The blue crab Callinectes ornatus is a decapod crustacean in the Portunidae
family. It is a strong and agile swimmer powered by a pair of flat, oar shaped
rear legs called swimmerets. Swimmerets allow C. ornatus to rapidly swim
backwards, sideways, and sometimes forward (Barnes 1980). The color of this
species varies considerably. Adult males have a carapace that is uniformly
olive to dark brown with a large orange spot posteriorly that can appear round
to blotchy (Gore and Grizzle 1974, Gore 1977, Williams 1984). There are
distinct ivory white tips on all the spines on the front of the carapace (Gore
1977). Juveniles are not as brilliantly colored appearing olive-yellow to
greenish. The length and curvature of the reproductive organs (gonopods) are
distinctive in mature males for each of the Callinectes species (Gore 1977,
Barnes 1980) See illustrations from Williams (1974) below.
Potentially Misidentified Species
It can be difficult to distinguish the juveniles, immature males, and adult
females of C. ornatus from C. danae and C. similis (Williams 1984). C.
ornatus is very similar to C. similis and the two were confused until the
1960's (Gore 1977).
C. similis can be distinguished from C. ornatus by the pale translucent blue
dactyls of the swimming legs and the propodi that are olive on the ends and
banded with translucent blue mesially.
Comparative detail of the reproductive structures of mature male Callinectes. Modified from Williams 1974.
HABITAT AND DISTRIBUTION
Callinectes ornatus is distributed from North Carolina to Rio Grande de Sul,
Brazil (Williams 1984, Branco et. al. 2002) living at depths of up to 75 meters
on sand and mud bottoms (Branco et al. 2002). The ornate blue crab is found in
river mouths but more commonly occurs offshore (Negreiros-Fransozo et al.
1999). Juveniles are usually found in shallower habitats.
Adults and juvenile of the ornate blue crab are common in seagrass beds in the
lagoon (Gore 1977).
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Male Callinectes ornatus are usually slightly larger than the females
measuring up to 60 mm while the female carapace can measure up to 58 mm
(Williams 1984). It is unknown whether males and females have different
mortality rates (Negreiros-Fransozo et al. 1999).
The ornate blue crab is common in the Indian River Lagoon and shallow tropical
habitats of warm waters in the eastern Atlantic oceans. In a population of
Callinectes ornatus from Ubatuba in Brazil, the males made up 63% of the
population outnumbering the females 1.7 to 1 (Negreiros-Fransozo et al. 1999).
Records of museum collections of oviparous females suggest that Callinectes
ornatus spawn year-round (Williams 1984). Adult females move offshore to find
temperature and/or salinity conditions that are best for spawning. One female
can mate with several males during the same reproductive period
(Negreiros-Fransozo et al. 1999).
In the Portunidae, there are generally 7 zoeal stages and 1 postlarval, or
megalopal stage. Occasionally an eighth zoeal stage is observed. Larval
release usually occurs at high tide assuring larval abundance is at its peak
during the ebbing tide. Crab larvae are advected offshore, and complete
development in the coastal shelf waters. The typical time for development
through the 7 zoeal stages is between 30-50 days before metamorphosis to the
megalopal stage. The megalop is capable of postponing metamorphosis to first
crab and may persist from 6-58 days. It is widely believed that the megalopal
stage subsequently returns to the estuaries for settlement, and recruitment to
Callinectes ornatus is usually found in tropical seas in temperatures ranging
from 18-31°C (William 1984).
Specimens have been trapped in fresh water but most collections of C. ornatus
come from waters with higher salinities (William 1984). Laboratory experiments
with portunid crabs in the genus Callinectes demonstrated that C. ornatus has
lower tolerance to hyposaline conditions (reductions in salinity). Individuals
of C. ornatus were shown to begin dying off when seawater was diluted by 25%
(8.7 ppt) whereas C. sapidus, C. exasperatus, and C. danae tolerated extreme
hyposaline conditions of 3.5 ppt (Norse 1978).
Callinectes ornatus is both a saprophagous species, feeding on decaying matter,
as well as an active predator. C. ornatus will dig into the substratum in
search of food, feeding on mollusks, especially bivalves, and other
crustaceans, including brachyura (true crabs), other species of Callinectes,
algae, polychaetes, echinoderms, and foraminifera (Branco et al. 2002).
Competitors of the ornate blue crab are other crustaceans, in particular C.
sapidus and C. similis.
Because Callinectes ornatus occupies the same habitats as the commercial
species, C. sapidus, it is impacted by the crab fishery along western Atlantic
coast. In the Ubatuba region of Brazil it is a major fishery
(Negreiros-Fransozo et al. 1999).
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