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A Talk on the Wild Side.

Mississippi: A Terrapin's View of Climate Change

Terrapin in profile

The Grand Bay National Estuarine Research Reserve is researching the diamondback terrapin turtle, whose habitat is likely to be inundated as the sea rises. Photo by Christina Mohrmann/Grand Bay NERR.

Photo iconPhotos: Terrapin photos on Flickr

The 10,216-acre Grand Bay National Wildlife Refuge is under threat from the very thing that gives it life – the Gulf of Mexico and its changing sea levels.

The refuge rests in a low-lying coastal area across state lines between Biloxi, Mississippi and Mobile, Alabama. Savannas cover the flatlands while bayous, marshes, and islands sprawl along the shoreline. Ospreys outnumber people.

The refuge is just inches above sea level. So is the adjoining Grand Bay National Estuarine Research Reserve, an 18,400-acre area funded by NOAA and administered by the State of Mississippi to promote estuarine research and education within the coastal zone.

It’s the home of the Mississippi diamondback terrapin, a feisty little water turtle that is slowly disappearing thanks to over-harvesting and habitat loss. The U.S. Fish and Wildlife Service has listed the terrapin as a species of concern, a sort of watch list for species in decline. 

Diamondback terrapin turtle in grass
The Diamondback terrapin turtle, once harvested to make turtle soup, now faces the threat of habitat loss due to sea level rise from climate change. Photo by Christina Mohrmann/Grand Bay NERR.

These smallish turtles are special in several ways. They are the only turtle species adapted to live in brackish waters, which are a mix of freshwater and sea water. As recently as the 1990s, they have been used to make turtle soup served in restaurants across the country. The turtles, which can live up to 40 years or more, have been slow to recover. In addition, the turtles have faced habitat loss due to erosion. That’s likely to worsen as the changing climate leads to accelerated sea level rise.

Service biologists are now turning their attention to a new threat to the terrapin: climate change. The most imminent impact is sea level rise and the possibility that the turtle’s habitat will one day be under water.

Already, a strong southern wind can completely submerge the road leading to the reserve and the refuge. Hurricanes flood the area entirely. Remarkably, recovery of the habitat is nearly as fast as it takes the waters to wane. The terrapin’s life moves on as before. But what will happen if the waters don’t recede, as could be the case with sea-level rise?

Grand Bay

As sea level rises, coastal shorelines like this will retreat, according to “A State of Knowledge Report” from the U.S. Global Change Research Program. Salinity is likely to increase in tidal rivers like this one in the Grand Bay National Wildlife Refuge. © Tom Carlisle.

The natural, undisturbed condition of this area and its low elevation make Grand Bay a perfect laboratory for studying the effects of sea level rise. To that end, the U.S. Environmental Protection Agency’s Gulf of Mexico Program and The Nature Conservancy recently started a SLAMM analysis of the area. SLAMM stands for “Sea Level Affecting Marsh Model” and is a modeling system that factors in the dominant processes involved in wetland conversion. The processes are inundation, erosion, overwash, saturation and accretion – and they all occur throughout the refuge and reserve.

Results of the SLAMM analysis will give managers some idea of how much land will be flooded and what plant communities will result from a given amount of sea-level rise.

The terrapin’s current home will likely be submerged, though their estuaries could migrate inland if not blocked by development. Another possible impact to the terrapin is warming temperatures. Terrapin sex determination depends on the temperature of the eggs. When the weather is warmer, more females hatch. When it’s cooler, males dominate.


Author: Douglas Hunt

Contact: Douglas Hunt, 228-497-6322, ext. 106

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