Blue Crab Facts

The blue crab (Callinectes sapidus) is known for its color and delicious flavor. The crab's scientific name means "savory beautiful swimmer." While blue crabs do have sapphire blue claws, their bodies are usually duller in color.

Description

Like other decapods, blue crabs have 10 legs. However, their hind legs are paddle-shaped, making blue crabs excellent swimmers. Blue crabs have blue legs and claws and olive to grayish blue bodies. The color comes mainly from the blue pigment alpha-crustacyanin and the red pigment astaxanthin. When blue crabs are cooked, heat deactivates the blue pigment and turns the crab red. Mature crabs are about 9 inches wide, 4 inches long, and weigh one to two pounds.

Blue crabs are sexually dimorphic. Males are slightly larger than females and have bright blue claws. Females have red-tipped claws. If the crab is flipped over, the shape of the folded surface of the belly (the apron) reveals the animal's approximate age and sex. Male aprons are t-shaped or resemble the Washington Monument. Mature female aprons are rounded and resemble the United States Capitol building. Immature female aprons are triangular in shape.

Habitat and Range

Blue crabs are native to the western Atlantic coast, ranging from Nova Scotia to Argentina. During their larval stages, they live offshore in high-salinity water and move into marshes, seagrass beds, and estuaries as they mature. Crabs traveling in ship ballast water have led to the species' introduction to the Black, North, Mediterranean, and Baltic Seas. It is now relatively common along European and Japanese coasts.

Diet and Behavior

Blue crabs are omnivores. They feed on plants, algae, clams, mussels, snails, live or dead fish, other crabs (including smaller members of their own species), and detritus.

Reproduction and Offspring

Mating and spawning occur separately. Mating occurs in brackish water during warm months between May and October. Mature males molt and mate with multiple females over their lifespan, while each female undergoes a single molt into her mature form and only mates once. As she nears the molt, a male defends her against threats and other males. Insemination occurs after the female molts, providing her with spermatophores for a year of spawning. The male continues to guard her until her shell hardens. While mature males remain in brackish water, females migrate to high salinity water to spawn.

Spawning occurs twice a year in some areas and year-round in others. The female holds her eggs in a spongy mass on her swimmerets and travels to the mouth of an estuary to release hatching larvae, which are carried away by the current and tides. Initially, the egg mass is orange, but it darkens to black as hatching nears. Each brood may contain 2 million eggs. The larvae or zoea grow and molt over 25 times before maturing and returning to estuaries and salt marshes to breed. In warm water, crabs reach maturity in 12 months. In cooler water, maturity takes up to 18 months. The blue crab lifespan ranges between 1 and 4 years.

Conservation Status

The International Union for Conservation of Nature (IUCN) has not evaluated the blue crab for a conservation status. Once abundant, fisheries report a severe decline in population numbers. However, state management plans are in place over much of the crab's native range. In 2012, Louisiana became the first sustainable blue crab fishery.

Threats

Blue crab populations naturally fluctuate, mainly in response to temperature and weather conditions. The continuing decline may be due to a combination of threats, which include disease, overharvesting, climate change, pollution, and habitat degradation.

Blue Crabs and Humans

Blue crabs are commercially important along the Atlantic and Gulf coasts. Overfishing of blue crabs significantly affects populations of fish that depend on their larvae for food and has other negative effects on the aquatic ecosystem.

Sources

• Brockerhoff, A. and C. McLay. "Human-mediated spread of alien crabs." In Galil, Bella S.; Clark, Paul F.; Carlton, James T. (eds.). In the Wrong Place – Alien Marine Crustaceans: Distribution, Biology and Impacts. Invading Nature. 6. Springer. 2011. ISBN 978-94-007-0590-6.
• Kennedy, Victor S.; Cronin, L. Eugene. The Blue Crab Callinectes sapidus. College Park, Md.: Maryland Sea Grant College. 2007. ISBN 978-0943676678.
• Perry, H.M. "The blue crab fishery in Mississippi." Gulf Research Reports. 5 (1): 39–57, 1975.
• Williams, A. B. "The Swimming Crabs of the Genus Callinectes (Decapoda: Portunidae)." Fishery Bulletin. 72 (3): 685–692, 1974.