||Callinectes sapidus Rathbun, 1896
||Sometimes confused with C. similis and C. ornatus, which also occur in east central Florida (Norse and Norse 1979)
Callinectes sapidus is a decapod crustacean of
the family Portunidae, which includes the swimming crabs. It is easily
identified by its body color which is generally a bright blue along the frontal
area, especially along the chelipeds. The remainder of the body is shaded an
olive brown color. As with other Portunids, the fifth leg is adapted to a
paddle-like shape to accommodate swimming. Females may be identified due
to their triangular or rounded aprons and red fingers on the chelae.
HABITAT AND DISTRIBUTION
Though the natural range of C. sapidus
is the western Atlantic Ocean from Nova Scotia to Argentina, it has also been
successfully introduced, accidentally or deliberately, into both Asia and Europe
(Milliken and Williams 1984).
Occurs throughout the Indian River Lagoon.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
C. sapidus may attain 25
cm carapace length, with carapace width being approximately twice the length.
New recruits enter estuaries in late fall and spring in Chesapeake Bay. Growth
is rapid during the first summer, with crabs growing from 70-100mm CL. Maturity
is reached by the second year at carapace lengths of 120-170 mm.
Growth in decapods is highly
dependent on temperature, molt frequency, food quality and availability, and
life stage. Low temperatures (<10°C) prevent molting and decrease growth
rates in blue crabs. Generally, growth occurs at temperatures over 15°C, and is
mostly unaffected by salinity conditions. Cadman (1990) observed blue crab
growth under laboratory conditions and noted that crabs are able to molt and
grow regularly at temperatures between 15 - 30°C, and salinities as low a 3 ppt.
Growth observed in blue crabs has been estimated to be between 12 - 35% per
Blue crabs exhibit
seasonal abundance cycles and show considerable variation in peak abundance
annually (Hines, Lipcius and Haddon 1987). In Florida, monitoring of commercial
and recreational fisheries shows that blue crabs are plentiful, ranking fifth in
abundance across all fisheries in the Indian River Lagoon.
C. sapidus, like
other Portunid crabs is an active swimmer, with its last pair of walking legs
adapted to a paddle-like shape to accommodate swimming. It also has three pairs
of walking legs, and a powerful set of chelae. Blue crabs are highly mobile, but
are more active during daylight hours than in the evenings. They are able to
move from 0-140 meters per hour, with an average of 15.5 m/hr. The total
distance traversed per day for these crabs is approximately 215 meters.
Spawning peaks in the
blue crabs are closely associated with the region inhabited. In Chesapeake Bay,
for example, spawning is initiated in May and June, with a second spawning in
August. In North and South Carolina, spawning occurs from March through October,
with peaks from April to August. Around the St. John's River in Florida,
spawning occurs from February to October, with peak spawning occurring from
March through September. In the Gulf of Mexico, 2 spawning periods are common:
one in February and March, and one in August and September. Unlike males, female
blue crabs mate only one time in their lives, following the terminal, or
pubertal molt. When approaching this molt, females release a pheromone in their
urine which attracts males. Male crabs vie for females and will protect them
until molting occurs. It is at this time that mating occurs. Mating may last as
long as 5-12 hours. Blue crabs are highly fecund, with females producing from 2
- 8 million eggs per spawn. Eggs are brooded 14-17 days, during which time
females migrate to the mouths of estuaries so that larvae may be released into
high salinity waters. C. sapidus larvae have a salinity requirement of at least
20 ppt., and show poor survival below this threshold.
There are usually 7 zoeal
stages and 1 postlarval, or megalopal, stage. On occasion, an eighth zoeal
stage is observed. Larval release is often timed to occur at the peak of high
tide, thus assuring that larval abundance is greatest when the tide begins to
ebb. Blue crab larvae are advected offshore, and complete development in coastal
shelf waters. Typical time for development through the 7 zoeal stages is between
30-50 days before metamorphosis to the megalopal stage. The megalopa then
persists between 6-58 days. It is widely believed that it is the megalopal stage
that subsequently return to estuaries for settlement, and eventual recruitment
to adult populations.
As the range of
C. sapidus extends from Nova Scotia to Argentina, and into Asia and Europe, it
is necessarily eurythermal. Growth occurs at temperatures from 15-30°C, but is
prevented at temperatures below 10°C. A hibernative state is induced in blue
crabs at temperatures below 5°C.
The larvae of C. sapidus
have a salinity requirement of at least 20 ppt.; however, as these crabs grow,
they are increasingly euryhaline. Both juvenile and adult blue crabs are able to
inhabit fresh water areas, as well as highly saline habitats; thus salinity is
not a major limiting factor in growth, molting or reproduction.
Other Physical Tolerances
Mortality of adult blue
crabs occurs under laboratory conditions when dissolved oxygen concentrations
fall below 0.6 mg/L for over 24 hours at a temperature of 24°C.
Predation by blue crabs
aids in regulation of marine bivalve populations in shallow, unvegetated soft
and hard bottom communities. (Eggleston 1990). Blue crabs prefer mollusks such
as oysters (Crassostrea virginica) and hard clams (Mercenaria mercenaria) as
their primary food sources, though older juveniles and adults sometimes
incorporate some plant material such as Ulva, eelgrass, and Spartina into the
diet. Foraging behavior is preceded by increases in gill bailing, antennule
movement and flexion of the mouthparts (Eggleston 1990). The dactyls of the
anterior walking legs are used to probe the substrate for buried bivalves, and
to manipulate them after they are located. Predators on blue crabs include fish
as well as other blue crabs. The major fish predators on blue crabs include the
Black Drum (Pogonias cromis), Red Drum (Scianops ocellata), the American Eel
(Anguilla rostrata), and the American Croaker (Micropogonias undulatus).
Competitors of blue
crabs are generally other crustaceans. Callinectes similis and C. ornatus occur
with C. sapidus in the Indian River Lagoon, and are thus closely related
competitors. Panopeus herbstii, Menippe mercenaria and Carcinus maenas also
compete for resources with blue crabs.
There is some evidence for habitat partitioning by blue crabs in terms of sex, size and molt stage.
Males predominantly utilize the head waters of rivers in Chesapeake Bay, and
molt inside tidal creeks. Further, of the crabs collected within these creeks,
those collected upstream tend to be in premolt stage, while those collected
downstream tended to be in postmolt stage (Hines, Lipcius and Haddon 1987).
Benefit in the IRL
Callinectes sapidus is
beneficial in terms of its value as a commercial and recreational fishery
species. See below.
The blue crab is a high value fishery species both within Florida and
nationally. The statewide commercial catch of hard shelled Callinectes
sapidus between the years 1987 - 2001 was 217.3 million pounds, with a
dollar value of over $142.5 million. Within the 5 county area
encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin
Counties) the commercial catch of hard shelled Callinectes sapidus
accounts for approximately 18% of the statewide total, with a harvest of 39.2
million pounds, and a value in excess of $25.1 million. This
ranks the blue crab sixth in commercial value within the IRL, and second in
Figure 1 below shows the dollar value of the blue crab
fishery to IRL counties by year. As shown, commercial catch ranged from a
low of $666,631 in 1991 to a high of over $2.8 million in 1997. Brevard County annually accounts for the largest percentage of the catch with
74% in total (Figure 2), followed distantly by Volusia County, which
accounts for 20% of the total. Indian River, St. Lucie and Martin Counties
make up the remaining 5% of the harvest with 1%, 3%, and 1% respectively.
Of interest is the growth of the blue crab fishery in Volusia county, where the
value of the blue crab harvest showed a tendency to increase annually between
1996 - 2001
(Tables 1, 2). During this same time period, there was a
corresponding decline in the blue crab fishery in Brevard County.
Figure 1. Annual dollar value of the commercial catch of blue crab to the 5-county area of the Indian River Lagoon.
Figure 2. Breakdown of total blue crab dollar value by county for the years 1987 - 2001.
Table 1. Total dollar value of the IRL harvest of hard-shelled blue crab, Callinectes sapidus, between 1987 -2001.
||Value to IRL
Table 2. By-county annual and cumulative percentages of the hard clam harvest for the years 1987-2001
Table 3. By county cumulative dollar value and percentage of total for the IRL blue crab harvest from 1987 - 2001.
In addition to its fisheries importance, the blue crab is an
important ecological species which may control the abundance of other species
within its range (Hines et al. 1990), especially juvenile populations of clams,
mussels and oysters, its preferred food items. Thus, its presence may
negatively impact other important fishery species.
Cadman LR, Weinstein MP. 1988. Effects of temperature and salinity on the growth of laboratory-reared juvenile blue crabs Callinectes sapidus Rathbun. J Exper Mar Biol Ecol 121: 193-207.
Eggleston DB. 1990. Behavioural mechanisms underlying variable functional responses of blue crabs, Callinectes sapidus feeding on juvenile oysters, Crassostrea virginica. J Animal Ecol 59: 615-630.
Hines AH, Haddon AM, Wiechert LA. 1990. Guild structure and foraging impact of blue crabs and epibenthic fish in a subestuary of Chesapeake Bay. Mar Ecol Prog Ser 67: 2.
Hines AH, Lipcius RN, Haddon AM. 1987. Population dynamics and habitat partitioning by size, sex, and molt stage of blue crabs Callinectes sapidus in a subestuary of central Chesapeake Bay. Mar Ecol Prog Ser 36: 55-64.
Milliken M, Williams A. 1984. Synopsis of biological data on the blue crab, Callinectes sapidus Rathbun. NOAA Natn Mar Fish Serv Tech Memo. US Dept Commerce 1: 1-39.
Report by: K. Hill,
Smithsonian Marine Station
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Page last updated: October 11, 2004