In a shifting ocean environment, what are the impacts on Pacific oysters?

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Seeking to understand the impacts of environmental stressors on Pacific oysters is the driving force behind a years-long research project involving scientists from the University of Washington and NOAA, and in collaboration with the oyster industry. A new paper about the project was made available online in Aquaculture on June 17, 2025. Critical in aquaculture, Pacific oysters are the dominant oyster species grown on the US West Coast, with the industry in the Pacific Northwest alone valued at over $270 million a year.

Oyster farm viewed from above, close to the shoreline.
Craig Norrie
An oyster farm viewed from the sky.

But this study drills down into the species one step further, looking into the differential performance of diploid, mated triploid, and induced triploid Pacific oysters under different environmental conditions. Compared to diploid oysters, triploid oysters have an additional set of chromosomes, they grow faster and are functionally sterile. As a result, they comprise a large proportion of oysters grown both in the Pacific Northwest and worldwide. Recent studies have found that the waters off the West Coast were acidifying faster than anywhere else in the world, and so studying the impact of changing oceans on oysters—and how it affects those with different chromosome numbers—can assist the shellfish aquaculture industry in making more informed decisions about their species portfolio.

Racks and cages pictured at low tide that are used on oyster farms.
Craig Norrie
The racks and cages used to grow oysters.

The team of researchers, led by Craig Norrie from the UW School of Aquatic and Fishery Sciences (SAFS), sought to understand how stressors such as temperature, dissolved oxygen (DO), and pCO2 , impacted Pacific oysters across a 4-week period. The study focused on whole organism physiological responses—growth, mortality and respiration—for genetically related juvenile diploid, chemically induced triploid, and mated triploid Pacific oysters.

What researchers found was an overall high survival in all groups across a broad range of temperature and DO levels. “They are a pretty hardy species, so to an extent you can see why survival was reasonably high in the temperature experiment—these guys are grown from Baja California up to Alaska so can tolerate a broad array of conditions,” Norrie said. “However, farmers report that over the summer period when its warmer, triploids generally die more—the high survival in our study could be due to the fact that they were younger oysters.”

For DO, this was a more surprising result for researchers. “It was reasonably surprising that they survived so well under different dissolved oxygen levels—everyone needs to breathe, right? How did they manage to hold their breath for so long?” Norrie asked. “Again, this could be because they grow in such a broad range of conditions.”

pCO2  was a different story. At mid pCO2, between 1450 and 1700 μatm (microatmospheres, a unit of pressure), mated triploids had lower survival than the other groups in the study, which suggests that production method or genetic background may contribute to their resilience or susceptibility to stress. “Oysters can adapt to local conditions over a few generations, and this can make them better equipped to deal with the conditions that they are likely to encounter naturally,” Norrie said. And this means in the case of these oysters which didn’t perform so well under low pH conditions, a lack of exposure in their family history to may mean they haven’t developed resilience to this environmental stressor. However, the team found that when pCO2 reached extreme levels of 2100 μatm, all oysters in the study died. This suggests that if conditions become extreme enough, there is the possibility that all oysters, regardless of ploidy or production method, will be impacted.

Four tanks in a laboratory.
Craig Norrie
The experimental tanks used for the project which examined the responses of Pacific oysters to environmental stressors.

As a culturally and economically important industry, developing new insights into how aquaculture will be impacted by changing oceans is critical. Considering the stressors that will be placed on species such as Pacific oysters will allow those working in aquaculture to make informed decisions on which type of oysters to select to ensure the future resilience of the industry.

The research team included Joth Davis from Baywater Shellfish, Shallin Busch and Paul McElhany from NOAA, and research scientists, professors, and undergraduate students from the University of Washington: Dereck Cordova (undergraduate student in the IBIS program), Hailey Dockery (undergraduate researcher), Craig Norrie (research scientist and project lead), and Jacqueline Padilla-Gamiño (SAFS professor).

Changing waters, changing views: Stakeholder perspectives on ocean acidification and adaptations in shellfish aquaculture

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Shellfish aquaculture is a vital industry in the US, but one which faces mounting challenges threatening both productivity and business viability. Research often fails to align with growers’ immediate needs, so researchers set out to help close this gap in a new study published in Aquaculture Reports, interviewing over 30 commercial shellfish growers across the US Pacific region.

Funded as part of NOAA’s Ocean Acidification Program, former Research Scientist at the University of Washington School of Aquatic and Fishery Sciences (UW SAFS) and now a Fisheries Resource Management Specialist with NOAA Fisheries, Connor Lewis-Smith led the research to document how industry participants perceive ocean acidification threats and evaluate emerging adaptation strategies that are actively being researched: parental priming and native species portfolio diversification.

The research team included scientists from NOAA Northwest Fisheries Science Center (NWFSC), Puget Sound Restoration Fund, UW SAFS, and the University of the Virgin Islands. They interviewed owners, field managers, hatchery managers, and other staff from operations across five states on the Pacific Ocean: Washington, Oregon, California, Alaska, and Hawaii. “Operations ranged in scale and included hatchery, nursery, and growout components. We also included tribally managed and tribally affiliated businesses,” Lewis-Smith said.

Aerial view of an oyster farm in the water.
Connor Lewis-Smith
Bird’s-eye view of an oyster farm.

Taking a step back in time to 2013, concern about ocean acidification among shellfish growers was four times higher than among the general public, a result of the hatchery crisis of the mid-2000s, where hatchery-produced oysters started dying by the billions along the Northwest coast. Today, ocean acidification remains a concern, but less so.  Based on interviews among growers in 2023-2024, the team found ocean acidification to be a lower-priority concern compared to other stressors such as temperature, disease, harmful algal blooms, and regulatory constraints.

“Many growers are unsure whether declining survival or productivity is due to ocean acidification, other environmental changes, or a combination,” Lewis-Smith said. “This nuance, where ocean acidification is seen as an ever-present “enemy on the hill,” but not necessarily the most urgent battle, points to the need for research and risk communication that reflects the interconnected nature of aquaculture stressors.”

Enhanced monitoring and adaptation to changing environmental conditions is actively supported across the industry, and this is where research plays a critical role, not only to deliver these adaptations, but to align them with growers’ practical realities and decision-making needs. In the study, the researchers looked at growers’ perceptions of two adaptation strategies to ocean acidification: parental priming and native species portfolio diversification.

Parental priming uses environmental conditioning of the parental generation to enhance the resilience of shellfish offspring. Native species portfolio diversification involves cultivating native species, such as Olympia oysters and geoduck clams, which may offer inherent resilience to ocean acidification.

An illustration of different shellfish, including oysters and a geoduck clam.
Connor Lewis-Smith
Shellfish portfolio, including oysters and a geoduck clam.

“Historically along the Pacific coast, the shellfish aquaculture industry has relied heavily on introduced species, such as Pacific oysters originally imported from Japan over a century ago, and they now account for the vast majority of production. Manila clams are another major contributor, also introduced,” Lewis-Smith shared. “These species became dominant in the early 20th century as native oyster populations like the Olympia oyster collapsed due to overharvest and habitat degradation.”

Researchers found higher levels of skepticism towards native species diversification stemming from regulatory hurdles, limited market demand, and slower growth rate of some species. Current regulations restrict the propagation of native species to preserve genetic diversity, while from an economic perspective, native species like Olympia oysters grow more slowly and may not meet market preferences for size, taste, or shucked-meat yield. There’s also an infrastructure concern to address, with restructured farming practices required for some native species. “We found that 69% of respondents cultivated at least one native species, and some are actively expanding their native offerings, however the industry’s core remains centered on introduced species,” Lewis-Smith said.

Aerial view of Hood Canal and an oyster farm.
Connor Lewis-Smith
An oyster farm located on Hood Canal.

On the flip side, parental priming was viewed as a promising, if still experimental, strategy—one that 64% of growers and hatchery operators would consider if backed by strong scientific evidence. By conditioning broodstock to low pH or other stressors during gonadal maturation—to enhance offspring resilience—this strategy doesn’t require overhauling product lines, shifting consumer preferences, or navigating regulatory pathways.  Concerns about this strategy were also uncovered during the study, emphasizing the financial and logistical burden of adopting new protocols, and stressing broodstock during critical life stages.

“We found that the relatively high interest in parental priming reflects a broader industry trend toward cautious innovation, where growers are open to new strategies, but only when those strategies are empirically validated, operationally feasible, and financially justifiable,” Lewis-Smith said.

In addition to gathering information on the industry’s perspective on environmental stressors and emerging strategies, the team concluded that collaboration between growers, researchers, and policymakers is essential for co-producing relevant adaptation strategies that are scientifically sound and operationally feasible. “The industry has already shown collaborative success in implementing monitoring and buffering systems after the 2005–2009 ocean acidification induced hatchery shortages,” Lewis-Smith said. “However, sustained engagement and support are needed to develop and scale newer strategies like priming or diversification, especially given the sector’s diversity and regulatory complexities.”

Climate change and Pacific oysters: what are the impacts of heat stress?

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What brings a biology student into the Roberts Lab at SAFS? Eric Essington, a senior in the UW Biology program, has been working on his independent research project in the Roberts Lab for the past year, looking into a familiar hard-shelled mollusk: the oyster. Why? To simulate temperature changes associated with climate change and explore the impact on oysters.

A group of Pacific oysters used for Eric’s experiment.

Looking specifically at the Pacific oyster, a commercially important species in Washington where the majority are farmed, one of the big issues facing the aquaculture sector are large summer die-offs due to warmer temperatures and other environmental stressors. Reaching up to 10 inches in length, Pacific oysters are also key filter feeders, meaning they clean the water as they eat.

Conducting his research at the Jamestown Point Whitney Shellfish Hatchery, which lies on the shores of Dabob Bay and Hood Canal on the eastern side of the Olympic Peninsula, Eric’s experiment started off with the arrival of more than 200 adult oysters, along 120 each of juvenile (one year old oysters), seed (young oysters large enough to be transplanted) and spat (at the life stage when the oyster has permanently attached to a surface).

The group of researchers preparing to simulate the acute thermal stress event, where the oysters were immersed in 32ºC water.

With the oysters divided into two groups, the experiment consisted of one group living in a tank mirroring their natural aquatic environment at 17ºC, and the other in a tank designed to simulate erratic and harsh heat stress associated with climate change. With an increase in temperature of 2ºC every hour until the water hits a stress-inducing 26ºC, this was maintained for six hours each day for seven weeks. A secondary, mechanical stress event was also implemented for adults and juveniles, designed to mimic the physical disturbance of tumbling in currents and encounters with predators and debris that oysters may face in their natural habitats.

The final stage of Eric’s experiment simulated an acute thermal stress event, where the oysters were immersed in 32ºC water for 30 minutes, following by the mechanical stress simulation, followed by tissue sampling for RNA and DNA analysis. The aim? To gauge the physiological response of oysters to compounded stressors.

Conducting this experiment with oysters at different life stages, Eric found that heat stress at the spat stage resulted in tolerance to a secondary stress that corresponds to increased growth. The energy trade-off from developing a resistance to temperature changes during stress events means they have more energy available for growth later on. This result could have real-world application for hatcheries, who could harden young oysters in a similar way before releasing them to grow, so that they provide improved yields during the summer months.

Recently presenting his research at the Mary Gates Research Symposium, Eric shares that next steps in this experiment would be to explore why increased growth and decreased transcription was only significant in the youngest life stage of an oyster.

Interested in more details about Eric’s work? Check out his lab notebook