feare, 1970; S p i g h t , 1977; P e c h e n i k , 1978), o s m o t i c s t r e s s (Feare, 1970; P e c h e n i k , 1982; 1983), t h e r m a l s t r e s s ( S p i g h t , 1977), and wave shock ( P e r r o n , 1981). As y e t , few s t u d i e s have examined t h e r e l a t i v e i m p o r t a n c e o f t h e s e s t r e s s e s i n t h e s u r v i v o r s h i p o f e n c a p s u l a t e d embryos. P r e d a t i o n appears t o be an i m p o r t a n t s o u r c e o f m o r t a l i t y f o r e n c a p s u l a t e d g a s t r o p o d embryos (Emlen, 1966; S p i g h t , 1977; B r e n c h l e y , 1982). C a p s u l a r cases a r e opened i n t h e l a b o r a t o r y and f i e l d by a v a r i e t y o f organisms, such a s : c r u s t a c e a n s (MacKenzie, 1961; Emlen, 1966; P h i l l i p s , 1969; S p i g h t , 1977; P e r r o n , 1981; B r e n c h l e y , 1982), p o l y c h a e t e s (Feare, 1970), c h i t o n s (Emlen, 1966; E a t o n , 1972), p r o s o b r a n c h s ( P h i l l i p s , 56 1969; West, 1973; Eaton, 1972; M c K i l l u p and B u t l e r , 1979; B r e n c h l e y , 1982; Race, 1982; Abe, 1983), echinoderms ( S p i g h t , 1977; M a r t e l and L a r r i v e e , 1986) and p o s s i b l y f i s h ( S p i g h t , 1977). However, r e l a t i v e l y few s t u d i e s have d i r e c t l y examined t h e i n t e n s i t y o f p r e d a t i o n on g a s t r o p o d egg c a p s u l e s i n t h e marine environment ( S p i g h t , 1977; B r e n c h l e y , 1982; Abe, 1983). A l t h o u g h some g a s t r o p o d s p e c i e s a c t i v e l y p r o t e c t t h e i r egg c a p s u l e s from p r e d a t o r s u n t i l embryonic development i s complete ( O s t e r g a a r d , 1950; D'Asaro, 1970; Eaton, 1972), i n t h e m a j o r i t y o f s p e c i e s p a r e n t a l c a r e i s p a s s i v e - l i m i t e d o n l y t o t h e p r o d u c t i o n o f c a p s u l a r c a s e s . R e c e n t l y , d i f f e r e n c e s have been n o t e d i n t h e s t r u c t u r e o f c a p s u l e s w i t h i n and among g a s t r o p o d s p e c i e s ( P e r r o n , 1981; P e r r o n and Corpuz, 1982; Chapter 1 ) . F o r example, P e r r o n (1981) n o t e d t h a t t h e s t r e n g t h o f Conus c a p s u l e s , as measured by w a l l p u n c t u r i n g t e s t s , was d i r e c t l y c o r r e l a t e d w i t h t h e de v e l o p m e n t a l t i m e o f t h e e n c a p s u l a t e d embryos. From t h e s e r e s u l t s he s u g g e s t e d t h a t t h i c k - w a l l e d c a p s u l e s might d e t e r p r e d a t o r s more e f f e c t i v e l y t h a n would t h i n - w a l l e d c a p s u l e s . Comparative s t u d i e s o f t h e r e s i s t a n c e o f t h i c k - and t h i n -w a l l e d c a p s u l e s t o p r e d a t o r s have not y e t been u n d e r t a k e n . The marine i n t e r t i d a l s n a i l , • N u c e l l a e m a r q i n a t a , i s a common i n h a b i t a n t o f r o c k y s h o r e s a l o n g t h e west c o a s t o f N o r t h A m e r i c a , r a n g i n g i n d i s t r i b u t i o n from C a l i f o r n i a t o A l a s k a . These s n a i l s d e p o s i t eggs w i t h i n t o u g h p r o t e i n a c e o u s c a p s u l e s which a r e a t t a c h e d t o h a r d i n t e r t i d a l s u b s t r a t e s . Embryos d e v e l o p w i t h i n c a p s u l e s f o r a p e r i o d o f up t o 80 days (Emlen, 1966), a f t e r w h i c h t h e y h a t c h as j u v e n i l e s n a i l s . 57 N u c e l l a e m a r g i n a t a egg c a p s u l e s a re known t o v a r y i n w a l l t h i c k n e s s and s t r e n g t h among s i t e s , w i t h c a p s u l e s from some p o p u l a t i o n s h a v i n g w a l l s up t o 25% t h i c k e r t h a n c a p s u l e s from o t h e r p o p u l a t i o n s (Chapter 1) . 13 The aim o f t h i s s t u d y was t o examine p r e d a t i o n on t h e egg c a p s u l e s o f t h e i n t e r t i d a l whelk N u c e l l a e m a r g i n a t a i n b o t h l a b o r a t o r y and f i e l d e n v i r o n m e n t s . L a b o r a t o r y e x p e r i m e n t s were co n d u c t e d t o i d e n t i f y p r e d a t o r s o f t h e c a p s u l e s and t o deter m i n e t h e e f f e c t i v e n e s s o f t h i c k - w a l l e d v e r s u s t h i n - w a l l e d c a p s u l e s i n p r o t e c t i n g d e v e l o p i n g embryos from s p e c i f i c p r e d a t o r s . F i e l d s t u d i e s were u n d e r t a k e n t o e s t i m a t e t h e e x t e n t o f p r e d a t i o n on n a t u r a l l y d e p o s i t e d egg c a p s u l e s and t o i d e n t i f y i n v e r t e b r a t e s r e s p o n s i b l e f o r opening egg c a p s u l e s a t two d i f f e r e n t i n t e r t i d a l l o c a t i o n s . 58 MATERIALS AND METHODS The p r o j e c t was conducted a t t h e B a m f i e l d M a r i n e S t a t i o n on t h e west c o a s t o f Vancouver I s l a n d from May-November 1988. E x p e r i m e n t a l s t u d y s i t e s were e s t a b l i s h e d a t i n t e r t i d a l l o c a t i o n s i n G r a p p l e r I n l e t and Ross I s l e t s , B a r k l e y Sound. O b s e r v a t i o n s were a l s o made a t a t h i r d s i t e a t Seppings I s l a n d . D e s c r i p t i o n s o f t h e s e h a b i t a t s a re g i v e n i n Cha p t e r 1. I . LABORATORY EXPERIMENTS S e v e r a l s p e c i e s 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 were c o l l e c t e d from f i e l d s i t e s t o det e r m i n e which might p r e y on N u c e l l a e m a r g i n a t a egg c a p s u l e s i n t h e l a b o r a t o r y . Groups o f i n d i v i d u a l s o f each s p e c i e s were p l a c e d i n a p p r o p r i a t e s i z e s o f m e s h - p a n e l l e d v i a l s (3x3x6 cm) and m e s h - p a n e l l e d c o n t a i n e r s (8x8x10 cm), and were p r o v i d e d w i t h i n t e r t i d a l s h e l l s o r bare r o c k s f o r s h e l t e r . C o n t a i n e r s were t h e n p a r t i a l l y immersed i n seawater t a n k s and p r o v i d e d w i t h a c o n t i n u o u s f l o w o f f r e s h s e a water. Test a n i m a l s were s t a r v e d f o r 24 h b e f o r e b e i n g p r e s e n t e d w i t h 8 i n t a c t N_s_ e m a r g i n a t a egg c a p s u l e s . C a p s u l e s were mounted on s m a l l f l a t r o c k s u s i n g " S u p e r g l u e " and a r r a n g e d i n a s t a n d a r d i z e d c i r c u l a r c o n f i g u r a t i o n . A p r e d a t o r was d e f i n e d t o have "opened" an egg c a p s u l e o n l y i f i t r u p t u r e d o r a t e t h r o u g h t h e c a p s u l e chamber wh i c h c o n t a i n e d t h e d e v e l o p i n g embryos. Thus, an a n i m a l was not r e q u i r e d t o eat embryos o r nu r s e eggs t o be termed a p r e d a t o r . C a p s u l e s were checked e v e r y 1-2 days f o r e v i d e n c e o f p r e d a t i o n and 59 e x p e r i m e n t s were c o n t i n u e d f o r a t l e a s t two weeks o r u n t i l a l l c a p s u l e s had been opened, w h i c h e v e r o c c u r r e d f i r s t . A summary o f t h e s p e c i e s t e s t e d i s g i v e n i n T a b l e I . F i v e t o t e n r e p l i c a t e s , i n c l u d i n g c o n t r o l s c o n s i s t i n g o f cages w i t h no p r e d a t o r s , were conducted f o r each s p e c i e s . L a b o r a t o r y e x p e r i m e n t s were a l s o c o nducted t o d e t e r m i n e t h e maximum r a t e a t w h i c h p r e d a t o r s c o u l d open egg c a p s u l e s . P r e d a t o r s o f v a r i o u s s i z e s were caged i n d i v i d u a l l y i n mesh c o n t a i n e r s (8x8x10 cm) and p l a c e d i n seawater t a b l e s . A n i m a l s were s t a r v e d f o r 24 h and t h e n each was p r e s e n t e d w i t h 8 i n t a c t N u c e l l a e m a r q i n a t a egg c a p s u l e s . C a p s u l e s were checked a t l e a s t once a day t o d e t e r m i n e t h e number t h a t had been opened. E x p e r i m e n t s were c o n t i n u e d f o r f i v e days o r u n t i l a l l c a p s u l e s had been opened. I I . FIELD CENSUSES OF PREDATION 1. G r a p p l e r I n l e t A l l f i e l d work was conducted i n an i n t e r t i d a l c h a n n e l l o c a t e d a l o n g G r a p p l e r I n l e t . The s u b s t r a t e c o n s i s t e d o f a f i n e s i l t y mud o v e r l a i d by clam s h e l l s and a meshwork o f m u s s e l - and b a r n a c l e - c o v e r e d r o c k s ( M y t i l u s e d u l i s , B a l a n u s  g l a n d u l a and Semibalanus c a r i o s u s ) . Large b o u l d e r s (1.0 m d i a . ) o c c u r r e d t h r o u g h o u t t h i s r e g i o n . I n May 1988 two t r a n s e c t s (10 m i n l e n g t h ) were e s t a b l i s h e d p a r a l l e l t o t h e s h o r e l i n e on t h e e a s t - f a c i n g s l o p e o f t h e c h a n n e l a t 1.2 and 2.2 m above z e r o c h a r t datum. E i g h t q u a d r a t s (0.25m2) were sampled a t 0.5-1.0 m i n t e r v a l s a l o n g t h e s e t r a n s e c t s t o d e t e r m i n e : a) t h e abundance and s i z e o f s n a i l s , b) t h e 60 abundance o f egg c a p s u l e s , and c) t h e number o f egg c a p s u l e s t h a t had been p r e y e d upon. Egg c a p s u l e s were c o l l e c t e d from each q u a d r a t and c a t e g o r i z e d on t h e b a s i s o f whether t h e c a p s u l e chambers were i n t a c t o r r u p t u r e d . The age o f i n t a c t c a p s u l e s was e s t i m a t e d by n o t i n g t h e d e v e l o p m e n t a l s t a g e o f t h e embryos. New c a p s u l e s were i d e n t i f i e d by t h e p r e s e n c e o f n u r s e eggs, w h i l e o l d e r c a p s u l e s c o n t a i n e d w e l l d e v e l o p e d embryos. Opened c a p s u l e s were examined t o d e t e r m i n e whether t h e y had been a t t a c k e d by p r e d a t o r s o r whether d e v e l o p i n g embryos had h a t c h e d n a t u r a l l y . I f c a p s u l e s were empty, but had been chewed i n t o t h e c a p s u l e chamber, t h e y were c o n s i d e r e d t o have been opened by p r e d a t o r s . Such c a p s u l e s were d e s c r i b e d by d i s t i n c t i v e " b i t e marks" on t h e c a p s u l e w a l l s . The abundance o f p o t e n t i a l p r e d a t o r s ( i d e n t i f i e d from l a b o r a t o r y work) was a l s o censused a l o n g t h e s e t r a n s e c t s . 2. Ross I s l e t s A l l f i e l d work was conducted on a n o r t h - f a c i n g beach i n t h e Ross I s l e t s . I n June 1988 t h r e e t r a n s e c t s were e s t a b l i s h e d p a r a l l e l t o t h e r o c k y s h o r e l i n e a t t i d a l h e i g h t s o f 1.9, 2.3 and, 2.6 m above z e r o c h a r t datum. The two h i g h e s t t r a n s e c t s were p o s i t i o n e d a l o n g a s t e e p l y s l o p i n g g r a n i t e w a l l w h i c h was s p a r s e l y c o v e r e d w i t h Fucus d i s t i c h u s , B a l a n u s q l a n d u l a , and Semibalanus c a r i o s u s . The l o w e s t t r a n s e c t was s e t a l o n g a b o u l d e r - c o v e r e d beach d i r e c t l y below t h e h i g h e r t r a n s e c t s . Data were c o l l e c t e d as d e s c r i b e d p r e v i o u s l y f o r t h e G r a p p l e r I n l e t s i t e . A l a r g e r o c k y o u t c r o p p i n g , a d j a c e n t t o t h e s t u d y s i t e , was a l s o censused i n 61 August 1988. The t o p o f t h i s promontory (16 m^) ranged from 2.8-3.1 m above z e r o c h a r t datum and was d e n s e l y c o v e r e d w i t h Fucus d i s t i c h u s , B a l a n u s g l a n d u l a and Semibalanus c a r i o s u s . F o r c e n s u s i n g , t h i s a r e a was d i v i d e d i n t o 6 e q u a l - s i z e d g r i d s and a q u a d r a t was thrown h a p h a z a r d l y i n t o each r e g i o n . S n a i l d e n s i t y , egg c a p s u l e d e n s i t y , and p r e d a t o r abundance were r e c o r d e d as d e s c r i b e d p r e v i o u s l y . 3. Seppings I s l a n d . The s t u d y a r e a was l o c a t e d i n a l a r g e b o u l d e r - l i n e d c h a n n e l , a p p r o x i m a t e l y 10 m wide. C a p s u l e s were r e g u l a r l y c o l l e c t e d t o d e t e r m i n e i f t h e c a p s u l a r remains were s i m i l a r t o t h o s e found a t t h e o t h e r s i t e s . Censuses o f p r e d a t i o n i n t e n s i t y o r p r e d a t o r abundance were not made a t t h i s s i t e . I I I . FIELD EXPERIMENTS E x p e r i m e n t a l cages were used t o a s s e s s t h e i m p o r t a n c e o f p r e d a t i o n on N u c e l l a egg c a p s u l e s and t o i d e n t i f y t h e i n v e r t e b r a t e s r e s p o n s i b l e f o r opening c a p s u l e s a t t h e G r a p p l e r and Ross I s l e t s t u d y s i t e s . Cages a l s o s e r v e d t o e x c l u d e d i f f e r e n t s i z e - c l a s s e s o f p r e d a t o r s from c a p s u l e s . Cages were c o n s t r u c t e d from round p l a s t i c c o n t a i n e r s (9 cm d i a . ) . Each cage c o n s i s t e d o f a base, mounted t o a heavy s l a t e p l a t e , and a frame t h a t screwed i n t o t h e base. Each frame c o n s i s t e d o f two p l a s t i c s u p p o r t s , two l a r g e openings c o v e r e d t o v a r y i n g degrees by window s c r e e n mesh (0.01 cm^), and a mesh l i d ( F i g . l a ) . Egg c a p s u l e s o b t a i n e d from l a b o r a t o r y p o p u l a t i o n s o f N u c e l l a e m a r g i n a t a were g l u e d onto s m a l l p l a s t i c s a u c e r s t h a t 62 b ) 11 1 !! i i S m a l l - H o l e Medium-Hole L a r g e - H o l e Open Fr a m e l e s s FIGURE 1. Predator exclusion cages, i l u s t r a t i n g : a) the cage base and detachable frame and, b) the f i v e cage types used to exclude various s i z e -classes of predators: the small-hole cage (holes: 0.1x0.lcm), medium-hole cage (holes: 0.5x0.5cm), large-hole cage (holes: 1.5x1.5cm), open cage (holes: 2.5x11.5cm) and the frameless cage. 63 screwed i n t o t h e base o f each cage. Four t y p e s o f cage frames were made t o p r o v i d e d i f f e r i n g degrees o f p r e d a t o r - a c c e s s t o egg c a p s u l e s ( F i g . l b ) . S i z e s o f e n t r y h o l e s were 0.1x0.1 cm ( s m a l l - h o l e c a g e ) , 0.5x0.5 cm (medium-hole c a g e ) , 1.5x1.5 cm ( l a r g e - h o l e cage) and 11.0x2.5 cm (open c a g e ) . To d e t e r m i n e t h e p r e d a t i o n i n t e n s i t y on u n p r o t e c t e d c a p s u l e s , c a p s u l e s were mounted on cage bases w i t h o u t a p r o t e c t i v e frame ( h e r e a f t e r r e f e r r e d t o as f r a m e l e s s c a g e s ) . 1. G r a p p l e r I n l e t A t t h e G r a p p l e r I n l e t s i t e cages were p l a c e d a l o n g e s t a b l i s h e d t r a n s e c t s (1.2 m and 2.2 m above z e r o c h a r t datum) i n June 1988. T w e n t y - f i v e cage bases were p l a c e d i n f i v e groups o f f i v e a l o n g b o t h h i g h and low t r a n s e c t s . Each group o f f i v e r e p r e s e n t e d a s a m p l i n g b l o c k . I n each b l o c k , cage bases were p l a c e d a p p r o x i m a t e l y 5 cm away from one a n o t h e r i n o r d e r t o m i n i m i z e p h y s i c a l and b i o l o g i c a l d i f f e r e n c e s among cages. D i f f e r e n t b l o c k s were p l a c e d 0.5-1.0 m a p a r t a l o n g t h e t r a n s e c t l i n e depending on where s u i t a b l e h a b i t a t s were a v a i l a b l e . To d e t e r m i n e i f d i f f e r e n t p r e d a t i o n r a t e s o c c u r r e d w i t h i n and among cage b l o c k s due t o a heterogeneous d i s t r i b u t i o n o f p r e d a t o r s or cage e f f e c t s , a p i l o t e x periment was p e r f o r m e d u s i n g f r a m e l e s s cages. T h i s gave an e s t i m a t e o f t h e n a t u r a l p r e d a t i o n r a t e on egg c a p s u l e s i n t h e f i e l d . E i g h t c a p s u l e s were g l u e d t o each p l a s t i c s a u c e r , which, i n t u r n , was screwed i n t o each cage base. To p r e v e n t c a p s u l e s from d r y i n g , b a r n a c l e - and m u s s e l - c o v e r e d r o c k s were c a r e f u l l y p l a c e d over 64 each cage base, c o v e r i n g c a p s u l e s from d i r e c t s u n l i g h t . C a p s u l e s were checked f o r s i g n s o f p r e d a t i o n on a l t e r n a t e days (except when t i d e l e v e l s were not low enough). C a p s u l e s t h a t d i s a p p e a r e d from t h e i r s a u c e r s d u r i n g t h e experiment were assumed t o have been l o s t due t o w a v e - a c t i o n o r c u r r e n t s , u n l e s s t h e r e was e v i d e n c e t h a t t h e y had been removed by p r e d a t o r s . L o s t c a p s u l e s were r e p l a c e d w i t h f r e s h c a p s u l e s from t h e l a b o r a t o r y . T h i s experiment was t e r m i n a t e d a f t e r 19 days, when a s u f f i c e n t number o f c a p s u l e s had been opened by p r e d a t o r s . F o l l o w i n g t h i s p i l o t e x p e r i m e n t , I t h e n used cage frames t o e x c l u d e c e r t a i n s i z e - c l a s s e s o f p r e d a t o r s . Four frames, one o f each t y p e , were randomly a s s i g n e d t o cage bases w i t h i n each b l o c k , and one cage base was l e f t w i t h o u t a frame. E i g h t c a p s u l e s were p l a c e d w i t h i n each cage. These were checked e v e r y second day f o r s i g n s o f p r e d a t i o n . At each check, a l l i n t a c t c a p s u l e s were r e p l a c e d w i t h t h e same number o f f r e s h c a p s u l e s from t h e l a b o r a t o r y . F i e l d - c o l l e c t e d c a p s u l e s were examined t h o r o u g h l y f o r s i g n s o f p r e d a t i o n and, i f d e v e l o p i n g embryos were s t i l l h e a l t h y and c a p s u l e s s t i l l s e c u r e l y g l u e d , t h e s e c a p s u l e s were r e u s e d . 2. Ross I s l e t s A t t h e Ross I s l e t s i t e , cages were p l a c e d a l o n g t h e low i n t e r t i d a l b o u l d e r beach (1.9 m above z e r o c h a r t datum) and h i g h e r i n t e r t i d a l r o c k y o u t c r o p p i n g (2.9 - 3.1 m above z e r o c h a r t datum), d u r i n g August and September 1988. Because o f t h e uneven s u b s t r a t e a l o n g t h e r o c k y o u t c r o p p i n g , cages were 65 not p l a c e d a l o n g a t r a n s e c t . I n s t e a d , cage b l o c k s were p l a c e d wherever t h e s u b s t r a t u m was r e l a t i v e l y f l a t and Fucus c o v e r abundant. P i l o t and p r e d a t o r - e x c l u s i o n e x p e r i m e n t s were c a r r i e d out as d e s c r i b e d p r e v i o u s l y f o r t h e G r a p p l e r I n l e t s i t e . As t h e s e e x p e r i m e n t s were co n d u c t e d over a much s h o r t e r p e r i o d a t Ross I s l e t s t h a n a t G r a p p l e r I n l e t , c a p s u l e s were o n l y r e p l a c e d i f t h e y had d r i e d o u t . E x p e r i m e n t s l a s t e d f o r 6-8 days. IV SUSCEPTIBILITY OF CAPSULES TO PREDATORS L a b o r a t o r y e x p e r i m e n t s were conducted t o d e t e r m i n e i f t h i c k - and t h i n - w a l l e d c a p s u l e s were e q u a l l y s u s c e p t i b l e t o p r e d a t i o n . C a p s u l e s d i f f e r e d s u b s t a n t i a l l y among s i t e s i n w a l l t h i c k n e s s (Chapter 1 ) . T h i c k - w a l l e d c a p s u l e s were found a t t h e G r a p p l e r I n l e t and Seppings I s l a n d s i t e s , w h i l e t h i n -w a l l e d c a p s u l e s were p r e s e n t a t Ross I s l e t s . P r e d a t o r y i s o p o d s , I d o t e a w o s n e s e n s k i i , were t e s t e d t o d e t e r m i n e i f t h e y e x h i b i t e d p r e f e r e n c e s f o r t h i c k - o r t h i n - w a l l e d c a p s u l e s . My f i e l d o b s e r v a t i o n s and a l s o t h o s e by Emlen (1966) i n d i c a t e d t h a t t h e s e might be i m p o r t a n t p r e d a t o r s o f N u c e l l a e m a r g i n a t a egg c a p s u l e s . I d o t e a (X = 2.1 cm i n l e n g t h ) were c o l l e c t e d from r o c k s i n G r a p p l e r I n l e t d u r i n g November 1988. Groups o f t h r e e I d o t e a were p l a c e d i n m e s h - p a n e l l e d cages (8x8x10 cm), which were t h e n p a r t i a l l y immersed i n t r a y s o f f r e s h seawater. These p r e d a t o r s were s t a r v e d f o r 24 h and t h e n g i v e n f i v e c a p s u l e s from each o f two s n a i l p o p u l a t i o n s (10 c a p s u l e s i n t o t a l ) . P r e d a t o r p r e f e r e n c e s were t e s t e d f o r : a) t h i c k vs 66 t h i n - w a l l e d c a p s u l e s ( G r a p p l e r v s . Ross, and Seppings v s R o s s ) , and b) t h i c k - v s t h i c k - w a l l e d c a p s u l e s ( G r a p p l e r vs Seppings) . C a p s u l e s were a r r a n g e d i n a^  c i r c u l a r c o n f i g u r a t i o n such t h a t c a p s u l e s from each p o p u l a t i o n were i n t e r s p e r s e d . Cages were checked d a i l y and t h e number o f c a p s u l e s opened was r e c o r d e d . E x p e r i m e n t s were t e r m i n a t e d when 4-6 out o f 10 c a p s u l e s had been opened. F i v e t o t e n r e p l i c a t e cages were used f o r each c o m b i n a t i o n o f c a p s u l e t y p e s . 67 RESULTS I. LABORATORY EXPERIMENTS Only three types of invertebrates tested opened Nucella  emarginata egg capsules i n the laboratory: isopods (Idotea  wosnesenskii), shore crabs (Hemigrapsus nudus and Hemigrapsus  oregonensis), and chitons (Mopalia spp.) (Table I ) . Idotea wosnesenskii regularly preyed upon egg capsules in laboratory experiments. Caged Idotea (1.6 - 3.2 cm i n body length; X = 2.2 cm) opened a mean of 4.5 Nucella capsules over a five-day period (Fig. 2a). Feeding rates varied among individuals, but not i n r e l a t i o n to size or sex. Newly hatched Idotea (5 mm i n length) did not prey on egg capsules in the laboratory. Other i n t e r t i d a l isopods (eg., Gnorimosphaeroma oregonense (X = 0.9cm) and Cirolana harfordi (X = 1.4cm)), nibbled extensively around the capsular plug, but never chewed through capsule walls. Idotea rea d i l y consumed both the contents of egg capsules, as well as the capsule walls. Of 51 capsules opened by Idotea i n laboratory tests, 16% were chewed to the stem, 53% were p a r t i a l l y chewed and emptied of a l l eggs, and 31% were p a r t i a l l y chewed but s t i l l contained developing embryos. Although the isopods often ate large portions of the capsular cases, they did not digest t h i s material extensively. Pieces of capsular wall passed through t h e i r guts apparently i n t a c t . The shore crabs Hemigrapsus nudus and Hemigrapsus  oregonensis frequently opened capsules i n the laboratory. Larger crabs opened considerably more capsules over the f i v e 68 TABLE I. Summary of the species tested f o r predatory a c t i v i t y on Nucella  emarginata egg capsules i n the laboratory. Groups of i n d i v i d u a l s of each species were presented with 8 i n t a c t egg capsules f o r a two-week period, or u n t i l a l l capsules had been opened. Five to ten r e p l i c a t e s (with controls) were conducted for each species. Species that were found to open capsules on a consistent basis are indicated with an "X". PHYLUM SPECIES TESTED PREDATORS NEMERTINEA Emplectonema aracile ANNELIDA Nereis vexillosa MOLLUSCA Mopalia spp. X Littorina scutulata Onchidella borealis Searlesia dira Teaula funebralis Nucella emarainata juveniles adults ARTHROPODA Paaurus aranosimanus Paaurus hirsutiusculus Hemiaraosus nudus X Hemiaraosus oreaonensis X Idotea wosnesenskii X Gnorimosohaeroma oreaonense Cirolana harfordi ECHINODERMATA Leotasterias hexactis Pisaster ochraceus CHORDATA Oliaocottus maculosus Anoplarchus purpurescens 69 a) CO LU _) 3 CO CL < o I— o < UJ m TIME (days ) b) < CO => CL < o o UJ m H E M I G R A P S U S N U D U S SMALL MEDIUM LARGE 2 3 4 TIME (DAYS) FIGURE 2. Mean number (+ 1 S.E.) of Nucella emarginata egg capsules remaining i n t a c t a f t e r 5 days exposure to: a) isopods, Idotea wosnesenskii (n = 11) and b) three s i z e - c l a s s e s of Hemigrapsus nudus (small: <1.5 cm carapace width (n=10); medium: 1.5-2.5 cm carapace width (n=18); and large: >2.5 cm carapace width (n=9)). A l l animals were confined i n d i v i d u a l l y with 8 i n t a c t egg capsules on Day 0, and the number of egg capsules remaining i n t a c t was recorded d a i l y . 70 -day p e r i o d t h a n s m a l l e r c r a b s ( F i g . 2 b ) . Hemigrapsus spp. e x h i b i t e d two methods o f opening t h e c a p s u l e s . L a r g e r c r a b s were a b l e t o r u p t u r e t h e p l u g by s q u e e z i n g t h e c a p s u l e body w i t h t h e i r c h e l a e . However, c r a b s u s u a l l y chewed t h r o u g h t h e p l u g r e g i o n d i r e c t l y i n t o t h e c a p s u l e chamber. A l t h o u g h Hemigrapsus spp. o f t e n consumed l a r g e p o r t i o n s o f t h e c a p s u l a r case i n t h i s p r o c e s s , l i k e I d o t e a , t h e y d i d not seem t o d i g e s t t h i s m a t e r i a l . Few N u c e l l a e m a r g i n a t a c a p s u l e s were opened by M o p a l i a spp. i n t h e l a b o r a t o r y t e s t s . Over a two week p e r i o d , 21 c h i t o n s o n l y opened 6 o f 56 c a p s u l e s . I d o t e a , Hemigrapsus, and M o p a l i a spp. l e f t v e r y d i s t i n c t i v e c a p s u l a r remains ( F i g . 3 ) . I d o t e a t e n d e d t o chew t h r o u g h t h e s i d e s o f c a p s u l e chambers and l e f t c h a r a c t e r i s t i c " b i t e marks". Hemigrapsus spp, i n c o n t r a s t , u s u a l l y chewed c a p s u l e s from t h e p l u g downwards and l e f t b r o a d "U-shaped" marks and sometimes s m a l l t e a r s i n t h e c a p s u l e w a l l . C a p s u l e s squeezed open by c r a b s showed no e v i d e n c e o f p r e d a t i o n o t h e r t h a n t h e absence o f a c a p s u l a r p l u g . C h i t o n s e x h i b i t e d t h e most v a r i a b l e t y p e o f p r e d a t i o n on c a p s u l e s . They u s u a l l y r a s p e d c a p s u l e s near t h e base o f t h e c a p s u l e chamber, sometimes c o m p l e t e l y s e v e r i n g t h e c a p s u l e body from t h e stem. However, t h e y c o u l d a l s o open c a p s u l e s by d r i l l i n g s m a l l h o l e s (approx. 0.03mm2) i n t h e c a p s u l e w a l l w i t h t h e i r r a d u l a e . I n summary, o n l y f o u r o f 17 i n v e r t e b r a t e s p e c i e s t e s t e d i n t h e l a b o r a t o r y were found t o open N u c e l l a e m a r g i n a t a egg c a p s u l e s . Of t h e s e , c r a b s and i s o p o d s appeared t o be t h e most p o t e n t i a l l y dominant p r e d a t o r s . As t h e c a p s u l a r remains o f 71 FIGURE 3. C h a r a c t e r i s t i c s of s p e c i e s - s p e c i f i c predation on Nucella  emarginata capsules by: Idotea wosenesenskii (A, E), Hemigrapsus spp. (B, F), Mopalia spp. (C, G), and an unknown predator (D, H). For each type of predator, a whole mount of the opened capsule i s shown (Mag: 8X), with a close-up below i l l u s t r a t i n g the c h a r a c t e r i s t i c "bite-marks" (Mag: 25X-50X). 73 each p r e d a t o r was d i s t i n c t , c a p s u l e s opened by t h e s e i n v e r t e b r a t e s were r e a d i l y i d e n t i f i a b l e i n t h e f i e l d . A l t h o u g h f i s h s p e c i e s were not b r o a d l y t e s t e d as p r e d a t o r s o f c a p s u l e s , t i d e p o o l s c u l p i n s ( O l i g o c o t t u s maculosus) and cockscomb p r i c k l e b a c k s (Anoplarchus p u r p u r e s c e n s ) d i d not appear t o eat c a p s u l e s i n t h e l a b o r a t o r y . I I . FIELD CENSUSES OF PREDATION 1. G r a p p l e r I n l e t N u c e l l a e m a r q i n a t a and t h e i r egg c a p s u l e s were most abundant i n t h e lower r e g i o n s o f t h e i n t e r t i d a l c h a n n e l (Table I I ) , w i t h egg c a p s u l e s b e i n g d e p o s i t e d deep w i t h i n t h e dense meshwork o f m u s s e l - and b a r n a c l e - c o v e r e d r o c k s . Three known p r e d a t o r s o f N u c e l l a c a p s u l e s , Hemigrapsus o r e g o n e n s i s (1.0 - 2.2 cm i n cara p a c e w i d t h ) , I d o t e a w o s n e s e n s k i i (2.1 -2.9 cm i n body l e n g t h ) and M o p a l i a spp. (2 - 6 cm i n body l e n g t h ) , were p r e s e n t i n t h i s r e g i o n , w i t h M o p a l i a spp. b e i n g t h e most numerous. A p p r o x i m a t e l y 18% o f c a p s u l e s c o l l e c t e d a l o n g t h e l o w e r t r a n s e c t had been opened by p r e d a t o r s (Tables I I and I I I ) . The m a j o r i t y o f t h e s e c a p s u l e s appeared t o have been e a t e n by i s o p o d s , even though t h e y were s c a r c e a t t h e t i m e o f c e n s u s i n g . Only 2 c a p s u l e s showed e v i d e n c e o f p r e d a t i o n by Hemigrapsus spp; however, t h e s e a n i m a l s may have been r e s p o n s i b l e f o r a number o f t o r n and chewed c a p s u l e s found a l o n g t h i s t r a n s e c t . Some c a p s u l e s had been emptied by means o f one or two b e v e l l e d h o l e s (0.4x0.2mm; F i g . 3 ) . The p r e d a t o r s o f t h e s e c a p s u l e s were p r o b a b l y i n t e r t i d a l g a s t r o p o d s , s i n c e t h e y have been r e p o r t e d t o make s i m i l a r 74 TABLE I I . Density (X + 1 S.D.) of Nucella emarginata. t h e i r egg capsules, and egg capsule-predators at study s i t e s i n Grappler Inlet and Ross I s l e t s . Estimates were based on censuses of 8 quadrats (0.25 m^ ) f o r s n a i l s and egg capsules and 9 quadrats f o r predators along each transect. Two transects, 1.2 m and 2.0 m above zero chart datum, were sampled at Grappler Inlet i n May 1988. Three i n t e r t i d a l transects, 1.9, 2.3, and 2.6m above zero chart datum, were sampled at Ross I s l e t s i n June 1988, and a fourth area, 2.8-3.1 m above zero chart datum, was sampled i n August 1988. The percentage of capsules opened by predators was determined by d i v i d i n g the number of torn and chewed capsules by the t o t a l number of egg" capsules c o l l e c t e d along each transect. ROSS ISLETS GRAPPLER ~- O 53 0 0 O 71 1 33 «< L J O • "3 H - -3 3 Z — n z ON 3 o o VS 3 X o 3 o £ 1 + C O L I ( T V ON O 1 + N ) C O ON 1 + o o VS M CN 1 + ON H-m o o + ON o VO ON o o VO ON 1+ to < j v o C i o ON 1+ ON o 3 Z It D J c 3 •1 o 0 en i O < T > H -H - rt-3 0 i 0 ) \ rt- 3 oi r v f l a n> 3 o 0 tn 0 1 m -v rt-0 1 c \ M 3 ra oi ^ o 0 0 1 - 1 13 n to m o> a 3 •a 0 i a> 0 1 r t a c 0 h - ' i-( C 3 ( H 0 1 0 1 m id 3 3 p - O » l-i H -1 - 1 0 1 T J U l c 0 1 \ 3 D 3 0 oi 3 O 2 n> J3 3 oi p 0 Ul 0 1 M l 3 CAPSULE CHAMBER INTACT CAPSULE CHAMBER OPENED CATEGORIZATION OF CAPSULAR REMAINS Tot a l * of Capsules Contained Ova Contained Embryos Hatched Naturally Opened by Predators Hemigrapsus Idotea Mopalia Bevelled Misc. Predation Predation Predation Holes Predation LOW (1.2 m) 255 88(35) 55(22) 55(22) 47(18) 2 (4) 20 (43) 1 (2) 8 ( 17) 16 (34) u HIGH (2.0 m) 19 13 (68) - - 6(32) 6(100) - -a 167 43(26) 75(45) 2(1) 43(26) 36 ( 84) - 1 (2) 6 ( 14) LOW INTERTIDAL BOULDERS (1.2 m) 140 26(19) 86 (61) - 24(17) 22(92) - - 2(8) 187 52 (28) 83(44) - 20(11) 2(10) 14(70) - - 4(20) LOW (1.8 m) 37 17(46) 2(5) 9(24) 9(24) 9(100) - -ETS MID (2.3 m) 139 27(19) 18(13) 63(45) 31(22) 24 ( 77) - - - 7(23) ISL HIGH (2.6 in) 10 10(100) _ _ _ _ _ _ . _ ROSS ROCKY OUTCROPPING (2.8-3.1 m) 1117 2(0) 75(7) 779(70) 242(22) 177(73) - - 1(0) 64(26) 78 d r i l l h o l e s i n o t h e r g a s t r o p o d egg c a p s u l e s (Abe, 1983). The d e n s i t y o f s n a i l s and egg c a p s u l e s was low a l o n g t h e h i g h t r a n s e c t a t G r a p p l e r I n l e t (Table I I ) . I n c o n t r a s t , egg c a p s u l e p r e d a t o r s (eg. Hemigrapsus and Idotea) were n o t a b l y more abundant t h a n i n t h e lower p a r t s o f t h e i n t e r t i d a l c h a n n e l . The p e r c e n t a g e o f c a p s u l e s opened i n t h i s r e g i o n was h i g h , w i t h a l l chewed c a p s u l e s showing e v i d e n c e o f p r e d a t i o n by I d o t e a (Table I I I ) . T a b l e I I I a l s o shows t h e e x t e n t o f p r e d a t i o n on c a p s u l e s c o l l e c t e d from t h r e e b o u l d e r s a l o n g t h e l o w e r i n t e r t i d a l t r a n s e c t . I d o t e a were o f t e n found amongst t o r n egg c a p s u l e s and appeared t o be r e s p o n s i b l e f o r t h e m a j o r i t y o f p r e d a t i o n on t h e s e c a p s u l e s . The p e r c e n t a g e o f c a p s u l e s opened by p r e d a t o r s ranged from 17 - 26 % on two o f t h e b o u l d e r s , a l t h o u g h t h e y were l e s s t h a n 0.5 m a p a r t . On t h e t h i r d b o u l d e r , a p p r o x i m a t e l y 10 m away, o n l y 11% o f c a p s u l e s had been opened. 2. Ross I s l e t s D e n s i t i e s o f s n a i l s and egg c a p s u l e s v a r i e d markedly among t r a n s e c t s a t t h e Ross I s l e t s s i t e (Table I I ) . A l l c a p s u l e s a t t h i s s i t e were a t t a c h e d t o v e r t i c a l s u r f a c e s or overhangs. The e x t e n t o f p r e d a t i o n on c a p s u l e s d e c r e a s e d w i t h i n c r e a s e d t i d a l h e i g h t , and c o r r e s p o n d e d w e l l w i t h t h e d e n s i t y o f Hemigrapsus nudus (0.6 - 2.4 cm i n c a r a p a c e w i d t h ) , t h e o n l y known p r e d a t o r s o f N u c e l l a egg c a p s u l e s a t t h i s s i t e . A l t h o u g h c r a b s were not p r e s e n t a l o n g t h e h i g h e r t r a n s e c t s when censuses were t a k e n , on subsequent v i s i t s c r a b s were 79 o c c a s i o n a l l y found i n s m a l l c r e v i c e s a l o n g t h e 2.3 and 2.6m t r a n s e c t s . The m a j o r i t y o f opened egg c a p s u l e s appeared t o have been e a t e n by Hemigrapsus spp. (Table I I I ) . Only 3 c a p s u l e s had b i t e marks s i m i l a r t o t h o s e a s s o c i a t e d w i t h I d o t e a , and o n l y one o f t h e s e i s o p o d s was e v e r found i n t h e s t u d y a r e a . Censuses o f t h e h i g h i n t e r t i d a l o u t c r o p p i n g a t Ross I s l e t s i n August 1988 a l s o i n d i c a t e d t h a t Hemigrapsus spp. were i m p o r t a n t p r e d a t o r s . Over 22% o f t h e s e c a p s u l e s appeared t o have been opened by p r e d a t o r s , w i t h t h e m a j o r i t y showing e v i d e n c e o f a t t a c k by Hemigrapsus. 3. Seppings I s l a n d Egg c a p s u l e s from Seppings I s l a n d showed e v i d e n c e o f b i t e - m a r k s by b o t h I d o t e a and Hemigrapsus. D e s p i t e t h e g r e a t e r l e v e l s o f wave a c t i o n a t t h i s s i t e , I d o t e a  w o s n e s e n s k i i and Hemigrapsus nudus were abundant, e s p e c i a l l y w i t h i n t h e t h i c k beds o f M y t i l u s c a l i f o r n i a n u s . C a p s u l e s were a l s o found w i t h b e v e l l e d h o l e s i d e n t i c a l t o t h o s e c o l l e c t e d from G r a p p l e r I n l e t ( F i g . 3 ) . I n summary, p r e d a t o r s were found t o have opened up t o 32% and 24% o f egg c a p s u l e s p r e s e n t a t t h e G r a p p l e r I n l e t and Ross I s l e t s s i t e s , r e s p e c t i v e l y . O b s e r v a t i o n s o f c a p s u l a r remains i n d i c a t e d t h a t t h e i n t e r t i d a l i s o p o d s , ( I d o t e a  w o s n e s e n s k i i ) , c r a b s (Hemigrapsus o r e g o n e n s i s ) , and unknown g a s t r o p o d s were r e s p o n s i b l e f o r t h e m a j o r i t y o f p r e d a t i o n a t G r a p p l e r I n l e t , whereas c r a b s , (Hemigrapsus nudus), were t h e o n l y numerous p r e d a t o r s a t t h e Ross I s l e t s s i t e . 8 0 I I I . FIELD EXPERIMENTS 1 . G r a p p l e r I n l e t a) P i l o t e x p e r i m e n t s C a p s u l e s were l e f t w i t h i n f r a m e l e s s cages f o r a p e r i o d o f 1 9 days. Over t h i s p e r i o d a mean o f 2.0 + 0.3 (X + 1 S . E . , n=25 cages) and 1.8 ± 0.3 c a p s u l e s (n=25 cages) were opened i n t h e low and h i g h i n t e r t i d a l cages, r e s p e c t i v e l y (out o f a p o s s i b l e 8 c a p s u l e s / c a g e ) . The number o f c a p s u l e s opened by p r e d a t o r s d i d not d i f f e r s i g n i f i c a n t l y w i t h cage p o s i t i o n w i t h i n o r among b l o c k s a l o n g each t r a n s e c t (low t r a n s e c t : ANOVA; F W I T H I N = 0 . 7 3 , p > 0 . 2 5 ; F ^ Q J J Q = 1 . 5 3 , p > 0 . 1 0 ; h i g h t r a n s e c t : ANOVA; F W I T H I N = 1 . 3 4 , p > 0 . 2 5 ; FJ^JQNG = 2 . 1 7 , p > 0 . 1 0 ) . Hence, p r e d a t i o n l e v e l s were r e l a t i v e l y c o n s t a n t a t each t i d a l l e v e l . A mean o f 6.1 c a p s u l e s were " l o s t " i n t o t a l from a l l cages (n=50) over a two day p e r i o d . A l t h o u g h t h e cause o f l o s t c a p s u l e s was unknown, I s u s p e c t e d t h a t c a p s u l e s became de t a c h e d due t o a f a i l u r e o f t h e g l u e . T a b l e IV shows t h e t y p e o f c a p s u l a r remains found i n t h e f r a m e l e s s cages a f t e r 1 9 days. A l o n g t h e low i n t e r t i d a l t r a n s e c t shore c r a b s (Hemigrapsus o r e g o n e n s i s ) appeared t o be r e s p o n s i b l e f o r t h e m a j o r i t y o f p r e d a t i o n ; however, i n some cas e s t h e p r e d a t o r s o f egg c a p s u l e s c o u l d not be i d e n t i f i e d . A l o n g t h e h i g h e r i n t e r t i d a l t r a n s e c t , i s o p o d s (Idotea) were t h e c h i e f p r e d a t o r s and were f r e q u e n t l y found e a t i n g c a p s u l e s . Fewer c a p s u l e s were opened by Hemigrapsus o r e g o n e n s i s o r d r i l l e d by o t h e r p r e d a t o r s i n t h i s r e g i o n . TABLE IV. Summary of Nucella emarginata egg capsules opened by predators i n the p i l o t experiment i n Grappler Inlet, June 1988. Capsules were c l a s s i f i e d by the b i t e and chew marks l e f t on the capsular chamber. C H A R A C T E R I S T I C S O F C A P S U L A R R E M A I N S Hemigrapsus Idotea B e v e l l e d Mopalia Misc. T o t a l # Chew Marks Chew Marks Holes r a s p i n g P r e d a t i o n Eaten LOW TRANSECT (1.2 m) 17 - 14 1 19 51 HIGH TRANSECT (2.0 m) 4 22 2 - 16 44 82 b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s P r e d a t o r - e x c l u s i o n e x p e r i m e n t s r e v e a l e d t h a t t h e major p r e d a t o r s o f c a p s u l e s a t t h e G r a p p l e r s i t e were l a r g e r t h a n t h e 2.25 cm 2 e n t r y h o l e s o f t h e l a r g e - h o l e cages ( F i g . 4a,b). The number o f c a p s u l e s opened a f t e r 20 days v a r i e d s i g n i f i c a n t l y among cage t y p e s ( K r u s k a l - W a l l i s One-Way ANOVA: low t r a n s e c t , K=10.41, P<0.05; h i g h t r a n s e c t , K=8.37, P<0.05) w i t h c a p s u l e s i n t h e open and f r a m e l e s s cages e x p e r i e n c i n g t h e most p r e d a t i o n . D u r i n g t h i s e x p e r i m e n t , c r a b s (Pagurus granosimanus, Pagurus h i r s u i t i s c u l u s , Hemigrapsus o r e g o n e n s i s ) , i s o p o d s ( I d o t e a w o s n e s e n s k i i ) and whelks ( N u c e l l a l a m e l l o s a , N u c e l l a  emarginata) were o f t e n found w i t h i n t h e open and f r a m e l e s s cages. Other i n t e r t i d a l s n a i l s ( S e a r l e s i a d i r a and L i t t o r i n a spp.) r e g u l a r l y e n t e r e d cages w i t h e n t r y h o l e s as s m a l l as 2.25 cm 2. Of t h e s e organisms, Hemigrapsus and I d o t e a were t h e o n l y a n i m a l s t h a t opened N u c e l l a e m a r g i n a t a c a p s u l e s i n t h e l a b o r a t o r y and, i n f a c t , t h e m a j o r i t y o f opened c a p s u l e s appeared t o have been chewed by Hemigrapsus. As no c a p s u l e s were opened i n t h e s m a l l - h o l e cages, s m a l l e r organisms o f t e n found i n t h e s e cages such as nemerteans, nematodes, and p o l y c h a e t e s were p r o b a b l y not i m p o r t a n t p r e d a t o r s . 2. Ross I s l e t s a) P i l o t e x p e r i m e n t s C a p s u l e s were p l a c e d i n f r a m e l e s s cages a t Ross I s l e t s f o r a p e r i o d o f 6 days. D u r i n g t h i s p e r i o d t h e i n t e n s i t y o f p r e d a t i o n on c a p s u l e s was s e v e r e compared w i t h t h e G r a p p l e r 83 a) tn UJ _ i 3 co < o i— o < o or UJ CD 3 2 8.0ii 7.6 7.2 6.8 6.4 6.0 o-• -V -.o FRAMELESS • OPEN V LARGE-HOLE •A MEDIUM-HOLE A SMALL-HOLE — i 1 — • — i 1 1 r — — i 1 1 1 1 1 1 1 1 1 1 1 1 , — 0 2 4 6 8 10 12 14 16 18 20 TIME (days ) b ) CO 3 00 CL < o y— < O or Ld CO 3 8.0 7.6 7.2 6.8 6.4 6.0 • -o-o-A -• -.• FRAMELESS •O OPEN •O LARGE-HOLE A MEDIUM-HOLE SMALL-HOLE 10 12 14 16 18 20 TIME (days ) FIGURE 4. Results of the predator-exclusion experiments i n Grappler Inlet, July 1988 f o r : a) the low i n t e r t i d a l transect (1.2 m above zero chart datum) and b) the high transect (2.0m above zero chart datum). Each point represents the mean number of capsules remaining i n t a c t i n f i v e r e p l i c a t e cages ( i e . one cage from each block) f o r each cage type . 84 I n l e t s i t e . A mean o f 7.7 + 0.3 (X ± 1 S.E., n=25 cages) and 4.8 +. 0.5 (n=25 cages) c a p s u l e s were opened i n t h e low and h i g h i n t e r t i d a l cages, r e s p e c t i v e l y . The d i f f e r e n c e i n p r e d a t i o n r a t e between t h e s e t i d a l h e i g h t s c o r r e s p o n d e d w e l l w i t h d i f f e r e n c e s i n t h e abundance of shore c r a b s (Table I I ) . P r e d a t o r s o f a p p r o x i m a t e l y 80% o f t h e low i n t e r t i d a l c a p s u l e s and 50% o f t h e h i g h i n t e r t i d a l c a p s u l e s c o u l d not be d e t e r m i n e d . Such c a p s u l e s had e i t h e r been c o m p l e t e l y chewed, l e a v i n g o n l y a stem, or t o t a l l y removed from cage b a s e s . M i s s i n g c a p s u l e s were assumed t o have been removed by p r e d a t o r s , s i n c e : 1) remains o f chewed c a p s u l e s were o c c a s i o n a l l y found nearby and, 2) i n s a u c e r s where c a p s u l e s were m i s s i n g , r e m a i n i n g c a p s u l e s had i d e n t i f i a b l e b i t e marks i n d i c a t i n g t h a t p r e d a t o r s had been a c t i v e . As l a r g e Hemigrapsus were t h e o n l y p r e d a t o r s a b l e t o remove g l u e d c a p s u l e s from r o c k s i n t h e l a b o r a t o r y , t h e s e c r a b s were b e l i e v e d t o be r e s p o n s i b l e f o r most c a p s u l e l o s s e s i n t h e f i e l d . Of t h e r e m a i n i n g chewed c a p s u l e s , 30 o f 32 low i n t e r t i d a l c a p s u l e s showed e v i d e n c e o f Hemigrapsus b i t e marks, w h i l e 53 o f 63 h i g h i n t e r t i d a l c a p s u l e s appeared t o have been a t t a c k e d by t h e s e c r a b s . The number o f c a p s u l e s e a t e n by p r e d a t o r s d i d not d i f f e r w i t h r e s p e c t t o t h e p o s i t i o n o f cages w i t h i n o r among b l o c k s a l o n g t h e low i n t e r t i d a l t r a n s e c t . A f t e r 6 days, a l l c a p s u l e s had been opened, except f o r 7 c a p s u l e s r e m a i n i n g i n one cage. Hence, p r e d a t i o n l e v e l s were r e l a t i v e l y c o n s t a n t i n t h i s r e g i o n . A l o n g t h e h i g h i n t e r t i d a l r e g i o n a few c a p s u l e s s t i l l r emained i n some cages a f t e r t h i s p e r i o d . A l t h o u g h t h e number 85 o f c a p s u l e s opened by p r e d a t o r s d i d not d i f f e r s i g n i f i c a n t l y among cage p o s i t i o n s w i t h i n b l o c k s (ANOVA: F W I T H I N = 0 . 7 4 , p>0.25), t h e number o f c a p s u l e s e a t e n d i d d i f f e r among b l o c k s (ANOVA; F A M 0 N G = 3 • 2 5 , p<0.05). Hence, p r e d a t i o n was p a t c h y a l o n g t h e h i g h i n t e r t i d a l a r e a . T h i s may have been because cage b l o c k s were not p l a c e d a l o n g a t r a n s e c t . S i t e s were o r i g i n a l l y s e l e c t e d f o r h a b i t a t c o v e r , w h i c h may have i n a d v e r t e n t l y l i m i t e d t h e a c c e s s i b i l i t y o f c e r t a i n cage b l o c k s t o p r e d a t o r s . b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s The r e s u l t s o f t h e p r e d a t o r - e x c l u s i o n e x p e r i m e n t s c o n f i r m e d t h a t c r a b s were t h e most i m p o r t a n t p r e d a t o r s a t t h e Ross I s l e t s t u d y s i t e ( F i g . 5 a , b ) . The number o f c a p s u l e s opened d i f f e r e d s i g n i f i c a n t l y among cage t y p e s ( K r u s k a l - W a l l i s t e s t : low t r a n s e c t , H=22.55, P<0.05; h i g h t r a n s e c t , H=17.23; P<0.05), w i t h most c a p s u l e s b e i n g e a t e n i n open and f r a m e l e s s cages. Crabs were o f t e n found w i t h i n t h e l a r g e - h o l e , open and f r a m e l e s s cages, and c a p s u l a r remains i n t h e s e cages were i n d i c a t i v e o f p r e d a t i o n by Hemigrapsus. Other i n v e r t e b r a t e s found r e g u l a r l y i n cages were amphipods, p r e s e n t i n a l l except t h e s m a l l - h o l e cages, and s n a i l s ( S e a r l e s i a d i r a ) , found o n l y i n t h e l a r g e - h o l e , open and f r a m e l e s s cages. C a p s u l e s were a l s o removed by p r e d a t o r s i n t h i s e x p e r i m e n t . F o r t y - f i v e and 57% o f opened c a p s u l e s d i s a p p e a r e d a l o n g t h e low and h i g h t i d a l cages, r e s p e c t i v e l y . No c a p s u l e s were removed i n cages i n a c c e s s i b l e t o Hemigrapsus. I n summary, t h e p r e d a t o r - e x c l u s i o n e x p e r i m e n t s i n d i c a t e d 86 a) TIME (days ) FIGURE 5. Results of the predator-exclusion experiments i n Ross I s l e t s , September 1988 f o r : a) the low i n t e r t i d a l region (1.8 m above zero chart datum) and b) the high i n t e r t i d a l region (2.8-3.1 m above zero chart datum). Each data point represents the mean number of capsules s t i l l i n t a c t i n f i v e r e p l i c a t e cages ( i e . one cage frome each block) f o r each cage type. 87 t h a t r e l a t i v e l y l a r g e organisms, such as I d o t e a and Hemigrapsus spp., were i m p o r t a n t p r e d a t o r s o f c a p s u l e s i n t h e f i e l d . I n c o n t r a s t , s m a l l organisms t h a t c o u l d e n t e r t h e cages w i t h e n t r y h o l e s s m a l l e r t h a n 0.25 cm 2 d i d not o f t e n p r e y on e n c a p s u l a t e d eggs. Caging e x p e r i m e n t s a l s o i n d i c a t e d t h a t p r e d a t i o n on egg c a p s u l e s was more i n t e n s e a t t h e Ross I s l e t s compared w i t h G r a p p l e r I n l e t ( F i g s . 4, 5 ) . These r e s u l t s were c o n t r a r y t o r e s u l t s o f t h e f i e l d c ensuses, which i n d i c a t e d s i m i l a r p e r c e n t a g e s o f c a p s u l e s opened by p r e d a t o r s at t h e two s i t e s . IV. SUSCEPTIBILITY OF CAPSULES TO PREDATORS I d o t e a opened t h i n - w a l l e d c a p s u l e s from Ross I s l e t s more f r e q u e n t l y t h a n t h i c k - w a l l e d c a p s u l e s from e i t h e r G r a p p l e r I n l e t o r Seppings I s l a n d ( F i g . 6 ) . In t e n t r i a l s comparing t h e r e l a t i v e s u s c e p t i b i l i t y o f Ross I s l e t o r G r a p p l e r c a p s u l e s t o t h e s e i s o p o d s , 35 Ross I s l e t c a p s u l e s were opened compared w i t h 15 G r a p p l e r c a p s u l e s ( F i s h e r ' s E x a c t T e s t , P=0.0001). Comparisons between t h e number o f Seppings v e r s u s Ross I s l e t c a p s u l e s opened by I d o t e a showed a s i m i l a r t r e n d , w i t h more Ross I s l e t c a p s u l e s b e i n g opened (16 Ross I s l e t c a p s u l e s v e r s u s 10 Seppings c a p s u l e s ; F i s h e r ' s T e s t , P=0.08). In c o n t r a s t , i s o p o d s d i d not e x h i b i t any p r e f e r e n c e s f o r Seppings v e r s u s G r a p p l e r c a p s u l e s (10 G r a p p l e r v e r s u s 9 Seppings c a p s u l e s ; F i s h e r ' s T e s t , P=0.50). In 2 o f 6 t r i a l s , none o f t h e s e t h i c k - w a l l e d c a p s u l e s were e a t e n d u r i n g a t e n day p e r i o d . Hence, t h e s e r e s u l t s were c o n s i s t e n t w i t h t h e p r e d i c t i o n t h a t t h i c k - w a l l e d c a p s u l e s a r e more r e s i s t a n t t o p r e d a t i o n t h a n t h i n - w a l l e d c a p s u l e s . 88 o LjJ z LU Q_ O CO UJ _ J CO Q_ < o o CQ < 5 + 4 3 + 2 1 0-O T • 1 R O S S VS G R A P P L E R (n=10) T O 1 T A 1 O R O S S • G R A P P L E R A S E P P I N G S R O S S VS S E P P I N G S (n=5) t A G R A P P L E R VS S E P P I N G S (n=6) FIGURE 6. Mean number of the f i r s t f i v e capsules opened by Idotea  wosnesenskii when given a choice of feeding on capsules from two d i f f e r e n t study s i t e s . Predators were placed i n cages with 10 capsules (5 from each site) and the f i r s t f i v e capsules to be opened were recorded. Capsules from Grappler and Seppings Island had walls 20 - 25 % t h i c k e r than ones from Ross I s l e t s . 89 DISCUSSION. P r o s o b r a n c h egg c a p s u l e s have been s u g g e s t e d t o p r o t e c t d e v e l o p i n g embryos from p r e d a t i o n i n t h e b e n t h i c marine environment (Pechenik, 1979; P e r r o n , 1981) . However, few t e s t s have been made o f t h i s a s s u m p t i o n . I f c a p s u l e s do p r o t e c t embryos from p r e d a t i o n , t h e n one would expect t o f i n d d i r e c t e v i d e n c e o f t h i s , i n t h a t : 1) c a p s u l e w a l l s s h o u l d p h y s i c a l l y l i m i t a c c e s s by p r e d a t o r s t o d e v e l o p i n g embryos and, 2) t h e s e s t r u c t u r e s s h o u l d not s e r v e as an energy s o u r c e t h a t might a t t r a c t p r e d a t o r s . Hence, t h e r e s h o u l d be l i t t l e e v i d e n c e o f p r e d a t i o n on egg c a p s u l e s i n t h e i r n a t u r a l h a b i t a t . F u r t h e r m o r e , i f p r e d a t i o n i s an i m p o r t a n t s e l e c t i v e p r e s s u r e a c t i n g upon t h e s t r u c t u r e o f c a p s u l e w a l l s , i n t r a -and 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 c a p s u l e w a l l t h i c k n e s s may a c t u a l l y r e f l e c t d i f f e r e n c e s i n abundance o f i n t e r t i d a l p r e d a t o r s . R e s i s t a n c e o f i n t a c t c a p s u l e s t o p r e d a t o r s I n t h i s s t u d y , egg c a p s u l e s o f N u c e l l a e m a r g i n a t a were found t o be r e s i s t a n t t o some i n t e r t i d a l p r e d a t o r s . Nemerteans (Emplectonema g r a c i l e ) a r e c a p a b l e o f e a t i n g N u c e l l a e m a r g i n a t a embryos c o n t a i n e d w i t h i n r u p t u r e d c a p s u l e s (Glynn, 1965), but t h e s e d i d not open i n t a c t N u c e l l a egg c a p s u l e s i n e i t h e r l a b o r a t o r y o r f i e l d e x p e r i m e n t s . Hermit c r a b s (Pagurus spp.) and s t a r f i s h ( P i s a s t e r o c h r a c e u s and L e p t a s t e r i a s h e x a c t i s ) are a l s o known t o f e e d on j u v e n i l e 90 N u c e l l a spp. ( S p i g h t , 1976; R i v e s t , 1983). However, t h e s e p r e d a t o r s d i d not p r e y upon e n c a p s u l a t e d embryos i n t h i s o r o t h e r s t u d i e s ( S p i g h t , 1977). C a p s u l a r cases t h e r e f o r e do p r o t e c t d e v e l o p i n g embryos from some i n t e r t i d a l p r e d a t o r s . E n c a p s u l a t e d N u c e l l a e m a r g i n a t a embryos were not s a f e from a l l i n t e r t i d a l p r e d a t o r s . Shore c r a b s , Hemigrapsus spp., and i s o p o d s , I d o t e a w o s n e s e n s k i i opened c a p s u l e s i n b o t h my l a b o r a t o r y and f i e l d t e s t s (see a l s o Emlen, 1966; S p i g h t , 1977). C a p s u l e s were a l s o opened by c h i t o n s , M o p a l i a spp., and an unknown p r e d a t o r , w h i c h made s m a l l b e v e l l e d h o l e s i n c a p s u l e w a l l s . I n s t u d i e s by Emlen (1966), F e a r e , (1970), and S p i g h t (1977), egg c a p s u l e s o f N u c e l l a spp. were a l s o e a t e n by c r a b s (Cancer o r e g o n e n s i s ) , sea u r c h i n s ( S t r o n g y l o c e n t r o t u s  d r o e b a c h i e n s i s ) , p o l y c h a e t e s , ( E u l a l i a v i r i d i s ) , s c u l p i n s (Enophrys b i s o n ) and s n a i l s , ( N u c e l l a e m a r g i n a t a ) . A l t h o u g h c a p s u l e w a l l s ' a r e o b v i o u s l y not r e s i s t a n t t o t h e s e organisms, such r e s u l t s do not n e c e s s a r i l y r e f u t e t h e i d e a t h a t c a p s u l e s have e v o l v e d t o p r o t e c t embryos from p r e d a t i o n . O b v i o u s l y , i f t h e s t r u c t u r e and s t r e n g t h o f c a p s u l e s r e p r e s e n t a s e l e c t i v e r e s p onse t o s p e c i f i c p r e d a t o r y s p e c i e s , t h e n t h e r e s i s t a n c e o f c a p s u l e w a l l s s h o u l d depend on t h e f r e q u e n c y t h a t p r e d a t o r s e n c o u n t e r t h e s e c a p s u l e s . Hence, t h e p r o t e c t i v e n a t u r e o f c a p s u l e s can o n l y be i n t e r p r e t e d by e x a m i n i n g t h e r e s i s t a n c e o f c a p s u l e w a l l s t o a n i m a l s t h a t r e g u l a r l y e n c o u n t e r t h e s e c a p s u l e s i n t h e f i e l d . 91 D i g e s t i b i l i t y and p a l a t a b i l i t y o f egg c a p s u l e w a l l s As n o t e d , i f c a p s u l a r cases have e v o l v e d t o p r o t e c t embryos from p r e d a t i o n , t h e n t h e s e s t r u c t u r e s might not o n l y be i m p e r v i o u s t o p r e d a t o r s , but a l s o i n d i g e s t i b l e o r u n p a l a t a b l e . C a p s u l a r cases can c o n t a i n up t o 47% o f t h e t o t a l energy i n v e s t e d i n r e p r o d u c t i v e p r o d u c t s i n some p r o s o b r a n c h s ( P e r r o n , 1981), and t h u s , r e p r e s e n t an energy s o u r c e almost e q u i v a l e n t t o t h a t o f t h e e n c a p s u l a t e d eggs. I n my s t u d y , a l t h o u g h I d o t e a and Hemigrapsus spp. r e a d i l y a t e l a r g e p o r t i o n s o f t h e c a p s u l e w a l l s , t h i s m a t e r i a l d i d not appear t o be d i g e s t e d . S i m i l a r r e s u l t s have been r e p o r t e d by B r e n c h l e y (1982) f o r t h e p r e d a t o r s , L i t t o r i n a l i t t o r e a . Other p r e d a t o r s have been shown t o f e e d e x c l u s i v e l y on t h e c o n t e n t s o f egg c a p s u l e s , r a t h e r t h a n on t h e c a p s u l e w a l l s (MacKenzie, 1961; Abe, 1983). Some p r e d a t o r s have been found t o d i g e s t c a p s u l e w a l l s . B r e n c h l e y (1982) found t h a t c r a b s , C a r c i n u s maenas and Pagurus  l o n g i c a r p u s , can d i g e s t c a p s u l a r cases o f t h e s n a i l I l y a n a s s a  o b s o l e t a . C a p s u l e s o f t h i s g a s t r o p o d s p e c i e s are t y p i c a l l y t h i n - w a l l e d (<10 urn, S u l l i v a n and Maugel, 1984) and c o n t a i n embryos w i t h s h o r t d e v e l o p m e n t a l p e r i o d s compared w i t h t h e t h i c k - w a l l e d c a p s u l e s (60-120yam, Ch a p t e r 1) and l o n g embryonic development t i m e s o f N u c e l l a e m a r g i n a t a . Hence, as P e r r o n (1981) found f o r Conus spp., t h e s e l e c t i v e p r e s s u r e s a c t i n g upon t h e s t r u c t u r e o f g a s t r o p o d egg c a p s u l e s may d i f f e r d epending on embryonic d e v e l o p m e n t a l t i m e . T h e r e f o r e , w h i l e t h e m a j o r i t y o f r e s u l t s would appear t o s u p p o r t t h e p r e d i c t i o n 92 t h a t c a p s u l a r c a s e s a r e not u t i l i z e d as a so u r c e o f energy, g e n e r a l i z a t i o n s about t h e p r o t e c t i v e q u a l i t y o f egg c a p s u l e s among a l l g a s t r o p o d s p e c i e s may be u n j u s t i f i e d . C l e a r l y t h e exposure t i m e o f embryos t o p r e d a t o r y s p e c i e s must a l s o p l a y a l a r g e r o l e i n s e l e c t i o n f o r s p e c i f i c t y p e s o f c a p s u l e s t r u c t u r e s . P r e d a t i o n on egg c a p s u l e s i n t h e f i e l d The n o t i o n t h a t a l l egg c a p s u l e s a r e e f f e c t i v e a t p r o t e c t i n g d e v e l o p i n g embryos has a l s o been c h a l l e n g e d i n s t u d i e s showing e x t e n s i v e p r e d a t i o n on egg c a p s u l e s i n t h e f i e l d . F o r example, B r e n c h l e y (1982) found t h a t 52% o f t h e c a p s u l e s o f t h e mud s n a i l , I l y a n a s s a o b s o l e t a , were opened by c r a b s o r s n a i l s d u r i n g 10 days o f a development p e r i o d l a s t i n g up t o 3 weeks. S p i g h t (1977) n o t e d t h a t p r e d a t o r s opened 77% o f N u c e l l a l a m e l l o s a c a p s u l e s i n some spawning a g g r e g a t i o n s . Other s t u d i e s , such as t h o s e by MacKenzie (1961), Haydock (1964), and Emlen (1966) have a l s o documented h i g h l e v e l s o f p r e d a t i o n on g a s t r o p o d egg c a p s u l e s . These f i n d i n g s t h u s a r e c o n t r a r y t o t h e p r e d i c t i o n t h a t p r e d a t i o n on egg c a p s u l e s i n t h e f i e l d s h o u l d be m i n i m a l . In my s t u d y , f i e l d e s t i m a t e s o f p r e d a t i o n on N u c e l l a  e m a r g i n a t a egg c a p s u l e s were c o m p a r a t i v e l y low. F o r example, one-time censuses o f p r e d a t i o n r e v e a l e d t h a t 18-32% o f c a p s u l e s c o l l e c t e d a t t h e w a v e - s h e l t e r e d G r a p p l e r I n l e t s i t e had been opened by p r e d a t o r s , whereas 0-24% o f c a p s u l e s a l o n g t r a n s e c t s a t Ross I s l e t s had been opened. These r e s u l t s 93 resembled t h o s e o f S p i g h t (1972), who found t h a t 22-25% o f N u c e l l a e m a r g i n a t a c a p s u l e s were opened d u r i n g t h e i r 80 day embryonic d e v e l o p m e n t a l p e r i o d . The e x t e n t o f p r e d a t i o n on egg c a p s u l e s i n t h e p r e s e n t s t u d y was not as s e v e r e as e x p e c t e d g i v e n t h a t : 1) l a b o r a t o r y - i d e n t i f i e d p r e d a t o r s I d o t e a  w o s n e s e n s k i i , and Hemigrapsus spp. were abundant and, 2) f i e l d o b s e r v a t i o n s i n d i c a t e d t h a t t h e s e p r e d a t o r s and o t h e r s d i d eat c a p s u l e s i n t h e f i e l d . N e v e r t h e l e s s , b o t h l a b o r a t o r y and f i e l d r e s u l t s i n d i c a t e d t h a t c a p s u l e s a c t u a l l y o f f e r e d l i t t l e s t r u c t u r a l r e s i s t a n c e t o t h e s e i s o p o d and c r a b p r e d a t o r s . The p o s i t i o n i n g o f c a p s u l e s i n t h e f i e l d by N u c e l l a  e m a r g i n a t a may h e l p t o p r o t e c t embryos from p r e d a t o r s . T h i s was e v i d e n t a t t h e Ross I s l e t s , where s n a i l s always l a i d c a p s u l e s on v e r t i c a l s u r f a c e s and overhangs, r a t h e r t h a n on h o r i z o n t a l s u r f a c e s . P r e d a t i o n on t h e s e c a p s u l e s ranged from 0 - 24%. I n c a g i n g e x p e r i m e n t s where c a p s u l e s were g l u e d onto h o r i z o n t a l s u r f a c e s , p r e d a t i o n was much more i n t e n s e . As c r a b s were abundant at t h i s s i t e , c a p s u l e s p o s i t i o n e d on v e r t i c a l s u r f a c e s were l i k e l y t o be l e s s a c c e s s i b l e t o p r e d a t o r y c r a b s t h a n c a p s u l e s g l u e d t o h o r i z o n t a l s u r f a c e s . In s u p p o r t o f t h i s , few c r a b s were seen a l o n g t h e 2.3 and 2.6m t r a n s e c t s a t Ross I s l e t s where t h e g r a n i t e w a l l s l o p e d s t e e p l y ; however, c r a b s were abundant a l o n g a h o r i z o n t a l b o u l d e r beach and a h i g h r o c k y o u t c r o p p i n g (1.8 and 2.8-3.1 m above z e r o c h a r t datum, r e s p e c t i v e l y ) i n t h e same a r e a . At G r a p p l e r I n l e t , t h e placement o f c a p s u l e s appeared t o be l e s s c r i t i c a l . B o t h f i e l d censuses and c a g i n g e x p e r i m e n t s 94 i n d i c a t e d t h a t t h e r a t e o f p r e d a t i o n was slow, perhaps because t h e d e n s i t y o f c r a b s was g e n e r a l l y lower a t t h i s s i t e . S u s c e p t i b i l i t y o f t h i c k - and t h i n - w a l l e d c a p s u l e s t o p r e d a t o r s T h i c k c a p s u l e s may be more d i f f i c u l t t o open o r r e q u i r e l o n g e r h a n d l i n g t i m e s by p r e d a t o r s t h a n t h i n n e r c a p s u l e s . Hence, t h i c k - w a l l e d c a p s u l e s might be s e l e c t e d f o r i n areas where p r e d a t o r s a r e abundant. The w a l l t h i c k n e s s o f N u c e l l a  e m a r q i n a t a c a p s u l e s has been shown t o v a r y i n t r a s p e c i f i c a l l y (Chapter 1 ) , w i t h t h i c k - w a l l e d c a p s u l e s b e i n g l a i d a t G r a p p l e r I n l e t and Seppings I s l a n d , and t h i n - w a l l e d c a p s u l e s b e i n g l a i d a t Ross I s l e t s . S i n c e t h e d e n s i t y o f c r a b s was h i g h e s t a t t h e Ross I s l e t s where c a p s u l e s were t h i n - w a l l e d , d i f f e r e n c e s i n w a l l t h i c k n e s s e s d i d not c o r r e s p o n d t o t h e d e n s i t y o f t h e s e p r e d a t o r s . I n c o n t r a s t I d o t e a w o s e n e s e n s k i i were o n l y found a t t h e G r a p p l e r and Seppings s i t e s where c a p s u l e s were t h i c k -w a l l e d . I d o t e a opened t h i n - w a l l e d c a p s u l e s more r e a d i l y t h a n t h i c k - w a l l e d c a p s u l e s i n my l a b o r a t o r y e x p e r i m e n t s . However, t h i c k - w a l l e d c a p s u l e s were not t o t a l l y r e s i s t a n t t o p r e d a t i o n , as a l l c a p s u l e s r e g a r d l e s s o f t h i c k n e s s were e v e n t u a l l y e a t e n . N e v e r t h e l e s s , t h e s e r e s u l t s suggest t h a t t h i c k e r c a p s u l e w a l l s may p r o t e c t d e v e l o p i n g embryos b e t t e r t h a n t h i n c a p s u l e w a l l s a g a i n s t c e r t a i n p r e d a t o r s . A l t h o u g h t h i c k - w a l l e d c a p s u l e s may have been s e l e c t e d f o r t h r o u g h t h e a c t i o n o f any number o f e n v i r o n m e n t a l s t r e s s e s (Chapter 1 ) , t h e p r e s e n c e o f p r e d a t o r y i s o p o d s would o b v i o u s l y be e x p e c t e d t o r e i n f o r c e s e l e c t i o n f o r 95 such s t r u c t u r e s . D e s p i t e some e n c o u r a g i n g r e s u l t s from t h i s s t u d y , i t was not p o s s i b l e t o a s s e s s t h e importance o f p r e d a t i o n p r e c i s e l y i n t h e e v o l u t i o n o f c a p s u l a r s t r u c t u r e s . A l t h o u g h p r e d a t i o n on egg c a p s u l e s can be i n t e n s e ( S p i g h t , 1977; B r e n c h l e y , 1982), i t i s not always s e v e r e . T h i s r a i s e s a number o f q u e s t i o n s . I f t h e i n t e n s i t y o f p r e d a t i o n on egg c a p s u l e s i s low i n an a r e a , i s t h i s because c a p s u l a r s t r u c t u r e s have been s e l e c t e d t o p r o t e c t embryos from p r e d a t o r s , o r a r e c a p s u l e s s i m p l y l a i d i n a r e a s where t h e abundance o f p r e d a t o r s i s l i m i t e d ? A l t e r n a t i v e l y , i f p r e d a t i o n on egg c a p s u l e s i s i n t e n s e , i s t h i s because s n a i l s a r e u n a b l e t o produce c a p s u l e s r e s i s t a n t t o p r e d a t i o n , or have s n a i l s responded t o d i f f e r e n t s e l e c t i v e p r e s s u r e s ? The key t o such q u e s t i o n s may l i e i n a b e t t e r u n d e r s t a n d i n g o f how t h e i n t e n s i t y o f p r e d a t i o n on egg c a p s u l e s r e l a t e s t o t h e d e v e l o p m e n t a l t i m e o f e n c a p s u l a t e d embryos. P r e d a t i o n s h o u l d not be e x p e c t e d t o e x e r t t h e same s e l e c t i v e p r e s s u r e on s p e c i e s w i t h s h o r t e n c a p s u l a t e d d e v e l o p m e n t a l t i m e s as i t does on s p e c i e s w i t h l o n g d e v e l o p m e n t a l t i m e s ( c f . P e r r o n , 1981). I t was apparent from t h i s s t u d y t h a t N u c e l l a e m a r q i n a t a embryos were not r e s i s t a n t t o a l l marine p r e d a t o r s . Crabs and i s o p o d s were i m p o r t a n t p r e d a t o r s o f t h e s e c a p s u l e s i n t h e f i e l d ; however, embryos were somewhat p r o t e c t e d from t h e s e by b e i n g d e p o s i t e d i n t h i c k e r c a p s u l a r s t r u c t u r e s and by b e i n g l a i d i n a r e a s i n a c c e s s i b l e t o p r e d a t o r s . A t t e m p t s t o g e n e r a l i z e about t h e p r o t e c t i v e r o l e o f a l l g a s t r o p o d egg 96 c a p s u l e s may prove t o be e x t r e m e l y d i f f i c u l t . C o n f l i c t i n g r e s u l t s i n t h e l i t e r a t u r e suggest t h a t t h e p r o t e c t i v e r o l e o f p r o s o b r a n c h egg c a p s u l e s d i f f e r s among s p e c i e s , and e l u c i d a t i o n o f any g e n e r a l t r e n d s among g a s t r o p o d s p e c i e s may be i m p o s s i b l e . 97 REFERENCES. Abe, N. 1983. B r e e d i n g o f T h a i s c l a v i g e r a (Kuster) and p r e d a t i o n o f i t s eggs by C r o n i a m a r g a r i t i c o l a ( B r o d e r i p ) . P r o c . Sec. I n t . Workshop Ma l a c o f a u n a Hong Kong. 381-392. B r e n c h l e y , G.A. 1982. P r e d a t i o n on e n c a p s u l a t e d l a r v a e by a d u l t s : e f f e c t s o f i n t r o d u c e d s p e c i e s on t h e g a s t r o p o d I l y a n a s s a o b s o l e t a . Mar. E c o l . P r o g S e r . 9: 255-62. D'Asaro, C. 1970. Egg c a p s u l e s o f p r o s o b r a n c h M o l l u s k s from South F l o r i d a and t h e Bahamas and n o t e s on spawning i n t h e l a b o r a t o r y . B u l l . Mar. S c i . 20: 414-40. Eat o n , C M . 1972. The r e p r o d u c t i v e and f e e d i n g b i o l o g y o f t h e P r o s o b r a n c h g a s t r o p o d F u s i t r i t o n o r e g o n e n s i s . ( R e d f i e l d ) (Fam. C y m a t i i d a e ) . MSc. T h e s i s . U. o f Washington. Emlen, J . 1966. Time, energy and r i s k i n two s p e c i e s o f c a r n i v o r o u s g a s t r o p o d s . Ph.D. t h e s i s . U n i v e r s i t y o f Washington. F e a r e , C.J. 1970. A s p e c t s o f t h e e c o l o g y o f an exposed shore p o p u l a t i o n o f dogwhelks N u c e l l a l a p i l l u s ( L . ) . O e c o l o g i a 5: 1-18. Glynn , P.W. 1965. Community c o m p o s i t i o n , s t r u c t u r e , and i n t e r r e l a t i o n s h i p s i n t h e marine i n t e r t i d a l E n d o c l a d i a  m u r i c a t a - Ba l a n u s g l a n d u l a a s s o c i a t i o n i n Monterey Bay, C a l i f o r n i a . B e a u f o r t i a 12: 1-198. Hawkins, L.E. and S. H u t c h i n s o n . 1988. Egg c a p s u l e s t r u c t u r e and h a t c h i n g mechanism o f Ocenebra e r i n a c e a (L.) ( P r o s o b r a n c h i a : M u r i c i d a e ) . J . Exp. Mar. B i o l . E c o l . 119: 269-283. Haydock, C . I . 1964. An e x p e r i m e n t a l s t u d y t o c o n t r o l o y s t e r d r i l l s i n Tomales Bay, C a l i f o r n i a . C a l i f . F i s h & Game 50: 11-28. L o r d , A. 1986. A r e t h e c o n t e n t s o f egg c a p s u l e s o f t h e marine g a s t r o p o d N u c e l l a l a p i l l u s (L.) a x e n i c ? Amer. Malac . B u l l . 4: 201-203. MacKenzie, C.L. J r . 1961. Growth and r e p r o d u c t i o n o f t h e o y s t e r d r i l l E u p l e u r a c a u d a t a , i n t h e York R i v e r , V i r g i n i a . E c o l o g y 42: 317-338. M a r t e l , A. and D . H . L a r r i v e e . 1986 B e h a v i o u r and t i m i n g o f c a p s u l a t i o n and e g g - l a y i n g i n t h e Neogastropod Buccinum  undatum L. J . Exp. Mar. B i o l E c o l . 96: 27-42. 98 M c K i l l u p S.C. and A . J . B u t l e r . 1979. M o d i f i c a t i o n o f egg p r o d u c t i o n and p a c k a g i n g i n response t o f o o d a v a i l a b i l i t y by N a s s a r i u s p a u p e r a t u s . O e c o l o g i a 43: 221-231. O s t e r g a a r d , J.M. 1950. Spawning and development o f some Ha w a i i a n marine g a s t r o p o d s . Pac. S c i . 4: 75-115. P e c h e n i k , J.A. 1978. A d a p t a t i o n s t o i n t e r t i d a l development: S t u d i e s on N a s s a r i u s o b s o l e t u s . B i o l . B u l l . 154: 282-291. P e c h e n i k , J.A. 1979. R o l e o f e n c a p s u l a t i o n i n i n v e r t e b r a t e l i f e h i s t o r i e s . Am. Nat. 114: 859-870. P e c h e n i k , J.A. 1982. A b i l i t y o f some g a s t r o p o d egg c a p s u l e s t o p r o t e c t a g a i n s t l o w - s a l i n i t y s t r e s s . J . Exp. Mar. B i o l . E c o l . 63: 195-208. P e c h e n i k , J.A. 1983. Egg c a p s u l e s o f N u c e l l a l a p i l l u s (L.) p r o t e c t a g a i n s t low s a l i n i t y s t r e s s . J . Exp. Mar. B i o l . E c o l . 71: 165-179. P e c h e n i k , J.A. 1986. The e n c a p s u l a t i o n o f eggs and embryos by m o l l u s k s : an o v e r v i e w . American M a l a c . B u l l . 4,165-72. P e r r o n , F.E. 1981. The p a r t i t i o n i n g o f r e p r o d u c t i v e energy between ova and p r o t e c t i v e c a p s u l e s i n marine g a s t r o p o d s o f t h e genus Conus. Am. Nat. 118: 110-118. P e r r o n , F.E. and G.C. Corpuz. 1982. Cost o f p a r e n t a l c a r e i n t h e g a s t r o p o d Conus pennaceus: Age s p e c i f i c changes and p h y s i c a l c o n s t r a i n t s . O e c o l o g i a 55: 319-324. P h i l l i p s , B.F. 1969. The p o p u l a t i o n e c o l o g y o f t h e whelk D i c a t h a i s a e g r o t a i n Western A u s t r a l i a . A u s t . J . Mar. Freshw. Res. 20: 225-56. Race, M.S. 1982. C o m p e t i t i v e d i s p l a c e m e n t and p r e d a t i o n between i n t r o d u c e d and n a t i v e mud s n a i l s . O e c o l o g i a 54: 337-347. R i v e s t , B.R. 1983. Development and t h e i n f l u e n c e o f nu r s e egg a l l o t m e n t on h a t c h i n g s i z e i n S e a r l e s i a d i r a (Reeve, 1 8 4 6 ) ( P r o s o b r a n c h i a : B u c c i n i d a e ) . J . Exp. Mar. B i o l . E c o l . 69: 217-241. S p i g h t , T. 1972. P a t t e r n s o f change i n a d j a c e n t p o p u l a t i o n s o f an i n t e r t i d a l s n a i l , T h a i s l a m e l l o s a . Ph.D. t h e s i s . U n i v e r s i t y o f Washington. S p i g h t , T.M. 1976. E c o l o g y o f h a t c h i n g s i z e f o r marine s n a i l s . O e c o l o g i a 24: 283-294. 99 S p i g h t , T.M. 1977 Do i n t e r t i d a l s n a i l s spawn i n t h e r i g h t p l a c e s ? E v o l u t i o n 31: 682-691. S u l l i v a n , C.H. and T.K. Maugel. 1984. F o r m a t i o n , o r g a n i z a t i o n and c o m p o s i t i o n o f t h e egg c a p s u l e o f t h e marine g a s t r o p o d , I l y a n a s s a o b s o l e t a . B i o l . B u l l . 167: 378-389. West, D.L. 1973. Notes on t h e development o f C o l u s s t i m p s o n i ( P r o s o b r a n c h i a : B u c c i n i d a e ) N a u t i l u s 87:1-4. 100 GENERAL CONCLUSIONS The two major o b j e c t i v e s o f t h i s s t u d y were: 1) t o examine i n t r a s p e c i f i c v a r i a t i o n i n morphology o f egg c a p s u l e s o f t h e marine i n t e r t i d a l whelk N u c e l l a e m a r q i n a t a and, 2) t o examine t h e r e s i s t a n c e o f t h e s e s t r u c t u r e s t o i n t e r t i d a l p r e d a t o r s . I showed i n Chapter 1 t h a t t h e s i z e , s t r e n g t h , and w a l l t h i c k n e s s o f N u c e l l a e m a r q i n a t a c a p s u l e s v a r i e d among p o p u l a t i o n s s e p a r a t e d a l o n g a wave-exposure g r a d i e n t . C a p s u l e s were t h i c k - w a l l e d a t w a v e - s h e l t e r e d G r a p p l e r I n l e t and wave-exposed Seppings I s l a n d , and were s i g n i f i c a n t l y t h i n n e r a t Ross I s l e t s , an a r e a exposed t o i n t e r m e d i a t e l e v e l s o f w a v e - a c t i o n . C a p s u l e w a l l s t r e n g t h d i d not d i r e c t l y r e f l e c t d i f f e r e n c e s i n w a l l t h i c k n e s s , as c a p s u l e s were s t r o n g e s t a t G r a p p l e r I n l e t , and were r e l a t i v e l y weak a t b o t h a t Seppings I s l a n d and Ross I s l e t s i t e s . As d i f f e r e n c e s i n c a p s u l a r morphology d i d not c o r r e s p o n d t o wave-exposure l e v e l s , I have s u g g e s t e d t h a t t h e s t r u c t u r e and s t r e n g t h o f c a p s u l e w a l l s may r e f l e c t a number o f d i f f e r e n t e n v i r o n m e n t a l s t r e s s e s a c t i n g upon d e v e l o p i n g embryos. F u r t h e r s t u d i e s w i l l be needed t o examine t h e p h y s i c a l r e s i s t a n c e o f t h i c k and t h i n c a p s u l e w a l l s t o such s t r e s s e s . I n t h e second c h a p t e r I showed t h a t p r e d a t i o n may be an i m p o r t a n t s o u r c e o f m o r t a l i t y among N u c e l l a e m a r q i n a t a embryos. C a p s u l e w a l l s p r o v i d e d l i t t l e r e s i s t a n c e t o a number o f i n t e r t i d a l p r e d a t o r s such as shore c r a b s , Hemigrapsus spp, i s o p o d s , I d o t e a w o s n e s e n s k i i , and c h i t o n s , M o p a l i a spp.. 101 However, I d i d f i n d some e v i d e n c e t o suggest t h a t d i f f e r e n c e s i n c a p s u l e w a l l t h i c k n e s s may a f f e c t t h e s u s c e p t i b i l i t y o f e n c a p s u l a t e d embryos t o p r e d a t o r s . W i t h r e s p e c t t o t h e i s o p o d p r e d a t o r s , I d o t e a w o s n e s e n s k i i , embryos c o n t a i n e d w i t h i n t h i c k c a p s u l e w a l l s were found t o be l e s s p r e f e r r e d p r e y t h a n t h o s e c o n t a i n e d w i t h i n t h i n - w a l l e d c a p s u l e s . T h i s i s t h e f i r s t s t u d y t o show a s e l e c t i v e advantage f o r t h e p r o d u c t i o n o f t h i c k - w a l l e d c a p s u l e s i n g a s t r o p o d s . The r e s u l t s o f t h i s s t u d y p r o v i d e t h e groundwork f o r f u r t h e r i n v e s t i g a t i o n s o f t h e f u n c t i o n a l s i g n i f i c a n c e o f ne o g a s t r o p o d egg c a p s u l e s . I t i s apparent t h a t s u b t l e d i f f e r e n c e s o c c u r i n t h e s t r u c t u r a l p r o p e r t i e s o f egg c a p s u l e s even among p o p u l a t i o n s o f one s p e c i e s . A s s o c i a t i o n s between i n t r a s p e c i f i c v a r i a t i o n i n c a p s u l e morphology and s p e c i f i c e n v i r o n m e n t a l s t r e s s e s s h o u l d u l t i m a t e l y enhance our u n d e r s t a n d i n g o f t h e p r o t e c t i v e r o l e o f p r o s o b r a n c h egg c a p s u l e s . 

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