Aquatic invasive species


(Carcinus maenas)

The Green crab is one of the ten most unwanted species in the world. This small coastal crab is native to Europe and North Africa. It was first observed in eastern Canada in the 1950's in the Bay of Fundy and entered Nova Scotia waters of the Gulf of St. Lawrence in 1994.


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.

Green crab - DFO  S. Pereira
DFO S. Pereira


  • Adult size: up to 10 cm;
  • Shell serrated and trapeze-shaped, with five obvious spines on each side and three between the eyes;
  • Colour variable: green, red or yellow;
  • Two claws of different size;
  • Tips of its back legs are pointed, slightly flattened and are hairy;
  • Aggressive, vigorous, can survive out of the water for several days.


Rock crab - DFO  R. Laroque
Rock crab
DFO R. Laroque
The Green crab is sometimes mistaken for native Rock crabs, Lady crabs or Mud crabs. Rock crab is larger (up to 15 cm), its peach-colored shell is wide and ovoid, with nine smooth notches on either side of the eyes. Lady crab is also large, has five notches like a Green crab but the hind legs are oval. Mud crab is smaller than the Green crab and usually has either white or black claw tips.


  • Changes balance between species in the ecosystems;
  • Can destroy shellfish beds;
  • Destroys eelgrass beds, which are essential habitats;
  • Reduces invertebrate and fish diversity;
  • This voracious predator threatens shellfish aquaculture;
  • Impacts the eel fishery by damaging the catch.
Green crab - AVC-UPEI  J. Davidson
AVC-UPEI J. Davidson


  • Learn how to recognize Green crab;
  • DO NOT RELEASE THE CRAB into new areas (Quebec, eastern New Brunswick and western Prince Edward Island), catch and freeze crabs; if not possible, destroy them;
  • Follow the general guidelines.