Assimilation of oil-derived carbon and remedial nitrogen applications by intertidal food chains on a contaminated beach in Prince William Sound, Alaska

Beaches in Prince William Sound, Alaska were heavily oiled by the Exxon Valdez spill in March 1989. Fertilizer supplements designed to stimulate oil degradation by indigenous bacteria were applied to beaches in the rocky intertidal zones. We used stable carbon (δ13C) and nitrogen (δ15N) isotopes to monitor trophic interactions following these treatments. Representative macroalgae and consumer organisms were sampled during the summers of 1989 and 1990. Microcosm experiments were conducted to trace bacterial assimilation of fertilizer nitrogen and to compare relative uptake of oil and indigenous substrates during 1990. Fertilizer nitrogen was the dominant source of bacterial nitrogen in the microcosm experiments. Bacteria preferentially assimilated indigenous substrates and used oil as a substrate only after more labile substrates were depleted. Following depletion of indigenous substrates, nitrogen supplements appeared to enhance assimilation of carbon from oil. The δ13C and δ15N values of bacteria growing on oil and fertilizer nitrogen were distinct in the rocky intertidal environment, providing a tracer to examine the link between bacterial production and higher trophic levels. No evidence, however, was found for a transfer of carbon or nitrogen assimilated by bacteria to higher trophic levels.