PHYSIOLOGICAL VARIABILITY OF EASTERN OYSTERS FROM APALACHICOLA BAY, FLORIDA

Eastern oysters, Crassostrea virginica, were collected monthly during a 1-y period from two study sites in Apalachicola Bay, FL, and several measurements were made of their physiologic condition. Continuous and intermittent temperature measurements at both sites shows highly coin cident ambient temperature regimens. Salinity measurements, however, w ere erratic and varied dramatically between sites. Oyster gonad size a nd gametogenic condition were highly synchronous at both sites, suppor ting the concept of temperature-driven reproductive cycles. Other meas urements, including condition index, wet:dry tissue weight ratio, dige stive tubule condition, and vesicular connective tissue condition, sho wed significant variability as the result of sampling month. but also differed because of site and/or interaction between date and site, ind icating that local effects influenced oyster physiology. Temperature c ontrol over condition index and wet:dry tissue weight seems apparent, bur it is not known whether the changes resulted directly from tempera ture or from temperature-driven reproductive and metabolic cycles. A s ignificant difference between site means at specific dates was observe d for digestive tubule condition and may relate to short-term salinity differences. Other physiologic variations could not be attributed to any of the physical conditions monitored (temperature, salinity, pH, a nd dissolved oxygen). The variability of oyster physiologic measuremen ts inherent at different sires and seasons must be well understood to properly interpret them in the context of biologic indicators of envir onmental condition.