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."