Wildlife

Invading Crabs

An aggressive breed of green crab is invading Maine's waters.

The crabs (Carcinus maenas) threaten blue mussels, soft-shell clams and the eelgrass beds off the state's rocky coast. The crustaceans are also just plain nasty: Researchers who work with the crabs say that instead of hiding from threats, the critters rush forward, pincers waving.

The crabs, which measure about 5 inches (13 centimeters) long, belong to the same species that has long lived in Maine's waters. But in the past few years, a genetically distinct population of this species has traveled south from Nova Scotia, Canada, according to research led by Markus Frederich, a professor of marine sciences at the University of New England. These non-native crabs chow down on marine animals that are important for Maine's economy, including mussels and clams, and the invaders shred native eelgrass habitat as they hunt.

Green crabs probably arrived in North America in the 1800s in the ballast water of ships from Europe. In the past decade, Maine's green crab population has exploded, a cycle probably linked to rising ocean temperatures, according to the marine resources department.