Larva of voracious green crab discovered on North Coast

Public asked to retain the carcasses of these invasive species for DNA testing

  • Jun. 5, 2020 12:00 a.m.
If you find an adult green crab do not return it to the water. Allow it to die then freeze it and contact DFO. (DFO photo)

If you find an adult green crab do not return it to the water. Allow it to die then freeze it and contact DFO. (DFO photo)

The public is asked to be on the lookout for invasive green crabs on the North Coast for DNA testing and geographic tracing by the Department of Fisheries and Oceans (DFO). The larva of this aggressive crab species was discovered last November in Lax Kw’alaams traditional waters near Rachel Island.

No adults have been found to date, but Lax Kw’alaams senior fisheries biologist Katherine Butts said warmer waters could now be providing the right conditions for the larva to develop.

“When you see one you want to get it out of the environment,” Butts said. “Every little bit counts.”

The European green crab is a small and resilient forager found in rocky, inter-tidal areas, adept at opening bivalve shells and feeding on an array of sea life, including clams, cockles, mussels and juvenile crabs. The voracious crustacean can upset the overall balance of the marine ecosystem and harm shoreline habitats of native species.

The green crab’s Latin name, Carcinus maenas, is translated as “raving mad crab”, according to DFO.

READ MORE: COVID-19 restrictions may aid B.C.’s ongoing battle against invasive mussels

The crabs are known to also damage eelgrass beds, which provide important nursery habitat for juvenile salmonids.

“If we end up seeing adult green crabs in the area it can be very dangerous,” Butts said. “They’re very aggressive feeders. They’re very competitive.

“A lot of the foods this species will target are key food sources for [Lax Kw’alaams] band members, and the potential biological and ecological impact overall is quite disturbing.”

The green crab is native to coastal Europe, North Africa and Asia. Its larva is known to drift on Pacific tides to Canada’s west coast, but in the case of Rachel Island it likely hitched a ride in the water ballasts of international cargo ships.

It was identified through regular testing for invasive species by a working group comprised of the Lax Kw’alaams Band, DFO, Prince Rupert Port Authority and Coast Mountain Community College.

READ MORE: Spread of invasive species in Canada costs billions, changes environment

If found, Butts urges the public to remove them from the water and let them die. Freeze the carcasses in a plastic bag and contact DFO (email below). DNA testing will allow DFO to determine which part of the world the larva originated from, and help authorities put preventive measures in place.

European green crab identification:

Carapace is generally oval 90mm across

Have five prominent marginal teeth

Three rostral bumps

Claws are not rounded

Last pair of walking legs are slightly flattened

Colouration is green, brown, reddish, typically with orange joint

To report green crab sightings or carcasses for DNA testing contact DFO biologist Renny Talbot at

AISPacific@dfo-mpo.gc.ca

Kitimat Northern Sentinel

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