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One of the World's Worst: Invasive Green Crab

Friends of Semiahmoo Bay Society

Invasive European Green Crab Project in Boundary Bay


The following is taken from Fisheries and Oceans Canada:

BC’s diverse, productive salt marshes, estuaries and eelgrass meadows now face a potentially destructive invader. The European Green Crab, Carcinus maenas, is considered one of the world’s worst invasive species. It can alter shoreline ecosystems and negatively impact economically and culturally important species and habitats including eelgrass beds that provide food and cover for juvenile salmon.

How to identify European Green Crabs: 5 spines or teeth to the outside of each eye, up to 10cm across the carapace, and wider in front than back. Referred to as green crab, the colour can actually vary from dark mottle green to orange.

European green crab shown from top view of carapace with 5 spines on each side clearly visible.

European Green crabs prefer sheltered areas such as lagoons, estuarine channels and bays with saltmarsh or eelgrass vegetation and a substrate of sand of mud. They have been found on gravel beaches too. Preferred prey is bivalves, small crabs, polychaete worms and they can negatively affect eelgrass beds in search of prey.


To see the most current confirmed sightings map and for more information on the DFO European Green Crab Monitoring Network go to:  and for more information visit: 


What can you do? REPORT – if you think you have seen a European Green crab, email a photo, date of observation and location to: AISPACIFIC@DFO-MPO.GC.CA 


Want to be involved or donate funds to help in Boundary Bay?

Contact Friends of Semiahmoo Bay Society,  or email:


Background (from the Strait of Georgia Data Centre)

The European green crab (Carcinus maenas) is a small coastal crab that has had major negative impacts on the marine environment of the east coast of North America.  It out-competes native species hunting for food and damages vital eelgrass meadow habitats.


The Green Crab has been spreading along the west coast of North America for the last 30 years and has been detected in BC on the west coast of Vancouver Island and parts of the Central Coast since 2006.


Eelgrass meadows are a habitat common to estuaries where juvenile salmon arrive in the ocean for the first time after hatching and rearing in freshwater streams. They provide an important temporary home for juvenile salmon by attracting their preferred food and providing protection from predators.


European green crab is known to destroy this habitat by creating burrows, digging for prey, or eating the grass shoots. One BC study found that in an area with minimal green crab occupancy, eelgrass meadow loss rate increased by 2.4 to 4 times when exposed to a high density of European green crabs.


The Department of Fisheries and Oceans Canada (DFO) Aquatic Invasive Species Program and a network of dedicated citizen scientists have been monitoring for presence of European green crab in BC. With approximately 500 traps being set in 2019, the citizen science network is set to expand in 2020 with new volunteers being trained and relationships developing with new partner organizations.


Pacific Salmon Foundation is partnering with Fisheries and Oceans Canada in order to broaden public outreach through the creation and distribution of educational brochures, posters and signage.


As a beach-going citizen, you are encouraged to contact Fisheries and Oceans Canada if you sight a European green crab in areas of BC other than the west coast of Vancouver Island.  Please take photos but leave the crab where you found it. Email photos and detailed location information to


Before contacting DFO, confirm that you are not viewing one of BC’s native crabs that appear green in colour.


detailed illustrations showing features of native helmet crab, native hairy shore crab and native kelp crab.


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