SEASONAL-VARIATION OF BACTERIA IN SEA-ICE CONTAMINATED BY DIESEL FUELAND DISPERSED CRUDE-OIL

The long-term effects of diesel fuel and ''Arabian light'' crude oil c ontamination on microbial communities was investigated in land-fast ic e located in the Terre Adelie area (Antarctica). After oil addition, t he changes in bacterial communities were studied in situ during a nine -month period in austral winter 1993. Weekly sampling in sea ice allow ed a regular survey of total, saprophytic, and hydrocarbon utilizing b acteria. 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 (<10(5) 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 Antarct ic bacterial communities to hydrocarbon contamination. Three orders of magnitude increases of bacterial counts occurred in sea ice after bot h diesel fuel and crude oil contamination. A concomitant enrichment in oil-degrading bacteria was generally observed from less than 0.001% o f the community in uncontaminated samples to 10% after 30 weeks of con tamination. Addition of fertilizer (Inipol EAP 22) enhanced both sapro phytic and hydrocarbon-utilizing communities. The natural winter decli ne of saprophytic bacterial abundance was totally absent in sea ice tr eated with diesel fuel oil supplemented with Inipol.