Toxic Algae Closes Important Maine Shellfish Region

The unprecedented late-season bloom may be linked to warming waters and could be a preview of things to come

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If recent hiccups in the weather and the dire warnings of scientists haven’t galvanized people to combat climate change, maybe this will: a rise in sea temperatures is the likely culprit behind recent blooms of toxic algae in Maine, which cut off the supply of some of the state’s shellfish, reports Fred Bever at NPR.

The story begins in the autumn of 2016. As Peter McGuire at the Portland Press Herald reports, in September of that year, the Department of Marine resources found that shellfish harvested in the Down East area tested positive for the biotoxin domoic acid, which is produced by a class of algae called pseudo-nitzschia. While the shellfish can accumulate the toxin without harm, humans consumption of excissive dominic acid can lead to short term memory loss, seizures and even death. The 2016 closure marked the first time Maine has had to close a fishery because of domoic acid. 

“A closure for this toxin in eastern Maine is unprecedented, that is not anything anyone has ever seen,” Darcie Couture, former head of the state’s marine biotoxin program told McGuire at the time. “No one on this coast is that experienced with a domoic acid event. I don’t think it is sinking in how serious this is.”

But it turns out, the closure wasn’t just a one-time occurrence. Since that first outbreak, Down East has had to close shell fish grounds twice more. Then in September, 2017, another new problem popped up in Casco Bay, the important fishing grounds surrounding the city of Portland, when a bloom of the phytoplankton Karenia mikimotoi  appeared. It was the first time a bloom of that species was found in Maine. While the toxins from that species are not harmful to humans, it does often lead to fish and shellfish die-offs, which are thought to happen when the blooming phytoplankton takes too much oxygen out of the water.  

Then, in early December the pseudo-nitzschia also showed up in Casco Bay, leading to unsafe levels of domoic acid. It is the first time the area has dealt with this biotoxin, and the late bloom was unprecedented. “We thought we were done. We haven’t seen Pseudo-nitzschia blooms resurge like this,” Kohl Kanwit, director of the Marine Resources Department’s public health bureau told the Press Harold's McGuire last year. “It is really late in the season.”

Bever reports that the bloom hasn’t let up, even as the water has grown colder, and for the last month much of the area has been closed to mussel, scallop, oyster, quahog and clam fishing. While larger operations that can afford to have samples tested before sending shellfish to market have been able to continue operations, the bloom has temporarily put smaller harvesters out of business.

While the state of Maine would like to get people back on the water, they don’t want to give the green light too early. “It’s not like red tide where we have decades and decades of experience managing this. We don't have any historic data here,” Kanwit tells Bever. “So we are trying to gather as much information as we can while this bloom is going on.”

There’s reason to be cautious. In 1987, a bloom of Pseudo-nitzschia multiseries in Canada’s Prince Edward Island contaminated local mussels with domoic acid, which led to three deaths and more than 100 people becoming ill.

While that particular bloom was caused by unusual meteorological conditions, Bever reports that researchers believe the outbreaks in Maine might be associated with climate change. Research suggests that the Gulf of Maine is one of the fastest warming spots on earth. Currently the area experiences 66 more days of summer-like water temperatures than it did in 1982. That change is causing some marine species like lobster and mackeral to move north, and drives more nutrients to the surface, which leads to toxic blooms.

That rapid change may mean toxic blooms in the fall will become a regular occurrence in the area. “We’re wondering whether the warming in the surface may actually be selecting more for pseudo-nitzschia, so that in the fall, when the bloom happens, there's more of a chance that pseudo-nitzschia will be the ones that are blooming,” Mark Wells, a marine science professor at the University of Maine tells Bever.

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