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Rising Seas Threaten Georgia's Economically Vital Salt Marshes

Experts say the marshes on Georgia's coast can't grow quickly enough to keep up with the current rate of sea level rise

By Bruce Dorminey,

Jul 31, 2011

DARIEN, Georgia—Some 60 miles south of Savannah, Dorset Hurley strides into chest-high cordgrass on the mainland side of the Sapelo Island ferry dock. Standing in elevated muck on a recent steamy summer's afternoon, he gestures toward a tidal creek running along an isolated spit of road.

"At high tide here, we would be ankle deep in water," says Hurley, an estuarine ecologist at Georgia's Sapelo Island . He snaps off the end of a dead cordgrass blossom and looks east long enough to notice that the tide has turned. In a few hours time, this tidal bank will again be inundated, but never for more than an hour or so each day. Once the tide rolls in, striped mullet feed on decaying cordgrass on the marsh’s soggy bottom. 

Like the tides on which these estuaries depend, Georgia's 100-mile coastline has waxed and waned for thousands of years, surviving by shifting miles in the process. And it's doing so once more; again driven by warming oceans and melting glaciers.

Mention "global warming" in this part of the world and most people's eyes will glaze over. Sea level rise, however, has tangibility that residents here experience with every high tide.

But that doesn't mean they've thought about how global sea level rise will impact them personally. In a recession-weary economy heavily dependent on tourism, real estate and the fishing industry, sea level rise hasn't exactly hit the top of the charts — yet.

The state's susceptibility to sea level rise is a function of the lay of the land. Because Georgia lies on a low continental slope, ecologists say that salt marsh loss is expected to be quite significant, both in terms of the area lost, and in reduced habitat for economically important local fisheries, such as shrimp, oysters and blue crabs.

Since Georgia's inception as a colony in 1732, this coast has depended on these marshes for a large part of its livelihood. A few miles south of here, the broad Altamaha River slips into tidal marshes near the old . There, landowners once used slaves and the estuary's natural ebb and flow to grow massive quantities of long-grained rice. Today, the plantation's dike and levee system lies in ruins, a poignant reminder of days gone by and the power of the sea.

But at dusk, when shrimp boats line the Darien River, some 50 miles south of Savannah, it's clear that a large chunk of the coastal Georgia economy still depends on these marshes. And it's these marshes, and in turn the fishermen and businesses that generate tourism dollars, that may suffer the most from the inexorable rise in sea levels as the oceans warm and polar ice sheets melt.

Although several of Georgia's barrier islands are highly developed, most remain undisturbed as wildlife refuges. This should only increase the ecological value of the state's coastal areas. That's at least until sea level rise arrives in full force.

In addition to providing habitat for oysters, shrimp, crab and fish, Georgia's roughly 300,000 acres of marsh are quite important for trapping carbon, otherwise known as "carbon sequestration." Clark Alexander, a coastal geologist at the , says the marshes' surface sediments can contain as much as 10 to 15 percent natural organic carbon, which is a factor in lessening the area's overall carbon footprint.

"White shrimp come in as larval shrimp and they find their optimal habitat in these tidal [marsh] creeks," says Hurley, noting that the shrimp use these same salt marshes as nurseries. "As they get larger, their habitat expands until they are fully developed. Then in a year's time, they use the currents to swim offshore."

Shrimp boat fisherman then scoop them up from the sea floor a few miles off the Georgia coast. White shrimp, blue crabs, and intertidal Georgia oysters all thrive in the salt marsh. 

Still, the marsh can only grow so fast, and likely not quickly enough to keep up with the current rate of sea level rise. 

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