Suzanne's Mom's Blog

Photo: Lilian Carswell/USFWS.
Sea otter.

According to the state of Washington’s Fish and Wildlife department (WDFW) , the European green crab is a menace. That is something we’ve noticed in Rhode Island, where it’s pushing out the delicious blue claw crabs.

WDFW says, “The European green crab (Carcinus maenas) is a globally damaging invasive species that poses a threat to native shellfish, eelgrass, and estuary habitat critical for salmon and many other species.

“Potential impacts include destruction of eelgrass beds and estuarine marsh habitats, threats to the harvest of wild shellfish and the shellfish aquaculture industry, salmon and forage fish recovery, and a complex array of ecological impacts to food webs. Research is ongoing regarding potential impacts on juvenile Dungeness crab and crab fisheries.

“In areas where European green crabs have been able to establish large populations for extended periods of time, they have had dramatic impacts on other species, particularly smaller shore crabs, clams, and small oysters. While green crabs cannot crack the shell of a mature oyster, they can prey upon young oysters, and will dig down six inches to find clams to eat.

One green crab can consume 40 half-inch clams a day, as well as other crabs its own size.

“Their digging can have significant negative impacts on eelgrass, estuary and marsh habitats.”

But here’s a ray of hope.

Manuela López Restrepo reports at National Public Radio (NPR), “A new study has found that a restored sea otter population might be the solution. …

“As it turns out, sea otters — which are listed as threatened under the Endangered Species Act — love to eat these crabs. One estimate by researchers in California found that a group of otters in Elkhorn Slough consumed somewhere between 50,000-120,000 crabs a year.

“A new study, published in the Biological Invasions journal, found that there was a direct relationship between the two species: if an area had a healthy population of sea otters, it would also have a low green crab population.

“Yes, says ecologist Rikke Jeppesen, whose team at Elkhorn Slough Reserve on the California coast published the recent study.

” ‘It’s really a win-win scenario if we can support a native threatened species, the sea otter, which in turn then helps control an invasive invertebrate,’ Jeppesen told ‘All Things Considered.’ … ‘Sea otters are our assistant managers of the estuary for invasive species control.’

“What’s more, they’re biologically predisposed to eating a lot of crabs, she said.

” ‘Sea otters rely on fur for insulation as opposed to seals, which rely on blubber. Blubber insulates much better, so sea otters have to eat a lot to keep warm,’ she said. ‘It’s basically a weasel in the water. And weasels are super active. They have a high metabolism. So to sustain sea otter health and keep warm, they just need to eat a lot.’ “

More at NPR, here. An interview with the researcher is here. And a previous study in Nature showed similar results, here.