Seasonal Variation of Bacteria in Sea Ice Contaminated by Diesel Fuel and Dispersed Crude Oil

Abstract

The long-term effects of diesel fuel and ``Arabian light'' crude oil contamination on microbial communities was investigated in land-fast ice located in the Terre Adelie area (Antarctica). After oil addition, the changes in bacterial communities were studied in situ during a nine-month period in austral winter 1993. Weekly sampling in sea ice allowed a regular survey of total, saprophytic, and hydrocarbon utilizing bacteria. A clear seasonality was observed. In uncontaminated samples, maximal values of bacterial biomass occurred during ice formation and just before summer thaw. Minimal bacterial abundance (<10⁵ cells ml⁻¹) was observed during winter. All the results (bacterial abundance, colony-forming units, and most probable number counts of hydrocarbon-utilizing bacteria) clearly revealed a significant response of Antarctic bacterial communities to hydrocarbon contamination. Three orders of magnitude increases of bacterial counts occurred in sea ice after both diesel fuel and crude oil contamination. A concomitant enrichment in oil-degrading bacteria was generally observed from less than 0.001% of the community in uncontaminated samples to 10% after 30 weeks of contamination. Addition of fertilizer (Inipol EAP 22) enhanced both saprophytic and hydrocarbon-utilizing communities. The natural winter decline of saprophytic bacterial abundance was totally absent in sea ice treated with diesel fuel oil supplemented with Inipol.