NOTE TO NEWS EDITORS: Photos can be downloaded from:
http://www.werc.usgs.gov/news/2002-11-12a.jpg
(Male diamondback terrapin from South Carolina. USGS; photo by Jeff Lovich)
http://www.werc.usgs.gov/news/2002-11-12b.jpg
(Head pattern of female diamondback terrapin from South Carolina. USGS; photo by Jeff Lovich)
http://www.werc.usgs.gov/news/2002-11-12c.jpg
(The Kiawah River (left) provides a corridor for female terrapins leaving the marsh to nest on the dunes seen in the background. Just beyond the dunes lies the Atlantic Ocean. USGS; photo by Jeff Lovich)
http://www.werc.usgs.gov/news/2002-11-12d.jpg
(Low tide exposes the soft mud of the salt marsh. Cord grass holds the resilient marsh together through tides and storms. USGS; photo by Jeff Lovich)
http://www.werc.usgs.gov/news/2002-11-12e.jpg
(Biologists from the University of Georgia, Savannah River Ecology Laboratory check their nets placed in Terrapin Creek to catch terrapins. USGS; photo by Jeff Lovich)
For more on the diamondback terrapin demographic study in South Carolina:
http://www.werc.usgs.gov/hq/gibbons.pdf

"Hurricane" Turtles of South Carolina’s Tidal Creeks

Hurricanes brush or hit Charleston, S.C., about once every five and a half years, often generating large storm surges on top of already impressive tides. A hurricane that hit Charleston in 1752 caused a storm surge that nearly covered the entire present downtown area, according to one source. When the wind shifted, the water level fell 5 feet in 10 minutes.

How could a turtle the size of a small hat survive such a storm in a tumultuous tidal creek?

“Swimmingly,” seems to be the short answer from a pair of scientists who have studied the turtle for two decades. Yet as a result of human impacts, terrapin populations are declining, with significant local declines documented for some areas in Florida and some parts of South Carolina.

In 1983, Dr. Jeff Lovich, scientist and Director of the USGS Western Ecological Research Center, and colleague Dr. Whit Gibbons of the University of Georgia, Savannah River Ecology Laboratory, began to document the daily lives and annual cycles of activity of diamondback terrapins at Kiawah Island, S.C. They wondered how these turtles have weathered centuries of hurricanes, until they discovered just how resilient these small turtles are to natural disasters.

“What we found was amazing,” said Lovich. “Despite their small size – rarely larger than 9 inches and weighing only about 1.5 pounds in the case of the average female in South Carolina -- terrapins are powerful swimmers. Females, the larger sex, are capable of making roundtrip nesting journeys of over 3 miles from salt marsh to beach dunes.”

Diamondback terrapins are the only species of turtle in the United States that routinely occupy brackish water habitats, occurring in tidal creeks of estuaries along the Atlantic and Gulf coasts from Cape Cod, Mass. to Corpus Christi, Texas. Some have distinctive markings on their heads and on their carapace, or upper shell. Facial patterns often look like the animals have a moustache or are wearing lipstick.

These terrapins have adapted to a surprisingly demanding natural environment. On the surface, the salt marshes and barrier islands of South Carolina appear to be tranquil and idyllic to most people who visit those enchanted shores. Gently waving palmetto trees and stately live oaks grace a landscape punctuated by wind-sculpted maritime forests and seemingly endless expanses of cord grass and tidal creeks. Land and water meet here, intimately, blurring the distinctions between the two elements in subtle ways that defy the imagination. Beyond this brackish interface are dunes covered in sea oats and sandy beaches, each molded by winds and waves as the land finally gives way to the embrace of the Atlantic Ocean.

This is the home of the diamondback terrapin. But beneath the apparent calm of this turtle habitat lies a world in tumult. Each day water levels fluctuate almost 6 feet as the creeks flush in and out with the inexorable pull of the tide. This causes profound changes in the direction and speed of tidal flow, water temperature and salinity. Hurricanes punctuate these daily changes.

“Given the relatively long lives of terrapins --perhaps up to 40 years -- they are likely to live through several hurricanes in South Carolina,” said Lovich.

For the most part, say the two scientists, terrapins are remarkable homebodies, being found not only in the same creek from year-to-year, but often in the same small reach of water. In a demographics study published in the journal Chelonian Conservation and Biology, of 442 individuals that Lovich and Gibbons recaptured a year or more after their initial capture, only 25 terrapins changed locations from one tidal creek to another. This site fidelity appeared unchanged, even after major hurricanes like Hurricane Hugo in 1989, which packed 140-mile-per-hour winds.

“Taken on the whole, the ability of terrapins to stay in the same tidal creek, despite daily tidal fluctuations and storms is but one reflection of the remarkable resiliency of the salt marsh ecosystem,” Lovich said. Palmettos and cord grass bend and flex in all but the most severe of hurricanes, and tidal meanders give way to waves and tides in ways that ultimately preserve the character of this dynamic landscape, he explained.

“It is all part of the cycle of life, much like fires are in forest systems,” Lovich added. “Only recently have scientists come to appreciate the value of natural disturbance in maintaining the health of ecosystems. Diamondback terrapins play a crucial role in the salt marsh ecosystem.”

Grasses that stabilize the salt marshes from the effects of tides and storms are grazed by a small snail called the periwinkle. The periwinkle in turn is preyed upon by blue crabs and diamondback terrapins. Recent studies by other scientists, said Lovich, have shown that removal of crabs and terrapins from experimental enclosures in marshes cause periwinkles to convert these productive grasslands to mudflats within eight months, suggesting that overharvest of crabs and terrapins may be contributing to the large die-off of salt marshes across the southeastern United States.

While the strongest hurricanes seem not to affect the terrapins, human activities past and present have. In the 1800’s and early 1900’s, terrapins were heavily exploited as a gourmet food source, earning them the label of “most celebrated of American turtles,” from Roger Conant, one of America’s most famous herpetologists.

“With increased demand for terrapins by epicures, prices soared and a market was born to supply the big eastern cities of Baltimore, Philadelphia and New York. The diamondback terrapin became one of the most economically important reptiles in the world,” said Lovich.

In recognition of the demand for terrapins, the state of Maryland enacted a law in 1878 providing a closed season and a size limit for the species. But it was almost too late. As demand increased, prices soared and wild stocks became depleted. In response, the U.S. government initiated studies of captive propagation. The terrapin fad finally died out about 1920, and populations recovered from the several decades of exploitation, said Lovich.

Today the terrapin again faces human threats, including death by drowning in crab traps, habitat degradation and negative interactions associated with human recreational activities. One study suggested that heavy beach use might reduce nesting by terrapins. It also noted increased rates of propeller injury on nesting females as boat use increased in the study area.

The site tenacity of this little turtle makes it especially vulnerable to incidental capture in crab traps set in creeks near public access points, warns Lovich. Limited movement among tidal creeks means that once terrapins are trapped out of one area, it will be a long time before another population can become established. Without continued protection the future looks uncertain for the terrapin that “out-swims” hurricanes.

The USGS serves the nation by providing reliable scientific information to: describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.

This press release and in-depth information about USGS programs may be found on the USGS home page: http://www.usgs.gov. To receive the latest USGS news releases automatically by email, send a request to listproc@listserver.usgs.gov. Specify the listserver(s) of interest from the following names: water-pr; geologic-pr; geologic-hazards-pr; biological-pr; mapping-pr; products-pr; lecture-pr. In the body of the message write: subscribe (name of listserver) (your name).
Example: subscribe water-pr joe smith.