A new study at Elkhorn Slough shows crabs can help drive marsh recovery, sometimes.

Elkhorn Slough, the federally protected estuary in Moss Landing, is estimated to have already lost more than 70 percent of its salt marshes – its dominating natural feature. A new study led by a UC Santa Barbara researcher and the Elkhorn Slough Foundation examines the main driver of estuary marsh loss and what factors lead to recovery.

Marsh loss, especially in Elkhorn Slough, is driven largely by the expansion of what are known as salt pannes – shallow, muddy pools that are hostile toward plant life and smell like rotten eggs. Although they are a natural feature of the estuary, lead author Kathryn Beheshti of UCSB says they are unusually prominent at Elkhorn Slough.

Salt pannes can show up along creek banks or in the interior marshlands. Although Beheshti says pannes are poorly understood along the West Coast, they are considered the Achilles’ heel of marsh resilience. However, after a two-year field study, Beheshti and the Foundation found that in the interior marshlands, marsh resilience and panne endurance are tied to crab populations.

“It’s crabs to the rescue, with a big caveat that they are good specifically for Elkhorn Slough in the marsh interior,” Beheshti says.

The findings were published Jan. 5 in the academic journal PLOS ONE.

The study links the formation of interior pannes to poor drainage and found that burrowing crabs increase drainage ability and shrink the pannes at a faster rate, leading to accelerated marsh recovery. However, the study found burrowing crabs negatively impact pannes along creek banks because they increase the potential for erosion.

Kerstin Wasson, research coordinator at Elkhorn Slough Foundation, says the findings will impact strategy at the estuary. “Knowing what makes salt marshes resilient or vulnerable is critical for designing wise conservation strategies,” she says. “This research helps us to understand what is behind panne expansion and contraction, which will help us better protect marshes in the future.”