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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.
II. HABITAT AND DISTRIBUTION
Regional Occurrence:
Adult Callinectes similis occur in the oceanic littoral zone in
salinities above 15ä at a depth of 100 meters along the eastern seaboard
from Delaware Bay to Key West, Florida and southern coasts of the United
States, to the Yucatan, Colombia and northern Jamaica (Williams 1984,
Piller et al. 1995). They are widely distributed along the northern Gulf
of Mexico in open bay habitats (Hsueh et al. 1992a). Juveniles are found
in estuaries in these same regions.
IRL Distribution:
Juveniles of the lesser blue crab are common in seagrass beds in the Indian River Lagoon (Gore 1977).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
The Callinectes similis male grows to a maximum width of 122 mm and the female grows to a maximum width of 95 mm. A study of populations in Mobile Bay in the Mississippi Sound reported a larger female to male ratio (Hsueh et al. 1993).
Abundance:
The lesser blue crab is common in marshes and estuaries. In the barrier reef marsh habitats of Mobile Bay, Alabama, Callinectes similis is reported to be the dominant crab in open bays (Hsueh et al. 1993).
Reproduction:
Callinectes similis has spring and fall spawning seasons (Williams 1984). The egg carrying females migrate to nearshore waters with higher salinities to release their larvae (Hsueh et al. 1993).
Embryology:
In Callinectes similis, there are generally 8 zoeal stages and 1 postlarval, or megalopal stage (Bookhout and Costlow 1977). 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 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 persists between 6-58 days. It is widely believed that the megalopal stage subsequently returns to the estuaries for settlement, and recruitment to adult populations (Barnes 1980, Hsueh et al. 1993).
IV. PHYSICAL TOLERANCES
Temperature:
Temperature may be a factor in the reproductive cycles of the lesser blue crab (Williams 1984).
Salinity:
Adult Callinectes similis are not usually encountered in estuaries
where salinities are below 15 ppt. Like its congener C. sapidus,
the lesser blue crab is a hyperosmoregulator able to respond to changes in
salinity by maintaining a high hemolymph osmolarity by active ion pumping
in the gills (Piller et al. 1995).
Juveniles of the lesser blue crab exhibit a higher tolerance for salinity
change than adults allowing them to inhabit estuaries with salinities as
low as 10 ppt (Guerin and Stickle 1997). In Mobile Bay, Alabama, juvenile
C. similis were encountered in the barrier reef marsh habitats with
salinities ranging from 8-28 5ppt (Hsueh et al. 1992a). In laboratory
experiments, C. similis juveniles survived in near freshwater (as
low as 5 ppt) to hypersaline conditions, but were reported to be best
adapted to 35 ppt (Hsueh et al. 1993).
Dissolved Oxygen:
Juveniles of the lesser blue crab tolerate high levels of hypoxia but will die under anoxic conditions. In laboratory studies, there was a noticeable decrease observed in feeding, growth and molting rates below normoxia. This adaptation may allow populations of Callinectes similis to survive seasonal occurrences of hypoxic water masses on continental shelves (Das and Stickle 1993).
V. COMMUNITY ECOLOGY
Trophic Mode:
Callinectes similis is an opportunistic predator feeding primarily on bivalves and other benthic macroinvertebrates crushing their prey with their claws. Stomach content studies also show that the lesser blue crab diet includes fish, crustaceans, squid, detritus, and plants (Hsueh et al. 1992a).
Associated Species:
The lesser blue crab is usually associated with Callinectes sapidis where they compete for food and other resources (Williams 1984). Typically, adult C. similis inhibits higher-salinity waters ( ³15ä) than C. sapidis (Guerin and Stickle 1997). However, juvenile C. similis and C. sapidis overlap considerably in estuaries where they can find refuge and abundant food sources.
VI. SPECIAL STATUS
Fishery:
Because Callinectes ornatus occupies the same habitats as the commercial species, C. sapidus, it is impacted by the crab fishery along western Atlantic coast (Hsueh et al. 1992).
VII.
REFERENCES
Barnes RD. 1980. Invertebrate Zoology. Saunders College/Holt, Rinehart
and Winston, Philadelphia, PA pp. 725
Bookhout CG and JD Costow, Jr. 1977. Larval development of Callinectes
similis reared in the laboratory. Bulletin of Marine Science
27:704-728.
British Towns and Villages Network. Available online.
Das T and WB Stickle. 1993. Sensitivity of crabs Callinectes
sapidus and C. similis and the gastropod Stramonita
haemastoma to hypoxia and anoxia. Marine Ecology Progress Series
98:263-274.
Gore RH 1977. Studies on decapod crustaceans from the Indian River region
of Florida. VII. A field character for the rapid identification of the
swimming crabs Callinectes ornatus Ordway, 1963 and C.
similis Williams, 1966 (Brachyura: Portunidae). Northeast Gulf Science
1:119-123.
Guerin JL and WB Stickle. 1997. Effects of salinity on survival and
bioenergetics of juvenile lesser blue crabs, Callinectes similis.
Marine Biology 129:63-69.
Hsueh PW, McClintock JB and TS Hopkins. 1992a. Comparative study of the
diets of the blue crabs Callinectes similis and C. sapidus
from a mud-bottom habitat in Mobile Bay, Alabama. Journal of Crustacean
Biology 12:615-619.
Hsueh PW, McClintock JB and TS Hopkins. 1992b. Factors affecting the
population dynamics of the lesser blue crab (Callinectes similis
Williams) in barrier island salt marsh habitats of the Gulf of Mexico.
Journal of the Alabama Academy of Science 63:1-9.
Hsueh PW McClintock JB and TS Hopkins. 1993. Population dynamics and
life history characteristics of the blue crabs Callinectes similis
and C. sapidus in bay environments of the northern Gulf of Mexico. Marine
Ecology 14:239-257.
Piller SC, Henry RP, Doeller JE and DW Kraus. 1995. A comparison of the
gill physiology of two euryhaline crab species, Callinectes sapidus
and Callinectes similis: energy production, transport-related
enzymes and osmoregulation as a function of acclimation salinity. Journal
of Experimental Biology 198:349-358.
Williams AB. 1984. Shrimps, Lobsters, and Crabs of the Atlantic Coast of
the Eastern United States, Maine to Florida. Smithsonian Institution
Press, Washington, D. C., pp 373-376.
Report by:
Melany P. Puglisi, Smithsonian Marine Station
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Page last updated: October 1, 2008 |
