Biology 103
2000 First Web Report
On Serendip

Malaclemys Terrapin Terrapin — The Northern Diamondback Terrapin

Wetlands have gone from being of little importance for biologist to being studied in excruciating detail. One major reason for this is the possible usefulness of wetlands in solving some of our current pollution problems, as well as its use as an effective barrier and an ideal habitat for much wildlife. Wetlands consist of numerous different plant and animal interactions, as well as many nutrient cycles, that must be maintained and protected in order to preserve. Among the many species that are threatened by human impacts on the wetlands is Malaclemys Terrapin Terrapin (2). Otherwise known as the Northern Diamondback Terrapin, this turtle’s function as a key predator in the Tidal Salt Marsh must be preserved. It is a unique species and is valuable not only for its functional qualities but its intrinsic ones as well.

There are seven subspecies of the Malaclemys Terrapin that have occurred as a result of their geographical distribution. Malaclemys Terrapins can be found from salt marshes along the coast in the Gulf of Mexico all the way up to Cape Cod (3). These subspecies differ not only in their geographic location but also in their individual coloration, markings, and their behavior. The Northern Diamondback Terrapin is the northern most of these subspecies, native to the tidal salt marshes between Massachusetts and North Carolina (2).

Physical Description:

Growing from the size of a quarter at birth, the mature Northern Diamondback Terrapin is a medium sized turtle averaging 19 cm for a female and 12 cm for a male (2). They have large, clawed, webbed back feet, spotted heads and legs. They are also identifiable by the concentric annuli on their carapace scutes--the scale like structures that appear in a mosaic type form on their upper shell (1). These are often diamond shaped–hence the name Diamondback. In differentiating between male and female, females also have much larger heads, and males much thicker tails than their opposing gender.

Habitat:

The Malaclemys Terrapin is a particularly unique species of turtle in that it is the only one, out of over 260 known species, that lives exclusively in brackish coastal marshes. The Northern Diamondbacks are year-round residents of the estuaries, and they are most commonly found in the spartina grass (saltwater cordgrass) salt marshes. These terrapins tend to like the shelter of a creek more than an open bay, although they have even been found (not often and not for extended periods) swimming in the Atlantic Ocean (3). This means that, although native to the brackish waters, they can actually tolerate a wide range of salinities. These salinities range from close to fresh water to the salt content in the open ocean. In addition, terrapins are, for the most part, aquatic. The only known times when these turtles leave the water for an extended period is to lay eggs or, sometimes, to bask on the mud flats in the intertidal zone (1).

Adaptations and Behavior:

Terrapins have a number of adaptations that allow them to survive and thrive under these varying conditions. These adaptations are both physical and behavioral. They have an unusually low skin permeability to salts and water which allows them to be protected from high salinities. They also have a powerful lachrymal salt gland, which helps them to excrete excess salt. Behavioral traits include the tendency to drink water, in thin layers, off of leaves, the ground, and even each others backs. A unique sloping jaw structure compliments this. These terrapins also have the unusual ability to intake as much as 15% of their body weigh in fresh water in just 15 minutes, which allows them to take full advantage any fresh water they encounter. Their behavioral tendency to eat more in fresh water and less in salt water also helps to keep their salt intake to a minimum (1).

Life History

During the early part of the summer, female terrapins come ashore to lay their eggs–making sure to find a sandy spot above the high tide line. The clutches usually contain 8-12 pinkish white leathery eggs, and females can lay one or more clutches per season. Later that summer or in early fall, after about a two month incubation period, the hatchlings come out of their nests and head, not toward the water, but toward the nearest vegetation. Most come out during the day and are in danger of being eaten by predator birds like gulls and herons, so this journey to the closest vegetation could be an instinctual protective measure against these predators. Some hatchlings actually stay in the nest until the spring, since a few months after they are born the winter hibernation period of the terrapin begins. Still, the infant mortality rate is very high, and many of the clutches are eaten by raccoons and foxes before they even get a chance to hatch (2).

Northern Diamondback Terrapins hibernate from November through March, either in groups or separately. They usually hibernate in or below the intertidal zone, although some take shelter elsewhere: in the bottom of creeks or among vegetation mats in high marshes (3).

Females mature at 6-7 years of age, males at the age of 3. The natural life span of the terrapin is unknown, although it is speculated at forty years or more. As a general rule, mature females are more abundant than mature males (3).

Feeding Habits

Diamondback Terrapins are a top carnivore in the tidal salt marsh ecosystem. About 77% of the Terrapin's diet are Littorina irrorata. Also known as Periwinkles, these small gray snails live on the stalks of Spartina grasses located in the upper intertidal zone. Their feeding habits, therefore, coincide greatly with the tide cycles; during high tide, the turtles swim to the grass stalks to feed on the snails. Diamondbacks are unique in that, behind their sharp mandibles, they have a flat, crushing surface that helps to crush and digest this type of prey. In addition, terrapins also eat fiddler crabs, mussels, and small fish, along with some grass pieces. In fact, studies have shown that the Northern Diamondback terrapin will eat virtually anything, a characteristic that could actually be negative as will be discussed later in terms of commercial crab traps (5).

Status

Currently, the Diamondback Terrapin is making a comeback after having been hunted to near extinction. For decades in the earlier part of the twentieth century, the Northern Diamondback terrapin was a delicacy and sold at over seven dollars per turtle. Its most common fate was in turtle soup, a dish that unfortunately is making a comeback. Today, in undisturbed salt marshes, however, the terrapin is actually quite abundant. It is a seemingly hardy species, and has actually been found to survive even in very polluted waters. Still, the terrapin is not thriving enough, and is currently being considered for formal addition to the national list of endangered species. While the individual state laws vary, in New Jersey hunting of the terrapin is legal during its hibernation period. This is actually one of the stricter states in terms of regulations on the Diamondback Terrapin (2).

Conservation Efforts

There are currently two well-known conservation efforts unique to the area that are fairly successful. The Turtle Patrol is a project of the Wetlands Institute and Stockton State College that involves searching for Diamondbacks killed while crossing the street to lay eggs. Many Northern Diamondback terrapins are killed in this way because the highway embankments resemble the dunes in which they normally would lay their eggs. This project collects the eggs from road-kill along a forty-mile stretch and, if not too damaged, hatches them in an incubator to be released the following year into the wild. Directed by Roger Wood, a biologist at Stockton State College, over 800 terrapins have been hatched since 1991. His success rate is 40%, which, according to him, still does not overcome the numbers of terrapins lost each year (6).

Another conservation effort is the Bycatch Reduction Apparatus. It is an excluder devise placed on commercial crab traps to keep Diamondbacks from entering the traps and drowning. It is simply a small rectangular structure than terrapins are less likely to fit through because of their rigid exoskeleton (their carapace and plastron.) The devise, invented by the Wetlands Institute in Stone Harbor, NJ, has recently been made mandatory for all commercial and recreational crab pots under 150 feet wide that are in the water during low tide. In addition to this, all pots set in a body of water, because of their potential to float away and become unmonitored, must also have a biodegradable exit panel (4).

Northern Diamondback Terrapins are an integral part of the tidal salt marshes of New Jersey and the surrounding area. They are unique in everything from their habitat and their appearance to their behavior and their adaptations. Furthermore, the dangers that human activities cause for the terrapins are unnecessary and, although actions are being taken to help the turtles, this had proven to be inadequate. In conclusion, by becoming more aware of the Northern Diamondback terrapin and its many distinct qualities, we can begin to understand their importance, both intrinsically and in terms of the wetland ecosystem.

Sources

(1)Davenport, John, "The Biology of the Diamondback Terrapin" Based on a lecture given at the U. of Bristol, May1992. Cited September 29, 2000 http://atschool.eduweb.co.uk/bcgonweb/testudo/diamondback.htm.

(2) Dove, L.E. and R.M. Nynam, eds. 1995. Living Resources of the Delaware Estuary, p229-304

(3) Loutrel, Mimi and Marvin Cornett "Diamondback Terrapin, Malaclemys Terrapin" updated March 1993 <http://www.tortoise.org/archives/malaclem.html> cited September 25, 2000

(4) New Jersey Department of Environmental Protection. "Change in Commercial Style Crab Pot Regulations." Updated January 21, 1998, Cited September 26, 2000 <http://www.state.nj.us/dep/fgw/news/crabegs.htm >

(5) Tucker, Anton D et al. "Shell Strength of Mud Snails May Deter Foraging by Diamondback Terrapins." The American Midland Naturalist, 1997. V138, p224-229

(6) Wood, Roger, "Turtles and Tires: The Impact of Roadkills on the Northern Diamondback Terrapin." http://www.nytts.org Cited September 29, 2000