Callinectes sapidus

thumb|Blue crab escaping from a net ([[Core Banks, North Carolina)]]

Callinectes sapidus, commonly known as the blue crab, Atlantic blue crab, or, regionally, the Maryland 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 considerable culinary and economic importance in the United States, particularly in Louisiana, the Carolinas, the Chesapeake Bay, Delaware, and New Jersey. It is Maryland's largest commercial fishery and has been designated its state crustacean. Due to overfishing and environmental pressures some of the fisheries have seen declining yields, especially in the Chesapeake Bay fishery.

Unlike the other fisheries affected by climate change, blue crab is expected to do well; warming causes better breeding conditions, more survivable winters, and a greater range of habitable areas on the Atlantic coast. Whether this will have negative effects on the surrounding ecosystems from an increased crab population is still unclear. Blue crabs may grow to a carapace width of . C. sapidus individuals exhibit sexual dimorphism. Males and females are easily distinguished by the shape of the abdomen (known as the "apron") and by color differences in the chelipeds, or claws. The abdomen is long and slender in males, but wide and rounded in mature females. A popular mnemonic is that the male's apron is shaped like the Washington Monument, while the mature female's resembles the dome of the United States Capitol. Claw color differences are more subtle than apron shape. The immovable, fixed finger of the claws in males is blue with red tips, while females have orange coloration with purple tips. A female's abdomen changes as it matures: an immature female has a triangular-shaped abdomen, whereas a mature female's is rounded.

Other species of Callinectes may be easily confused with C. sapidus because of overlapping ranges and similar morphology. One species is the lesser blue crab (C. similis). It is found further offshore than the common blue crab, and has a smoother granulated carapace. Males of the lesser blue crab also have mottled white coloration on the swimming legs, and females have areas of violet coloration on the internal surfaces of the claws. C. sapidus can be distinguished from another related species found within its range, C. ornatus, by number of frontal teeth on the carapace. C. sapidus has four, while C. ornatus has six.

The crab's 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 bright orange-red color.

Organochlorides are found by Sheridan et al 1975 to be transferred to the C. sapidus hepatopancreas. They find that among organochlorides, DDT specifically is converted both to DDE and DDD in this crab.

Distribution

thumb|Blue Crab as invasive species in the Adriatic Sea

C. sapidus is native to the western edge of the Atlantic Ocean from Cape Cod 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. In Italy, public awareness of the detrimental impact of this species on local molluscs is rapidly growing and, especially in the Po delta area and on the Adriatic Sea coast, eradication efforts are undergoing, both by local authorities and by local fishermen.

Ecology

Some of the natural predators of C. sapidus include eels, drum, striped bass, spot, trout, some sharks, humans, cownose rays, and whiptail stingrays. C. sapidus is an omnivore, eating both plants and animals. It typically consumes thin-shelled bivalves (such as clams, mussels, and oysters), crustaceans, annelids, small fish, plants (such as eelgrass), and nearly any other item it can find, including carrion, other C. sapidus individuals, and animal waste. In salt marshes, C. sapidus will eat marsh periwinkles, Littoraria irrorata during high tides. Although an aquatic predator, C. sapidus will remain in shallow pits in salt marshes at low tide and ambush intertidal prey such as fiddler crabs (e.g., Minuca pugnax) and purple marsh crabs (Sesarma reticulatum) 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 abundant.

C. sapidus is subject to a number of diseases and parasites. These 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.

In 2021, scientists from the University of Maryland completed DNA sequencing on C. sapidus's genome in Baltimore after six years of research to help better understand the species. This genetic map is expected to help scientists understand how the blue crabs will be affected by climate change and warmer water temperatures, along with which mutations cause disease, traits that influence meat production, and which females have the best reproductive ability.

Life cycle

Growth

Eggs of C. sapidus hatch in high-salinity waters of inlets, coastal waters, and mouths of rivers, and are carried to the ocean by ebb tides.

Male blue crabs tend to grow broader and have more accentuated lateral spines than females. During spawning, a female extrudes fertilized eggs onto her swimmerets and carries them in a large egg mass, or sponge, while they develop. Females migrate to the mouth of the estuary to release the larvae, the timing of which is believed to be influenced by light, tide, and lunar cycles. Blue crabs have high fecundity; females may produce up to 2 million eggs per brood. After mating, the female crab travels to the southern portion of the Chesapeake, using ebb tides to migrate from areas of low salinity to areas of high salinity, fertilizing her eggs with sperm stored during her single mating months or almost a year before.

Spawning events in the Gulf of Mexico are less pronounced than in estuaries along the East Coast, like the Chesapeake. In northern waters of the Gulf of Mexico, spawning occurs in the spring, summer, and fall, and females generally spawn twice. During spawning, females migrate to high -salinity waters to develop a sponge, and return inland after hatching their larvae. They develop their second sponge inland, and again migrate to the high-salinity waters to hatch the second sponge. After this, they typically do not re-enter the estuary. Blue crabs along the southernmost coast of Texas may spawn year-round.]]

Commercial 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 importance. In the 21st century, most commercial crabs have been landed in four states: Maryland, Virginia, North Carolina, and Louisiana. The first commercial processing plant in Louisiana opened in Morgan City in 1924. Other plants opened soon after, although commercial processing of hard blue crabs was not widespread until World War II. In 2013, crab landings were valued at $18.7 million from Maryland waters and $16.1 million from Virginia waters. Although crab populations are currently declining, blue crab fishing in Maryland and Virginia remains a livelihood for thousands of coastal residents. As of 2001, Maryland and Virginia collectively had 4,816 commercial crab license holders. Three separate licenses are required for each of the three major jurisdictional areas: Maryland, the Potomac River, and Virginia waters. While the Bay's commercial sector lands the majority of hard crab landings and nearly all peeler or soft crab landings, the recreational fishery is also significant. In 2013, an estimated of blue crab were harvested recreationally. This tendency may have made it difficult for managers to predict the severe decline of the Chesapeake's blue crab populations. Once considered an overwhelmingly abundant annoyance, the declining blue crab population is now the subject of anxiety among fishermen and managers. Over the decade between the mid-1990s to 2004, the population fell from 900 million to around 300 million, and harvest weight fell from . Revenue fell further, from $72 million to $61 million. Long-term estimates say that the overall Chesapeake population decreased around 70% in the last few decades. Even more alarming, the number of females capable of reproducing, known as spawning age females, has plummeted 84% in just a few decades. Survival and addition of juveniles to the harvestable crab population is also low. Many factors are to blame for low blue crab numbers, including high fishing pressure, environmental degradation, and disease prevalence. The 2018 reduction in H-2B visas available for seasonal workers is affecting Maryland's 20 crab processors, which typically employ about 500 foreign workers, but the effect this will have on the crab fishery is not yet clear.

Crabbing gear

thumb|Blue crab pot

Many types of gear have been used to catch blue crabs along the Atlantic and Gulf Coasts. Of important concern is the diamondback terrapin, Malaclemys terrapin. The blue crab and diamondback terrapin have overlapping ranges along the East and Gulf Coasts of the United States. Because the funnels in a crab pot are flexible, small terrapins may easily enter and become entrapped. Traps are checked every 24 hours or less, frequently resulting in drowning and death of terrapins. Crab pot bycatch may reduce local terrapin populations to less than half. To reduce terrapin entrapment, bycatch reduction devices (BRDs) may be installed on each of the funnels in a crab pot. BRDs effectively reduce bycatch (and subsequently mortality) of small terrapins without affecting blue crab catch.

Efforts to manage fisheries

thumb|A scientist holding a female (left) and male (right) Maryland blue crab (Chesapeake Bay, 1972)

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. It was the first and remains the only certified sustainable blue crab fishery worldwide. For the state to maintain its certification, it must undergo annual monitoring and conduct a full re-evaluation five years after the certification date.

Sports

The blue crab is the namesake of the Jersey Shore BlueClaws team in minor-league baseball playing in the South Atlantic League. They are located in Lakewood, New Jersey, and are a high-A affiliate of the Philadelphia Phillies.

Blue crabs are also the namesake of the Southern Maryland Blue Crabs, a professional baseball team located in Waldorf, Maryland.

Blue crabs inspired the branding of the Annapolis Blues Football Club in Annapolis, Maryland.

References

External links

Female Blue Crab Anatomy - Callinectes sapidus - Dana Point Fish Company
Crab diagram
Blue crab life cycle
Boy crabs boogie to bring females out of hiding – the wild dance of male blue crabs propels a jet of pheromones to attract would-be lovers, New Scientist, 7 April 2008
Chesapeake watermen fear blue crab not coming back – Associated Press, July 16, 2008
Blue Crab Info
Carolina Blue Crab
Blue Crab - North Carolina Division of Marine Fisheries
Blue Crab - North Carolina Watermen
Blue Crab Fact Sheet