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A short overview of the biodiversity of Antarctic marine bacteria is given with respect to morphology and metabolic activity. The importance of spatial and temporal variability is described. The physiological adaptation and ecological function of Antarctic marine bacterioplankton are discussed.

During a 1-year period, systematic observations of the Antarctic coastal marine bacterioplankton were recorded. Three field stations were sampled weekly in 1989 in “Terre Adelie” area. The survey included physicochemical (temperature and particulate organic matter) and bacteriological (total and heterotrophic counts, estimation of bacterial production) measurements. The bacterial community structure was investigated by carrying out 27 morphological and biochemical tests on 254 strains isolated during each season. Gram-negative non-fermentative rods were always dominant. However, an obvious difference exists between the communities inhabiting ice-free and ice-covered seawater. The potential metabolic abilities which were relatively significant in the summer community were severely reduced in the winter community. A general increase in bacterial biomass and production was observed in surface water after sea ice formation. The results suggest a close coupling between heterotrophic bacterioplankton and the input of allochthonous organic carbon, for example from the overlying sea-ice communities or from nearby penguin rookeries.

Previous Antarctic studies have pointed out the ecological importance of ornithogenic soils. However, few data exist to determine the impact of the bird's manuring on surrounding seawater microbial populations. In order to evaluate the influence of birds manuring, the relationships between the spatial distributions of seawater bacterial microflora and some related biological (chlorophyll pigments) and physicochemical (seston, NH4 + & NO3 −) parameters were studied during the Antarctic summer 1988 in the Terre Adelie land area. The clearly decreasing gradient from the shore towards the open sea previously reported for bacterial microflora (from 104 to 1 CFU ml−1 for heterotrophic bacteria and from 105 to 5.0103 cells ml−1 for total bacteria) was also observed for organic and mineral nutrients (from 1.09 mg Cl−1 to 0.1 mg Cl−1 for POC and from 196 to 17 μmole l−1 for NH 4 + ) but not for chlorophyll pigments. The absence of any observable phytoplankton enrichment in the coastal area suggests a direct interaction between the birds manuring and the bacterial seawater microflora.

Previous antarctic studies have pointed out the ecological importance of ornithogenic soils. However, few data exist to determine the impact of such guanoenriched soils on surrounding seawater microbial populations. In order to evaluate the influence of birds, the relationships of spatial distribution of seawater bacterial microflora to penguin repartition were studied during the antarctic summer 1986 in Terre Adelie land area and in January 1984 in the subantarctic Kerguelen Archipelago. With bacterial estimates as high as 1.7×108 cells ml-1 for total counts and 2.3×107 CFU ml-1 for aerobic heterotrophic populations, ornithogenic soil analyses confirmed previous results from similar sites. In seawater a clear decreasing gradient from the shore towards the open sea was found. All bacterial parameters studied (epifluorescence direct counts, frequency of dividing cells estimation and viable counts) were correlated significantly with penguin populations. Complementary numerical taxonomy confirmed the major role played by the bird manuring in such antarctic ecosystems.

A large mussel bed occurs in one of the largest fjords in Kerguelen archipelago. In January 1986, seawater and bivalves were collected at four tidal levels to determine whether a specific heterotrophic bacterial community could be observed in the mussels, especially in the stomach and in the fecal pellets, and to compare these microflora to seawater bacterial communities. The investigation was carried out using morphological and biochemical tests. Test results were analysed by a numerical taxonomic method. Almost all the heterotrophic mesophile isolates, grown on Zobell medium, were non-fermentative Gram-negative rods. The bacterial communities in the mussel fecal pellets were clearly different from the other communities studied. This specific bacterial microflora was characterized by the existence of Vibrionaceae.

The abundances of the heterotrophic bacteria in relation to the degradation of the stranded kelp bed of Macrocystis pyrifera of the Morbihan Bay (Kerguelen Archipelago) were studied. During a one year period between the austral autumns 1982 and 1983 systematic observations of viable and direct counts of bacteria were recorded for three stations along a transect including kelp bed, intertidal and offshore waters. Quantitatively the microflora was very similar to that found in more temperate regions. Seasonal fluctuations were correlated with successive periods of deposit and degradation of the stranded kelp debris. After each new deposit, a very fast growing phase of the microbial population were observed. Doubling time (approximately 1.5 days) and biovolumes of the total bacteria showed rapid increases (from 0.16 to 0.38 μm3). At the same time the ratio direct counts/viable counts showed a significant decrease and reached values close to 1. Decreasing number of bacteria were observed along the transect studied but the impact of kelp deposits on bacterial growth reached also offshore waters.