Green crabs, originally from Europe, are one of the most invasive species in marine environments. California has been struggling with an invasion of green crabs, causing damage to the ecosystem. However, a group of adorable, fluffy, and hungry foodies have unexpectedly come to the rescue of California to solve this ecological problem.
In the Elkhorn Slough National Estuarine Research Reserve in California, a group of recently revitalized local southern sea otters have been feasting on a large number of invasive European green crabs. Researchers state that these voracious sea otters have successfully tackled the issue that has plagued the West Coast for years.
Green crabs, which originated in Europe, arrived on the U.S. West Coast around the 1980s. Despite their small size of only four inches wide, they have been known to destroy sea grass, consume salmon, and disrupt the coastal ecosystems ranging from California to Alaska, impacting species like Dungeness crab, king crab, and other shellfish industries.
Various states in the U.S. are investing millions of dollars to protect their waterways from the invasion of these small crabs. Washington State announced plans in September last year to allocate around $12 million to combat the green crab population, while Oregon encourages crabbers to catch a maximum of 35 green crabs per day. Scientists in 2021 mentioned that even after spending several years trying to eradicate green crabs from a river mouth in Stinson Beach, California, they kept resurfacing.
However, in the Elkhorn Slough in California, a reserve area with around 120 southern sea otters, these adorable top predators consume up to 120,000 of these invasive species each year, nearly driving green crabs to extinction and helping restore balance to the estuarine ecosystem.
“Sea otters are super greedy predators,” said Kerstin Wasson, research coordinator at the reserve, to USA Today. “We have calculated that the otters here currently consume approximately 50,000 to 120,000 green crabs per year.”
“In 2000, the green crab population was quite substantial,” Wasson said. However, he stated that in the past decade, they began to disappear.
During this period, a few things happened. The tidal estuary of Monterey Bay, stretching seven miles, became cleaner. Native eelgrass beds were restored. The natural tidal exchange of water and marshes started to recover.
And the sea otters returned.
Southern sea otters on the West Coast were pushed to the brink of extinction due to their thick, soft fur and were hunted almost to extinction until California declared them a “fully protected mammal” in 1913. Despite this, the hunting did not cease.
It wasn’t until 1977 that sea otters were listed as a threatened species and designated as a federally protected species. They began a slow recovery.
Wasson told The Washington Post that the first male sea otters arrived at Elkhorn Slough in the 1990s. He stated that when female sea otters arrived in the early 21st century, they began reproducing. Additionally, the Monterey Bay Aquarium released some otters into the marsh.
The ecosystem quickly saw improvements. Sea otters feed on a variety of crabs, allowing snails, the crabs’ prey, to multiply. The snails then feed on algae that blocks sunlight from reaching seagrass. More seagrass provides protection for juvenile fish, and serves as food for migratory birds.
Ecologist Rikke Jeppesen told The Washington Post that the impact of sea otters on the green crab population became evident around 2010. In 2014, a researcher witnessed a sea otter consuming about 30 green crabs in an hour while catching crabs from traps.
California researchers stated that their studies have proven that the return of sea otters to their natural habitat can bring unexpected benefits. Jeppesen mentioned that nowadays, when researchers set traps, they typically catch fewer than 10 green crabs each time.
“If this can help protect native species, it’s a win-win,” Jeppesen concluded.