Perfect storm' of factors including last year's heat wave resulted in shellfish death - Kitsap Sun

New research from a team led by the Unversity of Washington found that last year's heat wave at the end of June resulted in an unprecedented die-off of shellfish in the region. 

Researchers found that the shellfish were victims of a "perfect storm" of factors that contributed to their death, according to a press release. 

In some areas the lowest tides of the day coincided with the hottest times of the day, leaving the shellfish out to bake in the sun. Scientists and community members noticed an uptick in dead and dying shellfish in Washington state and British Columbia. In total, they gathered 203 observations from 108 unique locations, ranging from central British Columbia to the Salish Seas down to Willapa Bay, Washington, according to the press release. 

"As one of our technicians put it, it smelled like a clambake out there," said Elizabeth Tobin, Jamestown S'Klallam shellfish program manager. Vultures circled the beaches. 

The University of Washington's team compiled hundreds of observations to create a comprehensive report of the impacts of the 2021 heat wave to shellfish. Results were published online in the journal Ecology on June 20. More than two dozen individuals contributed data for the project. The study was funded by Washington Sea Grant with data contributions from tribes, state and federal agencies, academic institutions and nonprofits.

"A report after the 2021 heat wave showed that these temperatures were virtually impossible without human-induced climate change," Tobin said. Tobin and study co-author Annie Raymond said they believe we will see these events in higher frequency in the future as temperatures continue to rise. 

"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 Raymond, a shellfish biologist with the Jamestown S'Klallam Tribe.

Shellfish are very important to the tribes, Tobin said. They're used for commercial sale, restoration, subsistence and ceremonial harvest. 

Researchers used quadrants to measure the abundance of shellfish in the surveyed areas, Raymond said. There was a lot of variation between locations and species. A lot of the death was noted visually by researchers on beaches. There were site-specific conditions such as groundwater, freshwater, heat exposure and others. 

Different species had different responses to the heat dome. Some shellfish that burrow deeply beneath the surface, like butter clams, did better than those that are just below the sand's surface, like cockles. 

"Manilla and little neck clams, cockles and Pacific oysters were affected more," Raymond said. Cockles were more widespread and are considered one of the tribes' primary first foods. 

Location of the shellfish also mattered. Those on the outer coast experienced low tide about four hours earlier than the shellfish on inland beach. Inland shellfish were hit with low tide right around solar noon while the sun was directly overhead. Air temperatures at inland sites were also higher than on the outer coast, causing more damage to those inland. 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, according to the press release. Water movement and wave action on the outer coast also may have helped the shellfish in those areas. 

"Because low tides occurred on the coast four hours before the heat of the day, there was not as much mortality," Tobin said. 

"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.

Local tribes saw death in their shellfish operations as well. Joseph Pavel, director of Skokomish Department of Natural Resources, said mortalities were investigated and though they have a small staff, many observations were made. 

"If you're six feet underwater maybe the heat is not so much an issue, but if you're laying out on the beach it's an issue," Pavel said. 

Researchers also found that where the shellfish lived in the intertidal zone contributed to their success or failure.  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 underwater, said the study.

Freshwater runoff seemed to be a contributing factor to their survival as well. Some shellfish on the same beach survived while others did not, based on things like the path of a freshwater runoff, or things like whether a tree was shading part of the sand, making it cooler for the shellfish. 

Long-term repercussions haven't been seen yet, but could be broad. The heat dome happened during a time when many shellfish are reproducing, so populations could be affected for years to come, according to the research. Long-term monitoring will be needed, said the researchers. 

"I don't think anyone expected those high temperatures at the lowest tides of the year," Tobin said. "Tribes really depend on these for cultural resources, and we recognize tribal resources are declining." 

With climate change, researchers are concerned that shellfish deaths like those last summer could become more common.

"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 the Washington Department of Fish and Wildlife. 

The Skokomish Tribe as a treaty tribe is entitled to harvest shellfish out of its customary fishing areas, which includes the entire hood canal watershed and drainages into Hood Canal. Tribal members are harvesters, and the fishery activities are managed by the tribal natural resources department. It establishes what the harvestable amounts of the populations are. 

"When an event like this comes by we're significantly challenged to respond," Pavel said. The reduction in numbers will lead to a reduction in harvest. He says wise use and responsible resource management need to be promoted. 

With shellfish also serving as filter feeders, water quality could also be a concern. Pavel said in past years, a type of seaweed took over and trapped shellfish beds. Dry periods can also cause extreme algae blooms to happen, causing environmental toxins that in turn can make the water dangerous to swim in and shellfish harmful to eat. 

Tobin said the shellfish were metabolically stressed, and the increasing heat events can promote more algae and phytoplankton. Heat can increase vibrio — a harmful bacteria that can cause food poisoning. If someone eats shellfish with vibrio, it can lead to food-borne illness. 

Biotoxins reduce harvest events, Raymond said. It's not uncommon for shellfishing to be closed for a few weeks over the summer because of safety problems. If these events become more prevalent they will be harmful to those who consume shellfish and rely on them for income.

"It's two weeks of harvest time that is very special to people," Raymond said. "It's sad to tell them no. People are bummed." 

Tribes, the Washington Department of Fish and Wildlife, and the University of Washington worked together on the project, and will continue to make longer-term observations with more specific data, Raymond said. Tobin said things are becoming a little bit more unpredictable. 

"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."

Raymond said there will need to be more discussion about what can be done. Ideas are being thrown around, Tobin said, such as reducing harvest pressure. 

From an aquaculture perspective, Raymond said the more resilient individuals can be selected to reproduce. 

"There's a lot of talk about doing work to select and breed those that are more heat tolerant," Tobin said. Lab trials in hatcheries will show if the more heat-tolerant can be cultivated and create seed that may be more resilient to these events. 

"This is a really cool example of how different groups can work together and put together information that I think is a path forward," Raymond said. "It's not doom and gloom everywhere."

"While there were areas hit really hard, there was resilience out there," Tobin said. This study produced an important line of communication, and researchers expect an event like this to happen again, she said. Now they can be better prepared to make observations that can help address challenging issues and conversations, Tobin said.