SEASONAL-CHANGES OF SUB-ANTARCTIC BENTHIC BACTERIAL COMMUNITIES

From December 1982 to February 1985 systematic observations of heterotrophic bacterial populations were recorded for a nearshore marine sediment of Kerguelen Archipelago. A weekly survey included physicochemical (temperature, mineral and organic C and N) measurements. Total (A.O.D C.) and saprophytic (M.P.N. on Zobell medium) counts were used for quantitative bacterial investigations. Heterotrophic microbial activities were estimated by C-14 glucose and C-14 glutamic acid uptake measurements. The bacterial community structure was investigated by carrying out 57 morphological and biochemical tests on 1742 isolated strains. Quantitative data were treated by principal component analysis. Qualitative data were analysed by a numerical taxonomy technique using similarity coefficients with WPGM algorithm. The % abundance of the various taxonomic groups varied greatly with season. Although non fermentative Gram-negative rods were generally dominant, the existence of a succession of populations during bacterial growth resulting from periodical organic enrichements is clearly demonstrated. The nutrient supply rather than the temperature seems to be the major factor determining microbial fluctuations in the studied subantarctic coastal marine environments.