How the P.E.I oyster fishery could find a way out of its MSX crisis

MSX, a pathogen deadly to oysters, has struck two different parts of the U.S. coast in the last 70 years.P.E.I. could look to that experience to mitigate the pain now that the disease has been found in Island waters.

MSX was found in Bedeque Bay, about 20 kilometres west of the Confederation Bridge, two weeks ago, and has since been identified in three other locations around P.E.I. Those areas have been quarantined, but the discovery raises questions about the future of the industry for the whole province.

Ryan Carnegie of the Virginia Institute of Marine Science has been researching MSX multinuclear sphere X for 22 years, and knows well the devastation it can cause in oyster populations.

"My fear is that there is a near-term period of some pain ahead with regard to the wild fishery in P.E.I.," he said.

"MSX is a very acute disease that can cause very high levels of mortality, and we've had a painful experience with that in the U.S."

Whileharmless to humans, MSX can cause mortalityof 80 to 90 per cent when it strikesa new population of oysters, Carnegiesaid.

'It's a sledgehammer'

MSX hit Chesapeake Bay in 1959.

At the time, the industry didn't know what to do about it, and the solution settled on was abandoning oysters altogether. The Chesapeake Bay industry turned to other species, such as clams.

A way out of the MSX crisis for P.E.I.'s oyster industry

2 months ago

Duration 7:52

Shellfish researcher Ryan Carnegie of the Virginia Institute of Marine Science tells Island Morning's Mitch Cormier about how the U.S. experience with MSX, a pathogen deadly to oysters, could help P.E.I. deal with the arrival of the disease.

Nature, however, had its own solution.

"It's not a gentle agent of natural selection. It's a sledgehammer," Carnegie said of MSX.

"The oysters that don't have the right set of genes are not going to survive for any length of time. So it very quickly will select for oysters that have what it takes to survive."

So while wild populations will crash, the progeny of those oysters that survive will carryMSX-resistant genes, and also survive. While the people making a living in the waters of Chesapeake Bay were looking the other way, the oysters returned.

No time to wait

Wild populations will recover from the advent of MSX, but it does take time. In evolutionary terms, because the pathogen is so deadly, this happens very quickly, said Carnegie, in two to three generations.

But that equates to eight to 10 years before an oysterpopulation gets seriously on the path to recovery too long for harvesters wondering how they are going to make a living.

When MSX hit the coast of Maine in 2002, the industry there did not wait.

"Those survivors of this MSX event, those can be the future of an intensive oyster aquaculture industry," Carnegie said.

"They knew by the mid-Atlantic experience that it was possible. Maine actually represents a really good case study for P.E.I. to look to."

That revamped industry would look different. Instead of collecting wild seed and spreading it on leases to grow to maturity, oyster growers would use seed from hatchery production of disease-resistant, domesticated oysters.

The P.E.I. industry would not have to depend on seed oysters from as far away as the Eastern Seaboard, said Carnegie. MSX infections in Cape Breton's Bras d'Or Lakehave created MSX-resistant oysters there.

A cycle that's not fully understood

For the most part, mortality rates in a resistant population are zero in MSX-infected waters, Carnegie said.

MSX does come and go in cycles, and the exception is years when the disease is just returning. It appears thatresistance to the disease in a population will wane over time.

Scientists have a good idea what makes MSX go away. It cannot survive cold winters, and also needs relatively high salinity in the water. A wet season can lower salinity in coastal waters, knocking the disease back.

What leads to the return of MSX is less understood.

"We haven't learned where MSX is lurking when it's not infecting oysters," Carnegie said.

Almost certainly there is an intermediate host, perhaps a worm or copepod, that carries the disease and reinfects oysters when the conditions are right. But scientists have been unable to identify that host.

"It's frustrating to a lot of people that we've not been able to solve this puzzle of what MSX is doing when it's not infecting oysters. It really restricts our ability to manage this parasite," Carnegie said.

"It's especially painful when we see what's happening in Prince Edward Island and can envision the pain that industry is going to experience as this plays out."

But ramping up domestication has been successful in the U.S., he said, and he believes it can work for P.E.I. too.