Carcinus maenas
Potential threat
Green crab pose a threat to Washington's native shellfish, which are important for recreational and commercial harvest as well as to the shellfish aquaculture industry, and native estuary ecosystems.
In areas where green crab have been able to establish reproducing populations, they have had dramatic impacts on other species, particularly smaller shore crab, clams, and small oysters. While green crab cannot crack the shell of a mature oyster, they can prey upon young oysters, and will dig down six inches to find clams to eat. One green crab can consume 40 half-inch clams a day, as well as other crabs its own size.
Limiting invasion
The Washington Department of Fish and Wildlife (WDFW) has focused much of its efforts in the early detection of green crabs by monitoring locations that offer good habitat for the species. If the species is detected at a new location, WDFW conducts rapid response actions to reduce or eliminate those new populations, and to prevent the spread of European green crab from established locations.
The state of Washington prohibits the release of non-native species into Washington’s waters and the intentional import of live green crabs. To reduce risk of unintentional introductions, WDFW restricts movement of shellfish from green crab areas and requires that anyone seeking to move live shellfish into or around state waters be approved for an import or transfer permit, which may include precautionary treatment measures to further reduce risk.
Join the Washington Sea Grant Crab Team
WDFW has teamed up with the Washington Sea Grant “Crab Team” who is leading a volunteer-based early detection and monitoring program for green crab. The Crab Team is also working to improve the understanding of native salt marsh and pocket estuary organisms and how they could be affected by green crabs. To learn more about early detection, monitoring, and volunteer opportunities, please visit the Sea Grant’s Crab Team website.
Description and Range
In Washington state, the European green crab is most often confused with native helmet crab or hairy shore crab. The most distinctive feature is not its color – which can vary from reddish to a dark mottled green – but the five spines or teeth on each side of the shell. There are three rounded lobes between the eyes; and the last pair of legs are somewhat flattened. The carapace is broader than it is long and seldom exceeds 3.5 to 4 inches across.
Green crabs in Washington
European green crab were discovered in 1998 in Willapa Bay and Grays Harbor. Since 2016, green crabs have been detected in Padilla Bay, Sequim Bay and the Dungeness Spit, and in the San Juan Islands.
North America
The European green crab first became established the United States in the mid-1800s, arriving by sailing ship to the Cape Cod region. In the early 1900s they spread northwards, where they are believed to have contributed to the dramatic declines in the soft shell clam fishery as far north as Nova Scotia. In 1989, green crabs were discovered on the West Coast, in San Francisco Bay, and made it into Oregon, Washington, and British Columbia estuaries in the late 1990s helped by strong El Nino currents.