Along much of the eastern U.S., grassy salt marshes provide a buffer between ocean and land. But rising seas threaten to overtake these marshes, and a burrowing crab is speeding up their destruction.

Small populations of the purple marsh crab have long lived in southeastern salt marshes, but the small crabs were typically spread out across the landscape.

As seas rise, high tides flood parts of the marsh for longer each day. And the crabs cluster in these areas because they like the wetter, softer soil.

“When they start to congregate in really high densities, not only are their burrowing impacts really amplified, so they turn the marsh into Swiss cheese, but they also overgraze the vegetation and create mud flats in the marsh,” says Christine Angelini of the University of Florida.

She says that without grass, marsh soil erodes, and tidal creeks form more rapidly.

“And what this is doing is turning a marsh that usually is sort of a continuous grassland into a fractured grassland that has many tidal creeks, or longer tidal creeks than what has historically been there,” Angelini says.

Salt marshes help buffer inland areas from storm waves and floods. So if they’re damaged or destroyed, the marshes may no longer protect the coast.

Reporting credit: Sarah Kennedy/ChavoBart Digital Media.