BOOTHBAY — Public health officials say they will use extreme caution to manage toxic algae blooms this year to prevent another expensive and potentially dangerous shellfish recall.

In the last two years, sudden toxic algae blooms of a previously unrecorded type of phytoplankton forced the Maine Department of Marine Resources to close huge sections of the Down East coast to shellfish harvesting and to issue rare recalls of tons of clams and mussels from as far away as Utah.

Recalls are bad for public health, business and Maine’s seafood brand, said Kohl Kanwit, head of the department’s public health division, during a workshop Tuesday for harvesters, seafood dealers, regulators and researchers at Bigelow Laboratory for Ocean Sciences in Boothbay.

“The risk is high; you never get 100 percent back” from a recall, Kanwit said. “It is really costly for the industry and bad all around.”

This year, the department isn’t taking any chances as it monitors for pseudo-nitzschia, a single-cell organism that can bloom unexpectedly and make domoic acid, a dangerous biotoxin that may cause amnesic shellfish poisoning, or ASP, in humans and animals. In serious cases, ASP can lead to memory loss, brain damage or even death. The first recorded ASP event, on Prince Edward Island in 1987, killed three people and made at least 100 sick.

The Department of Marine Resources plans more vigorous and sensitive monitoring for pseudo-nitzschia blooms and will immediately close harvesting areas if it detects toxin in the water, Kanwit said.

That approach is more conservative than previous years, when areas were closed after shellfish tests showed domoic acid levels at or above 20 parts per million, the federal health limit.

The problem is that between weekly testing, toxin levels can spike, from single digits to twice the federal limit. Once shellfish test above that limit, it takes two subsequent scores of below 20 parts per million two weeks apart before an area can legally reopen. Those restrictions meant some harvesting areas in Washington County and around Mount Desert Island were closed for almost two months in autumn 2016 and 2017.

The department is committed not to let that happen again, even if it means shorter, but more frequent closures, Kanwit said.

The department can reopen harvesting areas once toxin screens show safe shellfish, kind of like flipping a switch on and off, she added. That will be aggravating for people who depend on growing or harvesting shellfish, but right now it is the only way to keep possibly tainted product off the market.

“We don’t want to make closures where there are no toxins present, but we are gun-shy right now with two recalls in two years,” Kanwit said.

The department is also trying to make exceptions for high-value wild harvesting areas and large aquaculture operations. In the case of a toxic bloom, big shellfish farms can keep running as long as regular tests show their product is under the federal limit. That won’t work for most wild harvesters or those that operate the roughly 400 small aquaculture plots, too many for the department to test, Kanwit said.

Maine officials are expert managers of red tide, a toxic algae bloom that can cause paralytic shellfish poisoning and recurs almost every year. But those blooms are predictable and easy to monitor compared to pseudo-nitzschia, which blooms without warning and can become very toxic at low cell concentrations.

That happened last December, when a surprise late-season bloom closed most Casco Bay shellfishing areas, some of the highest areas of wild harvesters and shellfish farms in the state. Paul Plummer, harbor master in Harpswell, said harvesters he talks to are worried about closures this year.

“I think people are concerned,” Plummer said. “There is so much uncertainty, that is the biggest problem.”

CHANGING CONDITIONS

There are at least 26 species of pseudo-nitzschia in the Gulf of Maine and not all are toxic and even toxic species don’t always become so, said Kate Hubbard, a harmful-algae-bloom specialist at the Florida Fish and Wildlife Conservation Commission who has worked in the Gulf of Maine.

Pseudo-nitzschia blooms across the world, and there are regular events on the U.S. West Coast, including a prolonged and expensive bloom in 2015 that shuttered the lucrative Dungeness crab industry.

In Maine, Pseudo-nitzschia Australis, a particularly toxic species, was prevalent during 2013 research, but researchers still don’t completely understand why and how the algae become toxic.

“We are continuously learning more about what can influence domoic acid production,” Hubbard said.

The direct cause of pseudo-nitzschia blooms since 2016 is also a mystery, but researchers from the University of Maine suspect a combination of abnormally warm ocean temperatures, changing currents and a drought that cut off nutrient flow into the Gulf of Maine may encourage toxic blooms.

If this year has another hot, dry summer, that could mean another bloom on the horizon, said Mark Wells, a professor at the university’s School of Marine Sciences.

“Are these going to start becoming more normal conditions? This provides one avenue to start thinking about it,” Wells said.

One thing is for certain: If pseudo-nitzschia blooms come back this year, it will mean further disruption for Maine’s clam, mussel and oyster fisheries, worth $22.5 million last year.

“I hope that you have an understanding of why this is so challenging,” Kanwit told the workshop. “This is not surgical, this is not connecting A to B.”

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

pmcguire@pressherald.com

Twitter: PeteL_McGuire