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Extreme weather could help invasive green crab crawl along Vancouver Island, B.C. coast

European green crab is identifiable by five spines on the side of each eye

An invasive crab lurks among the native species of the Salish Sea, but where they appear next is relatively unknown.

Across Greater Victoria, signs at busy beach accesses alert visitors to be on the lookout for this small crab that can irreversibly alter ecosystems.

The European green crab is present all the way up the west coast, but that invasion has been going on for over two decades, said Tom Therriault, a research scientist with Fisheries and Oceans Canada (DFO).

First found on the east coast in 1951 in the waters off New Brunswick, they have expanded to many locations in the Atlantic. In the west, the European green crab likely arrived in the late 1990s through larval transport.

They moved naturally, through larval drift, up the West Coast and were first reported on the U.S. side of the border in fall 2016, with subsequent discoveries in 2018. They remain pretty sporadic on the Canadian side, Therriault said.

Now they’re found along the entire west coast of Vancouver Island. Whether the invasive crab is crawling up the inside coast remains largely unknown.

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The DFO is working with local government and staff in Haida Gwaii to create delineation there – the furthest north they’ve encountered adult crabs – after multiple sightings were documented in July 2020.

“We’re now seeing conditions outside the ‘normal’ for us in B.C. and we don’t necessarily understand how that’s going to affect the invader,” Therriault said. Extreme weather events, such as last summer’s heat dome and changing precipitation patterns, can shift the ecology and if that proves in favour of green crab larvae, they could flourish.

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The European green crab is one of the 10 most unwanted species in the world, according to the DFO.

It destroys beds of shellfish and feeds on native animals such as clams, oysters, mussels, small fish and young crabs and lobster – often beating native species to the buffet.

While there’s no reason not to expect to see a green crab on Island beaches, it’s impossible to have site-specific predictions, Therriault said. For that reason, signs dot the busiest beaches in Greater Victoria and elsewhere on Vancouver Island. The signage targets high-use beaches to educate those flipping rocks and taking walks about what is native and what is critical to report.

One key identifier makes the outlier obvious – five clear spines on the side of each eye. While called green, it could be yellow, orange, or mottled and can be as large as four inches across.

Anyone who finds a European green crab on Vancouver Island shorelines should report the invasive species. Take photos and note the exact location, with GPS coordinates if possible, along with the date and identifying features. DFO can be reached toll free at 1-888-356-7525 or via email at

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