Invasive European green crabs expanding in Alaska

European green crabs are increasing their range in Southeast Alaska, with a recent detection of crab molts in Refuge Cove in Ketchikan during a University of Alaska Southeast–Ketchikan class. The species was first detected in the state in July 2022 by the Metlakatla Indian Community on Annette Island. Since then, the community has taken proactive steps to better understand and respond to this ecological threat. A growing network of partners are working on early detection, outreach and public awareness. New detections are updated on a map, as crabs and molts are found. 

Barbara Morgan, one of the instructors of the class that reported the crabs in Ketchikan this month, said they found the crab shells on the last day of the class. They did not find crabs in more remote areas, such as George Inlet, where they had been detected before. Morgan was surprised to find the crabs in Refuge Cove, “It’s still a bit of a mystery as to where European green crabs are being found and where they aren’t.” 

European green crabs are small, usually no more than three inches across the carapace, but they have a big impact. These non-native crabs are prolific breeders—females have up to 250,000 eggs and spawn twice per year. The offspring float in the water as plankton, which makes it easy for them to move into new areas. They then settle to the ocean floor, feeding on a broad range of prey, including clams, oysters, mussels, barnacles, worms, and even each other. They thrive in a wide range of temperatures and salinities and are found in almost all types of nearshore habitats. 

Why we are concerned

Predation: Green crabs are effective predators, especially of young clams, a vital subsistence food. They can dig up to six inches into the seafloor and consume as many as 40 clams a day.

Competition: These invaders pose a threat to native species, including Dungeness crab, by competing for food and space. In places like California, their presence has been linked to a decline in native shore crab.

Habitat destruction: Green crabs destroy eelgrass beds, critical habitat for juvenile salmon, Pacific cod, and other fish and shellfish.

What’s next?

Partners throughout Alaska, including Tribes, U.S. Forest Service wilderness managers, Kachemak Bay National Estuarine Research Reserve managers, University of Alaska Southeast faculty, Alaska Department of Fish and Game and NOAA biologists, and other agencies and grassroots organizations, are building the capacity needed to respond to this invasive species. But there’s still much work to be done. Continued community engagement, monitoring, and cross-agency collaboration will be key in the fight to protect Alaska’s marine ecosystems.

Want to learn more or get involved?

The Alaska Department of Fish and Game provides an array of information on European green crab and ways to help, including protocols for early detection monitoring. Order a sticker from Alaska Sea Grant to help you identify European green crab on your local beach, or contact Alaska Sea Grant to help with early detection efforts. Take photos of any suspect crab and call the ADF&G Invasive Species Hotline to report it at 1-877-INVASIV. Every shell counts.