An unwelcome visitor has arrived on Cortes Island’s shores, triggering alarm among scientists and conservationists. The invasive European green crab (*Carcinus maenas*)—considered one of the world’s most damaging marine invaders—was confirmed in Mansons Lagoon in 2024, marking the first documented sighting in the Discovery Islands. The species’ appearance has set off a coordinated response from Fisheries and Oceans Canada (DFO), the Klahoose First Nation, and Friends of Cortes Island (FOCI).
From Europe to the Pacific Northwest: A Timeline
Native to Europe and North Africa, green crabs first arrived in North America in the early 1800s via ship ballast water. After decades of devastation on the U.S. east coast, they reached San Francisco Bay in the late 1980s.
“They’re believed to have landed on our coast in around 1998/99, originally on the west coast of Vancouver Island,” explained Renny Talbot, Aquatic Invasive Species Coordinator for DFO. “Now they’re spreading north… into Alaska as well.”
By the mid-2010s, warming ocean temperatures and changing currents enabled them to cross into the Salish Sea, with incursions into Ladysmith, Boundary Bay, and the Sunshine Coast.
“The European Green Crab that we currently have in the Salish Sea… are believed to have arrived as a result of the warm water blob back in 2015/16,” said Talbot.
The first confirmed green crab on Cortes was trapped in Mansons Lagoon in 2024, as part of a DFO earlier detection monitoring initiative carried out with Klahoose Guardians and FOCI volunteers. “Unfortunately, the traps produced a single fully mature female,” recalled volunteer Mike Moore. While subsequent traps did not yield more crabs, the discovery triggered intensive monitoring.
Why Green Crabs Are a Threat
European green crabs are aggressive predators and ecosystem bulldozers. Each female can produce up to 185,000 eggs per spawn, and may reproduce twice a year. Once established, their populations can explode.
“They eat everything,” Talbot warned. “They compete for food with our native shore crab. They prey on bivalve species, and other shore crab—including juvenile Dungeness crabs.”
Their feeding habits also threaten marine nurseries. “. They can destroy eelgrass habitat and that’s one of the most important habitats in the marine environment… including juvenile salmon.” said Helen Hall, Executive Director of FOCI
The consequences are broad. As Talbot put it: “Salmon are very dependent on estuarine environments… that European green crab have a tendency to destroy.”
How Close Is the Threat?
Prior to the 2023 discovery on Cortes, there had been no confirmed green crab sightings north of Nanaimo. However, FOCI had been proactively monitoring Mansons Lagoon with DFO since 2022.
“This year DFO came back and said this is a project they want to keep doing,” said Hall in a 2023 interview. “We found lots and lots of Graceful Crabs… but luckily, no green crabs—yet.”
Two FOCI volunteers working together with someone from DFO – photo courtesy FOCI
That luck ran out in April 2024. Since then, FOCI and DFO have expanded their efforts, including:
– Monthly trapping using both prawn and minnow traps.
– DNA testing of water samples to detect larvae.
– Public education campaigns, signs at docks, and training resources.
FOCI has also raised community awareness through newsletters, posters, and educational outreach.
What Can We Do?
The arrival of a single green crab signals the potential for a wider invasion—but it’s not too late.
1. Report Sightings: If you suspect you’ve seen a green crab, take a photo and email FOCI at friendsofcortes@gmail.com. “One crab can produce a vast population,” Talbot warned. “It’s very important that even one crab be reported to us.”
2. Know What to Look For: Green crabs are not always green. They can be red, yellow, or orange—but always have five spines on either side of their eyes. Patty Menning of DFO describes them as having a distinctive “diamond or triangular shape.”
3. Volunteer: Join trapping and monitoring programs. As Mike Moore noted, volunteers have played a key role in retrieving traps and collecting DNA samples.
4. Clean Gear: Boats, trailers, and fishing equipment can transmit larvae between water bodies. Wash and dry gear thoroughly.
5. Stay Informed: Online training is available via the Invasive Species Council of BC and the Pacific Salmon Foundation, which also tracks sightings province-wide.
The Road Ahead
The fight against European green crabs is ongoing, but coordinated efforts on Cortes Island show that early intervention is possible. “If the Green Crab gets in, it’s really bad news,” Hall emphasized. Still, the unified response offers hope.
As Talbot summed up: “We still have limited crab in the Salish Sea. We respond quickly—and to date, we’ve been able to get a handle on all the populations we’ve found.”
The future of Cortes Island’s shorelines may well depend on staying one step ahead.
The Cortes Island Resonance Series:
- Restoring Life to Dillon Creek
- Friends of Cortes Island at Mansons Landing Provincial Park
- 30 Years of Foreshore Monitoring on Cortes Island
- European Green Crabs Reach Cortes Island
- Sabina Leader Mense & the Wolves of Cortes: A Story of Coexistence
- Vanishing Voices: The Global At Risk Species Crisis and Cortes Island
- The Call That Changed Everything: Western Screech Owls Return to Cortes Island
- The Story of the Island’s Streamkeepers
Top image credit: Someone holding up a European Green crab – courtesy FOCI
The Cortes Island Resonance series is produced with financial assistance provided by the Strathcona Regional District ‘s Grant In Aid Program and the Cortes Island Community Foundation.