European Green Crab
Carcinus maenas
Jeff Adams
Vectors of spread:
ID Characteristics
Size: Adults can reach up to 10 cm.
Behaviour: Aggressive and territorial.
Colour: Carapace colour is variable but usually a mottled, dark brown or green.
Shell Shape: Shell is serrated and trapeze-shaped with three spines between the eyes and five on each side.
Claws and Legs:
- Walking legs are green and speckled with black. The second and third pair of walking legs are the longest and a little bit larger than the carapace. The fourth pair of legs are a bit shorter than the first and are somewhat flattened with setae.
- Claws are different sizes and the back legs are pointed, slightly flattened and hairy.
Life Span: 4-7 years.
Not to be confused with:
- Jonah Crab (Cancer borealis, native): Can be distinguished from the Green Crab by its scallop-shaped shell, consisting of nine rounded teeth on either side of the eyes.
- Lady Crab (Ovalipes ocellatus, native): Larger than the Green Crab. It has five notches but the tips of its hind legs are oval.
Habitat and Origin
Origin: Native to Europe and northern Africa, this species was first found in Canadian waters in 1951 in southwest New Brunswick. The European Green Crab arrived in B.C. in the late 1990’s, likely introduced by larvae drifting on currents flowing from south of our border.
Recently, scientists have discovered that there are actually two different types of European Green Crabs found in eastern Canada. The crabs found in northern waters are better able to survive in colder waters because they likely came from a Northern European stock.
Habitat: The European Green Crab can tolerate a wide range of water temperatures and salinities. Common in salt marshes, sandy beaches or rocky coasts – this crab prefers sheltered areas. The European Green Crab is often found on muddy, sandy or pebble ocean floors or in vegetation.
Reproduction
Females can release up to 185,000 eggs once or twice per year. Larval stage is long (50-80 days).
Current Distribution
Source: DFO
Vectors of Spread
The European Green Crab undergoes a long larval stage (50-80 days) which allows it to drift with the currents and settle in new areas and/or survive ballast water tanks.
The European Green Crab is also very tough and can survive out of the water for about a week. This allows it to easily hide in fishing gear and equipment, or at the bottom of crates, buckets and boats.
Impacts
Economic: Feeds on native shellfish, so poses grave risk to shellfish aquaculture. The European Green Crab also outcompetes native crabs and lobsters for food and shelter, which reduces the abundance of species harvested.
Ecological: The European Green Crab is a dominant predator. It is very aggressive and it feeds on and outcompetes many native organisms. Due to its aggressive behaviour, it reduces marine biodiversity, impacting wild shellfish populations and damaging eelgrass beds.
What Can I Do?
European Green Crabs have been found along the West and Central Coasts of Vancouver Island, but have not been found in the Strait of Georgia, nor Howe Sound so PREVENTION is key:
- Clean, Drain and Dry all aquatic equipment and vessels.
European Green Crab can be controlled by:
- Mechanical Control: Sustained trapping and removal. 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 population size.
- Biological Control: Predators of Green Crabs are other crabs, fish species, birds, mink otters, seals, etc. A parasite was considered for use as a biocontrol agent in BC, but was deemed inappropriate due to the risk of off-target damage.
References
References:
- Department of Fisheries and Oceans Canada, European Green Crab, https://www.dfo-mpo.gc.ca/species-especes/profiles-profils/europeangreencrab-crabevert-eng.html
- E-Fauna BC: Electronic Atlas of the Fauna of British Columbia, European Green Crab, https://linnet.geog.ubc.ca/efauna/Atlas/Atlas.aspx?sciname=Carcinus%20maenas&ilifeform=102
- Adams, J., & Grason, E. (2017, January 25). Eyes on the beach and boots on the mud – european green crab monitoring on our coastline [Webinar]. In ISCBC Webinar Series. Retrieved from https://bcinvasives.ca/documents/2017-01-25_ISCBC_(1).pdf
Map Reference: Department of Fisheries and Oceans, Summary of Locations in British Columbia, Canada Supporting Invasive Tunicate Species and European Green Crab as of 2017, p. 7