The green crab (Carcinus maenas) is commonly found in tide pools along the East Coast of the United States from Delaware to Nova Scotia, but this species is not native to these areas. This now-abundant species is thought to have been introduced into U.S. waters from Europe.
Green Crab Identification
Green crabs are a relatively small crab, with a carapace that is up to about 4 inches across. Their coloration varies from green to brown to reddish orange.
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Crustacean
- Class: Malacostraca
- Order: Decapoda
- Family: Portunidae
- Genus: Carcinus
- Species: maenas
Where Are Green Crabs Found?
Green crabs are widespread in the eastern U.S., but they aren't supposed to be here. The green crab's native range is along the Atlantic coast of Europe and northern Africa. However, in the 1800s, the species was transported to Cape Cod, Massachusetts and is now found in the eastern U.S. from the Gulf of St. Lawrence to Delaware.
In 1989, green crabs were discovered in San Francisco Bay, and now they inhabit the West Coast up to British Columbia. Green crabs have also been recorded in Australia, Sri Lanka, South Africa and Hawaii. It is thought that they were transported in the ballast water of ships, or in seaweed that was used to pack seafood.
The green crab is a voracious predator, feeding primarily on other crustaceans and bivalves such as soft-shelled clams, oysters, and scallops. The green crab moves quickly are dexterous and are capable of learning, so that it can improve its prey-handling skills while it is foraging.
Reproduction and Life Cycle
Female green crabs can produce up to 185,000 eggs at a time. Females molt once each year, usually during the summer. During this time, the crab is very vulnerable until its new shell hardens, and the male green crab guards the female by pairing with her in "pre-molt cradling," defending the female from predators and other males.
A few months after mating, the female's egg sac appears. The female carries this egg sac for several months, then the eggs hatch into free-swimming larvae, which stay in the water column for 17-80 days before settling to the bottom.
Green crabs are estimated to live up to 5 years.
Green crab populations have expanded rapidly from their native home in the Eastern North Atlantic, and they have been introduced into many areas. There are several ways that the green crab can be transported to new areas, including in the ballast water in ships, in seaweeds that are used as packing materials to ship marine organisms, as bivalves shipped for aquaculture, and movement on water currents. Once they are introduced, they compete with native shellfish and other animals for prey and habitat.
- MIT Sea Grant. 2009. Introduced Species (Online). MIT Sea Grant Center for Coastal Resources. Accessed May 23, 2009.
- National Heritage Trust. 2009. European Shore Crab (Carcinus maenas). National Introduced Marine Pest Information System, CRIMP No. 6275. Accessed May 23, 2009 (link no longer active as of June 2014).
- Perry, Harriet. 2009. Carcinus maenas. (Online) USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Accessed May 23, 2009.
- Prince William Sound Regional Citizens' Advisory Council. 2004. Green Crab (Carcinus maenas). (Online) Non-Indigenous Aquatic Species of Concern for Alaska. Accessed May 23, 2009.
- Washington Department of Fish and Wildlife. 2009. Carcinus maenas (Green Crab). Washington Department of Fish and Wildlife Invasive Species Fact Sheets. Accessed May 23, 2009, online. As of August 2010, no longer online.