THE LIFE-HISTORY OF THE SAND CRAB HIPPA CUBENSIS SAUSSURE

LIVING ON A SMALL ISLAND

by

ARTHUR JOHN HANSON

BSc., University of B r i t i s h Columbia, 1965

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF MASTER

OF SCIENCE

in the Department

of

ZOOLOGY

We accept t h i s thesis as conforming

to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA

March 1969

In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an

a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e

L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r

a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y

p u r p o s e s may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n ­

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

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

D e p a r t m e n t n f Zoology

T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a

D a t e yigig A p r i l 5 , 1969

ABSTRACT

The closely related sand crabs Hippa and Emerita both

inhabit the i n t e r t i d a l zone of t r o p i c a l sandy beaches but

Emerita i s absent from many oceanic islands while Hippa i s absent

from most mainland coasts. The d i s t r i b u t i o n patterns are

explained by comparing the l i f e - h i s t o r y of H. cubensis, l i v i n g

i n the West Indies, with published information on Emerita

species.

Size d i s t r i b u t i o n s and beach habits of the 2 genera

were si m i l a r and differences i n egg production and l a r v a l devel­

opment times are considered to be temperature-dependent and

not generic differences. 1

A preference of Hippa for coarse sand beaches, found

mainly on islands, partly accounts for the d i s t r i b u t i o n of

this genus. The preference i s accounted for by the absence of

an e f f e c t i v e respiratory tube and behavioral adaptations traced

to feeding habits.

Hippa appears to be r e l a t i v e l y stenothermal, which

would account for i t s absence from warm temperate areas

occupied by Emerita.

The d i s t r i b u t i o n patterns of Emerita are not readi l y

explained. The p o s s i b i l i t i e s of predation of Emerita on

extremely l i g h t or dark sand, as found on islands or predation

of young Emerita by Hippa are considered.

i i

TABLE OF CONTENTS

Page

ABSTRACT . . • i i

LIST OF TABLES V

LIST OF FIGURES v i

ACKNOWLEDGMENTS v i i i

INTRODUCTION , . . ' • 1 Description of Study Areas . . . 6

Barbados Martinique and St. Lucia Trinidad

METHODS . . . . . . . . . . . . . . . 9

Beach studies Laboratory studies

RESULTS . . . . . . . . . 15

General Biology - . . . 15

Size D i s t r i b u t i o n Feeding Beach Ecology Population Density Coloration

Reproduction and Larval Development . 30

Annual Egg Production Larval Development F i r s t Zoea Second Zoea Third Zoea Fourth Zoea F i f t h Zoea Sixth Zoea Megalopa Larval Recruitment by Downstream Gyrals

i i i

Effects of Substrate Size 51

Sand Preference i n the Laboratory-D i s t r i b u t i o n of Hippidae i n Trinidad Respiratory Currents

DISCUSSION • 63

General Biology 63

Size D i s t r i b u t i o n Feeding Beach Ecology Coloration

Reproduction and Larval Development 66

Annual Egg Production Larval Development Larval Recruitment by Downstream Gyrals

Sand Preference 70

E f f e c t on Hippa D i s t r i b u t i o n

Further Considerations . '. . 72 Temperature and the D i s t r i b u t i o n of Hippa D i s t r i b u t i o n of Emerita

SUMMARY 76

BIBLIOGRAPHY 78

i v

LIST OP TABLES

Table Page

I. Population r a t i o s i n H. cubensis . . . 18

II. Analysis of gut'contents of 768 H. cubensis (9.5-24.5 mm carapace length) from Barbados , 23

III . Environmental variables measured i n June 1967 on the beach behind Paynes Bay f i s h market . . 2 5

IV. Measurements (in mm) of laboratory-reared larvae of H. cubensis at d i f f e r e n t stages . . . 36

V. Sand grain size preferences among crabs of of 3 size-groups 53

VI. F a c t o r i a l ANOVA on data' of Table V 54

VII. Analysis of covariance on data of Figure 20 . . . 60

v

LIST OF FIGURES

Figure Page

1. Map of Barbados (15°N, 59°W) showing r e l a t i v e density of H. cubensis around the i s l a n d i n July 1966 7

2. Size d i s t r i b u t i o n of 396 H. cubensis sampled at d i f f e r e n t levels of the beach at high tide . . . 16

3. Size d i s t r i b u t i o n , by sex, of 2540 H. cubensis taken i n monthly samples at B e H a i r s beach, from Sept. 1966 to July 1967 17

4. Movements of H. cubensis, at intermediate tid e levels to a b a i t of f l y i n g f i s h (Hirundichthys a f f i n i s ) . 20

5. .H. cubensis feeding on a f l y i n g f i s h (HirundTchthys a f f i n i s ) on the beach . . . . . . 22

6. D i s t r i b u t i o n of H. cubensis on the beach at high, medium and low tide levels . . . . . . . . 26

7. Size d i s t r i b u t i o n of 233 H. cubensis i n zones 1 to 4 (see Table III) at high tide 27

8. Color v a r i a t i o n i n H. cubensis 29

9. Percentage of gravid females i n monthly samples from B e l l a i r s beach, August 1966-July 1967 . . . 31

10. Maximum fecundity and crab size i n H. cubensis co l l e c t e d on the west coast of Barbados . . . . 32

11. Changes i n diameter during zygote maturation of H. cubensis at 26-27°C. i n the laboratory, Feb. 1967 3 3

12. Zoeal stages of H. cubensis 37

13. Appendages of zoeal stages of H. cubensis 39

14. Mouthparts and scaphognathite of H. cubensis zoeae 40

v i

Figure Page

15. Ventral view of telson of zoeal stages of H. cubensis 42

16. Antennule, antenna and mouthparts of megalopa of H. cubensis 48

17. Megalopa of H. cubensis 49

18. Interaction of crab and sand sizes i n sand-size preference experiments 55

19. D i s t r i b u t i o n of H. cubensis and E. portoricensis and sand grain size of beaches on the north and east coasts of Trinidad during July 1967 . . 57

20. E f f e c t of sand size on the d i r e c t i o n of the respiratory current of s i m i l a r - s i z e d H. cubensis 59

21. E f f e c t of crab size on the d i r e c t i o n of the respiratory current of H. cubensis buried i n fine sand (median diameter 0.25-0.149) . . . 61

22. Relationship of l a r v a l development time of 3 species of Emerita and H. cubensis to culture temperature . . . . 69

23. The world d i s t r i b u t i o n of Hippa species 73

v i i

ACKNOWLEDGMENT S

I would l i k e to thank Dr. J. B. Lewis, Director of

B e l l a i r s Research Ins t i t u t e of McGill University, for providing

laboratory space for this study and for his help throughout the

study. My wife took an active part i n the entire study,

es p e c i a l l y during the l a r v a l culture work. Margaret Knight,

Scripps I n s t i t u t e of Oceanography, and Dr. A. J . Provenzano,

Insti t u t e of Marine Science, University of Miami, provided very

useful c r i t i c i s m s of the section on l a r v a l development. I am

grateful to Dr. G. Scudder, Department of Zoology and

Dr. A. Lewis, I n s t i t u t e of Oceanography, University of B r i t i s h

Columbia for t h e i r c r i t i c i s m s of the manuscript. F i n a l l y , I

would l i k e to extend my thanks to Dr. T. Carefoot, Institute

of Marine Science, McGill University, for his comments and

ideas during the l a t t e r part of the study and Dr. I. E. Efford,

Department of Zoology, U.B.C, for his suggestion of the

research topic and aid throughout as supervisor.

v i i i

INTRODUCTION

Anomuran sand crabs of the family Hippidae are abun­

dant on the i n t e r t i d a l zone of sandy beaches throughout the

t r o p i c a l and warmer temperate seas of the world.

Differences have been found i n the d i s t r i b u t i o n s of

2 genera i n t h i s family. Emerita (formerly Hippa) species are

predominantly dwellers of mainland coasts (Efford, MS), while

Hippa (formerly Remipes) are mainly r e s t r i c t e d to islands.

An example i s the d i s t r i b u t i o n of Emerita and Hippa

i n the Caribbean and on the coast of northeast South America.

H. cubensis, with a range from F l o r i d a to B r a z i l , i s abundant

on many Caribbean islands, but has been reported from only a

few mainland locations. Within th i s range 3 species of

Emerita have been found along the mainland coasts (Schmitt,

19'35) . Only E. portoricensis has been found on islands away

from the mainland and i t i s absent from some islands such as

Barbados.

These d i s t r i b u t i o n a l patterns have not been s a t i s f a c ­

t o r i l y explained. Without an accurate knowledge of the l i f e -

history and habits of the 2 genera a l l attempts at an explana­

tion are purely speculative.

The l i f e - h i s t o r y of several Emerita species i s well

known (Weymouth and Richardson, 1912; MacGinitie, 1938;

Wharton, 1942) but publications on Hippa have been concerned

1

2

mainly with taxonomy and records of d i s t r i b u t i o n .

In t h i s study the l i f e - h i s t o r y of H. cubensis i s

examined and compared with published data on Emerita. The

information i s used to determine whether the observed d i s t r i ­

bution patterns of Hippa and Emerita could be caused by: (a)

differences i n beach c h a r a c t e r i s t i c s on mainlands and islands,

(b) differences i n reproductive pot e n t i a l and l a r v a l devel­

opment or (c) some other difference, previously unknown, i n

the l i f e - h i s t o r y .

The size of substrate p a r t i c l e s has been shown to

l i m i t the d i s t r i b u t i o n s of some beach dwelling invertebrates.

Wade (1967) reported that the beach clam Donax denticulatus

i s r e s t r i c t e d to fine sand beaches, which are more stable

than loose coarse sandy beaches. Weiser (19 59) found that

sand grain size profoundly af f e c t s the i n t e r s t i t i a l fauna of

sandy beaches i n Puget Sound.

Sand-dwelling animals must have a means of drawing

water, free of sand, over the g i l l s . In fine sand the

p a r t i c l e s are more closely packed making i t more d i f f i c u l t to

draw the necessary water through the sand (Webb, 1958), and

increasing the chance of inhaling sand p a r t i c l e s . Some crabs

are adapted to r e s p i r i n g i n fine sand by using either the

antennules, as i n Emerita and Albunea or the antennae, as i n

Corystes, as a respiratory siphon (Weymouth and Richardson,

1912; Garstang, 1897). I f Hippa lacked t h i s adaptation i t

might not be able to colonize fine sand beaches.

Chapman (1954) has noted that t r o p i c a l i s l a n d beaches,

3

s i m i l a r to those of many Caribbean i s l a n d s , formed from

calcareous reef deposits and volcanic mater ia l are composed

of coarse sand. Hedgpeth (1953) reported that mainland beaches

along the Texas coast are composed of very f ine sand.

Mainland coasts might be expected to have f iner sands

than i s lands for 2 reasons: (a) greater geo log ica l age of

mainlands and consequently more time for abrasion of p a r t i c l e s

and (b) the depos i t ion of f ine a l l u v i a l sands from mainland

r i v e r s . Coarse sand on mainland beaches could be expected

where the substrate i s r e s i s tan t to abras ion, where there are

no a l l u v i a l deposits and where there are offshore c o r a l reefs .

In the Gulf of Mexico and northwest South America

there are a number of large r i v e r s discharging from the main­

land. The i n f l u x of fresh water and sediment along these

coasts l i m i t s the presence of c o r a l reefs (Wells, 1957).

Concerning c e r t a i n of the l i f e cycle d e t a i l s which

might be important i n the d i s t r i b u t i o n of animals with plank­

tonic l arvae , the most obvious i s the time spent as l a r v a l

stages. On long coast l ines planktonic larvae discharged from

shore could d r i f t long distances l a t e r a l l y and s t i l l remain

within an area su i table for s e t t l i n g . Coastal currents on

long coast l ines may a id i n l a r v a l retent ion (Hedgpeth, 1957a).

The problem of l a r v a l recruitment to i s o l a t e d oceanic

i s l a n d s , t y p i c a l of those occupied by Hippa, i s exemplified

by Barbados. This i s l a n d i s pos i t ioned to the east of a l l

the other Caribbean i s lands . . Current flow i s westerly with

contr ibut ions from both North and South Equator ia l Currents .

4

Thus pelagic larvae from Barbados might d r i f t to the other

islands and s e t t l e there. However larvae released from these

islands would have to swim against the current to s e t t l e

around Barbados. Lewis (19 60) has pointed out that many of

the rocky shore i n t e r t i d a l invertebrates of Barbados have a

shortened pelagic l a r v a l l i f e .

It i s known that Emerita species have a r e l a t i v e l y

long l a r v a l l i f e (Knight, 1967; E f f o r d , i n press). This could

account for the absence of Emerita from most t r o p i c a l islands

i f Hippa has a short l a r v a l l i f e to prevent i t from being

swept out of s e t t l i n g range of the islands. However a short

l a r v a l l i f e would not explain the absence of Hippa from main­

lands.

The only published descriptions of the l a r v a l devel­

opment of Hippa are the fourth zoeal stage of H. cubensis

from planktonic specimens off the west coast of A f r i c a (Lebour,

1959) and the f i r s t zoea of H. adactyla from a laboratory

hatching (Al-Kholy, 1959).

Insular repopulation might also be enhanced by an

increase i n the t o t a l number of larvae produced, either by

having a larger number of smaller-eggs per female or by pro­

longing the reproductive period.

A system of downstream gyrals which would return

larvae to Barbados mainly along the west coast, has been pro­

posed as an a l t e r n a t i v e method of population recruitment

(Emery, 1964). If t h i s theory i s true, the l a r v a l development

time could be long and s t i l l allow an animal to s e t t l e near

5

the isl a n d .

The general lack of knowledge of the l i f e - h i s t o r y of

Hippa leaves the p o s s i b i l i t y that the d i s t r i b u t i o n patterns

of Hippa and Emerita could be caused by some previously unsus­

pected difference i n growth, s i z e , l i f e span, feeding or beach

ecology. This p o s s i b i l i t y warrants a thorough study of these

aspects of the l i f e - h i s t o r y .

The islands of the eastern Caribbean provide an i d e a l

study area since both mainland and i s o l a t e d oceanic islan d

environments can be found within a r e l a t i v e l y small radius.

Barbados i s an i s l a n d formed of co r a l deposits and i s uniquely

positioned for studies on l a r v a l d i s t r i b u t i o n . The neighbor­

ing islands of St. Lucia and Martinique provide beaches of

dark volcanic sand while Trinidad, an islan d of continental

o r i g i n , has both fine and coarse sand. Since both E. porto-

r i c e n s i s and H. cubensis have been reported from Trinidad

(Schmitt, 1935), t h i s i s l a n d i s p a r t i c u l a r l y suited to studies

on sand preference.

A l l laboratory work and most f i e l d studies were

carried out at B e l l a i r s Research Ins t i t u t e of McGill University

in Barbados, between July, 1966 and July, 1967. To obtain

information on sand preferences and population c h a r a c t e r i s t i c s

from beaches of d i f f e r e n t composition than those of Barbados,,

co l l e c t i o n s were made i n Trinidad, St. Lucia and Martinique.

DESCRIPTION OF STUDY AREAS

BARBADOS

Barbados l i e s about 90 miles east of the islands of

the Lesser A n t i l l e s . I t has a maximum length of 21 miles

and width of 11 miles.

Lewis (1960) described the major environmental factors

a f f e c t i n g the rocky shores of the island as follows: (a)

tides are of a mixed semidiurnal type, with a mean range of

about 0.7 m, (b) annual temperature range of the coastal

waters i s approximately 25 - 29°C., with a d a i l y f l u c t u a t i o n

of about 1°C., (c) wave action on the east coast has an

amplitude of 4-8 times that of the 1 m surf on the west coast.

Beach areas around Barbados are shown i n Figure 1.

No fine a l l u v i a l sands are found. Along the east coast the

sand i s generally a brown quartz of medium diameter (Macintyre,

1967) while the sands of the west and south coasts are medium

to coarse white c o r a l , sometimes mixed with c o r a l l i n e algae. .

Sand size classes are based on Wentworth (1922).

Beach slope i s inversely related to sand size (Bascom,

1964). Most of the beaches around Barbados are of medium

slope (10%).

MARTINIQUE AND ST. LUCIA

These 2 volcanic islands of the Lesser A n t i l l e s l i e

approximately 100 miles west of Barbados.

6

7

N

Figure 1. Map of Barbados (15°N, 59°W) showing - r e l a t i v e density of H. cubensis around the is l a n d i n July 1966. Number of samples i s shown in -parentheses. - A to H are stations where crabs were colle c t e d for food analysis (see Table I I ) .

8

Most of the beaches are volcanic sand. Generally they

are of medium slope and medium to coarse sand. A s t r i k i n g

feature i s the black color. There are also limited areas of

a l l u v i a l sand and calcareous reef deposits on both islands.

TRINIDAD

Trinidad l i e s just o f f the coast of Venezuela, about

175 miles southwest of Barbados.

The beaches on t h i s continental islan d have a variable

composition, depending on t h e i r location. The southern half

of the east coast i s almost a l l a continuous f l a t beach.com­

posed of f i n e , hard-packed a l l u v i a l sand (Wade, 1967), while

the northeast coastline i s mainly rocky shores with i s o l a t e d

medium to steeply sloped coarse sandy beaches. The composi­

t i o n of these beaches r e f l e c t s the parental rock. Along the

northcen'tral coast there are 2 fine-sand beaches at the head

of Maracas and Las Cuevas Bays.

Both the north and east coasts of Trinidad are exposed

to heavy wave action s i m i l a r to that of the east coast of

Barbados.

METHODS

BEACH STUDIES

Hippa were coll e c t e d using 2 d i f f e r e n t techniques.

The crabs emerged and could be c o l l e c t e d by hand when a b a i t

of f l y i n g f i s h (Hjrundichthys a f f i n i s ) or other f i s h was

dropped on the beach. This was the most frequently used

method. A more d i f f i c u l t procedure was to sieve sand samples

through a 1 mm mesh screen. Sides and back were welded onto

an ordinary shovel to provide a scoop capable of sampling a

wedge-shaped volume of sand 32 x 26 x 10 cm deep without

losing the crabs. Thus crabs of a l l sizes would be taken i n

t h e i r r e l a t i v e abundance.

Monthly samples' of 200-250 H. cubensis from B e l l a i r s

beach (see Figure 1) were taken from August 1966 to July 1967

by hand c o l l e c t i n g crabs attracted to a b a i t . The size d i s ­

t r i b u t i o n , male:female r a t i o and breeding season were deter­

mined from these samples. The size d i s t r i b u t i o n of Hippa

from Barbados was compared with that of crabs co l l e c t e d i n

Martinique and St. Lucia during March, 19 67.

A beach, with a large Hippa population, at Paynes •

Bay (see Figure 1) was intensively studied to provide com­

parative information on size d i s t r i b u t i o n , population density,

the e f f e c t of tide changes and the size zonation on a beach

r e l a t i v e to surf and sand s i z e . Six stations were chosen at

9

10

approximately equal i n t e r v a l s along a 110 m section of beach.

At each station physical measurements and sand samples, using

the modified shovel described above, were taken at 20% i n t e r ­

vals between high and low tide marks. Each sample series

consisted of 5 shovelfuls of sand from each of the 5 v e r t i c a l

zones at a station. In a l l , 38 sample series were obtained

at high, intermediate and low tide l e v e l s .

To determine whether Hippa i s r e s t r i c t e d to the i n t e r -

t i d a l zone numerous dredgings, using a shovel and SCUBA gear,

were made off the west coast beaches near B e l l a i r s . Baits of

f l y i n g f i s h were also set out below the i n t e r t i d a l zone.

Two other large c o l l e c t i o n s of H. cubensis were made.

Egg counts were made on"the most fecund females of d i f f e r e n t

sizes selected from a sample of 500 gravid females c o l l e c t e d

from beaches a l l around Barbados. The proventriculus contents

of 768 crabs, from various locations around Barbados were

examined.

The r e l a t i v e abundance of H. cubensis on beaches a l l

around Barbados, was measured during July 1966 to examine the

hypothesis of insular repopulation by downstream gyrals

(Emery, 1964). A weighted fiberglass screen (40 x 70 cm) was

baited with a small whole f i s h , Harengula clupeola (Cuvier)

and placed on the beach so that i t was just covered by every

wave at an intermediate tide l e v e l . The number of Hippa

crossing t h i s screen during a 5-minute period was recorded.

To see whether either genus preferred a p a r t i c u l a r

sand s i z e , the d i s t r i b u t i o n of H. cubensis and E. portoricensis

11

was studied along beaches of the north and east coasts of

Trinidad. A 200 m section of 20 beaches was sampled. Hippa

was attracted to baits of f l y i n g f i s h while Emerita was

obtained by sieving sand samples. Sand grain size was deter­

mined by c a l c u l a t i n g median diameter of dried sand taken from

the middle of the i n t e r t i d a l zone.

LABORATORY STUDIES

Experiments were conducted to see whether H. cubensis

taken from the coarse sands of Barbados showed a preference

for a habitat of a p a r t i c u l a r sand grain size and to see

whether any preference varied according to the size of the

crab. Four p l a s t i c trays (21 x 21 x 7 cm each) were snugly

f i t t e d into a high-sided wooden box with mesh-covered holes

d r i l l e d along a l l 4 sides just above the l e v e l of the top of

the tray. Each tray could be f i l l e d with unsieved sand or

sand of a known diameter. The apparatus was kept i n a water-

table f i l l e d with constantly flowing sea water. For each

experiment 10 newly captured crabs were placed i n the centre

of each of the four trays (quadrants). Each crab was f i r s t

marked on the carapace with a f e l t pen. Different colors

were used for each quadrant. A 1 mm mesh screen cover was

placed over the apparatus and the crabs were l e f t undisturbed

for 24 hours. The sand from each quadrant was then sieved and

the crabs counted. There were 12 repetitions of t h i s pro­

cedure i n each experimental s e r i e s . A f t e r every 3 repetitions

the trays were s h i f t e d to a new quadrant. The t o t a l number

of animals used i n each series was 480.

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The e f f e c t of substrate on respiratory current d i r e c ­

tion was studied by i n j e c t i n g a d i l u t e suspension of India

ink i n sea water near crabs held i n d i v i d u a l l y i n 200 cc

fingerbowls under 3 conditions: (a) no sand, (b) i n s u f f i c i e n t

sand to bury and (c) s u f f i c i e n t sand to bury to a depth where

only the antennules were v i s i b l e . The d i r e c t i o n of the

respiratory current was measured i n i t i a l l y and at 5 subsequent

hourly i n t e r v a l s . A t o t a l of 150 H. cubensis were tested.

For comparison, 8 large Albunea were s i m i l a r l y tested under

condition (a) and another 8 under condition (c).

To determine the e f f e c t of a l t e r i n g the crab s i z e :

sand size r a t i o on the respiratory current d i r e c t i o n , further

experiments under condition (c) were carried out on Hippa.

In one series 4 d i f f e r e n t sand grain sizes were used while

i n the other sand size was held constant and crabs of d i f ­

ferent sizes were.used.

The maturation period from the appearance of eggs

on the pleopods to t h e i r release as free-swimming zoeae was

determined by holding marked gravid females i n the laboratory

u n t i l t h e i r eggs hatched. Samples of 10 f e r t i l i z e d eggs were

taken i n i t i a l l y and at 3-4 day i n t e r v a l s . Diameters of the

spherical eggs were measured with the aid of an ocular micro­

meter. A curve of egg diameter against time to hatching was

extrapolated to the minimum diameter found i n a sample of

about 700 gravid females to give the approximate time for

embryonic maturation. From these data and from information

on egg number and breeding season, the annual production of

13

young per female was estimated.

For the egg maturation experiment and for general

observations on Hippa, crabs had to be kept a l i v e for periods

of weeks or months. Ten-gallon aquaria with constantly flow­

ing natural sea water were used. The bottoms were covered

with a thick layer of sand with sea water percolating from

beneath to prevent deoxygenation. Strips of f l y i n g f i s h were

provided as food.

The l a r v a l development of H. cubensis was studied by

rearing newly-hatched larvae i n the laboratory. Females

with mature embryos were obtained from B e l l a i r s beach on 30

October, 1966. Each female was placed i n a fingerbowl u n t i l

the embryos were hatched as f i r s t zoeae, within 2 days.

Some -of the newly released zoeae were pipetted'to

compartmented p l a s t i c trays, each compartment containing

50 cc of sea water and one zoea. .. Newly hatched zoeae were

also transferred into p l a s t i c trays which held 3 animals in

150 cc of sea water, and to mass cultures (50 to.100 larvae)

i n 10 00 cc fingerbowls. At the f i f t h zoeal stage some larvae

were transferred from the p l a s t i c trays to i n d i v i d u a l 200 cc

fingerbowls.

The sea water was passed through f i l t e r paper before

use. No a n t i b i o t i c s were added. The culture dishes were

kept i n a water table f i l l e d with continuously flowing water

pumped d i r e c t l y from the ocean. The cultures were shaded

from d i r e c t sunlight. Laboratory fluorescent l i g h t s usually

extended the period of l i g h t i n g to 16-18 hours per day.

14

Daily inspections for dead larvae and exuviae were

made. Every second day the larvae were transferred to clean

containers with new water. Recently hatched Artemia n a u p l i i

were added d a i l y as food.

Exuviae and dead larvae were preserved in 5% neutralized

formalin i n sea water. These were dissected and stained, when

necessary, i n basic fuschin. Drawings were made using a

camera lu c i d a , and detailed descriptions of a l l l a r v a l stages

were prepared. For a l l numerical data at least 10 specimens

were examined.

RESULTS

GENERAL BIOLOGY

SIZE DISTRIBUTION

H. cubensis ranged from 4 to 26 mm in.carapace length

(from t i p of rostrum to indentation at posterior end). Length-

frequency d i s t r i b u t i o n s of the B e l l a i r s monthly samples showed

close conformation to those obtained by the more exact pro­

cedure of sieving sand samples from d i f f e r e n t l e v e l s of the

beach, except for the smallest crabs (4-8 mm carapace length).

Only 17.8% of the B e l l a i r s samples were in t h i s size range

while 39.2% of the crabs from the Paynes Bay sieved samples

were i n t h i s range.

The r e l a t i v e numbers in each size range, for the Paynes

Bay population, are shown i n Figure 2. Length-frequency histo­

grams, by sex, for the B e l l a i r s population (Figure 3) show

that males did not grow as large as females. The maximum

recorded size of a male was 15.5 mm. The decline i n male abun­

dance was sudden and began at the size when most females f i r s t

became gravid. Sex could not be determined i n crabs below

8 mm.

The o v e r a l l sex r a t i o was approximately 1:1 (see

Table I ) . Between 8 and 15 mm only about 31% of the crabs were

females. The r a t i o of females above and below 15 mm (including

half of the small crabs whose sex was uncertain) was

15

16

Figure 2. Size d i s t r i b u t i o n of 396 H. cubensis sampled at d i f f e r e n t levels of the beach at high t i d e , Paynes Bay, June-July, 1967.

L- J

17

Figure 3. Size d i s t r i b u t i o n , by sex, of 2540 H. -cubensis taken i n monthly'samples at B e l l a i r s beach; from Sept. 1966 to July 19 67.

18

TABLE I

POPULATION RATIOS IN HIPPA CUBENSIS. THREE INCLUDES 1/2 OF THE TOTAL NUMBER OF UNSEXED CRABS

(4 to 8 mm)

Size Range (mm)

Population Location

Relative Numbers

Ratio

1. Male:Female 8 - 2 4 B e l l a i r s 1095:1169 1:1.07

2. Male:Female 8 - 15 B e l l a i r s 1095:496 2.21:1

3. Small Female: 4 to 15 - Paynes Bay 113:103 1.10:1

Large Female 16 to 24

19

approximately 1:1.

No differences were found when size d i s t r i b u t i o n s of

Hippa from Martinique, St. Lucia and Trinidad were compared

with those from Barbados.

FEEDING

H. cubensis was found to be a scavenger. Any sort of

f l e s h including beef, chicken, shrimp, octopus, sea urchin

eggs, shark and other f i s h would a t t r a c t the crabs. In the

laboratory wounded Hippa and very small ones were sometimes

siezed by larger Hippa. The antennules, antennae and proven-

t r i c u l u s of a number of crabs were examined for plankton but

none was found.

On the beach, the crab normally l i e s buried just

below the surface of the sand, with no trace of eyes or

antennae showing. If a b a i t i s staked out on the sand crabs

emerge from as f a r as 4 m a f t e r only one or two waves have

passed over the b a i t . Figure 4 shows tracings made on the

movements of several crabs towards a dead f l y i n g f i s h staked

at the top of the wash zone. The crabs are ca r r i e d dia­

gonally down the beach with the receding wave wash so that

within one or two waves they are buried at the bottom of the

beach, d i r e c t l y below the f i s h . The crab faces seaward during

this downward migration. To f i n a l l y reach the b a i t Hippa

emerges from the sand and scuttles backward up the beach along

the crest of the incoming wash. Several waves may pass before

the crab f i n a l l y grasps the b a i t . Between waves the crab

buries.

20

< I EH

CO

fi­

fed cd n E W Q

O •J

S o Pd h 1 .

- 2

o N

fa O CH

o

LOW TIDE MARK

DISTANCE(m) FROM BAIT

Figure 4. Movements of H. cubensis, at intermediate tide levels to a ba i t of f l y i n g f i s h (Hirundichthys a f f i n i s ) . Tracings show movement- of individuals from point of emergence to burrowing during the passage of a single wave over the beach. See Table III for environmental conditions at'each l e v e l .

21

The bait i s held with the t h i r d maxillipeds. These

have a sharply pointed dactylus and are reflexed so that they

act as a claw.

Hippa w i l l bury down into the sand with the food, i f

possible. Sometimes 20 or more crabs w i l l be clustered

around a small piece of f i s h at a depth of 0-5 cm i n the sand.

If the food i s too large to be buried, the crab w i l l remain

p a r t i a l l y buried or even completely exposed (Figure 5). If a

wave sweeps the b a i t away, the Hippa are swept with i t down

the beach.

Most of the 768 Hippa examined for proventriculus

contents were obtained a f t e r a period of high surf i n May

1967, when more food than normal would be expected on the

beaches. 77.6% of the proventriculus samples were completely

empty (see Table I I ) . The contents r e f l e c t e d the uneven

d i s t r i b u t i o n of certain foods around the isl a n d . Physalia

are often washed up i n quantity along the east coast and

constitute an important part of the d i e t of crabs l i v i n g there.

The amphipods and copepods were abundant i n the debris from

a Thalassia bed at Station C, but were scarce i n most other

parts of the i s l a n d .

Laboratory and f i e l d observations indicated that

there was a considerable size range i n the food consumed. The

smallest amphipods found i n the proventriculus analyses were

about 4 mm i n length. Very large pieces of f l e s h were accept­

able as long as the crabs could penetrate the surface covering.

22

Figure 5. H. cubensis feeding on a f l y i n g f i s h (Hirundichthys a f f i n i s ) on the beach.

TABLE II

ANALYSIS OF GUT CONTENTS OF 768 ADULT CRABS (10.0-25.0 mm CARAPACE LENGTH) FROM BARBADOS

Loca t i o n 3 A A B C D E F G H

Date (1967) Feb. 2 7 May 5 May 13 May 6 May 29 May- 3 May 11 May 3 May 3

Gut Contents . Crustacea

Amphipods 10 Copepods 1 Decapod appendages 8 2 6 Other parts 2 2 9 4 1 1

Annelida 1 5 Physalia 33 b 2 Other j e l l y f i s h . 1 Fish (scales, bones) 1 1 2 4 1

. Eggs 1 Sea urchin (?) 1 3 5 1 Seaweed - 1 Gastropod 1 Unidentified

Setae 3 6 2 4 4 Flesh 7 5 1 1 2 6 10 3 Other organic material 1 12 8 3 2 7 9

Sand 5 5 6 3 7 3 11 15

Total no. examined 66 90 98 88 52 56 50 223 45

% empty 50.0 82. 2 85.7 55.7 71.2 82.1 80.0 84. 8 57. 8

aSee Figure 1 for locations •'-'Specimens checked only for presence or absence of Physalia.

24

BEACH ECOLOGY

The d i s t r i b u t i o n a l l i m i t s of H. cubensis were the high

and low tid e marks. Dredgings below the i n t e r t i d a l zone

yielded no Hippa, although specimens of the related sand crabs

Albunea and Lepidopa were obtained. Bait staked out below the

low tide mark f a i l e d to attract.any crabs. At the low tide

mark there i s a sudden drop-off of 15-20 cm. When crabs were

dropped into a receding wave they were never swept over t h i s

drop-off, but always buried before reaching i t .

Some c h a r a c t e r i s t i c s of the t y p i c a l c o r a l beach at

Paynes Bay are given i n Table III. The average slope of t h i s

beach was 1:11.

The area colonized by Hippa changed with the tide

l e v e l (Figure 6). At high tide the crabs were f a i r l y uniformly

d i s t r i b u t e d across the beach, except for zone 5 (top 20% of

the beach), which contained almost no crabs at any time. As

the tide l e v e l drops the area without crabs increased. At

low tid e the animals were clustered i n a zone 2 m, or l e s s ,

at the bottom of the beach.

No crabs were taken i n core samples from exposed

areas of the beach at low t i d e . From f i e l d observations

(Table I I I ) , a combination of about 30°C. and 2 0% moisture

were the approximate tolerance l i m i t s of Hippa. To remain

within these l i m i t s the crab would have to bury to a depth of

30 to 50 cm i n zone 4 at low t i d e .

At high tide there was an uneven size d i s t r i b u t i o n of

individuals i n zones 1-4 (Figure 7). The smallest crabs were

TABLE III

ENVIRONMENTAL VARIABLES MEASURED IN JUNE 19 67 ON THE BEACH BEHIND PAYNES BAY FISH MARKET

Zone Av. d i s t . to Range of median Wave action Temperature Moisture top of zone sand diameter (Typical values) (Typical values) from L.T. H.T. L.T. H.T. L.T. H.T. L.T.

(m) (mm) (°C) (%)

1 2.06 1.0 - 2.0 A B 28.2 28.0 Saturated Saturated

(Same as surf)

2 4.12 0.71 - 0.50 A-B B-C 28.2 30.0 Saturated 21.05

3 6.18 0.50 - 0.25 C C-E 28.0 33.8 20.74 . 19.39

4 8.24 0.50 - 0.25 C-D E 29.5 33.9 21.31 9.91

5 10. 30 0.50 - 0.25 D E 31.1 35.0 11.39 4.78

aA - zone constantly covered; B - covered and uncovered by most waves; C - wash, uncovered by every wave; D - spray and some wash; E - spray only.

26

50 -,

25 -

50 -

25 -

75 -

50 -

25 -

HIGH TIDE n = 3 3 9

LOW T I D E M A R K HIGH T I D E H A R K

BEACH LEVEL

Figure 6. Di s t r i b u t i o n of H. cubensis on the beach at high, medium and low tide l e v e l s . Paynes Bay, June-July, 1967. See Table III for-environmental conditions at each l e v e l .

27

QO-l

CARAPACE L E N G T H (mm)

Figure 7. Size d i s t r i b u t i o n of 233 H. cubensis in zones 1 to 4 (see Table III) at high t i d e .

28

confined almost exclusively to zones 3 and 4. Most of the

crabs above 15 mm carapace length were i n zones 1 and 2..

Thus, at high t i d e , the larger crabs were found i n the coarser

sand where the surf was breaking, while the smallest crabs

inhabited the wash zone, composed of f i n e r sand. At low tide

there was considerable mixing of the sizes at the bottom of

the beach.

POPULATION DENSITY

Dense aggregations of Hippa were observed only when

a large b a i t was placed on the beach. When the b a i t was

removed the crabs dispersed.

An average density of 16 .crabs per square metre of

beach was calculated for Paynes Bay, during high t i d e . At

low tide the crabs were r e s t r i c t e d to.such a narrow band that

50 crabs were sometimes obtained i n a single shovelful of sand.

COLORATION

Beaches v i s i t e d during t h i s study ranged, i n color,

from the creamy white of'the coral and c o r a l l i n e algae types

to the black volcanic sand of Martinique and St. Lucia.

H. cubensis matched the color of the beach very cl o s e l y

i n a l l c o l l e c t i o n s . The range of the color on the dorsal

surface of the carapace was from cream to a purple-black (see

Figure 8). Often there was a complex pattern of darker colors

against a l i g h t e r background. The ventral surface and most

areas of the appendages are creamy-white i n a l l crabs, regard­

less of beach color.

H. cubensis and sand from t y p i c a l coral beach, Barbados.

30

REPRODUCTION AND LARVAL DEVELOPMENT

ANNUAL EGG PRODUCTION

H. cubensis breeds year-round, with 70 to 9 3% of the

females above 15 mm bearing eggs on the abdominal pleopods

(Figure 9). The minimum carapace length of a gravid female was

11.5 mm. In the 12 to 15 mm range the percentage of gravid

females ranged from a low of 3% i n November 19 66 to 83% i n

A p r i l 1967.

Maximum egg number i s dependent on crab size (Figure 10),

with a range of about 500 to 2700. Most crabs i n the sample

of 5 00 gravid females produced only 1/3 to 2/3 of the maximum

for t h e i r s i z e . '

I t i s uncertain whether the spherical eggs are f e r t i ­

l i z e d i n t e r n a l l y before they pass from the oviduct to the

pleopods or aft e r t h e i r attachment to the pleopods. Within

days aft e r t h e i r appearance on the pleopods cleavage stages

can be c l e a r l y distinguished, i n d i c a t i n g f e r t i l i z a t i o n has

occurred. The f e r t i l i z e d eggs,.at f i r s t colored a bright

orange by the abundant yolk gradually become transparent,

revealing the d e t a i l s of the developing embryo. The embryonic

c u t i c l e retains the spherical shape of the egg as i t increases

in diameter during maturation. During the early cleavage

stages, however, there i s l i t t l e increase i n diameter (Figure 11).

From Figure 11 the t o t a l development time from appear­

ance of eggs oh the pleopods to release of the f i r s t zoeae was

estimated at 15 days to 3 weeks. Two crabs which became gravid

31

100 - i

I 1 1 1 1 1 1 1 1 1 1 1 A u g Sept Oct Nov Dec Jan Feb Mar Apr May June July

Figure 9. Percentage of gravid females i n monthly samples from B e l l a i r s beach, August 1966-July 1967. Females of 15 mm carapace length and above - - - - ) ; females between 12 to 15 mm ( ). Total sample sizes for the l a t t e r group are shown.

Figure 10. Maximum fecundity and crab s ize i n H. cubensis c o l l e c t e d on the Wesjt' coast -of Barbados. Egg number = 210.75^'x carapace length - 2664.

33

0-70 -i

0-66 -

0-62 -

2 0-58 -

0-54 -

0-50 -

• 1 . • .

i 10

DATS TO HATCHING 15

- I 20

Figure 11. Changes i n diameter of the embryonic c u t i c l e during zygote maturation on the pleopods of H. cubensis at 26-2 7°C. i n the laboratory~, Feb. 19 67 . Surf temperatures at~this time were 2 6 - 2 8 ° C .

34

i n the laboratory released t h e i r larvae within t h i s time span.

After release of larvae 4 females became gravid again within

3 to 4 days without moulting. Most other females moulted

within days a f t e r l a r v a l release.

From the low percentage of females above 15 mm carapace

length but without developing embryos and the estimated 15-21

day embryonic development time on the pleopods, i t i s reason­

able to conclude that at least one l a r v a l hatch per month

could be produced by each female. The maximum number of eggs

carr i e d by an average sized female was about 1500 (Figure 9).

From these data the average annual l a r v a l production per

female was calculated as approximately 18,000 (1500 x 12).

Since most females produced only 1/3 to 2/3 of the maximum egg

number, a more r e a l i s t i c figure might be about 9000. This

c a l c u l a t i o n assumes that females l i v e for a year after reaching

reproductive s i z e .

LARVAL DEVELOPMENT

Temperature declined steadily from a high of 2 8°C.

at the s t a r t of the study to 25.5°C. i n late January, at the

conclusion. Daily fluctuations did not exceed 1°C. S a l i n i t y

varied from 34.45°/ob to 35.8°/oo during the study.

H. cubensis moulted through either 5 or 6 zoeal stages

before a metamorphosis to the s e t t l i n g stage (megalopa).

Sixteen megalopae and one post-megalopa were obtained from 50 0

f i r s t zoeae. Five megalopae passed through 5 zoeal stages i n

an average time of 60.6 days (range: 59-64) while the remaining

35

11 passed through 6 zoeal stages i n an average time of 76.7

days (range: 71-82). The single post-megalopa spent 12 days

as a megalopa.

Except'for the second zoea, there was a progressive

increase i n the time spent at each zoeal stage. The mean

duration values given below do not include animals which died

i n the subsequent stage.

There was a certain amount of va r i a t i o n among zoeae

of the same moult. Size of the animal, number of setae,

aesthetascs, and the time of the f i r s t appearance of the

thoracic appendages and pleopods were not always i d e n t i c a l .

However, the moults could be distinguished and thus were c a l l e d

stages. The most r e l i a b l e means of determining the p a r t i c u l a r

stage was to count the number of plumose setae on the exopodite

of the f i r s t or second maxilliped. Careful examination of a

minimum of 10 specimens of each moult showed no va r i a t i o n from

the values described below. Measurements of the larvae (see

Table IV) were useful for determining the developmental stage.

Counts of the plumose setae along the margin of the scaphogna-

t h i t e of the maxilla were not always conclusive evidence of

the developmental stage as there was some.overlap between

stages.

A l l scales on drawing are i n mm.

FIRST ZOEA (Figure 12 a, g)

Duration: 5 to 10 days, mean 6.5 days.

The eyes are stalked, carapace i s rounded and i s pro­

duced into a short, triangular rostrum, ante r i o r l y . Lateral

TABLE IV

MEAN SIZE (IN mm) OF LARVAE AT EACH STAGE, BASED ON A MINIMUM OF 10 OBSERVATIONS FOR EACH ENTRY. RANGE IS GIVEN IN BRACKETS.

Stage

I II III IV V VI Meg.

Max. carapace 0.98 1.33 1.87 2.74 3.25 3.87 3.85

length (0.87-1.07) (1.23-1.43) (1.62-2.08) (2.29-2.93) (3.00-3.60) (3.57-4.43) (3.29-4.14)

Max. carapace 0.88 1.28 1.77 2.35 2.80 3.05 2.95

width (0.83-0.93) (1.15-1.47) (1.57-2.03) (2.07-2.64) (2.30-3.10) (2.86-3.43) (2.79-3.14)

Telson length 0.65 0.91 1.26 1.68 2.26 2.81

( i n c l . spines) (0.62-0.68) (0.87-0.93) (1.20-1.35) (1.60-1.78) (2.10-2.43) (2.63-3.10)

Telson width 0.66 0.-91 1. 23 1.58 1.98 2.36

(0.65-0.67) (0.87-0.93) (1.18-1.37) (1.48-1.61) (1.87-2.05) (2.20-2.46)

Rostrum length 0.30 .. ;1. 4 8 2.6 3 4.10 5.40 6.61

(0.29-0. 32) (1.30-1.60) (2. 46-2.80) (3.76-4.30) (-4.83-5.83) (5.99-7.49)

Lateral spine 0.61 1.23 2.05 2.51 2.99

length (0.57-0.63) (1.13-1.33) (1.81-2.26) (2.16-2.76) (2.50-3.16)

37

Figure 12. Zoeal stages of H. cubensis . a-f , l a t e r a l views of stages 1 to 6 r e spec t ive ly ; g, h , dorsa l views of-stages 1 and 6 re spec t ive ly .

38

spines are absent. Chromatophores are absent and the entire

zoea i s almost transparent. In general appearance the zoea

resembles Emerita species very c l o s e l y .

The antennule (Figure 13a) bears a single long

aesthetasc and 1 to 3 setae of variable length terminally.

The stout antenna (Figure 13g) terminates in avnotched

spine. An inner process of equal or greater length, but

smaller diameter, .arises from the base of the thicker spine.

Situated at the base of t h i s inner spine i s a small dentiform

process.

The mandible i s a simple structure terminating i n a

series of processes of varying.sizes, as i l l u s t r a t e d i n F i g ­

ure 14a. No major change i n the mandible occurs throughout

further zoeal development.

The coxal endite of the maxillule (Figure 14b) has 3

long isodiametric setae terminally and a shorter seta 1/3 down

the l a t e r a l margin. The basal endite i s flattened and i s

divided into 2 long curved spines at the t i p . The smallest

lobe, the endopodite, bears a single long, inwardly curved

seta.

The protopodite of the maxilla (Figure 14d) bears 3

terminal setae, either c l o s e l y clustered or with one near the

scaphognathite. A tiny sub-terminal seta i s present along the

inner margin. The elongate scaphognathite bears from 10 to

12 (mean 11) plumose setae along the margin, but not extending

to the posterior end.

The f i r s t maxilliped (Figure 13m) has a short coxopodite.

39

Figure 13. Appendages of-zoeal 's tages of H.-cubensis . a"-f, antennule of stages* 1 to 6 respec t ive ly ; g-1, antenna of stages 1 to'6 re spec t ive ly ; ITV, f i r s t max i l l iped 'o f zoea 1; n, second m a x i l l i p e d ' o f z o e a l ; o, t h i r d max i l l iped of zoea 6; p - t , f i r s t to f i f t h ' t h o r a c i c appendages of zoea 6.

4.0

Figure 14. Mouthparts and scaphognathite of H. cubensis zoeae. a, mandible of zoea 1; b , . m a x i l l u l e of zoea 1; c, maxi l lu le of zoea 2; d - i , scaphognathite of maxi l la of zoea 1-6 re spec t ive ly .

41

The basipodite i s long and has 7 setae along i t s outer margin.

These are arranged i n groups 1-1-2-3, proceeding d i s t a l l y .

One seta i n the most d i s t a l group i s larger and i s armed with

tiny spines. The endopodite i s divided into 4 segments of

approximately equal length. Setae are present on each segment,

grouped 3-2-2-4, proceeding d i s t a l l y . Only the most d i s t a l

group i s located terminally. One seta i n each of the 2 most

proximal groups i s spined. The exopodite has no subterminal

setae and i s composed of a long proximal and a short d i s t a l

segment. The d i s t a l segment bears 4 plumose setae terminally.

These are used for locomotion and are important for i d e n t i f y ­

ing the stage of l a r v a l development. The number of plumose

setae increases by 2 per zoeal moult.

The second maxilliped (Figure 13n) resembles the f i r s t

i n general appearance and function. The basipodite bears

only 3 setae, grouped 1-2. The endopodite has setation of

3-1-2-4 from basal to terminal segment. The 2-segmented

exopodite bears 4 plumose setae terminally. This number

increases by 2 during each subsequent zoeal stage..

The t h i r d maxilliped and thoracic appendages are not

v i s i b l e at t h i s stage.

The abdomen i s composed of 5 segments, but the f i r s t

i s not r e a d i l y distinguished.

The telson (Figure 15a) i s paddle-shaped and s l i g h t l y

concave. Width s l i g h t l y exceeds length at t h i s stage (Table IV).

The l a t e r a l edges are tipped with a small spine p o s t e r i o r l y .

Along the posterior margin are 29 to 32 (mean 30.3) spines

42

•Figure 15. Ventra l view of te l son of zoeal stages of H. cubensis. a-f , -zoeal stages 1 to 6 respec t ive ly .

43

with a variable number of smaller denticles (not shown i n

Figure 15a) between each. The space between the spines and

the number of denticles declines toward the centre.

SECOND ZOEA (Figure 12b)

Duration: 4 to 6 days, mean 5.1 days.

The carapace now bears 2 short l a t e r a l spines. The

rostrum has increased greatly i n length.

The antennule (Figure 13b) bears a single long,

inwardly-curved aesthetasc at i t s t i p . Two or 3 small setae

are present around the base of the aesthetasc.

The antenna (Figure 13h) i s unchanged, except for a

s l i g h t size increase.

The maxillule (Figure 14c) has an additional long

curved spine on the basal endite. The inner 2 spines are

ar t i c u l a t e d at t h e i r base. This arrangement i s unchanged

throughout subsequent zoeal stages.

The scaphognathite of the maxilla (Figure 14e) has 11

to 15 (mean 12.5) plumose setae along the margin.

The exopodites of the f i r s t and second maxillipeds

have 6 plumose setae.

The number of spines along the posterior edge of the

telson (Figure 15b) i s 30 to 34 (mean 32.1).. There i s no s i g ­

n i f i c a n t change i n t h i s number during the l a t e r zoeal stages.

However, there i s an increase i n the number of denticles

between the spines.

44

THIRD ZOEA (Figure 12c)

Duration: 4 to 16 days, mean 6.7 days.

The terminal end of the antennule (Figure 13c) bears

a long inwardly curved aesthetasc, 2 smaller aesthetascs

or i g i n a t i n g s l i g h t l y apart from the large one and 1 or 2 very

small setae at the base of the aesthetascs. This p a r t i c u l a r

terminal grouping i s common throughout the subsequent zoeal

stages. Occasionally an additional aesthetasc i s present i n

the higher stages.

The largest process of the antenna (Figure 13i) bears

an additional spine along both edges. The precise size and

location of the spines i s variable.

The.scaphognathite of the maxilla (Figure 14f) has from

17 to 30 (mean 21.6) plumose setae along i t s margin. These

setae now extend a l l the way to the posterior end.

There are 8 plumose setae on the exopodite of the

f i r s t and second maxillipeds.

Three or 4 pairs of undifferentiated buds are usually

present along the sides of the cephalothorax. These w i l l

develop into the t h i r d maxillipeds and thoracic appendages.

Paired, uniramous uropods are present on the anterior-

ventral telson surface (Figure 15c). They are divided into a

short basal segment and a long d i s t a l one (exopodite). The

exopodite bears 2 long inwardly curved setae at i t s t i p . The

presence of uropods shows that the sixth abdominal segment i s

incorporated into the telson.

45

FOURTH ZOEA (Figure 12d)

Durat ion: 6 to 22 days, mean 11.1 days.

A subterminal t i e r of 2 aesthetascs i s present on the

medial edge of the antennule (Figure 13d). Rare ly , a second

subterminal t i e r with 1 aesthetasc i s present below the f i r s t .

A d d i t i o n a l spines are present along the t i p of the

largest process of the antenna (Figure 13j) . The inner spine

i s now notched at the t i p .

The scaphognathite (Figure 14g) has 29 to 37 (mean 32.

plumose setae along i t s margin.

The number of plumose setae on the exopodite of the

f i r s t and second maxi l l ipeds i s 10.

The exopodite of the uropods (Figure 15d) bears 3 to

5 (mean 3.6) setae of unequal length. The endopodite i s a

barely not iceable bud.

FIFTH ZOEA (Figure 12e)

Duration: 11 to 30 days, mean 19.8 days.

There are from 6 to 12 subterminal aesthetascs on the

antennule (Figure 13e). 8/12 i n d i v i d u a l s had 3 subterminal

t i e r s (mean:6.5 aesthetascs) , while 4/12 had 4 t i e r s (mean:

10.1 aesthetascs) . T y p i c a l patterns are 2-2-2; 3-2-2; 3-3-2-2

4-4-2-2; 4-2-2-1. The same i n d i v i d u a l may have d i f f e r e n t

arrangements on l e f t and r i g h t antennules.

Both processes of the antenna (Figure 13k) bear addi ­

t i o n a l spines at t h e i r d i s t a l ends.

The scaphognathite of the maxi l la (Figure 14h) bears

46

35 to 59 (mean 48) plumose setae along the margin.

There are 12 plumose setae on the exopodite of the

f i r s t and second maxillipeds.

The exopodite of the uropods (Figure 15e) bears 4 to 8

(mean 6) setae. The longest seta i s usually near the middle.

SIXTH ZOEA (Figure 12f,h)

Duration: 15 to 32 days, mean 24.1 days.

The number of sub-terminal aesthetascs on the antennul

(Figure 13f) i s 17 to 20 (mean 18.3). These are i n six groups

variably arranged: e.g. 4-5-4-2-2-2; 2-4-4-3-2-2; 3-3-6-3-2-2

proceeding from the d i s t a l end.

An additional 1 or 2 spines are present on the 2

processes of the antenna (Figure 13 1).

The scaphognathite (Figure 14i) bears 56 to 67 (mean

59.5) plumose setae along the margin.

There are 14 plumose setae on the exopodite of the

f i r s t and second maxillipeds.

The t h i r d maxilliped and the 5 thoracic appendages

(Figure 13o-t) have gradually enlarged and d i f f e r e n t i a t e d .

The f i f t h thoracic i s the smallest and i s curved to l i e

beneath the others.

A pair of uniramous, unsegmented pleopods are present

on the ventral surface of segments 2 to 5 of the abdomen.

Occasionally pleopods were found on f i f t h stage zoeae.

The exopodites of the uropods (Figure 15f) have 7 or

8 setae. The outer 3 or 4 are longest, the innermost shortest

47

The endopodite length i s variable but i s usually about the

same as the length of the basal segment.

MEGALOPA (Figure 17f)

The megalopa resembles adult Hippa. The carapace i s

elongate and has a series of setose pockets along the l a t e r a l

margins. The main differences are the large eyes and setose

pleopods of the megalopa.

The antennule (Figure 16b) has 3 basal segments, each

bearing stout setae. The second and t h i r d segments have

blunt projections, which are also armed with setae. A 13 or

14-segmented flagellum i s also present. From segments 3 or

4 on t h i s flagellum a pair of spiny, progressively longer

setae are found near the edges.of each segment. Shorter setae

are present on segments 3 to 7 on the medial edge of the

flagellum. The most d i s t a l 8 or 9 segments each bear from 1

to 5 long, t h i n aesthetascs between the stout marginal setae.

The antenna (Figure 16a) i s composed of 3 basal com­

ponents and a 3-segmented flagellum. Stout setae, some bearing

spines, are found on a l l components.

The mandible (Figure 16c) has a 2-segmented palp and

a gnathal lobe. The basal segment of the palp has 4 stout

setae along i t s l a t e r a l margin. The terminal segment, which

i s mounted perpendicularly on the basal component, bears a row

of spiny setae.

The coxal endite'of the maxillule (Figure 16d) i s

thick and crowned with stout setae bearing tiny hairs at t h e i r

t i p s . Thin, spiny setae are also present. The basal endite

48

Figure 16. Antennule, antenna and mouthparts of megalopa of H. cubensis. a, antenna; b, antennule; c , mandible; d , max i l lu l e ; e , .scaphognathite of max i l l a ; f - h , f i r s t / s e c o n d and t h i r d maxi l l ipeds re spec t ive ly .

49

I

Figure 17. Megalopa of H. cubensis. a-e, pereiopods 1 to 5 respec t ive ly ; f , • d o r s a l view of megalopa; g, dorsa l view of -abdomen and te l son; h-k, abdominal pleopods on segments 2 to 5 re spec t ive ly .

50

i s slimmer and rounded terminally. A series of stout setae

and. several thinner spiny setae are present " d i s t a l l y . The

curved t i p of the endopodite has a small seta on each side

of i t s base.

The scaphognathite of the maxilla (Figure 16e) bears

from 98 to 108 (mean 101.6) plumose setae along i t s margin.

These setae now extend up the medial edge into the groove

between scaphognathite and the basal part of the appendage.

The bilobed coxal endite bears spiny setae. The basal endite

i s also equipped, terminally, with setae. An unarmed t r i ­

angular endopodite l i e s between the basal endite and

scaphognathite.

The flattened,protopodite of the f i r s t maxilliped

(Figure 16f) has a dense row of very short setae along the

margin, as well as other setae on i t s surface. The exopodite

i s a 2-segmented paddle-shaped structure bearing plumose

setae along the l a t e r a l margin of the proximal segment and

a l l around the margin of the d i s t a l segment. The endopodite

i s slender and bears numerous cons t r i c t i o n s .

The exopodite of the second maxilliped (Figure 16g)

is divided into a long unarmed proximal segment and a short

d i s t a l one, which has afimarginal row of plumose setae. The

endopodite i s 4-segmented and bears many setae, some spiny.

The f i r s t and second maxillipeds now function i n feeding and

not i n locomotion.

The t h i r d maxilliped (Figure 16h) i s composed of 2

small basal segments, a broad meropodite and a narrow,

51

3-segmehted terminal end. Setae are present on a l l components.

The pereiopods (Figure 17a-e) resemble those of the

adult. A l l are very setose. The f i r s t 3 pairs point a n t e r i ­

o r l y and the fourth p o s t e r i o r l y . The f i f t h pair are chelate

and l i e inserted i n the branchial chamber.

The 6-segmented abdomen (Figure 17g) i s flexed so that

the telson l i e s beneath the carapace. There are biramous

pleopods on segments 2 to 5 (Figure 17h-k). The exopodites

have from 16 to 21 plumose setae around the margin. The number

increases p o s t e r i o r l y . There i s a s l i g h t increase i n the size

of the endopodites on the more posterior segments. The

megalopa often extends the telson and uses the pleopods for

swimming.

The biramous uropods (Figure 17g) extend from the

sixth abdominal segment and are fringed with both plumose and

naked setae along the margins. The plumose nature of the

setae i s not shown i n Figure 17g.

LARVAL RECRUITMENT BY DOWNSTREAM GYRALS

The r e l a t i v e number of Hippa on beaches around Barbados

was greatest on the west and southwest coasts of the i s l a n d

(Figure 1), with west coast'values being 5 to 10 times greater

than the east coast, during periods of high surf on both coasts.

EFFECTS OF SUBSTRATE SIZE

SAND PREFERENCE IN THE LABORATORY

Four series of experiments were carr i e d out using the

square box with quadrants, each f i l l e d with sand of the same

52

or d i f f e r e n t grain size from the others. The n u l l hypothesis

to be tested was that, after an i n i t i a l placement by the

experimenter, the crabs burrowed without preference for any

quadrant.

In the f i r s t series, crabs from 10 to 23 mm were used.

Unsieved sand from the middle of the i n t e r t i d a l zone of a

coral beach (median diameter: 0.5-0.25 mm) was used in a l l 4

quadrants. Of 474 crabs, the to t a l s i n a l l 4 quadrants were:

115, 115, 120, 124. If no preference were shown, the expected

value for each quadrant would be: -i^p- = 118.5. AT*-2 value of

0.481 was not s i g n i f i c a n t and the n u l l hypothesis was accepted.

These results indicated that there was no a t t r a c t i o n to a

p a r t i c u l a r quadrant because of the design of the experimental

apparatus. Only 29.6% of the crabs were found i n the same

quadrant i n which they had been o r i g i n a l l y placed.

Three further series were carr i e d out, using d i f f e r e n t

sand grain sizes i n each quadrant. In each series crabs of

only one size range (mean carapace lengths: 5.6, 12.7 and

20.0 mm) were used. The results are shown i n Table V. The

data were analyzed with a s p l i t - p l o t f a c t o r i a l design i n which

the whole unit treatment t o t a l s were fixed (120). Thus each

r e p l i c a t e consists of a fixed number of individuals allowed

to d i s t r i b u t e themselves among 4 quadrants. The results of

the analysis are shown i n Table VI. Only the in t e r a c t i o n term

(sand size by crab size) i s s i g n i f i c a n t (.025 <C p y .01).

The nature of the in t e r a c t i o n (Figure 18) explains, the small

F r a t i o for the sand size e f f e c t . A l l 3 crab sizes prefer the

TABLE V

SAND GRAIN SIZE PREFERENCES AMONG H. CUBENSIS OF 3 SIZE GROUPS

Sand grain s ize

5.00-2.00 2.00-1.41 1.00-0.71 0.25-0.15 Range (mm) Granules V. Coarse Coarse Fine C l a s s i f i c a t i o n

Sand Sand Sand Crab s ize (mm) Replicates 1 2 3 4 Tota ls

Small 1 19 46 39 16 120 (4.5-9.5) 2 32 33 33 22 120 X = 5.6 3 17 27 30 46 120

4 20 34 33 33_ 120 88 140 135 117 U80

Medium 1 30 37 27 26 120 (10.0-16.0) 2 27 36 31 26 120

x = 12.7 3 20 38 28 34 120 4 3_5 31 28 26 120

112 142 114 112 480

Large 1 37 39 20 24 120 (17.0-26.0) 2 35 42 24 19 120

x = 20.0 3 28 50 24 18 120 4 45 37 23_ 15 120

145 168 91 76 480

Totals 345 450 340 305 1440

54

TABLE VI

FACTORIAL ANOVA ON DATA OF TABLE V

Source of v a r i a t i o n df SS MS

Whole unit

Replication 3 0

Crab size 2 0

Error 6 0

Subunit

Sand size 3 979.17 326.39 1.9 (3,6) N.S.

Sand size x Crab size 6 1023.83 170.64 3.3

(6,27) (.05^p7.01) Error 27 1395.00 5.67

Total 47 3398

55

1 1 P

S M L CRAB SIZE

Figure 18. Interact ion between crab s ize and sand s ize i n sand preference experiments. ' Ordinate scale i s the number of crabs out of 480 choosing a p a r t i c u l a r grain s i ze . ' Sand-grain s izes (in mm): 1-5.00 to 2.00; 2-2.00 to 1.41; 3-1.00 to 0.71; 4-0.25 to 0.15.. See Tables V, VI and text for further d e t a i l s .

56 0

very coarse sand (size 2) but large crabs show a strong

secondary preference for grade 1 (granules). This e f f e c t i s

counterbalanced by the preference of small crabs for the f i n e r

sand grades (3 and 4).

DISTRIBUTION OF HIPPIDAE IN TRINIDAD

The d i s t r i b u t i o n of H. cubensis, E. portoricehsis and

sand grain size i s shown i n Figure 19. Emerita was found

mainly i n fine sand and Hippa i n r e l a t i v e l y coarse sands. An

exception was Matura beach, which i s a steep-sloped coarse

sand beach. The population of Emerita here was the largest

of any of the beaches examined. No b a i t was available when

this beach was v i s i t e d and no Hippa were found i n the sieved

samples. There was only one beach where Hippa and Emerita

were present together.

RESPIRATORY CURRENTS

Two respiratory current patterns were found i n Hippa,

depending on the nature of the substrate. Crabs kept under

conditions of no sand or i n s u f f i c i e n t sand to bury had a

posterior to anterior current d i r e c t i o n , with water entering

the g i l l chamber around the bases of the pereiopods and

e x i t i n g between the antennules and antenna. A variable number

of crabs buried i n sand to a depth where only the antennules

were v i s i b l e had an anterior to posterior current d i r e c t i o n ,

with the inhalent stream entering at the base of the antennules

and antennae and the exhalent leaving at the base of the

pereiopods.

57

X H i p p a c u b e n s i s

o E m e r i t a p o r t o r i c e n s i s

No c r a b s f o u n d

Figure- 19. D i s t r i b u t i o n of H. cubensis and E. portoricensis and sand grain size of beaches on the north and east coasts of Trinidad during July 1967. Median sand diameters are: 1- 1.41-1.00 mm•(very coarse) ; 2- 1.00-0.50 mm (coarse); 3- 0.50-0.25 mm (medium); 4- 0.25-0.105 (fine to very~fine). Sand c l a s s i f i c a t i o n a f t e r Wentw.orth (1922).

58

The actual percentage of anterior to posterior current

d i r e c t i o n observations varied depending on both sand and crab

size. The number of observations of anterior to posterior

current increased with a decrease i n the diameter of substrate

p a r t i c l e s (Figure 20). An analysis of covariance performed

on the data barely rejected the hypothesis of no difference

between slopes at the .05 l e v e l , but the hypothesis was

accepted at the .01 l e v e l (Table VII). Since r e j e c t i o n was

not clear-cut, the estimate of the common slope, b = -9.06 was

used to test the hypothesis of zero slope. This hypothesis was

rejected (F(l,18) = 31.9**). The elevations of the in d i v i d u a l

regressions were s i g n i f i c a n t l y d i f f e r e n t so no common regression

formula was calculated. The reason for the s i g n i f i c a n t d i f f e r ­

ence i n l e v e l of response i s not apparent. A l l experiments

were started at the same time of day and animals were held for

equally short periods p r i o r to the s t a r t of the experiment.

When -a series of crabs of d i f f e r e n t sizes were a l l observed i n

sand of the same"size, the larger crabs showed an anterior to

posterior current more frequently than the smaller crabs

(Figure 21). The mean maximum percentage of anterior to

'posterior current d i r e c t i o n did not exceed 60% for the largest

crabs i n the f i n e s t sand available.

The long dorsal rami of the antennules of H. cubensis

were never held together as a breathing tube i n the laboratory

experiments. The inhalent channel for anterior -to posterior

breathing was formed with the short ventral rami of the

antennules as the dorsal components and the flattened setose

59

80 - i

60 -

H Z H w

40

20-

3

9

a 3

0.1 T 1 1 1 1 I I I |

05 10 i i — | i i i i • —

50 100 SAND D I A M E T E R (mm)

Figure 20. E f f e c t of sand size on the di r e c t i o n of the respiratory current of si m i l a r - s i z e d (mean = 16.5 mm) H. cubensis. "Percent -observations where anterior to posterior d i r e c t i o n occurred i s plotted against sand size (log scale). 1000 observations-were made on 200 crabs -during 5 experiments. F - t e s t s o n the i n d i v i d u a l slopes (l',2 d.f.) for experiments I, 2 and 4 were • no t - s i g n i f i c a n t (;25<p> . 1 ) but were'signifi­cantly greater than zero (p<.05) i n experiments 3 ( • ) and 5 ( S ) . See Table VII and text for further d e t a i l s .

60

TABLE VII

ANALYSIS OF COVARIANCE ON DATA OF FIGURE 20 X = log 10 (sand s i z e ) , Y = percent of observations

where anterior to posterior respiratory current was noted.

Deviations from Source < x ^ ;£xy £ y 2 regression

^ . d.f. S.S. M.S.

Within Experiment i 6. 24 -31. 64 224. 75 2 64. 29 32. 14

n 2 6. 24 -17. 93 88. 73 2 37. 19 18. 60 ii 3 6. 24 -88. 62 1306. 45 2 47. 51 23. 75 II 4 6. 24 -54. 42 634. 51 2 159. 70 79. 85 n 5 6. 24 -89. 96 1430. 30 2 133. 00 66. 51

10 441.69 44.2

Pooled 31.20 -282.57 3684.74 14 1124.81 80.34

Difference between slopes 4 683 .0 171.0

Between + Pooled

31.20 -282.56 9084.29 18 6524.37

Between adjusted means 4 5399.55 1349.89

Comparison of slopes: F(4,10) = 171/44.2 = 3. 86 (.05 4 p 7.01)

Comparison of elevations: F(4,14) = 1349. 9/80 = 16.87 (p <.005)

a B a r t l e t t * s t e s t for homogeneity of residual variances not s i g n i f i c a n t (M = 3.43).

61

CARAPACE L E N G T H (mm)

Figure 21. E f f e c t of crab size on the d i r e c t i o n of the respiratory current of H. cubensis buried i n fine sand (median diameter: 0.25-0.15 mm). Percentage of 600 observa­tions on 120 crabs where the anterior to posterior-current' d i r e c t i o n was shown i s plotted against crab size; Least squares regression" highly - s i g n i f i c a n t (p^.01), r = 0.76.

62

antennae, held together, as the base. These structures are

i l l u s t r a t e d i n Snodgrass (1952) and Figure 16a,b of the

megalopa.

In contrast to the current d i r e c t i o n i n Hippa, a l l 16

of the Albunea tested under condit ions of no sand and suf­

f i c i e n t sand to bury showed an anter ior to pos ter ior current

d i r e c t i o n at every observat ion.

DISCUSSION

GENERAL BIOLOGY

SIZE DISTRIBUTION

The maximum size attained by H. cubensis i s i n t e r ­

mediate between the extremes reported for Emerita, of 18 mm

(carapace length) for E. h o l t h u i s i (Sankolli, 1965) and 34 mm

in E. rathbunae (Efford, 1967). Measurement of carapace

lengths of museum specimens (Man, 1896; personal observations

of author on co l l e c t i o n s of Dr. I. E. Efford and Smithsonian

Institute) indicate that H. cubensis i s intermediate, a medium-

sized member of the.genus. A 33.5 mm female H. ovalis i s the

largest specimen i n the Smithsonian c o l l e c t i o n .

The size difference between male and female H. cubensis

has also been found i n a l l known species of Emerita except

E. austroafricana and E., h o l t h u i s i (Efford, 1967), being

explained either by differences i n l i f e span and growth rate

(Wharton, 1942; Efford, 1967) or possibly by sex reversal of

the males (Goodbody, 1965).

It i s d i f f i c u l t to determine whether any of these 3

mechanisms account for the male-female size difference i n

H. cubensis since no sa t i s f a c t o r y growth data were obtained

for H. cubensis because: (a) continuous breeding and there­

fore constant recruitment to the population made mean carapace

length of sequential monthly samples i d e n t i c a l and (b) no

64

s a t i s f a c t o r y mark and recapture method was found to overcome

the problems of moulting and surf action. Information might

be obtained by studying a more northerly-located population,

i f i t were not continuously breeding.

With an annual temperature v a r i a t i o n of about 4 ° C ,

there i s no reason to suggest a winter die-o f f i n H. cubensis,

as occurs i n temperate species of Emerita (Efford, 1967;

Wharton, 1942). The high r a t i o of males to females i n the 8-15

mm size group and the 1:1 r a t i o of small to large females

indicates that when H. cubensis reach maximum size they may

accumulate, with an i n d e f i n i t e l i f e span.

Sex reversal of male H. cubensis remains a p o s s i b i l i t y .

The sudden drop-off i n male abundance at the size when most

females f i r s t become gravid, and the 1:1 r a t i o of small to

large females, which suggests the p o s s i b i l i t y of recruitment

to females or a very low mortality rate among the older

animals, support t h i s idea.

It can be concluded that although the same patterns

of size d i s t r i b u t i o n are present i n H. cubensis and most

Emerita species, i t i s s t i l l now known whether the mechanism

involved i s the same for both genera. Since there i s no

d r a s t i c difference i n size between the genera, there seems no

reason to suspect.that size d i s t r i b u t i o n i s important i n

l i m i t i n g zoogeographical d i s t r i b u t i o n .

FEEDING

The scavenging food habits of H. cubensis are si m i l a r

to those reported for H. p a c i f i c a (Bonnet, 1946; Matthews,

65

1955) and other species of Hippa (Borradaile, 1906; Dahl,

1952) . Matthews (1955) found that H. p a c i f i c a sensed food

with chemoreceptors located on the antennules and antennae.

In contrast, Emerita species are a l l f i l t e r feeders, extract­

ing p a r t i c l e s from the wave wash with the setose antennae

(Efford, 1966). The profound e f f e c t s of t h i s difference

w i l l be discussed below.

BEACH ECOLOGY

The beach ecologies of Hippa and Emerita are si m i l a r

i n a number of ways. Both genera are r e s t r i c t e d to the i n t e r -

t i d a l zone, except E. talpoida which has been found i n o f f ­

shore seine samples (Wharton, 19 42) and H. p a c i f i c a taken in

dredgings from 6-7 fathoms i n the Maldives (Borradaile, 1906).

Most observations indicate that Emrita, l i k e Hippa, migrates

with the tide to maintain the same r e l a t i v e temperature and

moisture conditions (Efford, 1965). MacGinitie (1939) reported

that some E. analoga actually bury deeply during low t i d e .

The uneven s i z e . d i s t r i b u t i o n of H. cubensis on the beach at

high tide i s sim i l a r to that found for at least 3 species of

Emerita (Alikunhi, 1944; Knox and Boolootian, 19 63; Efford,

1965).

The large aggregations reported for many species of

Emerita (Efford, 1965) were not found for H. cubensis. Thus

i t i s d i f f i c u l t to compare population densities of the 2 genera.

The difference i n feeding habits may. account for the lack of

aggregations i n Hippa. Wide dispersal across the beach would

ensure e f f i c i e n t scavenging.

66

COLORATION

There i s no evidence which indicates that Emerita

shows as much color v a r i a t i o n as H. cubensis (Efford, personal

communication, 1967). Unfortunately color i s often described

from faded museum specimens, so that i t i s impossible to

decide whether other species of Hippa also show t h i s a b i l i t y

to match background sand color.

The si g n i f i c a n c e of adaptive coloration l i e s i n reduc­

tion of predation, i n t h i s case either by shore birds and

other animals or surf fishes. I f Emerita i s unable to match

carapace color with sand color, i t might be eliminated by

predation on i s l a n d beaches where the extremes of white (coral)

and black (volcanic) sands occur. Without laboratory testing

and more f i e l d data, t h i s idea must remain speculative.

REPRODUCTION AND LARVAL DEVELOPMENT

ANNUAL EGG PRODUCTION

The annual egg production per female of H. cubensis

was about 2 to 3 times greater than an estimate of 5000 for

the temperate species E. analoga (Efford, i n press). Seasonal

breeding (Boolootian, et a l . , 1959) and a longer egg incubation

period, estimated at 29-32 days (Knox and Boolootian, 1963) to

4-5 months (MacGinitie, 1938), account for the lower production

i - n E. analoga. No estimates of annual egg production of a

t r o p i c a l Emerita species i s avai l a b l e , but E. portoricensis

i s known to be a continuous breeder (Goodbody, 19 65). Thus

i t might be expected that the annual egg output i n t h i s species

67

would be si m i l a r to H. cubensis.

LARVAL DEVELOPMENT

The l a r v a l development of H. cubensis clo s e l y p a r a l l e l s

that of Emerita species. However differences e x i s t which make

i t possible to d i f f e r e n t i a t e H. cubensis larvae from, those of

the 4 species of Emerita whose development has been described

f u l l y (Menon, 1933; Johnson and Lewis, 1942; Rees, 1959;

Knight, 1967).

In size (as measured i n Table IV), H. cubensis i s

generally larger than the corresponding stage of Emerita

species. Both telson spine counts and the number of plumose

setae on the scaphognathite are higher i n Hippa. The number

of plumose setae on the exopodite of the f i r s t and second

maxillipeds i s i d e n t i c a l i n both genera. However there was

no v a r i a b i l i t y within each stage i n Hippa, as has been reported

i n Emerita.

Anatomical differences i n the antennules and antennae

of the l a r v a l stages can be related to the d i f f e r e n t feeding

habits of the adults. The antennule of older Hippa larvae

bears many more aesthetascs than the corresponding stage of

Emerita. The antenna of Emerita develops a long flagellum i n

the fourth or f i f t h zoeal stage. This flagellum p e r s i s t s

through the megalopa stage of Emerita, where i t i s used for

f i l t e r - f e e d i n g (Efford, 1966). This flagellum i s e n t i r e l y

lacking i n Hippa.

The number of zoeal stages preceding the megalopa i n

68

Emerita laboratory cultures has varied from 6 i n E. h o l t h u i s i

(Sankolli, 1965b) and E. talpoida (Rees, 1959) to 9-11 i n

E. analoga (Efford, i n press). H. cubensis passed through

only 5 or 6, possibly because the larvae s t a r t o f f at a larger

size than those of Emerita:

The 59-82 day l a r v a l development time for H. cubensis

i s intermediate i n length compared to the extremes of 2 8 days

for E. talpoida (Rees, 1959) and 131 days for E. analoga

(Efford, MS). It i s d i f f i c u l t to compare these results

d i r e c t l y , since i t i s known that temperature can af f e c t l a r v a l

development time (Costlow, 1960). When temperature was

plotted with t o t a l l a r v a l development time (Figure 22) for

H. cubensis and 3 species of Emerita, a l l reared i n the labora­

tory, using the same sort of culture containers, i t was

apparent that l a r v a l development time of Hippidae i s i n f l u ­

enced by temperature and that the development time for

H. cubensis l i e s i n the same range as Emerita species. Con­

sequently H. cubensis i s not adapted to insul a r repopulation

by having a short l a r v a l l i f e .

LARVAL RECRUITMENT BY DOWNSTREAM GYRALS

Since Hippa does not have a shortened l a r v a l develop­

ment period, an alternative hypothesis must explain r e c r u i t ­

ment to is o l a t e d oceanic islands, such as Barbados. The d i s ­

t r i b u t i o n of H. cubensis around Barbados was simi l a r to what

would be predicted from Emery's (19 64) hypothesis of downstream

gyrals. These gyrals would return larvae mainly to the west

69

Figure 22. Relationship of l a r v a l development time of 3 species of Emerita and H. cubensis to culture temperature. Squares indicate t o t a l temperature range during experiments, with mean development time, where available, indicated by ( • ). E. talpoida cultured at a constant 30°C. ' Diagonal lines indicate -probable range of regression.

70 .

coast of Barbados, where the largest sand crab populations

are actually found, The results shown i n Figure 1 are not

conclusive evidence for t h i s theory since the p o s s i b i l i t y '

exists that crab numbers on the east coast were adversely

influenced by differences i n the sand type and wave action

from the west coast. However Ward (19 67) has recently found

a s i m i l a r d i s t r i b u t i o n for the rocky shore limpet F i s s u r e l l a

barbadensis, which has a short planktonic l i f e (Lewis, 1960).

Examination of a concentric series of plankton

samples, taken from stations a l l around the i s l a n d , for d i f ­

ference i n abundance of indicator species might give a more

d e f i n i t e proof of the hypothesis.

SAND PREFERENCE

EFFECT ON HIPPA DISTRIBUTION

In Jamaica E. portoricensis colonizes fine a l l u v i a l

sand (e.g. Green Bay, median diameter 0.175 (Wade, 1967),

while H. cubensis i s r e s t r i c t e d to the coarser calcareous sands

(Goodbody, 1965). Estampador (1939) found H.. testudinarius

inhabiting coarse, loose sand i n the Philippines. Borradaile

(1906) found Hippa to be very abundant i n loose sand.

H. cubensis were found only on the coarser sands i n Trinidad

and preferred coarse sand i n the laboratory experiments, during

the present study.

The ultimate factor determining sand, preference can be

linked to the method of feeding i n Hippa. The long dorsal

ramus of the antennules are modified for chemoreception and do

71

not function as a respiratory tube as they do i n Emerita and

Albunea. A consequence i s that the preferred respiratory

current d i r e c t i o n i n Hippa i s from posterior to anterior, even

when the crab i s buried i n sand. In coarse sand H. cubensis

i s obviously capable of drawing water through the porous

substrate, since most of the crabs showed a posterior to

anterior d i r e c t i o n i n coarse sand, i n the laboratory experi­

ments. As the median sand diameter decreases, the i n t e r s t i t i a l

spaces become clogged, and water passes through the sand less

r e a d i l y (Weiser, 1959). This would not cause a problem i f a

respiratory tube i s being used as i n Emerita. For Hippa fine

sand would mean using a very short respiratory tube composed

of the ventral ramus of the antennules. This was done i n the

laboratory i n some instances, but the effectiveness of t h i s

short siphon was not determined under the more rigorous condi­

tions of the beach.

The scavenging habits of Hippa necessitate frequent

movements and rapid burrowing to obtain food without being

swept away by wave action. This must be accomplished with

greater ease i n coarse, loose sand than f i n e , hard-packed

sand and constitutes another reason why Hippa may prefer

coarse sand.

As pointed out e a r l i e r , sand size on islands generally

would be expected to be coarser on t r o p i c a l islands than on

mainlands. Thus the observed coarse sand preference of Hippa

can s a t i s f a c t o r i l y , e x p l a i n the zoogeographical d i s t r i b u t i o n

of t h i s genus, mainly on islands. Where coarse sand i s found

72

on mainlands, Hippa might also be expected to occur. There

are at least 2 mainland areas where Hippa are known to occur

regularly: (a) H. cubensis along the mainland and islands of

the west coast of A f r i c a (Monod, 1956) and (b) H. s t r i g i l l a t a

at Cape St. Lucas, Baja, Lower C a l i f o r n i a (Miers, 1878) and

elsewhere along the west coast of Mexico (from specimens i n

the personal c o l l e c t i o n of Dr. I. E. Efford). Further samples

from these areas, with data on the types of beaches where the

crabs are present or absent, would provide valuable informa­

tion to prove or disprove the hypothesis that sand preference

l i m i t s the d i s t r i b u t i o n of Hippa.

FURTHER CONSIDERATIONS

TEMPERATURE AND THE DISTRIBUTION OF HIPPA

The t o t a l absence of Hippa from certain temperate

areas where Emerita species are found cannot be explained

so l e l y by sand preference, since some coarse or at least

medium-sized sand beaches are present along the coast of south­

ern C a l i f o r n i a , U.S.A. (Hedgpeth, 1953), where no Hippa occur.

The known world d i s t r i b u t i o n of Hippa (see Figure 23)

follows c l o s e l y the zones of t r o p i c a l marine fauna established

by Ekman (1953), based mainly on temperature (Hedgpeth, 1957).

In contrast the range of E. analoga l i e s both north and south

of the boundaries of t r o p i c a l fauna on the west coast of North

and South America. E. austroafricana and E. talpoida are 2

other examples of Emerita species, which l i e outside the zones

of t r o p i c a l fauna. These d i s t r i b u t i o n a l patterns indicate

Figure 2 3 . T h e -world • d i s t r i b u t i o n of Hippaspecies . Tropical, faunal zones are from Sverdrup et a l . (1942) and Ekman (1953). Hippa' d i s t r i b u t i o n a l - records from: Miers (1878); deMan (1896); Ortmann (1896); Borradaile (1906); Monod (1956); specimens i n the Smithsonian; Institute' and the'personal-collection of Dr. I. E. Efford, examined by the author. The wide"distribution^and overlap*of some species may be due to taxonomic synonyms and m i s i d e n t i f i c a t i o n s .

that Hippa may be r e l a t i v e l y stenothermal compared to Emerita

and could explain i t s absence from warm temperate areas, even

where coarse sand i s present.

DISTRIBUTION OF EMERITA

This study has shown that Hippa and Emerita are si m i l a r

i n many aspects of t h e i r l i f e history and that the r e s t r i c t e d

d i s t r i b u t i o n of Hippa can be explained by a preference for

areas of coarse sand. I t i s apparent that Emerita i s capable

of colonizing both fine and coarse sand. This genus has also

been reported i n coarse sand on the west coast of North

America (Efford, personal communication, 1967).

Despite the a b i l i t y of Emerita to colonize coarse

sand, i t i s rarely found on the same beaches as Hippa. In

Trinidad Emerita was found on only 1 of 6 locations where Hippa

was present. In Jamaica E. portoricensis does not occur on the.

coral cays where Hippa i s present (Goodbody, 1965).

This d i s t r i b u t i o n a l pattern suggests the p o s s i b i l i t y

of competition between the genera. Since Hippa prefers coarse

sand, the competition would only occur when Emerita colonized

coarse sand beaches inhabited by Hippa. There i s no evidence

that space on the beaches i s l i m i t i n g and theilfood requirements

of the 2 genera are completely d i f f e r e n t . Therefore these 2

common competitive mechanisms are probably not important i n

th i s case.

Predation of young Emerita as they se t t l e d on the beach

could account for the absence of Emerita from areas inhabited

by Hippa. I t i s known from t h i s study that Hippa w i l l feed on

75

amphipods of about the same size as Emerita' megalopae. Very

small Hippa were consumed by larger ones i n the laboratory,

but obviously are not exterminated on the beach. However

young Emerita must remain i n one spot, exposed, while feeding,

and consequently might be easier prey than the mobile young

Hippa.

An excellent area for predation studies would be

Cape St.' Lucas, Lower C a l i f o r n i a , where both Emerita and Hippa

are found, although i t i s not known whether they inhabit the

same beaches. U n t i l a detailed study i s carried out the

p o s s i b i l i t y that predation by Hippa r e s t r i c t s the d i s t r i b u t i o n

of Emerita must remain speculation.

SUMMARY

The zoogeographical d i s t r i b u t i o n of Hippa appears to

be controlled, by 2 factors: (a) species are found only where

t r o p i c a l temperature conditions occur, i n contrast to Emerita,

which are found i n both t r o p i c a l and warmer temperate areas,

(b) food habits of Hippa have resulted i n anatomical and

behavioral adaptations causing a preference for a habitat of

coarse sand, more frequently found on islands than mainlands.

Larval development time and reproductive pote n t i a l are con­

t r o l l e d by temperature and are probably similar for both

genera, although differences were found when temperate species

°f Emerita were compared with t r o p i c a l H. cubensis. The other

aspects of the l i f e - h i s t o r y , such as population size structure

and limits, of beach range r e l a t i v e to tides and surf are

generally s i m i l a r i n both genera and consequently would not

account for d i s t r i b u t i o n differences.

The absence of Emerita from many t r o p i c a l islands

remains unexplained. Sand grain size i s not important since

Emerita inhabit both coarse and fi n e sand beaches. A possible

answer i s that i n a b i l i t y of Emerita to match extremes of sand

color would cause great predation on th i s genus on the white

coral and black volcanic sands of islands. The observation

that Emerita are rarely found on the same beach as Hippa, even

where both genera inhabit the same coastline suggests the

77

p o s s i b i l i t y of predation of young Emerita by Hippa. These 2

ideas were not tested i n t h i s study and are therefore only

speculative.

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