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Our long-term goals are to understand how complex mixtures of contaminants influence benthic communities at the levels of microorganisms, microalgae, invertebrate grazers, and fish predators. In particular, we are interested in how contaminants influence foodweb interactions among these groups of organisms. Our research examines the interactive effects of metal (Cu, Cr, Cd, Hg, and Pb) and diesel-fuel contaminants on the benthic food web of a coastal salt marsh, the specific role that Cu plays in this suite of contaminants, and how hypoxia influences the manifestation of toxic effects. Specifically, we are examining how diesel and metal contaminants interact to influence the microbial (bacteria and microalgae), invertebrate, and juvenile fish components of the benthic community, and how their interactions influence trophic relationships among organisms. Previous studies have focused on either the ecotoxicological effects of metals or the effects of hydrocarbons, but essentially nothing is known about how these two classes of contaminants interact. The modes of toxicity of hydrocarbons and metals are quite different, and individually they may elicit different, sometimes opposite, ecological responses. Impacted field sediments, especially in harbors, are typically contaminated with both metals and hydrocarbons, and thus ecological impacts may be a consequence of their interactive effects. Our experimental approach to this problem will provide fundamental information on the ecological manifestations of metals-hydrocarbons interactions, and provide the basis for making ecologically sound decisions concerning appropriate bioremediation or mitigation strategies for contaminated field sites., Prepared in collaboration with the Dept. of Oceanography and Coastal Sciences and the Institute for Environmental Studies, Louisiana State University, Baton Rouge.

The influence of diesel fuel on benthic food webs in coastal salt marshes were examined in a series of microcosm experiments. Diesel contamination resulted in high mortality to all copepods except Cletocamptus deitersi, while nematode abundance increased. Blooms of benthic microalgae that developed in contaminated sediment were primarily a response to reduced copepod grazing, and secondarily a consequence of enhanced NH4+ flux from sediments. Microalgal grazing by nematodes and copepods was enhanced in contaminated sediments, and was a consequence of C. deitersi competition with copepods other than C. deitersi.