European Green Crab
Carcinus maenas

Report a discovery in an unlisted area

If you think you’ve seen or caught a European Green Crab:

  • Do not release it into the water.
  • Catch it and keep it frozen. If you can’t do that, destroy it.
  • Note the location (with GPS coordinates if possible) as well as the observation date.
  • Contact Fisheries and Oceans Canada.

The European Green Crab is one of the ten most unwanted species in the world. This small coastal crab, which is highly resilient, competes for prey and has the potential to upset the overall balance of the marine ecosystem.

Identifying features

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.

Similar species (native)

Rock crab (Cancer irroratus)

Larger (up to 15 cm), its peach-coloured shell is wide and ovoid with nine smooth notches on either side of the eyes.

Jonah crab (Cancer borealis)

Can be distinguished by its scallop-shaped shell, consisting of nine rounded teeth on either side of the eyes.

Lady crab (Ovalipes ocellatus)

Larger than the green crab. It has five notches, like the green crab, but the tips of its hind legs are oval.

Where it has been found

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. They are commonly found in southern Gulf of St. Lawrence along New-Brunswick, Prince Edward Island and Gulf shores of Nova Scotia. Their current boundaries include northeastern New-Brunswick and parts of southern Newfoundland.

This species arrived in B.C. likely through larval transport between 1998 and 1999. In B.C., this species is found along the entire West Coast of Vancouver Island from Barkley Sound to Winter Harbour with isolated, potentially ephemeral, populations in the Central Coast. This species has not been observed in the Strait of Georgia.

Habitat

Found in shallow water, generally on muddy, sandy or pebble bottoms or in vegetation. Prefers sheltered areas. Common in salt marshes, on sandy beaches and on rocky coasts. Can tolerate a wide range of salinities.

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.

European Green Crab distribution in Gulf region

European Green Crab distribution in Gulf region
Click image to enlarge

Ecological and economic impacts

Green crab may pose a serious threat to Canadian estuarine and marine ecosystems.

Ecological threats

European Green Crab may pose a serious threat to estuarine and marine ecosystems as they are voracious predators feeding on a variety of intertidal animals, including oysters, mussels, clams and juvenile crabs. This species changes the balance between species in the ecosystems and impacts their diversity. Green crab is such an efficient predator that it out-competes native crab species for food. Also, this species is known to disrupt eelgrass beds; productive habitat for many juvenile fish species and can destroy beds of bivalve shellfish. The European Green Crab threatens molluscs, crustaceans and fish, because of its large numbers, its huge appetite and its fierce competition with other species.

Unless controlled, this new aquatic invasive species will have a significant impact on biodiversity and habitat in the Canadian ecosystems.

Socioeconomic threats

Harmful to the fishing and aquaculture industries: Green crabs compete with native crabs and lobster for food and shelter, reduces the abundance of species harvested (fish, molluscs and crustaceans). This species harms the marine aquaculture industry because of its huge appetite for molluscs. The European Green Crab impacts the eel fisheries by damaging the eels when they enter the traps. This species primarily feeds on shellfish and other crustaceans, but has been observed eating small and juvenile finfish in eelgrass beds.

Origins and mode of arrival

Native 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.

East coast

Arrived in North American waters at the beginning of the 1800s. Observed for the first time in Eastern Canada in the Bay of Fundy, in the 1950s.

West coast

Brought to San Francisco Bay in 1989 via packing material. Arrived in British Columbia, probably through larval transport, between 1998 and 1999.

Mode of dissemination

Spread

This crab go through a long larval stage (up to 90 days) and it can drift with the currents and settle in new areas.

Human activity

Ballast water: Given its long larval stage (up to 90 days), the green crab can survive in ballast water tanks for a long time.

Fishing gear movements and discards: Adult green crabs can survive for a long time in fresh water or out of the water. They can also be introduced if fishing gear is moved to a new area or if crabs are intentionally discarded with the bycatch outside their catch area.

Government action

Scientific research

Fisheries and Oceans Canada is studying the Green Crab population to improve its understanding of how it reacts and adapts to Canadian conditions.

Controlling abundance

Once green crabs have started to invade an area though, it is practically impossible to eradicate them, but it is feasible to limit population spread and hence the damage caused by this species

In 2008 and 2009, Fisheries and Oceans Canada collaborated with fish harvesters, the Fish, Food and Allied Workers of Newfoundland, Memorial University of Newfoundland and the provincial Department of Fisheries and Aquaculture to try out various methods to fight the green crab, specifically including trapping and removing these crabs. The results show that, in areas where sustained removal of green crabs took place, the catch rate for these crabs decreased considerably and the native species, the Jonah crab, regained this territory.

In some areas, Fisheries and Oceans Canada distributes nuisance permits to fishermen. Fishermen who have these permits may destroy any green crabs they catch in an effort to reduce the population size.

European Green Crab in Newfoundland

Discovery and Survey Findings

Click image to enlarge.

Distribution Location and Bay
  • Arnolds Cove: Placentia Bay
  • Baine Harbou:r Placentia Bay
  • Baker Cove: Placentia Bay
  • Bakers Cove: Placentia Bay
  • Beau Bois: Placentia Bay
  • Bests Harbour: Placentia Bay
  • Bittern Cove: Placentia Bay
  • Black River: Placentia Bay
  • Bloody Point: Placentia Bay
  • Boat Harbour: Placentia Bay
  • Browns Cove: Placentia Bay
  • Butlers Island: Placentia Bay
  • Civil East Cove: Placentia Bay
  • Clay Cove: Placentia Bay
  • Cocks and Hens Cove: Placentia Bay
  • Come by Chance: Placentia Bay
  • Cook Brook: Bay of Islands
  • Coopers Cove: Placentia Bay
  • Corner Brook: Bay of Islands
  • Crabbe Cove: Placentia Bay
  • Davis Cove: Placentia Bay
  • Deer Brook: Bonne Bay
  • Dog Harbour: Placentia Bay
  • Doting Hole: Placentia Bay
  • East of Placentia Mans Pt: Placentia Bay
  • Fair Haven: Placentia Bay
  • Flat Island St.: Georges Bay
  • Fox Harbour: Placentia Bay
  • Garden Cove: Placentia Bay
  • Goose Arm: Bay of Islands
  • Great Brule: Placentia Bay
  • Great Sandy Harbour: Placentia Bay
  • Gulch: Placentia Bay
  • Hollets Cove: Placentia Bay
  • Hound Island: Placentia Bay
  • Jean Cove: Placentia Bay
  • Jeffery Cove: Placentia Bay
  • Kingwell: Placentia Bay
  • La Plante Cove: Placentia Bay
  • Lamaline: Placentia Bay
  • Lawn: Placentia Bay
  • Little Bay: Placentia Bay
  • Little Harbour East: Placentia Bay
  • Little Harbour West: Placentia Bay
  • Little Port Harmon St.: Georges Bay
  • Little Sandy Harbour: Placentia Bay
  • Little St Lawrence: Placentia Bay
  • Lomond: Bonne Bay
  • Long Harbour: Placentia Bay
  • Maggotty Cove: Placentia Bay
  • Marystown: Placentia Bay
  • Mattis Point: St. Georges Bay
  • Mooneys Point: Placentia Bay
  • Muddy Hole: Placentia Bay
  • NE Arm Placentia: Placentia Bay
  • Neddies Harbour: Bonne Bay
  • North Arm: Western NL
  • North Harbour: Placentia Bay
  • North of Baker Cove: Placentia Bay
  • North of Brimstone: Point Placentia Bay
  • North Tilt Island: Placentia Bay
  • Old Cove: Placentia Bay
  • Penguin Arm: Bay of Islands
  • Piccadilly: Port au Port Peninsula
  • Pipers Hole: Placentia Bay
  • Placentia: Placentia Bay
  • Placentia Sound: Placentia Bay
  • Point au Mal: Port au Port Peninsula
  • Pools Cove: Fortune Bay
  • Port Harmon St.: Georges Bay
  • Port Saunders: Northern Peninsula West
  • Prowseton: Placentia Bay
  • Red Island: Placentia Bay
  • Rock Harbour: Placentia Bay
  • Rocky Cove: Placentia Bay
  • Rocky Harbour: Bonne Bay
  • Rose Blanche: Southwest Coast
  • Sandy Cove St.: Georges Bay
  • Sandy Harbour: Placentia Bay
  • SE Arm Placentia: Placentia Bay
  • Shallop Cove: St. Georges Bay
  • Ship Harbour: Placentia Bay
  • Southern Harbour: Placentia Bay
  • Spanish Room: Placentia Bay
  • Spencers Cove: Placentia Bay
  • St Andrews: Southwest Coast
  • Staceys Point: Placentia Bay
  • Stephenville Crossing St.: Georges Bay
  • Swift Current: Placentia Bay
  • The Hole: Placentia Bay
  • Woods Island: Bay of Islands
  • Woody Island: Placentia Bay
  • York Harbour: Bay of Islands

In August 2007, European Green Crab was confirmed in the northern regions of Placentia Bay. This discovery raised significant concerns because of the potential negative impact of this species on biodiversity and habitat in these regions. Following the initial discovery of European Green Crab in North Harbour, Placentia Bay, the Science Branch of Fisheries and Oceans Canada in collaboration with Memorial University of Newfoundland and the provincial Department of Fisheries and Aquaculture, conducted several rapid assessment surveys for aquatic invasive species in Placentia Bay. The largest green crab population was observed in North Harbour. It was also found in smaller numbers in surrounding areas and along the west and southwest coasts of Placentia Bay. This raised concern as small populations may expand rapidly. Green crab was also found on the west coast of Newfoundland in St. George's Bay near Stephenville in 2008, and spread to Bonne Bay by 2010. Aquatic Invasive Species (AIS): Green Crab Distribution in Newfoundland Waters (see map)

For further information

References

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