For the oyster industry in the Canadian province of Prince Edward Island (PEI), this winter has been no ordinary offseason.
Less than a year ago, Multinucleate Sphere Unknown (MSX), a disease caused by the parasite Haplosporidium nelsoni, was first discovered on PEI, and oyster farmers and harvesters are now anxiously waiting to see what will become of their livelihood when the ice thaws.
“Everybody's kind of holding their breath, not sure what the spring will bring when we raise our equipment,” Aaron Sweet, a fourth-generation farmer and the owner of PEI oyster-farming firm Sweet Oyster Co., said. “We wish we would have had insurance for this type of thing, but now that the disease is here, you can't really insure a burning building.”
Though the industry is waiting with bated breath, at least so far, the impacts of MSX have been minimal, according to Bob Creed, the executive director of the Prince Edward Island Seafood Processors Association.
“Overall, 2024 was a pretty good year. There were some fatalities in the spring fishery, but the commercial fall fishery was positive,” Creed said. “We’re in the early days of the detection of MSX, so it’s still evolving.”
What remains unclear, however, is how quickly MSX will spread and whether it will lead to mortalities.
According to data from past MSX infections in the U.S. and Nova Scotia, the time frame from detection of MSX to mortality can vary from several weeks, to up to 10 years, to no mortalities occurring at all.
“For high mortality, you need to have the right combination of host, environment, and pathogen,” said Ryan Carnegie, a professor of marine science at the Virginia Institute of Marine Science (VIMS), in a study titled “Living and Working with MSX – an Oyster Industry Perspective,” which was prepared for the PEI aquaculture industry. “Sometimes, it is very quick, but some cases present no mortality. Or, it takes a long time to reach a mortality event. In some areas, MSX was detected decades prior to a major mortality event.”
When MSX was discovered in Cape Breton, Nova Scotia, in 2002, the time between discovery and mortality varied greatly depending on the area. In some areas, oysters never experienced mortality, but in areas like the northeastern Nyanza Bay, oysters died around a year after detection.
When MSX does lead to mortalities, it is often devastating.
The parasite has a mortality rate of up to 95 percent, with the ability to wipe out entire operations. MSX in the Bras D’Or Estuary of Cape Breton wiped out 80 percent of oyster production in Nova Scotia in the early 2000s.
At a January 2025 meeting between a PEI legislative standing committee and industry stakeholders, Legislator Peter Bevan-Baker, who represents the New Haven-Rocky Point region, emphasized the gravity of the situation.
“At some point, there has to be an acknowledgement that this is going to have an incredible and devastating impact on the incomes and our society in general,” Bevan-Baker said.
That’s why industry stakeholders on PEI are hurriedly meeting with legislators and federal officials to prepare for the worst.
At the same January legislative meeting, Bob MacLeod, president of the PEI Shellfish Association, laid out steps the industry needs to take to weather the storm, which includes securing funding for breeding programs, hatcheries, and nurseries to develop an MSX-resistant seed; increased surveillance and testing for MSX; license buy-back programs for the province’s wild fishery; and a potential compensation plan.
The development of MSX-resistant seed stock, which is not guaranteed to be effective, will take at least six years, according to experts, meaning short-term pain in the industry is almost certain.
“The genetics of resistant strains, the best options for distribution of the genetic line to ensure widespread accessibility, and the potential for increased cost of hatchery-produced stock all need to be determined,” the “Living and Working with MSX – an Oyster Industry Perspective” study said. “The expense of such an effort should not be underestimated. It will require long-term investment in research, infrastructure, and technical capacity.”
Nevertheless, the industry is pushing forward; on 6 February, the PEI Shellfish Alliance announced a down payment on a nursery that will grow MSX-resistant oyster seeds.
“We're in uncharted territories here,” Creed said. “But, we've learned a lot talking with folks who have gone through this before.”
