June 20, 2018
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Maine scientists work to combat fatal oyster disease

By Abigail Curtis, BDN Staff

DAMARISCOTTA, Maine — Officials from the Maine Department of Marine Resources spent part of Thursday diving in the Damariscotta River to gather oysters to test for the disease MSX, which is deadly to the lucrative bivalve.

The disease is caused by the parasite haplosporidium nelson. It  doesn’t hurt humans or other sea life, and also presently appears to be confined to the Damariscotta River, which went under emergency quarantine orders in October in an effort to halt its spread.

Jon Lewis, a biologist at the Maine Department of Marine Resources, said Thursday that 96 percent of the wild oysters scientists have tested there have MSX.

The river’s warm, shallow waters produce about 75 percent of the oysters in Maine. And though infection does not always lead to death, he said, the disease’s prevalence in the river, which produces about $1.5 million worth of oysters annually, is a big concern.

It is also leading to genetic research at the University of Maine, where scientists are aiming to develop a brood stock of oysters that are resistant to the disease.

“It’s here. It’s liable to kill off larger oysters,” he said. “The best hope is that the cold weather will knock it down.”

Biologists and oyster farmers don’t yet know if the winter temperatures slowed its spread, which is “inflamed” by warmth, Lewis said.

Chris Davis of the Pemaquid Oyster Co. and director of the Maine Aquaculture Innovation Center said growers on the river are definitely being impacted by the MSX outbreak.

“The growers are seeing 50 to 90 percent mortality — it’s not good,” said Davis. “It means everyone’s going to have a lot less product from the Damariscotta. It seems to be killing older animals as they get closer to market.”

Oysters are continuously pumping water through themselves, explained Davis, and the thought is as they take in more and more of the parasite, they finally reach their breaking point and die.

Lewis said that he believes MSX has about a 30 percent mortality rate.

The parasite that has been identified in the Damariscotta River appears to be genetically closely related to a parasite that has caused “dramatic” problems for the oyster industry in Massachusetts, Lewis said. It is not closely related to a parasite that has been found to have affected oysters in much smaller quantities in two other midcoast rivers, the New Meadows River and the Sheepscot River.

Those oysters are not dying, he said, contrary to what is happening in Damariscotta. This information has led scientists to believe that the parasite was somehow introduced in the Damariscotta River. He said that could have happened in numerous ways and that it is “completely unlikely” that the source will be identified.

Because of the quarantine, oysters can not be taken from the Damariscotta River or Johns Bay and placed into another body of water, Lewis said.

“But this doesn’t mean that people can not continue to harvest out of the Damariscotta River,” he said. “They are harvesting.”

Since one method of control against MSX is to harvest the oysters early, Lewis said that consumers may spot somewhat smaller oysters on the market.

The thinking is that when the next crop comes online, farmers will be able to harvest the oysters before they die, taking them a bit earlier. While it varies from farm to farm, most will be doing that harvest by midsummer, said Davis.

Another control method would be to develop resistant oysters, which is what is happening now at a veterinary diagnostic laboratory at the University of Maine.

Most oyster growers use derivatives of MSX-resistant oyster lines developed at Rutgers University in New Jersey. Maine growers haven’t had to use them, as MSX hasn’t been a problem here, said Davis.

But Maine aquaculturists are bringing in those lines now, and the Aquaculture Innovation Center is collaborating with the University of Maine to crossbreed those lines with some Maine stock that grows faster than other oysters, said Davis.

Scientists and oyster farmers are working closely together in an effort to mitigate MSX’s detrimental effects.

“People have their fingers crossed,” Lewis said.

The outbreak will mean tough times for some businesses. At least one grower isn’t harvesting, and the crews aren’t working, said Davis. His farm continues to harvest, Davis said.

“It’s going to be a little tougher until things get going,” he said.

BDN reporter Matt Wickenheiser contributed to this report.

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