Alaskans can help identify invasive crab species

A new crab species was spotted in Alaska for the first time last year, and it has the potential to disrupt native species and ecosystems. Alaska Sea Grant is asking Alaskans to help monitor the invasive European green crab on local beaches.

European green crabs are considered invasive in the United States. They were first identified in Alaska at Annette Island in July 2022. Biologists working with the Metlakatla Indian Community found a crab carapace, or shell, on the beach at Tamgas Harbor.

Since that initial find, the community has trapped more than 800 European green crabs, including egg-bearing females.

Adult European green crabs may prey on juvenile Dungeness and other small native crabs, including shore, kelp and rock crab, as well as mussels, snails, oysters and worms. European green crabs also dig for clams, tearing up eelgrass, an important habitat for juvenile fish.

Alaska Sea Grant, the Metlakatla Indian Community, the National Marine Fisheries Service and the Alaska Department of Fish and Game have joined forces to address the impacts an expanding population of the invasive crabs could have on habitat and native crab species. 

They encourage Alaskans to keep an eye out for European green crabs by walking along the wrack line (the high tide mark where debris accumulates) and examining every crab carapace encountered. 

European green crabs can be identified by the number of spines on the leading edge of the shell. Invasive crabs have five prominent spines on each side of the eyes and three rounded bumps between the eyes. It is important to note that the crabs are not always green. 

To meet the need for increased monitoring, Alaska Sea Grant recently co-hosted an early detection workshop for community members and other stakeholders. Participants learned about the invasive crab’s history and biology, how to distinguish them from native crab species and how to monitor for their presence by collecting crab shells on beach walks or by trapping live specimens. They traveled to Tamgas Harbor to see live European green crabs in their habitat and to practice trapping.

The two-day workshop was attended by 33 participants from 10 Southeast Alaska communities, including representatives from government agencies, tribal organizations, universities and ecotourism operators. In addition to Alaska Sea Grant, co-hosts included the Metlakatla Indian Community, the National Oceanic and Atmospheric Administration, ADFG, Southeast Alaska Tribal Ocean Research and the Organized Village of Kasaan.

Citizens who find European green crabs on Alaska beaches should note the location, take a picture and call the ADFG invasive species hotline at 1-877-INVASIV. Free stickers are available to help people identify the invasive crab. 

For more information, contact Sunny Rice, Alaska Sea Grant’s Marine Advisory Program agent based in Petersburg.

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