Parts of the Down East coast have been reopened to shellfish harvesting because of declining levels of a potentially harmful biotoxin produced by an unusual algae bloom.

On Thursday, the Department of Marine Resources re-opened some of the coastline between Calais and Cutler for the harvest of clams, mussels and carnivorous snails, and said clamming will be allowed on a portion of the coast between Isle Au Haut to Winter Harbor.

Shellfish harvesting on much of the Down East coast remains restricted because of an algae bloom that produces a toxin that can cause amnesic shellfish poisoning, or ASP, in humans.

It is unclear if the limited reopening Thursday means the bloom is clearing up or if harvesting bans will be removed in other areas soon.

“We can’t speculate, but we continue to test shellfish and phytoplankton along the coast, both inside and outside the impacted areas, and will re-open areas as soon as test results allow,” said Jeff Nichols, a spokesman for the department of Marine Resources.

Lifting the emergency restrictions was a relief to clammers who have been kept off the flats for the last two weeks.

Tim Sheehan, who buys clams through his company Gulf of Maine Inc. in Peabody, said some clammers started digging in Cobscook Bay as soon as the opening was announced. He planned to keep his store open late on Thursday to buy product to make up for the shutdown.

“We probably won’t get much, only about a third of our good flats are open,” Sheehan said. “At least it’s better than nothing.”

Roughly one-third of Maine’s coastline was closed two weeks ago after tests of clams and mussels showed highly elevated levels of domoic acid, the toxin linked to ASP. Approximately five tons of clams, mussels and quahogs caught around the Jonesport area were recalled because of possible contamination.

Mussel harvesting is still closed from Deer Isle to Machiasport, and clam harvesting is restricted from Bar Harbor to Machiasport. There also are closures for quahogs and carnivorous snails in those areas.

Maine periodically closes shellfishing areas because of red tide – a different harmful algae bloom that can produce the toxin that causes paralytic shellfish poisoning. But it has never had to close off harvesting areas out of concern for ASP. Domoic acid is sometimes produced by a marine phytoplankton called Pseudo-nitzschia that grows quickly, or blooms, in the right conditions. Filter feeders like mussels and clams eat the algae and store the toxin and can transmit it to humans.

At high levels, domoic acid can cause gastrointestinal discomfort and illness, and more severe symptoms such as respiratory problems, brain damage, memory loss and even death. Although cases of ASP in humans are rare, researchers believe it is more common in marine mammals like sea lions.

The federal limit for domoic acid is 20 parts per million in shellfish flesh. Harvesting areas are usually closed if testing shows that level or higher. Test scores for Maine shellfish in the state’s affected areas were as high as 129 parts per million, Nichols said two weeks ago.

A Pseudo-nitzschia bloom also has forced shellfishing closures in southern New England.

A week ago, Rhode Island authorities closed major shellfishing areas in Narragansett Bay and most of its eastern coastline because of a major toxic algae bloom. The closure remains in effect, although early tests show no toxins in shellfish. This is the first time the state has issued closures because of a harmful algae bloom, the Rhode Island Department of Environmental Management said.

Massachusetts put a shellfish closure on Buzzard’s Bay, bordering Rhode Island, at the same time as its neighbor. Massachusetts expanded its closure this week to all the waters south of Cape Cod, including Martha’s Vineyard and Nantucket.

Kate Hubbard, an expert on harmful algae blooms in Florida who sometimes works with the Woods Hole Oceanographic Institute on Cape Cod, said Pseudo-nitzschia is common in New England waters, but it is still unclear what factors produced a toxic bloom this year. Wind, sunlight, hydraulic conditions and ocean water temperatures could be involved, and there is no indication how long the bloom could last, she said.

“We are still very much in the process of working to try and understand why this year was so special,” Hubbard said.

Peter McGuire can be contacted at 791-6325 or at:

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