Morgan Kelly and Jerome La Peyre

Louisiana’s eastern oyster fishery is the largest in the nation, yielding nearly 5.5 thousand tons worth more than $68 million in 2016. However, recent years have signaled trouble for this culturally and economically important fishery, with sharp declines in some areas in the natural production of juvenile oysters, called spat. One reason for these declines may be changes in the amount and timing of freshwater inputs into Louisiana estuaries. Oysters thrive in habitats where fresh water from the land mixes with salt water from the ocean. Too much seawater brings disease and predators, while too much fresh water can stop oysters from feeding and reproducing. Prolonged fresh water may even lead to death, especially for sensitive juveniles. Increasingly, diversions and large rain storms are bringing large pulses of fresh water to Louisiana oyster reefs, potentially threatening their survival.

In a Louisiana Sea Grant-funded project, LSU researchers are seeking to understand the effects of increased fresh water on oysters in Louisiana. In particular, they are trying to understand how fresh water might affect some populations differently than others. Every oyster, just like every human, is genetically unique. Each oyster’s unique genetic makeup affects how it handles stress, with some handling it better than others. The researchers hypothesized that oysters from habitats with a long history of low salinity might already be better adapted to those conditions. To test this, they collected stocks of oysters from three sites: Lake Calcasieu (relatively high salinity), Sister Lake (mid salinity) and Vermilion Bay (low salinity). These stocks were spawned at the Louisiana Sea Grant Hatchery in Grand Isle, and juvenile oysters from all three parental stocks were placed back in the wild at high-, mid- and low-salinity sites for one year. Researchers monitored the oysters every couple of months, measuring their growth and checking for mortality and disease. Meanwhile, they took tissue samples from four oyster populations to the lab to sequence their DNA and test for genetic differences among populations. They found that oysters from different stocks do indeed differ in their growth rates, mortality and susceptibility to disease. They also identified several genes that differ among populations and may be responsible for their differing growth rates and disease resistance.

Results from this project will have important applications to management and conservation of Louisiana oysters. As conservation efforts move toward hatchery production and restoration, this research will help managers identify parental stocks most resistant to disease and those best suited to outplant sites with differing levels of fresh water.

Morgan Kelly is an assistant professor of biology at LSU, and Jerome La Peyre is a professor in the School of Animal Sciences.

Graduate student Hollis Jones prepares to take tissue samples from oysters. Photo by Morgan Kelly

Graduate student Joanna Griffiths prepares to measure sizes of oysters from a field experiment. Photo by Hollis Jones

Shucked eastern oyster. Photo by Morgan Kelly