The 2021 heat wave created a ‘perfect storm’ for shellfish die-offs

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It’s hard to forget the excruciating heat that blanketed the Pacific Northwest in late June 2021. Temperatures in Oregon, Washington and British Columbia soared well above 100 degrees Fahrenheit, with Seattle setting a record all-weather heat of 108 degrees on June 28.

During the heat wave, also known as the heat dome, scientists and community members noticed a disturbing increase in dying and dead crustaceans on some beaches in Washington and British Columbia, both in the Salish Sea and along the outer coast. The observers quickly realized that they were experiencing an unprecedented event and they organized themselves to document the massive shellfish mortalities in real time.

Now, a team led by the University of Washington has compiled and analyzed hundreds of these field observations to produce the first comprehensive report of the impacts of the 2021 heat wave on seashells. The researchers found that many crustaceans fell victim to a “perfect storm” of factors that contributed to widespread death: the lowest low tides of the year occurred on the hottest days of the year – and during the hottest hours of the day. The results were published online June 20 in the journal Ecology.

“You really couldn’t have come up with a worse-case scenario for intertidal organisms,” said lead author Wendel Raymond, a researcher at UW Friday Harbor Laboratories. “This analysis gave us a very good overall picture of the impact of the heat wave on shellfish, but we know that’s not even all.”

The research team leveraged existing collaborations between tribes, state and federal agencies, universities, and nonprofit organizations. They designed a simple survey and five-point scoring system (1 = much worse than normal to 5 = much better than normal) and asked participants to provide scores based on their knowledge of a species at that place. In total, they collected 203 sightings from 108 unique locations, from central British Columbia to Willapa Bay, Washington.

“The strength of this study and what it really highlights is the value of local knowledge and also the importance of understanding natural history,” said co-author P. Sean McDonald, associate professor at the UW in Environmental Studies and Aquatic and Fisheries Sciences. “It’s the first step and a snapshot, if you will, of what seashells experienced on beaches during the heatwave.”

The researchers found that each species’ ecology contributed to its overall success or failure in surviving extreme heat. For example, some seashells that naturally burrow deep below the surface, such as butter clams, generally fare better than those that typically rise at low tide to just below the surface of the sand, such as cockles.

They also found that location was important. Shells on the outer coast experienced low tide about four hours earlier than shells on the inner beaches. For inland crustaceans, low tide – or when most crustaceans were exposed – hit around solar noon, when the sun was directly overhead.

Additionally, air temperatures were much higher at interior sites compared to the outer coast, which caused more stress on interior populations. For example, California mussels, found almost exclusively on the outer coast, mostly survived the heat while bay mussels, found in more inland coastal sites, were more likely to die from exposure to heat. heat. Increased water movement and wave action on the outer coast also likely contributed to mitigating the effects of heat on shells along these beaches.

“The timing of low tide helps determine when and where organisms may be exposed to heat stress and can structure behavior and distribution. In this case, organisms at locations that are already exposed to air at the day were very unlucky that temperatures soared so high,” said co-author Hilary Hayford, director of habitat research at the Puget Sound Restoration Fund.

Many seashells don’t tend to move around much on a given beach, so where they naturally live in the intertidal zone also contributed to their success or failure, the researchers found. For example, acorn barnacles that live higher on shore have generally been more affected than clams and oysters that are lower on the beach and more likely to remain underwater.

“Although this event had negative effects on marine life, there is hope in this work. Not all places and species were affected equally, offering clues to the pathways resilience in the future,” said co-author Annie Raymond, a shellfish biologist from the Jamestown S’Klallam Tribe.

Perhaps most surprisingly, the researchers noticed interesting trends in shellfish survival rates on the same beach. In some places, the shells in the path of the freshwater runoff on part of the beach survived, while others a few miles away perished. If a tree hung over part of a beach and shaded the sand, those shells usually made it out while others didn’t. Co-author Julie Barber, a senior shellfish biologist with the Swinomish Indian tribal community, recalls seeing these patterns while walking on the beaches of Skagit Bay and, in some places, being surrounded by dead cockles in all directions. directions.

“It was quite unsettling, and I’ve never seen anything like it,” Barber said. She remembers exchanging emails with colleagues across the region as they noticed similar mass deaths on their local beaches, then realizing they had an urgent need to coordinate and document this. that was happening.

“This effort was a great demonstration of how collaborators can come together around a common cause — which, in our case, was trying to figure out what happened to those seashells,” Barber said.

Because the heat wave occurred during the reproductive period of many shellfish, mass mortality could impact these populations for at least several years, highlighting the need for long-term monitoring, the researchers said. . And as climate change continues to produce more frequent extreme heat events, seashell deaths like those of last summer could become a more common occurrence.

“The Swinomish Indian Tribal Community is proud to be a leader in this important scientific research that assessed in real time the devastating effects on our shellfish resources from last summer’s unprecedented heat dome. Shellfish are a priority food that our tribal community relies on for spiritual nourishment and sustenance Last summer’s extreme weather event confirmed to us that we need to act faster to ensure climate resilience for health and well-being long-term impact of our community,” said Swinomish Tribe Chairman Steve Edwards.

“Once the effects of the heat wave began to become apparent, the collaboration that emerged was incredible as managers and scientists worked quickly to mount a rapid response to capture information,” the co said. -author Camille Speck, Puget Sound Intertidal Bivalve Manager for Washington. Department of Fish and Wildlife. “We still have a lot to learn about the effects of the heat wave on marine ecosystems in the Salish Sea, and more work to do as managers to prepare for the next one and develop informed responses. These conversations have place now, and it is our hope that we will be better prepared for what comes next.”

Other co-authors are Megan Dethier of UW; Teri King of Washington Sea Grant, based at UW; Christopher Harley of the University of British Columbia; Blair Paul of the Skokomish Indian Tribe; and Elizabeth Tobin of the Jamestown S’Klallam Tribe. More than two dozen people contributed data to this project.

This analysis was funded by the Washington Sea Grant with data contributions from tribes, state and federal agencies, academic institutions, and nonprofit organizations.

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