Culprit Behind Summer Mass Shellfish Mortality Events in Washington Discovered

In a new paper, scientists outline how certain algae species could have killed off oysters and clams in summer mortality events that have occurred since the 1930s. Read the paper at

Back in the summers of 2018 and 2019, the shellfish industry in Washington state was rocked by mass mortalities of their crops. “It was oysters, clams, cockles — all bivalve species in some bays were impacted,” says Teri King, aquaculture and marine water quality specialist at Washington Sea Grant. “They were dying, and nobody knew why.”

Now, King and partners from NOAA National Centers for Coastal Ocean Science, NOAA Northwest Fisheries Science Center, Northwest Indian College, and AquaTechnics Inc. think that they have finally sleuthed out the culprit: high concentrations of yessotoxins, which are produced by blooms of certain phytoplankton. The researchers’ findings have been published in a new open-access paper in the Elsevier journal Harmful Algae.

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