Hungry Crabs May be Killing Northeast Saltmarshes

Scientists may have just discovered what exactly is killing the coastal saltmarshes of southern New England and Long Island. They've found that the herbivorous Sesarma crab may be to blame.

In order to examine the health of the saltmarshes and figure out exactly what might be causing their decline, the researchers conducted field studies at 14 sites around Rhode Island's Narragansett Bay. There, they ran several tests during the summer at sites where die-off ranged from less than five percent to 98 percent.

The scientists tested whether tides were eroding the marshes away by making chalk blocks and placing them at each site. This allowed them to see how quickly they dissolved. The researchers also planted healthy grass in each site to determine whether growing conditions were poor or not.

In the end, the researchers found that herbivory was the main cause for the retreat of marsh grasses. In fact, differences in herbivory at each site explained 73 percent of the variation in die-off at each site. The only other factor at play was soil hardness, though that was also related to herbivory and crabs.

"Substrate hardness influences crab herbivory by limiting crab burrowing in hard and soft substrates, leading to a peak in herbivory in medium hardness substrates where burrows can be easily constructed and maintained," the authors wrote in their article within PLOS One.

The findings reveal that crabs could certainly be the cause for retreating grasses. It also highlights the importance of taking steps in order to prevent this issue in the future.

The findings are published in two papers in PLOS One and Ecology Letters.