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green crab Invasive Species Alert! green crab
Plants and animals that are introduced into habitats where they are not native are called non-indigenous, exotic, introduced, or invasive species. They can have devastating biological and/or economic effects upon the habitats they invade. Non-indigenous species can reduce or eliminate populations of native species by out competing native species for food, habitat, as well as preying on them.

There are many ways non-indigenous species can be introduced to a new habitat. Common methods are through aquaculture, importation of live seafood, shipping (attached to ship hulls and through ballast water), research and academic institutions, deliberate introductions, pet stores and public aquaria, and natural dispersal. Recently, attention in the Puget Sound area has been focused on the potential impacts from the introduction of the European green crab Carcinus maenas. This crab has the potential to cause serious effects to the commercial shellfish industry in the Pacific Northwest. The green crab has already caused significant losses to shellfish growers in northern California. Many adult green crabs have been found in Willapa Bay and Grays Harbor on the outer coast of Washington, but so far none have been found in Puget Sound.

Green Crabs found in British Columbia!

On June 17,1999, a live 60 mm female green crab was collected at the head of Barkley Sound in Useless Inlet (west coast of Vancouver Island). It was found at the 0.3 m (1 ft.) tide level under a layer of seaweed. Due to the size of the crab, it may have arrived a year or two ago.

Also in Useless Inlet, Barkley Sound, the first male green crab was found on June 29,1999.

Fisheries and Oceans Canada is working with the Province of British Columbia, the Bamfield Marine Station on Vancouver Island, and other stakeholders to organize a broader inspection of Barkley Sound this summer. For additional information contact The Department of Fisheries and Oceans Canada.

Green Crab

green crab The European green crab, Carcinus maenas, is a small shore crab whose native distribution is the Atlantic coasts of Europe and northern Africa from Norway south to Mauritania. Habitat preferences include protected rocky shores, cobble beaches, and sand flats. Although it is commonly referred to as the green crab, the shell color can vary from dark green to orange and red, with yellow blotches on the dorsal surface. Identifying characteristics include five spines located on either side of the dorsal carapace, and a relatively flat last pair of hind walking legs. Adults can reach up to 3 inches across but most are approximately 2.5 inches. This crab is a very effective predator and can outcompete native crabs for food and habitat. They consume many types of prey including bivalves (clams, oysters, and mussels), crustaceans (including crabs the same size as themselves), and polychaete worms. Since green crabs are such voracious predators of shellfish, many shellfish growers are very concerned about this species invading Puget Sound.

green crab

This crab was first seen on the west coast in San Francisco Bay in 1989. Since then, the crabs have been moving north and live crabs have been found in bays in Oregon and Washington. Over two hundred adult green crabs have been found in bays on the outer coast of Washington! Green crabs can tolerate a wide range of environmental conditions including water salinities ranging from 5 to 30 ppt and temperatures ranging from 5 to 30 degrees C, which means that their northward expansion could be as far north as Alaska.

green crabSee some additional photographs of green crabs.

For more information specific to King County, please contact Kim Stark at the King County Department of Natural Resources (address on marine home page).

For possible sightings of the European green crab in Puget Sound or for more information, please contact Scott Smith at the Washington State Department of Fish and Wildlife, or visit their web site listed below.

For more general information, visit the web pages listed below.


Spartina is an invasive grass that is already well established in many areas of Puget Sound. It grows tenaciously in the intertidal area of mud or pebble marine beaches. Spartina chokes out native vegetation, does not provide food or habitat for many native animals, and can even increase flooding. Spartina reproduces both with seeds and massive runners, which makes it a difficult plant to control. Both the Washington Water Trails Association and Adopt-a-Beach have programs in King County to monitor for this invasive species. To find out more information, visit the web sites listed below.

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For questions about information on this page, please contact Daniel Smith

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Updated: May 17, 2000

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