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Callinectes sapidus is a common swimming crab in the Indian River Lagoon. It is easily identified by its body color which is generally a bright blue along the frontal area and legs, especially along the chelae, or claws.  The top of the carapace is shaded an olive brown color, with the underside being white. C. sapidus, like other swimming crabs, has adapted its last pair of walking legs into paddle-like swimmerets. It also has three pairs of walking legs, and a powerful set of chelae. The carapace is much wider than its length, and tapers to sharp points at the sides.  Maximum carapace width, as measured at the tips of the lateral spines, is approximately 9 inches (25 cm).  Pre-adult females are identified by their triangular aprons, while adult females are identified by larger, rounded aprons.  Females also have red "fingers" on the tips of the chelae.  All females are easily distinguished from males, which possess thin, straight aprons, and lack red markings on the chelae. 

Callinectes sapidus
utilizes a variety of habitats depending upon the particular requirements of each life history stage. Spawning females and the earliest larval stages, inhabit the lower reaches of estuaries and adjacent coastal waters where salinity exceeds 20 ppt, a level necessary for proper larval development. Older larvae reenter estuaries and adopt benthic lifestyles, growing into juvenile crabs.  Juveniles are associated with low salinity waters and muddy sediment bottoms, often adjacent to seagrass habitats. Adult blue crabs occur on a variety of bottom types in fresh, estuarine, and shallow coastal waters.  Adult blue crabs can also be distributed with respect to sex and salinity. Typically, males predominate in low salinity areas while females predominate in high salinity areas.

Similar Species: 
Callinectes sapidus is sometimes confused with related crabs such as the lesser blue crab, C. similis, and the ornate blue crab, C. ornatus, which are both common in east central Florida.  One common way to distinguish these species is that the carapace of C. sapidus has only 2 teeth between the eyes, while the other species each have 4 teeth.  C. sapidus and C. similis are difficult to distinguish from one another except that C. similis is smaller, rarely reaching more than 5 inches in carapace length.  C. ornatus, as its name suggests, is more highly colored than C. sapidus, with blue-toned walking legs, and coral coloration along the margin of its swimmerets.  C. ornatus also has may fine hairs on the carapace.

The natural range of C. sapidus is the western Atlantic Ocean from Nova Scotia to Argentina.  Blue crabs are common throughout the Indian River Lagoon and into its freshwater tributaries.

Male blue crab in defensive posture. Photo courtesy of  D. Elliot. 
Male (left) and female (right) blue crabs are easily differentiated by the shapes of their abdomens.  They are further distinguished by females having red fingers on their claws. Photo courtesy of D.  Elliot.

An easy way to remember how to tell the difference between male and female blue crabs is that the apron of a male blue crab is shaped like the Washington Monument, while adult female blue crabs have aprons shaped like the dome of the Capitol Building.