The European Green Crab is an invasive species that destroys and degrades eelgrass habitats by foraging and burrowing into the seabed, much more so than native crabs of the Pacific Northwest. Eelgrass is vitally important for fish that attach their eggs to eelgrass during spawning, which in turn provides food for other marine life. Green crabs feed on clams, oysters, mussels, and small crustaceans affecting the larger marine eco system and they also threaten aquaculture operations.
The transported invasive crab or larva may find its new environment favorable in which to live and even flourish; other times the environment may be unfavorable. The European Green Crab has been found in a few places in Washington State like Grays Harbor and Padilla Bay near Anacortes. The first Green Crab found in Washington inland waters was discovered in Westcott Bay on San Juan Island in 2016. This invasive crab seems more prevalent around the waters of Greater Vancouver, British Columbia and in Barkley Sound on West Vancouver Island.
How The Green Crab Got Here. The larva of Green Crabs is found in ballast water of commercial vessels. Commercial marine vessels take on and discharge millions of tons of water for ballast each day, which often contain aquatic intruders. Additionally, Green Crabs are sometimes found in seaweeds used as packing around shipments of lobsters and oysters. Recreational boaters can transport species in bait buckets, boat wells, or fouled hulls without realizing it. Inspecting and cleaning boat hulls can reduce the chances of unwanted stowaways. Government agencies have put into place a number of preventive measures, including required permits for movement of shellfish farms and equipment, both commercial and recreational.
How to Identify the Green Crab. While this invasive crab is predominantly green, it can morph into different colors – brownish, reddish, purplish, and yellowish. Its shell is serrated and pentagon-shaped, with five sharp spines or points on the side of each eye. The back legs are hairy and pointed, while the front claws are larger and each a different size.
Where to Report Sightings. As boaters, we can help by keeping our eye out for the European Green Crab. If you discover this invasive species, take a photo, record the location, leave it where you found it, and email the information to AISPACIFIC@dfo-mpo.gc.ca in Canada. In Washington State, report your findings to firstname.lastname@example.org. It is illegal to be in possession of a European Green Crab.
Once the species has been confirmed at a site, aggressive trapping and removal can take place and will help reduce its numbers. Early detection is more likely to eliminate a potential invasion along inland shorelines.
Photos: University of Washington