Diamondback Terrapin (Malaclemys terrapin centrata)
The only turtle that lives entirely in brackish water is the diamondback terrapin (Malaclemys terrapin). This turtle is a habitat specialist, restricted to salt marshes, estuaries, and tidal creeks along the eastern and Gulf coasts of the United States. They are among the most variable of North American turtles, having an array of colors and patterns among the 7 subspecies. The species is sexually dimorphic in that the males grow to approximately 13 cm, while the females grow to an average of around 19 cm and have a larger head and jaws than males. They also have a variable diet depending on geographic location, but common foods include periwinkle snails, bivalves, crustaceans, crabs, and scavenged fish. They are primarily diurnal and usually spend the night buried in sediment. Juvenile terrapins are rarely encountered. It is unknown what turtles two years old or younger do, as they are almost never seen.
The diamondback terrapin was once a food staple so cheap that 18th-century tidewater slaves protested the amount of terrapin in their diet. In the 19th-century, though, the diamondback made an unfortunate transition from despised staple to gourmet delicacy. Even though the commercial hunt has largely collapsed, these turtles continue to decline due to coastal development, disturbance on their nesting beaches, road mortality of nesting females, boat injuries, and pollution. They continue to drown in large numbers in pot traps designed for crabs. Maryland, Delaware, and New Jersey laws require terrapin excluders on crab traps, and some states are considering requiring them. In Georgia the terrapin is considered a “species of concern”.