Study of 15 Research Reserves Finds Crabs Pose No Large-Scale Salt Marsh Threat

The Takeaway: While specific crab species can cause local damage, rising seas appear to be a bigger threat to salt marshes nationwide.

A study in the journal Ecology found it unlikely that crabs pose a major threat to U.S. salt marshes on a broad scale. The study, which focused on the types of crabs living in salt marshes, was conducted at 15 NOAA national estuarine research reserves in 13 coastal states.

“What is true at one scale may not be true at another,” notes Kerstin Wasson, PhD, of California’s Elkhorn Slough Research Reserve, the study’s lead author. “We found that crabs can cause a lot of harm at a local scale, in some parts of some marshes, but they don’t seem to be a main cause of marsh dieback at a national scale.”

While crabs did not have a strong overall influence on salt marshes, elevation did. Lower marsh areas are submerged more often and tend to have poorer health. This study suggests that rising sea levels associated with climate change pose a bigger threat to the nation’s salt marshes than do crabs. However, since the study found that crabs are more abundant and cause more harm at low elevations, increased crab burrows amid rising seas can deliver a double threat to marsh health.

Restoration measures that help salt marshes stay higher, where they are less likely to be susceptible to rising seas or crab burrows, can help protect these habitats, which provide economic benefits to communities nationwide. A study now underway across eight research reserves will show whether adding soil to raise marshes will aid their future survival. (2019)

Partners: The Chesapeake Bay-Virginia, Delaware, Elkhorn Slough, Great Bay, Guana Tolomato, Mission-Aransas, Narragansett Bay, North Carolina, North Inlet-Winyah Bay, San Francisco Bay, Sapelo Island, South Slough, Tijuana River, Waquoit Bay, and Wells National Estuarine Research Reserves