TERRAPINS ARE SENTINELS OF THE SALT MARSH
October 16, 2011
for diamondback terrapins began in 1983, when we initiated a terrapin
study in the salt marshes surrounding Kiawah Island, S.C. Since then teams
of researchers and students have measured and marked hundreds of the animals,
before releasing them where they were caught. Restricted to the narrow
brackish region between saltwater and fresh, from Cape Cod to Texas, terrapins
are the only turtle in the world to live exclusively in coastal salt marshes.
Sea turtles live in the ocean; freshwater turtles inhabit inland waters.
Of the world's approximately 300 species of turtles only a few in Southeast
Asia, India, and New Guinea enter brackish-water habitats and all of these
also inhabit fresh water. Terrapins possess a salt gland not found in
other nonmarine species that allows them to excrete salt to maintain a
Diamondback terrapins are my favorite turtle, with the dreamy eyes of
a baby harp seal and the unassuming face of a manatee; the docile temperament
of a dolphin and the beauty of a seashell. For extra credit include perseverance
in the face of natural hazards such as coastal weather and a sea full
of predators. Terrapins are highly variable in color. Some are black,
others milky gray, and some have splashes of yellow, green, or orange.
The face and legs of diamondback terrapins are speckled or mottled. Brightly
colored, diamond-shaped concentric markings are visible on the upper shell
of many. Females get three times as large as males, which are little larger
than a person's hand. This attractive little turtle is also tough. Unfortunately,
the perils that threaten large populations of diamondback terrapins in
their environmentally fragile coastal habitats continue to increase. As
in so many cases of environmental peril, the terrapins' situation is exacerbated
by human activities.
The Kiawah terrapin study, which has been sampling the population many
days each year for almost three decades, is now under the direction of
Michael Dorcas, a professor at Davidson College. Mike's students, as well
as those from other colleges and universities, continue to sample the
terrapin population. More than 3,400 captures and recaptures of Kiawah
terrapins have now been recorded, and the terrapins' situation is nowhere
near as pretty as the turtle itself. In the Kiawah salt marshes and tidal
creeks, which once harbored hundreds of terrapins, these beautiful, nonthreatening
animals are declining in numbers.
No single culprit has been identified in the population decline, but two
human activities--overdevelopment and crab pots--are indisputable threats
to the terrapins. A terrapin that cannot escape from a crab pot will drown.
Dead terrapins have been found in both commercial and recreational crab
traps along the Kiawah River. Sadly, one activity that causes terrapin
deaths is a result of laziness--or forgetfulness. Each year, tourists
abandon thousands of traps in coastal states; these "ghost traps"
continue to kill terrapins and other marsh wildlife long after the tourists
have returned to their homes.
Another threat to terrapins in many areas is the loss of nesting habitat.
On Kiawah, a major, and avoidable, problem looms. A development company
wants to put up a concrete revetment between the salt marsh and the sand
dunes where terrapins nest (see www.kiawahriver.org).
The construction will further aggravate the problem of terrapin population
decline by reducing recruitment of young turtles, which could spell doom
for the terrapins of Kiawah. Coastal development designed to attract people
to an area while marring the beauty of the habitat they come for is textbook
The decline of terrapins means more than merely the loss of a spectacular
turtle. By eating periwinkle snails, which eat spartina grass, the dominant
vegetation characterizing a salt marsh, the terrapins contribute to the
overall environmental health of the marsh. A decline in terrapins indicates
that the coastal marshes themselves are being environmentally stressed
beyond a sustainable limit.
Last week on Kiawah Island we saw diamondback terrapins in the wild. Whether
we can make such a statement in the future will depend on how this little
turtle fares in the face of coastal development.
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