The diamondback terrapin or simply terrapin (Malaclemys terrapin) is a species of terrapin native to the brackish coastal tidal marshes of the East Coast of the United States and the Gulf of Mexico coast, as well as in Bermuda. It belongs to the monotypic genus Malaclemys. It has one of the largest ranges of all turtles in North America, stretching as far south as the Florida Keys and as far north as Cape Cod.
The name "terrapin" is derived from the Algonquian word . It applies to Malaclemys terrapin in both British English and American English. The name originally was used by early European settlers in North America to describe these brackish-water turtles that inhabited neither freshwater habitats nor the sea. It retains this primary meaning in American English. In British English, however, other semi-aquatic turtle species, such as the red-eared slider, might also be called terrapins.
Description
The common name refers to the diamond pattern on top of its shell (carapace), but the overall pattern and coloration vary greatly. No two diamondback terrapins look alike. The carapace is usually wider at the back than in the front, has a more or less pronounced central ridge running lengthwise, and from above it appears somewhat wedge- or kite-shaped. The carapace coloring can vary from brown to grey, with a lighter plastron (belly shell), and its body color can be grey, brown, yellow, or white. Almost all have a unique pattern of wiggly, black markings or spots on their body and head. The diamondback terrapin has large webbed feet. The species is sexually dimorphic in that the males grow to a carapace length of approximately , while the females grow to an average carapace length of around , though they are capable of growing larger. The largest female on record was just over in carapace length. Specimens from regions that are consistently warmer in temperature tend to be larger than those from cooler, more northern areas.Davenport, John (1992)."The Biology of the Diamondback Terrapin Malaclemys Terrapin (Latreille)" , Tetsudo, 3(4) Male diamondback terrapins weigh on average, while females weigh around . The largest females can weigh up to .
Diamondback terrapins can live up to 40 years in captivity, but scientists estimate they typically live for about 25 years in the wild.
Adaptations to their environment Terrapins look much like their freshwater relatives, but are well adapted to the near shore marine environment. They have several adaptations that allow them to survive in varying salinities. They can live in full strength salt water for extended periods, and their skin is largely impermeable to salt. Terrapins have lachrymal salt glands, not present in their relatives, which are used primarily when the turtle is dehydrated. They can distinguish between drinking water of different salinities. Terrapins also exhibit unusual and sophisticated behavior to obtain fresh water, including drinking the freshwater surface layer that can accumulate on top of salt water during rainfall and raising their heads into the air with mouths open to catch falling rain drops.
Terrapins are strong swimmers. They have strongly webbed hind feet, but not flippers like sea turtles do. Like their relatives (Graptemys), they have strong jaws for crushing shells of prey, such as clams and snails. This is especially true of females, who have larger and more muscular jaws than males.
Subspecies Seven subspecies are recognized, including the nominate race, but not all of them may be truly distinct:
M. t. terrapin (Schoepff, 1793) – northern diamondback terrapin (Connecticut, Delaware, Maryland, Massachusetts, New Jersey, New York, North Carolina, Rhode Island, Virginia; from Cape Cod to Cape Hatteras). Carapace blackish to olive-brown, with strong "diamond" pattern and a barely notable central ridge, plastron orange-yellow to grayish-green. M. t. centrata (Latreille, 1801) – Carolina diamondback terrapin (Georgia, Florida, North Carolina, South Carolina; Cape Hatteras to extreme northeastern Florida). Similar to M.t.terrapin, but with a low carapace ridge. M. t. pileata (Wied, 1865) – Mississippi diamondback terrapin (Alabama, Florida, Louisiana, Mississippi, Texas; from westernmost Florida to easternmost Texas). Similar to M.t.centrata, but with the tailward half of the carapace ridge forming prominent round bumps, and the upper head, neck and legs almost black. M. t. littoralis (Hay, 1904) – Texas diamondback terrapin (westernmost Louisiana to Texas). Similar to M. t. pileata, but plastron and top of the head paler. M. t. macrospilota (Hay, 1904) – ornate diamondback terrapin (west coast of Florida). Similar to M.t.centrata, but carapace ridge with prominent narrow tips for its entire length, and center of carapace shields yellow to orange. M. t. rhizophorarum Fowler, 1906 – mangrove diamondback terrapin (Florida Keys). Carapace more narrow and elongated than in other subspecies, brown to blackish and with rounded bumps along the entire ridge; head and forelegs with few to no black spots. M. t. tequesta Schwartz, 1955 – East Florida diamondback terrapin (east coast of Florida). Similar to M.t.macrospilota, but with a bumpy tailward carapace ridge like M.t.pileata
The isolated Bermudan population, which arrived in Bermuda on its own rather than being introduced by humans, has not yet been officially assigned to a subspecies but, based on mtDNA, it is closely related to the population from the Carolinas.
Distribution and habitat
Diamondback terrapins live in the very narrow strip of coastal habitats on the Atlantic and Gulf Coasts of the United States, from as far north as Cape Cod, Massachusetts, to the southern tip of Florida and around the Gulf Coast to Texas. In most of their range, terrapins live in Spartina marshes that are flooded at high tide, but in Florida they also live in mangrove swamps. This turtle can survive in freshwater as well as full-strength ocean water, but adults prefer intermediate salinities. Despite its preference for salt water, it is not a true sea turtle and is not fully marine. They have no competition from other turtles, although common snapping turtles do occasionally make use of salty marshes. It is unclear why terrapins do not inhabit the upper reaches of rivers within their range, as in captivity they tolerate fresh water. It is possible they are limited by the distribution of their prey.Coker, R. E. 1906. The natural history and cultivation of the diamond-back terrapin with notes of other forms of turtles. North Carolina Geological Survey Bulletin. 14:1-67 Terrapins live quite close to shore, unlike sea turtles, which wander far out to sea; however, a population of terrapins on Bermuda has been determined to be self-established rather than introduced by humans. Terrapins tend to live in the same areas for most or all of their lives, and do not make long-distance migrations.
Life cycle Adult diamondback terrapins mate in the early spring, and clutches of 4–22Brennessel, Barbara. "Diamonds in the Marsh," Hanover: University Press of New England, 2006 eggs are laid in sand dunes in the early summer. They hatch in late summer or early fall. Maturity in males is reached in 2–3 years at around in length; it takes longer for females: 6–7 years (8–10 years for northern diamondback terrapins) at a length of around .
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,Barney, R.L. 1922. Further notes on the natural history and artificial propagation of the diamondback terrapin. U.S. Bureau of Fisheries. Economic Circular No. 5, rev. 91-111 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 FloridaBaldwin, J.D., L.A. Latino, B.K. Mealey, G.M. Parks, and M.R.J. Forstner. 2005. "The diamondback terrapin in Florida Bay and the Florida Keys: Insights into Turtle Conservation and Ecology". Chapter 20 In: In: W. E. Meshaka Jr., and K. J. Babbitt, eds. Amphibians and Reptiles: status and conservation in Florida. Krieger Publishing Company, Malabar, 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.
Seasonal activities Because nesting is the only terrapin activity that occurs on land, most other aspects of terrapin behavior are poorly known. Limited data suggest that terrapins hibernate in the colder months in most of their range, in the mud of creeks and marshes.
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.
Conservation
Status In the early 1900s, the species was considered a delicacy and was hunted almost to extinction. The population also decreased due to the development of coastal areas, terrapins being susceptible to wounds from the propellers on motorboats.