For oysters, sometimes stress can kill, especially as larvae transition to adulthood. Potentially, reducing carryover effects might help more oysters survive the stress.
As Jan McDowell, co-leader of the research project, puts it: "If you have a match between the conditions you’re reared in as a larva and the conditions you’re reared in during the grow-out phase as an adult, do you perform better? Do you grow faster? Also, do you experience less mortality?"
An oyster's genetics dictate its ability to respond to change, and every oyster's genes are a little different.
Part of the research process involves studying the genetic diversity of the oysters at different life stages, especially when the larvae transition to adulthood and after the oysters have been growing out in the Bay for a while. This will allow the researchers to see if the water conditions cause the oyster populations to lose genetic diversity as some oysters die off.
Hatcheries carefully breed oysters with particular genes that allow them to remain healthy as adults and grow large enough for the farmers to sell. But carryover effects from water quality changes might counteract the hatchery's efforts to grow healthy oysters. Matching hatchery water quality to the grow-out water quality may increase the number of oysters that survive, and in turn, the genetic diversity within each group.
But why does the genetic diversity make a difference? The natural world is full of potential threats like disease, so a more diverse group of shellfish is more likely to contain oysters with the characteristics needed to survive and flourish in the face of disease or poor water quality. More genetic diversity, which is responsible for diverse oyster characteristics, will result in a group of oysters that is more likely to grow fast and remain healthy overall. Even though these oysters won’t reproduce, maintaining genetic diversity within the group throughout their different life stages will help maximize the number of oysters that survive.
If oysters have a better survival rate when water conditions remain consistent across their lifespan, this would tell researchers that carryover effects from water quality can have a negative impact on adult oysters. Lessened carryover effect means less death and greater overall diversity in an oyster population, strengthening the group of adult oysters as a whole. "If there's no diversity, then the oysters aren't resilient to pressures like disease or environmental change," McDowell says. "It's very important to have genetic diversity so that the oysters can adapt."