Crab Feast
Elkhorn Slough marine reserve (credit: NOAA)
Most everyone loves a crab feast and not just humans. Sea otters have become effective ecosystem engineers by consuming an invasive crab species that is disrupting the coastal marine ecology along the Pacific coast. They are restoring the ecology of a marine estuary in central California by setting off an ecological trophic cascade of positive feedback loops as they devour the invaders.
According to a report published by Biological Invasions, staff at the Elkhorn Nature Reserve near Monterrey and researchers with the University of California Santa Cruz and the National Oceanic and Atmospheric Administration (NOAA), otters in this estuary are keeping populations of the invasive green crab at bay.
Green crabs (Carcinus meanas) first appeared in the slough in 1994. The Crustation was unintentionally introduced to the San Francisco Bay area hitching a ride in 1989 on a merchant ship from Europe. Since then, it has been an aggressive invader of bays and estuaries from Elkhorn Slough to Alaska. It damages seagrass beds by borrowing beeneth them and consuming small prey important to feeding migratory shorebirds. Once established, their populations persist with very high numbers. In Oregon, no catch limits are set on how many green crabs can to taken by crab pots.
California otter eating green crab (credit: Elkhorn Slough marine reserve)
However, in Elkhorn Slough, the crab population have drastically declined from its previous highs as the sea otter population has significantly increased in the slough. Otter numbers are now at their highest while the green crab population is at its lowest. Using US Geological Service data on otter foraging, the investigators calculated that up to 120,000 green crabs/year are being consumed by the resident otters.
The global conservationist, Jane Goodall, paid a visit the slough to support Sea Otter conversation and the ongoing work of restoring the marine mammals to California's coastline where they were once common. She gave lectures to guests aboard the first all electric sailing vessel on the West Coast operated by Monterey Bay Eco Tours. Her presentation can be heard in this article from the Monterey Herald.
Sea otters were hunted to near extinction for the fur hat trade in the early 20th Century. This rebound along the California coast is excellent news. The ongoing ecological study also offers further evidence that recovery of a top predator, such as this keystone species, has multiple knock-on benefits by not only controlling an invasive species but also by restoring an ecosystem in the process. The otters are having a tasty crab feast as well. WHB