Spatial Distribution Patterns of Heterotrophic Bacterial Population in a Coastal Ecosystem (Thau basin, France)

The abundances of culturable heterotrophic bacterial populations on the scale of a coastal ecosystem (Thau basin, France) were measured by systematic sampling at 63 stations in all four seasons. Distribution maps produced by the 'kriging' method indicate that bacterial distribution patterns correspond to gradients that decrease from points of continental water input and extend for 2 to 10 km. Variograms were used to analyse variance of abundances with distance and to classify distribution patterns according to local and large-scale variance. The mean abundances of bacteria in the waters of the ecosystem appeared to depend on fluctuations of watershed inputs. The heterogeneity of abundances was affected by fluctuations in wind speed and the related changes in convective and advective currents. Estimations of local and larger-scale variance can also be useful in determining the most suitable sampling strategies for describing and analysing the distribution of bacteria in aquatic ecosystems.