Subsamples (10-30 ml) were concentrated on 25 mm black polycarbonate filters (pore size 0.2 µm), stained with DAPI for 10 min (Porter, Feig, 1980) and filtered. Under epifluorescence microscopy heterotrophic bacteria were counted using UV excitation.Subsamples (10-30 ml) were concentrated on 25 mm black polycarbonate filters (pore size 0.6 µm), stained with DAPI for 10 min (Porter, Feig, 1980) and filtered. Under epifluorescence microscopy, heterotrophic (HF), photototrophic (PF) and mixotrophic (MF) nanoflagellates were distinguished using UV and blue excitation and enumerated. Nanoflagellates were classified in size categories and the biovolume was calculated.