Marine Neurotoxin More Widespread Than Ever Before

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Neurotoxins produced by algae have been blamed for deaths of sea lions, like this one found on Hermosa Beach, California, and have been found in a wide variety of marine animals. Lucy Nicholson / REUTERS

An enormous bloom of algae in 2015 off the U.S. West Coast created an unprecedented amount of a neurotoxin called domoic acid, which has since been found in many types of marine mammals like sea lions and, for the first time, in the meat of various commonly consumed commercial fish species.

Although the amount of the neurotoxin found in fish is still well below the limit deemed safe for human consumption, other types of seafood have been seriously contaminated, says Raphael Kudela, a professor of ocean sciences at University of California, Santa Cruz (UCSC). Authorities have detected significant levels of domoic acid in California populations of anchovies, sardines, Dungeness and rock crabs, mussels, clams and oysters, leading to closure in all of these fisheries at some point in 2015 off California and other Western states. Dungeness crabs have been particularly hard hit, and they still show high levels of the toxin.

"Fishermen, and communities that rely on fisheries, are being devastated," says Kudela, who presented his findings at the American Geophysical Union annual meeting in San Francisco on December 18.

Domoic acid is produced by a type of algae called Pseudo-nitzschia, which flourished in massive blooms from April to October of this year off the U.S. West Coast, nurtured by above average water temperatures and high levels of nutrient runoff. Usually blooms are localized and pop up only in the spring and fall, when cold upwelling water is less prevalent. But not so in 2015, Kudela says. And forecasts suggest that due to a strong showing of the weather pattern called El Niño, 2016 may be in for warmer-than-average water temperatures as well, perhaps the warmest since 1997.

A study by UCSC researcher Peter Cook and his colleagues published December 14 in the journal Science found that exposure to domoic acid damages the spatial memory of sea lions, leading some to get lost and die. Domoic acid behaves similarly to the neurotransmitter glutamic acid, binding to and eventually killing receptors in the hippocampus and causing short- and long-term memory loss in mammals, including humans.

In 1987, an outbreak of domoic acid poisoning in contaminated Prince Edward Island shellfish killed three and sickened more than a hundred people. Since then, authorities have regularly tested for the substance and shutdown fisheries when it's detected.