A marine algae bloom that can carry a potentially deadly neurotoxin has forced the suspension of shellfish harvesting in parts of Down East Maine.

The state Department of Marine Resources reported Thursday that it was monitoring an active bloom of Pseudo-nitzschia, an ocean phytoplankton that carries domoic acid, a toxin that can cause sickness, memory loss and brain damage in humans. It’s the second year in a row that a toxic Pseudo-nitzschia bloom has halted harvesting of mussels, clams and oysters along large parts of the coast.

Before 2016, there was no record of a toxic bloom of this type in the Gulf of Maine.

The department’s public health section found levels of domoic acid that exceeded health standards in shellfish tested between Mount Desert Island and Gouldsboro. That area has been closed to harvesting and the department enacted a precautionary closure from Deer Isle to Machiasport, almost a third of Maine’s coastline.

Department spokesman Jeff Nichols said officials were monitoring the situation closely. There is no indication that contaminated shellfish have made their way to consumers, he said.

“It is impossible to determine at this point if the concentrations of domoic acid will increase in other areas,” Nichols said. “But we know that the phytoplankton that produces it grows rapidly, so we are carefully monitoring the entire coast and will be able to rapidly detect harmful levels of domoic acid and take action to protect the health of Maine’s shellfish consumers.”

Shellfishing areas are routinely closed by the state to protect consumers from tainted product because of stormwater runoff or “red tide,” another kind of algae bloom that produces a toxin known to cause paralysis or death in humans.

There is no way to tell if the current bloom is a repeat of last year, when some shellfish samples had over 100 parts per million of domoic acid, more than five times the food safety limit. That bloom triggered a rare recall of five tons of shellfish and an immediate harvesting suspension on a third of the state’s coastline. It took more than a month to reopen all harvesting areas.

It’s not yet clear what economic impact the current closure might have.

“We don’t know how the bloom is developing or how extensive it is going to be,” said Steve Archer, a senior research scientist with the Bigelow Laboratory for Ocean Sciences in Boothbay, where the state’s shellfish is tested.

“It is pretty small-scale at the moment compared to what it was. It has a long way to go to match last year’s event,” he said.

Blooms can be triggered by a variety of environmental factors, and it is unknown if this event was caused by the same species of Pseudo-nitzschia as last year, Archer said.

Domoic acid is stored in shellfish tissue and can cause amnesic shellfish poisoning, or ASP, if ingested. The poison targets the brain and can cause memory loss, sickness and brain damage. In a three-decade-old case from Prince Edward Island, two people died after eating shellfish tainted with domoic acid. Areas of the West Coast periodically undergo intense Pseudo-nitzschia blooms that have killed marine birds and mammals and caused extended closures of important fisheries, including razor clams and Dungeness crabs.

Fiona de Koning, co-owner of Hollander and de Koning mussels, spent Thursday morning calling customers to tell them about the closure. The company has five aquaculture leases around Mount Desert Island and Deer Isle. Only one is outside the current harvesting ban, de Koning said.

The Department of Marine Resources “has rigorous standards they stick to, that is why people have high confidence in the seafood from Maine,” de Koning said. “They know it is safe and healthy and they can enjoy it.

“Our customers like to have a consistent supply; of course it is not ideal, but they understand,” she said.

Maine’s shellfish monitors are experts at predicting toxic “red tides.” In the spring and summer, when red tides typically bloom, state monitors conduct weekly water and shellfish flesh tests at about 80 sites in the state, looking for elevated phytoplankton toxins. After the unexpected Pseudo-nitzschia bloom last September, the department updated protocols to monitor for a similar event and prevent another shellfish recall.

De Koning said she’s never had a red tide closure, but her mussel farms, and at least two dozen other aquaculture leases for oysters and mussels, have been at the epicenter of Pseudo-nitzschia blooms for two years. It’s a new problem, but uncertainty is part of farming shellfish, she said.

“This is just one of those things that happens when you are working with nature,” she said. “Whatever nature throws at us we have to adapt to and learn from.”

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

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