Malaclemys terrapinDiamondback Terrapin

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Geographic Range

Malaclemys terrapin occurs along parts of the eastern coast of the United States from as far north as Cape Cod, Massachusetts, to the southernmost Florida Keys. The turtles are also abundant in the Gulf Coast, from Florida to Texas. (Loutrell and Cornett 1993).

Habitat

Diamondback terrapins inhabit saltwater habitats, including brackish channels, lagoons, tidal flats, marshes, estuarine areas, and coastlines. They particularly favor reedy marshes, and while they live near saltwater, they require fresh water for drinking purposes (Garrett and Baike 1987).

Physical Description

A grayish to nearly black carapace usually has spots or streaks of black on gray skin, making Malaclemys terrapin one of the darkest turtle species. The species is also distinguished from the other species by a tuberculate, or a knobbed keel; a higher shell with deeper bridge; a deeper gular notch; a consistently white upper lip; and a uniformly colored carapace and plastron (Alderton 1988). The skull has a long, bony temporal arch. The hind legs are relatively large and the toes are webbed beyond the bases of the nails. This species is known to have the greatest sexually dimorphic size disparity found in any North American turtle. Males are usually smaller in both body and head size, while the females are large. Females often attain carapace length of 9 inches, while males usually reach a maximum of 5.5 inches. Malaclemys terrapin is the only diamondback terrapin to occur in Texas (Carr 1952).

  • Average mass
    720 g
    25.37 oz
    AnAge
  • Average basal metabolic rate
    0.140702 W
    AnAge

Reproduction

While all turtles reproduce by eggs, the genus Malaclemys usually does not produce more than 4-8 eggs in a clutch. Females typically nest several times annually. The duration of incubation varies between 60 and 85 days, depending on soil temperature and nest depth. During April and May, the female digs a nest cavity 4-8 inches deep in sand. The oval eggs are 1 * inches long, pinkish-white, and covered with leathery shells.

Wild hatchlings may spend their first years upstream in creeks. These creeks may either be brackish or relatively fresh water. As the hatchlings age, they move down to the salty marshes where nutrients and good nesting sites are plentiful. Hatchlings are 1 to 1.5 inches long and are known to be able to produce eggs for several years after a single mating. Females reach sexual maturity in approximately 7 years and males a little earlier. Interestingly, the sex ratio appears to favor females. In a sample of 1,433 individuals, females outnumbered males nearly six to one (Alderton 1988).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • Average number of offspring
    9
    AnAge
  • Average gestation period
    84 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    2190 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    910 days
    AnAge

Behavior

In the wild, these wary turtles are quick to flee and difficult to observe. It may be possible to observe them basking on or walking between oyster beds and mudflats. Though mild mannered, they are excellent swimmers and will head for water if approached (Garrett and Baike 1987).

In captivity, the diamondback terrapins are known to recognize habits, and learn quickly what times people are normally around. They seem very sociable except when their cage is too small. They enjoy basking together, often one on top of another (Loutrel and Cornett 1993).

Food Habits

Malaclemys terrapin eat snails, other mollusks, crustaceans, fish, insects, and carrion (Bartlett and Bartlett 1999). They use the ridges in their jaw to crush their prey. Therefore, M. terrapin will only eat the soft-shelled mollusks and crustaceans (Tucker, et al 1997).

Conservation Status

In the past, Malaclemys sp. were often considered a delicacy because of the sweet meat. These turtles were almost brought to extinction in the early years of the present century. They were either relentlessly hunted for their flesh or died of drowning in underwater crab traps. The group suffered worse than the snapping turtles of family Chelydridae, but has since recovered in numbers (Dixon 1987).

Currently, seaside development has led to the loss of nesting beaches. Tire tracks from vehicles used on the sand pose a hazard to hatchlings. The tiny turtles get trapped in the tire tracks and die of dehydration before reaching water.

To prevent extinction, however, diamondbacks are protected in several states. Interestingly, in some places the native beachgrass is now also protected and removal is against the law. Researchers have found that the presence of the beachgrass lowers the temperature of the nesting areas and can affect the sex of the hatchlings. The terrapin populations were also revived by activists who consider the gentle creature a good pet (Loutrel and Cornett 1993).

Other Comments

As part of the most successful family of Chelonians, the genus Malaclemys includes a single species with seven subspecies, six of which are distributed in the salt and brackish waters from New England to Texas and possibly Mexico. The closest relatives are probably the genus Graptemys. They both have almost no apparent fossil record. The differing characteristics of the two genera are the dark head markings on a light background in Malaclemys and light stripes on a darker background for Graptemys (Alderton 1988).

Contributors

Ida Park (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Alderton, D. 1988. Turtles and Tortoises of the World. NY: Facts On File Publications.

Bartlett, R., P. Bartlett. 1999. A Field Guide to Texas Reptiles and Amphibians. Houston: Gulf Publishing Company.

Carr, A. 1952. Handbook of Turtles. Ithaca: Cornell University Press.

Dixon, J. 1987. Amphibians and Reptiles of Texas. College Station: Texas A&M University Press.

Garrett, J., D. Baike. 1987. A Field Guide to Reptiles and Amphibians of Texas. Texas Monthly Press, Inc..

Loutrel, M., M. Cornett. March 1993. "Diamondback Terrapin--Malaclemys terrapin" (On-line). Accessed Septemeber 19, 1999 at http://www.tortoise.org/archives/malaclem.html.

Tucker, A., S. Yeomans, J. Gibbons. 1997. Shell strength of mud snails (Ilyanassa obsoleta) may deter foraging by Diamondback Terrapins (Malaclemys terrapin). The American Midland Naturalist, 138: 224-229.