Why a blue crab turns orange-red in the cooking pot
A live blue crab owes its colour to a pigment called alpha-crustacyanin that grips a red one, astaxanthin, and shifts it to greenish blue. Heat destroys the first pigment, leaving only the red behind, which is why the crab emerges from the pot bright orange.
Its scientific name is a compliment: Callinectes comes from Greek words for beautiful swimmer, and sapidus is Latin for savoury. Native to the western Atlantic from Cape Cod to Argentina and all around the Gulf of Mexico, the blue crab is Maryland's biggest commercial fishery and its official state crustacean, and it matters economically from Louisiana to New Jersey. The Powhatan word for crabs was tuttascuc.
A member of the swimming crab family, it can reach 23 centimetres across the shell. Males and females are told apart by the shape of the abdomen, called the apron, and by the colour of the claws. Ballast water has carried the species to Japan and Europe, where it was first recorded in 1901 at Rochefort, France, and it now turns up in the Baltic, North, Mediterranean and Black Seas. Sightings north of Cape Cod may reflect warming seas. Unusually among fisheries, this one is expected to benefit from climate change through better breeding and milder winters, though what a bigger crab population would do to its neighbours is uncertain.
It will eat nearly anything: clams, mussels, oysters, worms, small fish, eelgrass, carrion and even other blue crabs. Eels, striped bass, sharks, rays and people eat it in turn. Life begins as a larva floating near the surface through seven stages before becoming a megalopa with tiny claws that rides incoming tides into brackish estuaries.
Growth happens in jumps. A crab sheds its exoskeleton about 25 times in a lifetime, and the new shell hardens fastest in low-salinity water, where water rushes into the soft body. Because each molt adds only a little, ageing a crab is difficult. Males may mate repeatedly, but a female mates just once, during her final molt, when her abdomen changes from triangular to semicircular. In 2021 University of Maryland researchers finished sequencing the species' genome after six years of work.
Source: Callinectes sapidus
