Considered one of the most invasive marine species on the planet, the European green crab (Carcinus maenas) severely impacts any ecosystem it invades. Found in San Francisco Bay around the late 1980s, the green crab has made its way to Oregon and Washington, causing concern for the preservation of native crab, oyster, and clam species. Here is how you can identify and prevent the further spread of European green crabs on the West Coast.
How to Identify
The European green crab can be distinguished from other crab species by its five spines found along the rim behind each eye, with three undulations between the eyes. Despite its name, the green crab’s color varies from green to brown, grey, or red, depending on both genetic and environmental factors. In terms of size, adult crabs can reach a carapace width of approximately 2.5 to 3.5 inches making this species smaller than a Dungeness or rock crab.
Spread
European green crab species can spread to new habitats in several ways. Human-meditated dispersal such as the movement of live seafood, bait buckets used for recreational boating, and ballast water discharge can inadvertently transport green crabs to new areas, posing a risk to native species. Natural dispersal through ocean currents also spread green crabs across coastal waters. Once introduced, European green crab can rapidly increase their range, surviving as plankton for up to 80 days before molting into juvenile crabs in the upper intertidal zone. With this, the green crab continues to reproduce invading numerous coastal communities while destroying native habitats.
Impact
The European green crab can have catastrophic environmental and economic impacts, threatening Dungeness crab, clam, and oyster fisheries across the West Coast. With few predators of its own, the European green crab aggressively hunts clams, oysters, mussels, marine worms, and small crustaceans, outcompeting native fish and bird species for food and habitat. Additionally, the green crab destroys eelgrass used by fish to hide from predators, while also spreading disease to local shorebirds. Its harmful effects have wreaked havoc on the East Coast and has contributed to the collapse of the soft-shell clam industry in Maine.
Prevention
Since their discovery on the West Coast in the late 1990s, Oregon and Washington states have taken measures to prevent the spread of European green crabs across the region. Currently, the Washington Sea Grant Crab Team monitors and protects the region’s salt marshes and pocket estuaries against the species, teaching volunteers how to detect green crab populations while educating groups on the importance of protecting our native habitats. Additionally, the Washington State Invasive Species Council allows citizens to report crab sightings on their website. In Oregon, new regulations passed by the Oregon Fish and Wildlife Commission have increased the bag limit for recreational crabbers from 10 to 35 European green crabs per day to eradicate the invasive species.
