Despite the date on the calendar, the sun was strong on my skin this weekend. As a warm-blooded creature, I don’t need the sun to stoke my metabolism but, boy, it sure felt good. That same sunlight is kicking off a mini-festival of sorts out in the Gulf of Maine among those powerhouses of the sea, phytoplankton. 

Each spring phytoplankton, tiny free-floating plants, take energy from strengthening sunlight as the northern hemisphere tilts once again closer to the sun. Due to the combination of available nutrients carried to the Gulf of Maine by its many rivers and the strong winds of the season, which cause mixing among layers of water, phytoplankton reproduce in great numbers. The sea turns green. That is good news for just about every creature that lives or passes through the Gulf of Maine. Fish, whales, sea birds, and young lobsters all find nourishment from phytoplankton. We do too. We eat the mussels, oysters, clams, and other filter-feeding animals that build up their body masses on phytoplankton.

In the fall there may be another, smaller bloom of phytoplankton in the Gulf. The sun, as my skin can attest, is still strong, although not as intense as it was in mid-summer. The surface layer of the Gulf is fairly warm, however the nutrients vital to phytoplankton have long since been used up. During the fall the atmosphere at our latitude becomes more turbulent, thus we have periods of strong winds that begin to mix the Gulf’s water together. The deep water layer, which still holds dissolved nutrients like nitrates and phosphates, intermingles with upper water layers. The phytoplankton in the warmer layers suck up those nutrients and bloom once again. 

Phytoplankton, like all living things, produce chemicals, some of which are harmful to humans. Phytoplankton aren’t alone in this ability. Think of mushrooms — certain species contain chemicals that can kill you very quickly. Consider the pufferfish, a delicacy known as fugu in Japan. Pufferfish contain tetrodotoxin, a substance up to 1,200 times more poisonous than cyanide, with no known antidote. 

One of the phytoplankton residing in the Gulf of Maine and throughout New England is a species called Pseudo-nitzschia. Recently the Maine Department of Marine Resources (DMR) closed shellfishing areas from the Canadian border to Penobscot Bay to all harvesting due to an outbreak of domoic acid, a biotoxin produced by Pseudo-nitzschia. Animals, such as clams, that filter seawater with high levels of domoic acid-producing Pseudo-nitzschia will eventually have high levels of the biotoxin in their tissues. Domoic acid doesn’t appear to harm shellfish, but in human beings it causes Amnesic Shellfish Poisoning (ASP). In low doses it causes permanent brain damage resulting in short-term memory loss. In higher doses, it kills you. 

Domoic acid has been a problem on the West Coast since 1991 (it also turned up on Prince Edward Island in 1987). Pseudo-nitzschia blooms in the spring and the fall led federal and state agencies to close the lucrative Dungeness crab and razor clam fisheries periodically since that time. In 2015 a bloom that sent domoic acid levels through the roof from southern California to northern British Columbia was linked to unusually warm ocean temperatures during the winter and spring of that year. The highest levels of domoic acid ever recorded were found in many marine species in 2015. 

While Pseudo-nitzschia is a common phytoplankton species in New England, it is not common to have a bloom of such intensity. In fact, a press release issued by DMR last week noted that “Maine has never experienced a toxic Pseudo-nitzschia bloom of this magnitude.” The bloom affects not only Maine but all coastal New England states. Rhode Island closed shellfishing areas in Narragansett Bay and along its eastern shore due to the presence of Pseudo-nitzschia. It was the first such closure ever, according to the state’s Department of Environmental Management (the ban was lifted last Saturday). Massachusetts closed shellfish beds in Buzzard’s Bay for the same reason, then expanded that closure to all waters south of Cape Cod, including Martha’s Vineyard and Nantucket. 

In time, this bloom will dissipate. Maine’s clams and mussels will get on with their business of straining the Gulf’s seawater for their suppers. The sun will wane in intensity, the water will chill, and winter will bring a temporary lull in the biological productivity of the Gulf. Then it will be spring and the phytoplankton will kick into high gear, again.