Blue crab range from Nova Scotia and Maine to northern Argentina and are found throughout the Gulf. There are likely two different blue crab stocks in the Gulf: a Florida or Eastern Gulf stock along the Florida coast (centered around Tampa Bay) and a Western Gulf stock from central Texas to Apalachicola Bay (centered in Louisiana).
Blue crab larvae are found in salty offshore waters. Post-larvae move into shallow, lower salinity estuarine waters. Juveniles remain in the upper and middle estuary in areas with marsh and sea grass, oyster reefs, as well as soft mud bottoms, all of which provide some protection from predators. As juvenile crabs grow larger, they move to fresher waters. Adult blue crabs are found on a variety of bottom types including submerged vegetation, unvegetated sediments, and marsh grass in fresh, estuarine, and shallow oceanic waters throughout the Gulf.
In the Gulf, most blue crabs typically mature within a year, when males and females are four and five inches shell width, respectively. They can live up to three years. Crabs grow by molting—their hard shell restricts growth so they must shed it to increase in size. Right after molting, they are “soft-shelled” and vulnerable to predators until their new shell hardens. Young crabs molt every few days, but as they grow, they molt less often.
Blue crabs generally mate and spawn year-round, but these events occur separately and in different areas. Blue crabs mate in brackish waters of the upper estuary just after the female molts, while her shell is still soft. After mating, the male stays to protect the female until her new shell hardens. The female stores the sperm in receptacles for several months and uses it in repeated spawnings. Females move to saltier coastal Gulf and estuarine waters to spawn. They push their eggs through the receptacles to fertilize them, then onto their abdomen where they’re carried in an egg mass or sponge. Depending on their size, females can carry up to 3.5 million fertilized eggs. The eggs hatch in about two weeks. Tides transport the newly hatched larvae from estuaries to adjacent continental shelf waters where they molt several times. Assisted by winds and tides, post-larval blue crabs gradually migrate back into shallower, less saline waters in middle and upper estuaries where they grow and mature. Temperature, habitat quality, and the availability of food all affect blue crabs’ growth and survival.
Blue crabs are opportunistic feeders, eating whatever food is available, and are an important part of the estuarine food web. Larval blue crab feed on plankton, but as they grow and settle to the bottom, their diet expands. Juveniles and adults feed on small fish, bivalves, crustaceans, plant material, and detritus. Blue crabs are also food for other species; shrimp, jellyfish, fish, and other plankton-eaters feed on larval blue crab, and a number of commercial and sport fish, turtles, birds, and alligators prey on juvenile and adult blue crabs. Blue crabs also eat each other.
Blue crabs are crustaceans with a hard upper shell, typically grey, blue, or brownish green in color. The shell is about 2.5 times as wide as it is long. Blue crabs have two large claws, six thin walking legs, and two paddle-like swimming legs. You can distinguish mature males from females by their claw color and abdomen shape. Males’ claws are blue on the inner and outer surfaces and tipped with red; the fingers of the females’ claws are orange tipped with purple. The male’s abdomen has a narrow and triangular shape (like the Washington Monument) and females have a broader, rounded abdomen (like the dome of the U.S. Capitol building).