Periwinkle snails, known to science as Littoraria irrorata, normally coexist happily with salt marsh. But the drought, which lasted from 1999 to 2001, weakened and killed marsh grasses such as cordgrass, or Spartina alterniflora, so extensively that the snails moved from finishing off stressed patches to decimating large pockets of otherwise healthy marsh in concentrated waves. The result: the loss of an estimated 250,000 acres of marsh stretching over 900 miles on the Gulf and southeastern coasts between 1999 and 2003.

So says a paper set to appear Friday in the journal Science.

"It's important to note that drought was the trigger that initiated these events and because drought stress is becoming more extreme with global warming, events like this could become both more frequent and intense," said Brian Silliman, the paper's lead author and an assistant professor in zoology at the University of Florida.

Salt marshes are key to healthy shorelines and oceans. They provide nurseries for juvenile fish and shellfish, filter water-borne pollutants and calm storm-driven waves, reducing the threat of hurricane-induced flood and erosion.

So scientists and citizens alike watched with alarm as the marshes started dying off from Louisiana to South Carolina beginning in 1999. Most earlier research pointed to the effects of a severe drought as the cause. The drought dried up soils, raised their acidity and boosted estuarine water and soil salinity levels -- all of which were blamed for stressing cordgrass and other marsh grasses beyond their limits.

Silliman and four other authors of the Science paper don't dispute the drought's impact on what scientists call "bottom-up" factors such as increased salinity. But, they say, decades of scientific tradition emphasizing only these
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Contact: Brian Silliman
brs@ufl.edu
401-261-3241
University of Florida
15-Dec-2005