Climate change bringing oyster bacteria to Atlantic Canada: study

Oysters harvested in Canada are seen at Bryan Szeliga's Fishtown Seafood in Haddonfield, N.J., Thursday, March 6, 2025.

For the last few years, many oyster farmers in the Maritimes have been dealing with diseases that cut into their supplies and bottom line. MSX and Dermo, which stunt the growth rates of oysters and increase their mortality, have both been found in Nova Scotia, New Brunswick and Prince Edward Island.

The diseases are causing problems for farmers and fishers as they try to collect enough oysters in the regular season, but a new study says a bacteria moving into Atlantic Canada could cause even more headaches.

The study, which was a collaboration between Mount Allison University and the federal government, found that Vibrio parahaemolyticus has increased its presence in the Gulf of St. Lawrence in the last 25 years as the waters have been warming due to climate change.

What are the symptoms?

The bacteria, which can survive in shellfish during warm seasons, causes diarrhea, abdominal cramps, chills, vomiting and low-grade fever in people, according to the federal government.

“Vibrio is very severe food poisoning,” said William Chapman, lead author for the study. “It’s a nasty group of bacteria. We really don’t want this around.”

Chapman, an environmental science graduate, said he was inspired to launch the study when he went to buy oysters around Labour Day 2022.

“I was at this oyster farm and they said to me it was the first weekend they were open since July,” he said. “They were closed for Vibrio. It was a really bad year.

“That’s where the project started, me trying to figure out what was happening.”

CFIA data

Dr. Josh Kurek, co-author of the study, said they obtained data from the Canadian Food Inspection Agency (CFIA) on the presence of Vibrio in oysters from 2017 to 2023, and compared it to water conditions going back 25 years, which helped establish a link with climate change.

“It’s likely it’s always been here in low abundances,” Kurek said. “The Gulf of St. Lawrence is among the fastest-warming oceans in the world. Because waters are warming, it’s becoming more common.”

Chapman said oysters in 2023 were up to 10 per cent more likely to fail a food inspection quality test for Vibrio than they were in 1998.

He also noted the CFIA has done a good job of ensuring oysters with Vibrio don’t make it to market.

“They started a surveillance program to monitor the whole country,” he said. “They’re very proactive about it.”

Strategies to follow

Unlike MSX and Dermo, Vibrio does not affect oysters, but removing impacted shellfish from the market as farmers are also dealing with diseases that lessen their supply could have severe financial implications for the industry.

“They’re going to have to evolve the industry in a future that likely has much warmer water,” Kurek said. “Farmers are aware of this and that’s how we became aware of it.

“There are strategies they can follow. When you buy oysters and you’re going to consume them raw, you should carry them in a cooler.”

Chapman said their study looked at the past, so he’s eager for the next stage of the research to think about the future as climate change continues.

“What’s the situation going to look like 40, 60, 80 years down the line?” he said.

“I absolutely will still eat oysters. We shouldn’t be scared all the time. The food inspection agency has done a really good job with their monitoring program.”