Description: A medium-sized (max. length females, 9 inches; males 5.5 inches brackish-water turtle known to frequent saline habitats. Toes webbed. Adult carapace oval, gray to nearly black, and unmarked; larger carapacial scutes with deep and obvious concentric growth rings. Midline of carapace with row of knobs or bumps, more prominent in females than males. Plastron creamy yellow with some dark spots or blotches. Head and neck smoky gray or light greenish-gray with round black spots. Top of head and limbs usually dark. Mouth consists of a sharp cutting edge and a wide grinding plate on the inner, upper surface. Females bulkier than males, with larger heads, more rounded snouts, deeper shells, and shorter tails. Carapace of juveniles rounder and lighter in color, but concentric carapacial rings darker in outline. Seven subspecies currently recognized.
Habitat: A resident of coastal salt marshes, estuaries, and tidal creeks, so it is restricted to the Gulf Barrier Islands and Coastal Marshes ecoregion. Although particularly associated with cord grass marshes, it does venture from these confines, occasionally being found on offshore sandy islands or on extensive tidal mudflats. Seems to prefer marshes having open channels with moving water nearby. May bask on mud flats or float in channels; not easily captured. Will venture into brackish streams, but will not tolerate fresh water for extended periods of time. May bury in mud. Juveniles may spend first few years under mats of flotsam or vegetation .
Range: The Mississippi diamondback terrapin is found from the Florida Panhandle to eastern Louisiana. In Alabama, confined to the estuaries, salt marshes, and nearby shallow waters of coastal Mobile and Baldwin Counties, including Dauphin Island.
Diet: The diamondback terrapin typically feeds on fish, crustaceans (such as shrimp and crabs) marine worms, marine snails (especially the saltmarsh periwinkle ), clams, barnacles, mussels, other mollusks, insects, carrion, and sometimes ingest small amounts of plant material, such as algae. At high densities the terrapin may eat enough invertebrates to have ecosystem-level effects, partially because periwinkles themselves can overgraze important marsh plants, such as cordgrass (Spartina alterniflora). Gender and age can greatly affect the diet of the diamondback terrapin, males and juvenile females tend to have less diversity in their diet. Adult females, due to their powerful, defined jaw, will occasionally feed on crustaceans such as crabs and are more likely to consume hard-shelled mollusks.
Reproduction: Like all reptiles, terrapin fertilization occurs internally. Courtship has been seen in May and June, and is similar to that of the closely related red-eared slider (Trachemys scripta). Female terrapins can mate with multiple males and store sperm for years, resulting in some clutches of eggs with more than one father.
Like many turtles, terrapins have temperature dependent sex determination, meaning that the sex of hatchlings is the result of incubation temperature. Females can lay up to three clutches of eggs/year in the wild, and up to five clutches/year in captivity. It is not known how often they may skip reproduction, so true clutch frequency is unknown.
Females may wander considerable distances on land before nesting. Nests are usually laid in sand dunes or scrub vegetation near the ocean in June and July, but nesting may start as early as late April in Florida. Females will quickly abandon a nest attempt if they are disturbed while nesting. Clutch sizes vary latitudinally, with average clutch sizes as low as 5.8/eggs/clutch in southern Florida to 10.9 in New York. After covering the nest, terrapins quickly return to the ocean and do not return except to nest again.
The eggs usually hatch in 60–85 days, depending on the temperature and the depth of the nest. Hatchlings usually emerge from the nest in August and September, but may overwinter in the nest after hatching. Nest predation is a large threat to Diamondback Terrapins. A study was done on 3159 nests finding that the greatest predator was racoons and predated nests were completely emptied of egg. Hatchlings sometimes stay on land in the nesting areas in both fall and spring and they may remain terrestrial for much or all of the winter in some places. Hatchling terrapins are freeze tolerant, which may facilitate overwintering on land. Hatchlings have lower salt tolerance than adults and Gibbons et al. provided strong evidence that one- and two-year-old terrapins use different habitats than do old individuals.
Growth rates, age of maturity, and maximum age are not well known for terrapins in the wild, but males reach sexual maturity before females because of their smaller adult size. In females at least, sexual maturity is dependent on size rather than age. Estimations of age based on counts of growth rings on the shell are as yet untested, so it is not clear how to determine the ages of wild terrapins.
Status: In Alabama they rare and possibly endangered in coastal marshes of Mobile and Baldwin counties. Formerly much more common, but declining due to variety of factors, including habitat degredation and mortality in crab traps.
Disclaimer: ITIS taxonomy is based on the latest scientific consensus available, and is provided as a general reference source for interested parties. However, it is not a legal authority for statutory or regulatory purposes. While every effort has been made to provide the most reliable and up-to-date information available, ultimate legal requirements with respect to species are contained in provisions of treaties to which the United States is a party, wildlife statutes, regulations, and any applicable notices that have been published in the Federal Register. For further information on U.S. legal requirements with respect to protected taxa, please contact the U.S. Fish and Wildlife Service.
){kind=link}
){kind=link}