New findings by a university-government research team show that levels of the marine bacterium Vibrio parahaemolyticus (Vibrio) have increased in tandem with water temperatures in the Gulf of St. Lawrence over the last quarter century.

For oyster growers already struggling with the oyster diseases known as MSX and Dermo, this adds a new source of financial risk.

MSX stands for multinucleate sphere unknown, an oyster disease caused by the parasite Haplosporidium nelsoni. Dermo (also called Perkinsosis) is caused by the parasite Perkinsus marinus. These diseases do not harm humans, but they can weaken oysters, slow their growth, cause high mortality, and devastate oyster farms.

Vibrio, in contrast, does not harm oysters, but it can cause severe foodborne illness in humans who eat raw or undercooked contaminated shellfish. For growers, it can mean harvest area closures, stricter handling requirements, and consumer confidence issues—all of which can hurt them financially.

“The Canadian Food Inspection Agency (CFIA) has only been monitoring for Vibrio in Atlantic Canada since about 2017, but oyster growers had been telling us they suspected a problem for a while,” says William Chapman, the study’s lead author and an MSc student at McGill University. “I hate to give more bad news to oyster growers, because they’ve had a tough time in the last few years. But it looks like Vibrio is only going to become a bigger issue.”

Oysters are the most common source of Vibrio foodborne illness in humans because they are often eaten raw. If levels of the bacteria are too high, oysters are deemed unfit for sale.

Vibrio populations have been increasing and spreading northward as the Atlantic Ocean warms due to climate change. When monitoring began in 2017, it was not known whether Vibrio was new to the area or had merely gone unnoticed.

The study was recently published in Global Change Biology Communications. Researchers used recent CFIA test results to build a computer model linking Vibrio levels to water temperature and other environmental conditions. They then used historical environmental data to estimate how Vibrio risk in the Gulf has changed since 1998. They found a substantial increase—and attributed it to warming ocean temperatures.

“No region or industry is immune to climate change. This marine organism is a harbinger of the many challenges facing the aquaculture sector as environmental change occurs,” says study co-author Dr. Josh Kurek, an associate professor of environmental science at Mount Allison University. “With global change, there will be winners and losers. Unfortunately, if ignored, an increase in Vibrio presents real risk to both human health and livelihoods.”

Despite the challenges, there may be a silver lining to this research.

“Our research can help the industry prepare for and mitigate the future impacts that Vibrio may bring as ocean waters continue to warm,” says Dr. Jeff Clements, a research scientist with Fisheries and Oceans Canada in Moncton and co-author of the study. For example, the findings could help growers better predict periods of elevated Vibrio risk and adjust their operations accordingly.

Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada.

This article was adapted and published with permission from Mount Allison University.

Photo credit: JC Clements