All of the areas closed due to red tide remained closed Friday.

PORTLAND (AP) – Officials have lifted a statewide ban on shellfishing but kept two-thirds of the coast off limits because of the most toxic red tide to hit Maine in decades.

All closures that were in effect before a ban was placed on the entire Maine coastline Monday remained in effect Friday. There also was a new closure for mussel harvests from Biddeford Pool to Flying Point in Freeport.

As of Friday, the Department of Marine Resources had imposed seven closures for soft shell clams and eight closures for mussels, whelks and carnivorous snails.

Many states close their entire coastlines during a red tide. Maine, however, has a complex testing and monitoring system that allows safe areas to stay open.

The toxin in red tide is among the most potent found in nature. At high levels in humans, it can cause numbness, dizziness, tingling, nausea and even death.

Levels of the toxin measured earlier this week were higher than they’ve been since the 1970s, according to the Department of Marine Resources.

David Townsend, director of the University of Maine’s School of Marine Sciences and professor of oceanography, said a foggy summer followed by abundant sunshine last month helped foster a late algae bloom.

“What happened I think is the (algae) cells were held in abatement at a time when they normally would reach high densities,” said Townsend. “They held off for so long that by the time the sunny weather hit, they showed explosive growth.”

Townsend, who has conducted research on red tide in the Gulf of Maine for the past five years, said the red tide is so toxic because of its high density.

“Whenever there are enough cells to turn the water a red color, that is a major bloom phenomenon, which is what just happened,” he said. “We get years like this every 20, 30 years.”

Townsend said red tide typically appears offshore, but wind or currents move the algae toward the shore where it affects mussels and clams.

Mussel dealers said the shutdown has hurt Maine fishermen, forcing dealers to import more mussels from Canada.

“This was definitely a setback for the week,” said Mark Peterson of Great Eastern Mussel Farms Inc. of Tenants Harbor. “We were bringing in product from Canada, so we weren’t really that short of product.”

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