Download Ontogeny and Overlap in the Diets of Four Tropical Callinectes</i

BULLETIN OF MARINE SCIENCE, 46(1): 3-12, 1990
ONTOGENY AND OVERLAP IN THE DIETS OF FOUR
TROPICAL CALLINECTES SPECIES
Allan W Stoner and Beverly A. Buchanan
ABSTRACT
The diets offour Callinecles spp., Portunidae, from a small tropical lagoon were examined
for ontogenetic and interspecific variation. The primary food organisms were crabs, fishes,
shrimp, amphipods, bivalves, and polychaetes; but the relative importance of each varied
greatly with crab species and size. Callinectes danae had the least varied diet, relatively low
proportions of detritus and consumed mostly large motile prey suggesting a diet more predacious than the other three species. Callinectes sapidus had a highly diversified diet with
three primary feeding types ontogenetically. Callinectes bocourti showed considerable dietary
overlap with C. sapidus, and Callinectes omalus demonstrated greatest ontogenetic variation.
Crabs of small size classes showed greatest interspecific variation within comparable size
classes. Dietary diversity was also greatest in small crabs and least in the largest size classes,
while prey size, in terms of kind of prey, increased with crab size. Overall, few strong
similarities occurred either within a species or between comparable size classes of different
species. This suggests that the incorporation of size and species specific trophic information
may be necessary for an understanding of community or ecosystem structure even when
considering closely related species.
Swimming crabs of the family Portunidae are abundant in coastal and estuarine
waters of temperate and tropical regions, particularly where wetland habitats
provide abundant food and shelter for the crabs and their young (Tagatz, 1968;
Norse, 1978). Because of the commercial significance of Callinectes sapidus, its
food habits have been examined in detail. The species was originally described
as a scavenger and cannibal (Hay, 1905), but has since been shown to consume
a wide variety of living organisms including crabs, shrimp, molluscs, fishes, and
polychaetes (Darnell, 1958; Tagatz, 1968). Laughlin's (1982) thorough investigation of C. sapidus in Apalachicola Bay, Florida, showed diets varied with crab
size, season, and location. Field and laboratory studies have confirmed that C.
sapidus selects particular prey species as well as prey sizes, and that the crabs
mediate prey population structure in certain cases (Hamilton, 1976; Hughes and
Seed, 1981; Blundon and Kennedy, 1982; Kneib, 1982; West and Williams, 1986).
The only other Callinectes spp. examined for diets, C. arcuatus and C. toxotes in
the Huizache-Caimanero lagoon of western Mexico, showed seasonal and spatial
as well as some interspecific variation in feeding ecology (Paul, 1981). The sizerelated differences in diets generally agreed with those found for C. sapidus (Laughlin, 1982).
In this study, we characterize intra- and interspecific variation in the diets of
a guild of four sympatric Callinectes spp. in a tropical estuary of Puerto Rico.
Where possible, temporal variation in diets were examined and related to prey
abundance.
MATERIALS AND METHODS
Callinectes spp. were collected monthly over a two-year period, from September 1984 through
August 1986, at five stations in Laguna Joyuda, Puerto Rico. The lagoon, previously described by
Buchanan and Stoner (1988), is a mangrove-fringed, polyhaline system, characterized by a relatively
homogeneous mud bottom. Submerged vegetation (Thalassia testudinum) is limited to small patches
near the inlet and in the north section of the lagoon.
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BULLETIN OF MARINE SCIENCE, VOL. 46, NO. I, 1990
Table I. List of the general food categories used for stomach contents of Ca//inectes spp. and the
codes employed in food habit histograms
Code
Food category
AM
BA
BI
CC
CR
CyC
DE
FO
FR
GA
HC
IE
Amphipod
Barnacle
Bivalve
Calanoid copepod
Crab
Cyclopoid copepods
Detritus
Foraminifera
Fish remains
Gastropod
Harpacticoid copepod
Invertebrate egg
• Miscellaneous-used
Code
MI·
NE
OS
PM
PO
PP
RU
SA
SH
TA
TH
Food category
Miscellaneous
Nematode
Ostracod
Plant material
Polychaete
Penaeus postlarvae
Ruppia
Sand
Shrimp
Tanaid
Thalassia
in food histograms for all above food categories making up <3% of the total mass.
A 5-m semiballoon otter trawl with 2.5-cm mesh panels and a 5-mm mesh cod-end liner was used
for collecting crabs. The net was towed with a small skiff at 2.5 knots for 70 m, and six replicate tows
were made at each station. The majority of the crabs had food in their guts because of crepuscular
feeding activities in Ca//inectes spp. (Ryer, 1987).
All shrimp, fish, and crabs were preserved in 10% formaldehyde diluted with lagoon water. Later,
all crabs were identified to species when possible, counted, measured (carapace width, including the
lateral spines), and transferred to 70% ethanol. Identifications were made using Williams (1974).
Analyses of distribution and abundance patterns were reported by Buchanan and Stoner (1988).
Numbers of crabs collected at each station were low; therefore, animals of individual size classes
and species were combined for individual dates or sets of dates. This is justified for several reasons:
I) All of the Ca//inectes spp. (except C. ornatus) were found at all stations (Buchanan and Stoner,
1988). 2) The lagoon is small (only 1.2 km2 in total surface area) and Callinectes spp. are highly
mobile. 3) The composition of prey species is relatively homogeneous in Laguna Joyuda (Stoner, 1986;
1988; Stoner and Acevedo, in press). Important macrofaunal prey species such as Dasybranchus
lumbricoides, Capitella capitata, Grandidierella bonnieroides. and Macoma brevifrom were abundant
and had similar biomass composition at the different stations,
Crab foreguts were pooled by individual species and size class, and preserved in 70% ethanol with
dilute rose bengal stain. Except for C. sapidus, crabs under 20 mm carapace width (CW) could not be
identified to species, and were omitted from the analysis. Crabs of 20-40 mm CW were divided by
species into 10-mm size classes, and crabs over 100 mm CW into 25-mm size classes. The gravimetric
sieve fractionation procedure (Carr and Adams, 1972) was used to analyze foregut contents. The
method is particularly useful in examining the diets of crustaceans (Leber, 1985) and has been used
with C. sapidus (Laughlin, 1982).
With two exceptions, all food particles were placed in mutually exclusive general categories for
statistical treatment (Table I). Categories such as amphipod, Foraminifera, and nematode were employed. The categories "animal remains" (unidentified tissue stained with rose bengal) and "plant
remains" were the only food categories that were not mutually exclusive from other groups. "Animal
remains" was not utilized since it would bias the analysis. The low number of prey species in the
lagoon precluded the possibility that there was an unknown prey which was not identified, and over
70% of the "animal remains" came from the smaller sieve sizes indicating that they were particles
from already identified prey. "Detritus" was material not stained by rose bengal and lacking the
pigments of living algae or seagrasses. Most of the material identified as detritus was brown and
contained the fibrous material of vascular plants, primarily mangroves. Whenever possible, more
specific information, such as the genus or species of food items, was recorded,
Similarities in diet between the various species and size classes were measured with Czekanowski's
coefficient (Bray and Curtis, 1957; Field and McFarlane, 1968) using proportions of foods of each
type. Dendrograms were constructed from the similarity matrices using average linkage classification.
Dietary diversity for each size class was calculated, using the Shannon-Weaver diversity index (H' =
p; log p.).
Where crabs were sufficiently abundant to examine temporal variation in diets, comparisons with
prey abundance were made. For this purpose, two measurements of prey abundance were used: I)
total number of penaeid shrimps per trawl, and 2) total number of anchovies (Engraulidae) and mojarras
(Gerreidae) per trawl. These two fish families comprised the majority of fishes in the crab diets.
STONER AND BUCHANAN:
CALLINECTES
5
SPP. DIETS
Table 2. Proportion of crabs for each species and size class with food in guts (% WF) and the proportion
of unidentified animal remains (% AR) in the gut contents
e. sapidus
e. danae
Size
10-20
21-30
31-40
41-60
61-80
81-100
101-125
126-150
X
%WF
82
83
80
64
83
78
88
79.7
%AR
10.4
6.8
4.6
3.1
4.0
2.8
2.4
4.8
%WF
%AR
92
72
82
87
83
70
94
68
81
17.4
13.5
21.5
14
12.4
9.1
11.5
6.7
13.3
e. bocourti
C. ornatus
%WF
%AR
%WF
%AR
77
92
100
87
88
11.9
13.8
13.1
7.3
2.8
92
67
83
64
50
75
16.6
13.1
15.2
3.2
5.7
8.6
71.8
10.4
88.8
9.8
RESULTS
Five-hundred thirty-six crabs were examined for gut contents of which 475
(80%) contained food items. The proportion of crabs with gut contents varied
between species and size classes, as did the proportions of "animal remains"
which were excluded from the analysis (Table 2). In general, however, more than
50% of the animals in all species and size classes had food in the guts, and
unidentified "animal remains" made up less than 20% of the gut contents in all
but one case. Dietary components varied both between species and size classes,
but the most common dietary items for the crabs were fish, detritus, crabs, and
bivalves. Other prey such as amphipods, polychaetes, shrimp, and gastropods
also made up measurable amounts of food weight in some size classes or species.
Size classes were clustered first within each species. Many natural clusters of size
classes were apparent at the 0.6 level of similarity (Fig. 1).
Callinectes danae showed the least ontogenetic variation in diets; all C. danae
between 20 and 125 mm CW formed a separate group. Dietary items of greatest
weight in the 21-125-mm size classes were crabs (mostly hermit crabs) which
were less important in the 126-150-mm size class. Fish weight increased from
the smaller to the larger size groups; and shrimp increased gradually over the size
classes within the first size group, then decreased to less than 2% in the 126-150mm crabs. Relatively little detritus was found in C. danae. Less important food
groups such as amphipods and gastropods generally decreased in weight with
increasing crab size. Dissimilarity between the largest size class and the others
was related to a high proportion of bivalves in the larger crabs.
Callinectes sapidus clustered into four major groups from the original 8 size
classes: 10-20,21-30,31-80,
and 81-150 mm CWo The two smallest size classes
were different from each other and other size classes, both in the major constituents
and the proportions. Amphipods which were major dietary constituents in the
10-20-mm crabs and foraminiferans which were important in the 21-30-mm
crabs, were rare or absent in diets of larger crabs. Polychaetes decreased in diets
with increasing crab size. Detritus, important in the smaller size groups, had less
weight in crabs over 80 mm CWo Crab and fish remains were important dietary
items in crabs above 30 mm CWo Bivalves occurred in 31-80-mm crabs, and
were uncommon, except in the 81-150-mm crabs.
Callinectes ornatus clustered into three major groups: 21-30, 31-80, and 81100 mm CWo Detritus and shrimp decreased in weight with crab size. Bivalves
and gastropods were absent in the smallest size group and increased with crab
size. The high proportion of amphipods and low proportions of fish and crabs in
6
BULLETIN OF MARINE SCIENCE, VOL. 46, NO.1,
JI
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FOOD ITEMS (%)
Figure 1. Diets of four Callinectes species in Laguna Joyuda, Puerto Rico, shown as a function of
crab size. Food categories are identified in Table I, and striped areas represent miscellaneous (MI).
The similarity index in the cluster diagrams in Czekanowski's coefficient.
the smallest and largest size groups, respectively, contributed to the differences
in clustering between these and the intermediate sized crabs.
Callinectes bocourti clustered into four major groups: 21-60, 61-80, 81-100,
and 101-125 mm CWo The proportions of crab remains (mostly hermit crabs and
some Callinectes spp.) and detritus decreased with increasing size, while fish
remains increased in weight with crab size. Polychaetes were common in the
STONER AND BUCHANAN:
C.S.
10-20
C.S.
21·30
C.O.
21-30
7
CALLINECTES SPP. DIETS
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SIMilARITY
Figure 2. Cluster diagram for the diets of crabs incorporating all species and size classes. Cluster
strategy is the same as that in Figure I. e.d. = Cal/inectes danae. e.s. = C. sapidus, e.o. = C. ornatus,
e.b. = C.
bocourti.
smaller size groups, though quite variable, and absent in the 61-80-mm size class.
Bivalves, although highly variable in contribution to food weight, were present
in most classes.
Dietary differences among both species and size classes were examined by
entering all data on all original size classes and species into a cluster analysis (Fig.
2). Consistent with the initial cluster analysis, C. danae showed the greatest ten-
8
BULLETIN OF MARINE SCIENCE, VOL. 46, NO. I, 1990
dency to cluster intraspecifically with all but the largest (> 125 mm) and smallest
(21-30 mm) size classes grouping at a similarity of 0.73 along with C. sapidus of
81-100 mm. This was due to similar high proportions of crabs, shrimps, and fish
in the diets. Callinectes sapidus of 101-125 and 126-150 mm clustered at a
similarity of 0.7 largely due to high proportions of crabs and bivalves, and these
clustered less strongly (0.6 similarity) with C. danae of 31-125 mm because of
high proportions of crabs in the diets. Callinectes bocourti from 31-60 mm grouped
with C. sapidus of 31-40 mm and 61-80 mm at a similarity of O. 7, due to similar
proportions of crabs, detritus, and polychaetes. Callinectes bocourti of 81-100
mm also grouped with C. sapidus of 41-60 mm in a separate grouping at the 0.7
level because of high proportions of polychaetes, fish, and bivalves in this group.
Callinectes bocourti of61-80 mm grouped with C. ornatus of61-80 mm (similarity of 0.76) largely due to high proportions of bivalves and gastropods, and
C. ornatus of 31-40 mm further grouped with these two at a similarity of 0.7.
The largest C. danae (126-150 mm) clustered less strongly (0.63) with the previously mentioned C. bocourti-C. ornatus complex because of a high percentage
of bivalves. The largest size classes of C. ornatus and C. bocourti differed from
all other groups; the largest C. bocourti had an extraordinarily high proportion of
fish in the guts (73%).
There was a tendency for the smallest size classes of all species to show relatively
low similarities (0.7) with other size classes of the same species or with each other.
In particular, C. sapidus of 10-30 mm and C. ornatus of 20-30 mm grouped with
no other size classes or species above a similarity of 0.5. Where similarities of
greater than 0.6 did occur in small size classes (such as with C. danae and C.
bocourtl), it was with other size classes of the same species rather than between
species. The high degree of dissimilarity between different species of small crabs
is due to a greater overall diversity in the types of food items consumed, such
that major prey groups differed. Small prey such as amphipods, forams, invertebrate eggs, and polychaetes became important in different species.
The diversity indices (Table 3) for all small, 21-30-mm CW, crabs were high
compared with the diversity indices for the individual species of that size, indicating again that different species of small crabs utilized different food items.
Diversity indices for the largest crabs of each species were all lower than the
diversity indices for other size classes of the same species. Callinectes danae tended
to have the lowest dietary diversity, but species differences were not large.
Species and genus identifications of prey items indicated no obvious differences
occurred between species or size classes except that remains of Callinectes spp.
occurred in large C. danae. Fish remains were rarely identifiable; the only ones
identified being Anchoa spp. and juvenile mojarra (Gerreidae). Shrimp (Penaeus
spp.), crabs (hermit crabs with a few incidences of Callinectes spp. and xanthids),
bivalves (mostly Macoma spp.), gastropods (all Nerita spp.), polychaetes (Dasybranchus /umbricoides or other capitellids), amphipods (all Grandidierella bonnieroides), and calanoid cope pods (Acartia tonsa with some Pseudodiaptomas spp.)
were all identifiable in the gut contents of Callinectes spp. examined.
Crabs were sufficiently abundant in only one trophic group (c. danae, 31-125
mm, plus C. sapidus, 81-100 mm) to provide a seasonal analysis of diets (Fig.
3). Detritus and crabs showed relatively little variation over time in the diets. On
the other hand, a switch from fish to shrimp was in evidence over the study period.
Fish comprised 40% of the diets in the fall quarter (October, November, December) and shrimp comprised 33% of the diets in the winter (January, February,
March). Dietary switching was associated with high abundance of anchovies and
mojarras from July to December, and high abundance of shrimps between February and June.
STONER AND BUCHANAN:
CALLINECTES
SPP. DIETS
Table 3. Dietary diversity in Callinectes species from Laguna Joyuda, Puerto Rico, by size class.
Values are Shannon-Weaver indices (H')
Carapace width
(mm)
Callinecles
danae
Cailinectes
sapidus
1.66
1.49
1.79
1.45
1.59
1.54
1.29
1.37
1.90
1.58
1.96
1.91
1.64
1.64
1.35
10-20
21-30
31-40
41-60
61-80
81-100
101-125
126-150
Ca/linectes
ornalUS
1.80
1.95
1.82
1.93
1.63
Callinectes
bocourti
All species
1.52
1.35
1.45
1.86
1.93
0.88
2.17
1.89
2.00
1.99
2.23
1.79
1.44
DISCUSSION
The dietary habits of Callinectes spp. in Laguna Joyuda differed strongly between size classes and species, though there were more apparent similarities between species than size classes. The smaller size classes of each species were
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Figure 3. The top graph illustrates seasonal gut contents for C. danae 31-125 mm CW and C. sapidus
81-100 mm CW. The bottom graph shows seasonal abundances of shrimp and fish (Engraulidae and
Gerreidae). Vertical bars represent standard errors for all replicates and stations.
10
BULLETIN OF MARINE SCIENCE, VOL. 46, NO. I, 1990
. particularly dissimilar, with each species having at least one different major prey
group. In contrast, Laughlin (1982) found some very high similarities (>0.8)
among size classes of C. sapidus. In general, plant material and detritus intake
decreased whiie shrimp, fish, and bivalve intake increased with crab size. Similar
results were found for two Pacific Callinectes species (Paul, 1981) and for C.
sapidus in Florida (Laughlin, 1982), with the differences in major constituents
being explained by differences in available prey types between areas. Bivalves,
which are not abundant in Laguna Joyuda (Stoner and Acevedo, in press) are
abundant in Apalachicola Bay and formed the highest percentage of the diets in
all size classes of C. sapidus examined by Laughlin (1982).
Callinectes danae in Laguna Joyuda demonstrated the least ontogenetic variation in diet, relatively low proportions of detritus, high amounts of animal
material, and occasional cannibalism. This did suggest that C. danae are capable
of handling larger and more motile prey. Callinectes ornatus exhibited the greatest
dissimilarity in diet ontogenetically and had a relatively high diversity of prey
items. Somewhat analogous to C. danae, observations on C. toxotes in the Pacific
though limited suggested that the species was more predacious and the diet less
varied than that of C. arcuatus (Paul, 1981). The similarities in food habits we
found between C. sapidus and C. bocourti may reflect morphological differences
from the other Callinectes spp. in ability to capture or handle different food types
because they are thought to be more closely related to each other than to the other
two Callinectes spp. (Norse and Fox-Norse, 1979).
Great variation in Callinectes feeding behavior has been documented in earlier
studies. An examination of foraging strategies of C. sapidus in Alabama Spartina
marshes showed distinct preferences for particular size classes of some visual
(epifaunal) prey such as Littorina and fish, but little size-selective preference for
infaunal prey such as the mussel, Geukensia sp. (West and Williams, 1986).
Additionally, prey species shifted with manipulations of overall prey density, as
we noted with our seasonal data. As opposed to C. sapidus, C. danae and C.
ornatus are known to be relatively oceanic in distribution (Norse, 1978), probably
living in clearer waters, and thus may have evolved more visually oriented feeding
strategies than C. sapidus and C. bocourti. Substrate type can also influence predation, as was found for Callinectes sapidus where predation on clams was lower
in sand than mud (Lipcius and Hines, 1986).
Our results suggest an ontogenetic trend of increasing predatory behavior with
increasing size; a trend found for C. sapidus in Florida (Laughlin, 1982) and some
Pacific Callinectes spp. (Paul, 1981). Laguna Joyuda has a lower number of large
prey species (Stoner and Acevedo, in press); therefore, larger crabs might be
expected to consume the same major prey items, with variation in proportions.
The largest crabs consumed more fish, shrimp, crabs, and molluscs in varying
proportions among species. Smaller crabs consumed a wider variety of prey which
were often small and probably not energetically useful as prey for larger crabs
(e.g., amphipods, foraminiferans, and polychaetes; especially in 2l-30-mm CW
crabs). Strong differences in prey among crab species in the smallest size classes
may indicate behavioral or morphological differences in feeding among species.
Strong differences among size classes suggest size-related changes in feeding apparatus, especially the size of feeding appendages.
Determination of crustacean diets on the basis of gut contents is associated with
a number of well recognized limitations such as different digestion rates for various
prey organisms and variation with season, site, sex, and gut fullness (Elner and
Campbell, 1987). Because numbers of crabs in our collection were not high and
because of our primary interest, the role of Callinectes spp. as predators in the
STONER AND BUCHANAN:
CALLINECTES
SPP. DIETS
11
lagoon system, we have not extracted all of the potential sources of variation in
diets, such as the switch in diets from fish to shrimp associated with changing
prey abundance.
Examination of stable carbon isotope ratios on Callinectes spp. and other components of the Laguna Joyuda system (Stoner and Zimmerman, 1988), however,
provides good evidence that the animals in the guts are the actual sources of
carbon for the crabs. Capitellid polychaetes, amphipods, penaeid shrimp, Macoma
brevifrons, hermit crabs, C. sapidus, and C. danae all had relatively high A13C
values (-15.4 to -18.8). Barnacles, other crab species, and copepods all had
highly negative values (- 23.0 to -25.9). Carbon isotope ratios do not permit
determination of the relative importance of the prey organisms, but Stoner and
Zimmerman (1988) showed that the food web leading to penaeid shrimps and
Callinectes spp. is not detritus-based as has been generally believed. Rather, th(:
blue-green algal mat which is very abundant on mangrove roots in the lagoon
and which covers much of the lagoon sediment (Rodriguez and Stoner, in press)
is the primary source of carbon to decapod consumers.
Data on sympatric Callinectes spp. from Laguna Joyuda show that portunidl
crabs are not readily accommodated in trophic levels or in concepts of feeding
guilds, and lends support to the suggestion of incorporating age-specific trophic
progressions in the analysis of systems functions (Livingston, 1980; 1982; 1984;
Stoner, 1980; Leber, 1983; Stoner and Livingston, 1984). Livingston (1982; 1984)
has been particularly successful using "ontogenetic trophic units": in the explanation of long-term, seasonal, and spatial relationships between fish community
structure and habitat characteristics. Similar strategy might be applied equally
well to decapod crustaceans, and a careful description of trophic interactions
constitutes an important first step in understanding any ecological system.
ACKNOWLEDGMENTS
This research was supported by the Office of Sea Grant, NOAA (Grant No. RJA-01-2) and a grant
from the National Science Foundation (No. R-II-86 10677). D. Corales participated in all ofthe field
work, and L. L. Cruz conducted the gut analyses. The manuscript was reviewed by Dr. K. M. Leber,
C. Perry and J. van Montfrans.
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DATE ACCEPTED:
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17, 1989.
(A. W.S.) Caribbean Marine Research Center. 100 E. 17th Street. Riviera Beach. Florida
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