the life-history of the sand crab hippa cubensis saussure living on a small
TRANSCRIPT
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.
12
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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