European green crab, or carcinus maenas, is a species that originated on the North and Baltic seacoasts. But over several decades, the green crab has invaded many coastal shores including Australia, both coasts of North America, and South Africa.
Adult crabs measure about 3 inches across and have shells ranging from dark green with yellow markings to orange or red. This highly adaptable and resilient crab is able to survive in a wide range of temperatures and salinities. Biologists theorize that one way the species spread is by crab larvae, which can travel up to 5 miles a day with the current. Other pathways of introduction include ballast water from incoming ships, bait buckets or boat wells from recreational boaters, and even seaweed packed lobsters. (Live lobsters are shipped to commercial markets in seaweed that may contain green crabs.) Green crabs were sighted in Willapa Bay and Grays Harbor as well as the west coast of Vancouver Island in 1998 and 1999.
This invasive species competes strongly with Dungeness crab for food and habitat. As small as the green crab is, the species is an efficient forager. It preys on numerous aquatic species, such as clams, oysters, mussels, and small crustaceans. Losses to Washington’s crab, clam, and oyster fisheries have the potential to be vast. (The commercial Dungeness crab fishery has an annual average value of almost $20 million, according to data collected between 1990 and 2002.)
Since 1991, funding from the Governor’s Office and the state Legislature has supported efforts to control and monitor the green crab. More than 100 monitoring sites and various control methods have kept down green crab populations in Washington. The Department of Fish and Wildlife has set trap lines for the green crabs in the northern most Washington estuaries. The trap lines will serve as an early detection device and enable the agency to respond rapidly to an invasion.