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Effect of reduced salinity conditions on the distribution and responses of the muricid intertidal snail… Johannsson, Ora E. 1971

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EFFECT OF REDUCED SALINITY CONDITIONS ON THE DISTRIBUTION AND RESPONSES OF THE MURICID INTERTIDAL SNAIL THAIS LAMELLOSA GMELIN by ORA E.JOHAMNSSON B.Sc . i U n i v e r s i t y o f B r i t i s h Columbia, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department < of Z oology We a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF J u l y , BRITISH COLUMBIA 1971 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of • ^ ot^v^-g; 7 7 The University of British Columbia Vancouver 8, Canada D a t e 0^1^ • /7ft/ i ABSTRACT L i m i t a t i o n o f the d i s t r i b u t i o n o f the i n t e r t i d a l gastropod, T h a i s l a m e l l o s a * by reduced s a l i n i t y c o n d i t i o n s near the mouth o f the F r a s e r R i v e r was i n v e s t i g a t e d by s t u d y i n g the s n a i l s ' r e s -ponses t o and t o l e r a n c e s o f such c o n d i t i o n s both i n the f i e l d and l a b o r a t o r y , and by d e t e r m i n i n g i t s p h y s i o l o g i c a l c a p a c i t y to con-t r o l body changes i n c o n j u n c t i o n w i t h d e c r e a s e i n s a l i n i t y . E v i d -ence o f i n c r e a s e d t o l e r a n c e o f low s a l i n i t y t h rough n a t u r a l s e l e c -t i o n was sought i n comparisons under v e r y low s a l i n i t i e s o f s n a i l s t r a n s f e r r e d t o S panish Banks from p o p u l a t i o n s n o r m a l l y e x p e r i e n c -i n g low (17%o: B r o c k t o n P o i n t ) and r e l a t i v e l y h i g h e r (24%o: L i l l y P o i n t ) s a l i n i t i e s d u r i n g maximum r u n o f f o f the F r a s e r . C h a r a c t e r -i s t i c s o f dominant s p e c i e s , such as T h a i s l a m e l l o s a , were a l s o d i s c u s s e d and r e l a t e d t o McNaughton and Wolf's (1970) h y p o t h e s i s o f s p e c i a l i z e d dominants. R e a c t i o n s were e v a l u a t e d i n terms o f f e e d i n g r a t e s , v e r t i c a l / h o r i z o n t a l d i s t r i b u t i o n , attachment and m o r t a l i t y . Decreases i n s a l i n i t y e f f e c t e d r e s p o n s e s i n a s p e c i f i c sequence: f e e d i n g d e c r e a s e s , a n i m a l s descend from exposed s u r f a c e s , a t t a c h -ment s t r e n g t h weakens, movement l e s s e n s , detachment and then m o r t a l i t y i n c r e a s e s . These a l t e r a t i o n s o v e r l a p c o n s i d e r a b l y due t o g r e a t v a r i a b i l i t y i n low s a l i n i t y t o l e r a n c e w i t h i n each p o p u l a t i o n . Immature s n a i l s and t h o se removed from the f i e l d i n summer were more t o l e r a n t than a d u l t s or those removed i n the w i n t e r . Dur-a t i o n o f exposure was c r i t i c a l t 0 s u r v i v a l . G r a d u a l a c c l i m a t i o n and f l u c t u a t i n g c o n d i t i o n s were thought t o be r e s p o n s i b l e f o r the g r e a t e r t o l e r a n c e s observed i n the f i e l d as compared w i t h the l a b o r a t o r y . S a l i n i t y t o l e r a n c e s o f Brockton P o i n t and L i l l y P o i n t s n a i l s were s i m i l a r , p o s s i b l y due t o lower s a l i n i t y c o n d i t i o n s a t i i L i l l y P o i n t i n the p a s t when the F r a s e r R i v e r emptied i n t o t h e sea v i a Boundary Bay. D i f f e r e n c e s i n movement and i n v e r t i c a l / h o r i z o n -t a l d i s t r i b u t i o n between the two p o p u l a t i o n s were r e l a t e d to t o p -o g r a p h i c a l d i f f e r e n c e s i n the two h a b i t a t s . L i l l y P o i n t c o n s i s t s of e x t e n s i v e sand t r a c t s i n the lower i n t e r t i d a l where wayward s n a i l s may become l o s t and/or d i e o f heat exposure and d e s i c c a -t i o n d u r i n g low t i d e s i n the heat o f summer; B r o c k t o n P o i n t i s r o c k y w i t h i n t e r s p e r s e d mats o f mussel s h e l l s . The s n a i l i s c a p a b l e o f d e t e c t i n g s a l i n i t y changes and o f moving t o more f a v o u r a b l e c o n d i t i o n s s u b t i d a l l y . At t h e ex-treme o f s p e c i e s d i s t r i b u t i o n i n S t a n l e y Park fewer an i m a l s were found i n the i n t e r t i d a l i n June, the month o f minimal s a l i n i t i e s , t h a n i n A p r i l o r J u l y . In a d d i t i o n the s p e c i e s l i m i t c o r r e s p o n d s w i t h t o l e r a n c e s d e f i n e d i n t h e f i e l d which suggests t h a t s a l i n i t y i s d i r e c t l y r e s p o n s i b l e f o r t e r m i n a t i o n o f d i s t r i b u t i o n r a t h e r t h a n a b i o l o g i c a l f a c t o r a c t i n g on an animal weakened by s a l i n i t y s t r e s s , a l t h o u g h t h i s h y p o t h e s i s has not been t e s t e d e x p e r i m e n t a l l y . S t u d i e s o f oxygen consumption and changes i n d r y weight i n d i c a t e t h a t metabolism f e l l w i t h d e c r e a s e s i n s a l i n i t y and t e m p e r a t u r e . D i f f e r e n c e s i n a v a i l a b l e energy were r e f l e c t e d i n l e v e l s o f a c t i v i t y r a t h e r than i n changes i n d r y weight. Presumably such a r e sponse i s i m p o r t a n t i n s u r v i v i n g u n f a v o u r a b l e p e r i o d s . With i n c r e a s e i n temperature males u t i l i z e d g o nadal m a t e r i a l w h i l e f emales appeared t o c o n s e r v e t h e s e p r o d u c t s . T h a i s l a m e l l o s a i s unable t o r e g u l a t e the s a l i n i t y o f i t s e x t r a c e l l u l a r f l u i d s but can c o n t r o l i t s volume t o some e x t e n t under s a l i n i t y s t r e s s , a p p a r e n t l y i n r e l a t i o n t o i t s degree o f e u r y h a l i n i t y . T h i s a b i l i t y d i f f e r e d between sexes a l t h o u g h mort-a l i t y due t o low s a l i n i t y exposure was independent o f sex. i i i TABLE OF CONTENTS Page ABSTRACT i TABLE OF CONTENTS 1 1 1 LIST OF TABLES v i LIST OF FIGURES x i ACKNOWLEDGEMENTS x i i i GENERAL INTRODUCTION 1 INTRODUCTION 1 EXPERIMENTAL METHODS 8 I n t r o d u c t i o n 8 Study Areas 8 L i f e H i s t o r y 1 6 E x p e r i m e n t a l P r o c e d u r e s ^ 1. S i z e C a t e g o r i e s ^ 2. Marking Techniques 20 3. F e e d i n g Experiments 20 4. F i e l d Cages 22 5. L a b o r a t o r y E x p e r i m e n t a l Arrangements 25 6. P r e - e x p e r i m e n t a l Maintenance o f Animals 26 SECTION I - ECOLOGICAL STUDIES IN THE FIELD INTRODUCTION 30 FEEDING RATES IN THE FIELD 34 I n t r o d u c t i o n * ' 34 Methods and M a t e r i a l s 34 R e s u l t s and D i s c u s s i o n 35 REACTIONS OF THAIS LAMELLOSA TO SPRING CONDITIONS AT SPANISH BANKS 41 I n t r o d u c t i o n 41 Methods and M a t e r i a l s 41 1. E x p e r i m e n t a l Procedures 41 2. A n a l y t i c a l P r o c e d u r e s 4 3 i v Page R e s u l t s 47 1. Comparison of 1969-1970 d a t a 47 2. Attachment S t r e n g t h 54 D i s c u s s i o n 54 SECTION I I - ECOLOGICAL STUDIES IN THE LABORATORY INTRODUCTION 60 EFFECTS OF CHANGES IN SALINITY AND TEMPERATURE 62 I n t r o d u c t i o n 62 Methods and M a t e r i a l s 62 1. E x p e r i m e n t a l Procedure 62 2. A n a l y t i c a l Procedure 65 R e s u l t s 68 1. F e e d i n g Response 68 2. Movement 79 3. Attachment S t r e n g t h 86 4. P r o p o r t i o n o f S n a i l s 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 93 5. P r o p o r t i o n o f S n a i l s A t t a c h e d t o the S u b s t r a t e 100 6. Water Content & Dry Weight R e l a t i o n s h i p s between R e p r o d u c t i v e & Non R e p r o d u c t i v e t i s s u e s 109 7. M o r t a l i t y 117 D i s c u s s i o n 123 1. D i s t r i b u t i o n & Responses R e l a t e d t o Changes i n S a l i n i t y and Temperature I * 3 2. Race - B r o c k t o n P o i n t v s . L i l l y P o i n t I 2 8 3. S i z e - Age 132 4. Metabolism 134 5. A c c l i m a t i o n 138 SECTION I I I - A PHYSIOLOGICAL STUDY OF RESPONSES TO CHANGES IN EXTERNAL SALINITY INTRODUCTION 140 DETERMINATION OF OSMOREGULATORY CAPACITY 144 I n t r o d u c t i o n 144 Methods and M a t e r i a l s 144 R e s u l t s 145 D i s c u s s i o n 145 V Page A STUDY OF VOLUME-REGULATION 1 4 9 I n t r o d u c t i o n 1 4 9 Methods and M a t e r i a l s 1 4 9 R e s u l t s 1 5 0 D i s c u s s i o n 15 3 1. - V a r i a t i o n i n Body D e n s i t y Between Sexes 15 3 2. Volume-Regulation 15 3 OXYGEN CONSUMPTION 158 I n t r o d u c t i o n 158 Methods and M a t e r i a l s 158 R e s u l t s 162 D i s c u s s i o n 162 GENERAL DISCUSSION 167 DISTRIBUTION AND LOW SALINITY TOLERANCE 167 CHARACTERISTICS OF DOMINANT SPECIES 1 7 1 LITERATURE CITED 1 7 4 v i LIST OF TABLES Page I . F l u c t u a t i o n s i n s a l i n i t y c o n d i t i o n s a t Sp a n i s h Banks and Ferguson P o i n t . 11 I I . S a l i n i t y o f water samples through d e p t h . 32 I I I . The s a l i n i t y o f s u r f a c e water d u r i n g d i f f e r e n t movements o f the t i d a l c y c l e . 33 IV. T - t e s t e v a l u a t i o n s o f t h e n u l l h y p o t h e s i s o f no d i f f e r e n c e between f e e d i n g r a t e s a t d i f f e r e n t beaches. 38 V. R e l a t i o n s h i p between t h e e f f e c t o f s u b s t r a t e and exposure t o warm summer atm o s p h e r i c c o n -d i t i o n s on the d i s t r i b u t i o n o f T h a i s l a m e l l o s a on r o c k s . 4 4 V I . E f f e c t o f s u b s t r a t e on attachment s t r e n g t h . 4 5 V I I . Comparison o f the e f f e c t s o f s a l i n i t y (9%o -20%o) and temperature (9 C - 18°C) on t h e r e l a -t i o n s h i p between f o o t - a r e a (dependent v a r i a b l e ) and s h e l l l e n g t h (independent v a r i a b l e ) , u s i n g an a n a l y s i s o f c o v a r i a n c e . V I I I . The volume o f the o u t f l o w o f the F r a s e r R i v e r as measured a t A g a s s i z , B.C. 48 49 IX. P r o b a b i l i t y o f observed d i f f e r e n c e , assuming no d i f f e r e n c e i n t h e m o r t a l i t y r a t e s o f s n a i l s from L i l l y P o i n t and B r o c k t o n P o i n t a t Spanish Banks ( s p r i n g 1970) and i n the m o r t a l i t y r a t e s between d i f f e r e n t i n t e r t i d a l h e i g h t s (3.5' -0-0'). 5 3 X. Frequency r e p r e s e n t a t i o n by attachment s t r e n g t h c l a s s e s , d a t a o b t a i n e d d u r i n g the ebbing t i d e a t S p a nish Banks and Br o c k t o n P o i n t i n the s p r i n g o f 1970. 5 6 X I . Attachment s t r e n g t h o f B r o c k t o n P o i n t and L i l l y P o i n t a n i m a l s a t Sp a n i s h Banks d u r i n g the s p r i n g o f 1970. 5 7 X I I . Comparison o f the e f f e c t s o f temperature (9°C, 12°C and 18°C) on the r e l a t i o n s h i p between s h e l l l e n g t h o f s m a l l s n a i l s (independent v a r i a b l e ) and f o o t - a r e a (dependent v a r i a b l e ) f o r t h r e e sep-a r a t e s a l i n i t i e s . 66 v i i Page X I I I . Comparison o f the e f f e c t o f s a l i n i t y (20%o, 15%o, 12%o) on the r e l a t i o n s h i p between s h e l l l e n g t h o f s m a l l s n a i l s (independent v a r i a b l e ) and f o o t -a r e a (dependent v a r i a b l e ) . 67 XIV. Comparisons between immature ( s m a l l ) and mature ( l a r g e ) s n a i l s u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s f e e d i n g i s t h e Q d e p e n d e n t v a r i a b l e , and temperature (9 C - 18 C) i s the independent v a r i a b l e . XV. Comparisons between s n a i l s removed from the f i e l d i n t he w i n t e r and summer u s i n g weighted c o -v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s f e e d i n g i s t h e dependent v a r i a b l e and temperature (9°C - 18 C) i s the independent v a r i a b l e . 70 69 XVI. XVII, XVIII, Comparisons between s n a i l s o r i g i n a l l y from B r o c k t o n P o i n t and L i l l y P o i n t u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s f e e d i n g i s t h e dependent v a r i a b l e and temperature (9 C - 18 C) i s the independent v a r i a b l e . 71 T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between t h e a r c s i n e o f the p r o p o r t i o n o f s n a i l s f e e d i n g on c o n s e c u t i v e weeks. T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f the p r o p o r t i o n o f s n a i l s f e e d i n g a t d i f f e r e n t s a l i n i t i e s w i t h i n each week. 72 73 XIX. Weekly p r o p o r t i o n s o f s n a i l s f e e d i n g a t two s a l i n i t i e s . 74 XX. T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no . d i f f e r e n c e between f e e d i n g r a t e s under d i f f e r e n t c o n d i t i o n s as determined i n the l a b o r a t o r y . XXI. E f f e c t o f age, p o p u l a t i o n h i s t o r y , and p r e v i o u s a c c l i m a t i o n i n the f i e l d on movement as e v a l u -a t e d by s t a n d a r d normal d e v i a t e s d e r i v e d from C h i Square c o n t i n g e n c y t a b l e s . X X II. E f f e c t o f changes i n temperature and s a l i n i t y on the tendency t o move as e v a l u a t e d by means o f st a n d a r d normal d e v i a t e s from C h i Square c o n t i n -gency t a b l e s . X X I I I . Summary o f movement c h a r a c t e r i s t i c s o f d i f f e r e n t groups o f s n a i l s as d e r i v e d from T a b l e XXI. XXIV. E f f e c t o f d e c r e a s e i n s a l i n i t y on the p r o p o r t i o n of s n a i l s moving more than 5 cm i n 20 minutes a f t e r d i s p l a c e m e n t . 77 80 82 84 85 v i i i XXV. L a b o r a t o r y comparison between the s t r e n g t h o f attachment o f s n a i l s o r i g i n a l l y from B r o c k t o n P o i n t and L i l l y P o i n t u s i n g c o v a r i a n c e a n a l y s i s ; attachment s t r e n g t h (g/cm ) i s the dependent v a r i a b l e and temperature (9°C-18°C) i s the i n d e -pendent v a r i a b l e . XXVI. T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between attachment s t r e n g t h o f s n a i l s w i t h changes i n s a l i n i t y and i n p r e v i o u s a c c l i m -a t i o n i n the f i e l d . Page 88 89 XXVII. Frequency d i s t r i b u t i o n o f attachment s t r e n g t h c h a r a c t e r i s t i c s w i t h i n each o f t h e t e m p e r a t u r e -s a l i n i t y c o m b i n a t i o n s s t u d i e d . X X V I I I . E v a l u a t i o n o f the e f f e c t o f p r e v i o u s a c c l i m a t i o n i n the f i e l d on f r e q u e n c y d i s t r i b u t i o n o f a t t a c h -ment s t r e n g t h v a l u e s . XXIX. Comparisons between immature ( s m a l l ) and mature ( l a r g e ) s n a i l s u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s 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 i s the dependent v a r i a b l e , and temperature (9 C - 18 C) i s the independent v a r i a b l e . 90 91 94 XXX. XXXI. XXXII. Comparisons between s n a i l s removed from the f i e l d i n t h e w i n t e r and summer u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s 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 i s the dependent v a r i a b l e and temperature " i s the independent v a r i a b l e . 95 (9°C - 18°C) Comparisons between s n a i l s from B r o c k t o n P o i n t and L i l l y P o i n t u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s a t t a c h e d t o a v e r t i c a l s u r f a c e i s t h e dependent v a r i a b l e and temperature (9 C -18 C) i s the independent v a r i a b l e . 96 T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f the p r o p o r t i o n o f s n a i l s 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 on con -s e c u t i v e weeks. 97 XXXI I I . T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f t h e p r o p o r t i o n o f s n a i l s 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 a t d i f f -e r e n t s a l i n i t i e s w i t h i n each week. 98 XXXIV. Weekly p r o p o r t i o n s o f s n a i l s 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 a t f o u r s a l i n i t i e s . 99 i x Page XXXV. Comparisons between immature ( s m a l l ) and mature ( l a r g e ) s n a i l s u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s a t t a c h e d t o the s u b s t r a t e i s Q t h e dependent v a r i a b l e , and temperature (9°C -18 C) i s the independent v a r i a b l e . 102 XXXVI. Comparisons between s n a i l s removed from the f i e l d i n t h e w i n t e r and summer u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s a t t a c h e d t o the s u b s t r a t e i s the dependent v a r i a b l e , and temper-a t u r e (9 C - 18 C) i s t h e independent v a r i a b l e . 1°3 XXXVII. Comparisons between s n a i l s o r i g i n a l l y from B r o c k t o n P o i n t and L i l l y P o i n t u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s a t t a c h e d t o t h e s u b s t r a t e i s the dependent v a r i a b l e and temperature (9 C - 18°c)is t h e independent v a r i a b l e . 104 X X X V I I I . T - t e s t e v a l u a t i o n s o f t h e n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f t h e p r o p o r t i o n o f s n a i l s a t t a c h e d t o the s u b s t r a t e on c o n s e c -u t i v e weeks. 105 XXXIX. T - t e s t e v a l u a t i o n s o f t h e n u l l h y p o t h e s i s o f no d i f f e r e n c e between t h e a r c s i n e o f the p r o p o r t i o n o f s n a i l s a t t a c h e d t o the s u b s t r a t e a t d i f f e r e n t s a l i n i t i e s w i t h i n each week. XL. Weekly p r o p o r t i o n s o f s n a i l s a t t a c h e d t o the s u b s t r a t e a t f o u r s a l i n i t i e s . 106 107 X L I . E f f e c t o f i n c r e a s e i n temperature on water c o n t e n t of gonad and body as e v a l u a t e d by means o f the s i g n t e s t . X L I I . T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between p e r c e n t a g e s o f water i n the gonad (a) a t d i f f e r e n t s a l i n i t i e s , and (b) i n d i f f e r e n t s exes. 110 111 X L I I I . T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between p e r c e n t a g e s o f water i n the body (a) a t d i f f e r e n t s a l i n i t i e s and (b) i n d i f f -e r e n t s e x e s . 112 XLIV. Dry weight o f the body and t - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between weights from d i f f e r e n t t e m p e r a t u r e - s a l i n i t y t r e a t m e n t s . XLV. Changes i n the r a t i o o f d r y weight o f t h e gonad/ body w i t h i n each e x p e r i m e n t a l r e p l i c a t e f o r a l l s a l i n i t y - t e m p e r a t u r e t r e a t m e n t s . 115 X Page XLVI. E v a l u a t i o n o f e f f e c t s o f s a l i n i t y and temper-a t u r e on the r a t i o of the d r y weights o f the gonad/body o f males i n t h e w i n t e r u s i n g v a r i a n c e a n a l y s i s . X L V I I . E v a l u a t i o n o f e f f e c t s o f p r e v i o u s a c c l i m a t i o n i n the f i e l d and o f s i z e on m o r t a l i t y r a t e s u s i n g C h i Square t e s t s of h e t e r o g e n e i t y , and F i s h e r ' s e x a c t p r o b a b i l i t y . X L V I I I . T a b u l a t i o n of c u m u l a t i v e m o r t a l i t i e s w i t h i n each e x p e r i m e n t a l t e m p e r a t u r e - s a l i n i t y comb-i n a t i o n . 116 119 120 XLIX. I n f l u e n c e o f sex on the s u r v i v a l o f l a r g e T h a i s  l a m e l l o s a under c o n d i t i o n s o f d e c r e a s e d s a l i n i t y and i n c r e a s e d t e m p e r a t u r e . 122 x i LIST OF FIGURES F a c i n g Page G e n e r a l map o f the d e l t a o f the F r a s e r R i v e r and a s s o c i a t e d c o a s t l i n e showing t h e v a r i o u s study l o c a t i o n s d e s c r i b e d i n the t e x t . 9 Map o f S t a n l e y Park d e p i c t i n g t h e r e l a t i v e abun-dance o f T h a i s l a m e l l o s a and v a r i a t i o n s i n s a l -i n i t y a l o n g the s h o r e . 10 3 Number o f T h a i s l a m e l l o s a p r e s e n t a t the l i m i t o f d i s t r i b u t i o n i n S t a n l e y Park d u r i n g the s p r i n g and summer o f 1970. 13 4 S e a s o n a l f l u c t u a t i o n s i n s a l i n i t y c o n d i t i o n s a t B r o c k t o n P o i n t , L i l l y P o i n t and S p a n i s h Banks. 14 5 S e a s o n a l f l u c t u a t i o n s i n seawater temperatures a t B r o c k t o n P o i n t , L i l l y P o i n t and S p a n i s h Banks. 15 6 Drawings o f immature and mature s n a i l s i l l u s t r a t i n g the t h i c k e n e d o u t e r l i p o f t h e a p e r t u r e and d e n t i -t i o n o f a d u l t a n i m a l s . 21 7 R e l a t i o n s h i p between d r y weight and a p e r t u r e l e n g t h o f the b a r n a c l e Balanus q l a n d u l a c o l l e c t e d from Br o c k t o n P o i n t on October 31st, 1969. 2 3 8 Diagram o f an aquarium from the l a b o r a t o r y study on the combined e f f e c t s o f temperature and s a l i n i t y on the r e s p o n s e s o f T h a i s l a m e l l o s a . 27 9 I l l u s t r a t i o n o f the method used t o randomly a s s i g n s n a i l s t o d i f f e r e n t t r e a t m e n t s y e t t o m a i n t a i n a s i m i l a r s i z e d i s t r i b u t i o n w i t h i n each. 28 10 F e e d i n g r a t e s of T h a i s l a m e l l o s a a t S p a n i s h Banks, B r o c k t o n P o i n t and L i l l y P o i n t f o r the y e a r August 1969 to J u l y 1970. 37 11 P i c t u r e - o f a s n a i l ' g r i p p e r ' used f o r d e t e r m i n i n g attachment s t r e n g t h s . 46 12 Responses o f T h a i s l a m e l l o s a a t Spanish Banks through the s p r i n g o f 1969 as measured by the p r o p o r t i o n o f s n a i l s (a) l o c a t e d up on the r o c k s , (b) u n a t t a c h e d and (c) dead on each p a r t i c u l a r day. 51 13 The r e s p o n s e s o f B r o c k t o n P o i n t and L i l l y P o i n t s n a i l s a t Spanish Banks d u r i n g the s p r i n g o f 1970 as determined by the p r o p o r t i o n o f s n a i l s (a) l o c a t e d up on the r o c k s , (b) u n a t t a c h e d , and (c) dead. ^2 x i i F a c i n g Page 1 4 A t t a c h m e n t s t r e n g t h o f l a r g e T h a i s l a m e l l o s a a t B r o c k t o n P o i n t and S p a n i s h Banks d u r i n g t h e s p r i n g o f 1 9 7 0 . 5 5 1 5 Changes i n a r c s i n e o f p r o p o r t i o n o f s n a i l s f e e d i n g i n t h e w i n t e r a t d i f f e r e n t s a l i n i t i e s w i t h t i m e . 75 1 6 Changes i n a r c s i n e o f p r o p o r t i o n o f s n a i l s f e e d i n g i n t h e summer a t d i f f e r e n t s a l i n i t i e s w i t h t i m e . 76 17 R e l a t i o n s h i p between f e e d i n g r a t e s c f T h a i s l a m e l l o s a and t e m p e r a t u r e . 78 1 8 R e l a t i o n s h i p between d e c r e a s e i n s a l i n i t y and s t r e n g t h o f a t t a c h m e n t . 9 2 1 9 R e l a t i o n s h i p between per. c e n t w a t e r c o n t e n t o f body and gonad i n c o n j u n c t i o n w i t h changes i n s a l i n i t y . 1 1 3 2 0 R e l a t i o n s h i p between s a l i n i t y o f e x t e r n a l medium and p e r i c a r d i a l f l u i d . 1 4 6 2 1 R e l a t i o n s h i p between d e c r e a s i n g s a l i n i t y and body d e n s i t y o f males and f e m a l e s . ^ t - ^ 2 2 A l t e r a t i o n s i n t h e w a t e r c o n t e n t o f wet t i s s u e w i t h c hanges i n s a l i n i t y . 1 5 2 2 3 Diagram o f a s n a i l p r e p a r e d f o r d e t e r m i n a t i o n o f i t s r a t e o f oxygen c o n s u m p t i o n . 1 6 0 2 4 E f f e c t o f d e c r e a s e i n s a l i n i t y on t h e oxygen c o n -s u m p t i o n o f l a r g e and s m a l l s n a i l s . 1 6 3 x i i i ACKNOWLEDGEMENTS I would l i k e t o thank my s u p e r v i s o r , Dr.Robin Harger, f o r t h e freedom he a l l o w e d me i n c h o o s i n g and e x e c u t i n g t h i s s tudy and f o r h i s guidance p a r t i c u l a r l y i n m a t t e r s o f s t a t i s t -i c a l p r ocedure and i n t h e w r i t i n g o f the t h e s i s . Throughout the c o u r s e o f t h i s study I have g r e a t l y a p p r e c i a t e d t h e c o n -t i n u o u s i n t e r e s t i n , a n d c r i t i c a l d i s c u s s i o n o f , t h e work on the p a r t o f bot h M r . C h r i s Wood and Dr.John Stimson. I am a l s o i n d e b t e d t o M r . N i e l G i l b e r t f o r g i v i n g me a g r a s p o f s t a t i s t i c s , Mr.Ronald Wood f o r h e l p i n g me c o n s t r u c t e x p e r i m e n t a l equipment, and Mr.Paul Breen, and Mi s s S y l v i a Behrens and Mr.Fred McConnell f o r t h e i r i n t e r e s t , a d v i c e and a s s i s t a n c e . In a d d i t i o n , I wish t o thank Mrs.Olga Wood f o r bot h her endurance and c h e e r f u l n e s s i n t y p i n g t h i s t h e s i s a g a i n s t a seemingly i m p o s s i b l e d e a d l i n e . P e r s o n a l f i n a n c i a l support was p r o v i d e d by N a t i o n a l R esearch C o u n c i l o f Canada S c h o l a r s h i p s as w e l l as a K i t M a l k i n S c h o l a r s h i p . The r e s e a r c h was funded by g r a n t s from the N a t i o n a l Research C o u n c i l . GENERAL INTRODUCTION INTRODUCTION A c c o r d i n g t o McNaughton and Wolf (1970), s p e c i e s which m a i n t a i n e x t e n s i v e d i s t r i b u t i o n s may do so i n one o f two ways: " e i t h e r dominant s p e c i e s a r e g e n e r a l i s t s w i t h a d a p t a t i o n s t o many more dimensions i n t h e i r n i c h e s and, as a r e s u l t , l e s s f r e q u e n t l y encounter a l i m i t i n g d i mension, o r t h e y a r e s p e c i a l i s t s t h a t have e v o l v e d a d a p t a t i o n s t o a s i n g l e dimen-s i o n which i s most l i k e l y t o be l i m i t i n g i n t h e c u r r e n t e n v i r o n m e n t a l a r r a y " . A l t h o u g h t h e s e a u t h o r s p r e f e r the l a t t e r h y p o t h e s i s , t h e i r examples a r e i n c o n c l u s i v e . A s p e c i e s whose d i s t r i b u t i o n extends over a l a r g e g e o g r a p h i c a l range o f t e n i s composed o f a s e r i e s o f f a i r l y d i s t i n c t i v e s e p a r a t e p o p u l a t i o n s c a l l e d r a c e s ( S t a u b e r , 1950 ; K i n c a i d , 195 7; C a i n , 1960). Gene f r e q u e n c i e s v a r y between d i f f e r e n t p o p u l a t i o n s because t h e s e l e c t i v e p r e s s u r e s o p e r -a t i n g a t each l o c a t i o n a r e u n i q u e . Geographic i s o l a t i o n p r e v e n t s annulment o f t h e s e changes from d i l u t i o n t hrough immi-g r a t i o n , a l l o w i n g a s e r i e s o f d i s t i n c t m i c r o g e o g r a p h i c p o p u l -a t i o n s t o e v o l v e . N o n e t h e l e s s , i t i s o f t e n t h e case t h a t nowhere a l o n g such a s e r i e s o f r a c e s a r e g e n e t i c changes l a r g e enough t o s e g r e g a t e t h e p o p u l a t i o n s i n t o s e p a r a t e s p e c i e s , a l t h o u g h p o p u l a t i o n s a t extremes o f the d i s t r i b u t i o n may v a r y s u f f i c i e n t l y t o p r e v e n t i n t e r b r e e d i n g when the y a r e p r e s e n t i n t h e same l o c a l i t y . An example o f t h i s type o f g r a d a t i o n i s found i n the g r e a t t i t , Parus major. T h i s b i r d extends from 2 England south through I n d i a t o C h i n a and Manchuria, a n o t h e r branch i n d i s t r i b u t i o n , which remains e x t r e m e l y s i m i l a r i n form t o the E n g l i s h b i r d j i s found a c r o s s the b r e a d t h o f R u s s i a . The two extremes o v e r l a p i n n o r t h e r n Manchuria, the s o u t h e r n forms have d i v e r g e d t o such an e x t e n t t h a t the two a r e no l o n g e r c a p a b l e o f i n t e r b r e e d i n g ( C a i n , 1960). There seem t o be f i v e p r i n c i p a l methods o f p r e s e r v i n g g e n e t i c d i v e r s i t y and hence p l a s t i c i t y . These a r e : random m u t a t i o n s , polymorphisms (presence o f both homozygous and h e t e r o -zygous a l l e l i c c o m b i n a t i o n s i n the p o p u l a t i o n ) , M endalian s e g -r e g a t i o n (the random s o r t i n g o f chromosomes from one g e n e r a t i o n t o t h e n e x t ) , chromosome r e c o m p o s i t i o n through c r o s s o v e r s (exchanges o f g e n e t i c m a t e r i a l between matched chromosomes), and f l u c t u a t i n g s e l e c t i v e p r e s s u r e s . Four o f t h e s e i n v o l v e m a n i p u l a t i o n o f the g e n e t i c m a t e r i a l per se, and t h e f i f t h i n v o l v e s a c h a r a c t e r i s t i c o f n a t u r a l s e l e c t i o n . The environment o f an organism i s dynamic, o f t e n f a v o u r i n g d i f f e r e n t c o m b i n a t i o n s o f genes a t d i f f e r e n t t i m e s o f t h e y e a r (Dobzhansky, 1943; Sheppard, 1951). A v a r i e t y o f genes a r e t h e r e f o r e kept i n the p o p u l a t i o n due t o c o n t i n u o u s f l u c t u a t i o n s i n s e l e c t i v e p r e s s u r e s . F u r t h e r v a r i a b i l i t y i s i n t r o d u c e d through random m u t a t i o n . F o r d (1965) i s o f the o p i n i o n t h a t most m u t a t i o n s i n a complex w e l l adapted system w i l l be d e l e t e r i o u s ; however, a few may i n some way be advantageous and s e l e c t e d f o r . When a m u t a t i o n e n t e r s a p o p u l a t i o n , the s c a r c i t y o f o c c u r r e n c e v i r t u a l l y e n s u r e s t h a t i t w i l l be p r e s e n t p r i n c i p a l l y i n the h e t e r o z y g o u s form ( i . e . Bb ) ( F o r d , 1965). T h e r e f o r e , t o a l l o w s e l e c t i o n f o r 3 t h e new a l l e l e the he t e r o z y g o u s arrangement and not the new homozygous one must be more b e n e f i c i a l t o the organism. When-ever t h e h e t e r o z g o t e i s t h e most advantageous form, the homo-zy g o t e s w i l l be m a i n t a i n e d i n t h e p o p u l a t i o n by Mendalian s e g r e g a t i o n , and a polymorphic s i t u a t i o n a r i s e s . Polymorphism i s a v e r y common g e n e t i c o c c u r r e n c e . Lewontin and Hubby (1966) e s t i m a t e d t h a t 30% - 40% o f a l l gene l o c i a r e polymorphic i n any one population.. T h e i r work has been c o n f i r m e d by t h e r e s u l t s o f Manwell and Baker (1968) and S e l a n d e r and Yang (1969). One g e n e t i c polymorphism may c o n t r o l many d i f f e r e n t f a c e t s o f the body from e x t e r n a l morphology t o m e t a b o l i c r a t e s and v i a b i l i t y ( S e d l m a i r , 1956; Lamotte, 1959; F o r d , 1965). The above mentioned s o u r c e s o f h e t e r o g e n e i t y a r e the b a s i s f o r the f a n t a s t i c d i v e r s i t y o f genotypes o b t a i n e d i n the r e s o r t i n g o f chromosomes d u r i n g m e i o s i s and f e r t i l i z a t i o n , and t h e k a l e i d o s c o p e o f v a r i a t i o n s i n each chromosome produced by c r o s s o v e r s . I t i s t h i s g r e a t p o o l o f v a r i a b i l i t y i n h e r e n t i n the p o p u l a t i o n due t o random m u t a t i o n , f l u c t u a t i n g s e l e c t i v e p r e s s u r e s , polymorphisms, s e g r e g a t i o n o f genes and chromosome a l t e r a t i o n s which p e r m i t s a s p e c i e s t o s u c c e s s f u l l y i n h a b i t new and d i f f e r e n t h a b i t a t s , and thu s form s e r i e s o f r a c e s and e v e n t u a l l y new s p e c i e s . Those s p e c i e s which form s e r i e s o f r a c e s over wide g e o g r a p h i c ranges must p o s s e s s the g e n e t i c p o t e n t i a l t o adapt t o many s i t u a t i o n s . The p r e s e n t i n v e s t i g a t i o n c o n c e r n s t h e s a l i n i t y t o l e r a n c e s o f a marine i n t e r t i d a l g a s t r o p o d , T h a i s l a m e l l o s a . T h i s animal i n h a b i t s t h e r o c k y i n t e r t i d a l and s u b t i d a l f o r s e v e r a l thousand m i l e s a l o n g the c o a s t o f the P a c i f i c ocean 4 from A l a s k a t o Monterey, C a l i f o r n i a ( R i c k e t t s , e_t a l . , 1968). U n l i k e i t s s o u t h e r n r e l a t i v e s , T h a i s l a m e l l o s a does not have a p l a n k t o n i c l a r v a l form (Burkenroade, 1931; K i n c a i d , 1957). T h e r e f o r e t h e young o f any p o p u l a t i o n a r e u s u a l l y t h e progeny o f t h e a d u l t s of t h e same p o p u l a t i o n . Due t o t h e l a r g e number o f g e o g r a p h i c b a r r i e r s e n c o u n t e r e d , e s p e c i a l l y a l o n g the Canadian c o a s t , i n t h e form o f s m a l l i s l a n d s s e p a r a t e d by deep c h a n n e l s and r o c k y p r o m e n t o r i e s b l a n k e t e d by i mpassable c r e s c e n t r i c g r a v e l or sand-mud beaches, l i t t l e m i g r a t i o n o f i n d i v i d u a l s between p o p u l a t i o n s o c c u r s ( C o n n e l l , 1970, K i n c a i d , 1957). T h e r e f o r e numerous s m a l l p o p u l a t i o n s d e v e l o p i n g e o g r a p h i c i s o l a t i o n f o r m i n g a s e r i e s o f r a c e s . Because t h i s s p e c i e s l i v e s s u c c e s s f u l l y over a l a r g e g e o g r a p h i c a l range where i t must t o l e r a t e v a s t d i f f e r e n c e s i n e n v i r o n m e n t a l c o n d i t i o n s , and because i t has demonstrated a h i g h degree o f polymorphism i n m o r p h o l o g i c a l c h a r a c t e r i s t i c s which v a r y from p o p u l a t i o n t o p o p u l a t i o n ( K i n c a i d , 1957), the s p e c i e s as a whole must c o n t a i n a l a r g e p o o l o f g e n e t i c v a r i a b i l i t y from which such o b v i o u s l y d i s t i n c t r a c e s , b o t h m o r p h o l o g i c a l l y and p h y s i o l o g i c a l l y c o u l d be d e r i v e d . A l o n g the n o r t h P a c i f i c c o a s t many major r i v e r s such as the F r a s e r , Columbia, S t i k i n e , Nassa, and Skeena, c o l l e c t water from v a s t a r e a s i n t h e mountains and r e l e a s e l a r g e volumes o f f r e s h water as flumes i n t o the ocean and a l o n g the c o a s t l i n e . M i x i n g o f the f r e s h and s a l t water forms g r a d i e n t s o f s a l i n i t y which v a r y w i t h depth, g e o g r a p h i c l o c a t i o n and season. As low s a l i n i t y may a f f e c t the s n a i l over a l a r g e a r e a o f i t s d i s t r i b u t i o n , i t seems r e a s o n a b l e t h a t a t l e a s t 5 some populations of the animals would have developed the capacity to l i v e under osmotic s t r e s s . Situated near the outflow of the Fraser River, Vancouver ( F i g . 1) provides an e x c e l l e n t opportunity to study the e f f e c t of low s a l i n i t y on the d i s t r i b u t i o n of Thais  lamellosa and to determine i f populations i n contact with ex-tremely low s a l i n i t i e s are more capable of coping with these conditions than members of the species i n l o c a t i o n s removed from such i n f l u e n c e s . S a l i n i t y tolerance i s a f f e c t e d by several f a c t o r s . Generally speaking, the young, non-reproductive, and adult phases are more t o l e r a n t than the o l d , reproductive, and egg or l a r v a l phases r e s p e c t i v e l y (Kinne, 1964; Broekema, 1941: Calabresse, 1969). For instance, F i s c h e r - P i e t t e (1931) found that the eggs of Thais l a p i l l u s , the A t l a n t i c r e l a t i o n of Thais lamellosa, were more s e n s i t i v e than the adults to low i o n i c concentrations. Tolerances can also be a f f e c t e d by the state of acclimation and other environmental f a c t o r s , e s p e c i a l l y temperature (Kinne, 1964). The Oxford Dictionary defines acclimation as "the process of habituating or being habituated to a new or unusual climate". F i s h e r (1958) further expands the concept i n these terms: " r e a c t i o n of the system i s slow compared with the change i n the environment, and ... the changes i n the system p e r s i s t f o r appreciable periods a f t e r the environmental change". Other authors (Precht, 1958; Ushakov, 1964) have stressed that the changes must also be r e v e r s i b l e . Acclimation r e s u l t s when an organism i s able to maintain i t s v i t a l functions at a 6 v i a b l e , often f a i r l y constant l e v e l regardless of environ-mental f l u c t u a t i o n s . With regard to temperature t h i s process appears to be executed at the c e l l u l a r l e v e l by means of i s o -enzymes, changes i n enzyme-substrate a f f i n i t y , and rearrange-ment of use of the major metabolic pathways, (Somero and Hochachka, 1969; Hochachka, 1968, 1967; Hochachka and Somero, 1968). To some extent temperature adaptation i s influenced by hormones, e s p e c i a l l y thyroxine and gonadtropine (Paskova, 1962, 1967). With regard to s a l i n i t y , a cclimation involves i n t e s t i n a l , r e n a l , g i l l and glandular ion pumps, permeability c o e f f i c i e n t s , and the concentrations and types of f r e e amino acids i n the c e l l (Lange and Mostad, 1967; Romer, 1962, Brown and Masoro, 1965; schultz and Zalusky, 1964). The time r e -quired f o r acclimation i s v a r i a b l e depending on the degree and type of stres s and species involved, but experimental cases have run from a few hours to several weeks (Segal, 1956; Sch 1 leper et, a l . , 1960; Schlieper,1969;Newell and Pye,1970 a ) . This i n v e s t i g a t i o n attempts to evaluate the e f f e c t s of changes i n some of these f a c t o r s on populations of Thais  lamellosa. The r e a c t i o n of two populations were followed i n the f i e l d under normal and low s a l i n i t y c o n d i t i o n s . In order to evaluate success i n responding to changes i n the environment^ feeding r a t e s , strength of attachment, and the a b i l i t y to move and to attach were determined f o r i n d i v i d u a l s n a i l s . Thais lamellosa feeds p r i n c i p a l l y i n the spring and f a l l ( F i g . 10), during which time the animals must recover from the previous winter's reproductive a c t i v i t i e s and prepare f o r the next. Low s a l i n i t y occurs i n the l a t e spring as the 7 r e s u l t of the thaw upcountry. I f t h i s a f f e c t s feeding i t w i l l a l s o influence reproductive p o t e n t i a l and v i a b i l i t y . Barnacles are the main food source f o r Thais lamellosa and these are gene r a l l y attached to exposed surfaces of rocks. S n a i l s must therefore be able to move and remain securely attached i n order to feed. I f s n a i l s are dislodged from rocks, they may be washed away by t i d a l currents before they can reattach, or i f they f a l l during a low t i d e when high temperatures are current, they may die of heat exposure and d e s i c c a t i o n . Of course i n a b i l i t y to move p r o h i b i t s feeding and i n a b i l i t y to attach leaves the s n a i l s at the mercy of the elements. A p a r a l l e l study was conducted i n the laboratory under c o n t r o l l e d conditions of temperature and s a l i n i t y , taking i n t o account e f f e c t s of age and of seasonal acclim-a t i o n . Respiratory rates were measured to determine the range of s a l i n i t y s t r e s s and i t s e f f e c t on the metabolism of the animals. The s n a i l ' s capacity f o r i o n i c and volumetric r e g u l a t i o n was also i n v e s t i g a t e d . 8 EXPERIMENTAL METHODS Introduction In t h i s section I s h a l l describe the l i f e h i s t o r y of Thais lamellosa and the study areas and procedures used repeatedly throughout the study. Study Areas A l l study l o c a t i o n s r e f e r r e d to i n the following s e c t i o n are depicted i n P i g s . 1 & 2. The Fraser River empties i n t o the S t r a i t of Georgia j u s t south of the C i t y of Vancouver. Much of the outflow i s c a r r i e d north by t i d a l currents around Point Grey where i t flows along the southern shore of Engl i s h Bay, and during the spring runoff occupies much of the southern h a l f of Vancouver Harbour. Fresh water a l s o passes under Lions Gate Bridge i n t o Burrard I n l e t . D i l u t i o n of sea water i n t h i s area i s augmented by the runoff of small l o c a l r i v e r s , e s p e c i a l l y the Capilano, Squamish, and Seymour. In a d d i t i o n , when the t i d e ebbs fr e s h water i s brought i n t o the I n l e t from Indian Arm. During spring runoff the southern shore of English Bay and the south west po r t i o n of Stanley Park are subjected to extremely low s a l i n i t i e s (5%o and l e s s ) while on the north east side of the Park i n Burrard I n l e t i t may drop to approximately 15%o (Table I ) . Except f o r a few sandy beaches and outcrops of sand-stone, most of the coast of Stanley Park i s g e o l o g i c a l l y s u i t a b l e f o r h a b i t a t i o n by Thais lamellosa. As depicted i n 9 F i g u r e 1 G e n e r a l map o f the d e l t a o f the F r a s e r R i v e r and a s s o c i a t e d c o a s t l i n e showing the v a r i o u s study l o c a t i o n s d e s c r i b e d i n the t e x t . t 10 F i g u r e 2 Map o f S t a n l e y Park d e p i c t i n g the r e l a t i v e abundance °f T h a i s l a m e l l o s a and v a r i a t i o n s i n s a l i n i t y a l o n g t h e s h o r e . Those numbers not i n b r a c k e t s are s a l -i n i t y d e t e r m i n a t i o n s from the 6th t o 8th of A p r i l , w h i l e those i n b r a c k e t s were taken on the 17th o f J u l y . D i s t r i b u t i o n o f the s n a i l s stopped a t the p o i n t marked (X) w i t h the e x c e p t i o n o f one group a t ( Y ) . S a l i n i t i e s were r e c o r d e d a t A and B on t h r e e o c c a s i o n s . Date A B 8/4/70 6/6/70 17/7/70 25.5%o 17.2%o 24.7%o 2 3.0%o l6 . 6 % o 22.8%o Prospect Lions Gate Bridge 11 T a b l e I F l u c t u a t i o n s i n s a l i n i t y c o n d i t i o n s a t Spanish Banks and Ferguson P o i n t . FERGUSON POINT SPANISH BANKS DATE (1969) SALINITY(%o) SALINITY(%o) January 24 27.0 27.3 28 26.2 25.6 31 27.5 28.3 F e b r u a r y 4 24.7 24.9 21 24.7 25.3 24 25.5 23.7 March 3 25.5 27.8 7 29.5 26.4 29 27.3 27.3 A p r i l 1 27.5 25.6 8 28.7 29.5 15 22.5 25.8 May 14 14.3 14.0 17 11.8 8.6 21 10.2 10.5 June 10 8.7 7.8 12 the map, Thais lamellosa i s abundant i n the Inner Harbour, notably between Brockton Point and j u s t short of Lions Gate Bridge. West of the bridge very few were found }none occurring from the point marked (X) between the bridge and Siwash Rock. An a d d i t i o n a l small group of animals was found at (Y). The beach was searched from Brockton Point past Ferguson Point and i n the rocky outcrops of English Bay. No l i v e s n a i l s were found on the southern shore, perhaps because the large amount of s i l t i n g from the Fraser has created vast mud-sand beaches and shelves i n t h i s area which could be p r o h i b i t i v e to d i s p e r s a l . However, i n a group of rocks (Z) near Spanish Banks, several o l d battered Thais lamellosa s h e l l s were found. Again no l i v e s n a i l s were found i n the rocky areas south of Point Grey u n t i l the causeway of the Tsawwassen Ferry Terminal was reached. Here the animals were sparse, a t t a i n i n g dense proportions at L i l l y Point on the south east corner of Point Roberts. Much of the foreshore on the west i s a l s o s i l t e d mud-sand f l a t s and small cobbles. L i l l y Point was used as the s i t e of the normal high s a l i n i t y population. I t was chosen f o r i t s proximity and r e l a t i v e l y high s a l i n i t y waters compared with the Stanley Park area. The s n a i l s at Brockton Point represented a low s a l i n i t y population. These i n d i v i d u a l s were quite capable of breeding and therefore of maintaining themselves. On t h i s b a s i s they were chosen rather than the animals on the west of Stanley Park which were so l i m i t e d i n number that they could e a s i l y have come from s u b t i d a l or adjacent i n t e r t i d a l pop-u l a t i o n s through d i s p e r s i o n ( F i g . 3). The rocky outcrop at 13 F i g u r e 3 Number o f T h a i s l a m e l l o s a p r e s e n t a t the l i m i t o f d i s t r i b u t i o n i n S t a n l e y Park d u r i n g the s p r i n g and summer o f 1970. 14 F i g u r e 4 Seasonal f l u c t u a t i o n s i n s a l i n i t y c o n d i t i o n s a t Brockton P o i n t , L i l l y P o i n t and Spanish Banks. £9-00 I LILLY POINT ui-oo lyn . . . . . . . . : — . 1 • • • • • • -J F M A M J J A S O N D J F M A M J J DATE 1969-70 15 F i g u r e 5 Seasonal f l u c t u a t i o n s i n seawater temperatures a t Brockton P o i n t , L i l l y P o i n t and Spanish Banks. DATE 1969-70 16 the second gun tower at Spanish Banks provided an e x c e l l e n t t e s t beach. I t had an ample supply of barnacles f o r food and numerous large rocks f o r s h e l t e r . In the summer i t ex-periences very low s a l i n i t y c o n d i t i o n s . The ye a r l y trends i n s a l i n i t y f l u c t u a t i o n s at these three beaches are presented i n F i g . 4, and temperature i n F i g . 5. I t can be seen that during the period of t h i s study L i l l y Point o s c i l l a t e d between approximately 30%o and 24%o reaching a minimum of 22%o; Brockton Point f l u c t u a t e d from 29%o to 17%o the lowest recording being 15%o, and Spanish Banks v a r i e d from 26%o i n the winter to 6%o i n the summer, the minimum being 1.5%o. These samples were taken at a depth of s i x to eight inches. L i f e H i s t o r y From Alaska to Monterey Thais lamellosa i n h a b i t s rocky areas, mats of mussels or oyster s h e l l s , p i e r p i l i n g s and other s o l i d substrates where barnacles l i v e (Ricketts et a l . , 1968). D i s t r i b u t i o n extends from the s u b t i d a l from 50* to 60* (Low, personal communication) i n t o the i n t e r t i d a l to a l e v e l of +3* to 5 1; the t o t a l t i d e range i s approximately 15•. The t i d e s i n the S t r a i t of Georgia are mixed semi-d i u r n a l with two unequal highs and lows every 25 hours. S n a i l s at upper l e v e l s are exposed on several consecutive days during the lowest of the low t i d e s . Due to the 25 hour p e r i o d i c i t y t h i s time f a l l s around midnight i n the winter and noon i n the summer, subjecting the animals f o r several hours to the h o t t e s t and c o l d e s t conditions of the year. A f t e r exposure to the hot summer a i r , the s n a i l s r e t r e a t during the 17 f o l l o w i n g high t i d e under or to the base of rocks, i n t o c r e v i c e s and under algae. These moist shaded areas protect them from d e s i c c a t i o n . During spring, summer and f a l l , the animals spend most of t h e i r time feeding except when in t e r r u p t e d by the low t i d e s . According to Connell (San Juan I s . , S t r a i t of Georgia, 1970) 43% and to Emlen (Port Townsend, S t r a i t of Georgia, 1966) 34% of the s n a i l s are a c t i v e l y feeding up on the rocks at any one time. At L i l l y Point the a c t i v e percentage v a r i e d from 66% on the large rocks i n the low i n t e r t i d a l , to 24% i n the adjacent cobbles. Generally Thais lamellosa eats barnacles and mussels j the l a t t e r are entered by d r i l l i n g a hole through the s h e l l with the radula. C a r r i k e r (1961) thinks they a l s o release a chemical from the abo; an accessory boring organ i n the f o o t , which a s s i s t s the radula by softening and loosening surface c r y s t a l s of s h e l l c a l c i t e . The exact method used on barnacles i s i n question. Kincaid (195 7) reports that the s n a i l s d r i l l a hole at the apex of the t e r g a l and sc u t a l p l a t e s , but whether they i n j e c t a n a r c o t i z i n g substance i s not known. Connell (personal communication) b e l i e v e s they i n j e c t such a substance i n t o the i n t e r s t i t i a l t i s s u e between two la y e r s of the s h e l l , and then enter at the t i p of the s c u t a l p l a t e s to feed. In the winter the adults gather i n huge aggregations on the large rocks i n the lower i n t e r t i d a l . Depending p a r t l y on the surface area a v a i l a b l e , these groups may c o n s i s t of hundreds of i n d i v i d u a l s who mate and lay thousands of egg capsules, 200/female (Emlen, 1966) over open surfaces, on top 18 of one another and o c c a s i o n a l l y on other capsules. S n a i l s s t a r t gathering i n September and by mid-October some have already deposited a few capsules. Information obtained from gonadal measurements on s n a i l s at Brockton Point lead Lambert (1970) to conclude that the major amount of reproductive a c t -i v i t y occurs about March, and by A p r i l and May the adults leave again i n search of food. The capsule s i t s on the end of a p e d i c l e attached to the surface with a f l a t d i s c . Chapmannand Banner (1949) counted an average of 23 eggs/capsule i n Oyster Bay (Washington, U.S.A.) while Emlen (1966) found that the number ranged from 20 to 150/capsule (average 83) at Port Townsend (Washington, U.S.A.). Both Emlen (1966) and Ahmed and Sparks (1970) i n c o n t r a d i c t i o n to Kincaid (1954) b e l i e v e that although other species of Thaids may have nurse eggs, Thais lamellosa does not. At Port Townsend, Emlen (1966) found that development required 140 daysj with v a r i a b i l i t y due to temperature infl u e n c e s on the r a t e of growth. Moore (1938 b) postulated that young Thais l a p i l l u s feed on a polychaetous worm, S p i r o r b i s b o r e a l i s , i n the low i n t e r t i d a l . However, newly hatched Thais lamellosa may eat the f r e s h l y s e t t l e d barnacles which are present at the same time (Emlen, 1966). No d e f i n i t i v e work has yet been done on t h i s aspect of feeding. Experiments by Connell (1970) i n d i c a t e that the crab, Cancer productus and s t a r f i s h , P i s a s t e r ochraceus, w i l l eat Thais lamellosa when given the opportunity, the former being more successful with the immature t h i n s h e l l e d i n d i v i d u a l s . This observation i s i n agreement with the m o r t a l i t y observed 19 by Kitching et a l . , (1966) of Thais l a p i l l u s from the crabs Carcinus maenas and Portuhus puber i n Lough Ine, I r e l a n d . Some b i r d s also feed on i n t e r t i d a l animals. The p r i n c i p l e species seen eating Thais lamellosa i n the v i c i n i t y of Vancouver were crows (Corus cavrinus) and glaucus winged g u l l s (Larus qlaucescens)• However, the oyster catcher (Haematopus  bachmcini), white-winged scoter (Melanitta deqlandi), and raven (Corus corax) were a l s o mentioned by Kincaid (1957). The same author reported cannabalism, as the adult s n a i l s eat the egg capsules of t h e i r own species. Experimental Procedures 1. Size Categories Growth of older mature s n a i l s i s d i f f i c u l t to detect as abrasion and growth work simultaneously on the s h e l l ; an attempt to document growth rates i n adults was unsuccessful. Moore (1938 a) was a l s o unable to measure growth r a t e i n adult Thais l a p i l l u s . Although i t i s d e s i r a b l e to d i s t i n g u i s h between d i f f e r e n t age groups since mature i n d i v i d u a l s often have more r e s t r i c t e d tolerance ranges than younger animals, t h i s was impossible and the s n a i l s were therefore grouped simply as mature or immature. Mature animals can be d i s t i n g u i s h e d by the thickened l i p of the aperture and the presence of a row of small teeth along the l i p ( F i g . 6 ) . During these studies no immature s n a i l s greater than 4.00 cm i n length were found nor mature ones l e s s than 3.00 cm,animals i n the v i c i n i t y of Vancouver probably mature when between 3.00 - 4.00 cm i n s h e l l length. A l l adult or " l a r g e " s n a i l s used i n the experiments were between 4.00 - 5.00 cm i n length unless otherwise i n d i c a t e d . 20 S n a i l s between 2.00 - 3.00 cm length were chosen to represent immature stages as i t was d i f f i c u l t to f i n d s u f f i c i e n t numbers of smaller animals. 2. Marking Techniques Abrasion of the s h e l l , due to such f a c t o r s as sand movement, necessitated use of a r e s i l i e n t marker f o r long term f i e l d s t u d i e s . Animals required f o r these experiments were tagged i n the laboratory before being t r a n s f e r r e d to t e s t s i t e s on other beaches. The s n a i l s were i n i t i a l l y placed on paper towels soaked i n sea water. When the s h e l l was bone dry, a number was i n s c r i b e d with India ink and pro-tected with two coats of dekophane (Frank, 1965), a c l e a r p l a s t i c cement. S n a i l s from d i f f e r e n t beaches were i d e n t i f i e d by a dab of an o i l base p a i n t . Markings were allowed to dry completely. No m o r t a l i t y occurred and the i d e n t i f i c a t i o n endured f o r a minimum of several months, and often more than a year. For laboratory experiments, where l i t t l e abrasion occurs, i t was s u f f i c i e n t to mark the d r i e d s h e l l of the animal with a f e l t pen. 3. Feeding Experiments Barnacles attach to any s o l i d substrate i n the environ-ment, i n c l u d i n g the s h e l l s of other animals, such as s n a i l s and mussels. Mussels supporting a large number of barnacles, the preferred food of Thais lamellosa, were c o l l e c t e d from the v i c i n i t y of Brockton Point, where they grow i n abundance to a large s i z e . The mussel s h e l l was unhinged and the meat removed from the va l v e s . A small hole was d r i l l e d i n the 21 . F i g u r e 6 Drawings o f immature and mature s n a i l s i l l u s t r a t i n g the t h i c k e n e d o u t e r l i p o f the a p e r t u r e and d e n t i t i o n o f a d u l t a n i m a l s . SPIRE APERTURE TEETH OUTER LIP OF APERTURE SPIRE BODY WHORL MATURE SNAIL SPIRE APERTURE (NO TEETH) OUTER LIP OF APERTURE SIPHONAL CANAL SPIRE BODY WHORL IMMATURE SNAIL 22 s h e l l so that i t could be fastened i n s i d e the experimental cages with a screw. Dead barnacles, empty s h e l l s and small mussels were removed. Feeding r a t e s were c a l c u l a t e d i n terms of biomass as i t was impossible to supply a l l the cages and treatments with barnacles of the same s i z e . Fortunately the s h e l l of a barnacle remains attached to the substrate f o r weeks or even months a f t e r the animal's death. Empty s h e l l s can be con-verted to a measure of the biomass eaten by use of a regression l i n e r e l a t i n g s h e l l opercular length to barnacle dry weight. The t o t a l biomass of the dead barnacles was corrected f o r death due to natural mortality, derived from c o n t r o l s . The regression r e l a t i o n s h i p was determined f o r 50 barnacles ranging i n s i z e from 3 - 7 mm opercular length ( F i g . 7); barnacles of a smaller s i z e were not touched during the experiments. That s n a i l s prefer to eat l a r g e r barnacles agrees with work done by Connell (1961, 1970). The s h e l l s were scrubbed clean before any measurements were taken. The animal was removed by softening the d r i e d body with b o i l i n g water and c a r e f u l l y scraping i t from the s h e l l . The d r i e d weights of the s h e l l and barnacle, and of the s h e l l alone were used to c a l c u l a t e the dry weight of the barnacle. 4. F i e l d Cages Two types of cages were employed i n the f i e l d : s t a i n l e s s s t e e l mesh cages (a v a r i a t i o n of Connell, 1961) f o r determination of feeding r a t e s , and large enclosures of hard-ware c l o t h f o r observation of small groups of s n a i l s under nat u r a l c o n d i t i o n s . The former were constructed of %" p l y ~ 23 F i g u r e 7 R e l a t i o n s h i p between d r y weight and a p e r t u r e l e n g t h o f the b a r n a c l e Balanus q l a n d u l a c o l l e c t e d from Bro c k t o n P o i n t on October 31st, 1969. l n d r y weight = -0.374 + 0.065 • l e n g t h OPERCULAR LENGTH (MM) -wood and s t a i n l e s s s t e e l mesh (10 mesh/inch), .025" wire d i a -meter, providing a 56% open area). The i n s i d e area a v a i l a b l e to each animal was 12.7 cm x 10.2 cm x 3.8 cm. The cage base board was screwed to four b r i c k s and cemented to the rocky i n t e r t i d a l at approximately the +3.5' t i d a l l e v e l . The l e v e l was determined by noting the height i n the Gulflow T i d a l Calender (Gulf of Georgia Towing Co.Ltd., Vancouver, B.C.) which corresponded to low t i d e at t h i s point on a calm day. A f t e r a year much of the cement had washed away and several of the cages were replaced. One compartment of the cage was maintained as a c o n t r o l to estimate barnacle m o r t a l i t y . Each of the other three contained one s n a i l , an adult, a j u v e n i l e and an i n t e r -mediate (3.00 - 4.00 cm s h e l l length). A mussel s h e l l , prepared as described above, was screwed to the wood i n the upper part of the compartment. This prevented death of the barnacles due to s i l t i n g , which r a r e l y occurred to any extent, but on occasion a centimetre of sand and debris was deposited at the bottom of the compartments. In ad d i t i o n , such a l o c -a t i o n approximated the normal l o c a t i o n f o r prey animals since s n a i l s must ge n e r a l l y move v e r t i c a l l y from the pro t e c t i o n of the rock bases to feed. The enclosures were constructed with s t r i p s of V hard-ware c l o t h 3.7 m by 0.4 m. A group of rocks at approximately the 3.5' t i d a l l e v e l was e n c i r c l e d with t h i s length and the bottom 0.1 m bent inwards i n an attempt to f i t the contours of the substrate. The c l o t h was supported on both sides with rocks and the overlapping ends were sewn together with nylon f i s h i n g l i n e . These cages were used to contain small groups of s n a i l s 25 f o r observation on a beach where they normally do not l i v e . They appeared not to be crowded at t h i s density (7/100 sq cm) as the rocks provided a great deal of v e r t i c a l surface area, a large population of barnacles was present, and Thais  lamellosa normally l i v e s i n c l o s e a s s o c i a t i o n with others of i t s own species. When c o l l e c t i n g animals f o r experiments, I often found them i n greater d e n s i t i e s than that r e f e r r e d to above. Another group of s n a i l s was released i n the same area, but not enclosed. These enclosures d i s i n t e g r a t e d f a i r l y r a p i d l y i n sea water and could only be used f o r a l i m i t e d time (several months) during periods of low s a l i n i t y , 5. Laboratory Experimental Arrangements The r e a c t i o n s of the s n a i l s i n the f i e l d to a low s a l i n i t y environment were checked against t h e i r responses under c o n t r o l l e d laboratory c o n d i t i o n s . A f a c t o r i a l e x p e r i -mental design i n v o l v i n g temperature and s a l i n i t y using twelve ten g a l l o n aquaria was used. The temperatures(9°C, 12°C, and 18°C) were maintained by an open system of continuously flowing water which was cooled and then passed through the tanks i n glass tubing. One inch styrofoam was used to i n s u l -ate the aquaria on the bottom and sides except between members of the same temperature group. The e n t i r e set up was l o o s e l y covered with a sheet of c l e a r p l a s t i c to prevent evap-o r a t i o n and exchange of heat while s t i l l permitting i l l u m i n -a t i o n of the tanks. In the winter the 12°C and 18°C temper-atures were obtained with heaters. However, i n the summer only the 18°C tanks required heating and an extra metal c o o l i n g c o i l was placed near the surface i n the 9°C tanks. This 26 continuous b a t t l e with the changing ground water and outdoor temperatures i s responsible f o r noticeable temperature f l u c -tuations during the experiments. The water was cleaned and aerated by means of external f i l t e r s . In a l l experiments sea water was d i l u t e d with d i s t i l l e d water to obtain the desired s a l i n i t i e s (20%o, 15%o, 12%o and 9%o). which were checked with a hydrometer every three days. Each tank ( F i g . 8) was divided i n h a l f by a c l e a r p l e x i g l a s s sheet perforated to allow water flow. A b r i c k with a piece of f i b e r g l a s s e d plywood (21 cm x 10 cm) glued to the top was placed perpendicularly and adjacent to the p l e x i g l a s s i n each h a l f of the aquarium. The b r i c k and wood provided a submerged platform to which prepared food could be attached f o r feeding experiments. The underside of the g l a s s bottom of the tanks was marked o f f i n a g r i d (2 cm x 2 cm). In order to maintain a s i m i l a r s i z e range of s n a i l s i n the aquaria, the fo l l o w i n g scheme which i s i l l u s t r a t e d i n Figure 9, was designed f o r s o r t i n g the s n a i l s . A l l animals of one s i z e c l a s s from a p a r t i c u l a r l o c a t i o n (e.g. lar g e , Brockton Point) were subdivided i n t o ten smaller groups each comprising a 0.1 cm range of s h e l l length (e.g. 4.20 -4.29 cm). The sequence of s n a i l s within these was random. The s n a i l s were then d i v i d e d i n t o 12 groups ( A - L) each having the same s i z e composition. 6. Pre-experimental Maintenance of Animals In the winter the s n a i l s were kept i n basins out of doors to maintain the low temperatures to which 27 F i g u r e 8 Diagram o f an aquarium from the l a b o r a t o r y study on the combined e f f e c t s o f temperature and s a l i n i t y on the r e s p o n s e s o f T h a i s l a m e l l o s a . FILTER PLEXIGLASS DIVISION GLASS COOLING COIL 28 F i g u r e 9 I l l u s t r a t i o n o f the method used to randomly a s s i g n s n a i l s t o d i f f e r e n t t r e a t m e n t s y e t t o m a i n t a i n a s i m i l a r s i z e d i s t r i b u t i o n w i t h i n each. STEP ONE S i z e C a t e g o r i e s cm s h e l l l e n g t h E n t r y o f s n a i l s i n t o a r r a y s A r r a y s 0 - 9 4.00- 4.10- 4.20- 4.30- 4.40- 4„50- 4.60- 4.70-4.09 4.19 4.29 4.39 4.49 4.59 4.69 4.79 1, 1, 4 4.80- 4.90-4.89 4.99 8. 9„ 8. STEP TWO E n t r y from a r r a y s 0-9 i n t o a r r a y s A-L s o r t i n g t h e s n a i l s t o m a i n t a i n a s i m i l a r s i z e d i s t r i b u t i o n i n each new a r r a y . A B C D E F G H I J K L 0, 0 : 0 3 • • • • 0 n 1, l z 1 3 1 H - i n sequence from a r r a y 0 e t c . u n t i l row i s f u l l , 2 H 2e l s 2 5 2, l f c 2 b 21(J 1, 2^ 2 u l ? . n - i n sequence from above a r r a y ; s n a i l s p l a c e d i n t o the 3rd column t o the r i g h t o f the l a s t e n t r y u n t i l the row i s f u l l - o t h e r 3 rows a r e f i l l e d i n t h e same manner as the 2nd row 2 9 they were accustomed. In the summer the animals were held indoors i n aerated buckets cooled to approximately 17°C. The s a l i n i t y was 27%o, c l o s e to conditions i n the f i e l d i n the winter, but higher than i n the summer. The water was changed frequently, depending on the number of animals i n the container and the presence of food (barnacles and mussels). Food was provided only i f the s n a i l s were held i n the basins or buckets f o r more than two days. SECTION I ECOLOGICAL STUDIES IN THE FIELD INTRODUCTION S a l i n i t y tolerance of i n d i v i d u a l s n a i l s v a r i e s throughout l i f e . As mentioned previously, eggs are the most s e n s i t i v e stage and tolerance increases with age. On the beaches near Vancouver Thais lamellosa l a y s i t s eggs i n the winter and e a r l y spring, when the outflow of the Fraser River i s minimal and s a l i n i t y g r e a t e s t . For t h i s reason, the d i s -t r i b u t i o n of the s n a i l i s not associated with l i m i t a t i o n of embryonic development caused by seasonally low s a l i n i t i e s . This i n v e s t i g a t i o n was therefore r e s t r i c t e d to mature and immature forms. Because newly hatched s n a i l s were d i f f i c u l t to f i n d , and l e s s than a dozen animals smaller than a centimeter i n s h e l l length were seen during the e n t i r e study period; older immature s n a i l s (2.00 - 3.00 cm i n s h e l l length) were the youngest group studied. Several c h a r a c t e r i s t i c s r e l a t e d to v i a b i l i t y were chosen to measure the e f f e c t s of s a l i n i t y s t r e s s . These were feeding r a t e , attachment strength, amount of movement and a b i l i t y to remain attached to the substrate. I t was hypothesised that as s a l i n i t y decreased these c a p a b i l i t i e s would be e f f e c t e d , one s l i g h t l y before another, and eliminated over a range of s a l i n i t i e s . Evaluation of several d i f f e r e n t f a c t o r s would, therefore, provide an i n d i c a t i o n of s t r e s s and t o l e r a n c e s . In the laboratory s a l i n i t y c onditions can be s t r i c t l y c o n t r o l l e d ; however, i n the f i e l d v a r i a t i o n s occur through time (both d a i l y and se a s o n a l l y ) , depth, and with movements of the t i d e . Seasonal f l u c t u a t i o n s at L i l l y Point, Brockton Point and Spanish Banks were shown i n Figure 4. Data from Spanish Banks i l l u s t r a t e v a r i a t i o n with depth and movements of water during the t i d a l c y c l e s (Tables II & I I I ) . S a l i n i t y increased with depth ( s a l t water has a greater s p e c i f i c g r a v i t y than f r e s h water). In the f i r s t 12 f e e t , the s a l i n -i t y changed 2.0 - 4.7%o, and was s i m i l a r f o r samples taken both through a v e r t i c a l depth of 14 f e e t offshore and along the surface of the substrate i n the l i t t o r a l region during high t i d e (to a depth of 14 f e e t ) . The greatest d i s p a r i t y with depth occurred during the period of minimal outflow of the Fraser River. S a l i n i t y of surface samples v a r i e d within each t i d a l c y c l e such that samples taken at the high or low t i d e were more s a l i n e than those from the ebb t i d e , which i n turn were more s a l i n e than those from the incoming t i d e . I t i s evident that i n the region around Spanish Banks i n t e r t i d a l animals are subjected to constantly changing s a l i n i t i e s . D e t a i l e d knowledge of the f i e l d s a l i n i t y c onditions experienced by the s n a i l s would nec e s s i t a t e continuous s a l i n i t y recordings; the surface water samples used i n t h i s study present an approximation of these c o n d i t i o n s . 32 T a b l e I I S a l i n i t y o f water samples through d e p t h . Two s e t s o f s e r i a l water samples were taken a t h i g h t i d e a t two f o o t v e r t i c a l i n -t e r v a l s o f f the second gun tower a t Spanish Banks. One s e t con-s i s t e d o f bottom samples over the l i t t o r a l r e g i o n t o a depth o f 14 1; the o t h e r o f o f f s h o r e v e r t i c a l samples t o t h e same d e p t h . S a l i n i t i e s were determined l a t e r by t i t r a t i o n . Samples were tak e n on t h r e e d i f f e r e n t days, and a s i m i l a r s e t was o b t a i n e d about two m i l e s f u r t h e r e a s t a l o n g t h e s h o r e . L o c a t i o n GUn Tower Gun Tower Gun Tower F u r t h e r E a s t Date June 26/69 August 25/69 March 8/70 June 22/70 S a l i n i t y * * S a l i n i t y S a l i n i t y S a l i n i t y Depth ( f t ) L i t - O f f - L i t - O f f - L i t - . O f f - L i t - Of f -t o r a l shore t o r a l shore t o r a l shore t o r a l shore 0 7.3 16.5 21.8 8.7 2 7.6 17.3 23.5 10.7 4 8.5 8.5 17.8 17.9 22.6 24.9 10.7 6 8.3 8.4 18.6 17.8 22.9 25.8 10.7 8 9.0 8.9 18.5 17.9 25.8 26.1 11.8 10 9.5 18.1 26.7 25.9 12.2 12 8.9 9.3 18.6 27.1 26.5 12.3 14 11.3 26.9 26.3 * d a t a were taken through 12 v e r t i c a l f e e t , a t which p o i n t bottom ( s u b s t r a t e ) was r e a c h e d . ** s a l i n i t y e x p r e s s e d as %o. 33 T a b l e I I I The s a l i n i t y o f s u r f a c e water d u r i n g d i f f e r e n t movements o f t h e tidal cycle. Top s e t o f d a t a were o b t a i n e d p e r i o d i c a l l y t h r o u g h -out the s p r i n g s o f 1969 and 1970 a t Spanish Banks (second gun t o w e r ) . Bottom s e t o f d a t a were c o l l e c t e d on two days i n the f a l l o f 1968 a t t h r e e beaches: S p a n i s h Banks, B r o c k t o n P o i n t and Ferguson P o i n t . L o c a t i o n Date S a l i n i t y o f Sample (%o) Ebbing Incoming Low T i d e High T i d e T i d e T i d e  2nd tower 18/6/69 7.5 6.5 tt 18/6/69 7.5 4.4 tt 7/5/70 22.9 15.2 tt 4/6/70 11.2 14.5 10.6 4.3 tt 17/6/70 9.6 1.5 tt 20/6/70 9.6 2.6 ft 2/7/70 5.3 5.2 tt 17/7/70 12.7 13.8 S.B.» 17/11/68 18.1 20.8 B.P. 17/11/68 24.4 24.7 F.P. 17/11/68 20.1 16.8 B.P. 24/11/68 25.2 25.7 F.P. 24/11/68 19.4 23.5 * a b b r e v i a t i o n s : S.B. S p a n i s h Banks: B.P. B r o c k t o n P o i n t : F.P. Ferguson P o i n t : 34 • FEEDING RATES Introduction To evaluate the e f f e c t of conditions of low s a l i n i t y on the feeding r a t e of Thais lamellosa on barnacles i n the f i e l d , the pattern of food intake was followed f o r one year at each of the three study beaclmes: L i l l y Point, Brockton Point, and Spanish Banks. The r e l a t i o n s h i p of feeding r a t e s between these beaches throughout the year provides a b a s i s from which deviations during periods of low s a l i n i t y can be evaluated. Methods and Materials Three s t a i n l e s s s t e e l mesh cages (p.22) were set out at L i l l y Point, s i x at Brockton Point and s i x at Spanish Banks at the 3.5• l e v e l i n the lower i n t e r t i d a l . As mentioned previously, the cages consisted of four compartments: one c o n t r o l , and three others each containing a d i f f e r e n t s i z e d s n a i l (2.00 - 3.00 cm; 3.00 - 4.00 cm; and 4.00 - 5.00 cm i n s h e l l l e n g t h ) . S n a i l s o r i g i n a l l y from L i l l y Point were placed i n three cages at each of the beaches while the extra three cages at Brockton Point and Spanish Banks contained Brockton Point animals. L i l l y Point s n a i l s could therefore be com-pared with two states of decreased s a l i n i t y and the Brockton Point with one. No Brockton Point animals were t r a n s f e r r e d to L i l l y Point because i t was assumed that they would already have compensated t h e i r feeding r a t e f o r reductions i n s a l i n -i t y , and therefore, i t was of i n t e r e s t to study t h e i r feeding 35 rate only under more severe conditions of low s a l i n i t y . In a d d i t i o n a lack of time demanded that only the e s s e n t i a l parts of the experiment be performed. The food source (Balanus qlandula) i n the cages was changed i r r e g u l a r l y depending on the feeding r a t e during the preceding period, but supplies were always maintained i n excess of consumption. Feeding r a t e s were c a l c u l a t e d as the dry body weight consumed/snail/day. Results and Discussion The data were v a r i a b l e and no s i g n i f i c a n t d i f f e r -ences were detected i n feeding rates at any of the beaches e i t h e r among the three s i z e categories or between animals o r i g i n a l l y from Brockton Point and L i l l y P oint. The r e s u l t s , therefore, were grouped within each l o c a t i o n and are presented i n Figure 10. When t h i s experiment was conducted i t was not r e a l i z e d that feeding r a t e can be dependent, up to some satu r a t i o n l e v e l , on the number of prey animals present. Below t h i s s a t uration l e v e l , the tendency to feed decreases. Murdoch (1969) found that 20-30 prey/container (12 cm x 11 cm x 7 cm) was the lower l i m i t of the saturation l e v e l f o r groups of two or more Thais emarqinata. The l e v e l f o r one Thais  lamellosa« i f such e x i s t s , i s not known. Since the s n a i l s i n t h i s study often consumed the vast majority of barnacles presented, the r e s u l t s do not n e c e s s a r i l y i n d i c a t e t h e i r maximum possible feeding r a t e s , but rather t h e i r r a t e of feeding under conditions of decreasing prey density. This i s probably a c l o s e r approximation of f i e l d c o n d i t ions f o r many animals feed i n the same general area and discovery of l i v e barnacles must become more d i f f i c u l t as feeding continues S i g n i f i c a n t d i f f e r e n c e s i n feeding between the s n a i l s at Brockton Point and L i l l y Point were found only during the e a r l y winter (December to January) (Table IV). In the winter of 1970, the s a l i n i t i e s measured at these two beaches were v i r t u a l l y the same, and the d e v i a t i o n , t h e r e f o r e , was not associated with t h i s v a r i a b l e . Hanks (195 7) working with a s i m i l a r gastropod, Urosalpinx cinerea, and Largen (1966) with Thais l a p i l l u s , found that decreased temperatures led to lowered feeding r a t e s . From the end of November to the beginning of March, the surface water temperature at L i l l y Point was 5.0°C. The period corresponds exactly with the low i n feeding rate at t h i s beach. On the other hand, temperatures at Brockton Point averaged 8.2°C during t h i s time the lowest temperatures i n t h i s l o c a t i o n occurring i n February when the feeding r a t e dropped to the winter l e v e l recorded at L i l l y Point. Temperature d i f f e r e n c e s may, therefore, be responsible f o r the observed reduction i n feeding. During the winter not only i s the temperature low, but the s n a i l s are a l s o occupied with reproductive a c t i v i t i e s , which have been shown to decrease or eliminate feeding (Thorson, 1958). The experiments reported here give no i n d i c a t i o n as to whether normal, uncaged r e p r o d u c t i v e l y a c t i v e i n d i v i d u a l s feed. I t i s possible therefore, that the d i f f e r -ences between Brockton Point and L i l l y Point may be due to v a r i a b i l i t y i n response to the unusual conditions of s o l i t u d e and c o n s t r a i n t during the reproductive season. 37 Figure 10 Feeding rates of Thais lamellosa at Spanish Banks, Brockton Point and L i l l y Point f o r the year August 191 to J u ly 1970. Each mean i s p l o t t e d with - 1 standard e r r o r . ( — ) Brockton Point ( ) L i l l y Point ( ) Spanish Banks 6.00-< H < CO \ Q W s & co Z O u fH X O H Cd Q s 5D0-4.00-j 3.00 H 2.0 Oi 4-1.001 0.00 AUG, I OCT. DEC. FEB l APR, JUN. AUG. SEASON OF THE YEAR (1969-1970) T a b l e IV T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between f e e d i n g r a t e s a t d i f f e r e n t beaches. Data were taken from F i g u r e 10. Date L i l l y P o i n t v . B r o c k t o n P t . L i l l y P t . v . S p a n i s h Banks Spanish Banks v . B r o c k t o n P t . d f t - v a l u e s i g df t - v a l u e s i q d f t - v a l u e s i q . Aug . 23 1.6495 n. s. 19 1.6584 n. s. 27 6.1815 B * * * S e p t . 23 0.3583 n. s. 19 2.6287 L 26 4.3189 B * * • Sep-Oct 22 0.3784 n. s 16 1.7137 n. s. 22 1.9415 n. s. Nov. 21 1.3166 n. s. 15 0.3878 n. s. 20 0.9784 n. s. Dec. 22 2.7218 B • » 24 2.5 742 L * 30 5.1099 B * • • J a n . 22 2.3719 B * S. cages l o s t S. cages l o s t Feb. 23 1.3360 n. s. Mat-Apr. 15 1.1680 n. s. 16 2.3860 L* 17 3.2503 B • • • Apr-May 21 0.5598 n. s. 19 2.6931 L ** 24 3.7656 B * » » May-Jun. 20 1.8666 n. s. 15 0.7802 n. s. 19 1.9803 n.s. J u n - J u l . L. cages l o s t L. cages l o s t 25 2.1252 B » A b b r e v i a t i o n s - B (Brockton P o i n t , L ( L i l l y P o i n t , S ( S p a n i s h Banks) A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s a t which beach the g r e a t e r f e e d i n g r a t e s were r e c o r d e d . 39 Feeding r a t e was c o n s i s t e n t l y lowest at Spanish Banks and d i f f e r e d s i g n i f i c a n t l y from Brockton Point at a l l times except during October, November, and June; and from L i l l y Point, except during October, November, June,and August (Table IV). The reasons f o r convergence at these times are not known. At a l l l o c a t i o n s two peaks of feeding occurred each year, i n the spring(March to May) and i n the f a l l (September to October). Periods of minimal feeding occurred i n the c o l d of winter (February) and i n the heat of summer (June to J u l y ) . The l a t t e r i s a period of extremely low t i d e s , frequently exposing the animals to the sun and warm a i r temperatures f o r several hours a day. In a d d i t i o n , i n the cases of L i l l y Point and Spanish Banks, the incoming t i d e passes over an extensive t r a c t of hot sand which prob-ably serves to r a i s e water temperatures to the v i c i n i t y of 20°C ( F i g . 5). Maximum feeding rates correspond to times of moderately warm temperatures (11.0°C)and long periods of sub-mergence. The s n a i l s on unshaded shores feed only when submerged during d a y l i g h t t i d e s (Connell, 1970); the low t i d e s at these times of year r a r e l y uncover them. Seasonal trends, presumably associated with temper-ature and exposure, obscure any e f f e c t s of s a l i n i t y on feeding rates during June, J u l y and August. Not only do the feeding rates descend during t h i s time at a l l three beaches, but the inconstant r e l a t i o n s h i p between the feeding rates at Spanish Banks and the other two beaches also prevents determination of an expected value at Spanish Banks (based on the r e l a t i v e performance at the three beaches during the r e s t of the year) 40 and comparison o f t h i s w i t h the observed v a l u e . However, reduced r a t e s a t Sp a n i s h Banks a r e a s s o c i a t e d w i t h s a l i n i t y f l u c t u a t i o n s between 5 - 15%o (August 1969, June 20 t o J u l y 17, 1970). The f e e d i n g r a t e a t L i l l y P o i n t was 1.38 g / d a y / s n a i l and a t B r o c k t o n P o i n t between 1.60 - 1.95 g / d a y / s n a i l d u r i n g t h i s t ime, w h i l e a t Sp a n i s h Banks i t was between 0.00 - 0.37 g / d a y / s n a i l ( t h e l a t t e r d a t a were v a r i a b l e and j u s t s i g n i f -i c a n t l y d i f f e r e n t from z e r o . T h e r e f o r e , the low s a l i n i t y c o n d i t i o n s a t S p a n i s h Banks may p r e s e n t a d d i t i o n a l a d v e r s i t y t o maintenance o f v i a b l e p o p u l a t i o n s . 41 REACTIONS OF THAIS LAMELLOSA TO SPRING CONDITIONS AT SPANISH BANKS  Introduction S n a i l s from both Brockton Point and L i l l y Point were t r a n s f e r r e d to Spanish Banks i n the e a r l y spring i n order that t h e i r a b i l i t y to perform bas i c l i f e functions could be studied i n r e l a t i o n to s a l i n i t y changes. The performance of the two groups were compared to determine whether members of the Brockton Point population would e x h i b i t greater tolerance of reduced s a l i n i t i e s than those from L i l l y Point. Methods and Materials 1. Experimental Procedures In the spring of both 1969 and 1970, s n a i l s were t r a n s f e r r e d to Spanish Banks. The f i r s t year 6 enclosures (see p.22) were b u i l t at the 3.5* t i d a l l e v e l and 54 large s n a i l s from Brockton Point were placed i n each. A month l a t e r a group of 155 uncaged animals was released i n the same v i c i n i t y . The enclosures prevented the d i s p e r s i o n of the s n a i l s ; the uncaged group was introduced to determine i f the enclosure was a f f e c t i n g the gross behaviour of the animals. In A p r i l 1970, a large enclosure was constructed at the same l o c a t i o n . One hundred large plus85 small Brockton Point s n a i l s and 100 large plus 105 small L i l l y Point animals were marked and placed i n s i d e . Among the rocks around the outside of the cage were placed an a d d i t i o n a l 194 large L i l l y Point and 156 large Brockton Point animals. A l l s n a i l s were 42 positioned with the foot against the lower edge of a rock to a s s i s t attachment. During the spring and e a r l y summer of both years, records were kept of s a l i n i t y , temperature, m o r t a l i t y r a t e s , the numbers of s n a i l s unattached l y i n g on the sand, and numbers attached to the upper portions of rocks ( i . e . no part of the s h e l l was i n contact with the sand). In a d d i t i o n i n 1970, a c o n t r o l area, s i m i l a r i n composition to the l o c a t i o n at Spanish Banks, was surveyed simultaneously at Brockton Point and attachment strengths of animals at both beaches were determined throughout the season. S n a i l s take protec-t i o n under algae and rocks or i n c r e v i c e s when exposed during low t i d e s (Table V). Therefore, the fo l l o w i n g schedule was devised to standardize the r e s u l t s and to obtain an accurate estimate of the p o s i t i o n s of the s n a i l s at the end of the previous s e r i e s of high t i d e s . On the f i r s t day of exposure the t o t a l number of Thais lamellosa v i s i b l e and the number of those up on the rocks were counted over the same t i d a l range at both beaches. The census at Spanish Banks included d i f f e r e n t i a t i o n between Brockton Point and L i l l y Point animals as well as t h e i r p o s i t i o n s . Dead and un-attached animals were also recorded. Attachment strength was measured during the ebbing t i d e at one beach and the next day at the other beach. Only animals that were s t i l l wet were tested since i t was observed that dry animals were e i t h e r r e a d i l y dislodged when disturbed or had extremely low attach-ment strengths. Substrate also influenced the r e s u l t s , attachment strength being l e s s on a l g a l and sand or mud 43 encrusted areas (Table V I ) . Only s n a i l s attached to hard 'clean' surfaces were considered. The attachment strength of the s n a i l was measured by means of a tension spring equipped with an e s p e c i a l l y designed ' s n a i l gripper' ( F i g . 11). A l l determinations were made at r i g h t angles to the surface of attachment. 2. A n a l y t i c a l Procedure The data were analyzed by grouping a l l s n a i l s i n enclosures i n 1969, and a l l s n a i l s , both uncaged and enclosed, i n 1970. The uncaged animals i n 1969 reacted i n the same manner as the enclosed i n d i v i d u a l s although trends became apparent i n the former group s l i g h t l y before the l a t t e r ( F i g . 12). This temporal d i s p a r i t y may have r e s u l t e d from acclimation d i f f e r e n c e s . The uncaged animals were not i n t r o -duced to Spanish Banks u n t i l May 5th, approximately the time s a l i n i t y dropped below 10%o. Consequently they were exposed suddenly to very low s a l i n i t y conditions whereas the animals i n the enclosures had been acclimating gradually to the decreasing s a l i n i t y f o r the previous month. In 1970, the enclosure commenced to d i s i n t e g r a t e as the r e s u l t of cor r o s i o n by s a l t water and within a few weeks the s n a i l s were capable of moving e a s i l y both i n and out of i t . Since there was no way of determining enclosed from uncaged i n d i v i d u a l s , and since most of the s n a i l s l e f t the enclosure, a l l were considered together. Small s n a i l s were disregarded because too few could be found at any one time to give an accurate i n d i c a t i o n of t h e i r responses. The data were c o r r e l a t e d with s a l i n i t y changes i n the environment and Chi square t e s t s were used to T a b l e V. R e l a t i o n s h i p between the e f f e c t o f s u b s t r a t e and exposure t o warm summer atmo-s p h e r i c c o n d i t i o n s on the d i s t r i b u t i o n o f T h a i s l a m e l l o s a on r o c k s ( i . e . n ot i n c o n t a c t w i t h the sand a t the base o f the r o c k ) . The d a t a were c o l l e c t e d on May 30th and June 4 t h 1969 at L i l l y P o i n t . I n t e r t i d a l S u b s t r a t e Rock D.of ' Ex. D.of Ex. D.of Ex. D.of Ex. Hei g h t Composition No. 2nd day 7th day 2nd day 7th day 1 0.72 (178)' 0.02 (52) ( T o t a l P r o p o r t i o n ) l a r g e 2 0.66 (170) 0.00 (15) 0.66 (414) 0.01 (84) b o u l d e r s + 2 f t 3 0.52 ( 66) 0.00 (17) c o b b l e s * * 0.24 (103) 0.00 (59) 0.24 (103) 0.00 (59) D.of Ex. D.of Ex. D.of Ex. D.of Ex. 4 th day 9th day 4th day 9th day l a r g e 4 0.42 ( 59) 0.00 ( 0) b o u l d e r s 5 0.00 ( 5) 0.00 ( 7) 0.38 ( 73) 0.10 (10) + 5 f t 6 0.33 ( 9) 0.33 ( 3) * the number i n b r a c k e t s i s the t o t a l sample s i z e *• a r e a 4' x 8' The second day o f exposure a t + 2 f t was the f i r s t i n a s e r i e s o f h o t sunny days. A b b r e v i a t i o n s - D.of Ex. (date o f exposure) 45 T a b l e VI E f f e c t o f s u b s t r a t e on attachment s t r e n g t h . Data were c o l l e c t e d from B r o c k t o n P o i n t on J u l y 4, 1971. SUBSTRATE MEAN S.E. N Rock (bare) 344 -40 12 B a r n a c l e s and/or Mussels 204 -16 14 A l g a e and/or Sand 108 -24 7 46 Figure 11 A spring balance equipped with a 'snail gripper' was employed to determine the attachment strength of the snails. The 'snail gripper* was constructed from a large safety pin with the ends cut off and replaced by two c i r c l e s of metal, a large one to f i t over the spire of the shell and a small one for the base of the columella. The device was attached to the base of the metal bar at the end of the spring in the balance by a screw and secured so that the force was directed through a straight l i n e . 47 evaluate d i f f e r e n c e s between s n a i l s o r i g i n a t i n g from Brockton Point and L i l l y Point, and between responses at d i f f e r e n t i n t e r t i d a l heights. The r e l a t i o n s h i p between strength of attachment and s h e l l length was derived from s n a i l s ranging i n length from 2 3.85 cm to 5.97 cm, and was converted to g/cm foot-area f o r the purposes of comparison. The foot-area of a number of s n a i l s at d i f f e r e n t s a l i n i t i e s and temperatures was determined by allowing the animals to attach to a sheet of p l e x i g l a s s i n laboratory aquaria. The sheet was removed and the o u t l i n e of the foot traced onto transparent p l a s t i c from below. The area, then being determined graphically^ was r e l a t e d to s h e l l length; no e f f e c t of s a l i n i t y or temperature was detected (Table V I I ) . Regression Line Large S n a i l s Foot-area = -1.095 + 0.547 s h e l l length cm Standard Errors slope (0.0004) i n t e r c e p t (0.0000) Data concerning attachment strength were analyzed i n two ways: (a) comparison of means from both beaches using t - t e s t s and 2 (b) c o l l a t i o n of frequencies f a l l i n g between 0 - 100 g/cm , 2 + 2 100 - 200 g/cm , and 200 g/cm , using Chi square to i n v e s t i -gate d i f f e r e n c e s . Results 1. Comparison of 1969 - 1970 Data The duration of the Fraser River spring runoff was greater i n 1969 than i n 1970 (Table VIII) and consequently s a l i n i t y at Spanish Banks f e l l below 10%o i n the middle of 48 T a b l e V I I Comparison o f the e f f e c t s o f s a l i n i t y (9%o - 20%o) and tempera-t u r e (9°C - 18°C) on the r e l a t i o n s h i p between f o o t - a r e a (dependent v a r i a b l e ) and s h e l l l e n g t h (independent v a r i a b l e ) , u s i n g an a n a l y s i s o f c o v a r i a n c e . The t a b u l a t i o n and c o - v a r i a n c e p rocedure are those o f L i (1964). Data were taken from the l a r g e s n a i l s i n v o l v e d i n t h e l a b o r a t o r y experiment (p. SOURCE d f mean square F S i g n i f i c a n c e R e g r e s s i o n 1 4.13 55.28 *** Among Sample S l o p e s 4 0.01 0.17 N.S. Y A d j u s t e d a t x = 4.47 I 4 0.12 1.67 N.S. P o o l e d R e s i d u a l 241 0.07 As t h e r e was no e f f e c t o f s a l i n i t y or temperature on t h e r e -l a t i o n s h i p , an o v e r a l l r e g r e s s i o n l i n e was c a l c u l a t e d : F o o t - a r e a = -1.095 + 0.547 ( S h e l l Length) s t a n d a r d e r r o r o f s l o p e = 0.0004 s t a n d a r d e r r o r o f intercept=0.0000 A s i g n i f i c a n c e l e v e l o f 0.05 was used throughout t h i s study; however, the number o f a s t e r i s k s i n d i c a t e the minimum s i g n i f -i c a n c e l e v e l a t which the r e l a t i o n s h i p i s s t i l l s i g n i f i c a n t l y d i f f e r e n t * = 0.05 = 0.01 *** = 0.001 T a b l e V I I I . The volume o f the o u t f l o w o f the F r a s e r R i v e r i s measured a t A g a s s i z , B.C. because t h i s town i s f a r enough up the r i v e r t o be beyond the i n f l u e n c e o f the t i d e s and y e t c l o s e enough t o the mouth t o i n c l u d e a l l major water s o u r c e s o f the r i v e r . A comparison o f the o u t f l o w both throughout the year and between d i f f e r e n t y e a r s p r o v i d e s a r e l a t i v e i n d i c a t i o n o f the e f f e c t o f the r i v e r on shores w i t h i n t h e r e a c h o f i t s flume. Outflow of the F r a s e r R i v e r i n Average ( A c r e - F t / d a y ) x 10 f o r each Month YEAR Jan. Feb. Mar. ADT. May. June J u l y Aug. S e p t . O c t . Nov. Dec. 1970 7.68 7.75 7.22 10.70 26.65 46.60 28.00 18.23 13.53 11.45 7.70 5.94 1969 7.55 7.25 6.64 17.00 36.45 45.33 29.16 22.55 19.90 18.19 14.87 11.29 1968 12.71 11.72 14.26 13.60 37.42 55.67 50.32 26.94 22.63 18.23 17.23 10.94 1967 8.22 9.34 8.13 10.82 40.95 75.04 47.39 26.07 17.34 1966 5.77 5.75 5.78 17.78 41.18 52.11 43.63 28.79 18.52 14.60 12.29 12.64 1965. 6.99 7.87 6.83 40.26 48.12 38.01 26.88 16.24 13.65 14.07 8.32 1964 30.40 15.14 7.65 1963 1962 5.96 8.95 1.95 13.21 27.65 51.18 46.50 25.62 18.33 1961 15.07 10.53 3.62 May i n 1969, but d i d not reach t h i s value u n t i l the end of May i n 1970. Although reactions of the s n a i l s could not be compared from year to year at s p e c i f i c times, t h e i r responses could be c o l l a t e d using the duration of low s a l i n -i t i e s . The proportions of animals dead, unattached and positioned up on the rocks are presented i n Figures 12 & 13 along with the corresponding f l u c t u a t i o n s i n temperature and s a l i n i t y . (a) Proportion of s n a i l s located up on the rocks A decrease i n the number of s n a i l s moving on the rocks was the f i r s t i n d i c a t i o n of adverse c o n d i t i o n s , and was associated with s a l i n i t i e s of 15%o and below. Complete e l i m i n a t i o n of movement above the base of the rocks occurred within 5 to 6 weeks. Neither i n t e r t i d a l height nor popul-a t i o n background ( i . e . L i l l y Point: Brockton Point) i n f l u -enced the response. I t was noted i n the f i e l d , however, that while s n a i l s moved downshore r e a d i l y during the period of low s a l i n i t y c o n d i t i o n s , they never moved upshore. (b) Proportion of unattached s n a i l s A f t e r s a l i n i t y conditions remained below 10%o s n a i l were found unattached. Within each day's census the propor t i o n of unattached i n d i v i d u a l s increased with the duration of low s a l i n i t y c o n d i t i o n s , u n t i l the m o r t a l i t y r a t e was so high that the majority of animals recorded i n a census were dead leaving only a small proportion unattached (e.g. 1969). In 1970 an increase i n s a l i n i t y ameliorated such conditions before many succumbed, allowing the unattached i n d i v i d u a l s t recover. Again neither i n t e r t i d a l height nor population 51 F i g u r e 12 Responses o f T h a i s l a m e l l o s a a t S p a n i s h Banks t h r o u g h t h e s p r i n g o f 1 9 6 9 as measured by t h e p r o p o r t i o n o f s n a i l s (a) l o c a t e d up on t h e r o c k s , (b) u n a t t a c h e d and ( c ) dead on each p a r t i c u l a r day. S a l i n i t y and t e m p e r a t u r e a r e p l o t t e d so t h a t changes i n r e s p o n s e s c o u l d be c o r r e l a t e d w i t h changes i n t h e s e p h y s i c a l f a c t o r s . The a v e r a g e sample s i z e f o r e n c l o s e d a n i m a l s was 118, and f o r uncaged a n i m a l s was 87. ( • ) e n c l o s e d s n a i l s ( ) uncaged s n a i l s ( x — x) s a l i n i t y r t e m p e r a t u r e PROPORTION OF SNAILS: 52 F i g u r e 13 The r e s p o n s e s o f Brockton P o i n t and L i l l y P o i n t s n a i l s a t Spanish Banks d u r i n g the s p r i n g o f 1970 as determined by the p r o p o r t i o n o f s n a i l s (a) l o c a t e d up on the r o c k s , (b) u n a t t a c h e d and (c) dead. Most o f the d a t a were taken a t the 3.5' t i d a l l e v e l and s p e c i a l r e f e r e n c e i s made to the two i n s t a n c e s when r e a d i n g s were p o s s i b l e a t the 0.0' l e v e l . S a l i n i t y and temperature d a t a a r e i n c l u d e d t o a l l o w comparison between changes i n r e s p o n s e s and changes i n thes e f a c t o r s . On an average 84 s n a i l s were counted i n each c e n s u s . fc-.-.o) c o n t r o l s n a i l s a t Broc k t o n P o i n t (• • ) L i l l y P o i n t s n a i l s a t 3.5' l e v e l a t S p a n i s h Banks (o o) L i l l y P o i n t s n a i l s a t 0.0' l e v e l a t S p a n i s h Banks (x x) Br o c k t o n P o i n t s n a i l s a t 3.5' l e v e l a t S p a n i s h Banks (a A) B r o c k t o n P o i n t s n a i l s a t t h e 0.0' l e v e l a t Spanish Banks (» «) s a l i n i t y (x x) temperature 53 T a b l e IX P r o b a b i l i t y o f observed d i f f e r e n c e , assuming no d i f f e r e n c e i n the m o r t a l i t y r a t e s o f s n a i l s from L i l l y P o i n t and Brock t o n . P o i n t a t Spanish Banks ( s p r i n g 1970) and i n the m o r t a l i t y r a t e s between d i f f e r e n t i n t e r t i d a l h e i g h t s (3.5'- 0.0'), u s i n g F i s h e r ' s e x a c t p r o b a b i l i t y ( S e i g e l , 1956). M o r t a l i t y Rates a t D i f f e r e n t I n t e r t i d a l H e i g h t s 3.5' 0.0' P r o b a b i l i t y o f obs e r v e d v a l u e s o r worse BROCKTON POINT  Dead A l i v e 4 10 1 46 0.0079** LILLY POINT  Dead A l i v e 3 12 0 60 0.0067** M o r t a l i t y Rates a t the 3.5' T i d a l L e v e l DEAD ALIVE B r o c k t o n L i l l y P o i n t P r o b a b i l i t y o f obs e r v e d v a l u e s o r worse 0 3 36 19 o . o o o r DEAD ALIVE 1 15 4 16 0.2097 n.s, 54 background influenced the r e s u l t s , (c) M o r t a l i t y M o r t a l i t y i s apparently determined by duration of exposure to conditions of low s a l i n i t y (below 10%o). On the 10th day a f t e r the onset of such c o n d i t i o n s , only 20% of the s n a i l s i n the census were dead, and i n 1969 a few animals l i v e d f o r more than 45 days under these c o n d i t i o n s . In mid-July 1970, the m o r t a l i t y of Brockton Point s n a i l s was s i g n i f i c a n t l y l e s s than that of L i l l y Point animals. I n t e r -t i d a l height also a f f e c t e d r e s u l t s i n that s n a i l s survived b e t t e r at the lower l e v e l (Table IX). 2. Attachment Strength Attachment strength data from Brockton Point and Spanish Banks animals d i f f e r e d : s i g n i f i c a n t l y only i n July; that i s , not u n t i l 30 days a f t e r the onset of conditions of low s a l i n i t y (Table X, F i g . 14). At t h i s time animals at Spanish Banks tended to be e i t h e r attached f i r m l y or extremely l o o s e l y , d i f f e r i n g from t h e i r previous condition, and that s t i l l present at Brockton Point, i n which 80% were attached so as to 2 withstand a p u l l of greater than 200 g/cm . Brockton Point s n a i l s at Spanish Banks were more strongly attached than those from L i l l y Point during t h i s same period (Table X I ) . Discussion The f i r s t d i s c e r n i b l e r e a c t i o n of Thais lamellosa to lowered s a l i n i t y i s detected as a decreased proportion of i n d i v i d u a l s up on the rocks. This i s followed by the onset of detachment and m o r t a l i t y . I f conditions p e r s i s t the number of s n a i l s on the upper portions of the rocks decreases to F i g u r e 14 Attachment s t r e n g t h of l a r g e T h a i s l a m e l l o s a a t Brockton P o i n t and S p a n i s h Banks d u r i n g the s p r i n g o f 1970. The v e r t i c a l l i n e s r e p r e s e n t - 1 s t a n d a r d e r r o r ; the sample s i z e i s g i v e n i n b r a c k e t s . The d e c r e a s e d attachment s t r e n g t h s i n e a r l y June a r e a s s o c i a t e d w i t h e x t r e m e l y warm low t i d e s . ( ) S p a n i s h Banks ( ) Brockton P o i n t T a b l e X Frequency r e p r e s e n t a t i o n by attachment s t r e n g t h c l a s s e s , data o b t a i n e d d u r i n g the ebb t i d e a t Sp a n i s h Banks and Brockton P o i n t i n the s p r i n g o f 1970. The a l t e r a t i o n i n f r e q u e n c y d i s t r i b u t i o n on June , 3rd-4th i s c o r r e l a t e d w i t h an e x t r e m e l y hot low t i d e . P r o p o r t i o n o f S n a i l s A t t a c h e d a t Three D i f f e r e n t S t r e n g t h s BEACH SB BR SB BR SB BR SB BR SB BR SB BR Attachment 200 + 0.93 0.88* 0.81 0.93* 0.77 0.27* 0.80 0.59 1 0.38 0.79| 0.42 0.54 S t r e n g t h 100-200 0.07 0.12' 0.19 0.07 1 0.18 0.53 1 0.20 0.4l' 0.16 0.2l' 0.25 0.46 g/cm O-1 100 ; 0.09 0.20 1 0.46 '; 0.33 Date 23 & 24/4 21 & 20/5 3 & 4/6 18 & 17/6 1 & 2/7 16 & 17/7 A b b r e v i a t i o n s -SB BR Spanish Banks Brockton P o i n t T a b l e XI Attachment s t r e n g t h o f Brockton P o i n t and L i l l y P o i n t animals a t S p anish Banks d u r i n g the s p r i n g o f 1970; the r e s u l t s o f e v a l u a t i o n by t - t e s t s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e i n attachment s t r e n g t h s o f t h e s n a i l s from the two d i f f e r e n t beaches are a l s o p r e s e n t e d . Date Brockton P o i n t S n a i l s L i l l y P o i n t S n a i l s N 8 * A t t . S t r . (g/cm 2) S.E. N A t t . S t r . (q/cm 2) S.E. A p r i l 2 3 430 37.9 5 264 26.0 May 21 251 38.4 5 305 28.2 10 n.s. June 3 303 33.0 2 233 34.2 8 n.s. June 17 237 29.8 6 309(only one v a l u e ) J u l y 1 306 19.7 3 93 33.0 10 * J u l y 16 220 25.7 6 90 40.6 6 * A b b r e v i a t i o n s A t t . S t r . S.E. N attachment s t r e n g t h s t a n d a r d e r r o r o f the mean sample s i z e 58 zero and the number of unattached or dead s n a i l s i ncreases. Duration as well as s e v e r i t y of low s a l i n i t y appears to be important i n causing these e f f e c t s . This i s brought out by a comparison of the m o r t a l i t y data f o r the two years. In 1969 a l l animals died within 59 days, whereas i n 1970 under apparently the same s a l i n i t y and temperature regime ( F i g s . 4 & 5) the majority of s n a i l s survived, presumably because the c o n d i t i o n of low s a l i n i t y decreased i n s e v e r i t y a f t e r 41 days. Great v a r i a b i l i t y i n s a l i n i t y tolerance i s inherent i n the populations as was shown p a r t i c u l a r l y at the end of June, since by t h i s time some s n a i l s had already died while others were s t i l l strongly attached. The d i s t r i b u t i o n i n attachment strength frequencies during J u l y , i n that the maj-o r i t y of s n a i l s were e i t h e r f i r m l y or very weakly attached, suggests that i n d i v i d u a l s n a i l s have d e f i n i t e tolerance l i m i t s , i . e . they do not lose t h e i r strength of attachment gradually through time under low s a l i n i t y s t r e s s , but move from being well attached to poorly attached over a short period. The great v a r i a b i l i t y i n response to s a l i n i t y s t r e s s suggests that the p o t e n t i a l e x i s t s f o r improved s a l i n i t y tolerance through natural s e l e c t i o n . I t was hypothesized i n the i n t r o d u c t i o n that Brockton Point s n a i l s , being normally subjected to lower s a l i n i t i e s would be more t o l e r a n t than the L i l l y Point animals, t h i s was substantiated with regard to attachment strength (July) and m o r t a l i t y (July 16th). This evidence i s not convincing of a general increase i n tolerance 59 among the Brockton Point population and allows only a t e n t -a t i v e conclusion to t h i s e f f e c t pending f u r t h e r experimentation. The f a c t that the s n a i l s at Spanish Banks moved only downshore toward a more s a l i n e environment (0* t i d a l l e v e l ) while t h e i r v e r t i c a l range extends to approximately the 5' l e v e l at Brockton Point and L i l l y Point, suggests that the animals are capable of detecting small s a l i n i t y d i f f e r e n c e s s u f f i c i e n t to guide them from unfavourable c o n d i t i o n s . That the s n a i l s possess t h i s high a degree of s e n s i t i v i t y and that a decreased rate of m o r t a l i t y was observed at the lower t i d a l l e v e l bespeaks of i t s s u r v i v a l value. - While Thais lamellosa cannot t r a v e l several miles h o r i z o n t a l l y along the coast to avoid unfavourable s a l i n i t y c o n d i t i o n s , i t can move s u b t i d a l l y , providing there i s a s u i t a b l e substrate. 60 SECTION I I ECOLOGICAL STUDIES IN THE LABORATORY INTRODUCTION In the f i e l d , studies were r e s t r i c t e d to the time of year when conditions of low s a l i n i t y were normally present, i . e . the spring and e a r l y summer. Since seasonal a c c l i m -a t i o n has been shown to infl u e n c e tolerance l i m i t s i n other studies (Precht, 1958; Van Winkle, 1968), the study was extended i n the laboratory to include a comparison between animals removed from the f i e l d i n the winter and those removed i n the summer. Populations from L i l l y Point and Brockton Point were f u r t h e r evaluated f o r d i f f e r e n c e s i n tolerance of reduced s a l i n i t y c o n d i t i o n s . Reactions of the s n a i l s to changing s a l i n i t i e s i n the f i e l d were gauged by feeding r a t e , attachment strength, m o r t a l i t y , and proportions of s n a i l s unattached, and up on the rocks. In the laboratory, however, although i t was pos s i b l e to make s i m i l a r measurements, these were not s t r i c t l y comparable. Animals i n the f i e l d do not feed when exposed, arid since no t i d a l regime was constructed i n the laboratory, feeding r a t e s , even though expressed i n the same u n i t s , are not comparable. In the f i e l d , attachment strength was found to depend on substrate; laboratory animals were attached to p l e x i g l a s s , which i s not as rough as s h e l l s or rocks. The proportion of animals up on the rocks r e a l l y measured the 61 tendency to move from cover, presumably i n search of food. The proportion of s n a i l s attached to v e r t i c a l surfaces i n the aquaria was a measure of the same tendency although i n t h i s case food was concentrated i n one l o c a t i o n . Unfortunately the r a t i o of the area of sand between rocks to the area of rock above the sand, which may e f f e c t the r e s u l t a n t d i s t r i -bution (Table V), was not known f o r the f i e l d ; i n any event, the normal s i t u a t i o n i n the two milieux was d i f f e r e n t . At the end of the acclimation period i n the laboratory, behaviour was f u r t h e r evaluated by measuring the rate of movement a f t e r displacement. M o r t a l i t y and the proportion of un-attached s n a i l s r e f e r to the same c h a r a c t e r i s t i c s i n both s t u d i e s . Laboratory animals were studied under constant salinity-temperature c o n d i t i o n s , whereas f i e l d animals l i v e d i n a continuously changing environment. For t h i s reason a l s o , i t i s impossible to s t r i c t l y compare the sets of r e s u l t s . Although small animals could r e a d i l y conceal them-selves i n the f i e l d under huge rocks and i n remote c r e v i c e s leaving only a small and unrepresentative sample to be e a s i l y located (without d i s r u p t i n g the h a b i t a t ) , t h e i r responses could be r e a d i l y followed i n aquaria. In a d d i t i o n i t was p o s s i b l e , i n the laboratory, through comparisons of dry body weight and sex r a t i o s of the s n a i l s s u r v i v i n g the experiment to determine whether the s n a i l s metabolized more when under s a l i n i t y s t r e s s , whether they p r e f e r e n t i a l l y u t i l i z e d stores of material i n the gonad during or outside of the reproductive season, and whether s a l i n i t y tolerance was associated with sex. 62 EFFECTS OF CHANGES IN SALINITY AND TEMPERATURE  I n t r o d u c t i o n The v a r i o u s measurements and q u e s t i o n s j u s t d i s c u s s e d were o r g a n i z e d i n t o one experiment. In t h i s way a l l r e s p o n s e s were e v a l u a t e d under i d e n t i c a l p h y s i c a l c o n d i t i o n s and were d i r e c t l y comparable. Methods and M a t e r i a l s 1. E x p e r i m e n t a l Procedures The d e s i g n o f t h i s experiment was p r e s e n t e d p r e v -i o u s l y (p. 25 ). The s a l i n i t i e s 20%o, 15%o, 12%o, and 9%o were chosen because t h e two former r e p r e s e n t e d summer f i e l d c o n d i t i o n s and p r e l i m i n a r y experiments had i n d i c a t e d t h a t the l a t t e r a d v e r s e l y a f f e c t e d t h e s n a i l s . Temperatures a l s o r e -p r e s e n t e d f i e l d c o n d i t i o n s ; 18°C warm summer water heated o v e r sand as o c c u r s a t S p a n i s h Banks and L i l l y P o i n t ; 12°C g u l f summer temperatures found a l o n g s t e e p shores not sub-j e c t e d t o water f l o w from the l a n d (San Juan I s . , C o n n e l l , 1970); and 9°C the l o w e s t temperature which c o u l d be o b t a i n e d i n t h e l a b o r a t o r y was warmer than w i n t e r c o n d i t i o n s (5°C). T h a i s l a m e l l o s a i s s u b j e c t e d t o low s a l i n i t i e s o n l y d u r i n g the summer and thus the i n a b i l i t y t o o b t a i n the lowest f i e l d t emperature was not c r i t i c a l t o t h i s s t u d y . At t he commencement o f t h i s experiment, L i l l y P o i n t s n a i l s were i n t r o d u c e d i n t o one s i d e o f each aquarium and Bro c k t o n P o i n t i n t o the o t h e r . The experiment was r e p e a t e d 63 f i v e t i m e s , t w i c e w i t h a n i m a l s adapted t o w i n t e r c o n d i t i o n s i n the f i e l d (January t o F e b r u a r y ) and t h r e e times w i t h i n -d i v i d u a l s adapted t o summer c o n d i t i o n s ( l a t e May t o J u l y ) . In each i n s t a n c e the p a t t e r n o f the p o s i t i o n s o f t h e B r o c k t o n P o i n t and L i l l y P o i n t s n a i l s t h r o u g hout the t w e l v e tanks was a l t e r e d . The a n i m a l s were mo n i t o r e d d a i l y commencing a t +1 hour by the f o l l o w i n g c r i t e r i a : number o f s n a i l s a t t a c h e d t o a v e r t i c a l s u r f a c e , number a t t a c h e d and number f e e d i n g . Any s n a i l s n ot r i g h t s i d e up a f t e r t h e f i r s t hour were p l a c e d i n t h a t p o s i t i o n so t h a t a b i l i t y t o a t t a c h was not confounded by the more r i g o r o u s motions r e q u i r e d i n t u r n i n g o v e r . For t he f i r s t t e n days b a r n a c l e c o v e r e d mussels ( i . e . Balanus q l a n d u l a on M y t i l u s e d u l i s ) were s u p p l i e d as f o o d . To determine f e e d i n g r a t e s o v e r the next f o u r t e e n days, p r e p a r e d mussel s h e l l s (p. 20 ) were screwed onto the wooden p l a t f o r m s which were a t t a c h e d t o the b r i c k s , w h i l e o t h e r s were backed w i t h s t a i n l e s s s t e e l mesh and suspended by n y l o n f i s h i n g l i n e from a bar a c r o s s the t o p o f the tan k . The former were a v i l a b l e t o t h e s n a i l s w h i l e t h e l a t t e r s e r v e d as c o n t r o l s t o check s u r v i v a l o f b a r n a c l e s . The experiment was t e r m i n a t e d on t h e t w e n t y - f o u r t h day. F e e d i n g r a t e s were c a l c u l a t e d as grams d r y weight consumed/snail/day. Rate o f movement was determined by c o n f i n i n g s n a i l s from one h a l f o f the aquarium on the bottom o f the tank i n a s m a l l i n v e r t e d m e s h e d - p l a s t i c b a s k e t f o r 20 m i n u t e s . The p l e x i g l a s s d i v i s i o n and b r i c k s were then removed and the p r e -v i o u s l y e n c l o s e d s n a i l s assembled a l o n g the m i d - l i n e o f the aquarium, the l a r g e and s m a l l a l t e r n a t e l y , a l l f a c i n g one d i r e c t i o n . Their p o s i t i o n s were recorded at 5 minute i n t e r v a l s f o r a t o t a l of 20 minutes using the 2 cm x 2 cm g r i d on the bottom of the tank. I f a s n a i l climbed onto another or came i n t o contact with the edges of the aquarium and stopped, the time i t spent i n these p o s i t i o n s was eliminated from the c a l c u l -a tions; i n the former instance because i t was impossible to determine how many cm the s n a i l had t r a v e l l e d while on the back of another, and i n the l a t t e r because contact with the wall often arrested movement. During t h i s period, the other animals from the aquarium were confined i n the inverted basket In t h i s way a l l s n a i l s were treated i n the same manner and none were removed from the experimental environment while t h e i r counterparts were being t e s t e d . To determine attachment strength of s n a i l s , the p l e x i g lass d i v i s i o n s were l a i d h o r i z o n t a l l y on top of the b r i c k s i n each aquarium. A l l s n a i l s i n the tank were placed on t h i s platform and allowed a minimum of 20 minutes to at t a c h . Under these conditions, where the s n a i l s were quite a c t i v e , many would crawl o f f the platform; therefore, each tank was tested twice i n order to measure the majority of the animals at l e a s t once. The scores of s n a i l s recorded twice were averaged. The p l e x i g l a s s , with s n a i l s attached, was removed from the aquarium without d i s t u r b i n g the s n a i l s and the o u t l i n e of the f e e t were traced onto transparent p l a s t i c . The p l e x i g l a s s was then lowered i n t o a p l a s t i c basin and water from the aquarium siphoned i n u n t i l the s n a i l s were j u s t covered. Attachment strength was then measured by means of a spring balance i n the manner reported previously (p. 4 6 ) . 65 Room temperature was extremely high i n the summer and those animals at lower temperatures r a p i d l y r e t r a c t e d within t h e i r s h e l l s when exposed. The foot-area of these s n a i l s was, therefore, estimated using the r e l a t i o n s h i p s between f o o t -area and s h e l l length determined from winter and a v a i l a b l e summer data (Tables VII, XII and X I I I ) . As mentioned pre-v i o u s l y neither s a l i n i t y nor temperature influenced the r e l a t -ionship f o r large s n a i l s ; however, i n the case of small s n a i l s a reduction i n s a l i n i t y f i r s t decreased and then increased the foot-area. When a l l other determinations were completed, the s h e l l of each adult s n a i l was cracked open and the body was sexed, removed from the s h e l l and b l o t t e d with a paper towel. The gonad and 'body without the gonad' were weighed separately both before and a f t e r being d r i e d to a constant weight at 103°C. The percentage of water was c a l c u l a t e d f o r use i n a l a t e r experiment (Section I I I ) . 2. A n a l y t i c a l Procedures (a) E f f e c t of temperature and s a l i n i t y on the propor-t i o n and acclimation of s n a i l s engaged i n various a c t i v i t i e s . In order to study acclimation, the experiment was di v i d e d i n t o three consecutive i n t e r v a l s l o o s e l y c a l l e d weeks of 1 - 8 days, 9 - 1 6 days, and 1 7 - 2 4 days. The d a i l y scores of the number of s n a i l s attached to v e r t i c a l surfaces, number feeding, and number attached to the substrate were summed over these periods and d i v i d e d by the maximum pos s i b l e value, i . e . the sum of the number a l i v e on each day over the given period. Proportions were c a l c u l a t e d f o r each e x p e r i -T a b l e X I I Comparison o f the e f f e c t s o f temperature (9°C, 12°C and 18°C) on the r e l a t i o n s h i p between s h e l l l e n g t h of s m a l l s n a i l s (independent v a r i a b l e ) and f o o t - a r e a (dependent v a r i a b l e ) f o r t h r e e s e p a r a t e s a l i n i t i e s , by a n a l y s i s o f c o v a r i a n c e . S a l i n i t y Source d f R e g r e s s i o n 1 Temperature e f f e c t among Bs 2 Temperature e f f e c t on Y, A d j u s t e d t o x = 2.43 2 Remainder 113 20%o m.s. F_ d f 0.95 1 0 8 . l l * * * 1 0.00 0.38n.s. 2 0.00 O . l l n . s . 2 0.01 118 15%o m.s. F_ d f 0.50 53.95*** 1 0.01 1.57 n.s. 1 0.02 2.42 n.s. 1 0.01 34 12%o  m.s. F_ 0.70 90.69*** 0.04 4.62n.s. 0.00 0.04n.s. 0.01 67 T a b l e X I I I Comparison o f the e f f e c t o f s a l i n i t y (20%o, 15%o, 12%O) on the r e l a t i o n s h i p between s h e l l l e n g t h o f s m a l l s n a i l s (independent v a r i a b l e ) and f o o t - a r e a (dependent v a r i a b l e ) . In T a b l e X I I i t was shown t h a t no temperature e f f e c t s e x i s t , and thus each s a l i n i t y c o n t a i n s d a t a from the e n t i r e temperature range s t u d i e d . * * * SOURCE d f m.s. F s i R e g r e s s i o n 1 2.17 243.65 S a l i n i t y E f f e c t s among Bs 2 0.05 5.83 S a l i n i t y E f f e c t on Y, A d j u s t e d t o x = 2.43 2 0.06 6.27 Remainder 276 0.01 R e g r e s s i o n E q u a t i o n s 20%o Y = -0.3226 + 0.3133X 15%o Y = -0.1450 + 0.2246X 12%o Y = -0.5031 + 0.3905X S.E. a: 0.092 b: 0.030 a: 0.097 b: 0.028 a: 0.091 b: 0.042 68 mental r e p l i c a t e , the d a t a b e i n g s e p a r a t e d a c c o r d i n g t o the f i v e v a r i a b l e s : s i z e , season, r a c e , s a l i n i t y and temperature The average temperatures o f t h e tanks w i t h i n the 9°C, 12°C and 18°C groups v a r i e d and a weighted r e g r e s s i o n a n a l y s i s was used t o e v a l u a t e temperature e f f e c t s w i t h i n t h e f o l l o w i n g t r e a t m e n t s f o r each s a l i n i t y : (a) l a r g e (mature) s n a i l s and s m a l l (immature) s n a i l s , (b) s n a i l s o r i g i n a l l y from B r o c k t o n P o i n t and those from L i l l y P o i n t , and (c) s n a i l s a c c l i m a t e d i n t h e f i e l d t o w i n t e r c o n d i t i o n s and t h o s e a c c l i m a t e d t o summer c o n d i t i o n s . I f no temperature r e l a t i o n s h i p e x i s t e d w i t h i n t h e s a l i n i t y t r e a t m e n t s , the o v e r a l l e f f e c t as w e l l as those o f reduced s a l i n i t y and time f o r a c c l i m a t i o n were i n v e s t -i g a t e d w i t h i n t h e s e d a t a by means o f t - t e s t s j when the r e -g r e s s i o n on temperature was s i g n i f i c a n t , by a n a l y s i s o f c o -v a r i a n c e . (b) Movement S i n c e d a t a r e l a t i n g t o movement w i t h i n any one group were e x t r e m e l y v a r i a b l e , t h e s n a i l s were c l a s s i f i e d i n t o two groups - t h o s e moving more than 5 cm d u r i n g t h e 20 minutes and t h o s e t h a t d i d n o t . D i f f e r e n c e s w i t h i n v a r i a b l e s ( e . g. s i z e , season, r a c e , s a l i n i t y and temperature) were e v a l u a t e d 2 by means o f X c o n t i n g e n c y t a b l e s . R e s u l t s 1. F e e d i n g Responses With r e g a r d t o f e e d i n g r a t e s and time spent f e e d i n g T h a i s l a m e l l o s a from B r o c k t o n P o i n t and L i l l y P o i n t responded s i m i l a r l y t o d e c r e a s e s i n s a l i n i t y and i n c r e a s e s i n temperature ( T a b l e s XVI, XX) i n t h a t temperature changes were w i t h o u t T a b l e XIV Comparisons between immature ( s m a l l ) a n d mature ( l a r g e ) s n a i l s u s i n g weighted c o v a r i a n c e a n a l -y s i s ; p r o p o r t i o n o f s n a i l s f e e d i n g i s the dependent v a r i a b l e , and temperature (9°C - 18°C) i s t he independent v a r i a b l e . SALIN-ITY (%o) CATE-GORY* SOURCE df WEEK 1 m.s. F or t s i q . d f WEEK 2 m.s. F o r t s i q . d f WEEK 3 m.s. F or t s i q . T R e g r e s s i o n 1 0.0184 0.0537 n.s. 1 0.9974 1.2324 n.s. 1 1.2450 0.8267 n.s. 20 L> c Remainder R e g r e s s i o n 22 1 0.3433 0.2086 0.2268 n.s. 28 1 0.8093 0.3500 0.3382 n.s. 2 7 1 1.5060 0.1390 0.1259 n.s. b Remainder 22 0.9199 28 1.0350 28 1.1040 t - t e s t 46 3.0958 S*** 56 2.5723 S** 57 1.6128 n.s. X R e g r e s s i o n 1 0.0000 0.0045 n.s. 1 0.0725 0.2901 n.s. 1 0.1351 0.4550 n.s. 15 L Remainder 22 0.0178 27 0.2497 26 0.2969 o R e g r e s s i o n 1 0.8931 2.2128 n.s. 1 0.2817 0.7315 n.s. 1 0.4268 0.4300 n.s. Remainder 22 0.4036 28 0.3851 26 0.9927 t - t e s t 46 2.3312 S* 57 0.6197 n.s. 56 1.7652 n.s. * C a t e g o r i e s o f s n a i l s i n t h a t L i m p l i e s l a r g e s n a i l s , and S s m a l l s n a i l s . **A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which c a t e g o r y o f s n a i l had the h i g h e r v a l u e . VD T a b l e XV Comparisons between s n a i l s removed from t h e f i e l d i n t h e w i n t e r and summer u s i n g weighted co v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s f e e d i n g i s the dependent v a r i a b l e and temperature (9°C - 18°C) i s the independent v a r i a b l e . SALIN- CATE- WEEK 1 WEEK 2 WEEK 3 ITY (%o) GORY* SOURCE d f m. s. P or t s i q . d f m. s • F o r t s i q . d f m. s. F or t s i q . T i l R e g r e s s i o n 1 0.0359 0 .0553 n.s. 1 0.0723 0.0885 n.s. 1 0.2630 0 .2275 n.s. W Remainder 22 0.0645 22 0.8168 21 1.1560 20 c R e g r e s s i o n 1 0.0003 0 .0037 n.s. 1 0.6327 0.6775 n.s. 1 0.8184 0 .6953 n.s. Remainder 22 0.8705 34 0.9339 34 1.1770 t - t e s t 46 0 .7143 n.s. 58 3.3405 s*** 57 3 .0719 s*-** w R e g r e s s i o n 1 0.0026 0 .0833 n.s. 1 0.0011 0.9664 n.s. 1 0.0015 1 .0506 n.s. Remainder 22 0.0312 22 0.0012 22 0.0014 15 R e g r e s s i o n 1 0.6548 1 .5168 n.s. 1 0.3537 0.8550 n.s. 1 0.0054 0 .0066 n.s. s Remainder 22 0.4317 33 0.4137 32 0.8199 t - t e s t 46 1 .5091 n.s. 57 4.6126 s*** 56 5 .8809 s*** • C a t e g o r i e s o f s n a i l s i n t h a t W i m p l i e s w i n t e r a n i m a l s , and S summer a n i m a l s . **A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which c a t e g o r y o f s n a i l had the h i g h e r v a l u e . o T a b l e XVI Comparisons between s n a i l s o r i g i n a l l y from Brockton P o i n t and L i l l y P o i n t u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s f e e d i n g i s the dependent v a r i a b l e and temperature (9°C - 18°C) i s the independent v a r i a b l e . SALIN— CATE- WEEK 1 WEEK 2 WEEK 3 ITY(%o) GORY* SOURCE d f m. s • F o r t s i q . d f m. s • F o r t s i q . d f m. s. F o r t s i q . B R e g r e s s i o n 1 0.1814 0.3377 n.s. 1 0.0004 0.0003 n.s. 1 0.1857 0.1656 n.s. Remainder 22 0.5370 28 1.0380 28 1.1210 20 T R e g r e s s i o n 1 0.0091 0.0096 n.s. 1 0.1555 0.1552 n.s. 1 0.0034 0.0025 n.s. Li Remainder 22 0.9474 28 1.0020 27 1.3470 t - t e s t 46 1.2124 n.s. 58 1.0825 n.s. 57 2.6751 L** B R e g r e s s i o n 1 0.4493 1.9242 n.s. 1 0.1020 0.3455 n.s. 1 0.2859 0.7809 n.s. Remainder 22 0.2335 28 0.2952 27 0.3661 15 T R e g r e s s i o n 1 0.0898 0.3516 n.s. 1 0.3418 0.9968 n.s. 1 0.9458 0.9619 n.s. Li Remainder 22 0.2553 27 0.3429 27 0.9833 t - t e s t 46 0.5150 n.s. 57 0.3070 n.s. 56 0.6660 n.s. • C a t e g o r i e s o f s n a i l s such t h a t B i m p l i e s Brockton P o i n t a n i m a l s and L, L i l l y P o i n t a n i m a l s . **A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which c a t e g o r y o f s n a i l had the h i g h e r v a l u e . 72 T a b l e XVII T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f the p r o p o r t i o n o f s n a i l s f e e d i n g on con-s e c u t i v e weeks. 20%o 15%o CATE- WEEK 1:2 CATE- WEEK 2:3 GORY* d f t - v a l u e s i g . GORY df t - v a l u e LaW 34 0.1379 n.s. WBLa 22 0.6589 n.s. LaS 34 3.4230 2 * * • WBSm 22 1.8084 n.s. SmW 34 0.0877 n.s. WLLa 21 3.4013 3*** SmS 34 2.3016 2* WLSm 21 1.6133 n.s. SBLa 34 2.0825 3* SBSm 34 0.1244 n.s. SLLa 34 3.3704 3*** SLSm 34 1.5559 n.s. LaW 46 1.3282 n.s. W 46 0.1414 n.s. LaS 57 4.1573 2 * * * S 67 2.2937 3* SmW 46 2.6789 1** SmS 5 7 0.7863 n.s. • C a t e g o r i e s were d e f i n e d by p r e v i o u s a n a l y s i s ( T a b l e s XIV, XV, and XVI) A b b r e v i a t i o n s - B (Brockton P o i n t s n a i l s ) , L ( L i l l y P o i n t s n a i l s ) W (removed from f i e l d i n w i n t e r ) , S ( i n summer) La ( l a r g e s n a i l s ) , Sm ( s m a l l s n a i l s ) A number i n the s i g n i f i c a n c e column i n d i c a t e s i n which week the g r e a t e r p r o p o r t i o n o f s n a i l s were f e e d i n g . 73 T a b l e X V I I I T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f t h e p r o p o r t i o n o f s n a i l s f e e d i n g a t d i f f -e r e n t s a l i n i t i e s w i t h i n each week. 2 3 CATE- :20%o:15%o GORY* df t - v a l u e La 46 4.4880 20** Sm 46 3.7641 20** LaW 34 3.0116 20** SmW 34 4.8781 20** LaS 51 3.8639 20** SmS 51 5.9392 20** WB 34 4.3396 20** WL 33 3.3429 20** SB 50 3.7932 20** SL 50 4.9419 20** • C a t e g o r i e s were d e f i n e d by p r e v i o u s a n a l y s i s ( T a b l e s XIV, XV and XVI) A b b r e v i a t i o n s - B ( B r o c k t o n P o i n t s n a i l s ) , L ( L i l l y P o i n t s n a i l s ) W (removed from f i e l d i n w i n t e r ) , S ( i n summer) La ( l a r g e s n a i l s ) , Sm ( s m a l l s n a i l s ) A number i n the s i g n i f i c a n c e column i n d i c a t e s a t which s a l i n i t y the g r e a t e r p r o p o r t i o n o f s n a i l s were f e e d i n g . T a b l e XIX. Weekly p r o p o r t i o n s o f s n a i l s f e e d i n g a t two s a l i n i t i e s ; no f e e d i n g o c c u r r e d 12%o. C a t e g o r i e s o f s n a i l s were d e f i n e d by p r e v i o u s a n a l y s i s ( T a b l e s XIV, XV, and XVI) Means are e x p r e s s e d - 1 st a n d a r d e r r o r ; and the sample s i z e i s g i v e n i n b r a c k e t s . ARCSINE OF PROPORTION OF SNAILS FEEDING S a l i n i t y Week 1 Week 2 Large Small Summer Winter Summer Win t e r 20%o 0.061 (24)-0.0l2 0.136 (24)^0.021 La 0.144 (18)±0.021 Sm 0.209 (18)±0.024 La 0.058 (12)^0.019 Sm 0.132 (12) i0.027 L 0.270 (18)^0.031 B 0.213 (18)^0.026 L 0.212 (11) ^ 0.041 B 0.075 (12) -0.017 Large Small Summer Winter Summer Winter 15%o 0.005 (24)±0.003 0.038 (24)±0.014 0.052 (35)^0.001 .0.001 (24)^0.001 0.098 (34)±0.016 0.001 (24)±0.001 A b b r e v i a t i o n s - B (Brockton P o i n t s n a i l s ) , and L ( L i l l y P o i n t s n a i l s ) L a ( l a r g e s n a i l s ) , and Sm ( s m a l l s n a i l s ) 75 F i g u r e 15 Changes i n a r c s i n e o f p r o p o r t i o n o f s n a i l s f e e d i n g i n the w i n t e r a t d i f f e r e n t s a l i n i t i e s w i t h t i m e . Animals were c o l l e c t e d from B r o c k t o n P o i n t and L i l l y P o i n t i n January and F e b r u a r y , and t h e i r f e e d i n g b e h a v i o u r was f o l l o w e d i n the l a b o r a t o r y f o r 24 days. V e r t i c a l l i n e s r e p r e s e n t - 1 s t a n d a r d e r r o r . No f e e d i n g o c c u r r e d a t 12%o. ( o ) s m a l l s n a i l s ( • ) l a r g e s n a i l s ( ) 15%o s a l i n i t y ( ) 2 0 % o s a l i n i t y 76 Figure 16 Changes i n arcsine of proportion, of s n a i l s feeding i n the summer at d i f f e r e n t s a l i n i t i e s with time. Animals were c o l l e c t e d from Brockton Point and L i l l y Point i n the middle of May, June and J u l y , and t h e i r feeding behaviour was followed i n the laboratory f o r 24 days. V e r t i c a l l i n e s represent - 1 standard e r r o r . No feeding occurred at 12%o. ( o ) small s n a i l s ( • ) large s n a i l s ( ) i s % 0 s a l i n i t y ( ) 20%o s a l i n i t y T a b l e XX. T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between f e e d i n g r a t e s under d i f f e r e n t c o n d i t i o n s as determined i n the l a b o r a t o r y . COMPARISONS BETWEEN BROCKTON POINT AND LILLY POINT Season Temperature 9°C W i n t e r ( 2 d f ) 12°C 18°C 9°C Summer(2df) 12°C 18°C t - v a l u e s i q . t - v a l u e s i q . t - v a l u e s i q . 20%o 1.3371 n.s. 15.1878 ••• 0.5846 .n.s. S a l i n i t y t - v a l u e s i q . t - v a l u e s i q . t - v a l u e s i q . 1.1326 n.s. 0.9134 n.s. 0.9813 n.s. 15%o 0.6117 n.s. 0.8220 n.s. 0.0000 n.s. 0.1954 n.s. 1.7741 n.s. 0.1670 n.s, COMPARISONS BETWEEN TEMPERATURES Season Comparisons W i n t e r ( 6 d f ) 9°C-12°C 12°C-18°C 20%o S a l i n i t y 15%o t - v a l u e s i g . t - v a l u e sic 0.1483 n.s. 0.5572 n.s. 0.5265 n.s. 1.2159 n.s. Summer(lOdf) 9°C-12°C  t - v a l u e s i g . 1.2903 n.s. 0.8202 n.s. 12°C-18°C  t - v a l u e s i q . 1.1958 n.s. 1.7997 n.s. COMPARISON BETWEEN SEASONS.' S a l i n i t y t - v a l u e ( 2 8 d f ) 20%o  t - v a l u e s i q . 2.7183 S*** 15%o  t - v a l u e s i q 4.4857 S*** COMPARISON BETWEEN SALINITIES Summer(34df) t - v a l u e s i q . 7.0153 20*** W i n t e r ( 2 2 d f ) t - v a l u e si< 5.0036 20*** A b b r e v i a t i o n s - S (animals removed from the f i e l d i n the summer/, L ( L i l l y P o i n t a n i m a l s ) A l e t t e r o r number i n the s i g n i f i c a n c e column i n d i c a t e s which group o f s n a i l s had the g r e a t e r f e e d i n g r a t e . 78 F i g u r e 17 R e l a t i o n s h i p between f e e d i n g r a t e s o f T h a i s l a m e l l o s a and temperature. F e e d i n g was measured over a 14 day p e r i o d a f t e r a c c l i m a t i o n f o r 10 days t o the s a l i n i t y and temperature regimes i n which the r a t e s were d e t e r m i n e d . The v e r t i c a l l i n e s r e p r e s e n t - 1 s t a n d a r d e r r o r . The w i n t e r e s t a i m a t e s are the average o f 4 s e p a r a t e d e t e r m i n a t i o n s , and the summer, o f 6. ( ) summer (—r ) w i n t e r ( o o r • ) 20%o s a l i n i t y ( • or • ) 15%o s a l i n i t y FEEDING RATE (MG DRY WEIGHT CONSUMED/ SNAIL/DAY) rO O ' 79 e f f e c t on e i t h e r t r a i t (Tables XIV, XV, XVI) while reduced s a l i n i t y lowered both the feeding r a t e and amount of time spent feeding (Tables XVIII, XX). Of a l l t r a i t s studied i n t h i s experiment, feeding response was the most s e n s i t i v e to s a l i n i t y s t r e s s being completely extinguished i n s a l i n i t i e s of 12%o and l e s s . For the f i r s t week or two a f t e r i n t r o d u c t i o n i n t o the experimental salinity-temperature regimes, small s n a i l s fed more often than large s n a i l s . As the experiment pro-gressed, the proportion of s n a i l s feeding increased among animals studied i n the summer, but not i n the winter (Tables XV, XIXj F i g s . 15, 16), and consequently feeding r a t e s were greater i n the summer (Table XX; F i g . 17). However, L i l l y Point s n a i l s were exceptional i n that they were feeding as often i n the winter as the summer i n the t h i r d week at high s a l i n i t y . In the winter, at the lowest s a l i n i t y where feeding occurred (15%o), inverse acclimation was observed, 1. e., the proportion of s n a i l s feeding decreased through time (Table XIX; Fig.15). 2. Movement With the exception of small s n a i l s acclimated to winter conditions i n the f i e l d , Thais lamellosa from Brockton Point possessed a greater tendency to move than those from L i l l y Point (Tables XXI, XXIII). This i s one of the few instances where a d i s t i n c t i o n can be made between the responses of the two populations. Generally d i f f e r e n c e s i n age and seasonal acclimation d i d not a l t e r movement (Table XXI). Two exceptions occurred: small s n a i l s from Brockton Point moved more i n the T a b l e XXI. E f f e c t o f age, p o p u l a t i o n h i s t o r y , and p r e v i o u s a c c l i m a t i o n i n the f i e l d on move-ment as e v a l u a t e d by st a n d a r d normal d e v i a t e s d e r i v e d from C h i Square c o n t i n g e n c y t a b l e s (Simpson e t a l . , 1960). S a l i n i t y and Temperature Comparison o f L:S o f a l l c o m b i n a t i o n s Winter Summer Comparison o f BP:LP  Win t e r Summer S t a t e s BP ; LP BP S L L 20%o 0.67 ; 2.-97*S 0.47 1.78 0.01 3.75'BP 1.70 2.58*BP 15%o 0.11 0.46 1.09 1.32 0.75 1.33 4.32'BP 3.19*BP 12%o 0.00 0.00 1.01 0.00 0.00 0.00 2.57*BP ]*40 9°C 1.02 0.38 -0.39 -0.27 0.57 -0.09 2.36*BP 1.77 12°C -1.44 1.34 0.39 0.39 0.41 3.19*BP 3.30*BP 2.61*BP 18°C -0.74 2.05*S 1.82 3.60*S -0.21 2.42*BP 1.61 3.10*BP SND f o r sum -0.62 2.08*S 1.12 1.78 0.51 3.11*BP 4.19*BP 4.15*BP A b b r e v i a t i o n s - BP means animals from Brockton P o i n t , and LP, from L i l l y P o i n t L means l a r g e a n i m a l s , and S, s m a l l a n i m a l s L e t t e r a f t e r a s t e r i s k i n d i c a t e s which c a t e g o r y o f s n a i l moved more CD o Table XXI. (Continued) S a l i n i t y and Comparison of Su:W Temperature L i l l y Point Brockton Point States S L _S L 20%o 0.04 2.01*Su 1.84 0.00 15%o 0.97 0.72 4.63*Su 1.56 12%o 0.00 0.00 2.06*Su 0.27 9°C 0.95 1.64 2.83'Su 3.17*Su 12°C -0.22 0.99 2.01*Su --0.59 18°C 0.34 0.14 1.93 1.48 SND f o r sum of a l l combinations 0.20 1.58 3.49* 0.97 Abbreviations - Su means animals removed from the f i e l d i n the summer, and W, i n the winter L means large animals, and S, small animals. Letter a f t e r a s t e r i s k indicates which category of s n a i l moved more co Table XXII. E f f e c t i v e changes i n temperature and s a l i n i t y on the tendency to move as evaluated by means of standard normal deviates from Chi Square contingency t a b l e s . Data were grouped i n accordance with previous a n a l y s i s (Table XXI). EFFECT OF CHANGES IN SALINITY S a l i n i t y Temper- Brockton Point L i l l y Point T o t a l Comparison ature larqe Wsmall Ssmall BWSmtLSm larqe SND 9°C 0.89 0.65 0.65 1.46 0.49 20%o:15%o 12°C 0.23 -0.21 -1.30 0.53 -1.02 18°C 0.35 0.84 -0.38 0.85 0.90 SND of a l l temperatures 0.85 0.74 -0.59 1.64 0.21 1.28 9°C 2.34*15 1.48 2.11*15 3.67*15 2.21*15 15%o:12%o 12°C 2.06*15 1.83 1.81 2.72*15 0.71 18°C 1.43 1.88 1.80 SND of a l l temperatures 3.42*15 2.34*15 3.35*15 4.87*15 2.60*15 6.81*1 Abbreviations - W ( s n a i l s removed from the f i e l d i n the winter) S ( i n the summer) B (Brockton Point s n a i l s ) L ( L i l l y Point s n a i l s ) Sm (small s n a i l s ) SND (standard normal deviate) A number a f t e r an a s t e r i s k indicates at which s a l i n i t y the greater movement occurred. Table XXII (continued) EFFECT OF CHANGES IN TEMPERATURE Temperature Brockton Point L i l l y Point T o t a l Comparison S a l i n i t y larqe Wsmall Ssmall BWSm:LSm larqe SND 20%o 1.00 -0.29 -1.00 -0.57 -2.21*12 9°C:12°C 15%o 1.55 1.12 0.96 0.55 0.72 12%o 0.45 0.00 0.81 0.00 0.00 SND of a l l s a l i n i t i e s 1.73 0.48 0.44 -0.01 -1.44 0.06 - 20%o 0.09 0.22 -0.26 0.77 1.38 9°C:12°C 15%o -1.11 -0.06 0.53 1.11 1.96*9 12%0 0.35 0.07 0.00 0.00 SND of a l l s a l i n i t i e s -0.39 0.11 0.20 1.08 1.87 0.30 Abbreviations - W ( s n a i l s removed from the f i e l d i n the winter) S ( i n the summer B (Brockton Point s n a i l s ) L ( L i l l y Point s n a i l s ) Sm (small s n a i l s ) SND (standard normal deviate) A number a f t e r an a s t e r i s k i n d i c a t e s at which .-temperature the greater movement occurred, T a b l e X X I I I Summary o f movement c h a r a c t e r i s t i c s o f d i f f e r e n t groups o f s n a i l s as d e r i v e d from T a b l e XXI, WINTER = SUMMER LILLY POINT BROCKTON POINT BROCKTON POINT LILLY POINT sma l l = s m a l l <^except< s m a l l s m a l l V || || • H l a r g e K. l a r g e l a r g e ^ l a r g e oo TABLE XXIV E f f e c t of decrease i n s a l i n i t y on the proportion of s n a i l s moving more than 5 cm i n 20 minutes a f t e r displacement. The data were grouped within each s a l i n i t y according to age, geographic o r i g i n and season as d i f f e r e n t i a t e d i n Table XXI. S a l i n i t y L i l l y Point Brockton Point (%o) larqe small larqe small(s) small(w) 20 0.2113 0.4444 0.5541 0.6829 0.4800 15 0.2845 0.3387 0.6977 0.3333 12 0.0000 0.0833 0.2593 0.0000 9 0.0000 0.0000 0.0000 0.0000 (s) = animals acclimated to summer conditions i n the f i e l d (w) = animals acclimated to winter conditions i n the f i e l d 86 summer; and young s n a i l s from L i l l y Point demonstrated a greater tendency to move than adults at high s a l i n i t i e s and temperatures (20%o, 18°C) i n both seasons* The former i s of unknown importance; the l a t t e r , of s i g n i f i c a n c e with regard to negative s e l e c t i v e pressures on movement at L i l l y Point due to large expanses of exposed sandy areas between l o c a t i o n s of s u i t a b l e h a b i t a t . This i s discussed i n d e t a i l l a t e r . To analyze the e f f e c t of changes i n s a l i n i t y and temp-erature on movement, the s n a i l s were grouped according to the d i f f e r e n c e s described above. No e f f e c t of increases i n temperature was detected, and decreases i n s a l i n i t y influenced the r e s u l t s only between 15%o-12%o (Table XXII). No movement occurred at 9%o (Table XXIV). 3. Attachment Strength In the winter, attachment strength of large Thais  lamellosa acclimated at 15%o was adversely a f f e c t e d by i n -creasing temperature, while that of small s n a i l s at 20%o showed a p o s i t i v e c o r r e l a t i o n . In no other instances d i d temperature in f l u e n c e attachment strength (Table XXV). However, i t was noticed i n another experiment that s n a i l s held at extremely low temperatures (0°C-4°C) were very weakly attached at low s a l i n i t i e s (12%o-15%6) apparently more so than those measured i n the laboratory experiment. Over an optimal range, therefore, changes i n temperature can be compensated f o r , but at extremes of temperature i n conjunction with conditions of low s a l i n i t y , attachment strength i s adversely a f f e c t e d . Decrease i n s a l i n i t y from 20%o exerted a marked e f f e c t on attachment strength; the r e l a t i o n s h i p was non-linear, p r o g r e s s i v e l y i n c r e a s i n g i n s e v e r i t y as s a l i n i t y decreased (Table XXVI; F i g . 18). As a consequence, the frequency of 2 i n d i v i d u a l s attached by a force greater than 200 g/cm also de-c l i n e d more abruptly at lower s a l i n i t i e s . However, r e s u l t s i n d i c a t e d , as f o r the f i e l d data, that at lower s a l i n i t i e s the majority of s n a i l s were e i t h e r strongly (200 + g/cm^) or 2 weakly (0 - 100 g/cm ) attached, i l l u s t r a t i n g a great v a r i a -t i o n i n s a l i n i t y tolerance within the populations (Table XVII). Not only were small s n a i l s more strongly attached i n the summer than i n the winter, but i n general greater attachment strengths were recorded at low s a l i n i t i e s compared with high s a l i n i t i e s among s n a i l s acclimated i n the f i e l d to summer conditions than among those acclimated to winter conditions (Tables XXVI, XXVII). That i s , the s n a i l s seem more t o l e r a n t of low s a l i n i t y conditions i n the summer. Strength of attachment at 20%o 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 that at high s a l i n i t i e s recorded i n the f i e l d . Under conditions of very low s a l i n i t y , however, attachment 2 2 strength f e l l to 150 g/cm i n the f i e l d and 60 g/cm i n the laboratory. This d i f f e r e n c e i s s i g n i f i c a n t and may be explain ed by the f a c t that the water conditions i n the laboratory were f a i r l y s t i l l and s n a i l s could, therefore, remain attached to the substrate with very l i t t l e strength, while i n the f i e l d the water constantly moves exerting a greater force on the s n a i l s , and consequently a greater strength of attachment i s required to maintain adherence. T a b l e XXV. L a b o r a t o r y comparison between the s t r e n g t h o f attachment o f s n a i l s o r i g i n a l l y from B r o c k t o n P o i n t and L i l l y P o i n t u s i n g c o v a r i a n c e a n a l y s i s ; attachment s t r e n g t h (g/cm ) i s t h e dependent v a r i a b l e and temperature (9°C-18°C) i s the independent v a r i a b l e . Large and s m a l l s n a i l s were t r e a t e d s e p a r a t e l y , as were animals removed from t h e f i e l d i n the summer and w i n t e r . Separate comparisons are made f o r each s a l i n i t y ( l 2 % o i 15%o and 20%o). SIZE SEASON SALINITY  SOURCE R e g r e s s i o n Among B's w i n t e r Among A's Remainder t - t e s t 20%o d f m.s. F o r t s i q . 1 256 0.0250 n.s. 1 263 0.0257 n.s. 1 4665 0.4562 n.s. 48 10225 15%o d f m.s. F o r t s i q . 1 52545 7.9265 *** 1 8827 1.3316 n.s. 1 1260 0.1901 n.s. 25 6629 12%o d f m.s. F o r t s i q . l a r g e 14 1.1460 n.s. R e g r e s s i o n Among B's summer Among A's Remainder t - t e s t 1 15386 1.6307 n.s, 1 5070 0.5373 n.s, 1 6271 0.6647 n.s, 71 94 35 1 3333 0.4343 n.s. i 1065 1 388 0.0506 n.s. i 4 7 5 7 1 2540 0.3309 n.s. 1 870 56 7675 10 31976 0.0333 n.s. 0.1488 n.s. 0.0272 n.s. R e g r e s s i o n Among B•s w i n t e r Among A's Remainder t - t e s t 1 82380 7.1647 *** 1 19737,1.7166 n.s. 1 26839 2.3340 n.s, 37 11498 1 1413 0.0580 n.s. 1 621 1 1704 0.0700 n.s. 1 9240 1 81459 3.3460 n.s. 1 8338 35 24345 22 3012 0.2062 n.s. 3.0677 n.s. 2.7683 n.s. s m a l l R e g r e s s i o n Among B's summer Among A's Remainder t - t e s t 1 9 0.0005 n.s. 1 7169 0.3599 n.s. 1 10690 0.5367 n.s, 55 19919 1 0 0.0000 n.s. 1 40469 1 119153 6.2861** 1 745 1 16405 0.8655 n.s. 1 3872 62 18955 26 8316 26 1.5945 n.s. 4.8664 n.s. 0.0896 n.s. 0.4656 n.s. 37 1.9349 n.s, Table XXVI T-test evaluations of the n u l l hypothesis of no d i f f e r e n c e between attachment strength of s n a i l s with changes i n s a l i n i t y and i n previous acclimation i n the f i e l d . In cases where the regres s i o n of attachment strength on temperature (9°C - 18°C) was s i g n i f i c a n t , the e f f e c t s of the r e l a t i o n s h i p were e l i m i n -ated by adjusting attachment strength to 12°C before comparisons were made. E f f e c t of Previous Acclimation (summer:winter) S a l i n i t y 20%o 15%o 12%o Size df t-value s i q . df t-value s i q . df t-value s i q . small 100 0.0279 n.s. 105 2.1486 S* 56 3.4090 S*** large 127 1.5548 n.s. 89 2.0325 S* 29 1.4771 n.s. E f f e c t of Changes i n S a l i n i t y S a l i n i t y Comparison 20%o-15%o 15%o-12%o Size Season df t-value s i g . df t-value s i g . summer 125 3.9831 20*** 96 7.6111 15*** small winter 80 1.9139 n.s. 65 6.6883 15*** summer 135 3.4780 20*** 74 2.8947 15*** large winter 81 2.7575 20*** 44 2.7852 15*** A number i n the s i g n i f i c a n c e column i n d i c a t e s which s a l i n i t y had the greater attachment strength. Table XXVII. Frequency d i s t r i b u t i o n of attachment strength c h a r a c t e r i s t i c s within each of the temperature-salinity combinations studied. Temperature S a l i n i t y Age (%o) 20 small 15 12 20 large 15 12 9°C 1 2 6 C 1 8 ° C :tach^ !g/cm ) 0-100 100-200 2 0 0 + 0-100 100-200 2 0 0 + 0-100 100-200 2 0 0 + Season winter 0.167 0.833 0.154 0.846 1.000 summer 0.143 0.857 1.000 0.059 0.941 winter 0.273 0.091 0.636 0.250 0.250 0.500) 0.231 0.154 0.615 summer 0.091 0.091 0.818 0.087 0.130 0.783 0.063 0.125 0.813 winter 0.789 0.158 0.053 0.929 0.071 summer 0.625 0.167 0.208 0.250 0.250 0.500 0.714 0.286 winter 0.056 0.112 0.833 0.048 0.952 0.125 0.875 summer 0.034 0.069 0.900 0.038 0.115 0.846 1.000 winter 0.353 0.647 0.294 0.117 0.588 0.900 0.100 summer 0.240 0.760 0.217 0.090 0.696 0.125 0.125 0.750 winter 0.813 0.125 0.062 1.000 summer 0.750 0.083 0.167 0.556 0.333 0.111 91 Table XXVIII Evaluation of the e f f e c t of previous acclimation i n the f i e l d on frequency d i s t r i b u t i o n of attachment strength values. High S a l i n i t y Conditions (20%o) 2 Attachment Strength Categories(g/cm ) 200* 100-200 0-100 winter 86 10 0 summer 125 11 0 Season X 2 = 0.3729 n.s. (of 200+ : 100-200) Under high s a l i n i t y conditions the proportions of s n a i l s i n a l l attachment strength categories are the same f o r animals removed from the f i e l d i n both the winter and summer^ S a l i n i t y 15%o Season Attachment Strength Categories(g/cm ) 0-100 100-200* winter 48 8 summer 35 21 X 2 = 7.9325 ••• S a l i n i t y !2%o Attachment Strength Categories(g/cm ) 0-100 100-200 + Season winter 43 37 summer 96 29 ,.2 = 11.8724 ••* X 2 (1 d f : « = 0.05) = 5.0239 92 F i g u r e 18 R e l a t i o n s h i p between d e c r e a s e i n s a l i n i t y and s t r e n g t h o f attachment. The d a t a from immature and mature s n a i l s were d i v i d e d i n accordance w i t h p r e v i o u s a c c l i m a t i o n i n the f i e l d on the b a s i s o f r e s u l t s from T a b l e XXVI. The means a r e p l o t t e d w i t h - 1 s t a n d a r d e r r o r . ( • ) mature ( l a r g e ) s n a i l s ( o ) immature ( s m a l l ) s n a i l s ( ) a c c l i m a t e d to summer c o n d i t i o n s i n the f i e l d (- ) a c c l i m a t e d t o w i n t e r c o n d i t i o n s i n the f i e l d SALINITY (%o) 93 4. Proportion of S n a i l s Attached to V e r t i c a l Surfaces Generally an increase i n temperature d i d not a l t e r the proportion of s n a i l s attached to v e r t i c a l surfaces (Tables XXIX, XXX, XXXI). Exceptions occurred i n the f i r s t week among winter animals at an intermediate s a l i n i t y (15%o) and i n the t h i r d week at high s a l i n i t y (20%o); i n both instances, increase i n temperature r e s u l t e d i n smaller proportions attached to the v e r t i c a l surfaces. Kinne (1964) reports that tolerance of one p h y s i c a l f a c t o r (e.g. temperature) may be r e s t r i c t e d when another s t r e s s (e.g. low s a l i n i t y ) i s imposed on the organism. Thus the r e s u l t s at 15%o may suggest that s n a i l s had d i f f i -c u l t y adjusting'to low s a l i n i t y conditions i n the winter, more so than i n the summer when the v e r t i c a l to h o r i z o n t a l d i s t r i b u t i o n was not influenced by temperature. This e f f e c t was probably not observed at lower s a l i n i t i e s because i n i t i a l l y very few s n a i l s were found on v e r t i c a l surfaces i n these aquaria and i n other weeks because the s n a i l s were able to acclimate to the temperature changes by that time. The reason f o r an i s o l a t e d e f f e c t of temperature at 20%o i s unknown. I t was not evident i n the f i r s t weeks of acclimation when the animals were presumably under greater s t r e s s due to the novelty of the experimental c o n d i t i o n s , and i t disappeared at lower s a l i n i t i e s . The proportion of s n a i l s attached to v e r t i c a l surfaces at a l l but the lowest s a l i n i t y increased with time; however, acclimation plateaus were reached at progressively lower pro-portions as s a l i n i t y decreased, i . e . the number of s n a i l s found on v e r t i c a l surfaces at one s a l i n i t y never reached the number observed at the next highest s a l i n i t y (Tables XXXII, Table XXIX. Comparisons between immature (small) and mature (large) s n a i l s using weighted co-variance a n a l y s i s ; proportion of s n a i l s attached to v e r t i c a l surfaces i s the dependent v a r i -able, and temperature (9°C - 18°C) i s the independent v a r i a b l e . SALIN- CATE- WEEK 1 WEEK 2 WEEK 3 ITY (%o ) GORY* SOURCE df m.s. F or t s i q . df m.s. F or t s i q . df m.s. F or t s i q . Regression 1 0.1384 0.2194 n.s. 1 0.5669 1. 0917 n.s. 1 7.5110 4. 8521 • 20 L Remainder 22 0.6307 28 0.5193 28 1.5480 S Regression Remainder 1 22 0.0726 0.2061 0.3521 n.s. 1 28 0.0029 0.2490 0. 0116 n.s. 1 28 2.5900 1.6740 1. 5508 n.s. t - t e s t 46 1.1350 n.s. 58 2. 2563L* 58 1. 4376 n.s. Regression 1 1.3290 0.8562 n.s. 1 0.0721 0. 3875 n.s. 1 0.4701 0. 3831 n.s. 15 L Remainder 22 1.5520 27 1.8530 26 1.2270 S Regression Remainder 1 22 2.2120 1.6350 1.3529 n.s. 1 28 0.7500 1.0280 0. 7296 n.s. 1 28 0.0074 0.9716 0. 0076 n.s. t - t e s t 46 3.6432 s*** 57 1. 0609 n.s. 56 2. 4364 S** Regression 1 0.4268 3.0883 n.s. 1 0.3819 0. 6481 n.s. 1 0.0173 0. 0393 n.s. 12 L Remainder 22 0.1382 19 0.5893 16 0.4402 S Regression Remainder 1 22 0.4043 0.3495 1.1570 n.s. 1 24 0.0281 0.8140 0. 0346 n.s. 1 20 0.0033 1.3410 0. 2461 n.s. t - t e s t 46 2.2868 S* 45 5. 2792 s* •* 38 2. 7654 S*** Regression 1 0.0244 0.7784 n..s. L Remainder 10 0.0313 9 S Regression Remainder t - t e s t 1 10 22 0.0003 0.0242 0.0108 0.0138 n.s. n.s. •Categories of s n a i l s such that L implies large s n a i l s and S small s n a i l s . •*A l e t t e r i n the s i g n i f i c a n c e column indicates which category of s n a i l had the higher value, VO T a b l e XXX. Comparisons between s n a i l s removed from t h e f i e l d i n the w i n t e r and summer u s i n g weighted c o v a r i a n c e a n a l y s i s ; p r o p o r t i o n o f s n a i l s 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 i s t h e depen-dent v a r i a b l e and temperature (9°C - 18°C) i s the independent v a r i a b l e . SALIN- CATE- WEEK WEEK WEEK ITY(%o) GORY* SOURCE df m. s. F o r t s i q . d f m. s. F o r t s i q . d f m.- s. F or t . s i q . R e g r e s s i o n 1 0.3417 1.6396 n.s. 1 0.0415 0.1723 n.s. 1 34.1600 15.1890 » • * W Remainder 22 0.2084 22 0.2409 22 2.2490 20 R e g r e s s i o n 1 0.0048 0.0072 n.s. 1 0.2145 0.4262 n.s. 1 0.0215 0.0968 n.s. S Remainder 22 0.6651 34 0.5033 34 0.2219 t - t e s t 46 0.5179 n.s. 58 0.2502 n.s. 58 1.4132 n. s^ , R e g r e s s i o n 1 9.6520 9.6231 • * • 1 2.0630 1.7543 n.s. 1 2.4440 1.2563 n.s. W Remainder 22 1.0030 22 1.1760 22 1.9470 15 R e g r e s s i o n 1 0.2326 0.0921 n.s. 1 0.1134 0.0785 n.s. 1 0.6542 0.2787 n.s. s Remainder 22 2.5250 33 1.4450 32 2.4040 t - t e s t 46 1.7614 n.s. 57 2.3182 S* 56 4.2053 s*** R e g r e s s i o n 1 0.3269 1.0775 n.s. 1 0.1850 0.1190 n.s. 1 0.0173 0.0361 n.s. w Remainder 23 0.3034 15 1.5500 14 0.4777 12 R e g r e s s i o n 1 0.1863 0.7934 n.s. 1 0.0323 0.0422 n.s. 1 0.3039 0.2439 n.s. s Remainder 21 0.2 348 28 0.7646 22 1.2460 t - t e s t 46 1.2771 n.s. 45 1.8466 n.s. 38 2.6919 S** R e g r e s s i o n 1 0.4889 0.5785 n.s. w Remainder 22 0.8450 9 s R e g r e s s i o n Remainder t - t e s t 1 22 46 0.0000 0.0000 0.0000 1.8500 n.s. n. s. • • C a t e g o r i e s o f s n a i l s such t h a t W i m p l i e s w i n t e r a n i m a l s , and S summer a n i m a l s . **A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which c a t e g o r y o f s n a i l had the h i g h e r v a l u e tn T a b l e XXXI. Comparisons between s n a i l s from Brockton P o i n t and L i l l y . P o i n t u s i n g weighted c o v a r i a n c e ana'lys'is; p r o p o r t i o n o f s n a i l s a t t a c h e d t o a v e r t i c a l s u r f a c e i s " the dependent v a r i a b l e and temperature (9 C - 18 C) i s the independent v a r i a b l e . SALIN- CATE- WEEK 1 WEEK 2 WEEK 3 s i q . ITY (%o) GORY* SOURCE df m. s. F or t s i q . d f m. s. F o r t s i g . d f m . s . F o r t R R e g r e s s i o n 1 0.0139 0.0613 n.s. 1 0.0642 0, .2974 n.s. 1 0.0306 0.1237 n.s. 20 D Remainder 22 0.2260 28 0.2158 28 0.2466 T, R e g r e s s i o n 1 0.2779 0.4577 n.s. 1 0.1964 0 .3652 n.s. 1 1.9020 7.5906 • * JU Remainder 22 0.6072 28 0.5378 28 2.3740 t - t e s t 46 1.4725 n.s. 58 1 .9588 n.s. 58 0.2980 n.s. B R e g r e s s i o n 1 2.9950 1.5656 n.s. 1 0.9149 .0 .6942 n.s. 1 0.5 344 0.5355 n.s. 15 Remainder 22 1.9130 28 1.3180 27 0.9979 R e g r e s s i o n 1 0.7840 0.3893 n.s. 1 0.0046 0 .0032 n.s. 1 0.0633 0.0505 n.s. L Remainder 22 2.0140 27 1.4360 27 1.2540 t - t e s t 46 1.4564 n.s. 57 2 .2759 B* 56 1.9697 n.s. 12 B B R e g r e s s i o n Remainder R e g r e s s i o n Remainder t - t e s t 1 0.3975 1.1131 n.s. 22 0.3571 1 0.0973 0.5419 n.s. 22 0.1795 46 1.4528 n.s. 1 0.0284 0.0027 n.s. 22 1.0660 1 0.0293 0.0025 n.s. 21 1.1680 45 0.4064 n.s. 1 1,5090 1.3020 n.s. 18 1.1550 1 0.0953 0.1367 n.s. 18 0.6973 38 2.2473 B* 1 0.0347 0.0767 n.s. 10 0.0452 1 0.0000 0.0005 n.s. 10 0.0022 22 1.7501 n.s. • C a t e g o r i e s o f s n a i l s such t h a t B i m p l i e s Brockton P o i n t a n i m a l s , and L L i l l y P o i n t animals. ••A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which c a t e g o r y o f s n a i l had t h e h i g h e r v a l u e . R e g r e s s i o n Remainder R e g r e s s i o n Remainder t - t e s t 97 T a b l e XXXII T - t e s t e v a l u a t i o n s o f t h e n u l l h y p o t h e s i s o f no d i f f e r e n c e be-tween the a r c s i n e o f the p r o p o r t i o n o f s n a i l s 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 on c o n s e c u t i v e weeks. In ca s e s where the r e g r e s s i o n on temperature was s i g n i f i c a n t t h e e f f e c t s o f t h e r e l a t i o n s h i p were e l i m i n a t e d by a d j u s t i n g the p r o p o r t i o n t o 12°C b e f o r e t he comparisons were made. CATE- WEEK 1:2 CATE- WEEK 2:3 SALINITY GORY* df t - v a l u e GORY d f t - v a l u e si£-20%o La 76 4.3167 2 • • • La 88 G.1652 n.s. Sm 76 2.6678 2 • * • Sm 88 0.1691 n.s. LaSB 40 8.4213 2 * * * LaSB 32 0.8555 n.s. LaSL 39 5.5421 2 * * * LaSL 31 1.4089 n.s. SmSB 40 4.8451 2 * * * SmSB 34 0.9535 n.s. 15%o SmSL 39 2.2215 2* SmSL 33 3.3906 3*** LaVJB 34 4.5256 2 » • » LaWB 22 1.26 38 n.s. LaWl 34 3.9661 2 • * * LaWL 22 0.3603 n.s. SmWB 34 1.7687 n.s. SmWB 22 0.2344 n.s. SmWL 34 0.840 9 n.s. SmWL 22 1.5139 n.s. La 43 2.1642 2** LaSB 24 2.2983 3* Sm 48 7.6715 2*** LaSL 24 0.6465 n.s. SmSB 31 2.5227 3** 12%o SmSL 31 0.2915 n.s. LaWB 23 1.1924 n.s. LaWL 23 0.9667 n.s. SmWB 28 0.0268 n.s. SmWL 28 2.0122 n.s. 9%o 82 2.3333 1* 47 0.0000 n.s. • C a t e g o r i e s were d e f i n e d by p r e v i o u s a n a l y s i s ( T a b l e s XXIX,XXX, and'XXXI). A b b r e v i a t i o n s - B (Br o c k t o n P o i n t s n a i l s ) , L ( L i l l y P o i n t s n a i l s ) W (removed from f i e l d i n winter), S ( i n summer) La ( l a r g e s n a i l s , Sm ( s m a l l s n a i l s ) A number i n the s i g n i f i c a n c e column i n d i c a t e s i n which week t h e g r e a t e r p r o p o r t i o n o f s n a i l s 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 T a b l e X X X I I I . T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between the a r c s i n e o f t h e p r o p o r t i o n o f s n a i l s 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 a t d i f f e r e n t s a l i n i t i e s w i t h i n each week. In c a s e s where the r e g r e s s i o n on temperature was s i g n i f i c a n t e f f e c t s o f t h e r e l a t i o n s h i p were e l i m i n a t e d by a d j u s t i n g the p r o p o r t i o n t o 12°C b e f o r e comparisons were made. 2 3 CATE- 20%o:15%o CATE- 15%o:12%o CATE- 12%o:9%o GORY* df t - v a l u e s i q . GORY df t - v a l u e siq.- GORY df t - v a l u e sig.-La 70 11.74 72 20*** La 46 5.3994 15*** La 72 1.1880 n.s. Sm 70 6.2922 20*** Sm 46 8.1153 15*** Sm 72 3.4555 12** • SBLa 46 2.6037 20** SBLa 37 12.0230 15*** La 45 3.4000 12** • SBSm 46 1.2670 n.s. SBSm 42 10.4010 15*** Sm 50 21.4375 12** • WBLa 40 4.5187 20*** WBLa 31 6.9197 15*** WBSm 40 3.4687 20*** WBSm 36 5.2244 15*** SLLa 45 5.2349 20*** SLLa 36 8.6692 15*** SLSm 45 4.1105 20*** SLSm 41 6.7905 15*** WLLa 40 6.4384 20*** WLLa 31 6.8225 15*** WLSm 40 5.4645 20*** WLSm 36 4.8556 15*** WLa 70 1.3563 n.s. SBLa 19 5.0331 15*** SBLa 16 3.6604 12** • WSm 70 0.9161 n.s. SBSm 23 4.5708 15*** SBSm 18 5.5034 12** * SLa 74 0.6091 n.s. WBLa 14 5.7978 15*** WBLa 15 5.5882 12»* • SSm 76 0.1779 n.s. WBSm 14 3.1793 15*** WBSm 15 2.1718 12* SLLa 19 9.3979 15*** SLLa 16 3.3960 12** • SLSm 23 6.7862 15*** SLSm 18 3.4127 12** * WLLa 14 6.7745 15*** WLLa 15 1.6591 n.s. WLSm 14 6.5098 15*** WLSm 15 5.3261 12** * • C a t e g o r i e s were d e f i n e d by p r e v i o u s a n a l y s i s ( T a b l e s XXIX, XXX, and XXXI) A b b r e v i a t i o n s B ( 3 r o c k t o n P o i n t ) , L ( L i l l y P o i n t ) , W(winter), S(summer), L a ( l a r g e ) , Sm(small) A number i n the s i g n i f i c a n c e column i n d i c a t e s a t which s a l i n i t y t h e g r e a t e r p r o p o r t i o n o f s n a i l s 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 . T a b l e XXXIV. Weekly p r o p o r t i o n s o f s n a i l s 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 a t f o u r s a l i n i t i e s . C a t e g o r i e s o f s n a i l s were d e f i n e d by p r e v i o u s a n a l y s i s ( T a b l e s XXIX, XXX, and XXXI). I n Q c a s e s where t h e e f f e c t o f the r e g r e s s i o n on temperature was s i g n i f i c a n t , the v a l u e a t 12 C i s p r e s e n t e d i n the t a b l e and the r e g r e s s i o n e q u a t i o n s a r e g i v e n below. Means a r e ex-p r e s s e d - 1 s t a n d a r d e r r o r ; and the sample s i z e i s g i v e n i n b r a c k e t s . ARCSINE OF PROPORTION OF SNAILS ATTACHED TO VERTICAL SURFACES S a l i n i t y 20%o 15%o 12%o 9%o Week 1 Week Large 2 Small Week 3 0.563 (48 ^ 0 . 0 1 7 0.704 (30)-0.028 0.629. (30)-0.018 0.667 (6O-0.224 Large :.' Small Summer Winter Summer Winter .0.178 (24)-0.028 (24)±0. 335 032 B 0.575 (18)±0.038 L 0.449 (17)±0.040 B 0.441 ( 1 2 ^ 0 . 0 5 1 L 0.379 (12)-0.042 La 0.528 (l 6 ) - 0 . 0 4 0 Sm 0.627 (18)+0.034 La 0.358 (12)-0.042 Sm 0.457 (12)±0.046 Large Small Large Small Summer BLa 0.194 ( 5)^0.053 Winter BLa 0.095 ( 4)±0.017 0.019 (24^0.009 (24)-0. 054 013 0.065 (21)^0.019 0.172 (26)^0.008 BSm ,0.319 ( 7)^0.058 LLa 0.085 ( 5K0.025 LSm 0.188 ( 7)±0.055 BSm 0.169 ( 4)^0.078 LLa 0.037 ( 4)^0.022 LSm 0.123 ( 4)^0.023 0.007 (48^0.003 0.000 (36)^0.000 0.000 1 (13)-0.000 A b b r e v i a t i o n s - B i m p l i e s Brockton P o i n t s n a i l s , L L i l l y P o i n t s n a i l s La i m p l i e s l a r g e animals, and Sm, s m a l l a n i m a l s R e g r e s s i o n E q u a t i o n ( w e i g h t e d ) f o r Week 3 20%o Y = 0.8559 - 0.0158X Y ( a r c s i n e o f p r o p o r t i o n ) X (temperature) 100 XXXIII, XXXIV). In the winter, of the s n a i l s exposed to the lowest s a l i n i t y , only a few attached to v e r t i c a l surfaces and a l l of these were i n the f i r s t week, whereas i n the summer they were never found attached to a v e r t i c a l surface. The pattern of acclimation was not i d e n t i c a l f o r a l l groups of s n a i l s , but d i f f e r e d between s n a i l s acclimated to summer and winter conditions i n the f i e l d and between large and small i n d i v i d u a l s (Table XXXIV). In the former case animals acclimated to both conditions responded i n a s i m i l a r manner i n i t i a l l y to the new temperature-salinity regimes i n the laboratory; however s n a i l s removed from the f i e l d i n the summer were b e t t e r able to acclimate to the experimental conditions than the winter animals. Differences detected between Brockton Point and L i l l y Point s n a i l s followed t h i s same pattern, the s n a i l s from Brockton Point showing a greater tendency to attach to v e r t i c a l surfaces under con-d i t i o n s of reduced s a l i n i t y than those from L i l l y Point. In the other case, immature animals were i n i t i a l l y b e t t e r adapted to the laboratory regimes and u s u a l l y t h i s r e l a t i o n s h i p was maintained throughout the study. In summary, the a c c l i -mation patterns suggest that both s i z e c l a s s e s can acclimate to changes i n temperature and s a l i n i t y better i n the summer, and that immature animals are endowed with a greater tolerance of low s a l i n i t y c o n d i t i o n s . 5. Proportion of S n a i l s Attached to the Substrate The a b i l i t y of Thais lamellosa to adhere to the sub-s t r a t e under conditions of reduced s a l i n i t y and/or increased 101 temperature was s i m i l a r f o r ani m a l s from both B r o c k t o n P o i n t and L i l l y P o i n t . I n c r e a s e i n temperature weakened t h i s r e s p o n s e a t h i g h e r s a l i n i t i e s ; a t 20%o d u r i n g the f i r s t two weeks, a t 15%o i n a l l t h r e e weeks, and a t 12%o i n the f i r s t week. In the l a t t e r two i n s t a n c e s the e f f e c t o f temperature was a s s o c i a t e d w i t h a n i m a l s a c c l i m a t e d t o f i e l d c o n d i t i o n s i n t h e w i n t e r . At lower s a l i n i t i e s any r e l a t i o n s h i p w i t h temperature c o u l d have been masked by t h e l a r g e v a r i a b - , i l i t y i n the number o f s n a i l s a t t a c h e d t o the s u b s t r a t e , which was p r o b a b l y due t o v a r i a b i l i t y i n t o l e r a n c e w i t h i n the p o p u l a t i o n s t o low s a l i n i t y c o n d i t i o n s . Adherence a l s o d e c l i n e d w i t h d e c r e a s e i n s a l i n i t y , e s p e c i a l l y between 15%o and 12%o. At both o f t h e s e s a l i n i t i e s , d i f f e r e n c e s i n t o l e r a n c e o f low s a l i n i t y c o n -d i t i o n s were r e v e a l e d between groups o f s n a i l s ; i n t h i s c a s e , s m a l l a n i m a l s , p a r t i c u l a r l y t h o s e . a c c l i m a t e d i n t h e f i e l d t o summer c o n d i t i o n s , were more t o l e r a n t . With the e x c e p t i o n s o f 20%o where no d e t e c t a b l e a c c l i m a t i o n t o s a l i n i t y changes o c c u r r e d , and 9%o where i n v e r s e a c c l i m a t i o n (p. 79) o c c u r r e d , the p r o p o r t i o n o f s n a i l s a t t a c h e d t o t h e s u b s t r a t e i n c r e a s e d w i t h time and i n some i n s t a n c e s r e a c h e d a p l a t e a u (15%o, s m a l l a t 12%o). These were a t p r o g r e s s i v e l y lower p r o p o r t i o n s as s a l i n i t y d e c r e a s e d . A c c l i m a t i o n t o changes i n temperature were observed a t 20%o and 12%o, Table XXXV. Comparisons between immature (small) and mature (large) s n a i l s using weighted co-variance a n a l y s i s : proportion of s n a i l s attached to the substrate i s the dependent v a r i a b l e , and temperature (9 C - 18°C) i s the independent v a r i a b l e . SALIN- CATE- WEEK 1 WEEK 2 WEEK ITY(%o) GORY* SOURCE df m. s. F or t s i q . df m. s. F or t s i q . df m. s. F or t s i q . Regression 1 0.2692 12.2531* 1 0.0603 3.6325 n.s. 1 0.0045 0.2404 n.s. 20 L Remainder 22 0.0220 28 0.0167 28 0.0184 Regression 1 0.1645 2.4512 n.s. 1 0.2708 7.4601 * * * 1 0.0064 0.2689 n.s. S Remainder 22 0.0671 28 0.0363 28 0.0238 t - t e s t 46 0.8775 n.s. 58 0.3050 n.s. 58 1.5210 n.s. Regression 1 1.6140 1.9532 n.s. 1 1.2580 4.0243 n.s. 1 0.8931 3.4390 n.s. 15 L Remainder 22 0.8263 27 0.3126 26 0.2597 Regression 1 1.0430 1.6920 n.s. 1 0.1254 0.3151 n.s. 1 0.1303 0.6655 n.s. S Remainder 22 6.1640 28 0.3980 28 0.1958 t - t e s t 46 2.0796 S* 57 2.0826 L* 56 1.2372 n.s. Regression 1 0.0478 0.0507 n.s. 1 0.3847 0.1253 n.s. 1 1.1260 0.8466 n.s. 12 L Remainder 22 0.9425 . 19 3.0710 16 1.1330 Regression 1 2.3050 0.7806 n.s. 1 0.0104 0.0080 n.s. 1 0.1232 0.0620 n.s. S Remainder 22 2.9530 24 1.6790 22 1.9860 t - t e s t 46 4.0973 s*** 45 2.7466 s*** 40 0.8335 n.s. Regression 1 0.0000 . 0.0000 n.s. 1 0.0088 0.5146 n.s. L Remainder 17 0.0000 2 0.0171 9 Regression 1 0.0030 2.1183 n.s. 1 0.0000. .0.0000 n.s. S Remainder 15 0.0014 4 0.0000 t - t e s t 44 0.7950 n.s. 34 1.3255 n.s. 8 2.6457 L** •Categories of s n a i l s such that L implies large animals, and S small animals. **A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which category of s n a i l had the higher value. Table XXXVI. Comparisons between s n a i l s removed from the f i e l d i n the winter and summer using weighted covariance a n a l y s i s : proportion of s n a i l s attached to the substrate i s the dependent v a r i a b l e , and temperature (9 C - 18°C) i s the independent v a r i a b l e . SALIN- CATE- WEEK 1 WEEK 2 WEEK 3 ITY(%o) GORY* SOURCE df m.s. F or t s i q . df m.s. F or t s i q . df m.s. F or t s i q . W Regression 1 0.6726 12.8777 • * • 1 0.1352 3.1080 n.s. 1 0.0156 0.6002 n.s. 20 Remainder 21 0.0522 22 0.0435 22 0.0259 Regression 1 0.0235 0.8987 n.s. 1 0.1559 7.2987 • • 1 0.0035 0.1875 n.s. s Remainder 23 0.0262 34 0.6214 34 0.0187 t - t e s t 46 0.2922 n.s. 58 0.7285 n.s. 58 0.6833 n.s. Regression 1 5.2470 11.1638 • • * 1 3.4560 7.9540 • • 1 2.0270 5.9652 • 15 w Remainder 22 0.4733 22 0.4345 22 0.3398 Regression 1 0.0001 0.0001 n.s. 1 0.0001 0.0004 n.s. 1 0.1674 2.8992 n.s. s Remainder 22 0.9304 33 0.2310 32 0.0577 t - t e s t 46 0.2551 n.s. 57 1.2387 n.s. 56 0.1668 n.s. w Regression 1 8.9690 7.9654 * * 1 4..5530 2.1137 n.s. 1 4.6426 3.1238 n.s. 12 Remainder 22 1.1260 15 2.1540 14 1.4860 Regression 1 0.1209 0.3356 n.s. 1 0.0799 0.0301 n.s. 1 2.7180 3.4073 n.s. s Remainder 22 3.6020 28 2.6560 22 0.7977 t - t e s t 46 1.8820 n. s. 45 2.0551 S* 40 3.0268 S*** w Regression 1 0.0363 0.8390 n.s. 1 0.0011 0.6403 n.s. 1 0.0022 0.1384 n.s. Remainder 22 0.0423 14 0.0017 7 0.0171 9 Regression 1 0.0052 0.3132 n.s. 1 0.0000 0.0000 n.s. 1 0.0000 0.0000 n.s. s Remainder 22 0.0167 18 0.0000 1 0.0000 t - t e s t 44 1.7733 n.s. 34 1.2485 n.s. 8 1.1686 n.s. •Categories of s n a i l s such that W implies winter animals, and S summer animals. **A l e t t e r i n the s i g n i f i c a n c e column indicates which category of s n a i l had the higher value. T a b l e XXXVII. Comparisons between s n a i l s o r i g i n a l l y from B r o c k t o n P o i n t and L i l l y P o i n t u s i n g weighted c o v a r i a n c e a n a l y s i g ; p r o p g r t i o n o f s n a i l s a t t a c h e d t o t h e s u b s t r a t e i s t h e dependent v a r i a b l e and temperature :(9 C - 18 C) i s the independent v a r i a b l e . SALIN- CATE- WEEK 1 WEEK WEEK ITY(%o) GORY* SOURCE df m.s. F o r t s i q . df m.s. F o r t s i q . d f m.s. F o r t s i q . R e g r e s s i o n 1 0.2332 3.1548 n.s. 1 0.3326 9.5575 1 0.0041 0.1847 n.s. 20 B Remainder 22 0.0739 28 0.0348 28 0.0224 R e g r e s s i o n 1 0.1934 11.8071 * » • 1 0.0363 1.6363 n.s. 1 0.0026 0.1252 n.s. L Remainder 22 0.0164 28 0.0222 28 0.0205 t - t e s t 46 0.0552 n.s. 58 0.2918 n.s. 58 1.2318 n.s. B R e g r e s s i o n 1 1.2590 2.0552 n.s. 1 0.3100 0.6760 n.s. 1 0.0856 0.2631 n.s. 15 Remainder 22 0.6126 28 0.4586 27 3.2520 R e g r e s s i o n 1 1.3000 1.4231 n.s. 1 0.8758 3.0751 n.s. 1 1.0020 7.7554 »• L Remainder 22 0.9135 27 0.2848 27 0.1292 t - t e s t 46 0.9625 n.s. 57 0.0362 n.s. 56 0.1668 n.s. B R e g r e s s i o n 1 0.2787 0.1129 n.s. 1 0.3431 0.1532 n.s. 1 0.0249 0.2289 n.s. 12 Remainder 22 2.4680 23 2.2400 18 1.0870 R e g r e s s i o n 1 0.9121 0.3067 n.s. 1 0.2819 0.0863 n.s. 1 0.9018 0.4922 n.s. L Remainder 22 2.9740 20 3.2670 18 1.8320 t - t e s t 46 0.1339 n.s. 45 0.1279 n.s. 40 0.6890 n.s. B R e g r e s s i o n 1 0.0129 0.5573 n.s. 1 0.0030 2.2476 n.s. 1 0.0142 0.5191 n.s. Remainder 20 0.0232 16 0.0013 4 0.0273 9 R e g r e s s i o n 1 0.0735 1.8607 n.s. 1 0.0000 0.0000 n.s. 1 0.0000 0.0000 n.s. L Remainder 22 0.0395 16 0.0000 4 0.0000 t - t e s t 44 0.2045 n.s. 34 1.3145 n.s. 8 0.9770 n.s. • C a t e g o r i e s o f s n a i l s such t h a t B i m p l i e s Brockton P o i n t a n i m a l s , and L L i l l y P o i n t a n i m a l s . **A l e t t e r i n the s i g n i f i c a n c e column i n d i c a t e s which c a t e g o r y o f s n a i l had the h i g h e r v a l u e . 105 Table XXXVIII T-test evaluations of the n u l l hypothesis of no d i f f e r e n c e be-tween the arcsine of the proportion of s n a i l s attached to the substrate on consecutive weeks. In cases where the regression on temperature was s i g n i f i c a n t , the e f f e c t s of the r e l a t i o n s h i p were eliminated by adjusting the proportion to 12°C before the comparisons were made. SALINITY CATE-GORY* WEEK 1:2 df t-value s i q . CATE-GORY WEEK 2:3 df t-value 20%o 106 0.0269 n.s. 118 0.0682 n.s. SLa 27 3.9071 2*** SLa 73 0.0330 n.s. 15%o SSm 27 0.5176 n.s. SSm 73 0.5048 n.s. WLa 22 0.3049 n.s. WLa 68 0.0519 , n.s. WSm 22 0.0005 n.s. WSm 68 0.4108 n.s. SLa 19 2.6472 2** SLa 14 1.7593 n.s. 12%o SSm 19 2.3382 2* SSm 17 0.9384 n.s. WLa 22 1.2591 n.s. WLa 21 1.2121 n.s. WSm 27 0.6035 n.s. WSm 29 0.0523 n.s. 9%o 80 1.1715 n.s. La 38 0.3075 n.s. Sm 40 1.3571 n.s. •Categories were defined by previous a n a l y s i s (Tables XXXV, XXXVI, and XXXVII). Abbreviations - W (removed from f i e l d i n winter), S ( i n summer) La (large snails), Sm (small s n a i l s ) A number i n the s i g n i f i c a n c e column i n d i c a t e s i n which week the greater proportion of s n a i l s were attached to the substrate Table XXXIX. T-test evaluations of the n u l l hypothesis of no d i f f e r e n c e between the arcsine of the proportion of s n a i l s attached to the.-, substrate at d i f f e r e n t s a l i n i t i e s w ithin each week. In cases where the regression on temperature was s i g n i f i c a n t e f f e c t s of the r e l a t i o n s h i p were eliminated by adjusting the proportion to 12°C before comparisons were made. 12%o:9%o  df t-value s i q . 56 2.4852 12** 56 5.2305 12*** 56 0.3016 n.s. 56 0.6563 n.s. 2 3 SLa 75 6.9496 20*** SLa 27 4.6522 15*** SLa 46 2.6106 12** SSm 75 4.2467 20*** SSm 32 2.0231 n.s. SSm 51 6.4938 12** WLa 70 1.5042 n.s. WLa 19 1.0737 n.s. WLa 45 2.7576 12** WSm 70 0.7076 n.s. WSm 19 0.7016 n.s. WSm 45 3.9544 12** 116 0.4336 n.s. SLa 67 1.3863 n.s. SLa 13 5.5738 12** SSm 70 0.8649 n.s. SSm 18 13.6347 12** WLa 63 2.5513 15** WLa 9 6.7569 12** WSm 66 2.1680 15* WSm 14 4.3465 12** •Categories were defined by previous analysis (Tables XXXV, XXXVI, and XXXVII) Abbreviations W (winter, S (summer), La (l a r g e ) , Sm (small) A number i n the s i g n i f i c a n c e column ind i c a t e s at which s a l i n i t y the greater proportion of s n a i l s were attached to the substrate CATE 20%o:15%o CATE- 15%o:12%o CATE-GORY* df t-value s i q . GORY df t-value s i q . GORY SLa 58 1.5489 n.s. SLa 75 0.4813 n.s. SLa SSm 58 0.7569 n.s. SSm 75 1.0775 n.s. SSm WLa 58 0.6575 n.s. WLa 70 0.2068 n.s. WLa WSm 58 0.3588 n.s. WSm 70 0.6202 n.s. WSm Table XL. Weekly proportions of s n a i l s attached to the substrate at four s a l i n i t i e s . Categories of s n a i l s were defined by previous analysis (Tables XXXV, XXXVI, and XXXVII). In cases where the e f f e c t of the regression on temperature was s i g n i f i c a n t the value at 12°C i s presented i n the table and the regression equation i s given below. Means are ex-pressed - 1 standard error and the sample siz e i s given i n brackets. ARCSINE OF PROPORTION OF SNAILS ATTACHED TO THE SUBSTRATE S a l i n i t y 20%o Week 1 0.852 (48)^0.195 Week 2 0.858 (60)±0.123 Week 3 0.850 (60)i0.011 Summer Winter Summer Winter 15%o La 0.5 39 (12)^0.053 Sm 0.703 (12)^0.026 La 0.611 (12)±0.310 Sm 0.655 (12)±0.513. La 0.796 (17)±0.039 Sm .0.72 3 (17)^0.027 La 0.769 (12)^0.414 Sm 0.655 (12^0.303 +°-(58)-0. 792 134 Summer Winter Summer Winter Summer Winter 12%o La 0.098 (12^0.035 Sm 0.382 (12)-0.071 La 0.067 (12)-0.187 Sm 0.203 (12)^0.380 La 0.348 (12)-0.088 Sm 0.595 (17)-0.057 La 0.317 ( 9)±0.067 Sm 0.437 ( 9)-0.072 La 0.569 ( l l ) i 0 . 0 8 9 Sm 0.668 (14)-0.049 La 0.427 ( 7)-0.050 Sm 0.430 (10)^0.099 Large Small 9%o + °-(46)-0. 010 003 0. (36)±0. 076 056 .0.058 ( 4)^0.022 0.000 ( 6)^0.000 Abbreviations - La implies large s n a i l s , and Sm, small s n a i l s . Table XL (continued) Weighted Regression Equations: Week 1 20%o Y = 1.0090 — 0.0131X Week 1 15%o (large, winter) Y = 0.8636 - 0.0210X Week 1 15%o (small, winter) Y 1.0780 - 0.0352X Week 1 12%o (large, winter) Y 0.2357 - 0.0141X Week 1 12%o (small, winter) Y = 0.5490 - 0.0288X Week 2 20%o Y 0.9596 - 0.0845X Week 2 15%o (large, winter) Y 1.1320 - 0.0303X Week 2 15%o (small, winter) Y 0.9494 - 0.0245X Week 3 15%o Y 0.9159 0.0104X X i s the temperature Y i s the arcsine of the proportion of s n a i l s attached to the substrate O CO 109 6. Water Content and Dry Weight Relationships between Repro-ductive and Non-Reproductive Tissues.  The pattern of change i n body water was followed throughout the experiment to determine the r e l a t i o n s h i p between body water content and reductions i n s a l i n i t y . This inform-a t i o n was used i n connection with l a t e r experiments to e v a l -uate the osmoregulatory capacity of the animals. The water content of the gonad and body minus gonad (henceforth c a l l e d body) increased i n reduced s a l i n i t i e s , but was i n no way a l t e r -ed by changes i n temperature (Tables XLI, XLII, X L I I I ) . In the winter months males held more water i n t h e i r t i s s u e s than females. These d i f f e r e n c e s were reduced i n the summer u n t i l i n the case of the body no e f f e c t of sex was detected. Since the s n a i l s breed during the winter, t h i s suggests that d i f f -erences present at that time were associated with reproductive a c t i v i t y , not only within the gonads but a l s o within accessory sex organs such as the capsule gland which i s well developed at t h i s time of year. Reproductive a c t i v i t y a l so a l t e r e d dry weight r e l a t i o n s h i p s i n that the greater weight of females compared with males i n the winter disappeared i n the summer, and was probably associated with the r e l a t i v e l y greater weight of the gonad and enlarged capsular gland at that time of year (Table XLIV). The r e s u l t s of t h i s part of the study are i n agreement with the values and trends described by Lambert (1970). Changes i n the dry weight of the body and i n the r a t i o between the dry weights of the gonad and body with changes i n s a l i n i t y and temperature were studied i n an attempt to determine i f the s n a i l s p r e f e r e n t i a l l y u t i l i z e d stores of 110 Table XLI E f f e c t of increase i n temperature on water content of gonad and body as evaluated by means of the sign t e s t ( S i e g e l , 1956). As Temperature Increased Water Content Went:  Up(+) Down(-) 17 20 17 22 Body Gonad In both cases a greater than 95% p r o b a b i l i t y existed that the chance of a p o s i t i v e observation equaled that of a negative observation; therefore no s i g n i f i c a n t d i f f e r e n c e e x i s t s . I l l Table XLII T-tes t evaluations of the n u l l hypothesis of no d i f f e r e n c e between percentages of water i n the gonad (a) at d i f f e r e n t s a l i n i t i e s , and (b) i n d i f f e r e n t sexes. (a) Comparisons between S a l i n i t i e s 12%o-15%o 15%o-20%o 12%o-20%o Season Sex df t-value s i q . df t-value s i q . df t-value s i q . M 37 3.5871 12*** 67 0.9359 n.s. winter F 22 0.5256 n.s. 34 1.7907 n.s. 26 2.1411 12* M 43 2.2776 12* 41 0.0544 n.s. summer F 40 0.3404 n.s. 65 1.6559 n.s. 44 2.1153 12* (b) Comparisons between Sexes Season S a l i n i t y df t-value s i g . 12%o 15 10.7295 M* * * o winter 15%o 44 11.0781 M* * * 20%0 57 8.7467 M* * * 12%o 22 3.9076 M* * * summer 15%o 61 2.3840 M* 20%o 72 4.6990 M* * * A l e t t e r or number i n the s i g n i f i c a n c e column i n d i c a t e s which group of s n a i l s had the greater percentage of water i n the gonad. Abbreviations - M (male, F (female) T a b l e X L I I I T - t e s t e v a l u a t i o n s o f the n u l l h y p o t h e s i s o f no d i f f e r e n c e between p e r c e n t a g e s o f water i n the body (a) a t d i f f e r e n t s a l i n i t i e s and (b) i n d i f f e r e n t s exes. (a) Comparisons Between S a l i n i t i e s Season Sex 12%o - 15%o !5%o - 20%o df t - v a l u e s i q . d f t - v a l u e s i q . M 36 8.8908 12*** 67 1.9809 n.s. Win t e r F 23 1.8841 n.s. 34 2.2404 15* Summer C 86 3.3719 12*** 138 2.9017 15*** Comparisons Between Sexes Season S a l i n i t y d f t - v a l u e siq» 20%o 55 3.9210 M* * * W i n t e r 15%o 45 4.1514 M* * * 12%o 14 43315 M* * * 20%o 73 0.1783 n.s. Summer 15%O 63 1.2990 n.s. 12%o 23 1.0019 n.s. A b b r e v i a t i o n s -M (males) F ( f e m a l e s ) C (males and females combined) 113 F i g u r e 19 R e l a t i o n s h i p between per c e n t water c o n t e n t o f body and gonad i n c o n j u n c t i o n w i t h changes i n s a l i n i t y . V e r t i c a l l i n e s r e p r e s e n t - 1 s t a n d a r d e r r o r . The sample s i z e i s g i v e n i n b r a c k e t s . Water c o n t e n t o f the two t i s s u e s i s s i g n i f i c a n t l y d i f f e r e n t f o r females a t a l l times and f o r males o n l y a t h i g h e r s a l i n i t i e s i n the w i n t e r ( T a b l e s X L I I and X L I I I ) . S A L I N I T Y (%o) Table XLIV. Dry weight of the body and t - t e s t evaluations of the n u l l hypothesis of no d i f f e r e n c e between weights from d i f f e r e n t temperature-salinity treatments. DRY BODY WEIGHT(q) Season Sex Temperature 9°C S a l i n i t y 20%o 0.5443 15%o 0.5 394 12%o 0.5401 Winter Males 12°C 0.4952 0.5169 0.5160 18°C 0.4989 0.5300 9°C 0.9092 0.8850 0.8093 Females 12°C 0.8965 0.8314 1.0505 18°C 0.9616 0.9350 9°C 0.6715 0.5205 0.5472 Summer  Combined 12°C ' 0.6617 0.5716 0.4779 Winter females have a greater body weight than males (t = 2.8411, 100 df) EVALUATION OF TEMPERATURE CHANGES(of summer body weights) Comparisons 9°C-18°C 12°C-18°C 9°C-12°C S a l i n i t y 20%o 15%o 12%o df t-value s i q . 47 2.0697 9* df t-value s i q . df t-value s i q . 46 1.7364 n.s. 46 1.2676 n.s. 21 1.3073 n.s, EVALUATION OF SALINITY CHANGES(of summer body weights) Comparisons Temperature 9°C 12°C 18°C 20%o-15%o  df t-value 51 2.5601 2 0 " 44 3.1069 20**' 36 0.4354 n.s. s i q . df 15%o-12%o t-value s i q . 40 0.9536 n.s. 27 3.2310 15*** 20%o-12%o df t-value 39 s i q . 2.5751 20** 18°C 0.5632 0.5478 A number i n the s i g n i f i c a n c e column i n d i c a t e s at which temperature or s a l i n i t y the body weight was greater. T a b l e XLV Changes i n the r a t i o o f d r y weight o f the gonad/body w i t h i n each e x p e r i m e n t a l r e p l i c a t e f o r a l l s a l i n i t y - t e m p e r a t u r e t r e a t m e n t s . SEASON CONDITIONS Temper S a l i n -a t u r e i t y (°C) (%6) Wi n t e r 12 18 20 15 12 20 15 12 20 15 12 RUN 1 % G/B F M 17.7 15.1 19.9 16.2 19.0 19.5 18.2 11.7 13.2 17.8 27.3 8.9 RUN 2 % G/B F M 24.8 8.1 15.8 16.1 20.6 20.8 12.9 9.6 17.7 12.7 25.7 21.0 6.1 19.2 11.8 Summer 9 12 18 20 15 12 20 15 12 20 15 12 RUN 4 F M 6.0 3.7 5.3 4.1 2.7 7.4 3.4 3.9 3.2 2.3 2.0 RUN 5 F M 1.3 2.9 3.5 2.1 3.8 4.0 3.9 3.0 6.9 2.8 3.2 7.6 1.9 3.4 3.1 RUN 6 F M 6.0 2.2 3.8 2.5 5.5 2.3 8.7 1.6 2.1 4.0 1.2 9.6 1.5 3.9 3.3 10.5 A b b r e v i a t i o n s - M (male), F (female) Table XLVI Evaluation of- e f f e c t s of s a l i n i t y and temperature on the r a t i o of the dry weights of the gonad/body of males i n the winter using variance a n a l y s i s . Procedure and terminology are those of Snedecor and Cochran, 1967. SOURCE S a l i n i t y Temperature (adjusted f o r s a l i n i t y ) Temperature S a l i n i t y (adjusted f o r temperature I n t e r a c t i o n Remainder df m.s. 2 365.56 1 3,94.45 2 126.15 1 433.87 3 10.95 70 18.57 £ si£ 10.47 *•* 23.36 0.59 n.s. 117 energy from the gonad under conditions of s t r e s s . The dry weight of the body was a f f e c t e d by changes i n neither temper-ature nor s a l i n i t y i n the winter months; however, i n the summer, i t was a f f e c t e d by both (Table XLIV). At t h i s time the greatest weights were found among s n a i l s at the highest s a l i n i t y and lower temperatures. At low s a l i n i t i e s , however, there was no r e l a t i o n s h i p between temperature and dry weight. In the summer, although the gonads were reduced, the gonad to body r a t i o was unaffected by such changes suggesting that the gonads respond i n the same manner as the body to a l t e r a t i o n s i n temperature and s a l i n i t y . In the winter the r a t i o between gonad and body increased with decreases i n s a l i n i t y and temp-erature i n the males (Table XLV, XLVI). No pattern of change exis t e d i n the females. The s t r a t e g i e s of energy u t i l i z a t i o n appear to d i f f e r between the sexes, the gonad being important as a source of energy only i n males removed from the f i e l d i n the winter. Although females d i d not p r e f e r e n t i a l l y use gonadal material under experimental conditions at t h i s time of year, i t i s s t i l l not p o s s i b l e to say whether they p r e f e r -e n t i a l l y conserved i t ; however, the d i f f e r e n c e i s i n t e r e s t i n g and suggests that the female gonad may be re t a i n e d i n a f u l l y developed state e i t h e r through unfavourable periods within the reproductive season or perhaps u n t i l the next reproductive season i f f o r some reason the products have not been u t i l i z e d during the previous winter. 7. M o r t a l i t y Low s a l i n i t i e s (12%o and 15%0) associated with high temperatures (12°C and 18°C) provided c r i t i c a l states where 118 d i f f e r e n c e s i n s u r v i v a l r e l a t e d to s i z e and previous acclim-a t i o n i n the f i e l d were detectable (Tables XLVII, XLVIII). M o r t a l i t y was higher among large s n a i l s than small and among s n a i l s acclimated i n the f i e l d to summer conditions than to winter conditions, though only at the highest temperature (18°C) i n t h i s l a t t e r case. The sex of the s n a i l i n no way influenced i t s l i f e expectancy (Table XLIX). The other environmental combinations were e i t h e r favourable i n that most animals l i v e d (20%o, 15%o e s p e c i a l l y at 9°C and 12°C), or so bad that most of them died (9%o, and 12%o e s p e c i a l l y at 18°C). A s i g n i f i c a n t i n t e r a c t i o n between temperature and s a l i n i t y was detected (Table XLVIII). Both an increase i n temperature and decrease i n s a l i n i t y tended to increase mort-a l i t y . Acting together these f a c t o r s were more e f f e c t i v e than e i t h e r alone as was i n d i c a t e d i n comparisons i n both the time la g u n t i l the maximum m o r t a l i t y r a t e was observed and i n the t o t a l number of deaths between the c o n d i t i o n of high temper-ature and low s a l i n i t y and that of low temperature and high s a l i n i t y . The r e l a t i o n s h i p between temperature and the time taken f o r h a l f of the s n a i l s to die within each temperature-s a l i n i t y combination ( i . e . the L.D. 50 of the group) was l i n e a r at ^ o (Table XLVIII). At 12%o more than h a l f of the s n a i l s died only at the two higher temperatures, and consequent-l y the r e l a t i o n s h i p was defined i n terms of L.D. 10's and L.D. 20*s. Since groups of s n a i l s showed d i f f e r e n t a b i l i t i e s to survive within t h i s s a l i n i t y (12%o), i t i s evident that a d i f f e r e n t r e l a t i o n s h i p would e x i s t f o r each, and thus the pattern at 9%o i s probably unique to conditions where v i r t u a l l y T a b l e XLVII E v a l u a t i o n o f e f f e c t s o f p r e v i o u s a c c l i m a t i o n i n the f i e l d and o f s i z e on m o r t a l i t y r a t e s u s i n g C h i Square t e s t s o f h e t e r o g e n e i t y , and F i s h e r ' s e x a c t p r o b a b i l i t y . Treatment 18°C, 15%o 12°C, 12%o Dead A l i v e Dead A l i v e Large 23 27 31 18 Small 8 42 19 30 X 2 10.5189*** 5.8800 * Treatment 18°C, 12%o Dead A l i v e W inter 40 0 Summer 35 19 P r o b a b i l i t y o f t h e s e 0.0000 v a l u e s o r worse T a b l e X L V I I I . T a b u l a t i o n o f c u m u l a t i v e m o r t a l i t i e s w i t h i n each e x p e r i m e n t a l t e m p e r a t u r e -s a l i n i t y c o m b i n a t i o n . The d a t a w i t h i n treatments were grouped ( l a r g e and s m a l l , o r summer and w i n t e r ) a c c o r d i n g t o d i f f e r e n c e s p r e s e n t e d i n T a b l e X L V I I . TEMPERATURE (°C) 9 12 18 SALINITY (%o) 20 15 12 9 i 20 15 12 9 120 15 12 9 NUMBER OF SNAILS 86 80 STARTING EXPERI- 99 98 99 . 99 98 96 95 69 1100 100 MENT GROUP OF SNAIL LL S L S Su W DAY 1 1 2 3 4 1 2 1 3 5 11 5 7' 6 33 6 1 9* 3* 10 19* 59 7 1 2 1 8 11 6* 13 27* 61 8 1 101 13 7 16 28 9 2 1 5 16* 17* 10* 22* 38* 80 10 3 2 9* 4 23* ! i 20* 24 SIS 11 1 3 7 31* 21 11 25 i i ! 12 9 11 42* 22 12 30* 39 IS! 13 6 17 14 50* 31 40 !!! Table XLVIII. (Continued) TEMPERATURE (°C) 9 12 18 SALINITY ( % o ) 20 15 12 9 ! 20 15 12 9 | 20 15 12 9 GROUP OF SNAIL L S L S Su W DAY 14 1 9 34* j 17 8 56* 23 33 Iii i i i 15 11 50* | 22 * 10 57 24 III i i i 16 16* 60* i 24 13* 66* 25 iii ill 17 78* j 2 26 16* 34 Uj iii 18 87 J 28 17 68 14 |i: J} j 19 89 | 27 iii iii 20 29 |i iii 21 21* 90 | 2 3 30 19 69 35 : s i HI 22 23 91 } i l l 28 22 36 i i i H I 23 92 | } j} | 29 | j j !!! TOTAL ALIVE AT END 98 97 76 7 i 96 93 46 o ; 99 49 10 0 DATE OF LD 50 ( O f 9%o) 15 { 12 6 DATE OF LD 20 ( O f 12%o) 21 12 15 6 6 DATE OF LD 10 ( o f 12%o) 15 9 11 5 4 Abbreviations mean L (large s n a i l s ) , S (small s n a i l s ) , Su (animals removed from f i e l d i n sum mer), W ( i n the winter), and LD ( l e t h a l death point of group) * (period of maximum death r a t e ) . Table XLIX Influence of sex on the s u r v i v a l of large Thais lamellosa under conditions of decreased s a l i n i t y and increased tempe ature. The r a t i o of the sexes at 20%o and at 9°C were con sidered normal and used to c a l c u l a t e the expected values at 12%o and at 18°C f o r the Chi Square t e s t s . S a l i n i t y S a l i n i t y (%o) 11 20 Male 22 79 Sex Female 19 57 X 2 m 0.19 (1 df; ^  = 0.05) Temperature ( C) 9 18 62 40 60 30 X 2 = 0.91 (1 df; cx = 0.05) X 2 (1 df; <x = 0.05) = 5.02 Temperature Male Sex Female a l l a n i m a l s d i e . The r e l a t i o n s h i p w i t h temperature o f t h e L.D. 10's and L.D. 20's from the 12%o s a l i n i t y treatment were n o n - l i n e a r ; g r e a t e r changes o c c u r r e d at lower temperatures, i . e . a t h i g h temperatures t h e L.D. 10's and L.D. 20's appeared t o approach a p l a t e a u ( T a b l e X L V I I I ) . D i s c u s s i o n 1. D i s t r i b u t i o n and Responses R e l a t e d t o Changes i n S a l i n i t y and Temperature.  Temperature and s a l i n i t y are two o f the more impo r t a n t f a c t o r s c o n t r o l l i n g the d i s t r i b u t i o n o f a q u a t i c organisms (Gunter, 1961; Andrewartha and B i r c h , 1954). Under c o n d i t i o n s o f p r o g r e s s i v e l y d e c r e a s i n g s a l i n i t y , t h e r e s p o n s e s o f s n a i l s i n the l a b o r a t o r y were a l t e r e d g r a d u a l l y and i n a s p e c i f i c sequence, which was a l s o d e l i n e a t e d by t h e f i e l d s t u d i e s and by the d a t a o f Todd (1960; L i t t o r i n a l i t t o r e a , L i t t o r i n a  l i t t o r i n a , and L i t t o r i n a s a x a t i l i s ) , H i l l (1967); M e r c i e r e l l a  e n i q m a t i c a ) , and L a r g e n (1966; T h a i s l a m e l l o s a under temper-a t u r e s t r e s s ) . d e c r e a s e i n p r o p o r t i o n f e e d i n g (15%o, 12%o) " attachment s t r e n g t h (15%o, 9%o) " p r o p o r t i o n 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 (15%o, 9%o) " movement r a t e (12%o, 9%o) " p r o p o r t i o n a t t a c h e d (12%o, 9%o2 m o r t a l i t y p r e s e n t 10% (15-12%o, 9~%o) The f i r s t number i n b r a c k e t s i s the s a l i n i t y i n which an a d v e r s e e f f e c t was f i r s t d e t e c t -ed; and the l a s t , the s a l i n i t y i n which the r e s ponse no l o n g e r o c c u r r e d . S i n c e by the end o f the experiment attachment s t r e n g t h i s d e c r e a s e d 25% - 33% between 20%o - 15%o, p r o l o n g e d r e d u c t i o n i n s a l i n i t y , e v e n t o 15%o, i n c r e a s e s the danger of b e i n g washed o f f exposed s u r f a c e s . S n a i l s must 124 come out on these surfaces to feed, and they therefore run a greater r i s k of being washed away i f they feed under conditions of low s a l i n i t y than high s a l i n i t y . However, i t i s probably l e s s dangerous to move about than to feed on exposed areas during times of reduced s a l i n i t y because the i r r e g u l a r jagged surface formed by the tops of barnacles does not permit as strong a suction as the rough comparatively f l a t surfaces of a rock (Table V I ) . In a d d i t i o n the movement of the body and foot required f o r d r i l l i n g a hole i n t o the prey ( C a r r i k e r , 1961) would f u r t h e r lessen the strength of attachment. Thais  lamellosa can detect d i f f e r e n c e s i n s a l i n i t y and may t r y to f i n d more s a l i n e conditions when they are no longer able to feed. Such a movement to more s a l i n e waters occurred at Spanish Banks i n the spring of 1970, although ex a c t l y what conditions t r i g g e r e d the s n a i l s to move i n t h i s instance could not be determined. As s a l i n i t y i s f u r t h e r reduced, attachment strength continues to decrease. The best strategy f o r sur-v i v a l under such conditions probably i s to remain s t a t i o n a r y , i n c r e v i c e s and other sheltered areas, and conserve energy i n order to o u t l a s t the period of low s a l i n i t y . However, i f the conditions p e r s i s t the s n a i l s slowly lose even the a b i l i t y to attach and soon d i e . The range of s a l i n i t i e s considered i n t h i s study spanned beyond the lower l i m i t of the s a l i n i t y tolerance range of the s n a i l s . Therefore, marked changes were observed i n the animals* responses. The temperature range, on the other hand, did not extend beyond values experienced normally by the s n a i l s i n the f i e l d , and many of them were able to f u l l y compensate 125 t h e i r responses, p a r t i c u l a r l y the amount of time spent attached to v e r t i c a l surfaces and feeding, f o r these changes. However, both m o r t a l i t y and the a b i l i t y to attach were a f f e c t e d by increases i n temperature. S n a i l s capable of attaching to the substrate over the e n t i r e temperature range appear to be s u f f i c i e n t l y strong p h y s i o l o g i c a l l y to compensate t h e i r other responses ( i . e . a b i l i t y to feed and attach to v e r t i c a l surfaces) f o r changes i n temperature, while s n a i l s which §re weakly attached at low temperatures are f u r t h e r stressed by increase i n temperature and unable to compensate. At higher temper-atures some of these detach, others detach and d i e . Studies^ mentioned previously, which extended beyond the temperature range of 9°C - 18°C helped to show that ex-tremes of temperature and s a l i n i t y together were more s t r e s s -f u l on the s n a i l s than e i t h e r alone (e.g. attachment strength, and those responses r e l a t e d to i t as discussed above). This phenomenon has also been recorded f o r other organisms (e.g. Calabresse, 1969, Mu l l n i a l a t e r a l i s ; Broekema, 1941, Crangon  crangon). Because of i t the responses of organisms exposed to changes i n temperature while under conditions of reduced s a l i n i t y , were taken from the l i t e r a t u r e , whenever p o s s i b l e , only between the extremes of temperature tolerance. Within the temperature range 0°C - 18°C an increase i n temperature decreased the a b i l i t y of Thais lamellosa to l i v e under such c o n d i t i o n s . A s i m i l a r trend was found i n Ostrea qiqas (Amemiya, 1928), Crangon v u l g a r i s (Schliepper et a l . , 1960), Crangon crangon (Broekema, 1941), Aequipecten i r r a d i a n s and Modiolus modiolus (Vernberg et a l . . 1963), L i t t o r i n a s a x a t a l i s , 126 L i t t o r i n a l i t t o r e a and L i t t o r i n a l i t t o r a l i s (Todd, 1964) and Homarus americanus (McLeese, 1956). The opposite tendency was noted f o r Carcinides maenas (BroeJchuysen, 1936), Modiolus  demissus and Crassostrea v i r q i n i c a (Vernberg ejb a i l . , 1963) and Cardium edule (Schliepper et a l . , 1960). Vernberg ejb a l . (1963), who found examples of both types i n t h e i r study, suggested that h a b i t a t determined the r e l a t i o n s h i p , greater tolerance at low temperatures being associated with cold-water, low i n t e r t i d a l or s u b t i d a l animals, and the reverse with warm-water, high i n t e r t i d a l species. Although t h e i r hypothesis i s not supported by the responses of L i t t o r i n a s a x a t i l i s , the other species mentioned f a l l i n t o the appropriate categories according to i n t e r t i d a l height. However, i n nature, at l e a s t i n temperate zones, estuarian and many i n t e r t i d a l organisms experience the lowest s a l i n i t i e s and highest temperatures of t h e i r environment simultaneously during the spring-summer runoff of l o c a l r i v e r s . This i s due to the greater volume of the flume at t h i s time of year. I f the temperature-salinity r e l a t i o n s h i p i s molded by the conditions experienced i n the organism's h a b i t a t , why are not low i n t e r t i d a l forms, found within the influence of these r i v e r s , more t o l e r a n t of r e -duced s a l i n i t i e s at high temperatures? The reason may be found i n the o r i g i n of estuarian populations. The vast majority of estuarian species are b a s i c a l l y euryhaline marine forms (Gunter, 1961; Klebovich, 1969). Since oceanic temp-eratures are generally lower than those present i n estu a r i e s these species have been selected to function best over the lower part of the temperature range they are now experiencing. Presumably only high i n t e r t i d a l forms have been subjected to 127 s u f f i c i e n t l y strong s e l e c t i v e pressures to reverse the r e -l a t i o n s h i p i n that they can now cope with low s a l i n i t i e s best at high temperatures. S u r v i v a l was greater i n the f i e l d under conditions of low s a l i n i t y than i n the laboratory. Such d i f f e r e n c e s between laboratory and f i e l d data are also reported by McLeese (1956), H i l l (1967) and Bassingdale (1943). Laboratory con-d i t i o n s are generally s t a t i c whereas the f i e l d environment f l u c t u a t e s continuously. Bassingdale (1943) believed t h i s v a r i a b i l i t y was important i n explaining the discrepancy between f i e l d and laboratory r e s u l t s , " t i d a l f l u c t u a t i o n s may be important and enable animals to l i v e f o r some months at s a l i n i t i e s higher than i s i n d i c a t e d by experiment"; however, he went on to say that prolonged exposure eventually would k i l l them. The same could be true f o r animals under low s a l i n i t y s t r e s s . In these studies, s n a i l s i n the f i e l d were acclimated gradually to the severe co n d i t i o n s , while laboratory animals were introduced d i r e c t l y i n t o the experimental combinations. Bassingdale (1943) and others have stressed that organisms can t o l e r a t e a much greater change i n s a l i n i t y and temperature i f they are tra n s f e r r e d gradually to the new regime. Therefore, the prolonged s u r v i v a l of f i e l d s n a i l s appears to be associated with gradual acclimation and f l u c t u a t i n g environmental con-d i t i o n s . Such gradual acclimation would also account f o r the increased tolerance observed i n the laboratory of s n a i l s removed from the f i e l d i n the summer as compared with those removed i n the winter. F i e l d data i n d i c a t e that the d i s t r i b u t i o n of Thais 128 l a m e l l o s a s h o u l d extend i n t o t e r r i t o r y s u b j e c t e d t o v e r y low s a l i n i t i e s , i . e . e x p e r i e n c i n g o s c i l l a t i o n s below I0%o, and t h a t the key t o s u r v i v a l i s the d u r a t i o n o f time they must l i v e under such c o n d i t i o n s . At any l o c a t i o n t h i s p e r i o d must v a r y from y e a r t o y e a r . In y e a r s o f p r o l o n g e d low s a l i n i t y , t he d i s t r i b u t i o n o f t h e s n a i l would be pushed back toward more s a l i n e waters, w h i l e i n l e s s s e v e r e y e a r s i t would advance a g a i n through d i s p e r s i o n o f an i m a l s near t h e l i m i t o f s p e c i e s d i s t r i b u t i o n . In a d d i t i o n , the s n a i l s a r e c a p a b l e o f s e n s i n g s a l i n i t y changes and o f moving toward more f a v o u r a b l e c o n -d i t i o n s ( e .g. downshore). In t h i s way, the l i m i t s o f t h e i r d i s t r i b u t i o n would not be s t a t i c but c o n t i n u o u s l y moving (a) a l o n g a p o r t i o n o f t h e c o a s t , and (b) through i n t e r -t i d a l r a n g e . 2. Race - Brock t o n P o i n t v s . L i l l y P o i n t With two im p o r t a n t e x c e p t i o n s , T h a i s l a m e l l o s a from L i l l y P o i n t and Br o c k t o n P o i n t responded s i m i l a r l y t o the changes i n s a l i n i t y and temperature imposed i n the l a b o r a t o r y . Animals from B r o c k t o n P o i n t tended t o move g r e a t e r d i s t a n c e s than those from L i l l y P o i n t e s p e c i a l l y under summer s a l i n i t y and temper-a t u r e c o n d i t i o n s . T h i s d i f f e r e n c e may be r e l a t e d t o the d i s t i n c t t o p o g r a p h i e s o f the two beaches. The shore a t Bro c k t o n P o i n t i s c o v e r e d w i t h s m a l l r o c k s and mats o f mussel s h e l l s . The s n a i l s can move f r e e l y w i t h o u t danger o f s t a r v -a t i o n , d e s i c c a t i o n and a e r i a l p r e d a t o r s f o r the mats and r o c k s p r o v i d e ample food and s h e l t e r . On the o t h e r hand, the upper beach at L i l l y P o i n t i s l i n e d w i t h c o b b l e s w h i l e the lower i s composed o f i s o l a t e d b o u l d e r s s e p a r a t e d by s t r e t c h e s o f sand. 129 A large number of s n a i l s l i v e on these boulders and t r a n s i t from one to another may involve exposure to predators, and de s i c c a t i o n and heat death during low t i d e i n the summer. The s n a i l s appear to have no way of knowing the r e l a t i v e l o c a t i o n of the boulders f o r the t r a i l s they leave when moving across the sand meander, r a r e l y following a s t r a i g h t l i n e . This may be an e f f e c t i v e means of f i n d i n g nearby rocksj however, when they are widely spaced, the process i s both time and energy consuming. The d i s t i n c t p o s s i b i l i t y e x i s t s that the s n a i l s may remain l o s t on the sands. Stimson ( i n press) analyzed exchange of s n a i l s between these boulders and found that e s s e n t i a l l y none occurred at distances greater than 30m. Young s n a i l s showed a greater tendency to move than adults under summer conditions i n d i c a t i n g that t h i s c h a r a c t e r i s t i c i s s t i l l under strong s e l e c t i v e pressure. Habitat may also be responsible f o r another d i f f e r e n c e i n the reactions of s n a i l s from the two populations to low s a l i n i t y c o n d i t i o n s . I t was observed that fewer L i l l y Point s n a i l s attached to v e r t i c a l surfaces when exposed to reduced s a l i n i t i e s than Brockton Point s n a i l s . I t can be hypothesized that the population at L i l l y Point has been selected f o r s n a i l s which remain near the base of the rocks f o r greater periods of time during reduced s a l i n i t i e s . This would prevent s n a i l s from being washed from exposed surfaces out on to the sand f l a t . At Brockton Point t h i s would not be as disastrous because the sub t i d a l i s rocky and inhabited by Thais lamellosa. S e l e c t i v e 130 pressures discouraging movement up on the rocks during periods of low s a l i n i t y would therefore have been greater at L i l l y Point. Studies with L i l l y Point and Brockton Point animals c a r r i e d out at Spanish Banks revealed that L i l l y Point s n a i l s were l e s s f i r m l y attached to the substrate i n conditions of reduced s a l i n i t y than Brockton Point s n a i l s and that the former had a greater m o r t a l i t y r a t e l a t e i n the season when s a l i n i t y was i n c r e a s i n g . Lack of confirmatory evidence from the laboratory studies and the scantiness of the f i e l d evidence supporting the hypothesis that the population at Brockton Point i s more t o l e r a n t of reduced s a l i n i t i e s than that at L i l l y Point implies (a) that the presence of a d i f f e r e n c e i s doubtful e s p e c i a l l y since d i f f e r e n c e s i n tolerance r e l a t e d to seasonal acclimation and age were r e a d i l y detected i n the laboratory, and (b) that i f a d i f f e r e n c e e x i s t s i t i s very s l i g h t . I t was s u r p r i s i n g to f i n d not only that the populations possess the same capacity to cope with reduced s a l i n i t i e s , but also that t h i s capacity extends much below the conditions they were found to experience i n the f i e l d . D i s t r i b u t i o n , as deter-mined by p h y s i c a l f a c t o r s , i s often influenced more by ex-tremes than mean values (Kinne, 1964). The s a l i n i t y and temperature data of t h i s study were c o l l e c t e d from the two beaches only f o r a period of 18 months, and neither of the springs was as severe, judging by the maximum d a i l y runoff of the Fraser River, as the f i v e others i n the past decade f o r which data were a v a i l a b l e (Table V I I I ) . In a d d i t i o n , although i n one case discharge was as much as 50% greater 131 than that In the 1969 or 1970 seasons, the r i v e r has not pro-duced a major flood since 1948. Therefore, the populations have had to survive much worse conditions i n the recent past than those observed i n t h i s study which would account f o r the extent of t h e i r low s a l i n i t y tolerance. S i m i l a r i t y of response, however i s not explained by these considerations because water flows from south to north i n the S t r a i t of Georgia and the currents push the majority of the flume of the Fraser River north. This helps to main-t a i n r e l a t i v e l y higher s a l i n i t y conditions at L i l l y Point, which i s south of the r i v e r ' s mouth, than at Brockton Point which i s north of the r i v e r and i s also influenced by other f r e s h water sources i n the v i c i n i t y (Capilano River, Seymour River and water from Indian Arm) ( F i g . l ) . For t h i s reason, the s e v e r i t y of the Eraser River runoff should not a l t e r the d i f f e r e n c e i n s a l i n i t y at these l o c a t i o n s providing t h i s p a t t -ern holds also i n years of maximum f l o o d i n g . Two hypotheses accounting f o r the s i m i l a r range of low s a l i n i t y tolerance suggest themselves. The a b i l i t y may be widely present i n populations from both s a l i n e and brackish conditions i n t h i s v i c i n i t y , being introduced i n t o the species sometime i n the past, perhaps during the r e t r e a t of the l a s t g l a c i e r when a large amount of f r e s h water washed the shores of the north P a c i f i c . Once i n the species makeup, i t may have been retained through linkage with a h i g h l y advantageous c h a r a c t e r i s t i c . However, i t i s more l i k e l y that s a l i n i t y tolerance was selected at L i l l y Point through exposure to low s a l i n i t y c o n d i t i o n s . P o s t - g l a c i a l l y Point Roberts was an i s l a n d i n the d e l t a of the 132 Fraser River when i t emptied into the S t r a i t of Georgia v i a Boundary Bay (Johnston, 1923). The more s a l i n i t y t o l e r a n t i n d i v i d u a l s of the species would have been the f i r s t to c o l o n i z e the area as the passage c l o s e d . Even today, those s n a i l s endowed with the greatest a b i l i t y to contend with low s a l i n i t y conditions should contribute more than usual to the generations immediately following a summer of r e l a t i v e l y severe s a l i n i t y c o n d i t i o n s , and i n t h i s way maintain the high l e v e l of tolerance formerly required of the s n a i l s to survive at t h i s beach. Since t h i s heritage would have been selected f o r at a much l a t e r date than the l a s t i c e age, and since i t would not require favourable linkage to ensure i t s continuance i n the population, the l a t t e r hypothesis i s the more probable. 3. Size - Age Kinne (1964) reported that tolerance of changes i n s a l i n i t y conditions could vary with age; supporting evidence was found i n the works of Broekhuysen (1936), Broekema (1941), Keys (1931), Kinne (1960), F i s c h e r - P i e t t e (1931) and Calabresse (1960). In the present study small immature i n d i v i d u a l s repeatedly demonstrated a greater tolerance of reduced s a l i n i t y c onditions than a d u l t s . In other studies such d i f f e r e n c e s were sometimes associated with the d i s t i n c t areas of d i s t r i b -u t ion of the various age groups which were ch a r a c t e r i s e d by d i f f e r e n t s a l i n i t y conditions (e.g. Broekema (1941) working with Crangon crangon). A l l members of the Thais lamellosa popul-a t i o n , however, are present i n the same geographic area and exposed to the same s a l i n i t y c o n d i t i o n s . The question, therefore, i s whether i t would be more advantageous to a 133 population when recovering from severe reductions i n s a l i n i t y which k i l l e d the majority of the s n a i l s , to s t a r t with a breeding stock composed p r i n c i p a l l y of young immature animals or older mature i n d i v i d u a l s . I f t h i s catastrophe occurs r a r e l y or on a somewhat regular basis implying that the environ-ment returns to that normally experienced by the animals i n the past then a breeding stock of mature i n d i v i d u a l s would perhaps be favoured because (a) they are already mature and capable of reproducing, (b) they are la r g e r and can, therefore, produce more young/female (the number of eggs increases with the s i z e of the female (Lambert, 1970; Emlen, 1966)), and (c) they have been better suited to the normal environment by a longer exposure to the forces of natural s e l e c t i o n . However, i f the extreme conditions are part of a trend towards a new environment then r e t e n t i o n of young animals f o r the breeding stock would be advantageous because they express a greater phenotypic v a r i e t y and thus ensure a better change of population s u r v i v a l under new conditions than the a d u l t s . In the long run, slow recovery from repeatedly experienced extremes and a greater a b i l i t y to change with new conditions would be the best s u r v i v a l strategy. How important these f a c t o r s were i n determining the present d i f f e r e n c e s i n s a l i n i t y tolerance i s not known. Decrease i n the range of s a l i n i t y tolerance may also e x i s t through a s s o c i a t i o n with d i f f e r e n c e s i n metabolic rates due to the more r a p i d growth of immature as compared with mature animals (Kinne, 1964; Thorson, 1958). A greater metabolic rate may mean a f a s t e r response to new conditions, which i n turn 134 may prevent damage to the organism before i t can e f f e c t i v e l y contend with the changed environment. 4. Metabolism The pattern of body and gonad dry weights from the d i f f e r e n t temperature-salinity treatments provides inform-a t i o n on the metabolism of the s n a i l s with changes i n these two p h y s i c a l f a c t o r s . In the summer the gonad/body r a t i o of s n a i l s was very low and constant; i . e . changes i n gonadal t i s s u e p a r a l l e l e d those of the body. Body weight was constant at lower s a l i n i t i e s but increased at high s a l i n i t y (20%o) and low temperatures, implying that energy derived from feeding at high s a l i n i t y was at l e a s t p a r t i a l l y converted to biomass. Since temperature d i d not a f f e c t feeding rate, and consequently the energy a v a i l a b l e within each s a l i n i t y was constant, and since increase i n temperature to 18°C decreased body weight at 20%o, more energy must have been u t i l i z e d at t h i s temper-ature. E i t h e r the s n a i l s were more a c t i v e , a c o n d i t i o n which was not supported by casual observation or by data from the study, or they have a higher basal metabolic r a t e at high temperatures. That i s , Thais lamellosa maintained feeding rates and normal patterns of movement at 18°C compared with lower temperatures, i n s p i t e of the f a c t that i t was more c o s t l y i n terms of energy. Newell and Pye (1970 a) reported that the basal meta-b o l i c r ates of Mytilus e d u l i s and L i t t o r i n a l i t t o r e a were com-p l e t e l y compensated f o r changes i n temperature a f t e r an acclim-a t i o n period of 7 to 21 days. Vernberg (1969) showed that the r e s p i r a t o r y rate of f i v e species of f i d d l e r crab (Uca), 135 a c c l i m a t e d t o the i n d i v i d u a l t e m p e r a t u r e s , i n c r e a s e d w i t h i n c r e a s e i n temperature i n a - n o n - l i n e a r f a s h i o n t e n d i n g t o form a p l a t e a u i n t h e middle o f the t h e r m a l range s t u d i e d . B u l l o c h ' s (1954) w e l l known h y p o t h e t i c a l model d e a l i n g w i t h r e s p i r a t o r y r e s p o n s e of animals a c c l i m a t e d t o a s e r i e s o f temperatures d e p i c t s an i n c r e a s e i n m e t a b o l i c r a t e w i t h i n c r e a s e i n temperature such t h a t a p l a t e a u i n the r e s -ponse i s approached i n t h a t r e g i o n o f temperatures p r e v a l e n t i n the s p e c i e s normal h a b i t a t . He p r e d i c t e d a c o l l a p s e a t h i g h e r temperatures ( i . e . r i g h t a f t e r the p l a t e a u ) . Vernberg (1969) found a marked i n c r e a s e i n t h i s r e g i o n a l t h o u g h the m e t a b o l i c r a t e would undoubtedly f a l l a t s t i l l h i g h e r temper-a t u r e s due t o heat coma and d e a t h . E x t e n t o f the p l a t e a u may be r e l a t e d t o temperature f l u c t u a t i o n s n o r m a l l y e x p e r -i e n c e d by t h e a n i m a l s . These would be g r e a t e r f o r i n t e r t i d a l a n i m a l s t h a n f o r s u b t i d a l and f o r c o n t i n u o u s l y exposed i n t e r -t i d a l a n i m a l s than f o r s h e l t e r e d forms e t c . ( N e w e l l , 1969). S u p p o r t i n g e v i d e n c e i s found i n the work o f Courtney and Newell (1965), Newell (1967), Barnes ( p e r s o n a l communication i n N e w e l l , 1969),and D a v i s (1967). T h a i s l a m e l l o s a a v o i d s exposure t o the sun i n t h e heat o f summer; i t may be a b l e t o compensate c o m p l e t e l y m e t a b o l i c a l l y f o r temperatures i n the v i c i n i t y o f 9°C - 12°C, but h i g h e r temperatures (18°C) a r e beyond the p l a t e a u . In comparison M y t i l i s e d u l i s which does not seek s h e l t e r , compensates c o m p l e t e l y t o 20°C (Newell and Pye, 1970 a: and b ) . The d a t a from males s t u d i e d i n t h e w i n t e r showed no i n f l u e n c e o f temperature o r s a l i n i t y on body weight, a l t h o u g h 136 the r a t i o of gonad/body declined with increases i n both. Energy requirements appear to have been supplied from food and from stores of material i n the gonad. The p o s s i b i l i t y a l s o e x i s t s that a constant amount was removed from the body i n a l l treatments. Since s n a i l s taken from the beach i n the summer ( i . e . u n t i l the end of July) had very small gonads (gonad/body r a t i o was approximately 4%), energy derived from feeding i n the spring and e a r l y summer went towards growth and maintenance per se. Lambert (1970) found that the gonads do not mature i n the population at Brockton Point u n t i l September. Since the gonads are i n a c t i v e i n the summer and since a l l temperatures studied (9°C - 18°C) were greater than the normal winter value (5°C), high temperature may have i n i t i a t e d atrophy of the gonad or allowed energy needs to be f u l f i l l e d p r i n c i p a l l y from stores of material i n t h i s organ. The i n c r e a s i n g r a t i o of gonad/body with decreases i n s a l i n i t y and temperature support the hypothesis that energy r e q u i r e -ments were l e a s t at low temperatures and s a l i n i t i e s . In the case of winter females neither the gonad nor body weights were influenced by temperature or s a l i n i t y . They presumably u t i l i z e d energy derived from feeding to o f f s e t the greater energy demands of l i v i n g at higher s a l i n i t i e s and temperatures as well as a constant amount from the body and/or gonad which would provide f o r energy needs at s a l i n i t i e s where feeding was impossible but no detrimental a f f e c t on dry weight was observed. I f increasing temperatures, representing the onset of summer, were responsible f o r u t i l i z a t i o n of gonadal material i n the males, the absence of a s i m i l a r decrease i n gonad/body r a t i o with incre a s i n g s a l i n i t y would suggest that 137 f o r females preservation of the gonad f o r use during the following winter's reproductive season i s an e v o l u t i o n a l l y adaptive response. Those conditions i n the laboratory which were conducive to increase i n biomass were s i m i l a r to the conditions present i n the f i e l d during periods of maximum feeding a c t i v i t y . At higher temperatures, the s n a i l s were feeding with the same i n t e n s i t y but apparently with no gain i n biomass to show f o r t h e i r e f f o r t s . Since other s n a i l s (at lower s a l i n i t i e s but the same temperature) did not feed, were r e l a t i v e l y i n a c t i v e , and had an equivalent biomass to the a c t i v e l y feeding i n d i v i -duals at the end of the experiment, i t i s p o s s i b l e the s n a i l s would be better o f f to stop feeding and wait out the period of warm weather. In t h i s manner more prey would be a v a i l a b l e at a l a t e r date when they could be u t i l i z e d more e f f i c i e n t l y . The s n a i l s i n the laboratory continued to feed at high temp-eratures; however, i n the f i e l d the feeding rates at L i l l y Point and Brockton Point dropped sooner than those at Spanish Banks with the onset of warm weather. I t may be that since s n a i l s at Spanish Banks consumed only h a l f as much as those at the other two beaches over the year, they were n u t r i t i o n -a l l y d e f i c i e n t and continued to eat as long as p h y s i c a l l y p o s s i b l e . While the s n a i l s at the other two beaches were s t i l l capable of eating,they d i d not do so; perhaps because they had been selected for decreased feeding rates i n warm weather due to the i n e f f i c i e n c y of energy conversion f o r the population as a whole. One of the s u r p r i s i n g aspects of the metabolic strategy of Thais lamellosa i s the constancy of body weight 138 over such a large range of environmental c o n d i t i o n s , i . e . the d i f f e r e n c e s i n a v a i l a b l e energy were r e f l e c t e d i n a c t i v i t y l e v e l s rather than i n body weights. This conservation of bo d i l y reserves may allow the s n a i l s to l i v e through periods of prolonged s t a r v a t i o n , e.g. years of poor barnacle s e t t l e -ment, periods during the winter when i t i s too c o l d to feed e f f e c t i v e l y and when the animals spend several months engaged i n reproductive a c t i v i t i e s , and periods during the summer of warm water temperatures and/or low s a l i n i t i e s . 5. Acclimation Precht (1958) c l a s s i f i e d acclimation responses i n t o f i v e categories: (a) complete (response at new s a l i n i t y equals that at the o r i g i n a l s a l i n i t y before a c c l i m a t i o n ) , (b) p a r t i a l (response changes toward the o r i g i n a l value but stops short of i t ) , (c) no acclimation (response i s the same before and a f t e r the acclimation period), (d) supra-optimal (response overshoots the o r i g i n a l v a l u e ) , and (e) inverse (instead of approaching the o r i g i n a l value the response r e -gresses from i t ) . In most instances i n t h i s study when the type of acclimation could be determined, i t was found to be p a r t i a l . The l e a s t s a l i n i t y s e n s i t i v e a t t r i b u t e , the proportion of s n a i l s attached, exhibited complete acclimation only at 15%o. On the other hand when the s n a i l s were exposed to severe s a l i n i t y s t r e s s a l l three c h a r a c t e r i s t i c s monitored ( i . e . proportion of s n a i l s (a) attached, (b) attached to v e r t i c a l surfaces and (c) feeding) followed the pattern of inverse acclimation. This same tendency was observed by Chapmann and Banner (1949) i n 139 t h e i r study of the s a l i n i t y tolerance of Thais lamellosa i n Puget Sound. Within each s a l i n i t y the s n a i l s may be acclimating to d i f f e r e n t a t t r i b u t e s at d i f f e r e n t r a t e s . Precht (1949; i n Precht, 1958) describes a s i m i l a r r e l a t i o n s h i p with regard to temperature a c c l i m a t i o n . The pattern of acclimation of one a t t r i b u t e can vary within a s a l i n i t y , such that two categories of s n a i l s would have d i f f e r e n t i n i t i a l values and thus proceed at d i f f e r e n t rates to the same plateau, or the rates and i n i t i a l points might be the same f o r the two groups, but where one reached a plateau the other would continue to acclimate. Generally when d i f f e r e n c e s occurred between large and small animals they followed the former pattern, and between winter and summer s n a i l s , the l a t t e r . 140 SECTION I I I A PHYSIOLOGICAL STUDY OF RESPONSES TO CHANGES IN EXTERNAL SALINITY INTRODUCTION M u l t i c e l l u l a r organisms have developed three l e v e l s of r e g u l a t i o n i n response to a l t e r a t i o n s i n the i o n i c and/or osmotic conditions of the external environment: (a) c o n t r o l of the c e l l u l a r i o n i c concentrations, (b) maintenance of the c e l l u l a r volume, and (c) r e g u l a t i o n of the i o n i c and osmotic concentrations of e x t r a c e l l u l a r f l u i d s . A l l c e l l s , whether as members of an organism or as i n d i v i d u a l s , a c t i v e l y c o n t r o l t h e i r i n t e r n a l i o n i c composition by maintaining concentration gradients across t h e i r c e l l mem-branes. I f a c e l l can c o n t r o l only i t s i o n i c concentrations the osmotic pressure of i t s c e l l u l a r f l u i d i s i d e n t i c a l to that of the surrounding environment, and i t s volume, therefore, v a r i e s i n v e r s e l y with the external osmotic pressure. Some c e l l s , however, are able to readjust the volume towards a "preferred s t a t e " . In 1967 Lange and Mostad proposed a hypothet i c a l model of volume-regulation. Lange (1964) had v found i n the sea urchin Strongylocentrotus droebachiensis that c e l l s f i r s t expanded to a new constant volume when s a l -i n i t y was lowered, but l a t e r decreased i n s i z e . The authors, therefore, f e l t that the f i r s t stage of r e g u l a t i o n consisted of the passive movement of water i n t o the c e l l from the external 141 medium i n order to restore osmotic e q u i l i b r i u m . At t h i s point unknown f a c t o r s t r i g g e r e d a response i n the c e l l which stim-ulated the return towards the o r i g i n a l volume by the excretion of an isomotic f l u i d . The volume of the solutes l o s t to the c e l l i s replaced with water. Therefore, i f the character-i s t i c s of the solutes involved i n r e g u l a t i o n are known, the volume of solutes replaced by water as the s a l i n i t y decreased can be determined mathematically, and an equation representing the r e l a t i o n s h i p between s a l i n i t y and the amount of water i n a given volume of t i s s u e at 100% r e g u l a t i o n constructed. I f an osmometer, (an instrument which swells with the passive i n f l u x of water as s a l i n i t y f a l l s ) i s allowed to represent a c e l l having no capacity to regulate volume, then a measure of the performance of a l i v i n g organism under osmotic s t r e s s can be obtained by comparing the change i n water content of a 3 cm of the animal with both the change exhi b i t e d by an osmo-meter of the same i n i t i a l volume and the t h e o r e t i c a l hydration during complete volume-regulation as mentioned above (Staaland, 1970). A process of greater e f f i c i e n c y than volume-regulation i s involved i n c o n t r o l of the osmotic pressure of the e x t r a -c e l l u l a r f l u i d s . The external environment does not act d i r e c t l y on the c e l l s , except on the body surface. Water flow occurs between i t and the blood passing through the g i l l s t r u c t u r e s ; the blood i n turn contacting the c e l l s of the body and a f f e c t i n g t h e i r osmotic pressure. I f the blood composi-t i o n can be c o n t r o l l e d the c e l l s would be protected from ex-t e r n a l v a r i a t i o n s . This homoiosmotic goal i s achieved by 142 " i o n i c pumps" and s p e c i a l i z e d permeability conditions which e x i s t across the g i l l and n e p h r i d i a l membranes. Many i n v e r t e -brates may osmoregulate at t h i s l e v e l e i t h e r completely or p a r t i a l l y , but many can not (Robertson, 1949). The degree to which an organism can c o n t r o l i t s i n t e r n a l state determines the range of i t s s a l i n i t y t o l e r a n c e . Khlebovich (1969) considers the s a l i n i t y range of 5%o to 8%o, c h a r a c t e r i z e d by a low species d i v e r s i t y , as a c r i t i c a l zone i n s a l i n i t y tolerances f o r i t i s a b a r r i e r to most f r e s h water and marine animals. He b e l i e v e s that organisms can survive i n water of l e s s than 5%o s a l i n i t y only i f they can maintain an i n t e r n a l s a l i n i t y of at l e a s t 5%o since l i v i n g t i s s u e cannot func t i o n at lower osmotic pressures. That i s , osmoconformers (organisms whose body f l u i d s are i n osmotic e q u i l i b r i u m with the external medium (Lange, 1968a))' cannot survive below t h i s range. However, among the osmoconformers can be found both s a l i n i t y t o l e r a n t (euryhaline) and i n t o l e r a n t (stenohaline) species. The greater the a b i l i t y of an osmoconformer to regulate i t s volume the wider i s i t s range of s a l i n i t y t o l e r -ance and the l a r g e r i t s area of p o t e n t i a l d i s t r i b u t i o n (Schliepper, 1964). The d i s t r i b u t i o n of aquatic species therefore r e s t s on the a b i l i t y to osmoregulate i n t r y i n g e i t h e r to maintain a constant i n t e r n a l osmotic pressure, or, i f that i s impossible, to regulate c e l l u l a r volume. In order to define the osmotic a b i l i t y of a marine invertebrate, i t s capacity to regulate both the volume of the c e l l and osmotic pressure of e x t r a c e l l u l a r f l u i d must be deter-mined. The l a t t e r n e c e s s i t a t e s the measurement of osmotic 143 pressure of both body f l u i d s and the external medium over a range of s a l i n i t i e s . Measurement of the density of soft body parts and t h e i r water content with s a l i n i t y change are required to c a l c u l a t e the degree of volume-regulation. DETERMINATION OF OSMOREGULATORY CAPACITY Introduction To determine the osmoregulatory a b i l i t y of Thais  lamellosa, the osmotic pressures of p e r i c a r d i a l f l u i d and. external media were compared over and beyond the lower s a l i n -i t y range inhabited by the animals i . e . 20%o, 18%o, 16%O, 14%o 12%o, and 10%o. The osmotic pressure of samples was measured according to the melting point procedure o u t l i n e d by Gross (1954). Data determined by t h i s method have a v a r i a -t i o n of 2% - 4%. Methods and Materials In molluscs the f l u i d i n the p e r i c a r d i a l c a v i t y i s produced by u l t r a f i l t r a t i o n of blood through the heart. The l i q u i d passes through the r e n o p e r i c a r d i a l canal i n t o the nephridium where ion r e s o r p t i o n occurs (Meglitsch, 1967). Therefore, the f l u i d i n the p e r i c a r d i a l c a v i t y i s i n osmotic e q u i l i b r i u m with the blood. P e r i c a r d i a l f l u i d was chosen as i t was e a s i l y obtained using a Hamilton syring without contamination by c e l l s and c e l l u l a r fragments,thus e l i m i n a t i n g the n e c e s s i t y f o r c e n t r i f u g a t i o n p r i o r to a n a l y s i s . In preparation, spot g l a s s hollows were l i n e d with melted beeswax and f i l l e d with p a r a f f i n o i l . Samples of p e r i c a r d i a l f l u i d and media were stored under o i l to prevent con-tamination and evaporation. Small volumes of f l u i d and o i l were p u l l e d a l t e r n a t e l y i n t o 5 u l glass c a p i l l a r y tubes which were sealed with wax and quick frozen. During the experiment only volumes of approximately equal s i z e were compared since 145 i t was found that volume g r e a t l y influenced the rate of heating of the sample. S i x t y s n a i l s 4.00cm - 4.50 cm i n length were c o l l e c t e d from Brockton Point at the end of May 1970 and allowed to acclimate f o r 5 to 7 days at 10°C to the s a l i n i t i e s mentioned above (20%o - 10%o). The water was changed d a i l y without temperature shock. The f i e l d temperature at t h i s time was 13.5°C; the s a l i n i t y , 24%o. Results The data are presented i n Figure 20. A systematic e r r o r necessitated r e j e c t i o n of a l l animals from the 14%o group. Since the osmotic pressure of the p e r i c a r d i a l f l u i d does not d i f f e r s i g n i f i c a n t l y from the external medium, Thais  lamellosa conforms osmotically to i t s environment over the range of s a l i n i t i e s i n v e s t i g a t e d . Discussion The r e s u l t s agree with the reported behaviour of most molluscs. With four known exceptions, a l l marine and brackish water molluscan species are osmoconformers (Robertson, 1964; tables pp. 285, 289 with o r i g i n a l authors). The four excep-t i o n s to t h i s g e n e r a l i z a t i o n were documented by Freeman and R i g l e r (1957) i n connection with S c r o b i c u l a r i a plana ( B i v a l v i a ) , and by Todd (1962) i n connection with L i t t o r i n a l i t t o r e a , L i t t o r i n a l i t t o r a l i s , and L i t t o r i n a s a x a t i l i s (Gastropoda). These species osmoconform over a range of higher s a l i n i t i e s , but maintain t h e i r blood hyperosmotic to the environment below 16%o ( L i t t o r i n i d a e ) , below 11.3%o ( S c r o b i c u l a r i a plana). 146 F i g u r e 20 R e l a t i o n s h i p between s a l i n i t y o f e x t e r n a l medium and p e r i c a r d i a l f l u i d . V e r t i c a l l i n e s r e p r e s e n t - 1 s t a n d a r d e r r o r ; sample s i z e i s g i v e n i n b r a c k e t s . The r e g r e s s i o n l i n e 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 the l i n e o f i s o t o n i c i t y ; nor d i d any of t h e i n d i v i d u a l d a t a means d i f f e r s i g n i f i c a n t l y from i s o t o n i c i t y as determined by t - t e s t s . F o r t h e s t a t -i s t i c a l computations i t was assumed t h a t the same v a r i a t i o n was i n h e r e n t i n both l i n e s . R e g r e s s i o n L i n e : Y = 1.94 x 0.87X L i n e o f I s o t o n i c i t y : Y = 0.00 + 1.00X Standard E r r o r s a ( l . O l ) b(0.06) SALINITY OF MEDIUM (%o) 1 4 7 Khlebovich (1969) fu r t h e r develops Beadle's (1959) argument whereby 5%o i s postulated as a boundary f o r l i f e . Below 5%o he beli e v e s an animal must be able to regulate i t s i n t e r n a l esmotic pressure to survive. Assuming s a l i n i t y i s the only l i m i t i n g f a c t o r Thais lamellosa could enlarge i t s d i s t r i b u t i o n by improving i t s tolerance of s a l i n i t i e s between 6%o and 12%o; f o r although the lowest s a l i n i t y recorded at Brockton Point was 15%o, i n the laboratory experiment in Section 1, s i g n i f i c a n t m o r t a l i t y d i d not occur u n t i l 12%o (23% - 80% m o r t a l i t y within twenty four days, depending on temperature). The r e s u l t s of f i e l d studies c a r r i e d out at Spanish Banks, i n which the animals endured extremely low s a l i n i t y con-d i t i o n s f o r a l i m i t e d period of time, suggest that the s n a i l s may be i n the process of extending t h e i r s a l i n i t y tolerance range below 12%o. Freshwater molluscs, and the few euryhaline i n d i v i d u a l s which can l i v e i n f r e s h water, maintain a minimum i n t e r n a l s a l i n i t y of approximately 2%o - 3%o (Robertson, 1964; p. 295 table with o r i g i n a l authors). Above t h i s l e v e l most osmoconform, although a few l i k e Theodoxus f l u v i a t i s r e t a i n s l i g h t l y hyper-osmotic blood values (Neumann, 1960). The remarkable aspect of osmotic r e g u l a t i o n i n t h i s group of animals i s the extremely small i n t e r n a l osmotic pressure at which the c e l l s can s t i l l f u n c t i o n properly. Although Khlebovich and Beadle mention the exception of freshwater molluscans, no attempt i s made to explain how some i n d i v i d u a l s manage to l i v e at lower s a l i n i t i e s without r e g u l a t i o n of i n t e r n a l osmotic pressure. U n t i l i t i s understood how these molluscs can survive such conditions, i t 148 i s impossible to know whether 5%o would be a boundary to Thais lamellosa. 149 A STUDY OF VOLUME-REGULATION Introduction Although Thais lamellosa lacks the a b i l i t y to regulate i t s internal osmotic pressure, i t i s euryhaline, inhabiting regions varying in s a l i n i t y from 15%o to f u l l sea water. The species, therefore, must exercise some degree of volume-regulation (Schliepper, 1964). This was investigated by using the relationship between s a l i n i t y and the proportion of body water of adult snails described in Section II (Fig. 19), and the corresponding body densities which were determined according to the method described by Staaland (1970), involving measurement of wet weight and buoyancy of the snails. In both experiments the gonads were removed and analyzed separately as their chemical composition varies between sexes and through-out the year (Lambert, 1970). Methods and Materials Forty large snails were collected from Brockton Point in mid-December 1970 and acclimated to 27.3%o, 20.4%o, 15.0%o, or I2.0%o for twenty six days. During this time they were kept in plastic basins outside to maintain the temperature and li g h t regimes to which they had been accustomed in the f i e l d . When the temperature dropped below freezing, they were transferred to a refrigerator (6°C) and held in 500 ml jars. The snails were not fed as they normally eat very l i t t l e during the winter months (Fig. 10). At the end of the acclimation period the wet weight and buoyancy of the body w e r e determined. Buoyancy i s the weight of the animal when 150 submerged i n d i s t i l l e d water. To prevent changes i n the body water content, established under d i f f e r e n t s a l i n i t y conditions, the s n a i l s were weighed i n a sample of water from the con-t a i n e r i n which they were kept. This value had to be corrected f o r the density of the water sample before the body d e n s i t i e s of the s n a i l s could be c a l c u l a t e d . Equations f o r Body Density Where: V o W(a) - W(w) - V(D(w) - 1.0) V a volume v " W(a) - W(w) W(a) = weight of D(w) body i n a i r D(b) = W(a) W(w) = weight of V body i n water D<*>) - W(a) D(w) W(a) - W(w) D(w) = density of water sample D(b) = density of body Results Animals i n the 12%o group were discarded due to a t e c h n i c a l e r r o r . The d i f f e r e n c e i n water content of the winter males and females was r e f l e c t e d i n the d e n s i t i e s of the sexes, s p e c i f i c g r a v i t y of the females being greater than that of the males at low s a l i n i t i e s ( F i g . 21). However, by about 25%o, the d i f f e r e n c e was no longer s i g n i f i c a n t . The 3 grams of water/cm were c a l c u l a t e d using the density and pro-portion of body water data presented i n Section I I (p. 113) The r e s u l t s are compared with the l i n e s of 0% and 100% volume-r e g u l a t i o n i n F i g . 22. Males show a l e s s e r capacity to cope with volumetric changes than females; the r a t i o s of "the d i f f e r e n c e between the experimental and 0% standard" to 151 Figure 21 Relationship between decreasing s a l i n i t y and body density of males and females. T-tests i n d i c a t e d that the l i n e s were s i g n i f i c a n t l y d i f f e r e n t at low s a l i n i t i e s . Means - 1 standard e r r o r are p l o t t e d with the sample s i z e i n brackets. Regression Line f o r Females: Density = 1.0418 + 0.0017 Standard Errors a(0.0058) bC0.0003) 152 F i g u r e 22 A l t e r a t i o n s i n the water c o n t e n t o f wet t i s s u e w i t h changes i n s a l i n i t y . The e x p e r i m e n t a l l i n e s f o r males and females were p l o t t e d from d a t a i n F i g u r e s 19 and 21. The t h e o r e t i c a l l i n e was de-r i v e d from a s i m i l a r c a l c u l a t i o n f o r M y t i l u s e d u l i s a d ductor muscle t i s s u e (Lange and Mostad, 1967), and the d a t a f o r the osmometer were taken from S t a a l a n d (1970). i The r e g u l a t i o n r a t i o s ( d e f i n e d i n t e x t ) f o r : Females = 0.48 Males o 0.38 0.0 0.2 OA 0.6 0.8 1.0 0 7 14 21 28 35" OSMOLARITY (OSM) SALINITY (%o) 153 "the d i f f e r e n c e between the two standards" are .38 and .48 r e s p e c t i v e l y . Discussion 1. V a r i a t i o n i n Body Density Between Sexes As body f a t holds e s s e n t i a l l y no water, the amount of body water i n d i f f e r e n t i n d i v i d u a l s i s t r u l y comparable only on the basis of the lean body weight, and when density i s used i n conjuntion with proportion of body water to estimate changes under s a l i n i t y s t r e s s , t h i s must be taken in t o account. I t was impossible to remove f a t before measuring these a n i -mals; so the assumption was made that the proportion of the body composed of f a t was equal i n a l l i n d i v i d u a l s . As t h i s assumption may not be s t r i c t l y t r u e, v a r i a t i o n i n density and water content may occur within samples. Furthermore, i f the body composition and metabolism at d i f f e r e n t s a l i n i t i e s d i f f e r e d g r e a t l y between males and females i n t h i s regard, the greater density of the l a t t e r might be explained on t h i s b a s i s . 2. Volume-Regulation Lange and Mostad's (1967) proposed model of volume-r e g u l a t i o n supposed that the water content of c e l l s changes i n accordance with two f a c t o r s : (a) the density of the c e l l s decreases as s a l i n i t y decreases (Lange, 1964); and (b) incomplete volume-regulation permits water accumulation as s a l i n i t y de-creases. To eliminate the confounding e f f e c t s of density changes on accumulation of water due to incomplete r e g u l a t i o n the absolute change i n water content of the c e l l i s determined 3 by c a l c u l a t i n g the "grams of water/cm of wet t i s s u e " and i s compared with a t h e o r e t i c a l l y derived value f o r 100%o volume-154 r e g u l a t i o n . 3 grams water/cm = t i s s u e density x proportion body water 3 3 e.g. 20%o female: grams water/cm = 1.0758 grams/cm x .742 = 0.8011 The authors determined t h i s value experimentally f o r Mytilus  e d u l i s adductor muscle t i s s u e and compared t h e i r r e s u l t s with the l i n e of 100% volume-regulation which they had c a l c u l a t e d p r e v i o u s l y . Although they knew the concentrations of the osmotically a c t i v e constituents of the i n t r a c e l l u l a r f l u i d , they d i d not know the composition of the f l u i d excreted by the c e l l during r e g u l a t i o n , and thus the volume vacated by solute p a r t i c l e s to be replaced with water. They assumed the two f l u i d s were i d e n t i c a l . Knowledge of the volume and weight of i n d i v i d u a l types of solute l o s t during r e g u l a t i o n enable c a l c u l a t i o n of both the volume replaced by water and the new d e n s i t y . The predicted r e l a t i o n s h i p d i f f e r s s l i g h t l y from the e m p i r i c a l suggesting a lack of complete r e g u l a t i o n . As mentioned previously, Staaland (1970) takes the estimation of an animal's capacity to volume-regulate one step f u r t h e r by comparing the experimental r e l a t i o n s h i p with two standards so obtaining a measure of the degree of volume-regulation. He studied volume changes i n the gastropod Buccinum undatum. Since the necessary information on solute concentration changes with s a l i n i t y and p a r t i a l molar volumes of the various solutes were unavailable, he used the same data as the above authors to obtain the t h e o r e t i c a l l i n e of 100%o volume-r e g u l a t i o n . By assuming that Thais lamellosa a l s o operates with the same r e l a t i v e composition of osmotically a c t i v e 155 constituents as Mytilus e d u l i s , a s i m i l a r t h e o r e t i c a l l i n e was c a l c u l a t e d . The experimental data f o r winter females and winter males were compared with the l i n e s of 100% and 0% volume-regulation. This method was also applied to Buccinum  undatum (Staaland, 1970; data a l t e r e d to c a l c u l a t i o n on whole body) and Mytilus e d u l i s (Lange and Mostad, 1967; adductor muscle). Buccinum undatum normally l i v e s at 20%o and above, dying experimentally at l l % c (Staaland, 1970); Thais lamellosa i s known to l i v e i n s a l i n i t i e s down to 15%o and die e x p e r i -mentally by 9%o; Mytilus e d u l i s survives well down to 4%o -5%0 (Segerstrale, 1957). The r e g u l a t i o n r a t i o s of these species are .31, .38 (males), .48 (females), and .62 respect-i v e l y . Although these are i n order with known s a l i n i t y d i s t r i b u t i o n s and tolerances of the species, the d i f f e r e n c e s are not r e l a t e d to t h e i r degree of e u r y h a l i n i t y . This discrepancy may be due to the f a c t that the former two were determined f o r the whole body and the l a t t e r f o r a s p e c i f i c t i s s u e . Under these circumstances the volume of e x t r a -c e l l u l a r f l u i d and proportion of f a t t y t i s s u e included i n the samples may d i f f e r g r e a t l y between the t i s s u e s studied. E x t r a c e l l u l a r f l u i d i s extremely v a r i a b l e though there are some i n d i c a t i o n s that i t may decrease with descending s a l i n i t y (Staaland, 1970; Weber and Dehnel, 1966). There i s no evidence of body weight changes with s a l i n i t y i n Thais lamellosa (Table XLIV). Assuming these two f a c t o r s are constant, i n -3 creases i n water content/cm with decreases i n s a l i n i t y are 3 r e a l l y increases on a b a s i s of l e s s than a cm . In t h i s way accumulation of water due to incomplete volume-regulation may 156 be only p a r t i a l l y observed. Correction of the r e g u l a t i o n r a t i o s f o r these two conditions would produce a greater de-crease i n the f i r s t three values (based on the whole body) than i n the l a t t e r (based on a s p e c i f i c t i s s u e ) as they contain more f a t and e x t r a c e l l u l a r f l u i d per u n i t of volume. Before a s e r i e s of r a t i o s , as given above, can be constructed to determine the s e n s i t i v i t y of the r e l a t i o n s h i p between the degree of volume-regulation and extent of e u r y h a l i n i t y , a l l measurements must be expressed on the bas i s of f a t f r e e t i s s u e s from which the volume of e x t r a c e l l u l a r f l u i d has been subtracted. Staaland's (1970) data were corrected f o r e x t r a -c e l l u l a r f l u i d , but no mention of f a t content has been made by e i t h e r him or Lange and Mostad (1967). Later Lange (1969) compared the r e l a t i o n s h i p between volume-regulation and s a l -i n i t y tolerance f o r several species of b i v a l v e s (muscle t i s s u e ) . Although he found that the more euryhaline species were b e t t e r able to regulate t h e i r volumes, i t was not c l e a r whether animals with j u s t s l i g h t l y d i f f e r e n t degrees of volume-r e g u l a t i o n also have detectable d i f f e r e n c e s i n s a l i n i t y t o l e r -ance. Again he made no mention of co r r e c t i o n s f o r e x t r a -c e l l u l a r f l u i d or f a t content. Volume-regulation i s associated with r e g u l a t i o n of the number of moles of i n t r a c e l l u l a r s o l u t e s . Together they c o n s t i t u t e isosmotic i n t r a c e l l u l a r r e g u l a t i o n as introduced by Duchateau and F l o r k i n (1956). Unlike the i n t e r s t i t i a l f l u i d between the c e l l s whose solutes are mainly inorganic ions, the osmotically a c t i v e p a r t i c l e s of the i n t r a c e l l u l a r f l u i d include a large pool (approximately 50%, Mytilus e d u l i s muscle t i s s u e ) 157 of small organic molecules, e s p e c i a l l y amino acids and taurine ( F l o r k i n , 1962; Bricteux-Gregoire, e_t a l . , 1964). The concen-t r a t i o n s of the d i f f e r e n t organic compounds are a l t e r e d by s a l i n i t y changes; that i s , some may increase while others decrease (Virkar and Webb, 1970; Lynch and Wood, 1966). However, the t o t a l osmotic e f f e c t of the organic component usually v a r i e s l i n e a r l y with s a l i n i t y (Lange, 1963, 1964; Lynch and Wood, 1966; Stephens and V i r k e r , 1966; V i r k e r and Wood, 1970). In t h i s way the pool acts as a b u f f e r dampening the f l u c t u a t i o n i n concentration of inorganic ions as s a l i n i t y changes. Therefore, both of the processes involved i n i s o -smotic i n t r a c e l l u l a r r e g u l a t i o n a i d the organism to cope with osmotic changes. Both stenohaline and euryhaline species demonstrated an a b i l i t y to volume-regulate, the l a t t e r being more adept than the former (Lange, 1968 a ) . That i s , isosmotic i n t r a c e l l u l a r r e g u l a t i o n i s not possessed by a species on an a l l or nothing b a s i s , but i s a process which can be f u r t h e r developed through e v o l u t i o n . Improvements w i l l be better selected f o r i n species subjected to s a l i n i t y s t r e s s over much of t h e i r d i s t r i b u t i o n . Thais lamellosa i s such a species. Therefore, the present a b i l i t y of some populations could be a state i n a t r a n s i t i o n towards greater s a l i n i t y tolerance and a more extended d i s t r i b u t i o n , i f s a l i n i t y i s the major l i m i t i n g f a c t o r , as i t appears to be i n the v i c i n i t y of Vancouver. 158 OXYGEN CONSUMPTION Introduction Animals require several days to readjust t h e i r v o l -umes; a f t e r osmotic shock. The echinoderm, Stronqylocentrotus  droebachiensis (Lange, 1964) required eight days f o r recovery and the molluscs, Mya arenaria (DuPaul and Webb, 1970) and Buccinum undatum, (Staaland, 1970), two or three. S a l i n i t y changes also e f f e c t the ra t e of oxygen consumption. Generally i n osmoregulating animals metabolic r a t e increases, and i n osmoconforming species, i t decreases during osmotic s t r e s s ( G h i r e t t i , 1964). Some researchers have reported lowered metabolic rates f o r broadly euryhaline species, such as Mytilus e d u l i s , before the animals were near the edge of t h e i r s a l i n i t y range (Bouxin, 1931; Lagerspetz et a l . , 1959). However Schlieper (1955) showed that g i l l t i s s u e of Mytilus  e d u l i s required several weeks to completely adjust to a new s a l i n i t y regime. Therefore oxygen consumption r a t e s immediately a f t e r volume-regulation but before r e s p i r a t o r y adjustment can be used to i n d i c a t e the degree of st r e s s s a l i n i t y exerts on the organism. Assuming Thais lamellosa a l s o needs only two to three days f o r volume-regulation, oxygen measurements made three to fourteen days a f t e r osmotic shock should delineate the r e l a t i o n s h i p between s a l i n i t y changes and osmotic s t r e s s on the animals. Methods and Materials The experimental procedure used f o r measuring oxygen consumption i s described i n Hoar (1967). The Winkler method 159 f o r determining water oxygen content was taken from S t r i c k l a n d and Parson's (1968) book on sea water a n a l y s i s . Water samples of the c o r r e c t s a l i n i t i e s were prepared before the experiment and f i l t e r e d through plankton n e t t i n g to eliminate other sources of oxygen consumption. They were cooled to 10°C; the waiting period allowed the water to reach an oxygen equi-l i b r i u m so no bubbles of gas were present. Large and small s n a i l s were placed i n each s a l i n i t y , t i e d i n i n d i v i d u a l p l a s t i c f l y s c r e e n bags. This eliminated d i f f e r e n c e s i n meta-b o l i c r a t e due to movement but allowed the s n a i l to extend i t s foot and to c i r c u l a t e water through the mantle c a v i t y (Fig.23). Each s n a i l was slipped i n t o a p i n t j a r which was then c a r e f u l l y sealed, e l i m i n a t i n g a l l a i r bubbles. The j a r s , i n c l u d i n g a blank (a j a r of water with no s n a i l present), were covered v/ith black p l a s t i c to prevent a l g a l photosynthesis. Oxygen consumption i s ge n e r a l l y expressed on a weight b a s i s . To prevent s a c r i f i c i n g the large number of animals involved(they were returned to the beach a f t e r the experiment), a sample of ten large and ten small s n a i l s were cracked open, removed from t h e i r s h e l l s and d r i e d to constant weight i n an oven (97°C). Oxygen consumption was determined on a dry weight rather than a wet weight basis because the water content of the c e l l s v a r i e d with s a l i n i t y ; that i s , the weight of an i n d i v i d u a l would p a r t i a l l y depend on i t s environmental c o n d i t -ions, and therefore the r e s p i r a t o r y r a t e on a wet weight basis would not be comparable. The average dry weight of small s n a i l s was 0.077 g (S.E. = -0.006) and of large 0.622 g S.E. = - 0.048). Knowing the average gram dry weight, the oxygen content 160 Figure 23 Diagram of a s n a i l prepared f o r determination of i t s r a t e of oxygen consumption. KNOT OF NYLON F I S H I N G L I N E S N A I L F LYSCREEN BAG 161 o f t h e e x p e r i m e n t a l water and bl a n k (both i n i t i a l l y and f i n a l l y ) , t h e volumes o f t h e p i n t j a r s used, and t h e time a l l o w e d f o r oxygen d e p l e t i o n , t h e mg oxygen consumed/g d r y weight/day was c a l c u l a t e d as f o l l o w s : 24 x T i t r e ^ - 24, x Titr e f c X AVO!^ X 0.1017 x 16 x A V o l 4 t e A t b AVolb 6 , where: At a time o f O2 consumption A v o l « volume o f j a r b: r e f e r s t o b l a n k e: r e f e r s t o experiment animal c o n s t a n t 0.1017 i s determined e x p e r i m e n t a l l y f o r r e a g e n t s In A p r i l 1970, f i f t y s m a l l (2.00 cm - 2.50 cm s h e l l l e n g t h ) and f i f t y l a r g e (4.00 cm - 4.50 cm s h e l l l e n g t h ) T h a i s  l a m e l l o s a were c o l l e c t e d from the f o r e s h o r e o f S t a n l e y Park j u s t west o f Brock t o n P o i n t . Groups o f e i g h t a n i m a l s were h e l d i n 500 ml o f water (changed d a i l y ) and a l l o w e d t o a c c l i m -a t e t o the s a l i n i t i e s 20%o, 18%o, 16%0, 14%0, 12%o, and 10%o f o r t h r e e t o f o u r t e e n d a y s . The temperature was m a i n t a i n e d at t h e c u r r e n t f i e l d v a l u e (10°C). Animals were a l s o o b t a i n e d a t t h e end o f A p r i l and m i d d l e o f May t o e n l a r g e t h e sample s i z e s . In a l l 145 s n a i l s were t e s t e d . As e n v i r o n m e n t a l s a l i n i t y and temperature had remained e s s e n t i a l l y c o n s t a n t over the sampling p e r i o d , the an i m a l s were assumed comparable. The l a r g e s n a i l s a t 20%o, 18%o, and 16%o and the s m a l l a t 20%o were removed from t h e experiment a t a p p r o x i m a t e l y p l u s 5 h o u r s . I f l e f t l o n g e r t h e y d e p l e t e d the oxygen s u p p l y d r a s t i c a l l y ; f o r example, o n l y 40% o f the oxygen remained a f t e r 22 h o u r s . In the o t h e r t r e a t m e n t s oxygen consumption was term-i n a t e d between 20 and 22 h o u r s . 162 Results Between 20%o and 16%o the r e s p i r a t o r y rate of adults dropped gradually, and again between 14%o and 10%o (Fig.24). However, i n the two %o between 16%O and 14%o i t f e l l abruptly. For the small s n a i l s , the r e l a t i o n s h i p was not s t r i c t l y l i n e a r , nor that shown by the adults; but appeared to plateau i n the area 14%o to 16%O. The r e s p i r a t o r y r ates of the young s n a i l s were 3 to 7 times greater than those of the a d u l t s . Discussion Oxygen consumption has been shown to vary with s a l i n -i t y , s i z e , sex, oxygen tension, temperature, season of the year, the previous p h y s i o l o g i c a l state and acclimation of the animal, and the time of day i n molluscs (Berg et al,., 1958; Newell and Pye, 1970 a & b; Van Winkle, 1968; Vernberg et a l . , 1963; Sandeem et a l . , 1953). In a d d i t i o n , photoperiod i n -fluenced the r e s p i r a t o r y rate of two i n t e r t i d a l crabs, Hemigrapsus nudus and Hemigrapsus oregonensis (Dehnel, 1958). Although no e f f e c t of photoperiod, per se, has yet been demon-str a t e d i n molluscs, i t may have been included i n seasonal trends. Of the i n f l u e n c i n g f a c t o r s , s i z e and s a l i n i t y were v a r i e d , sex and s t a r v a t i o n were not important ( S t i c k l e and Duerr, 1970) and oxygen tensions were maintained at high l e v e l s (near s a t u r a t i o n ) . A l l animals were c o l l e c t e d within a one month period at the end of the breeding season. No a c t i v e l y reproducing i n d i v i d u a l s were taken. During t h i s time temper-ature and s a l i n i t y had remained constant though photoperiod had changed s l i g h t l y . Therefore, a l l animals came from essen-t i a l l y the same season and i n i t i a l p h y s i o l o g i c a l s t a t e . Ocean 163 Figure 24 E f f e c t of decrease i n s a l i n i t y on the oxygen con-sumption of large and small s n a i l s . Animals were e q u i l i b r a t e d to the s a l i n i t y conditions f o r 3 - 1 4 days at 10°C. V e r t i c a l l i n e s represent - 1 standard erro r ; sample s i z e i s given i n brackets. I SALINITY (%o) 164 and experimental temperatures were i d e n t i c a l , 10°C. Metabolic rates were determined over the same period of every day - from noon to approximately 10:00 a.m. the next morning, except f o r the four groups on a f i v e hour time l i m i t . These were tested i n the afternoon and evening. Thus d i u r n a l rhythms were not completely c o n t r o l l e d and could account f o r some of the i n -creased v a r i a b i l i t y at high s a l i n i t i e s . In conclusion, s a l i n i t y and s i z e e f f e c t s have not been confounded by other f a c t o r s i n f l u e n c i n g oxygen consumption with the exception of d i u r n a l rhythms at higher s a l i n i t i e s . Osmotic s t r e s s a f f e c t s both mature and immature s n a i l s s i m i l a r l y i n that oxygen consumption was decreased under con-d i t i o n s of reduced s a l i n i t y . In s p i t e of the i r r e g u l a r i t y of response i n young s n a i l s , Figure 22 i n d i c a t e s that r e s p i r -a t i o n f a l l s sharply at one point to a minimal l e v e l . In the case of the adults t h i s point l i e s between 14%o and 16%O, and of the young, between 12%o and 14%o. The e f f e c t of age, immature being more t o l e r a n t than mature s n a i l s of conditions of low s a l i n i t y i s i n agreement with the work of Kinne (1960, 1964), Broekhuysen (1936) and Keys (1931), and the r e s u l t s from the laboratory experiment discussed previously i n Section I I . The points of major stress agree with the s a l i n i t y tolerance l i m i t s defined at that time. At 15%o the animals were able, to nearly as well as those at 20%o except with regard to feeding rate s ; however, below t h i s l e v e l the a b i l i t i e s of the s n a i l s were much impaired. Exactly how d i f f e r e n c e s i n osmotic pressure a l t e r the oxygen consumption of osmoconformers i s not known. Many 165 organisms, l i k e Thais lamellosa, attempt to decrease t h e i r body-water contact under osmotic stres s by secreting mucous (Kinne, 1964). This occurs only at extremes of s a l i n i t y tolerance and could not po s s i b l y account f o r the immediate reduction i n r e s p i r a t o r y r a t e observed i n both young and o l d s n a i l s . The f a c t that changes i n s a l i n i t y g e n e r a l l y r e s u l t i n a decreased oxygen consumption i n osmoconformers, but not i n osmoregulators i n d i c a t e s that the e f f e c t i s operating at the c e l l u l a r l e v e l . The increase i n c e l l volume may a l t e r the i n t r a c e l l u l a r geometry and thus e f f e c t c e l l u l a r functions (Lange, 1968 a ) . Changes i n the concentration of inorganic ions may a f f e c t the a c t i v i t y of enzymes which i n turn would a l t e r the e f f i c i e n c y of metabolism (Lange, 1968 a ) . Therefore, organisms may produce a s e r i e s of isoenzymes each e s p e c i a l l y adapted f o r a p a r t i c u l a r range of osmotic conditions; t h i s development has been found by Somero and Hochachka (1969) f o r l a c t a t e dehydrogenase with regard to temperature changes. A f a l l i n r e s p i r a t o r y r a t e could also be explained i f these changes a l t e r e d the rate of c i l i a r y beat, which i s responsible f o r water and thus oxygen flow through the mantle c a v i t y . Vernberg e_t al_. (1963) showed that i n the case of Crassostrea  v i r q i n i c a . Modiolus modiolus, and Aequipecten i r r a d e n s i s c i l i a r y a c t i v i t y decreased i n the region of minimal s a l i n i t y tolerance a f t e r e q u i l i b r a t i o n f o r 24 hours. I t i s p o s s i b l e that decrease i n c i l i a r y f u n c t i o n i s responsible f o r the sudden drop i n oxygen consumption near the edge of s a l i n i t y tolerance. In a l l p r o b a b i l i t y , p h y s i o l o g i c a l a l t e r a t i o n s are required i n a l l instances of osmotic shock, which would account 166 f o r a gradual decrease i n r e s p i r a t o r y r a t e about optimal s a l i n i t y conditions ( i . e . those to which the organism i s com-p l e t e l y acclimated), but the marked decrease i n oxygen consumption observed near the lower edge of s a l i n i t y t o l e r -ance most l i k e l y involves major p h y s i o l o g i c a l disturbances which may decrease c i l i a r y a c t i v i t y . Conservation of energy under conditions of low s a l i n i t y appears to be imposed by a reduced capacity to r e s p i r e rather than to have evolved as a strategy to survive unfavourable con-d i t i o n s . Considering the p h y s i o l o g i c a l adjustments to reduced s a l i n i t y on the parts of both the isosmotic i n t r a c e l l u l a r reg-u l a t i o n and the r e s p i r a t o r y systems, a l t e r a t i o n s i n s a l i n i t y tolerance are quite complicated and evolutionary changes un-doubtedly require a r e l a t i v e l y long time. Although Thais. lamellosa i s often exposed to s a l i n i t y b a r r i e r s along the coast of B r i t i s h Columbia, they have only inhabited t h i s area f o r approx-imately the l a s t 8,000 years; that i s since the l a s t i c e age (Kincaid, 1957). This time may be too short to f i n d large evolutionary changes i n s a l i n i t y tolerance of l o c a l populations. 167 GENERAL DISCUSSION DISTRIBUTION AND LOW SALINITY TOLERANCE The g e o l o g i c a l f o r m a t i o n o f the shore o f S t a n l e y Park i s f o r the most p a r t s u i t a b l e f o r h a b i t a t i o n by T h a i s l a m e l l o s a . By a p p l y i n g knowledge o f s a l i n i t y t o l e r a n c e l i m i t s d e l i n e a t e d i n t he f o r e g o i n g e x p e r i m e n t s , a p r e d i c t i o n can be made r e g a r d -i n g t h e expected d i s t r i b u t i o n o f the s p e c i e s w i t h i n t h i s a r e a . Ferguson P o i n t , b e i n g w e l l w i t h i n the s o u t h e r n h a l f o f Vancouver Harbour, e x p e r i e n c e s v e r y s i m i l a r s a l i n i t y c o n d i t i o n s t o Spanish Banks. In the s p r i n g o f 1969 a l l e x p e r i m e n t a l a n i m a l s t r a n s -f e r r e d t o Spanish Banks succumbed d u r i n g the p e r i o d o f extreme-l y low s a l i n i t y a s s o c i a t e d w i t h t h e s p r i n g r u n o f f o f the F r a s e r R i v e r . Records on the volume o f water d i s c h a r g e d from the r i v e r i n d i c a t e t h a t t h e flume d u r i n g t h i s p a r t i c u l a r s p r i n g was l e s s e x t e n s i v e than u s u a l , and c o n s e q u e n t l y ' c o n d i t i o n s would r a r e l y be f a v o u r a b l e enough t o p e r m i t s u r v i v a l o f the s n a i l s i n t h e s e r e g i o n s . The s a l i n i t y c o n d i t i o n s a t Broc k t o n P o i n t a re w e l l w i t h i n the t o l e r a n c e s o f the a n i m a l s . S i n c e water c u r r e n t s f l o w p a r a l l e l t o the shore from P r o s p e c t P o i n t t o Brockton P o i n t ( T i d a l P u b l i c a t i o n No. 22, Canadian Hydro-g r a p h i c S e r v i c e ) , t h i s e n t i r e r e g i o n s h o u l d e x p e r i e n c e s i m i l a r s a l i n i t y f l u c t u a t i o n s . T h e r e f o r e the l i m i t o f d i s t r i b u t i o n , as d e f i n e d by s a l i n i t y t o l e r a n c e , should f a l l between P r o s p e c t P o i n t and Ferguson P o i n t . S e v e r a l c e n s i taken i n the s p r i n g and summer o f 1970 p l a c e the l i m i t o f d i s t r i b u t i o n w i t h i n t h i s 168 region, approximately h a l f way between Prospect Point and Siwash Rock (Fig.3). Although d i s t r i b u t i o n c o r r e l a t e s with changes i n s a l i n i t y conditions, i t may not be terminated d i r e c t l y by t h i s p h y s i c a l f a c t o r . The weakening of the animal under s t r e s s may reduce i t s e f f e c t i v e n e s s as a competitor or i n escaping predators. One of the p r i n c i p a l competitors and predators of the s n a i l , which i s present i n t h i s region, i s the s t a r f i s h P i s a s t e r ochraceous. I f competition f o r food were more severe here than i n other sections of the beach, the s n a i l s should be dwarfed and food should be scarce. However food was p l e n t i f u l and the animals were of a normal siz e as gauged by i n s p e c t i o n . Whether the s t a r f i s h i s eating the s n a i l s more r e a d i l y than at other l o c a t i o n s i s not known; however, fu r t h e r evidence points to a ph y s i c a l rather than a b i o l o g i c a l l i m i t a t i o n of the species. The censi conducted along t h i s p ortion of the coast documented three important points:, (1) a l l s n a i l s were located below the 2.5' t i d a l l e v e l , (2) the number of s n a i l s recorded decreased during June, the month of minimal s a l i n i t y conditions, and (3) with one exception a l l of the animals were ad u l t s . The f i e l d studies at Spanish Banks suggested that the s n a i l s were capable of detecting s a l i n i t y changes and moving i n the d i r e c t i o n of more favourable c o n d i t i o n s . Both the low i n t e r -t i d a l l o c a t i o n as compared with s n a i l s at Brockton Point and L i l l y Point, and the decrease i n numbers i n the i n t e r t i d a l region i n June support t h i s hypothesis as well as i n f e r that low s a l i n i t y conditions bear d i r e c t l y on s u r v i v a l at the l i m i t of d i s t r i b u t i o n . The presence of only adults i n t h i s region 169 might imply that they are migrants from other populations e i t h e r f u r t h e r north along the coast or s u b t i d a l l y , and that the i n t e r -t i d a l i t s e l f may not be able to support a population. Unfortunately the comparison of a high and low s a l -i n i t y population appears to be a comparison of two low s a l i n i t y populations. The question s t i l l remains whether genetic t r a i t s endowing an equal degree of low s a l i n i t y tolerance are present i n populations not experiencing such c o n d i t i o n s . In part t h i s w i l l depend both on the previous h i s t o r y of the animals and the length of time such information i s retained by the species, and i n part on the r a p i d i t y of evolutionary changes i n s a l i n i t y tolerance. The l i t e r a t u r e on acclimation and isosmotic i n t r a c e l l u l a r r e g u l a t i o n suggests that adjustments of the body and i t s functions f o r volume and ion concentration changes i s quite complex. Acclimation times f o r b o d i l y functions, such as r e s p i r a t i o n , attachment and normal patterns of movement, often require several weeks. Chance improve-ment on the best genetic combination f o r low s a l i n i t y tolerance within the species may well require a long period of time, although e x a c t l y how long i s not known. At the present time, Thais lamellosa from populations exposed to low s a l i n i t y conditions can withstand f l u c t u a t i o n s below 10%o f o r a l i m i t e d time i f acclimated gradually. Sur-v i v a l of reduced s a l i n i t y conditions i s better when they are i n a s s o c i a t i o n with low temperatures; although, i n the f i e l d low s a l i n i t i e s and high temperatures occur simultaneously. In one sense t h i s i s fortunate because the consequent period of i n a c t -i v i t y does not i n t e r f e r e with normal feeding or reproductive patterns. As noted previously, feeding rates at Brockton 170 P o i n t and L i l l y P o i n t d e c r e a s e d a t t h i s time, p o s s i b l y i n r e -sponse t o a d e c l i n e i n m e t a b o l i c e f f i c i e n c y at h i g h temper-a t u r e s . The escape response from such c o n d i t i o n s i s t r i g g e r e d w h i l e the anim a l s a r e s t i l l c a p a b l e o f moving from the a r e a , but presumably a f t e r a r r e s t m e n t o f f e e d i n g a c t i v i t y . I f no escape i s p o s s i b l e the s n a i l s g r a d u a l l y weaken and a l l d i e i f kept below 10%o f o r more than f o r t y days. The d u r a t i o n o f low s a l i n i t y endurance i s p o s s i b l y augmented by a lowered m e t a b o l i c r a t e and consequent c o n s e r v a t i o n o f energy. 171 CHARACTERISTICS OF DOMINANT SPECIES A c c o r d i n g t o McNaughton and Wolf (1970), "dominant s p e c i e s are g e n e r a l i s t s w i t h a d a p t a t i o n s to many more dimensions i n t h e i r n i c h e s , and as a r e s u l t , l e s s f r e q u e n t l y encounter a l i m i t i n g d i mension, or they are s p e c i a l i s t s t h a t have e v o l v e d a d a p t a t i o n s t o a s i n g l e dimension which i s most l i k e l y t o be l i m i t i n g i n the c u r r e n t e n v i r o n m e n t a l a r r a y " . T h a i s l a m e l l o s a i s a dominant s p e c i e s w i t h an e x t e n s i v e d i s t r i b u t i o n . I t i s known f o r i t s g r e a t m o r p h o l o g i c a l d i v e r i s t y ; o r i g i n a l l y the s t a t u s o f many o f the l o c a l r a c e s was i n q u e s t i o n due t o e x t e n -s i v e v a r i a t i o n i n s h e l l form, s i z e and c o l o u r ( K i n c a i d , 1957). As d i s c u s s e d p r e v i o u s l y , polymorphisms, such as t h e s e , can be i n t i m a t e l y r e l a t e d t o o t h e r t r a i t s o f b e h a v i o u r , m e t a b o l i c e f f i c i e n c y and t o l e r a n c e s . T h a i s l a m e l l o s a a l s o e x h i b i t s i n t e r n a l d i v e r s i t y i n t h a t i t t o l e r a t e s a wide range o f b o t h s a l i n i t i e s and temperatures throughout i t s d i s t r i b u t i o n as w e l l as m a i n t a i n i n g e x t e n s i v e v a r i a b i l i t y i n response t o f l u c t u a t i o n s i n p h y s i c a l f a c t o r s w i t h i n each p o p u l a t i o n . F u r t h e r , g e n e t i c d i f f e r -e n t i a t i o n was r e v e a l e d i n experiments where the s n a i l s demon-s t r a t e d an a b i l i t y t o adapt t o d i f f e r e n t s i t u a t i o n s ; i n p a r t i -c u l a r t o d i f f e r e n c e s i n h a b i t a t which demanded r e s t r i c t i o n o f movement a t L i l l y P o i n t . The s n a i l s appear, t h e r e f o r e , t o be g e n e r a l i s t s c a p a b l e o f a d a p t i n g t o a v a r i e t y o f new s i t u a t i o n s , not s p e c i a l i s t s . 172 McN-sughton & Wolf (1970) p r e f e r r e d the h y p o t h e s i s t h a t the dominant s p e c i e s i s a s p e c i a l i s t , on the b a s i s o f e v i d e n c e from C o n n e l l (1961) and Smith (1967) i n which one dimension i s s t u d i e d ; i n the former i n s t a n c e , i n t e r t i d a l h e i g h t and i n the l a t t e r , s a l i n i t y . These i n d i c a t e t h a t the s p e c i e s w i t h t h e b r o a d e r t o l e r a n c e a l o n g t h e s e dimensions a r e t h e more r e s t r i c t e d i n d i s t r i b u t i o n . However, t h e r e i s a l i a b i l i t y i n c l a s s i f y i n g s p e c i e s by a s i n g l e d i m e n s i o n . Balanus b a l a n o i d e s and Chthalamus s t e l l a t u s , d i s c u s s e d i n C o n n e l l ' s (1961) paper a r e both w i d e l y d i s p e r s e d a l o n g the c o a s t s o f Europe. C h t h a l - amus s t e l l a t u s i s a s o u t h e r n s p e c i e s and can w i t h s t a n d d e s i c -c a t i o n and h i g h temperature b e t t e r than Balanus b a l a n o i d e s , w h i l e the l a t t e r can grow f a s t e r a t low t e m p e r a t u r e s . C o n n e l l ' work was c a r r i e d out a t the extreme n o r t h e r n l i m i t o f the d i s -t r i b u t i o n o f Chthalamus s t e l l a t u s (Southward and C r i s p , 1955). N a t u r a l l y Balanus b a l a n o i d e s was the more abundant s p e c i e s . I f the study had been c a r r i e d out a t the extreme so u t h e r n l i m i t o f Balanus b a l a n o i d e s ' d i s t r i b u t i o n I q u e s t i o n whether Chthalamus  s t e l l a t u s would not have been the more abundant animal^and t h e r e f o r e c o n s i d e r e d the dominant s p e c i e s ? Then the dominant s p e c i e s would a l s o be t h e g e n e r a l i s t . Smith's (1967) work wit h c a t t a i l s i n d i c a t e d t h a t the two s p e c i e s Typha l a t i f o l i a and Typh  dominqensis were found i n the same l o c a t i o n s w i t h i n the geo-g r a p h i c range o f the l a t t e r , w i t h the e x c e p t i o n o f e x t r e m e l y s a l i n e s o i l s where Typha l a t i f o l i a was unable t o l i v e . Typha  l a t i f o l i a was the more abundant s p e c i e s , but d i d not have as g r e a t a p h y s i o l o g i c a l t o l e r a n c e o f s a l i n e c o n d i t i o n s . However, i t s g e o g r a p h i c range extended f a r beyond t h a t o f Typha dominqen-s i s ; t h a t i s , i t had a much g r e a t e r p h y s i o l o g i c a l t o l e r a n c e o f 173 d i f f e r e n t c l i m a t i c conditions and i n t h i s sense was both a g e n e r a l i s t and the dominant species. In conclusion, from the example reported here, dominant species are l i k e l y g e n e r a l i s t s able to adapt to a wide v a r i e t y of environmental conditions and e f f e c t i v e l y dominate t h e i r part-i c u l a r niche over a large geographical area. The species as a whole as well as l o c a l races within the species are s p e c i a l i z e d i n some respects, the former, to f a c t o r s present over much of the species range, and the l a t t e r , to f a c t o r s i n t h e i r p a r t i c u l a r h a b i t a t s . In order to respond i n t h i s manner the species must contain a large amount of genetic and phenotypic d i v e r s i t y . Competitors can e x i s t through the presence of refuge zones where i n some one dimension they can outcompete the dominant species. T h i s , however, does not make the dominant species a s p e c i a l i s t . 174 LITERATURE CITED Ahmed, M. and A.K.Sparks. 1970. Note on chromosome number 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 g a s t r o p o d g e n u s , T h a i s i o f the U n i t e d S t a t e s P a c i f i c c o a s t . The V e l i g e r 12: 293-295. Amemiya, I . 1928. 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