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Timothy Alexander Rawlings, 1989 .... b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s. 85 ...... F=0.57, p>0.25), Seppings and Ross Islets snails laid capsules.
FUNCTIONAL MORPHOLOGY OF EGG CAPSULES IN A MARINE

GASTROPOD

NUCELLA EMARGINATA

By Timothy B.Sc. ( H o n s . ) /

Alexander

Rawlings

U n i v e r s i t y o f B r i t i s h Columbia,

THESIS SUBMITTED I N PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (ZOOLOGY)

We a c c e p t t h i s a s c o n f o r m i n g to the required

standard

THE UNIVERSITY OF B R I T I S H COLUMBIA August Timothy

1989

A l e x a n d e r R a w l i n g s , 1989

1986

In

presenting

degree freely

at

of

department publication

partial

fulfilment

University of

British

Columbia, I agree

for

and

the

available

copying

this

this or of

thesis

reference

thesis by

in

for

his

scholarly

or

this thesis

for

her

Z o o l

The University of British C o l u m b i a Vancouver, Canada

DE-6 (2/88)

I further

purposes

representatives.

financial gain

permission.

Department of

study.

of

the

requirements that

agree

may

be

It

is

shall not

that

the

an

advanced

Library shall make

permission for

granted

be

for

by

the

understood

that

allowed

without

head

it

extensive of

my

copying

or

my written

ii ABSTRACT

Egg

c a p s u l e s o f t h e marine whelk N u c e l l a emarqinata

were

examined w i t h r e s p e c t t o i n t r a s p e c i f i c v a r i a t i o n i n c a p s u l e morphology and r e s i s t a n c e t o i n t e r t i d a l Capsules separated weight,

predators.

were c o l l e c t e d from t h r e e i n t e r t i d a l

along a wave-exposure g r a d i e n t .

and p r o t e c t i v e q u a l i t y o f c a p s u l e s

populations

Wall thickness, dry differed

e x t e n s i v e l y among t h e s e p o p u l a t i o n s ; h o w e v e r , t h e s e

capsular

p r o p e r t i e s d i d not r e f l e c t d i f f e r e n c e s i n wave-exposure levels.

Capsule

s i z e was f o u n d

to wave-sheltered s i z e among

shores

and p a r a l l e l e d d i f f e r e n c e s i n s n a i l

sites.

Laboratory

experiments,

p r e d a t o r - e x c l u s i o n cages,

and f i e l d t e s t s i n c o r p o r a t i n g

were u s e d t o d e t e r m i n e

p r e d a t i o n on N u c e l l a e m a r q i n a t a capsule predators. i n t e r t i d a l predators and

t o i n c r e a s e from wave-exposed

isopods,

Capsule such

a t two s t u d y

c a p s u l e s and t o i d e n t i f y

c a s e s were r e g u l a r l y e a t e n by

as shore

Idotea wosnesenskii.

r e s p o n s i b l e f o r opening sites.

the extent of

c r a b s , Hemiqrapsus spp., These i n v e r t e b r a t e s were

a maximum o f 3 2 % o f c a p s u l e s

D e s p i t e d i f f e r e n c e s i n t h i c k n e s s and

s t r e n g t h o f c a p s u l e s among p o p u l a t i o n s , no c a p s u l e s completely

present

r e s i s t a n t t o t h e s e p r e d a t o r s ; however,

were

thick

c a p s u l e w a l l s d i d a p p e a r t o c o n v e y some p r o t e c t i v e a d v a n t a g e . Preliminary laboratory tests indicated that thin-walled c a p s u l e s were p r e f e r e n t i a l l y

opened by I d o t e a

wosnesenskii.

iii TABLE OF CONTENTS Page ABSTRACT

i

TABLE OF CONTENTS

i

L I S T OF TABLES

i

i

i

v i i

L I S T OF FIGURES

viii

ACKNOWLEDGEMENTS

x

GENERAL INTRODUCTION

1

CHAPTER 1. I N T R A S P E C I F I C VARIATION I N CAPSULE MORPHOLOGY INTRODUCTION

3

STUDY S I T E DESCRIPTIONS

7

MATERIALS AND METHODS

12

I. Differences II.

i n s n a i l m o r p h o l o g y among s i t e s . . .

Capsule morphology

12 12

1. R e l a t i o n s h i p b e t w e e n s n a i l capsule s i z e

s i z e and

12

2. M i c r o m o r p h o l o g y o f L . e m a r g i n a t a egg 3.

capsules

15

I n t r a c a p s u l a r v a r i a t i o n i n w a l l t h i c k n e s s 15

4. V a r i a t i o n i n c a p s u l e among p o p u l a t i o n s 5. V a r i a t i o n i n c a p s u l e

wall

thickness

wall

thickness

16

w i t h i n a n d among c l u t c h e s

17

6. V a r i a t i o n i n d r y w e i g h t o f c a p s u l e s

17

I I I . V A R I A T I O N I N CAPSULE CONTENTS AMONG S I T E S . . . 18 1. E g g number a n d v o l u m e 2. Number a n d s i z e o f h a t c h i n g IV.

CAPSULE STRENGTH 1. R e s i s t a n c e

t o puncturing

18 snails

19 19 . 19

iv Page 20

2. R e s i s t a n c e t o s q u e e z i n g RESULTS

22

I . D i f f e r e n c e s i n s n a i l m o r p h o l o g y among s i t e s . . .

22

II.

22

Capsule morphology 1. R e l a t i o n s h i p b e t w e e n s n a i l capsule size

size

and

22

2. M i c r o m o r p h o l o g y o f tL_ e m a r q i n a t a egg c a p s u l e s

27

3.

27

Intracapsular variation i n wall thickness

4. V a r i a t i o n i n c a p s u l e w a l l among p o p u l a t i o n s

thickness 30

5. V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n and among c l u t c h e s l a i d by different snails

33

6. V a r i a t i o n i n d r y w e i g h t o f c a p s u l e s

35

I I I . VARIATION IN CAPSULE CONTENTS AMONG S I T E S . . . 1. Egg

number and v o l u m e

2. Number and

s i z e of hatching s n a i l s

I V . CAPSULE STRENGTH

37 37 39 41

1. R e s i s t a n c e t o p u n c t u r i n g

41

2. R e s i s t a n c e t o s q u e e z i n g

41

DISCUSSION Advantages of t h i c k ,

43 strong capsule w a l l s

43

Intraspecific differences i n capsular structure..

44

E f f e c t s of environmental

47

Tradeoffs i n capsule

structure

E f f e c t s of environmental REFERENCES

s t r e s s e s on e m b r y o s

s t r e s s e s on a d u l t s n a i l s

48 49 51

V Page CHAPTER 2. LABORATORY AND F I E L D TESTS OF PREDATION INTRODUCTION

.

MATERIALS AND METHODS

55 58

I . LABORATORY EXPERIMENTS....

58

II.

59

III.

IV.

F I E L D CENSUSES OF PREDATION 1. G r a p p l e r I n l e t

59

2. R o s s I s l e t s

60

3. S e p p i n g s I s l a n d

61

F I E L D EXPERIMENTS

61

1. G r a p p l e r I n l e t

63

2. R o s s I s l e t s . . . . .

64

S U S C E P T I B I L I T Y OF CAPSULES TO PREDATORS

RESULTS

65 67

I . LABORATORY EXPERIMENTS .

67

II.

73

III.

F I E L D CENSUSES OF PREDATION 1. G r a p p l e r I n l e t

73

2. R o s s I s l e t s

78

3. S e p p i n g s I s l a n d

79

F I E L D PREDATION EXPERIMENTS

80

1. G r a p p l e r I n l e t

80

a) P i l o t e x p e r i m e n t s

IV.

80

• b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s

82

2. R o s s I s l e t s

82

a) P i l o t E x p e r i m e n t s

82

b) P r e d a t o r - e x c l u s i o n e x p e r i m e n t s

85

S U S C E P T I B I L I T Y OF CAPSULES TO PREDATORS

87

vi Page DISCUSSION

89

Resistance of intact capsules t o predators

89

Digestibility

91

and p a l a t a b i l i t y

P r e d a t i o n on e g g c a p s u l e s Susceptibility

of thick-

capsules t o predators REFERENCES GENERAL CONCLUSIONS

of capsule w a l l s . .

i n the f i e l d

92

and t h i n - w a l l e d 94 97 100

vii LIST OF TABLES Page CHAPTER 2 I. II.

III. IV.

Summary o f t h e s p e c i e s t e s t e d f o r p r e d a t o r y a c t i v i t y on N u c e l l a e m a r g i n a t a e g g c a p s u l e s i n t h e l a b o r a t o r y . .

68

D e n s i t y o f N u c e l l a emarginata, t h e i r egg c a p s u l e s , and c a p s u l e p r e d a t o r s a t s t u d y s i t e s i n G r a p p l e r I n l e t and Ross I s l e t s

74

Summary o f e g g c a p s u l e s c e n s u s e d a t G r a p p l e r and Ross I s l e t s t u d y s i t e s

76

Inlet

Summary o f N u c e l l a e m a r g i n a t a e g g c a p s u l e s o p e n e d b y predators i n p i l o t experiments a t Grappler I n l e t , J u n e 1988

81

viii LIST OF FIGURES Page

CHAPTER 1 1.

2. 3. 4. 5.

6.

L o c a t i o n of study s i t e s along the southern s h o r e s o f B a r k l e y Sound on t h e w e s t c o a s t o f V a n c o u v e r I s l a n d , B.C

8

N u c e l l a e m a r g i n a t a egg c a p s u l e , i l l u s t r a t i n g t h e t h r e e measurements t a k e n f o r each c a p s u l e

14

T e c h n i q u e s u s e d t o compare t h e s t r e n g t h o f egg c a p s u l e s

21

Size-frequency histograms from each study s i t e

23

o f 50 s n a i l s

collected

R e l a t i o n s h i p between c a p s u l e body l e n g t h and l e n g t h f o r l a b o r a t o r y l a i d capsules f o r each study s i t e

snail 24

R e l a t i o n s h i p between c a p s u l e - c h a m b e r volume and snail

length for laboratory populations

7.

M i c r o s t r u c t u r e of N u c e l l a emarginata

8.

V a r i a t i o n i n w a l l t h i c k n e s s a l o n g t h e c a p s u l e chamber of f i e l d - c o l l e c t e d N u c e l l a emarginata capsules V a r i a t i o n i n w a l l t h i c k n e s s and c a p s u l e w i d t h w i t h i n one N u c e l l a e m a r g i n a t a c a p s u l e f r o m G r a p p l e r I n l e t . . . .

31

V a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h c a p s u l e body l e n g t h f o r 30 N u c e l l a e m a r g i n a t a c a p s u l e s f r o m e a c h laboratory population

32

11.

V a r i a t i o n i n w a l l t h i c k n e s s w i t h i n and between c l u t c h e s of N u c e l l a emarginata capsules

34

12.

D r y w e i g h t o f empty c a p s u l a r c a s e s as a f u n c t i o n o f c a p s u l e b o d y l e n g t h f o r e a c h l a b o r a t o r y p o p u l a t i o n . . . . 36

13.

R e l a t i o n s h i p b e t w e e n t h e number o f e g g s p e r c a p s u l e . . . 38 and t h e v o l u m e o f t h e c a p s u l e - c h a m b e r f o r S e p p i n g s , Ross I s l e t s , and G r a p p l e r c a p s u l e s .

14.

Mean h a t c h i n g s i z e o f embryos a s a f u n c t i o n o f t h e number o f e m b r y o s c o n t a i n e d w i t h i n e a c h c a p s u l e f o r Seppings, Ross I s l e t s and G r a p p l e r p o p u l a t i o n s

9. 10

egg c a p s u l e s

26 28 29

40

ix

Page CHAPTER 2 1.

P r e d a t o r e x c l u s i o n c a g e s , i l u s t r a t i n g : a) t h e c a g e b a s e a n d d e t a c h a b l e f r a m e , a n d b) t h e f i v e c a g e t y p e s used t o exclude v a r i o u s s i z e - c l a s s e s of predators

62

Mean number o f N u c e l l a e m a r g i n a t a e g g c a p s u l e s r e m a i n i n g i n t a c t a f t e r 5 days exposure t o : a) i s o p o d s , I d o t e a w o s n e s e n s k i i (n = 11) a n d b) t h r e e s i z e - c l a s s e s o f H e m i g r a p s u s n u d u s

69

C h a r a c t e r i s t i c s o f s p e c i e s - s p e c i f i c p r e d a t i o n on N u c e l l a emarginata capsules by: Idotea wosenesenskii H e m i g r a p s u s s p p . , M o p a l i a s p p . , a n d an unknown predator

71

4.

R e s u l t s of the p r e d a t o r - e x c l u s i o n experiments G r a p p l e r I n l e t , J u l y 1988

in

83

5.

R e s u l t s of t h e p r e d a t o r - e x c l u s i o n experiments I s l e t s , S e p t e m b e r 1988

i n Ross

2.

3.

6.

Mean number o f t h e f i r s t f i v e c a p s u l e s o p e n e d b y I d o t e a w o s n e s e n s k i i when g i v e n a c h o i c e o f f e e d i n g on c a p s u l e s f r o m t w o d i f f e r e n t s t u d y s i t e s .

86

88

X ACKNOWLEDGEMENTS

First,

I w o u l d l i k e t o t h a n k my s u p e r v i s o r D r . Thomas

C a r e f o o t f o r h i s a d v i c e and h e l p d u r i n g t h e c o u r s e o f t h i s study.

I w o u l d a l s o l i k e t o t h a n k my c o m m i t t e e

Dr. Jamie Smith and Dr. John G o s l i n e , this project. the

Much c r e d i t

fortheir

input

many h o u r s s h e s p e n t s h o w i n g me how t o d e v e l o p

Lois Hollett

mention

into

i s due a l s o t o G l e n y s G i b s o n f o r

and a l s o f o r h e r m o r a l s u p p o r t d u r i n g t h i s up.

members,

photographs

long-winded

write-

and E l i z a b e t h Carefoot deserve a s p e c i a l

f o r t h e i r help i n producing the figures.

I am a l s o

i n d e b t e d t o D r . J o h n S t e e v e s f o r a l l o w i n g me t o u s e h i s m i c r o s c o p e a n d c a m e r a s y s t e m t o p h o t o g r a p h my c a p s u l e w a l l sections.

Finally,

I would l i k e t o acknowledge

the director

a n d s t a f f o f B a m f i e l d M a r i n e S t a t i o n who made my s t a y a n extremely e n j o y a b l e and rewarding e x p e r i e n c e .

1 GENERAL INTRODUCTION

Marine gastropods e x h i b i t a v a r i e t y o f r e p r o d u c t i v e and developmental patterns in the reproductive

(Webber, 1 9 7 7 ) .

ecology

evolution of internal

o f these

fertilization

Neogastropoda

( G a l l a r d o and Perron,

fertilization

has allowed

reproductive patterns stage,

An i m p o r t a n t

advance

organisms has been t h e i n t h e Meso- a n d 1982).

Internal

f o r t h e d e v e l o p m e n t o f new

associated with a non-pelagic

larval

such as t h e d e p o s i t i o n o f eggs i n t o p r o t e c t i v e

g e l a t i n o u s envelopes o r i n t o e l a b o r a t e egg c a p s u l e s . meso- a n d n e o g a s t r o p o d s e m b r y o s a r e c o n f i n e d w i t h i n egg

capsules

period.

f o r some, i f n o t a l l , o f t h e i r

The a d a p t i v e

I n many benthic

developmental

s i g n i f i c a n c e o f such s t r u c t u r e s i s

g e n e r a l l y t h o u g h t t o be a s s o c i a t e d w i t h a r e d u c t i o n i n t h e development t i m e o f embryos w i t h i n t h e p l a n k t o n and, consequently, (Pechenik, The

a n i n c r e a s e i n t h e s u r v i v o r s h i p o f embryos

1979) .

c o n f i n e m e n t o f embryos w i t h i n b e n t h i c egg c a p s u l e s ,

h o w e v e r , h a s i t s own r i s k s .

Embryos f r e e o f m o r t a l i t y

a s s o c i a t e d w i t h a p l a n k t o n i c e x i s t e n c e a r e exposed t o a v a r i e t y o f new e n v i r o n m e n t a l marine environment. these

Little

stresses within the benthic i s known a b o u t t h e i m p o r t a n c e o f

s t r e s s e s on t h e s u r v i v o r s h i p o f e n c a p s u l a t e d

embryos.

R e c e n t s t u d i e s , h o w e v e r , h a v e shown t h a t t h e w a l l s t r e n g t h o f many n e o g a s t r o p o d e g g c a p s u l e s time o f encapsulated

embryos

i s r e l a t e d t o t h e development (Perron,

1981).

These

results

2 suggest that greater

variation

goals

stresses.

o f t h e p r e s e n t s t u d y w e r e : 1) t o e x a m i n e

i n t h e morphology o f egg c a p s u l e s

of the i n t e r t i d a l

snail Nucella

among

This

emarginata, and

embryos from

predators.

t h e s i s i s d i v i d e d i n t o two c h a p t e r s .

presents

d a t a on t h e m o r p h o l o g y o f N u c e l l a

capsules

c o l l e c t e d from t h r e e

gradient.

Differences

s i t e s along

i n egg c a p s u l e

Chapter 1

emarginata egg a wave-exposure

wall thickness are

e x a m i n e d w i t h i n a n d among s i t e s a n d c o r r e l a t e d measurements o f c a p s u l e

strength.

with

reference

to the possible

extra-embryonic structures. of predation Potential

i n t e r t i d a l predators

predator

preferences

examined.

The e x t e n t

morphology.

capsules.

s t u d i e s , and evidence o f

i n the f i e l d

i s described.

of f i e l d predation

i s discussed

may h a v e p l a y e d

o f such

are i d e n t i f i e d through a

f o r t h i c k - o r t h i n - w a l l e d egg

e m a r g i n a t a egg c a p s u l e s predation

function(s)

e m a r g i n a t a egg

and l a b o r a t o r y

species-specific predation

wall thickness are

Chapter 2 i n v e s t i g a t e s the extent

on i n t e r t i d a l N u c e l l a

combination of f i e l d

with

The i m p l i c a t i o n s o f i n t r a -

i n t e r s p e c i f i c d i f f e r e n c e s i n capsule

discussed

are

populations

t o determine the e f f e c t i v e n e s s of these s t r u c t u r e s i n

protecting developing

and

a

s t r u c t u r e may a l s o be c o r r e l a t e d w i t h d i f f e r e n c e s i n

l e v e l s of s p e c i f i c environmental The

2)

d e v e l o p m e n t t i m e s may be a s s o c i a t e d w i t h

r i s k o f embryonic m o r t a l i t y and, hence, d i f f e r e n c e s i n

capsular the

longer

Also,

capsules

on N u c e l l a

i n terms o f t h e r o l e

i n the evolution of

capsule

that

3 CHAPTER 1 FUNCTIONAL MORPHOLOGY OF MARINE GASTROPOD EGG I N T R A S P E C I F I C VARIATION

IN SIZE,

CAPSULES:

WALL THICKNESS

STRENGTH OF NUCELLA EMARGINATA EGG

AND

CAPSULES

INTRODUCTION

The c o n f i n e m e n t is

o f d e v e l o p i n g embryos w i t h i n e g g

a common phenomenon among m a r i n e i n v e r t e b r a t e s .

N e o g a s t r o p o d m o l l u s c s e n c l o s e t h e i r embryos structurally

complex p r o t e i n a c e o u s

their

larval

life.

Gastropod

c o n s i d e r e d t o be " p r o t e c t i v e " P e r r o n and Corpuz,

1982),

against i s unclear. thought

t o reduce

(Pechenik, osmotic 1988), shock

However,

(Pechenik,

1979; P e r r o n ,

(Pechenik,

bacterial

attack

in

(Lord,

1982; 1983, H a w k i n s a n d

( S p i g h t , 1977; P e c h e n i k , 1986),

1978),

Hutchinson, temperature (Perron,

o n l y a few s t u d i e s h a v e s p e c i f i c a l l y

examined

factors

1978; 1982; 1983; B r e n c h l e y ,

1984; L o r d , 1986; H a w k i n s a n d H u t c h i n s o n ,

field

situations.

1982;

1988)

i s known a b o u t t h e s u r v i v o r s h i p o f e n c a p s u l a t e d

actual

1986),

a n d wave a c t i o n

( S p i g h t , 1977; P e c h e n i k ,

little

1981;

s t r e s s e s as: p r e d a t i o n

t h e r e s i s t a n c e o f e n c a p s u l a t e d embryos t o t h e s e

Davies,

all,

Commonly, t h e e g g c a p s u l e s h a v e b e e n

( S p i g h t , 1977; P e c h e n i k ,

1981).

some, i f n o t

egg c a p s u l e s a r e f r e q u e n t l y

such environmental

desiccation

embryos

b u t what t h e y p r o t e c t e m b r y o s

1979; P e r r o n , 1 9 8 1 ) ,

changes

within

c a p s u l e s , and

develop w i t h i n these capsules f o r at l e a s t of

capsules

and embryos

4 An

examination of i n t r a -

the

s t r u c t u r e o f egg

the

r o l e that capsules

Variation capsular

i n capsule

be

can

w a l l s may

play

be

useful in

i n gastropod

w a l l s t r e n g t h and

positively

(Perron,

1981).

life-histories.

the

Furthermore, capsule

and

Corpuz, 1982).

a c c o u n t f o r a l m o s t 50%

capsules

(Perron,

have e v o l v e d

energy i n v e s t e d

Perron

As

long encapsulated

been

i n some s p e c i e s

of the

development

capsular

energy i n v e s t e d i n

cases

intact

1981), s t r o n g , t h i c k - w a l l e d capsules

may

f o r increased p r o t e c t i o n of encapsulated

and

in

w a l l s a r e known t o

w i t h long-term exposure to environmental s t r e s s e s 1981;

assessing

c o r r e l a t e d w i t h embryonic developmental

t h i c k e r i n Conus s p e c i e s w i t h

(Perron

interspecific variation in

c a s e s among s p e c i e s w i t h i n t h e g e n u s Conus has

f o u n d t o be time

capsule

and

Corpuz, 1982).

I f s e l e c t i o n has

embryos

(Perron, also

responded t o i n t e n s i t y of these environmental f a c t o r s , then i n t r a s p e c i f i c comparisons of capsular

s t r u c t u r e across

a

v a r i e t y of h a b i t a t s could r e v e a l d i f f e r e n c e s a s s o c i a t e d s p e c i f i c sources of m o r t a l i t y . specifically

examined i n t r a -

As

s p e c i e s may

be

i n the

s t u d i e s have

or i n t e r s p e c i f i c v a r i a t i o n i n

structure of gastropod capsules Differences

y e t , no

s t r u c t u r e o f egg

capsules

within a

separated

sharp environmental gradients,

s u c h as

Stresses

o r g a n i s m s a r e known t o

intertidal

(Menge, 1 9 7 8 a ;

Menge and

Sutherland,

h a v e shown t h a t

increases

i n w a v e - e x p o s u r e a r e m a t c h e d by:

predation

intensity,

Studies

along

wave-exposure.

g r e a t l y along wave-exposure g r a d i e n t s 1987).

the

among d i f f e r e n t h a b i t a t s .

most a p p a r e n t among p o p u l a t i o n s

i m p o s e d on

with

differ 1978b;

1) d e c r e a s e s i n

as wave a c t i o n g e n e r a l l y t e n d s t o

disrupt

5 predator foraging a c t i v i t i e s

( K i t c h i n g e t a l . , 1959;

1 9 7 8 a ; 1978b; R o b l e s ,

and

stress, 1971;

as a r e a s

1987),

2) d e c r e a s e s

Wave-action i t s e l f

i s known t o

s e v e r e p h y s i c a l s t r e s s e s upon i n t e r t i d a l

abrasion Wright, to

(Denny, 1985,

(Craik, 1986).

organisms,

1980),

Denny e t a l . , 1985;

and w a t e r - b o r n

rocks

impose to

Etter,

1987),

(Shanks

and

capsules are

stresses similar to sessile

a w a v e - e x p o s u r e g r a d i e n t may

(Dayton,

o r g a n i s m s due

A s s u m i n g t h a t b e n t h i c egg

environmental

in desiccation

s p l a s h e d by waves s u f f e r l e s s d r y i n g

Menge, 1 9 7 8 a ) .

dislodgement

Menge,

exposed

intertidal

provide a

convenient

means o f c o m p a r i n g c a p s u l e s t r u c t u r e a c r o s s a r a n g e

of

environmental c o n d i t i o n s . In

order that i n t r a s p e c i f i c d i f f e r e n c e s i n capsule

s t r u c t u r e c a n be

interpreted,

i t i s essential to

understand

c e r t a i n c o n s t r a i n t s i m p o s e d on t h e m o r p h o l o g y o f g a s t r o p o d capsules. et

F o r i n s t a n c e , i t i s known f r o m t h e work o f

a l . (1974),

S p i g h t and E m l e n

(1976) and P e r r o n and

c a p s u l e s i s r e l a t e d t o female

size.

(Strathmann

gastropod

C o n s t r a i n t s may

be p l a c e d on c a p s u l e s t r u c t u r e by t h e r e q u i r e m e n t s d e v e l o p i n g embryos

and C h a f f e e ,

oxygen or waste p r o d u c t s H e n c e , t h e r e may

restrict

and t h u s r e d u c e

1984).

For low

the d i f f u s i o n

embryo

also

of

i n s t a n c e , t h i c k c a p s u l e w a l l s or c a p s u l e shapes w i t h s u r f a c e a r e a t o v o l u m e r a t i o s may

Spight Corpuz

(1982) t h a t t h e l e n g t h , v o l u m e and w a l l t h i c k n e s s o f egg

egg

of

survivorship.

be t r a d e o f f s i n c a p s u l e d e s i g n , s u c h

that

t h i c k - w a l l e d c a p s u l e s p r o t e c t embryos b e t t e r from p r e d a t i o n o r physical

s t r e s s , b u t may

surviving.

l i m i t t h e number o f e m b r y o s

T h e r e f o r e , a s t u d y o f c a p s u l e f u n c t i o n must

6 i n v o l v e a knowledge o f t h e i n t e r r e l a t i o n s h i p s between

capsule

morphology, c a p s u l e w a l l t h i c k n e s s , and t h e packaging o f embryos w i t h i n The

capsules.

marine i n t e r t i d a l

snail,

common i n h a b i t a n t o f r o c k y s h o r e s and

ranges

isa

from C a l i f o r n i a t o A l a s k a

across wide extremes i n wave-exposure.

s n a i l s d e p o s i t eggs w i t h i n which

N u c e l l a emarginata,

These

6-10 mm-long v a s e - s h a p e d c a p s u l e s ,

they a t t a c h d i r e c t l y t o the substratum.

T h r e e t o 35

embryos a r e e n c l o s e d w i t h hundreds o f n u r s e eggs, u s e d as f o o d by t h e d e v e l o p i n g l a r v a e . 1966),

A f t e r approximately

80 d a y s

(Emlen,

e m b r y o s emerge f r o m t h e e g g c a p s u l e s a s j u v e n i l e

snails. In t h i s

study,

I examined i n t r a s p e c i f i c v a r i a t i o n i n

c a p s u l e m o r p h o l o g y w i t h i n a n d among p o p u l a t i o n s o f N u c e l l a emarginata.

P o p u l a t i o n s were c h o s e n from t h r e e

separated along a g r a d i e n t o f wave-exposure.

sites

Data were

c o l l e c t e d o n : 1) t h e s i z e a n d s h a p e o f s n a i l s w i t h i n a n d among populations,

2) i n t r a s p e c i f i c d i f f e r e n c e s i n c a p s u l e s i z e a n d

w a l l t h i c k n e s s , 3) v a r i a t i o n i n t h e p a c k a g i n g

o f eggs and

e m b r y o s w i t h i n c a p s u l e s , a n d 4) t h e r e l a t i o n s h i p b e t w e e n c a p s u l e w a l l t h i c k n e s s and c a p s u l e s t r e n g t h , f o r each

site.

7 STUDY SITE DESCRIPTIONS

T h i s p r o j e c t was c o n d u c t e d

at t h e Bamfield Marine S t a t i o n

on t h e w e s t c o a s t o f V a n c o u v e r I s l a n d (125°10'N, Fig.l).

48°50'W;

S t u d y s i t e s w e r e e s t a b l i s h e d i n B a r k l e y Sound f o r t h e

purpose o f c o l l e c t i n g N u c e l l a emarqinata capsules.

a d u l t s and t h e i r egg

Three l o c a t i o n s were chosen t o r e p r e s e n t a g r a d i e n t

o f wave-exposure from s h e l t e r e d t o exposed: G r a p p l e r Ross I s l e t s ,

and Seppings I s l a n d .

s t u d i e s have ranked

these

areas

Although

Inlet,

no e m p i r i c a l

i n B a r k l e y Sound w i t h

respect

t o w a v e - e x p o s u r e , my r a t i n g s y s t e m , b a s e d on v i s u a l observations, corresponded

w i t h s u b j e c t i v e exposure s c a l e s

e m p l o y e d b y o t h e r s i n t h e same g e o g r a p h i c Druehl,

and Haven, 1971; K i t c h i n g ,

1. G r a p p l e r The

region (Austin,

1976; C r o t h e r s ,

Inlet

Grappler

Inlet

exposed study area

s i t e represented the least

(Fig. 1 ) . Although

considerable t i d a l

r e p r e s e n t e d an e x t r e m e

(Crothers, Grappler

exchange.

distributional

which a r e n o r m a l l y absent 1984).

i t was s u b j e c t t o a

c u r r e n t due t o t h e c o n s t r i c t e d w i d t h o f t h e

and l a r g e volume o f t i d a l

emarqinata,

wave-

t h e a c t u a l s i t e was t o o

f a r up t h e i n l e t t o r e c e i v e o c e a n i c s w e l l ,

channel

1984).

This

limit

site

f o r Nucella

from p r o t e c t e d

inlets

A g e n e r a l s e a r c h f o r N. e m a r q i n a t a

along

I n l e t r e v e a l e d t h a t t h e y were p r e s e n t

a r e a s : a t my s t u d y

o n l y i n two

l o c a t i o n a n d on r o c k y b e a c h e s a r o u n d t h e

mouth o f t h e i n l e t . The

s i t e was l o c a t e d i n a n i n t e r t i d a l

channel,

a b o v e z e r o c h a r t datum, c o n n e c t i n g t h e m a i n l a n d

1.6m

and a s m a l l

8

FIGURE 1. The l o c a t i o n of study s i t e s a l o n g the southern shores of B a r k l e y Sound on the west c o a s t of Vancouver I s l a n d , B.C. Study l o c a t i o n s were chosen a l o n g a wave-exposure g r a d i e n t . Wave-exposure l e v e l s were p r e d i c t e d t o be lowest at G r a p p l e r I n l e t , h i g h e s t at Seppings I s l a n d , and i n t e r m e d i a t e at the Ross I s l e t s s i t e .

9 piece of land isolated at high t i d e .

The

intertidal

s u b s t r a t e c o n s i s t e d o f f i n e s i l t y mud o v e r l a i d b y c l a m and

a meshwork o f m u s s e l - a n d b a r n a c l e - c o v e r e d

edulis,

Balanus qlandula

e m a r q i n a t a were p r e s e n t t i d a l height

and Semibalanus c a r i o s u s ) . throughout t h e channel

of approximately

Other gastropods present dira,

channel.

2.6m

(Mytilus Nucella

and ranged t o a

above z e r o

chart

datum.

were N u c e l l a l a m e l l o s a , S e a r l e s i a

Onchidella borealis,

chitons Mopalia

rocks

shells

and v a r i o u s l i m p e t

species.

The

spp. were a l s o abundant t h r o u g h o u t t h e

The p o l y c h a e t e s ,

N e r e i s v e x i l l o s a and s e v e r a l

s p e c i e s o f s c a l e worms w e r e a s s o c i a t e d w i t h t h e m u s s e l - a n d barnacle-covered ubiquitous.

rocks, while

Three i s o p o d

s e v e r a l nemertean s p e c i e s

s p e c i e s were

present:

Gnorimosphaeroma oreqonense, C i r o l a n a h a r f o r d i , wosnesenskii.

Hemigrapsus oregonensis

t h e c o m p a c t mud f o u n d i n h i g h e r H. n u d u s w e r e r a r e l y be

seen.

were

and Idotea

burrows were e v i d e n t i n

intertidal

Hermit crabs

regions;

however,

(Pagurus spp.) c o u l d

f o u n d i n amongst t h e meshwork o f m u s s e l s , b a r n a c l e s a n d

rocks.

Fucus and U l v a were t h e p r e d o m i n a n t i n t e r t i d a l

2. R o s s This

Islets s i t e was c h o s e n t o r e p r e s e n t

intermediate

wave-exposure

(Fig. 1).

a region

these

waves b r e a k i n g

areas

channel.

s i t e s received only small swells r e s u l t i n g

from

on t h e s o u t h - f a c i n g s h o r e s o f t h e i s l e t s a n d on

a r e e f between two n e i g h b o u r i n g The

with

The c o l l e c t i n g

w e r e l o c a t e d on b o t h s i d e s o f a w a v e - p r o t e c t e d Normally

algae.

intertidal

islands.

substrate i n this

g r a n i t e bedrock, w i t h a boulder

region consisted of

beach c o v e r i n g

some o f t h e

10 lower r e g i o n s . intertidally:

Three b a r n a c l e s p e c i e s were p r e s e n t Balanus

Chthamalus d a l l i . patchy

clumps.

g l a n d u l a , S e m i b a l a n u s c a r i o s u s and

M y t i l u s c a l i f o r n i a n u s were p r e s e n t

N u c e l l a emarginata

high- i n t e r t i d a l

were found

z o n e s b e t w e e n 1.8

- 3.1

i n the mid-

lamellosa,

Other

Tegula

limpet species.

littoral

gastropods

funebralis, The

boulder

p r e s e n t were N u c e l l a

S e a r l e s i a d i r a and

c h i t o n s , M o p a l i a spp.,

o c c a s i o n a l l y on g r a n i t e p r o m o n t o r i e s .

various

were seen

Intertidal

and n e m e r t e a n s w e r e s p a r s e , w i t h N e r e i s v e x i l l o s a Emplectonema g r a c i l e b e i n g t h e o n l y o b v i o u s these groups.

The

p u r p l e shore

porcelain crabs, P e t r o l i s t h e s in

t h e b o u l d e r b e a c h e s and

Starfish,

polychaetes and

r e p r e s e n t a t i v e s of

c r a b s , Hemigrapsus nudus,

spp. were abundant u n d e r

i n some h i g h e r i n t e r t i d a l

distichus,

The

predominant h i g h i n t e r t i d a l

3. S e p p i n g s T h i s was

a l g a was

2.6

- 2.9

t h e most w a v e - e x p o s e d s i t e

(Fig. 1).

l o c a t e d i n a large b o u l d e r - l i n e d channel,

facing a r e l a t i v e l y unobstructed oceanic bordered

on t h e o t h e r by a l a r g e r o c k y p r o m o n t o r y c o v e r e d

Mytilus californianus.

on one

swell.

and

- 2.0

tide

The

c h a n n e l was

0.3

Fucus

m a b o v e z e r o c h a r t datum.

The

from

boulder

Island

c o l l e c t i n g a r e a was 10 m w i d e ,

rocks

d i s t r i b u t e d i n a d i s t i n c t v e r t i c a l band at a

height of approximately

and

crevices.

P i s a s t e r - o c h r a c e u s , w e r e a l s o common i n t h e

beach area.

to

m above z e r o c h a r t

datum, and w e r e p r e s e n t o c c a s i o n a l l y i n t h e l o w e r beach r e g i o n .

in

Boulders

m diameter.

s i d e by a h i g h g r a n i t e w a l l

i n the channel

ranged

During w i n t e r storms,

o f t e n were r e d i s t r i b u t e d t h r o u g h o u t

with

the i n t e r t i d a l

in size

boulders area

by

11 wave

action. The c o l l e c t i n g c h a n n e l

barnacles dalli,

(Balanus

was c h a r a c t e r i z e d by a v a r i e t y o f

g l a n d u l a , Semibalanus c a r i o s u s , Cthamalus

and P o l i c i p e s p o l y m e r u s ) ,

N. c a n a l i c u l a t a , gastropods

whelks

(Nucella

emarginata,

and C e r a t o s t o m a f o l i a t u m ) and o t h e r

(Ocenebra l u r i d a ,

Tegula

funebralis,

Calliostoma

l i g a t u m and v a r i o u s l i m p e t s p e c i e s ) .

Idotea wosnesenskii

the only i n t e r t i d a l

Hemigrapsus nudus were

present

isopods present.

i n l a r g e numbers u n d e r n e a t h t h e r o c k y b o u l d e r s ,

were s m a l l h e r m i t

crabs

(Pagurus

(Petrolisthes cinctipes).

Algae

i n the high i n t e r t i d a l

as

spp.) a n d p o r c e l a i n c r a b s consisted of Laminaria

I r i d a e a s p e c i e s i n t h e low i n t e r t i d a l limitata

were

and

a r e a , and P e l v e t i o p s i s

regions.

12 MATERIALS AND METHODS

I . DIFFERENCES

I N SNAIL MORPHOLOGY AMONG SITES

Shell-length t o aperture-length

r a t i o s were u s e d t o

compare s h e l l m o r p h o l o g y among s i t e s ,

as t h e s e . r a t i o s a r e t h e

q u i c k e s t and s i m p l e s t method o f d e t e r m i n i n g variation

i n t h e genus N u c e l l a

were c o l l e c t e d from each s t u d y

shell-shape

(Crothers, 1984). area

Nucella

e m a r q i n a t a from a g i v e n a r e a t o a v o i d any b i a s e s size,

o r shape.

Snails considered

( l e s s t h a n 10 mm i n l e n g t h ) variation

i nshell

were r e p l a c e d ,

s h a p e i s known t o o c c u r

j u v e n i l e development (Crothers,

1984).

l e n g t h s were measured t o t h e n e a r e s t calipers.

for shell

t o be j u v e n i l e s as c o n s i d e r a b l e during early

S h e l l and a p e r t u r e -

0.1mm w i t h v e r n i e r

S h e l l - l e n g t h was d e f i n e d a s t h e maximum

between t h e s h e l l

snails

i n t h e s p r i n g o f 1988.

C o l l e c t i o n s w e r e made b y r e m o v i n g a l l l i v i n g

colour,

Fifty

length

apex and a n t e r i o r t i p o f t h e s i p h o n a l

canal,

w h i l e a p e r t u r e - l e n g t h was t h e maximum d i s t a n c e b e t w e e n t h e p o s t e r i o r corner siphonal

II.

o f the aperture

l i p and a n t e r i o r t i p o f t h e

canal.

CAPSULE MORPHOLOGY 1. R e l a t i o n s h i p b e t w e e n s n a i l

s i z e and capsule

I n o r d e r t o compare t h e s i z e o f e g g c a p s u l e s snails

from each s i t e ,

collected

approximately

from each study

area.

l a i d by

50-100 s n a i l s

were

S n a i l s were b r o u g h t i n t o t h e

laboratory, tagged f o r i d e n t i f i c a t i o n , specific p l a s t i c containers

size

and assigned

(32x26x12cm, w i t h 20x8cm

to sitelmm-pore

13 mesh w i n d o w s i n e a c h o f t h e f o u r s i d e s ) .

Approximately

s n a i l s were h e l d i n each c o n t a i n e r and were p r o v i d e d barnacles

f o r food.

Containers

40-50

with

were k e p t submerged i n

l a b o r a t o r y seawater t a b l e s and s u p p l i e d w i t h a c o n t i n u o u s of f r e s h seawater. every

E a c h l a b o r a t o r y p o p u l a t i o n was c h e c k e d

two days o v e r a s i x - w e e k p e r i o d t o i d e n t i f y

l a y i n g egg c a p s u l e s . egg

capsule

capsule

flow

A s n a i l was r e c o g n i z e d

snails

t o b e l a y i n g an

o n l y i f i t was f o u n d a c t u a l l y m o l d i n g a new

with i t s v e n t r a l pedal

gland.

Such c a p s u l e s

c o u l d be

i d e n t i f i e d r e a d i l y by t h e i r

s o f t w a l l s and m i l k y - y e l l o w

appearance.

were c o l l e c t e d w i t h t h e n e w l y - l a i d

Other capsules

ones o n l y i f t h e y clutch. laid

were c o n s i d e r e d

t o be p a r t o f t h e same

A c l u t c h was d e f i n e d t o b e a n y number o f c a p s u l e s

i n w i t h i n a f e w mm o f one a n o t h e r t h a t w e r e s i m i l a r i n

shape and o r i e n t a t i o n ( G a l l a r d o , 1979). capsules

A maximum o f 5

was c o l l e c t e d f r o m e a c h f e m a l e a t a n y s p a w n i n g c h e c k .

Capsule-laying

f e m a l e s were measured f o r s h e l l

returned t o t h e i r containers.

l e n g t h and

C a p s u l e s were p r e s e r v e d

i n 5%

f o r m a l i n f o r subsequent measurement. Three measurements were t a k e n 1)"capsule

f o r each capsule

body l e n g t h " , w h i c h e x c l u d e d

t h i s was known t o be e x t r e m e l y 1976); 2)"capsule chamber h o u s i n g

(Fig.2):

t h e stem l e n g t h as

v a r i a b l e (Spight and Emlen,

chamber l e n g t h " , r e p r e s e n t i n g t h e l e n g t h o f

t h e e m b r y o s a n d n u r s e e g g s ; a n d , 3) t h e

"maximum c a p s u l e

width",

w h i c h was t h e maximum w i d t h

capsule-chamber.

The " c a p s u l e

using t h e formula

f o ra prolate ellipsoid,

where a = t h e c a p s u l e

chamber v o l u m e " was

ofthe estimated

V=4/37T(a/2) ( b / 2 ) 2 ,

chamber l e n g t h a n d b = t h e maximum

14

Capsular Hug

Capsule Body Length

Capsule Chamber Length

Stem

Maximum Capsular Width 1

2mm

Scale

FIGURE 2. N u c e l l a emarginata egg c a p s u l e , i l l u s t r a t i n g t h e t h r e e measurements taken f o r each c a p s u l e : capsule-body l e n g t h , capsule-chamber l e n g t h , and maximum c a p s u l e width. The c a p s u l a r - p l u g r e g i o n and the stem are a l s o i n d i c a t e d .

15 capsule

width

(Pechenik,

1982).

2. M i c r o - m o r p h o l o g y o f N u c e l l a e m a r g i n a t a egg Representative

egg

capsules

o f N u c e l l a e m a r g i n a t a were

s e c t i o n e d u s i n g a f r e e z e microtome. of each capsule and

was

1968;

capsules

o f N.

lapillus

M a u g e l , 1984;

Intracapsular variation emarginata capsules

was

laboratory, these

maintained before,

(0%)

then i n d i v i d u a l l y

f r o z e n on

were t a k e n

length of the capsule

were t a k e n

at the

capsule-chamber.

1988).

thickness

f r o m any

one

Nucella

C a p s u l e s were minimize

female.

in cylindrical

In

The

and

C a p s u l e s were measured by

removing the

j u n c t i o n between the

as

capsular

a f r e e z e microtome.

plug,

Sections,

a t 10 p e r c e n t i l e i n t e r v a l s chamber.

The

first

sections

opening of the plug region i n t o last

the

vials

2.0x2.5cm lmm-pore mesh p a n e l s )

emptied of a l l contents

along the

(Bayne,

clutches within a s i t e to

i n f l o w i n g seawater.

e a c h 10-12yum t h i c k ,

other muricids

i n the w a l l t h i c k n e s s of

were t h e n p l a c e d

(3.5x3.5x6cm w i t h two

studies

examined f o r each s i t e .

from d i f f e r e n t

microscope

histological

D'Asaro,

the chance of o b t a i n i n g c a p s u l e s

and

and

Intracapsular variation in wall

collected

wall microstructure

e x a m i n e d u s i n g a compound l i g h t

S u l l i v a n and

3.

the

The

i n t e r p r e t e d with respect to previous

on t h e egg

capsules

section

(100%) was

c a p s u l e - c h a m b e r and

were mounted i n a s e a w a t e r - s o l u b l e

taken stem.

m o u n t i n g medium

the

close to Sections and

measurements t a k e n

u s i n g a compound m i c r o s c o p e w i t h c a l i b r a t e d

ocular micrometer.

E i g h t measurements o f w a l l t h i c k n e s s were

16 taken at a p p r o x i m a t e l y equal i n t e r v a l s around each c a p s u l e section.

The

average w a l l t h i c k n e s s w i t h i n each s e c t i o n

used i n a l l subsequent

was

data analyses.

4. V a r i a t i o n i n c a p s u l e w a l l - t h i c k n e s s among p o p u l a t i o n s . I n o r d e r t o e x a m i n e w a l l t h i c k n e s s d i f f e r e n c e s among a l a r g e number o f egg c a p s u l e s , a l a b o r a t o r y p o p u l a t i o n o f s n a i l s was

e s t a b l i s h e d from each s i t e .

S n a i l s w e r e s e x e d by

a l l o w i n g e a c h a n i m a l t o a t t a c h t o a r o c k s u r f a c e and gently p u l l i n g the s h e l l

60

away f r o m t h e b o d y mass.

then

A male

c o u l d be i d e n t i f e d b y t h e p r e s e n c e o f a p e n i s l a r g e r t h a n i t s right tentacle Palmer,

1984).

(rather than the smaller penis of the female; F i v e m a l e and f i v e

female s n a i l s

s i t e were a l l o c a t e d t o each o f s i x r e p l i c a t e

from

each

cages

(26x16.5x13cm, w i t h 8x16cm lmm-pore mesh p a n e l s i n e a c h and were s u p p l i e d w i t h b a r n a c l e s f o r f o o d .

Female s n a i l s

s e l e c t e d so t h a t e a c h r e p l i c a t e c a g e h a d a s i m i l a r mean size

( G r a p p l e r : X=3.0 cm;

X=2.0 cm).

side)

R o s s I s l e t s : X=2.3 cm;

were

snail

Seppings:

A l l cages were k e p t c o m p l e t e l y . i m m e r s e d i n f l o w i n g

seawater. E v e r y two weeks f r e s h l y

l a i d c a p s u l e s were c o l l e c t e d

placed i n small mesh-panelled v i a l s .

V i a l s were

d a t e d , and immersed i n f l o w i n g s e a w a t e r u n t i l needed.

and

labelled,

c a p s u l e s were

C a p s u l e s c o n t a i n e d i n t h e s e " c a p s u l e v i a l s " were u s e d

i n s e v e r a l e x p e r i m e n t s as

follows.

To e x a m i n e v a r i a t i o n i n c a p s u l e w a l l t h i c k n e s s w i t h i n among p o p u l a t i o n s , each r e p l i c a t e v i a l

f i v e c a p s u l e s were s e l e c t e d randomly (n=30 c a p s u l e s / s i t e ) .

C a p s u l e s were

and

from

17 measured i n d i v i d u a l l y

and marked a t a p o i n t 70% a l o n g t h e

length of the capsule

chamber w i t h a f i n e S t a e d t l e r L u m o c o l o u r

pen.

Previous

capsule

data

on w a l l t h i c k n e s s v a r i a t i o n w i t h i n a

i n d i c a t e d that capsules

thickness

were t h i n n e s t and w a l l

least variable i n this region.

C a p s u l e s were

e m p t i e d by removing t h e p l u g and t h e n s e c t i o n e d microtome.

Sections

on t h e f r e e z e -

w e r e c o l l e c t e d o n l y when t h e b l a d e

reached the p o r t i o n of the capsule

chamber m a r k e d w i t h i n k .

F i v e s e c t i o n s , e a c h 10-12yum t h i c k , w e r e t a k e n f o r e a c h and

capsule

one s e c t i o n was c h o s e n f o r m e a s u r e m e n t .

5. V a r i a t i o n i n c a p s u l e clutches

w a l l t h i c k n e s s w i t h i n a n d among

l a i d by d i f f e r e n t females

I n t r a - and i n t e r c l u t c h v a r i a b i l i t y

i n wall thickness

examined t o determine i f females w i t h i n a p o p u l a t i o n

was

laid

capsules

of different wall thicknesses.

capsules

was c o l l e c t e d f r o m e a c h o f f i v e r e p l i c a t e c a g e s f o r

each o f t h e three by its

One c l u t c h o f e g g

s i t e s t o e n s u r e t h a t a l l c l u t c h e s were

d i f f e r e n t females.

E a c h c l u t c h was c o l l e c t e d a n d k e p t i n

own l a b e l l e d m e s h - p a n e l l e d c o n t a i n e r u n t i l

needed f o r s e c t i o n i n g .

laid

Representative

capsules

capsules

were

were s e l e c t e d

randomly from each c l u t c h , measured under a d i s s e c t i n g microscope, and t h e n s e c t i o n e d length of the capsule w e r e made a s d e s c r i b e d

chamber.

at a point Wall

thickness

measurements

previously.

6. V a r i a t i o n i n d r y w e i g h t o f c a p s u l e s Dry

70 % a l o n g t h e

w e i g h t measurements o f c a p s u l e s

among

populations.

were t a k e n f o r each

18 p o p u l a t i o n to determine corresponded

i f d i f f e r e n c e s among

sites

to d i f f e r e n c e s i n capsule w a l l thickness.

For

each p o p u l a t i o n , r e p r e s e n t a t i v e c a p s u l e s were c o l l e c t e d each of s i x r e p l i c a t e capsule v i a l s .

Capsules

and t h e n o p e n e d t o remove a l l c o n t e n t s . from c a p s u l e s t o minimize capsules.

Capsules

variability

from

were measured

Stems w e r e r e m o v e d

i n weight

among

were r i n s e d t w i c e i n d i s t i l l e d water

t h e n d r i e d f o r 48 h r s a t 75°C.

and

A f t e r d r y i n g , c a p s u l e s were

w e i g h e d t o O.Olmg.

I I I . VARIATION IN CAPSULE CONTENTS AMONG SITES 1. Egg Egg

number and

volume

c a p s u l e c o n t e n t s were examined t o d e t e r m i n e

i f the

number o r s i z e o f e g g s p e r c a p s u l e d i f f e r e d w i t h p o p u l a t i o n differences i n capsule structure. were c o l l e c t e d each s i t e

Three newly l a i d

capsules

from each of s i x r e p l i c a t e c a p s u l e v i a l s

(18 c a p s u l e s / s i t e ) .

Capsules

were measured,

sliced

o p e n , and t h e i r c o n t e n t s w a s h e d w i t h f i l t e r e d s e a w a t e r small p e t r i dish.

As n u r s e

eggs t e n d e d

for

into

t o clump t o g e t h e r ,

eggs were g e n t l y a g i t a t e d a p a r t w i t h a p i p e t t e .

A l l nurse

e g g s and e m b r y o s w i t h i n a c a p s u l e w e r e c o u n t e d .

Before

c o u n t s w e r e made, h o w e v e r , e m b r y o s w e r e e x a m i n e d t o t h a t t h e y had not advanced p a s t t h e second LeBoeuf

(1971) and L y o n s and

once p a s t t h i s d e v e l o p m e n t a l f e e d i n g on e n c a p s u l a t e d n u r s e As

egg

Spight

veliger

these

ensure stage.

(1973) h a v e n o t e d

that

s t a g e , e m b r y o s become c a p a b l e eggs.

s i z e w i t h i n a c a p s u l e was

a

relatively

o n l y f i v e eggs were sampled from each c a p s u l e .

constant, Length

and

of

19 w i d t h measurements were t a k e n

f o r each egg.

E g g v o l u m e was

e s t i m a t e d by u s i n g t h e f o r m u l a f o r a p r o l a t e e l l i p s o i d as described previously.

2. Number a n d s i z e To d e t e r m i n e

of hatching

snails.

i f t h e r e was a d i f f e r e n c e i n t h e number o f

embryos p e r c a p s u l e from e a c h s i t e , embryos were a l l o w e d t o hatch i n the laboratory. their

l a r v a e developed

capsule v i a l s u n t i l development neared

this point, individual their

Encapsulated

own m e s h - p a n e l l e d

i n seawater

within

completion.

At

c a p s u l e s from each s i t e were p l a c e d i n vials

(600 yUm mesh p o r e ) a n d s u b m e r g e d

u n t i l t h e embryos h a t c h e d .

Capsules

were

checked

e v e r y two d a y s a n d a s s o o n a s an embryo h a d emerged, t h e c a p s u l e was m e a s u r e d a n d e m p t i e d All

l i v e embryos were c o u n t e d

o f a l l r e m a i n i n g embryos.

and t h e i r

shell-lengths

measured.

I V . CAPSULE STRENGTH MEASUREMENTS 1. R e s i s t a n c e t o p u n c t u r i n g This index determined

the resistance of capsule w a l l s to

p u n c t u r i n g a n d was b a s e d on P e r r o n ' s Conus e g g c a p s u l e s . were t a k e n

(1981) p r o c e d u r e f o r

Newly l a i d N u c e l l a emarginata

from t h e i r

capsules

r e s p e c t i v e c a p s u l e v i a l s , measured, and

t h e n marked a t a p o i n t 70% a l o n g t h e l e n g t h o f t h e c a p s u l e chamber.

Capsules

w e r e t h e n b i s e c t e d by c u t t i n g a l o n g t h e two

seams o f t h e c a p s u l e chamber a n d t h e i r

contents discarded.

E a c h c a p s u l e h a l f was m o u n t e d i n d i v i d u a l l y of p l e x i g l a s s

b e t w e e n two p i e c e s

(8.5x5cm) a n d o r i e n t a t e d s u c h t h a t a 1mm d i a .

20 h o l e i n e a c h p i e c e o f p l e x i g l a s s was p o s i t i o n e d d i r e c t l y t h e marked r e g i o n o f t h e c a p s u l e taken

chamber

(Fig. 3a).

t o i n s u r e t h a t t h e r e w e r e no f o l d s o r c r e a s e s

capsule

s e c t i o n and t h a t i t remained m o i s t .

device, c o n s i s t i n g of a blunt-ended

needle

A

over

Care

was

i n the

puncturing

(0.36 mm^

area)

mounted b e n e a t h a f l a t w e i g h i n g

p a n , was p o s i t i o n e d o v e r t h e

plexiglass

r e s t e d at r i g h t angles

such t h a t t h e needle

exposed capsule w a l l . weighing

Five-gram weights

pan u n t i l t h e n e e d l e

punctured

E a c h c a p s u l e p i e c e was o n l y p u n c t u r e d

2. R e s i s t a n c e This index

to

were added t o t h e the capsule

wall.

once.

squeezing

of capsule

s t r e n g t h measured t h e f o r c e needed

t o squeeze t h e p l u g out o f i n t a c t c a p s u l e s .

Shore crabs

o f t e n seen t o r u p t u r e N u c e l l a e m a r g i n a t a egg c a p s u l e s squeezing

to the

them i n t h e i r c h e l a e .

Laboratory

capsules

were

by were

c o l l e c t e d from r e p l i c a t e c a p s u l e v i a l s and measured. Individual capsules

were mounted w i t h " S u p e r g l u e "

onto a

metal

p l a t e , w h i c h was t h e n b o l t e d t o a v e r t i c a l p i e c e o f p l e x i g l a s s (Fig.

3b).

S t r a i n gauges, g l u e d t o t h e p l e x i g l a s s ,

c o n n e c t e d t o an a m p l i f i e r a n d c h a r t r e c o r d e r .

were

A second

metal

p l a t e was a t t a c h e d t o a s p i n d l e so t h a t t h i s p l a t e c o u l d be h a n d - c r a n k e d t o w a r d s t h e mounted c a p s u l e . provided capsule.

A chart

recorder

a r e c o r d o f t h e f o r c e r e q u i r e d t o r u p t u r e t h e egg T h i s s y s t e m was c a l i b r a t e d w i t h known

weights.

21

a)

Weights Loading Pan

Stand Blunt Pin Plexiglass Plates Clamp Piece of Capsule Wall

b)

Capsule Metal Plate

Metal Plate

Plexiglass with Strain Gauge

immmmimmmn.

Hand Crank

I'i-x-l'i-iji-i-x-w

Metal Spindle

FIGURE 3. Techniques used t o compare t h e s t r e n g t h o f egg c a p s u l e s : a) p u n c t u r i n g method used t o c a l c u l a t e t h e f o r c e r e q u i r e d t o p i e r c e c a p s u l e w a l l s , and b) s q u e e z i n g method used t o determine t h e r e s i s t a n c e o f i n t a c t capsules t o squeezing f o r c e s .

22 RESULTS.

I . DIFFERENCES I N SNAIL MORPHOLOGY AMONG

SITES

The s i z e a n d s h a p e o f s n a i l s d i f f e r e d e x t e n s i v e l y study

sites

Island,

( F i g . 4 ) . N u c e l l a emarginata from Seppings

t h e most w a v e - e x p o s e d a r e a , h a d t h e s m a l l e s t mean

(X=1.9cm) a n d t h e l o w e s t (X / +S.D.=1.42+0.05). L

among

length/aperture Snails

A

collected

size

ratio from t h e l e s s exposed

Ross I s l e t s s i t e had a g r e a t e r range o f s h e l l l e n g t h s , a larger

mean s i z e ,

length/aperture

(X=2.1cm),

r a t i o s than s n a i l s

(X / +S.D.=l.53+0.07). L

and p r o p o r t i o n a l l y from Seppings

Wave-sheltered s n a i l s

A

larger

from Grappler

I n l e t were i n t e r m e d i a t e i n body shape between S e p p i n g s and Ross I s l e t s s n a i l s shell

(X / +S.D.=1.49+0.06), b u t h a d t h e l a r g e s t L

A

lengths of a l l three populations

differences

w i t h wave-exposure, w i t h s h e l l

from wave-exposed t o w a v e - s h e l t e r e d

Changes i n l e n g t h / a p e r t u r e to not

Islet

II.

size

shores.

r a t i o s among s i t e s d i d n o t a p p e a r

r e f l e c t changes i n wave-exposure, as G r a p p l e r follow

These

i n t h e a v e r a g e s h e l l l e n g t h o f s n a i l s showed a n

obvious r e l a t i o n s h i p increasing

(X=2.7cm).

snails did

t h e same t r e n d i n b o d y s h a p e a s S e p p i n g s a n d R o s s

snails.

CAPSULE MORPHOLOGY 1• R e l a t i o n s h i p b e t w e e n s n a i l s i z e a n d c a p s u l e F i g u r e 5 shows t h e r e l a t i o n s h i p

snail

shell-length

population larger

within

size

between c a p s u l e

a n d among p o p u l a t i o n s .

s i z e and

Within each

females produced s i g n i f i c a n t l y l o n g e r egg

23 16S E P P I N G S ISLAND 12-

8-

4-

R O S S ISLETS 12>

Z3 o LL)

h n G R A P P L E R INLET 12-

4-

m h 1.0

1.5

2.0

2.5

3.0

3.5

4.0

SNAIL LENGTH ( c m )

FIGURE 4. S i z e - f r e q u e n c y histograms o f 50 s n a i l s c o l l e c t e d from each study s i t e i n March, 1988. S n a i l s s m a l l e r than 10 mm i n s h e l l l e n g t h were not included. Wave-exposure l e v e l s i n c r e a s e d from G r a p p l e r I n l e t t o Seppings Island. The mean s h e l l l e n g t h s o f s n a i l s were: 1.9, 2.1 and 2.7 cm f o r Seppings, Ross I s l e t s , and G r a p p l e r I n l e t s n a i l s , r e s p e c t i v e l y .

24

SNAIL LENGTH ( c m )

FIGURE 5. R e l a t i o n s h i p between c a p s u l e body l e n g t h and s n a i l l e n g t h f o r l a b o r a t o r y l a i d c a p s u l e s f o r each study s i t e . S n a i l s s m a l l e r than 1.7, 2.1 and 2.7 cm from Seppings, Ross I s l e t s and G r a p p l e r p o p u l a t i o n s d i d not spawn i n t h e l a b o r a t o r y . R e g r e s s i o n e q u a t i o n s f o r each s i t e a r e : Seppings: Y = 3.185X - 0.111, r =0.740, n = 23; Ross I s l e t s : Y = 3.139X - 1.232, r = 0.867, n = 23; G r a p p l e r I n l e t : Y = 2.206 + 1.481, r = 0.650, n = 20.

25 capsules

than s m a l l e r females.

r e l a t i o n s h i p s d i d not v a r y

The

slopes of

significantly

among s i t e s

f o r s l o p e s ; F=1.20, p > 0 . 2 5 ) , h o w e v e r , s l o p e d i f f e r e d s i g n i f i c a n t l y between the populations

these

elevations

S e p p i n g s and

Ross

Islets

(ANCOVA f o r e l e v a t i o n s ; F=14.84, p < 0 . 0 0 1 ) ,

Seppings s n a i l s producing

disproportionately large

S u b s t a n t i a l d i f f e r e n c e s were a l s o e v i d e n t spawning s n a i l s

i n the

Although

overlapped

i n s i z e range

1.4-2.9cm; G r a p p l e r :

l a b o r a t o r y w e r e 1.7,

l e n g t h f o r Seppings, Ross I s l e t s ,

populations,

respectively.

This

Islets:

range i n s i z e of

females from each p o p u l a t i o n b a r e l y c o i n c i d e d . s n a i l s t o spawn i n t h e

greatly

1.4-2.2cm; R o s s

1.8-3.5cm), t h e

of

as shown i n

laboratory snail populations (Seppings:

with

capsules.

size

from each l a b o r a t o r y p o p u l a t i o n ,

F i g u r e 5.

shell

(ANCOVA

The

2.1,

and

smallest

and

2.7

cm

in

Grappler

suggests t h a t the

r e p r o d u c t i v e m a t u r i t y v a r i e d among s i t e s ,

spawning

onset

of

w i t h wave-exposed

s n a i l s m a t u r i n g a t a much s m a l l e r s i z e t h a n

wave-sheltered

snails. Snail

s i z e was

d i m e n s i o n s , as

also r e f l e c t e d i n other

l a r g e r s n a i l s produced capsules

chamber v o l u m e s t h a n s m a l l e r s n a i l s among s i t e s

capsular

showed t h a t , a l t h o u g h

r e l a t i o n s h i p s d i d not

differ

F=0.57, p > 0 . 2 5 ) , S e p p i n g s and

(Fig. 6).

the

greater

Comparisons

slopes of

significantly

with

these

(ANCOVA f o r s l o p e s ;

Ross I s l e t s s n a i l s l a i d

w i t h l a r g e r chamber v o l u m e s t h a n s i m i l a r - s i z e d s n a i l s Grappler

Inlet

(ANCOVA; F=5.56, p < 0 . 0 1 ) .

As

( S p i g h t and

from

chamber v o l u m e s

a r e known t o r e f l e c t t h e number o f e g g s c o n t a i n e d capsules

capsules

within

Emlen, 1976), such d i f f e r e n c e s i n

the

capsule

26

SNAIL LENGTH ( c m )

FIGURE 6. R e l a t i o n s h i p between capsule-chamber volume and s n a i l l e n g t h f o r l a b o r a t o r y p o p u l a t i o n s e s t a b l i s h e d from each study s i t e . Regression e q u a t i o n s f o r each s i t e a r e : Seppings: Y = 18.245X - 15.257, r = 0.628, n = 23; Ross I s l e t s : Y = 28.193X - 41.722, r = 0.749, n = 23; G r a p p l e r , Y = 24.006X - 37.710, r = 0.690, n = 20.

27 s i z e can

also i n d i c a t e important

of these

populations.

d i f f e r e n c e s i n the

2. M i c r o m o r p h o l o g y o f N u c e l l a e m a r g i n a t a egg The

m i c r o s t r u c t u r e o f IsL. e m a r g i n a t a egg

i n F i g u r e 7.

C a p s u l e w a l l s o f N. (L^, L2

three d i s c r e t e laminae s t r u c t u r e to the M a u g e l , 1984; capsule

(L2)/

wall.

This

as t h i s was lamina

( L 2 b ) , w h i c h was layers the

{l>2a

capsule

e g g s , and of the

a n c

L

T

^

e

chamber and

enclosed

( F i g . 7D).

3.

and of

middle capsule

The

lamina

(L3)

lamina

embryos,

i n the was

capsule,

s t e m and

region

actually composed o f

s t r u c t u r e of these

the

lined

nurse

apical

a p p e a r e d t o be

homogeneous t h r o u g h o u t t h e s e c t i o n s through

homogeneous

capsule

as

i s shown

capsular-plug

( F i g . 7C,D).

Serial

s e c t i o n s along the

in wall thickness. capsule

chamber o f N u c e l l a

e m a r g i n a t a showed c o n s i d e r a b l e v a r i a t i o n

thickest

(Sullivan

from the

transparent,

Sections

p l u g and

Intracapsular variation

(Fig.8).

in

A l l measurements

developing

indicated that this

longitudinal

were s i m i l a r

innermost capsule

similar material

regions

and

solely

two

intracapsular fluid.

not

L3)

F i g . 7A,B).

s a n d w i c h e d by

capsule

by

and

the t h i c k e s t p a r t of the

connected to the

w a l l s was

i s shown

c o n s i s t e d a dense, f i b r o u s middle l a y e r

* 2c^ •

capsule

capsules

emarginata c o n s i s t e d of

w a l l t h i c k n e s s were t a k e n

lamina

capsules

capsule w a l l s of other muricids

D ' A s a r o , 1988;

fecundity

Within

individual

i n t h e p l u g and

capsules,

stem r e g i o n s

i n wall thickness

w a l l s tended to and

be

t h i n n e s t about

75%

a

FIGURE 7. M i c r o s t r u c t u r e o f N u c e l l a emarginata egg c a p s u l e s : a) t r a n s v e r s e s e c t i o n 70 % a l o n g t h e chamber o f a c a p s u l e from Ross I s l e t s (mean t h i c k n e s s = 60juun), b) t r a n s v e r s e s e c t i o n 70% a l o n g t h e chamber o f a c a p s u l e from G r a p p l e r I n l e t (mean t h i c k n e s s = 90^wm), c) l o n g i t u d i n a l s e c t i o n through t h e stem r e g i o n o f a N^. emarginata c a p s u l e , d) l o n g i t u d i n a l s e c t i o n t h r o u g h t h e plug r e g i o n of a e m a r g i n a t a c a p s u l e . O u t e r ( L ^ ) , middle (I^) and i n n e r ( L 3 ) c a p s u l e w a l l laminae a r e i n d i c a t e d , as a r e t h e t h r e e component l a y e r s (l>2a, 2 b , 2 c ^ °^ n^-ddle lamina. The c a p s u l e p l u g (P) and stem (St) a r e a l s o shown. L

L

t

h

e

29

180

40 -I 0

1

1

1

1

1

10

20

30

40

50

1 —

60

1

— i

70

POSITION A L O N G C A P S U L E C H A M B E R

1

80

1

90

100

{%)

FIGURE 8. V a r i a t i o n i n w a l l t h i c k n e s s a l o n g the c a p s u l e chamber of f i e l d c o l l e c t e d N u c e l l a emarginata c a p s u l e s from G r a p p l e r I n l e t , Ross I s l e t s , and Seppings I s l a n d . Values are e x p r e s s e d as X + 1 S.E. f o r n = 8 c a p s u l e s from each p o p u l a t i o n .

30 a l o n g t h e c a p s u l e chamber.

Although

changes i n c a p s u l e

width

a l s o o c c u r r e d a l o n g t h e l e n g t h o f t h e chamber, t h e s e d i d n o t appear t o correspond

with variation i n wall thickness

Sections through emarginata

capsules

among t h e G r a p p l e r populations. 70%

the w a l l s of f i e l d - c o l l e c t e d N u c e l l a

revealed obvious Inlet,

differences i n thickness

Ross I s l e t s ,

and

Seppings I s l a n d

Comparisons of w a l l t h i c k n e s s data

from a p o i n t

a l o n g t h e chamber chamber i n d i c a t e d t h a t c a p s u l e s

Ross I s l e t s were s i g n i f i c a n t l y t h i n n e r t h a n c a p s u l e s S e p p i n g s and

Grappler

(means o f 61,

ANOVA: F=29.9, p

1+ ON

oi J3 p 03Ul 01

Ml

3

C A P S U L E CHAMBER INTACT Total * of Capsules

Contained Embryos

55(22)

255

88(35)

19

13 (68)

167

43(26)

75(45)

140

26(19)

187

(1.8 m)

MID (2.3 m)

LOW

(1.2 m)

HIGH (2.0 m)

u a LOW INTERTIDAL BOULDERS (1.2 m)

LOW

ROSS ISLETS

Contained Ova

HIGH (2.6 in) ROCKY OUTCROPPING (2.8-3.1 m)

-

C A P S U L E CHAMBER OPENED Hatched Naturally

Opened by Predators

55(22)

47(18)

-

CATEGORIZATION

Hemigrapsus Idotea Predation Predation

2 (4)

20 (43)

OF CAPSULAR

REMAINS

Mopalia Bevelled Predation Holes

1 (2)

8 ( 17)

Misc. Predation

16 (34)

6(32)

6(100)

2(1)

43(26)

36 ( 84)

86 (61)

-

24(17)

22(92)

-

-

2(8)

52 (28)

83(44)

-

20(11)

14(70)

-

-

4(20)

37

17(46)

2(5)

-

-

139

27(19)

18(13)

10

1117

10(100)

2(0)

2(10)

9(24)

9(24)

9(100)

63(45)

31(22)

24 ( 77)

-

-

-

-

1 (2)

-

_

_

_

_

_

_

75(7)

779(70)

242(22)

177(73)

-

-

-

.

1(0)

6 ( 14)

7(23)

_

64(26)

78 drill

holes i n other gastropod The

d e n s i t y of s n a i l s

h i g h t r a n s e c t at Grappler capsule predators

The

Idotea

i n the

percentage

c a p s u l e s was

(Table I I ) .

transect.

the

In c o n t r a s t ,

egg

were n o t a b l y intertidal

o f c a p s u l e s opened i n t h i s showing evidence

region

was

of predation

I I I a l s o shows t h e e x t e n t o f p r e d a t i o n on along the lower

I d o t e a were o f t e n found

a p p e a r e d t o be

capsules

intertidal

amongst t o r n egg

capsules

responsible f o r the m a j o r i t y of predation

capsules.

The

percentage

o f c a p s u l e s opened

p r e d a t o r s r a n g e d f r o m 17 - 26 % on two a l t h o u g h t h e y were l e s s t h a n boulder,

1983).

low a l o n g

Idotea)

lower p a r t s of the

c o l l e c t e d from t h r e e b o u l d e r s

on t h e s e

(Abe,

(Table I I I ) .

Table

and

egg

Inlet

h i g h , w i t h a l l chewed c a p s u l e s by

capsules

( e g . H e m i g r a p s u s and

more a b u n d a n t t h a n channel.

and

egg

approximately

0.5

of the

m apart.

On

by

boulders, the

third

10 m away, o n l y 1 1 % o f c a p s u l e s

had

been opened.

2. R o s s

Islets

Densities of snails

and

egg

capsules varied

among t r a n s e c t s a t t h e R o s s I s l e t s capsules at t h i s overhangs.

The

(Table I I ) . A l l

s i t e were a t t a c h e d t o v e r t i c a l

surfaces

or

e x t e n t o f p r e d a t i o n on c a p s u l e s d e c r e a s e d

i n c r e a s e d t i d a l h e i g h t , and o f H e m i g r a p s u s nudus

corresponded

(0.6 - 2.4

cm

o n l y known p r e d a t o r s o f N u c e l l a egg Although

site

markedly

c r a b s were not p r e s e n t

when c e n s u s e s w e r e t a k e n ,

with

w e l l w i t h the d e n s i t y

i n carapace

width),

capsules at t h i s

the

site.

along the higher t r a n s e c t s

on s u b s e q u e n t v i s i t s c r a b s

were

79 occasionally transects.

found The

i n s m a l l c r e v i c e s a l o n g t h e 2.3

m a j o r i t y o f o p e n e d egg

h a v e b e e n e a t e n by H e m i g r a p s u s s p p .

and

2.6m

capsules appeared t o

(Table I I I ) .

Only

3

c a p s u l e s had b i t e marks s i m i l a r t o t h o s e a s s o c i a t e d w i t h I d o t e a , and study

o n l y one

o f t h e s e i s o p o d s was

ever

found

i n the

area. Censuses of the h i g h i n t e r t i d a l

Islets

i n A u g u s t 1988

o u t c r o p p i n g a t Ross

a l s o i n d i c a t e d t h a t Hemigrapsus

were i m p o r t a n t p r e d a t o r s .

O v e r 22%

of these capsules

spp. appeared

t o h a v e b e e n o p e n e d by p r e d a t o r s , w i t h t h e m a j o r i t y s h o w i n g evidence

3.

o f a t t a c k by

Seppings Egg

Hemigrapsus.

Island

c a p s u l e s from

bite-marks

by b o t h

Seppings

I s l a n d showed e v i d e n c e

I d o t e a and H e m i g r a p s u s .

g r e a t e r l e v e l s o f wave a c t i o n a t t h i s wosnesenskii

site,

Despite

the

Idotea

and H e m i g r a p s u s n u d u s w e r e a b u n d a n t ,

w i t h i n t h e t h i c k beds o f M y t i l u s c a l i f o r n i a n u s .

especially Capsules

a l s o found w i t h b e v e l l e d holes i d e n t i c a l t o those from G r a p p l e r I n l e t

(Fig. 3). to

24%

o f egg

capsules present at the Grappler I n l e t

Ross I s l e t s

sites,

respectively.

Observations

remains i n d i c a t e d t h a t the i n t e r t i d a l wosnesenskii), crabs gastropods

were

collected

I n summary, p r e d a t o r s w e r e f o u n d t o h a v e o p e n e d up 32% and

of

isopods,

and

of capsular (Idotea

( H e m i g r a p s u s o r e g o n e n s i s ) , and

unknown

were r e s p o n s i b l e f o r t h e m a j o r i t y o f p r e d a t i o n a t

G r a p p l e r I n l e t , whereas c r a b s ,

(Hemigrapsus nudus),

o n l y numerous p r e d a t o r s a t t h e R o s s I s l e t s

site.

were t h e

80

III. 1.

F I E L D EXPERIMENTS Grappler

Inlet

a) P i l o t

experiments

Capsules 19 days.

were l e f t w i t h i n

Over t h i s

n = 2 5 c a g e s ) and t h e l o w and possible

frameless cages f o r a p e r i o d of

p e r i o d a mean o f 2 . 0 + 0 . 3

1.8 ±

0.3 c a p s u l e s

h i g h i n t e r t i d a l cages,

8 capsules/cage).

The

respectively

I

T

H

I

N

= 0.73,

t r a n s e c t : ANOVA; F p>0.10).

w i t h cage

(n=50) over c a p s u l e s was

detached

T

due

Table

I

=

N

a two

day

1.53,

p>0.25;

period.

p>0.10;

FJ^JQNG

=

of the

in total

Although

unknown, I s u s p e c t e d

to a failure

high

2.17,

constant

at

from a l l

the cause

crabs

1 9 days.

of

t h a t c a p s u l e s became

glue.

I V shows t h e t y p e o f c a p s u l a r r e m a i n s f o u n d

shore

responsible

A l o n g the low

(Hemigrapsus oregonensis)

i n the

intertidal appeared t o

be

f o r t h e m a j o r i t y o f p r e d a t i o n ; h o w e v e r , i n some

c a s e s t h e p r e d a t o r s o f egg Along

1.34,

c a p s u l e s were " l o s t "

f r a m e l e s s cages a f t e r transect

H

=

position

level.

A mean o f 6.1

lost

I

F^QJJQ

by

(low t r a n s e c t :

Hence, p r e d a t i o n l e v e l s were r e l a t i v e l y

each t i d a l

cages

W

p>0.25;

(out o f a

number o f c a p s u l e s o p e n e d

w i t h i n o r among b l o c k s a l o n g e a c h t r a n s e c t W

1S.E.,

(n=25 cages) were opened i n

p r e d a t o r s d i d not d i f f e r s i g n i f i c a n t l y

ANOVA; F

(X +

c a p s u l e s c o u l d n o t be

the higher i n t e r t i d a l t r a n s e c t , isopods

identified.

(Idotea)

were

t h e c h i e f p r e d a t o r s and w e r e f r e q u e n t l y f o u n d e a t i n g c a p s u l e s . F e w e r c a p s u l e s w e r e o p e n e d by H e m i g r a p s u s o r e g o n e n s i s d r i l l e d by

other predators i n t h i s

region.

or

TABLE IV. Summary o f N u c e l l a emarginata egg c a p s u l e s opened by p r e d a t o r s i n the p i l o t experiment i n G r a p p l e r I n l e t , June 1988. Capsules were c l a s s i f i e d by the b i t e and chew marks l e f t on t h e c a p s u l a r chamber.

CHARACTERISTICS Hemigrapsus Chew Marks

LOW

TRANSECT

(1.2

HIGH

(2.0

m)

Bevelled Holes

REMAINS

Mopalia rasping

Misc. Predation

Total # Eaten

17

-

14

1

19

51

4

22

2

-

16

44

m)

TRANSECT

Idotea Chew Marks

OF CAPSULAR

82 b)

Predator-exclusion

experiments

P r e d a t o r - e x c l u s i o n experiments predators t h e 2.25 The

revealed that the

of capsules at the Grappler cm

s i t e were l a r g e r

e n t r y h o l e s of the l a r g e - h o l e cages

2

major than

( F i g . 4a,b).

number o f c a p s u l e s o p e n e d a f t e r 20 d a y s v a r i e d

significantly

among c a g e t y p e s

( K r u s k a l - W a l l i s One-Way ANOVA:

l o w t r a n s e c t , K=10.41, P