Based on extensive field studies, the work challenges six decades of salt marsh science. Ecologists have long thought that stressed soil too much salt, not enough oxygen was the main killer of this critical marine habitat.

But Brian Silliman, a Brown University research fellow and a University of Florida assistant professor, said drought-stressed soils pave the way for predatory periwinkles that spread fungal disease as they graze on cordgrass.

"Snails can transform healthy marsh to mudflats in a matter of months," said Silliman, lead author of the Science paper. "This finding represents a huge shift in the way we see salt marsh ecology. For years, scientists thought marsh die-off was simply a 'bottom-up' problem related solely to soil conditions. We found that the trouble also comes from the top down. Drought makes the marsh vulnerable, then the snails move in."

Thousands of acres of salt marsh have disappeared from South Carolina to Texas since 2000, according to several scientific studies. In Louisiana alone, more than 100,000 acres of marsh were severely damaged between June 2000 and September 2001. This drastic decline poses a serious threat to the ecology and economy of the southeastern seaboard and the Gulf Coast. Salt marshes serve as nursery grounds that support commercial fisheries, protect coastline from storm-induced floods, and filter fresh water before it flows out to sea.

Mark Bertness, chair of the Department of Ecology and Evolutionary Biology at Brown and a co-author of the paper, said a better understanding of the causes of salt marsh loss will point to better ways to protect them.

"Loss of blue crabs and turtles, which prey on periwinkles, allows the snails to flourish," Be
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Contact: Wendy Lawton
Wendy_Lawton@brown.edu
401-863-1862
Brown University
15-Dec-2005