Research Product

Eastern oysters, Crassostrea virginica, were collected monthly during a one-year period from two study sites in Apalachicola Bay, Florida, and several measurements were made of their physiological condition. Continuous and intermittent temperature measurements at both sites showed highly coincident ambient temperature regimes. Salinity measurements however, were erratic and varied dramatically between sites. Oyster gonad size and gametogenic condition were highly synchronous at both sites, supporting the concept of temperature-driven reproductive cycles. Other measurements, including condition index, wet:dry tissue weight ratio, digestive tubule condition and vesicular connective tissue condition, showed significant variability due to sampling month, but also differed due to site and/or to interaction between date and site, indicating that local effects influenced oyster physiology. Temperature control over condition index and wet:dry tissue weight seems apparent, but it is not known whether the changes resulted directly from temperature or from temperature-driven reproductive and metabolic cycles. A significant difference between site means at specific dates was observed for digestive tubule condition and may relate to short-term salinity differences. Other physiological variations could not be attributed to any of the physical conditions monitored (temperature, salinity, pH and dissolved oxygen). Variability of oyster physiological measurements inherent at different sites and seasons must be well understood to properly interpret them in the context of biological indicators of environmental condition.