June 18, 2018
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Red tide season may have ended

By Kevin Miller, BDN Staff

BELFAST, Maine — Maine’s red tide season appears to have ended almost as quickly as it began.

And although it is too early to say for sure, one red tide researcher said this year’s abbreviated season could be an indication that Arctic melting due to climate change is already altering red tide trends in the Gulf of Maine.

After a sudden spike in numbers in late June and early July, the algae that cause red tide have largely dissipated in most Maine coastal waters, although some areas remain closed to certain types of shellfish harvesting.

The abbreviated season — if sustained — will likely come as welcome news to a shellfish industry that has been hit hard by harvesting restrictions in recent years. Consuming shellfish harvested from areas affected by red tide can cause paralytic shellfish poisoning, a potentially fatal disorder.

“Hopefully, we will have a nice, early end to the red tide season,” said Darcie Couture, director of the Maine Department of Marine Resources program charged with monitoring shellfish beds and regulating harvesting due to red tide. “We will continue sampling because we don’t want to rule out the possibility that we may have another bloom in the fall.”

David Townsend, a professor of oceanography at the University of Maine School of Marine Sciences, likewise couldn’t rule out a fall bloom.

But during a weeklong research cruise of the Gulf of Maine and George’s Bank that just wrapped up on Friday, Townsend and his colleagues found only a single sample of the algae that causes red tide. And that sample was on the southern edge of George’s Bank.

“There is nothing out there,” Townsend said.

So why the rapid disappearance in Maine waters?

Couture pointed out that shellfish bed closures in Maine often occur when northeasterly winds blow surface water carrying the algae into coastal areas. Maine has experienced far less of these types of winds this year than last year, when the state experienced widespread closures, especially in the Cobscook Bay area.

Water temperature, nutrient levels and sunlight also appear to play a factor in red tide blooms.

Townsend said he also believes the 2010 red tide season ended early because of lower-than-typical nutrient levels in the Gulf of Maine. And Townsend suggested that could be the result of the melting of Arctic sea ice.

Alexandrium fundyense, the algae that cause red tide and therefore paralytic shellfish poisoning, require both sunlight and nitrogen to thrive. But Townsend said nitrogen levels were lower than normal this year, suggesting that although there were large numbers of Alexandrium cells early on, they essentially ran out of food.

But Townsend and other researchers believe there may be a bigger change taking place that could affect both the algae that causes red tide and other organisms.

“The [waters] of the Gulf of Maine are going through some changes that I and some of my colleagues believe is related to Arctic melting, and that is changing the nutrient regime,” Townsend said.

In particular, Townsend and his colleagues are exploring the possibility that the Gulf of Maine is becoming “fresher” — i.e. less salty — and cooler due to accelerated melting in the Arctic. This fresher water flowing down from the north via the Labrador Current contains fewer nutrients, according to a research co-written by Townsend that was published in the journal Continental Shelf Research.

Townsend said Saturday that they believe those low-nutrient levels could continue.

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