European Green Crab

Author: 
Lilly Powell and Emma Hornell

 

European Green Crab

Common name: European Green Crab

Scientific name: Carcinus maenas

Size Range: 

The European Green Crab is commonly between 60mm long and 90mm wide but has been noted to grow up to 101mm wide in non-native areas such as British Columbia.

Identifying Features:

The European green crab is not always pure green, its dorsal shell being mottled dark green to brown with yellow patches on the ventral surface. However, the crab's shell may change to orange or red during the molting cycle. Some of the most identifiable features of the Carcinus maenas are the array of five spines on either side of the eyes on the front end of the carapace, and three rounded bumps between its eyes.

Habitat:

European Green Crabs are an invasive alien species that originated in the Baltic Sea, in the Atlantic Ocean off the coast of Western Europe and Northern Africa. It is believed they first came to North America in the 1800's in the dry ballasts or ballast water of large ships. They first became established on the west coast of North America in Central California near California.  Though most invasive species in British Columbia are thought to come in ballast water of visiting ships it is thought the Green Crab most likely arrived as larvae that drifted on northern currents from the central California area.  They can now be found from Central California all the way up to Southern British Columbia. Green Crabs are very adaptive and can tolerate a wide range of salinity (4-54 ppt) and temperatures (0-33°C). Green Crabs can be found in a variety of habitats in the intertidal zone such as: protected rocky shores, cobble beaches, sand flats, and tidal marshes.

Prey:

The European Green Crab will feed on anything it can get its claws on, its most common prey being: clams, oysters, mussels, and other small native crabs. The crab is extremely dexterous, and has many ways to open the shellfish it eats.

Known Predators:

In its native habitat Carcinus maenas' predators include the Conger Eel, the Trigla Lucerna, Bass, and the Fivebeard Rockling. The crab's defenses include its ability to rotate its claws over its back to defend against predators coming from behind, and being able to live outside of water in the sun for up to a week.

Reproduction & Life Cycle:

European Green Crabs typically mate during the summer, when the female crab has just molted and is vulnerable. During this time, the male green crab guards the female by pairing with her in a "pre-molt cradling", protecting her from other males and predators. The egg sac appears a few months after mating and is carried for several months. The eggs then hatch into free-swimming larvae that stay in the water for 17 to 80 days before settling to the bottom as tiny crabs. The European green crab lives for up to five years and reaches sexual maturity at two or three years.

Impacts:

Known as The Most Invasive Crab in the World, the European Green Crab is a huge threat to our waters. Its floating larval stage contributes largely to its rapid migration and its feeding habits and environmental tolerance enables it to adapt to many places. Marine biologists believe the crab will also wipe out many commercial fish after already being discovered as a leading natural contributor to the dramatic declines in soft-shell clam fishery (aided by its ability to consume over 40 small clams a day). Also a threat to vital Eel-Grass habitats for many small creatures, the crab will snap the plants at their base, effectively preventing the grass from growing and reproducing.

References:

Carcinus maenas - Details. (n.d.). Encyclopedia of Life. Retrieved January 22, 2014, from http://eol.org/pages/128502/details

Conservancy of Canada (NCC). (n.d.). European green crab. NCC:. Retrieved January 22, 2014, from http://www.natureconservancy.ca/en/what-we-do/resource-centre/invasive-species/european_green_crab.html

Department of Fish & Wildlife. (n.d.). European Green crab (Carcinus maenas) - Aquatic Invasive Species . Washington Department of Fish & Wildlife. Retrieved January 19, 2014, from http://wdfw.wa.gov/ais/carcinus_maenas/

Lamb, A and Hanby, B.P. (2005) Marine Life of the Pacific Northwest: A photographic encyclopaedia of invertebrates, seaweeds and select fishes. Madeira Park, B.C. : Harbour Publishing

Ross, I. (2007, October). Sault is bug-eyed for invasive species lab. Northern Ontario Business, 27(12), 8. Retrieved January 22, 2014 from http://go.galegroup.com/ps/i.do?id=GALE%7CA170116367&v=2.1&u=61vhss&it=r&p=CPI&sw=w&asid=472df8f18415a9c172a1265c593865f5