By Jonathon Kline, student intern at the Shinnecock Bay Restoration Program
Callinectes sapidus, commonly referred to as the Blue Crab, is a crustacean found along the North American Eastern Seaboard, where it is found mainly in places like the Chesapeake Bay, Nova Scotia, and of course, Shinnecock Bay. There are a large number of blue crabs of all sizes located in Shinnecock Bay, where we are currently conducting biweekly trawl surveys that provide us information on many fish and invertebrate species in the bay, including the blue crab. We are able to record how many are caught, their gender, and size on these surveys. This kind of information helps us better understand the role of the blue crab in the local ecosystem.
Unlike male blue crabs, female blue crabs can only reproduce once in their lifetime -- which is right after their only molt (at which time the female becomes mature). Before molting, the female crab will release hormones into the water to attract potential mates; since the female can only reproduce once, male crabs try to protect the female crab and fight off other potential suitors. Once the female fully molts, she mates with the male, which results in millions of fertilized eggs, which are released, or spawned, into the water column. The newly hatched larvae follow currents offshore, where they grow, and molt, in higher salinity waters. Once they mature, they will return to the Bay and continue the life cycle once again.
The sex of a blue crab is easily identifiable by their underbelly, or abdomen. Males appear to have an “upside down T” to describe their apron, while females have a broader shape that more gradually comes to a point. Also, female blue crabs appear to have red-tipped claws, while male claw tips are blue. However, both the male and female crabs have the bluish tinge on their undersides, hence their namesake, while the top part of their body has an olive green color.
While the blue crab is extremely vulnerable to prey, especially when they are young and in their larval stages, they have adapted a mechanism by which they can escape their predators; regeneration of missing limbs. This is a phenomena not often seen in the wild.
Blue crabs also prefer certain environments; while they are normally found in shallow waters, the blue crab will migrate to deeper areas should the temperature fall below 50 degrees Fahrenheit. On the contrary, water that is 91 degrees Fahrenheit or hotter is lethal to a blue crab, making their temperature range rather small compared to other species. In addition to this, blue crabs can live comfortably in both high and low salinity areas.
In some areas such as the Chesapeake, the blue crab is important to both the ecosystem and the economy of the local region; however, in Shinnecock Bay there is some concern about the large population of blue crabs. Some of our colleagues at SoMAS have found that blue crabs prey heavily on juvenile winter flounder, and the population of these fish in the bay is already extremely low. Our scientists are trying to better understand the role of blue crabs in the Shinnecock Bay environment.
Smithsonian Marine Station at Ft. Pierce
Chesapeake Bay NOAA