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Callinectes sapidus (from the Greek calli- = "beautiful", nectes = "swimmer", and Latin sapidus = "savory"), the blue crab, Atlantic blue crab, or regionally as the Chesapeake blue crab, is a species of crab native to the waters of the western Atlantic Ocean and the Gulf of Mexico, and introduced internationally.
C. sapidus is of significant culinary and economic importance in the United States, particularly in Louisiana and in the Chesapeake Bay. It is the Maryland state crustacean and is the states largest commercial fishery. Louisiana harvests the most blue crab of all states in America by a significant margin. Most crabs sold in Maryland were caught in Louisiana. 
Callinectes sapidus may grow to a carapace width of 230 mm (9.1 in). It can be distinguished from a related species occurring in the same area by the number of frontal teeth on the carapace; C. sapidus has four, while C. ornatus has six.
Males and females of C. sapidus can be distinguished by the sexual dimorphism in the shape of the abdomen (known as the "apron"). It is long and slender in males, but wide and rounded in mature females; one popular mnemonic is that the male's is shaped like the Washington Monument, while the female's resembles the dome of the United States Capitol. A female's abdomen changes as it matures: an immature female has a triangular-shaped abdomen, whereas a mature female's is rounded.
The blue hue stems from a number of pigments in the shell, including alpha-crustacyanin, which interacts with a red pigment, astaxanthin, to form a greenish-blue coloration. When the crab is cooked, the alpha-crustacyanin breaks down, leaving only the astaxanthin, which turns the crab to a red-orange or a hot pink color.
Callinectes sapidus is native to the western edge of the Atlantic Ocean from Nova Scotia to Argentina and around the entire coast of the Gulf of Mexico. It has been introduced (via ballast water) to Japanese and European waters, and has been observed in the Baltic, North, Mediterranean and Black Seas. The first record from European waters was made in 1901 at Rochefort, France. In some parts of its introduced range, C. sapidus has become the subject of crab fishery, including in Greece, where the local population may be decreasing as a result of overfishing.
The natural predators of C. sapidus include eels, drum, striped bass, spot, trout, some sharks, humans, and cownose sting rays. C. sapidus is an omnivore, eating both plants and animals. C. sapidus typically consumes thin-shelled bivalves, annelids, small fish, plants and nearly any other item it can find, including carrion, other C. sapidus individuals, and animal waste. C. sapidus may be able to control populations of the invasive green crab, Carcinus maenas; numbers of the two species are negatively correlated, and C. maenas is not found in the Chesapeake Bay, where C. sapidus is most frequent.
Callinectes sapidus is subject to a number of diseases and parasites. They include a number of viruses, bacteria, microsporidians, ciliates, and others. The nemertean worm Carcinonemertes carcinophila commonly parasitizes C. sapidus, especially females and older crabs, although it has little adverse effect on the crab. A trematode that parasitizes C. sapidus is itself targeted by the hyperparasite Urosporidium crescens. The most harmful parasites may be the microsporidian Ameson michaelis, the amoeba Paramoeba perniciosa and the dinoflagellate Hematodinium perezi, which causes "bitter crab disease".
In the Chesapeake Bay, C. sapidus undergoes a seasonal migration. Female blue crabs mate only once in their lifetimes. After mating, the female crab travels to the southern portion of the Chesapeake, using ebb tide transport to migrate from areas of low salinity to areas of high salinity. fertilizing her eggs with sperm stored exclusively during her months or almost a year before. Up to two million eggs may be produced in a single brood, and a single female can produce over 8,000,000 eggs in her lifetime. After brooding the eggs as an orange mass on her pleopods for around two weeks, the female crab releases her eggs in November or December. The crabs hatch into larvae and float in the mouth of the bay for four to five weeks, after which the juvenile crabs make their way back into the bay.
Range of Fisheries
Fisheries for C. sapidus exist along much of the Atlantic coast of the United States, and in the Gulf of Mexico. Although the fishery has been historically centered on the Chesapeake Bay, contributions from other localities are increasing in volume. In 2002, around two-thirds of the total U.S. market of C. sapidus came from four states – Louisiana (22%), North Carolina (17%), Maryland (14%), and Virginia (13%). No other state contributed more than 3%, with 17% of the market being supplied by imports, especially from Indonesia (6% of the total U.S. market) and Thailand (4%); no data are available on the amounts exported from the U.S.
Louisiana has the world's largest blue crab fishery. The industry was not commercialized for interstate commerce until the 1990s, when supply markedly decreased in Maryland due to problems in Chesapeake Bay. Since then, Louisiana has steadily increased its harvest. In 2002, Louisiana harvested 22% of the nation's blue crab. That number rose to 26% by 2009 and 28% by 2012. The vast majority of Louisiana crabs are shipped to Maryland, where they are sold as "Chesapeake" or "Maryland" crab.
Chesapeake Bay Fishery
The Chesapeake Bay, located in Maryland and Virginia, is famous for its blue crabs. The crab harvest constitutes the most important economic fishery for both states. In 1993, the combined harvest of C. sapidus was valued at around US$100 million. Over the years, the population of C. sapidus has dropped, and the amount captured has fallen from over 125,000 t (276,000,000 lb) in 1993 to 81,000 t (179,000,000 lb) in 2008.
In the Chesapeake Bay, the population fell from 900 million to around 300 million, and capture fell from 52,000 t (115,000,000 lb) in the mid-1990s to 28,000 t (62,000,000 lb) in 2004, with revenue falling further, from $72 million to $61 million.
Efforts to Manage Fisheries
Because of its commercial and environmental value, C. sapidus is the subject of management plans over much of its range. In 2012, the C. sapidus population in Louisiana was recognized as a certified sustainable fishery by the Marine Stewardship Council.
- Beautiful Swimmers – a Pulitzer Prize-winning book with an extensive discussion of the crabs and their life cycle
- Crab cake
- She-crab soup
- Soft-shell crab
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