<p>Mark Bertness and his students have traced marsh die-offs along the Northeast coast to excess herbivory by Sesarma crabs left unchecked by predators because of fishing. Now they warn it may be more than just a local environmental problem. It may also mean more greenhouse gasses are entering the atmosphere. (<a href="http://news.brown.edu/pressreleases/2014/04/sesarma">Return to release</a>)</p>

PROVIDENCE, R.I. [Brown University] — In a study published in March in the journal PLoS ONE, Bertness’ team, led by former student and lab manager Tyler Coverdale, estimated that the loss of carbon-rich grasses and the erosion of sediments under them may be liberating hundreds of billions of grams of carbon from sequestration. It is not clear, however, where all the carbon is going.

“Increased herbivory by native crabs is driving die-off via a tropic cascade mediated by recreational overfishing,” the authors wrote. “In areas along the grazing front, peat stability deteriorates and large sections of creek bank tear from the marsh and calve into tidal creeks. We demonstrate that indirect human impacts can cause previously unreported habitat loss and may contribute significantly to global anthropogenic carbon emissions.”

Bertness said the marsh die-off has set environmental processes back by centuries.

“Over the past 30 years consumer-driven marsh die-off has destroyed 200 to 300 years of marsh accretion,” he said.

In addition to Coverdale and Bertness, other authors are Caitlin Brisson, Eric Young, and Stephanie Yin of Brown and Brown alumnus Jeffrey Donnelly of Woods Hole Oceanographic Institution.

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