Why a tiny green crab could be a big problem in Quebec

It’s been years since the tiny but aggressive European green crab made its way over to the Magdalen Islands, and some researchers in Quebec are warning it could be headed for the Gaspé next.

The green crab was first spotted off the coast of the Magdalen Islands in 2004, but its population really began to surge in the area around 2023. 

The creature is characterized by its serrated, pentagon-shaped shell, and can grow up to 10 centimetres in size.

While the invasion is nowhere near as severe as it is in other provinces, researchers in the Lower St. Lawrence are working to track its movements to better predict where and when it might migrate next.

Piero Calosi, a professor of evolutionary physiology and biology at the Université du Québec à Rimouski, says the progressive warming of the Gulf of St. Lawrence has facilitated its migration. 

“We expected the change, but we didn’t expect the change to be so rapid,” said Calosi, who’s leading a study on the green crab. “Once an invasive species has arrived and the conditions are good, eradication is almost impossible.” 

The green crab feasts on about 150 different organisms, including everything from mussels and clams to baby lobster, posing a threat to the local marine ecosystem.

“Wherever he’s arrived, he has caused trouble,” he added. 

It’s the same temperature changes and climate phenomena that has led the nordic shrimp population to all but disappear off the coast of Matane, Calosi said.

“Although we only detect it presently in Quebec waters on the Magdalen Islands, given the context of climate change, how water temperatures are evolving ... I expect in the future that we will find it in more and more sites in Quebec," said Kathleen MacGregor, an aquatic sciences biologist with the department of Fisheries and Oceans Canada, who has been working on the same project. According to their mapping so far, she said, the green crab could even spread as far as the Côte-Nord. The larvae often travel with the current, but adult green crabs have also been known to hitch rides on lobster cages or on boats. 

While it may no longer be the principle way the species is spreading, MacGregor warns it’s important for boaters to clean anything that has touched the water to avoid inadvertently spreading the species. 

“Green crabs are particularly resistant. They can live for a couple of weeks out of water," MacGregor said. "They can hang out in the bottom of your car, for example, if one made it in there, waiting to get somewhere new.” 

The Comité ZIP, an environmental advocacy group on the Magdalen Islands, has been setting up traps and disposing of green crabs found in the area by freezing them. 

They did two major capture operations in 2025, catching about 1,000 of the creatures, and have been working closely with Calosi and researchers with the department of Fisheries and Oceans Canada to prevent the invasion from getting out of control.