Quantitative and qualitative bacteriology of the marine water surface microlayer in a sewage-polluted area

The thin microlayer constituted of organic matter which is present at the seaair interface has been shown to accumulate bacteria and, therefore, represents a phenomenon of sanitary significance. The enrichment of indicator bacteria observed within the neuston, in relation to subsurface water contamination, has been followed in three stations presenting different contamination levels and various types of pollution. The bacterial enrichment in the neuston has been estimated to range from 24- to 720-fold in comparison with subsurface water. For a given sampling station the enrichment observed for the four bacterial groups considered is rather homogeneous. In contrast, clear differences appear between the stations. The value of the enrichment factor seems to be influenced by the organic contamination in the surface film. A qualitative analysis of bacteria isolated from surface and subsurface water has pointed out some differences between these two groups of samples.