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Heat wave of 2021 created ‘perfect storm’ for shellfish die-off

New study: 2021 heatwave triggered 'perfect storm' for shellfish die-off

Dead oysters spotted along a Washington state shoreline, after a record heat wave in the summer of 2021. Credit: Blair Paul

It’s hard to forget the unbearable heat that engulfed the Pacific Northwest in late June 2021. Temperatures in Oregon, Washington and British Columbia soared well above 100 degrees Fahrenheit, with Seattle setting an all-time high of 108 degrees on June 28.

During the heat wave, also known as a heat dome, scientists and community members noticed an alarming increase in dying and dead shellfish on some beaches in Washington and British Columbia, both in the Salish Sea and offshore. The observers soon realized they were experiencing an unprecedented event and they organized to document the death of crustaceans in real time.

Now a team led by the University of Washington has collected and analyzed hundreds of these field observations to produce the first comprehensive report of the effects of the 2021 heat wave on crustaceans. The researchers found that many shellfish fell victim to a “perfect storm” of factors that contributed to widespread mortality: The lowest ebb of the year occurred during the hottest days of the year — and at the warmest times of the day. The results were published online in the magazine on June 20th Ecology

“You really couldn’t have imagined a worse scenario for intertidal organisms,” said lead author Wendel Raymond, a research scientist at UW Friday Harbor Laboratories. “This analysis has given us a very good overall picture of how shellfish were affected by the heat wave, but we know that’s not even the full story.”

The research team leveraged existing collaborations between tribes, state and federal agencies, academia, and non-profit organizations. They devised a simple survey and five-point rating system (1 = much worse than normal to 5 = much better than normal) and asked participants to provide ratings based on their knowledge of a species in that location. In total, they collected 203 observations from 108 unique locations, from central British Columbia to Willapa Bay, Washington.

Heat wave 2021 caused 'perfect storm' for shellfish dying

Joe Williams, front, and Darrell Williams with the Swinomish Indian Tribal Community’s Fisheries Department dig mussels on a beach in Skagit Bay as part of a study being conducted to estimate mussels’ biomass. Credit: Northwest Indian Fisheries Commission

“The strength of this study and what it really emphasizes is the value of local knowledge and also the importance of understanding natural history,” said study co-author P. Sean McDonald, an associate professor of environmental studies and aquatic and fisheries sciences. “This is the first step and a snapshot, if you will, of what shellfish experienced on the beaches during the heat wave.”

The researchers found that the ecology of each species contributed to the overall success or failure to survive the extreme heat. For example, some shellfish that naturally burrow deep below the surface, such as butter mussels, tended to outperform shellfish that normally burrow just below the sand surface at low tide, such as cockles.

They also found that location mattered. Shellfish on the outer shores experienced low tide about four hours earlier than shellfish on inner beaches. For inland shellfish, low tide — or when most shellfish were exposed — hit around midday sun, when the sun was directly overhead.

In addition, air temperatures inland were much higher than on the outer coast, which put more stress on the inland populations. California mussels, which are found almost exclusively on the outer coast, tended to survive the heat, while bay mussels, which are found in more inland coastal areas, were more likely to die from heat exposure. Increased water movement and wave action on the outer coast also likely helped reduce the effects of the heat on shellfish along those beaches.

Many shellfish don’t tend to move much on a particular beach, so where they naturally live in the intertidal zone also contributed to their success or failure, the researchers found. For example, acorn barnacles living higher up the coast were generally more affected than mussels and oysters lower on the beach and more likely to remain submerged.

Heat wave 2021 caused 'perfect storm' for shellfish dying

Julie Barber, senior shellfish biologist with the Swinomish Indian Tribal Community, quantifies recent buttershell deaths on a beach in Skagit Bay, Washington, in July 2021, following a record heat wave. Credit: Northwest Indian Fisheries Commission

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

Perhaps most surprisingly, the researchers noticed interesting patterns in shellfish survival rates on the same beach. In some locations, shellfish survived in the path of freshwater runoff on part of the beach, while others died just a few miles away. If a tree overhangs part of a beach and shaded the sand, those shellfish generally made it, while others didn’t. Co-author Julie Barber, a senior shellfish biologist with the Swinomish Indian Tribal Community, recalls seeing those patterns while walking the beaches of Skagit Bay, and in some locations, surrounded by dead clams in all directions.

“It was pretty disturbing, and I’ve never seen anything like it,” Barber said. She recalls exchanging emails with colleagues from across the region when they noticed similar mass deaths on their local beaches, then realized they urgently needed to coordinate and document what was happening.

“This effort was a nice demonstration of how collaborators can come together for one common goal — in our case trying to understand what was happening to these shellfish,” Barber said.

Because the heat wave occurred during the time frame when many shellfish reproduce, the mass die-offs could affect those populations for at least several years, highlighting the need for long-term monitoring, the researchers said. And as climate change increasingly causes extreme heat, shellfish deaths like last summer’s could become a common reality.

Heat wave 2021 caused 'perfect storm' for shellfish dying

Dead cockles seen on a beach after record heat in July 2021 in Skagit Bay, Washington. Credit: James McArdle

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

“As the effects of the heat wave started to become apparent, the collaboration that emerged was amazing as managers and scientists worked quickly to react quickly to capture information,” said study co-author Camille Speck, intertidal bivalve manager of Puget Sound. for Washington. Department of Fish and Wildlife. “We still have so much to learn about the effects of the heat wave on the marine ecosystems of the Salish Sea, and there is more work to be done as managers to prepare for the next and develop informed responses. These conversations are taking place now And it’s our hope that we’ll be better prepared for what comes next.”

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


Yessotoxins produced by phytoplankton caused massive shellfish deaths in Washington summer


More information:
Wendel W. Raymond et al, Assessing the Effects of an Unprecedented Heat Wave on Intertidal Shellfish of the Salish Sea, Ecology (2022). DOI: 10.1002/ecy.3798

Provided by the University of Washington


Quote: 2021 heat wave created ‘perfect storm’ for shellfish die-off (2022, June 21) retrieved June 21, 2022 from https://phys.org/news/2022-06-storm-shellfish-die-off.html

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