VARIATIONS IN TRACE-METAL CONCENTRATIONS IN AMERICAN OYSTERS (CRASSOSTREA-VIRGINICA) COLLECTED FROM GALVESTON BAY, TEXAS

Nearly one thousand oysters (Crassostrea virginica) were collected at 15 sites on four sampling trips to Galveston Bay during 1992-1993. Iro n, silver, arsenic, cadmium, copper, lead, and zinc were determined in the whole soft part of the individual oysters. Trace metal concentrat ions were found to vary among individuals within a site on a given tri p, and spatially and temporally around the Galveston Bay estuarine sys tem. Differences in metal concentrations from site to site were a fact or of 5 or more for some metals, and similar differences were found fr om time to time at a given site. Zinc was found in anomalously high co ncentrations at several sites, mainly along the west side of Galveston Bay. Isolated high values of other metals were found scattered throug hout the bay; however, only one site (GBSL, near Swan Lake in lower Ga lveston Bay) was found to have significantly higher than average conce ntrations for several metals (Ag, Cu, Ph, and Zn). One obvious trend f ound in this study was that metal concentrations, except for As, were highest in the summer, followed by the fall, and lowest in the winter and spring. The temporal changes in metal concentrations in oysters ca nnot be explained by changes in body weight in different seasons, and are apparently caused by changes in environmental conditions (e.g., me tal input, salinity) or biological activity (e.g., metabolism, depurat ion).