Research paper points to reasons for decades of shellfish mortality

Photo by US Fish & Wildlife Service

Researchers have found that yessotoxins, produced by certain phytoplankton, are likely to be the cause of the summer mass shell mortality events in Washington.

In a new article, shared to KXRO by Washington Sea Grant, scientists describe how certain species of algae may have killed oysters and clams in summer mortality events since the 1930s.

During the summers of 2018 and 2019, Washington state’s shellfish industry was rocked by massive mortalities of their crops. “It was oysters, clams, cockles – all bivalve species in some berries were affected,” said Teri King, aquaculture and marine water quality specialist at Washington Sea Grant. “They were dying, and no one knew why. “

Now King and his partners at the NOAA National Centers for Ocean Science, NOAA Northwest Fisheries Science Center, Northwest Indian College and AquaTechnics Inc. believe they have finally found the culprit: high concentrations of yessotoxins. , which are produced by the blooms of certain phytoplankton.

The researchers’ findings were published in a new paper in free access in the Elsevier Harmful Algae newspaper.

In the article, it is stated that Willapa Bay was “not routine monitoring sites for SoundToxins”, but was a site “where shellfish mortalities have occurred”.

Because yessotoxins are not a threat to human health, their presence in Washington has not been closely monitored.

The researchers excavated the data that had been collected by the NOAA Northwest Fisheries Science Center and the NOAA National Centers for Coastal Ocean Science for different purposes, paired it with current observations from the SoundToxins phytoplankton monitoring program, and found that these species of algae, Protoceratium reticulatum and Akashiwo sanguinea, are correlated with shellfish mortality events dating back to the 1930s.

In 2018 and 2019, with the eyes of SoundToxins partners 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 shell samples. and water for analysis. This set the table to help answer the mystery of what was causing “summer mortality” in shellfish in Washington state.

Later in the document, he refers to events in the spring of 2018 that saw shellfish farmers in Willapa Bay report “unusual” clam mortality events that saw the bivalves resurface before they died.

Growers at the time reported losses of Japanese clams of 30-90% on commercially grown beds in Willapa Bay.

After investigation, it was suggested that an algae bloom may have produced a toxin or substance that caused massive tissue inflammation resulting in the death of affected clams.

These findings have important implications for shellfish farmers in the region.

“We are working to be able to help growers count the cells of yessotoxin-producing organisms in water and correlate them to an action level,” says King. “SoundToxins has conducted similar work for the Washington Department of Health for three ‘human health’ marine biotoxins since 2006. Adding the ‘shell-killer’ plankton species to the partnership’s real-time mapping capability SoundToxins would allow shellfish producers and resource managers to make informed decisions, such as harvesting their product early or strategizing to save as much harvest as possible.

King says this research is also a demonstration of the value of partnerships between shellfish producers, plankton checkers, native tribes, agencies and researchers.

“We were a team of oceanographers, biologists and chemists working together to answer these questions,” King said. “People are able to think differently when you have different people at the table. Sometimes that’s even the key to solving long-standing mysteries unfolding in your backyard.

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