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From its first discovery 30 years ago in P.E.I., amnesic shellfish poisoning has become a baffling global scourge. A new study says ocean warming is the cause.

From its first discovery 30 years ago in P.E.I., amnesic shellfish poisoning has become a baffling global scourge. A new study says ocean warming is the cause

The odd symptoms started in Prince Edward Island on November 11, 1987, and continued showing up for a month: vomiting, diarrhea, memory loss and confusion, disorientation, seizures, coma. By the time the outbreak was over, 153 people had fallen ill, and three people were dead.

Quickly, investigators discovered that all the victims had feasted on blue mussels farmed off the island’s east coast. Still, they were baffled: the illness didn’t match the symptoms of any shellfish poison known anywhere in the world. A task force appointed by the federal government swiftly sprang into action. Just five days later, it identified a potent neurotoxin called domoic acid.

It was the first time it had been found in shellfish and the first report of illness in those who ate it. How had it gotten into the mussels? The investigators suspected that the mussels, too, had eaten something toxic. So they got out their plankton tow-nets and hit the water. Their findings were shocking: the toxin was being produced by a type of diatom, a microscopic marine plant with a hard silica shell. There is no antidote. Its poison is unaffected by cooking. They dubbed its effects amnesic shellfish poisoning.

Today, 30 years later, the toxic algae (in the genus Pseudo-nitzschia) have been found all over the world. In North America, fishery closures to avoid domoic acid poisoning have become routine. In March, high domoic acid levels closed commercial shellfishing off British Columbia and Rhode Island. California has had closures nearly every year since 2000.

Domoic acid has been found to affect many species, moving up the food chain from the creatures that eat the toxic plankton to the successive creatures that eat them. Among the victims: razor clams, Dungeness crabs, lobsters, sardines, anchovies, mussels, finfish, brown pelicans and cormorants. Mass die-offs of sea lions and northern fur seals in California are tied to the toxin. Necropsies show that the hippocampus sections of the mammals’ brains, used for navigation and memory, have lesions, much as they have in humans who have Alzheimer’s disease. Further, a recent paper suggests domoic acid may be responsible for mass strandings of long-finned pilot whales in Tasmania that have lost their ability to find their way. And a retrospective study in 2012 proved that Alfred Hitchcock’s 1963 horror movie The Birds was inspired by an incident near his home two years earlier when masses of sooty shearwater birds, driven crazy by domoic acid, attacked the shores in North Monterey Bay, California, vomiting anchovies.

Despite all the implications for public and wildlife health, scientists have struggled to find out precisely which environmental conditions make the algae appear. Now, a study led by Morgaine Mckibben of Oregon State University that was reported on in the January 2017 edition of the Proceedings of the National Academy of Sciences has found the answer. They discovered it by diving back through the records of outbreaks (domoic acid has been monitored among shellfish along the west coast of the U.S. since 1991) and matching them against ocean conditions.

The analysis revealed for the first time that outbreaks of domoic acid in shellfish along the west coast of North America were related to water temperature, possibly leading to changes in cellular and metabolic processes in the plankton. The warmer the water, the more likely the toxin is to appear at harmful levels and the more dangerous and widespread the poison becomes. Among the phenomena that affect the Pacific Ocean along the west coast of North America are two recurring ones: the Pacific Decadal Oscillation and the El Niño Southern Oscillation. From 2013 to 2015, there was an additional phenomenon known as a Northeast Pacific warm anomaly. Each of these produce huge shifts in water temperature, ocean currents and the dynamics of marine food webs that can last for months or even years. The weird warming through the Northeast Pacific in 2015 led to an unprecedented, record-setting episode of domoic acid poisoning in marine life.

The larger problem is the ocean is on track to get much warmer. We have burned so many fossil fuels, loading the atmosphere with so much heat-trapping carbon-based gas, that the ocean is soaking up some of the extra heat. The unavoidable implication is that, over time, domoic acid poisoning will become yet more common and persistent, rippling remorselessly through the ecosystem.

This is one of those unforeseen fallouts from climate change. A warmer world triggers a tiny change in the inner workings of common algae, and as a result vast swathes of sea life are at risk from a poison unknown just three decades ago. It makes you wonder: what else can we expect?a

ALFRED HITCHCOCK’S 1963 HORROR CLASSIC THE BIRDS WAS INSPIRED BY A FLOCK OF SOOTY SHEARWATERS, DRIVEN CRAZY BY DOMOIC ACID, ATTACKING THE SHORES NEAR HIS CALIFORNIA HOME