Measurements of biomass and activity of neustonic microorganisms

Microlayer samples from a coastal marine area near Marseilles (France) collected in 1979 and 1980 have been analysed for POC, PON, chlorophyll a, ATP, cell counts, carbon fixation and in some cases for heterotrophic activity. Comparison of microlayer data with those of underlying water showed in most cases enrichment of organic matter and microorganisms in the surface microlayer. Carbon fixation values were comparable to those observed at 0·50 m except in the slicks, where phytoneustonic activity was higher than that of the underlying phytoplankton. Though total heterotrophic activity was higher in the surface film, the turnover time was not significantly different in both microlayer and underlying water. Our data show that enrichment is highly dependent on sea conditions; whenever slicks are present, the surface film seems to function like an eutrophic system, including active living material, although detritus is regularly present in large amounts.