Salinity is a determining environmental factor of the health of oyster reefs in Florida. Many of the estuaries in Florida have small watersheds and tidal amplitudes less than 1 meter. Optimal salinities and habitat for oysters (Crassostrea virginica) often occupy a zone less than 10 km, about one third of the total estuarine portion of the rivers. Extreme variation in salinity can occur from localized rainfall events as well as from managed releases of freshwater from upstream structures. In the St. Lucie River (monitored as part of the Comprehensive Everglades Restoration Plan = CERP) salinity can vary by 15 on a single tide, and by 20 or more over a few days (see below, top). The percentage of the day where salinity conditions are optimal, stressful, or detrimental to long-term oyster health can decline or improve within just a few days (see below, bottom).
Many studies focus on the metric of daily- or even longer-term mean salinity, but oysters may be able to exploit or benefit from short-term variations during daily tides. While oyster behavior may be limited, the ability to close, alter gape width, and vary filtration rate for feeding or respiration over time frames of an hour or less may allow a refugia from some of the extreme estuarine variability. Oyster health is further complicated by other factors including season, temperature, location in the estuary, reproductive status, and size and age of the oysters. Our study will be used to refine the Habitat Suitability Index models used for planning restoration of oyster habitat in CERP estuaries.