Callinectes sapidus
blue crab

Although the natural range of Callinectes sapidus spreads from the western Atlantic Ocean from Nova Scotia to Argentina, it was introduced, accidentally or deliberately, into both Asia and Europe. It has also been introduced into Hawaii and Japan. Callinectes sapidus is mostly found from Cape Cod (Massachussets) to Uruguay, but is also found north to at least Massachusetts Bay. (Hill, 2004; Shapiro, 2011)

Callinectes sapidus, the blue crab, is a bottom-dweller found in a variety of habitats ranging from the saltiest water of the gulf to almost fresh water of the back bays. Especially common in estuaries, this species ranges into fresh water, and may be found offshore. The blue crab's habitat ranges from the low tide line to waters 120 feet (36 m) deep. Females remain in higher salinity portions of an estuary system, especially for egg laying. During times of the year when temperatures are colder, C. sapidus tends to migrate to deeper water. (Shapiro, 2011; Texas Parks and Wildlife, 2009)

Callinectes sapidus is easily identified by its body color which is generally a bright blue along the frontal area, especially along the chelipeds (the appendages bearing a "chela" or pincher-like claw). The remainder of the body is shaded an olive brown color. To accommodate swimming, the fifth leg is adapted to a paddle-like shape, as is the same with other portunids. Females have broad triangular or rounded aprons and red fingers on the chelae, whereas in the male the abdominal flap, or apron, is shaped like an inverted "T". Callinectes sapidus can grow to 25 cm in carapace length (CL), with carapace width being approximately twice the length. Growth is rapid during the first summer, with crabs growing from 70-100 mm CL. By the second year, maturity is reached at carapace lengths of 120-170 mm. Callinectes sapidus grows to adult size after 18 to 20 molts. (Hill, 2004; Steele, 1979; Texas Parks and Wildlife, 2009)

Callinectes sapidus usually goes through seven zoeal stages and 1 postlarval, or megalopal stage. Sometimes an eighth zoeal stage is observed. Larval abundance is greatest when the tide begins to recede, because the larval release often occurs at the peak of high tide. Blue crab larvae are advected offshore, completing development in coastal shelf waters. Typical development through the seven zoeal stages is between thirty and fifty days before metamorphosis to the megalopal stage. The megalopa persists between six and fifty-eight days. The megalopal stage returns to estuaries for settlement, and eventual recruitment to adult populations. (Hill, 2004; Texas Parks and Wildlife, 2009)

Spawning peaks in Callinectes sapidus are closely associated with the region they inhabit. Unlike males, female C. sapidus mate only once in their lifetime, after the pubertal or terminal molt. When approaching this final molt, females attract males by releasing a pheromone in their urine. Male crabs compete for females and until molting occurs they will protect them. At this time mating occurs, and may last as long as 5-12 hours. (Hill, 2004)

Callinectes sapidus is highly fertile, with females producing from 2 - 8 million eggs per spawn. When females are in their soft-shell stage immediately after molting, the males transfer their sperm to them for storage. The male then protects the female until her new shell hardens. The females will spawn two to nine months after mating, laying up to eight million eggs. Spawning season is from December to October, with a peak both in spring and summer. When females are ready to spawn, they fertilize the eggs with the stored sperm and place them on the tiny hairs of the appendages on their abdomen. The female is called a "sponge" or "berry" crab while she carries eggs like this. The blue crab's incubation time is 14-17 days, which is when the eggs are brooded. During this time females migrate to the mouths of estuaries so that larvae may be released into high salinity waters. Blue crab larvae have a salinity requirement of at least 20 ppt, and show poor survival below this threshold. The megalops (or larvae) pass through eight stages in about two months before they begin to resemble adult crabs. Usually only one or two crabs survive to become adults, and they have a lifespan up to three years. (Hill, 2004; Texas Parks and Wildlife, 2009)

Males tend to stay and protect the female until she has grown her hard shell after molting, but males have no interaction with the young. The female will protect the young while they hatch, but do not have a significant role in parenting. This is because there are so many eggs, and the maturing time is much too long for her to watch over them. They have to be independent from the time they hatch, which is why most of them will die before they reach the adult age. (Hill, 2004)

Callinectes sapidus has an average life span of 1-2 years. Many are harvested by humans before they would die naturally. In the St. Johns River, some blue crabs survive to four years of age. (Steele, 1979; Zinski, 2006)

Callinectes sapidus is very aggressive when threatened, except when it has recently molted and still has soft shells leaving it vulnerable. The crab will also burrow into the sand to hide. Callinectes sapidus is an active swimmer and has its last pair of walking legs adapted to be shaped like a paddle to accommodate swimming. It also has three pairs of walking legs, and a powerful set of chelae. Since C. sapidus is highly mobile, the total distance traveled per day is about 215 meters. This species tends to be more active during the day than in the evening. The blue crab moves from zero to 140 meters per hour, with an average of 15.5 meters per hour. Crabs in general can also regenerate legs or pinchers lost while fighting or protecting themselves. (Hill, 2004; Shapiro, 2011; Texas Parks and Wildlife, 2009)

Callinectes sapidus is both colorful and highly visually responsive, yet almost all studies of their courtship have focused on chemical cues. In the underwater environment of C. sapidus, visual cues may function more rapidly and over a longer distance than chemical cues. Given that C. sapidus is aggressive and cannibalistic, visual cues may allow them to quickly evaluate potential mates from safer distances. The crabs will use color vision and color in mate choice with males having a preference for females with red claw dactyls. (Baldwin and Johnson, 2009)

Callinectes sapidus eats a large range of foods. Typically this species eats clams, oysters, and mussels as well as almost any vegetable or animal matter. This species will scavenge freshly dead animals but not long dead animals. The crabs will sometimes also eat young crabs. (Texas Parks and Wildlife, 2009)

Callinectes sapidus is preyed on by the red drum, Atlantic croaker, herons, sea turtles and humans. They are also an important link in the food chain, being both predator and prey. They feed on fish, aquatic vegetation, mollusks, crustaceans, and annelids. (Steele, 1979; Texas Parks and Wildlife, 2009)

Parasites are very common on Callinectes sapidus. Barnacles, worms and leeches attach themselves to the outer shell; small animals called isopods live in the gills or on the abdomen; and small worms live in the muscles. Although C. sapidus is a host to many parasites, most of these do not affect the life of the crab. (Texas Parks and Wildlife, 2009)

The main positive economic importance of Callinectes sapidus for humans is for food. The blue crab is often eaten because the meat is tasty and can be prepared in a number of ways. Commercially, crabs are captured in traps that are rectangular, two feet wide, and are made of wire. The crabs are lured in by being baited with freshly dead fish. In some areas, crabs are also caught in trawls and by trotlines. Many people also crab since it is easy and inexpensive. Although there aren't any harvest limits, there is a 5-inch minimum body width as measured from spine to spine. (Texas Parks and Wildlife, 2009)

There are no known adverse effects of Callinectes sapidus on humans.

Callinectes sapidus is not listed by any conservation programs. (Hill, 2004; Texas Parks and Wildlife, 2009)