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Callinectes sapidus - adult male.  Photo courtesy of: D. Elliott

Megalopa of Callinectes sapidus: carapace length approximately 1.7 mm.  Photo courtesy of: J. Dineen, Smithsonian Marine Station at Fort Pierce.

Species Name: 
Callinectes sapidus Rathbun, 1896

Common Name:
Blue Crab

Species Description:
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.

Synonymy:
Sometimes confused with C. similis and C. ornatus, which also occur in east central Florida (Norse and Norse 1979).

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
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).

IRL Distribution:
Occurs throughout the Indian River Lagoon.

III. 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 molt.

Abundance:
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.

Locomotion:
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.

Reproduction:
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.

Embryology:
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.

IV.  PHYSICAL TOLERANCE

Temperature:
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.

Salinity:
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.

V.  COMMUNITY ECOLOGY

Trophic Mode:
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:
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.

Habitat:
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).

VI. SPECIAL STATUS

Special Status:
Fisheries.

Benefit in the IRL:
Callinectes sapidus is beneficial in terms of its value as a commercial and recreational fishery species. See below.

Fisheries Importance:
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 pounds harvested.   

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.
 

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.

Broad-scale Cost/Benefit:
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 fisher