Drought, Snails and Salt Marsh Death
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Periwinkle snail, an abundant marsh grazer in
the southern United States.
[Image courtesy of Brian Silliman]
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Drought conditions combined with snail grazing are largely responsible
for the recent, large-scale die offs of salt marshes in the southern
United States, according to a new field study in the 16 December 2005
issue of the journal Science.
These findings help to clarify the roles of drought and snails in
this massive marsh die off and may have implications for the conservation
and management of salt marshes and other coastal systems in North
America and beyond.
Brian Silliman and colleagues surveyed over 1200 kilometers of coastline
in Georgia and Louisiana and found high densities of plant-grazing
snails — up to 1500 snails per square meter — mowing down
cordgrass (Spartina alterniflora) and other marsh plants
at 11 of 12 marsh die-off sites.While drought stress is thought to
have primarily initiated the die off, armies of snails found at the
edges of these die-off zones spread across remaining healthy areas
and converted marshes to exposed mudflats, the scientists found.
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Marsh die-off area in GA 2002. Snails have doubled
the size of the mudflat.
[Image courtesy of Brian Silliman]
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These field experiments, combined with model analyses, reveal strong
interactions between drought and grazing pressure from snails, both
potentially related to human environmental impacts, the authors say.
These interactions may lead to further degradation or even collapse
of these environmentally and economically critical coastal ecosystems.
16 December 2005
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