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Researchers Discover Yessotoxins to be a Culprit Behind Summer Mass Shellfish Mortality Events in Washington

Published on: 06/21/2021

Dying clams on Hood Canal, Rocky Bay, 2019.King et al, Harmful Algae, 2021

Back in the summers of 2018 and 2019, the shellfish industry in Washington state was rocked by mass mortalities of their crops, but the precise causes of these events were unclear. Now, researchers 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, which outlines how certain algal species could have killed off oysters and clams in summer mortality events that have occurred since the 1930s.

Prior research by NCCOS scientists established the presence of yessotoxins in several Pacific Northwest shellfish species, but because yessotoxins are not a threat to human health, their presence in Washington has not been closely monitored.  In 2018 and 2019, with SoundToxins partners’ eyes on the water and reports of dying shellfish from the Washington Department of Fish & Wildlife and the shellfish industry, the research team was able to collect shellfish and water samples for analysis.  This set the table to help answer the mystery of what was causing “summer mortality” in Washington state shellfish.

The researchers dug through data that had been collected by NOAA for different purposes, coupled it with current observations from the SoundToxins phytoplankton monitoring program and discovered that two yessotoxin-producing algal species, Protoceratium reticulatum and Akashiwo sanguinea, have been are correlated with shellfish mortality events stretching as far back as the 1930s. Supporting analytical data provided by NCCOS and Northwest Indian College investigators also confirmed that yessotoxins were present in some of these shellfish.

These findings have significant implications for shellfish growers in the region. SoundToxins has been conducting similar work for the Washington Department of Health for three ‘human health’ marine biotoxins since 2006. Adding the ‘shellfish killing’ plankton species to the real-time mapping capability of the SoundToxins partnership would allow for shellfish producers and natural resource managers to make informed decisions, such as harvesting their product early or otherwise strategizing to save as much crop as possible.

This research is also a demonstration of the value of partnerships between shellfish producers, plankton monitors, Native tribes, agencies and researchers. The study was led by scientists from NOAA’s National Centers for Coastal Ocean Science and Northwest Fisheries Science Center, Washington Sea Grant, Northwest Indian College, and AquaTechnics Inc. Support was provided, in part, by the NCCOS Monitoring and Event Response for Harmful Algal Blooms (MERHAB) project Monitoring and Management of Lipophilic Shellfish Toxins in Washington State.

Around the U.S., NCCOS is focused on supporting efforts that will help shellfish growers and managers mitigate the impacts of these (and other) HAB species that are a threat to aquaculture, including the recently established Aquaculture Phytoplankton Monitoring Network (AQPMN).

For more information, view the Washington Sea Grant press release.

Citation: Teri L. King, Nancy Nguyen, Gregory J. Doucette, Zhihong Wang, Brian D. Bill, Melissa B. Peacock, Shelbi L. Madera, Ralph A. Elston, and Vera L. Trainer. 2021. Hiding in plain sight: Shellfish-killing phytoplankton in Washington State. Harmful Algae, Volume 105, 102032. https://doi.org/10.1016/j.hal.2021.102032.

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