Invasive European Green Crab in British Columbia
An aquatic invasive species of concern
Aquatic invasive species are non-native plants, animals and parasites that may cause economic or environmental harm and spread quickly to other areas. They are of great concern in the Strait of Georgia as they may outcompete native species and damage the ecosystem. One invasive in particular is posing an increasing threat:
European Green Crab (Carcinus maenas)
The European green crab (EGC) is a small coastal crab that has had major negative impacts on the marine environment. It is an invasive species that has been spreading over the last couple decades and is considered one of the 10 most unwanted species in the world¹.
EGC 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. EGC was detected in the Strait of Georgia for the first time in 2019.
The time animated map shows positive detections of EGC in BC made by Department of Fisheries and Oceans Canada (DFO) from 2006 to 2021.
Drivers of Spread
- Heat wave events result in increased reproduction².
- During the larval stage (up to 90 days) they can drift with the currents and settle in new areas¹.
- Human-mediated transport: Ballast water - Given its long larval stage, EGC can survive in ballast water tanks for a long time¹.; Fishing gear movements and discards - EGC can be introduced if fishing gear is moved to a new area or if crabs are intentionally discarded with the bycatch outside their catch area¹.
EGC can alter BC shoreline ecosystems and negatively impact economically and culturally important species and habitats, including eelgrass beds that provide critical food and cover for juvenile salmon and forage fish.
Impact to Salmon
Eelgrass meadows are a habitat common to estuaries where juvenile salmon arrive for the first time after hatching and rearing in freshwater streams³. They provide an important temporary home for juvenile salmon by attracting their preferred food and providing protection from predators⁴.
EGC is known to destroy this habitat by creating burrows, digging for prey, or eating the grass shoots. This poses a threat to juvenile salmon and forage fish that depend on this habitat³.
The interactive map shows areas with positive detections of EGC (DFO, 2021) compared to eelgrass inhabited areas (BCMCA, 2009).
Threat to other species
EGC prey upon intertidal bivalves (clams, oysters) and shore crabs. EGC may compete with local Dungeness and Red Rock crabs and have the potential to impact Indigenous, commercial and recreational bivalve and crab fisheries¹.
Identifying a European Green Crab
Watch the video below from Department of Fisheries and Oceans Canada to learn more about EGC's threats and how to accurately identify a EGC:
Invasive European Green Crab video produced by Fisheries and Oceans Canada (DFO)
Despite its name, the term “green crab” is not entirely accurate, as both adult and juvenile crabs can have many colour and pattern variations. Therefore color is not its distinguishing feature. The actual color can vary from dark mottled green to orange. As many of our native crab species are green, it is easy to misidentify the European Green Crab:
Images of native crabs not to be confused with EGC: Top-Native Kelp Crab, Middle-Native Helmet Crab, Bottom- Native Hairy Shore Crab (Images: DFO Pacific Region; Art: Pacific Salmon Foundation)
EGC Identifying features
The best way to identify EGC is by looking for 5 spines (or marginal teeth) to the outside of each eye. EGC are the only crab that has this feature¹.
Image of EGC with identifiable 5 spines (Photo credit: DFO Pacific Region)
Other ways to identify¹:
- Adult size: up to 10 cm
- Shell serrated and trapeze-shaped, with three spines between the eyes and five on each side
- Two claws of different sizes
- Colour variable: green, red or yellow
- Aggressive, territorial and vigorous, can survive out of the water for several days
What you can do
As a beach-going citizen, you are encouraged to contact Fisheries and Oceans Canada (DFO) if you sight a European green crab. Please take photos but leave the crab where you found it. Email photos and detailed location information to AISPACIFIC@dfo-mpo.gc.ca .
Where does that information go?
In collaboration with the Strait of Georgia Data Centre , coordinates of new detections are collected through DFO and updated into a map of new detections. This keeps this map and information displayed current. DFO also offers official data for locations of detections through their Open Data Portal.
The map on the right produced by the Strait of Georgia Data Centre displays confirmed sightings of EGC - last updated Aug 2021.
Since 2018, EGC have been detected in Esquimalt Lagoon, Witty’s Lagoon, Salt Spring Island, Haida Gwaii, Boundary Bay and Madeira Park. Intensive sampling, eradication and DNA analysis have been undertaken by DFO in partnership with local Indigenous governments and stewardship groups.
Why is this important?
Early detection of EGC in new areas can help to halt the spread of this dangerous invasive species. DFO has established a collaborative monitoring program for the Salish Sea, partnering with First Nations, citizen volunteers, and stewardship groups. Many are concerned about the impact that increased numbers of EGC will have on the environment. This is particularly true of First Nations whose food security depends on coastal ecosystems¹.
Photo credit: DFO Pacific Region
It is imperative that people have the information necessary to identify EGC, as well as know the recommended options for helping stop the spread. The only known measure to control EGC is to trap and remove/eradicate. Therefore if we can detect EGC before the population can become established (i.e. self-sustaining) there is a higher likelihood of success to control this population.
Use of Citizen science to monitor for EGC
The DFO Aquatic Invasive Species Program and a network of dedicated citizen scientists have been monitoring for presence of EGC in BC. With over 16 regularly monitored sampling stations, the citizen science network is set to expand within the Salish Sea in 2021 with new volunteers.
Contact AISPacific@dfo-mpo.gc.ca to get involved in the EGC Sampling Program
Left: Esquimalt Lagoon Stewardship Initiative Volunteers (DFO),⠀Middle: Photo credit from Coastal Restoration Society,⠀Right: Site where EGC is monitored (DFO)
Use of signs to ensure accurate detections
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. The program hopes to educate the public on EGC identification and to ask the public to report EGC.
The program has partnered with First Nations, stewardship groups and municipal governments to install the signs in the best locations. This builds partnerships in local communities and encourages local participation in EGC programs.
Over 70 signs have been distributed to partner organizations, and distribution of signs continues to expand in 2022. View the map on the left to see locations of these signs in the Strait of Georgia.
The next phase is the installation of signs where EGC is not established and areas outside of the Salish Sea. This signage will help the public to identify EGC early so there can be a high success of trapping and controlling populations before they can become established.
Signs will also be installed in areas where EGC are established like on the West Coast of Vancouver Island. These will look similar to the existing sign but without the request to report as the population has been documented.
If you are interested in brochures and EGC signs please contact AISPacific@dfo-mpo.gc.ca . A downloadable brochure as produced by Pacific Salmon Foundation and DFO is also available by clicking the button below.
Education is imperative to ensure we detect European Green Crab before it is too late to halt their spread. Increasing awareness is the first step of many to preventing the damage these crabs can cause and their further establishment in the Salish Sea.
