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