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 to well above 100 degrees Fahrenheit, with Seattle of 108 degrees on June 28.

During the heat wave, also called a heat dome, scientists and community members alike noticed a disturbing on some beaches in Washington and British Columbia, both in the Salish Sea and along the outer coast. The observers quickly realized they were living through an unprecedented event and they organized to document the shellfish die-offs as they happened in real time.

Now, a team led by the 91̽�� has compiled and analyzed hundreds of these field observations to produce the first comprehensive report of the impacts of the 2021 heat wave on shellfish. The researchers found that many shellfish were victims of a “perfect storm” of factors that contributed to widespread death: The lowest low tides of the year occurred during the year’s hottest days — and at the warmest times of day. The were published online June 20 in the journal Ecology.

“You really couldn’t have come up with a worse scenario for intertidal organisms,” said lead author , a research scientist at 91̽��Friday Harbor Laboratories. “This analysis has given us a really good general picture of how shellfish were impacted by the heat wave, but we know this isn’t even the full story.”

The research team leveraged existing collaborations across tribes, state and federal agencies, academia and nonprofits. 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 gathered 203 observations from 108 unique locations, from central British Columbia down 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 , a 91̽��associate teaching professor in environmental studies and aquatic and fishery 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 each species’ ecology contributed to its general success or failure to survive the extreme heat. For example, some shellfish that naturally burrow deep beneath the surface, like butter clams, usually fared better than ones that typically ride out low tide just below the sand’s surface, such as cockles.

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

Additionally, air temperatures were much higher at inland sites compared to the outer coast, causing more stress on inland populations. For example, California mussels, found almost exclusively on the outer coast, mostly survived the heat while bay mussels, found in more inner coastal sites, were more likely to die from heat exposure. More water movement and wave action on the outer coast also likely helped lessen the impacts of the heat on shellfish along those 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 hottest time of day were very unlucky that temperatures soared so high,” said co-author Hilary Hayford, habitat research director at Puget Sound Restoration Fund.

Many shellfish don’t tend to move much on any 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 the shore generally were more impacted than clams and oysters that are lower on the beach and more likely to remain under water.

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

Perhaps most surprisingly, the researchers noticed interesting patterns in survival rates among shellfish on the same beach. In some locations, shellfish in the path of freshwater runoff on one section of beach survived, while others just a few miles away perished. If a tree hung over part of a beach and shaded the sand, those shellfish generally made it while others didn’t. Co-author , senior shellfish biologist with the Swinomish Indian Tribal Community, remembers seeing those patterns while walking the beaches of Skagit Bay and, in some locations, being surrounded by dead cockles in every direction.

“It was pretty unsettling, and I’ve never seen anything like it,” Barber said. She remembers exchanging emails with colleagues from around the region as they noticed similar mass die-offs on their local beaches, then realizing that they urgently needed to coordinate and document what was happening.

“This effort was a beautiful demonstration of how collaborators can come together with one common cause — which in our case was trying to understand what happened to these shellfish,” Barber said.

Because the heat wave occurred during the time frame when many shellfish are reproducing, the mass die-offs could impact those 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, shellfish deaths like those of last summer may become more of a common reality.

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

“Once the effects of the heat wave started to become apparent, the collaboration that emerged was amazing as managers and scientists worked quickly to put together a rapid response to capture information,” said co-author Camille Speck, Puget Sound intertidal bivalve manager for Washington Department of Fish and Wildlife. “We still have so much to learn about the effects of the heat wave on Salish Sea marine ecosystems, and more work to do as managers to prepare for the next one and develop informed responses. These conversations are happening now, and it is our hope that we will be better prepared for whatever comes next.”

Other co-authors are Megan Dethier of the UW; Teri King of UW-based Washington Sea Grant; Christopher Harley of 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.

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

For more information, contact:

• Wendel Raymond, 91̽�� and lead author: wraymond@uw.edu
• Sean McDonald, 91̽��: psean@uw.edu
• Julie Barber, Swinomish Indian Tribal Community: jbarber@swinomish.nsn.us
• Camille Speck, WDFW (contact Ben Anderson, communications manager): Benjamin.Anderson@dfw.wa.gov
• Teri King, Washington Sea Grant: guatemal@uw.edu

Back in the summers of 2018 and 2019, the shellfish industry in Washington state was rocked by .

“It was oysters, clams, cockles — all bivalve species in some bays were impacted,” said Teri King, aquaculture and marine water quality specialist at Washington Sea Grant based at the 91̽��. “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’ were published last month in the open-access journal Harmful Algae.

Because are not a threat to human health, their presence in Washington has not been closely monitored. The researchers dug through data that had been collected by the NOAA Northwest Fisheries Science Center and NOAA National Centers for Coastal Ocean Science for different purposes, coupled it with current observations from the SoundToxins phytoplankton monitoring program, and discovered that these algae species, Protoceratium reticulatum and Akashiwo sanguinea, are correlated with shellfish mortality events stretching as far back as the 1930s.

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.

These findings have significant implications for shellfish growers in the region.

“We are working towards being able to help growers count the cells of yessotoxin-producing organisms in the water and correlate it to an action level,” King explained. “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.”

King said this research is also a demonstration of the value of partnerships between shellfish producers, plankton monitors, 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, it’s even the key to solving the longstanding mysteries that have been taking place right in your backyard.

For more information, contact:

MaryAnn Wagner, Washington Sea Grant, 206-371-7656, maryannb@uw.edu
Michael Milstein, NOAA Northwest Fisheries Science Center, michael.milstein@noaa.gov
Sierra Sarkis, NOAA/NCCOS, NCCOS, sierra.sarkis@noaa.gov
Barbara Lewis, NW Indian College,  bjlewis@nwic.edu

The next time you eat sashimi, nigiri or other forms of raw fish, consider doing a quick check for worms.

A new study led by the 91̽�� finds dramatic increases in the abundance of a worm that can be transmitted to humans who eat raw or undercooked seafood. Its 283-fold increase in abundance since the 1970s could have implications for the health of humans and marine mammals, which both can inadvertently eat the worm.

Thousands of papers have looked at the abundance of this parasitic worm, known as Anisakis or “herring worm,” in particular places and at particular times. But this is the first study to combine the results of those papers to investigate how the global abundance of these worms has changed through time. The were published March 19 in the journal Global Change Biology.

“This study harnesses the power of many studies together to show a global picture of change over a nearly four-decade period,” said corresponding author , an assistant professor in the 91̽��School of Aquatic and Fishery Sciences. “It’s interesting because it shows how risks to both humans and marine mammals are changing over time. That’s important to know from a public health standpoint, and for understanding what’s going on with marine mammal populations that aren’t thriving.”

Despite their name, herring worms can be found in a variety of marine fish and squid species. When people eat live , the parasite can invade the intestinal wall and cause symptoms that mimic those of food poisoning, such as nausea, vomiting and diarrhea. In most cases, the worm dies after a few days and the symptoms disappear. This disease, called or anisakidosis, is rarely diagnosed because most people assume they merely suffered a bad case of food poisoning, Wood explained.

After the worms hatch in the ocean, they first infect small crustaceans, such as bottom-dwelling shrimp or copepods. When small fish eat the infected crustaceans, the worms then transfer to their bodies, and this continues as larger fish eat smaller infected fish.

Humans and marine mammals become infected when they eat a fish that contains worms. The worms can’t reproduce or live for more than a few days in a human’s intestine, but they can persist and reproduce in marine mammals.

Seafood processors and sushi chefs are well-practiced at spotting the worms in fish and picking them out before they reach customers in grocery stores, seafood markets or sushi bars, Wood explained. The worms can be up to 2 centimeters in length, or about the size of a U.S. 5-cent nickel.

“At every stage of seafood processing and sushi preparation, people are good at finding worms and removing them from fish,” Wood said.

Some worms can make it past these screening steps. Still, Wood — who studies a range of marine parasites — said she enjoys eating sushi regularly. For sushi consumers who remain concerned about these worms, she recommends cutting each piece in half and looking for worms before eating it.

For the analysis, the study’s authors searched the published literature archived online for all mentions of Anisakis worms, as well as another parasitic worm called Pseudoterranova, or “cod worm.” They whittled down the studies based on set criteria, ultimately keeping only those studies that presented estimates of the abundance of each worm in fish at a given point in time. While Anisakis worms increased 283-fold over the study period of 1978 to 2015, Pseudoterranova worms did not change in abundance.

Although the health risks of these marine worms are fairly low for humans, scientists think they may be having a big impact on marine mammals such as dolphins, whales and seals. The worms actually reproduce in the intestines of these animals and are released into the ocean via the marine mammals’ feces. While scientists don’t yet know the physiological impacts of these parasites on marine mammals, the parasites can live in the mammals’ bodies for years, which could have detrimental effects, Wood said.

“One of the important implications of this study is that now we know there is this massive, rising health risk to marine mammals,” Wood said. “It’s not often considered that parasites might be the reason that some marine mammal populations are failing to bounce back. I hope this study encourages people to look at intestinal parasites as a potential cap on the population growth of endangered and threatened marine mammals.”

The authors aren’t sure what caused the large increase of Anisakis worms over the past several decades, but climate change, more nutrients from fertilizers and runoff, and an increase in marine mammal populations over the same period could all be potential reasons, they said.

Marine mammals have been protected under the since 1972, which has allowed many populations of seals, sea lions, whales and dolphins to grow. Because the worms reproduce inside marine mammals — and their rise occurred over the same time period as the mammals’ increase — this is the most plausible hypothesis, Wood said.

“It’s possible that the recovery of some marine mammal populations has allowed recovery of their Anisakis parasites.” Wood said. “So, the increase in parasitic worms actually could be a good thing, a sign that the ecosystem is doing well. But, ironically, if one marine mammal population increases in response to protection and its Anisakis parasites profit from that increase, it could put other, more vulnearble marine mammal populations at risk of increased infection, and that could make it even more difficult for these endangered populations to recover.”

Other co-authors are , who completed the work as a 91̽��graduate student; , a graduate student in the 91̽��School of Aquatic and Fishery Sciences; of Bates College; of Washington Sea Grant; and of the 91̽��School of Public Health’s Department of Environmental and Occupational Health Sciences; and of NOAA’s Northwest Fisheries Science Center.

This study was funded by Washington Sea Grant, the National Science Foundation, the Alfred P. Sloan Foundation and the 91̽��.

For more information, contact Wood at chelwood@uw.edu.