The geographic distribution of population health and contaminant body burden in Gulf of Mexico oysters

As part of NOAA's National Status and Trends Mussel Watch Program, oysters were sampled along the Gulf of Mexico coast each winter from 1986 to 1993 ( The present analysis deals with 1986-1993 Mussel Watch data; the Mussel Wat ch project itself continues at this printing) and analyzed for trace metal, polynuclear aromatic hydrocarbons and pesticide body burden, plus a series of biological variables designed to assess population status and health. W e identified contaminant and biological variables in which large-scale spat ial processes played an important role in establishing population values by examining the likelihood that neighboring bays tended to have populations with body burdens or population attributes more similar than expected by ch ance. Local or watershed-dependent factors, such as land use and freshwater inflow, are important in controlling the bay-to-bay variation in body burd en in most contaminants. However, the bay-to-bay variations in body burden of some metals (As, Cd, Hg, Ni, Se) appear to be principally influenced by larger-scale climatic factors. These metals and the biological variable she ll length demonstrated a strong degree of similarity between bays over a la rge regional area reminiscent of the pattern shown by climatic factors, suc h as temperature and precipitation. In contrast, among the organics, none o f the PAHs showed even a moderately strong climatic signal. Among the pesti cides, only two did (dieldrin, total DDTs). These pesticides and the biolog ical variables, reproductive stage and Perkinsus marinus prevalence and inf ection intensity, had spatial patterns that suggested both a local and a re gional influence to their geographic distributions. This same pattern is ex hibited by freshwater runoff. Metal contaminants also behaved distinctively compared to organics in the temporal influence of climate in establishing the interannual variability in body burden. For the organics, trends in int erannual variability were strongly influenced by climate, whereas spatial t rends were not. In contrast, most metals were unaffected by climatic forcin g both spatially and temporally. However, all of the metals having a spatia l pattern strongly influenced by climate (As, Cd, Hg, Ni, Se) also exhibite d interannual variations related to variations in climate.