European Green Crab

Description

The European Green Crab is a small, highly adaptable, and aggressive marine crustacean. It is identifiable by its serrated, pentagon-shaped shell, distinct spines near the eyes, and different-sized front claws. It can grow up to ten centimeters and exhibits colors ranging from green to red or yellow. Its territorial and aggressive nature makes it a formidable predator and competitor within marine ecosystems.

  • Scientific name: Carcinus maenas

  • Common name(s): European Green Crab

  • French common name: Crabe vert

  • Regulatory status: Recognized as a highly invasive species, the European Green Crab poses a significant threat to marine ecosystems, leading to various management and control efforts across its invaded range.

European green crab on beach

European Green Crab © Ian Cruickshank, some rights reserved (CC BY-NC)

Identifying Features

  • Shell: Serrated, pentagon-shaped, with five sharp spines beside each eye.

  • Legs: Back legs have hairy, pointed, and slightly flattened tips.

  • Claws: Differently sized front claws.

  • Size: Can grow up to ten centimeters.

  • Colour: Varies from green to red or yellow.

  • Temperament: Notably territorial and aggressive.

Distribution and Invasiveness

Native to Europe and North Africa, European Green Crab has spread widely across Canada’s coastlines. Its introduction to North America is attributed to ballast water from ships and ocean currents. Distinct populations have established themselves in both Atlantic (late 1950s) and Pacific regions (1990s), showing variations in cold tolerance and adaptability.

Habitat

European Green Crabs thrive in shallow waters, including salt marshes, eelgrass beds, rocky shores, and sandy beaches. They can tolerate a wide range of temperatures and salinity, contributing to their invasiveness [1]. The adult crabs are particularly hardy, able to survive out of water for over five days, utilizing hiding spots such as crates, boats, buckets, and various types of gear. Make sure to inspect any fishing gear for signs of European Green Crab.

Impacts

  • Lifespan: European Green Crabs can live 4 to 7 years.
  • Diet: They consume a wide variety of plants and animals, significantly impacting the local food web.
  • Reproduction: Females can release up to 185,000 eggs once or twice a year, facilitating rapid population growth.
  • Ecological Damage: These crabs disrupt native ecosystems by destroying shellfish beds and preying on native species such as clams, oysters, mussels, small fish, juvenile crabs, and other crustaceans, including juvenile lobsters [2]. Their feeding activity disrupts eelgrass beds, an important habitat for juvenile fish.

Response and Management

Management efforts focus on preventing their spread through early detection, containment, and control measures. Partnerships between government agencies, academia, and community groups aim to educate and train on identification and control strategies. Despite challenges in eradication, efforts like the Clean, Drain, Dry initiative for watercraft and equipment aim to minimize the spread and impact of European Green Crabs.

What You Can Do:

Report it: If you think you have found an aquatic invasive species report it to Fisheries and Oceans Canada. Never return it back to the water.

Additional Information

For more details on the European Green Crab, including management strategies and how to report sightings, visit: https://www.dfo-mpo.gc.ca/videos/green-vert-eng.html

Resources

Management efforts focus on preventing their spread through early detection, containment, and control measures. Partnerships between government agencies, academia, and community groups aim to educate and train on identification and control strategies. Despite challenges in eradication, efforts like the Clean, Drain, Dry initiative for watercraft and equipment aim to minimize the spread and impact of European Green Crabs.

1. Gehrels, H., Knysh, K.M., Boudreau, M. et al. Hide and seek: habitat-mediated interactions between European green crabs and native mud crabs in Atlantic Canada. Mar Biol 163, 152 (2016). https://doi.org/10.1007/s00227-016-2927-6
2. Matheson, Kyle & Mckenzie, Cynthia & RS, Gregory & Robichaud, David & Bradbury, Ian & Snelgrove, Paul & GA, Rose. (2016). Linking eelgrass decline and impacts on associated fish communities to European green crab Carcinus maenas invasion. Marine Ecology Progress Series. 548. 31-45. 10.3354/meps11674.

Invasive Species Categories

Stop The Spread: Report Invasive Species

How to Prevent and Manage Invasive Species

The Impact of Invasive Species on Canada’s Ecosystems and Economy

Invasive Species Resources: Guides, Manuals, and Best Practices