Oyster Sentinel uses the eastern oyster, Crassostrea virginica, to monitor the environmental health of estuaries along the Gulf of Mexico. The eastern oyster and its principal parasite Perkinsus marinus, are bio-indicators of mesohaline salinity regimes, and their distributions can be used to evaluate the Freshwater Resources needed to sustain oysters, control parasites and predators, and support other estuarine-dependent organisms.