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The microbial biomass present in Windmill Islands soils, under varying degrees of Adelie penguin (Pygoscelis adelie) influence, was estimated using four different approaches. Average concentrations of 1200, 180, and 440 mug microbial C g-1 (measured as ATP) were detected in active colonies; extinct colonies and soils possessing visible algal growth respectively. This compared with an average of 12 mug C g-1 in control samples from sites remote from penguin colonies. Biomass estimates based on substrate-induced-respiration rates were 1-4 times higher than the equivalent ATP estimates.

The soil microbiota of active penguin colonies was dominated by bacteria (92% of the total biomass) with tetrad-forming cocci comprising 35% of the total biovolume. Away from the immediate colony site, algal biomass, measured as chlorophyll a, accounted for 78-96% of the total biomass of carbon while bacterial biomass measured microscopically accounted for 4-22%. Yeasts accounted for <1% of the total biomass. Too few fungal hyphae were detected to make useful direct counts and their biomass appeared to be less than for yeast-like forms. Increasing algal predominance corresponded with decreasing soil pH and a 10,000-fold increase in fungal biomass compared to bacterial microbiota, as measured by colony counts.