Extreme weather could help invasive green crabs crawl along the BC coast – Salmon Arm Observer


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

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

The European green crab is present all along the west coast, but this invasion has been going on for more than two decades, said Tom Therriault, researcher with Fisheries and Oceans Canada (DFO).

First found on the east coast in 1951 in waters off New Brunswick, they have spread to many places in the Atlantic. In the west, the European green crab probably arrived in the late 1990s by larval transport.

They moved naturally, by larval drift, to the west coast and were first reported on the US side of the border in the fall of 2016, with subsequent discoveries in 2018. They remain quite sporadic on the Canadian side, a said Therriault.

They are now found throughout the west coast of Vancouver Island. Whether the invasive crab crawls along the inland coast remains largely unknown.

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

“We are now seeing conditions outside of ‘normal’ for us in BC and we don’t necessarily understand how this is going to affect the invader,” Therriault said. Extreme weather events, such as last summer’s heat dome and changing rainfall patterns, can alter the ecology and if this proves in favor of green crab larvae, they could thrive.

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

It destroys shell beds and feeds on native animals such as clams, oysters, mussels, small fish, and young crabs and lobsters – often beating native species at the buffet.

While there’s no reason not to expect to see a green crab on the island’s beaches, it’s impossible to have site-specific predictions, Therriault said. For this reason, signs line the busiest beaches in Greater Victoria and elsewhere on Vancouver Island. Signage targets busy beaches to educate those flipping rocks and walking about what’s native and what’s essential to report.

A key identifier makes the outlier obvious – five clear spines on the side of each eye. Although called green, it can be yellow, orange, or mottled and can measure up to four inches in diameter.

Anyone who finds a European green crab on the shores of Vancouver Island should report the invasive species. Take photos and note the exact location, with GPS coordinates if possible, as well as the date and identifying details. DFO can be reached toll-free at 1-888-356-7525 or by email at [email protected]

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