European Green Crab

(Carcinus maenas)

What is it?

It is a small, near-shore crab with a carapace (shell) up to 10 centimetres wide. It is usually green but can be reddish-orange or tan with darker or yellowish spotting. The carapace is trapezoidal shaped with five obvious “teeth” along the top edge on each side and three rounded lobes lobes between the eyes. The two front claws are usually the same size and the tips of its backs legs are pointed, slightly flattened and hairy.

Where did they come from?

European Green Crab
European Green Crab

The green crab originally came from the North Atlantic coast of Europe and North Africa. It is believed to have first arrived in North America around 1817, most likely as adults carried in the holds of wooden ships. Green crabs are now thought to spread mostly during their larval stage through ballast water transfers or drifting on ocean currents.

Where are they now?

European Green Crab
European Green Crab

Green crabs were first found in Canadian waters in 1951 in southwest New Brunswick and have since expanded to many other locations in Atlantic Canada. They entered Nova Scotia waters in 1953/1954, and reached just south of Halifax in 1966. By 1982-1983, green crabs were present along the eastern shore of Nova Scotia. They were seen in Cape Breton and the Bras d’Or Lakes in 1991-1995 and they entered the Gulf of St. Lawrence by 1994, Magdalen Islands in 2004 and Newfoundland in 2007. Their current boundaries include eastern PEI and parts of southern Newfoundland.

It has recently been discovered that there are actually two different types of green crabs found in eastern Canada. Looking at their genetic makeup, scientists have learned that the first green crab populations that invaded the Bay of Fundy and Atlantic coast of Nova Scotia (south of Halifax) are different from the green crab populations that arrived in the 1980s and 1990s north of Halifax and in the Gulf of St. Lawrence. The crabs found in the more northern waters are better able to survive in the colder waters because they likely came from a Northern European stock (the North Sea and Scandinavia). Scientists are looking at where these hardier crabs may invade next.

How/where do they live?

European Green Crab
European Green Crab

Green crabs are found in shallow ocean waters and they preferred sheltered areas. They are common in salt marshes, in shallow water of sandy beaches and on rocky coasts.

The green crab can live four to seven years and can tolerate a wide range of water temperatures and salinities (salt content). Females can release up to 185,000 eggs once or twice per year. They have a long early life (larval stage) of 50 to 80 days when they drift in the ocean current before settling to the bottom.

The adult green crab is very hardy and can survive out of the water for five or more days, hiding in fishing gear and equipment or, at the bottom of crates, buckets and boats. It is an aggressive crab and a dominant predator, feeding upon many shellfish species such as clams, mussels, oysters, smaller crabs and other crustaceans and even small fish. The predators of green crabs are other crabs, fish species, birds, mink, otters, seals, etc.

What are the Effects on Native Species and Habitats, or Human Uses of the Oceans?

Did you Know?

The European green crab is one of the 10 most unwanted species in the world. While green crabs are now established in many locations in North America, they are still of great concern and they can expand their range up to 100 kilometres in one year!

Green crabs compete with native crabs and lobster for food and shelter, reduce invertebrate and fish diversity, can destroy shell fish (quahog, oyster, clam and scallop) beds, threaten shellfish aquaculture, and impact the eel fisheries by damaging the eels when they enter the traps. They damage eelgrass beds, which are essential habitats for many species, by foraging for food, digging, uprooting and clipping off shoots.

What can you do to Help?

It is impossible to wipe out green crabs once they are established in an area. In some areas, efforts have been made to control their numbers by intensive and frequent trapping before there are too many.

For more information visit
www.qc.dfo-mpo.gc.ca/publications/envahissant-invasive/carnet_anglais.pdf [PDF 13.2 MB]