Photo Credit (Pixabay)
The tale of native animals protecting our coastlines from European-introduced green crabs that pillage comes from California.
This clawed cancer has found a mate in the southern sea otter, which has destroyed native crab hatcheries, hunted juvenile salmon, and levelled eelgrass beds.
A recently revitalised otter population at Elkhorn Slough National Estuarine Research Reserve has surprised biologists by mostly avoiding the crabs’ damage to this delicate ecology.
One of the most damaging invasive species in US maritime waters is the green crab. They most likely hitched a voyage in the ballast water of European trade ships when they were first brought to North America in the 1800s.
After the state governor issued an emergency order in 2022, Washington wildlife managers had captured over a million green crabs, at a cost of $12 million to the state. After years of attempting to eradicate them from the Seadrift Lagoon at Stinson Beach, California, researchers from the University of California Davis discovered that they had returned. Crabbers in Oregon are urged to aim for a minimum of 35 catches per trip.
Green crabs have been living in Elkhorn Slough since 2000, but as time went on, managers became aware of something unusual. Without human intervention, their numbers were declining.
In the 19th century, southern sea otters were almost exterminated for their furs; they only received some protection in 1913 before being added to the Endangered Species List in 1977. Because they don’t have the blubber layer that other marine mammals do, sea otters must consume a lot of food to stay warm. It turned out they developed an insatiable hunger for green crabs.
The only otter-repopulated estuary of its kind in the Southern United States is Elkhorn Slough. There, 120 is located.
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According to Rikke Jeppesen, an estuarine ecologist with the Elkhorn Slough National Estuarine Research Reserve and the lead author of a paper published on December 10th about the otters and their effects on the ecosystem, “the otters eating the crabs benefited the eelgrass, which contributed to better water quality,” which benefited the otters.
“We thought the green crabs were going to take over Elkhorn Slough back in 2003-2004 when the otter population was at its lowest,” she told USA Today. After then, they didn’t. And we are grateful to the otters for that.
In the past, Jeppesen and her coworkers could catch 100 green crabs in a single trap, but now they might only get five.
The southern sea otter has been slowly repopulating, and although Elkhorn Slough is the only estuary where they may live to their full potential, about 3,000 of them are found in U.S. waters. Hopefully, their recovery will undo the decades of damage caused by the crabs and stop them from reoccupying areas they have already taken over.
