If the team was right about Sesarma herbivory thriving in the absence of predator threats, then the marsh should surely suffer much more in the plots where cages shielded the burrowing Sesarma crabs from all their above-ground foes.
Sure enough, the team reported in Ecology Letters that "excluding predators for a single growing season rapidly led to a more than 100-percent increase in Sesarma herbivory, a more than 60-percent decrease in aboveground cordgrass biomass, a more than 95-percent increase in Sesarma substrate disturbance, and a more than 150-percent increase in unvegetated bare space in comparison to control plots."
There are still experiments the team would like to do to further understand the ecosystem dynamics that lead to the marsh die-off, but next summer the Bertness lab will also focus on determining what the marsh loss to excess herbivory could mean.
"We're moving on as well in Narragansett Bay and in Cape Cod to look at sea level rise and die-off under the assumption that these are the mechanisms that are causing it," Crotty said. "Combining impacts that we should see in the future, what does die-off mean for the future of marshes?"
It's a problem that, properly understood, must now be managed.
|Contact: David Orenstein|