Oysters are benthic filter feeders important to coastal environments all over the world. In the Chesapeake Bay, the eastern oyster (Crassostrea virginica) is our only native oyster species and helps keep the ecosystems of the Bay healthy. Fixed to the spot they settled on as larvae, oysters filter the water when they feed and breathe; they build reef structures that provide habitat and safe haven for critters hiding from predators. The eastern oyster also supports a healthy and growing aquaculture industry that brings oysters to our plates.
Most oyster farmers use the waterways where oysters naturally occur to grow their own oysters for human consumption. This makes sense, of course; if oysters can survive there naturally, it’s highly likely they can be cultivated there. However, these waterways are changing, and their suitability for growing oysters is also changing. While the oyster is accustomed to environments that fluctuate on a wide variety of time scales, from daily changes occurring with incoming and outgoing tides to seasonal cycles of temperature, salinity, and food availability, everyone has their limits. The fact that an organism designed to cope with changing environments is having trouble tolerating the changes we’ve induced in our planet is alarming.
So what are we going to do about it?
In the near term, we need solutions to help oysters survive in these conditions. Scientists have developed some amazing techniques for mitigating the uncertainty of the environment by finding creative ways to use principles like natural selection. In nature, those equipped for the stress of their environment survive to pass their genes on to the next generation. In an aquaculture setting, scientists simply make this decision. They select oysters that survive in certain conditions, like low-salinity, or have genetic markers that tell us they’re resistant to certain diseases. They breed these oysters so that their offspring are more likely to survive these conditions than by natural selection alone. This technique is highly effective but slow, as it takes generations to create these lines. My work has been focused on testing a new technique that focuses within a generation of oysters.
Stress conditioning
Stress conditioning is the idea that when we expose an organism to a stressor, they make molecular changes that prepare them for that stressor in the future. One stress I’ve conducted work for has been salinity stress. Oysters prefer a salinity range 5-35 ppt; in the Chesapeake Bay, we are on the lower end of that range, so drops in salinity due to increased rainfall or extreme weather events can push salinity dangerously low. The most severe account of this in the last decade was in 2019, but in 2024 we also had unseasonably fresh water in the Bay. So what would happen if we exposed oysters to a short burst of low salinity? Would they be more likely to survive during a long exposure to low salinity? These are some of the questions I’m looking to answer with my research.
In controlled experiments, we did see less mortality in our juvenile oysters that were stress-conditioned, and increased growth compared to oysters that were not stress-conditioned but exposed to a long period of low salinity stress. The next steps for this work were to test it out in the field, where other things like temperature, food availability, and dissolved oxygen availability are less controlled. We selected three sites along the Choptank River to deploy our stress-conditioned oysters. One on the mainstem of the river, where the salinity is well within the oyster’s comfort zone. A second site on a tributary upstream, where the salinity begins to drop, and a third site further upstream at Suicide Bridge, where the salinity is low.
Over the course of six months, we’ll go out to check on these oysters periodically. We’ll assess how many have survived the conditions and if the conditions have affected how well they grow. As we collect more data, I’ll have a better idea of how helpful stress conditioning for low salinity is for our oysters. From there, we can consider if this technique is something oyster farmers should use to help toughen up their oysters in the face of variable conditions.
