The Comeback

In California’s Elkhorn Slough, a furry ally has emerged in the fight against one of the West Coast’s most notorious invasive species: European green crabs.

A new study found that these destructive crustaceans – once abundant in the tidal estuary – are now on the decline thanks to the big appetites of southern sea otters.

European green crabs (Carcinus maenas), introduced to North America in the 1800s, are notorious for destroying eelgrass beds, preying on juvenile salmon, and disrupting coastal ecosystems. They’ve spread along the Pacific Coast since the 1980s, becoming one of the most invasive species in marine environments, explained Smithsonian Magazine.

Southern sea otters (Enhydra lutris nereis), on the other hand, were nearly hunted to extinction by the early 1900s for their thick fur. Conservation efforts and federal protections have helped their population rebound to around 3,000 individuals, including a thriving group of 120 at Elkhorn Slough.

Known for their insatiable appetites – they consume up to 25 percent of their body weight daily – these otters have turned green crabs into a main course.

“The otters are a just super voracious predator,” co-author Kerstin Wasson told USA Today. “We calculated that the current otter population here eats somewhere between 50,000 and 120,000 green crabs a year.”

Wasson and her team added that the mammals’ impact has been transformative.

At the height of the green crab invasion in the early 2000s, traps often yielded 100 crabs. Today, traps rarely catch more than 10.

“I’ve studied green crabs in estuaries on three coasts and two continents for decades, and this is one of the first pieces of good news we’ve gotten,” ecologist and co-author Rikke Jeppesen said in a statement.

The team added that the otters’ presence has allowed native eelgrass beds to recover, improving water quality and restoring balance to the ecosystem.

Elkhorn Slough is now the only West Coast estuary where green crab populations have remained low, offering a rare success story in the fight against invasive species.

Jeppesen noted that the study underscores the need to protect apex predators to help biodiversity and provide a natural solution to ecological challenges.

“The sea otters, they’re like an assistant manager for us,” she quipped to USA Today.