Microcystin is commonly measured in freshwater environments. However, during high rainfall events Microcystis and the corresponding toxin, microcystin, can be introduced through drainage to brackish or marine environments. The high rainfall events also introduce freshwater into marine environments, decreasing salinity in these systems. Oysters in the systems are then exposed simultaneously to microcystin and low salinity. Potential increases in rainfall place the health of wild and farm raised oysters in danger. Oysters are sessile, benthic filter feeders. Their feeding methods directly expose them to microcystin in the water column. Microcystin accumulates in the tissues of oysters, which could also impact their microbiomes. Oysters are highly sensitive to changes in salinity; however, the effects of low salinity in combination with microcystin on oyster microbiomes and oyster health have not been examined. This study will measure potential changes in the microbiomes of oysters after exposure to microcystin and low salinity. Crassostrea virginica will be experimentally tested for microbiomes changes after microcystin exposure (3ug and 8ug) in low (10 ppt) and regular salinity (20 ppt) measurements. Oysters will be exposed to high or low salinity and co-exposed to low or high microcystin concentrations. Knowledge of the response of easter oyster microbiomes to low salinity and microcystin will further our understanding of the physiology and microbiome of eastern oysters.