Succession of bacterivorous protists on laboratory-made marine snow

Colonization and succession over time by bacterivorous protists on laboratory-made marine snow were analysed in five assays during 1994. Marine snow was made from natural seawater using rolling tanks. In all experiments, the macroaggregates were stable in size and consistency after the fourth day, and the colonization and succession processes were similar. Newly formed macroaggregates became colonized by heterotrophic nanoflagellates on the fourth day, most of them kinetoplastids (Bodo designis and Rhynchomonas nasuta) and bicosoecids (Pseudobodo tremulans and Bicosoeca sp.). Sarcodines and ciliates appeared 1 day later. Among the former, the most abundant genus was Vannella sp., while scuticociliates (Uronema marinum) and hypotrichs (Euplotes vannus and Aspidisca steini) were the most abundant ciliates. Most of the species observed in the study were more common to benthic habitats than to pelagic ones. The planktonic existence of the genera Bodo, Rhynchomonas, Bicosoeca, Euplotes and Aspidisca depends on the presence of surfaces because they are poor swimmers or immotile, and Pseudobodo and Vannella need attachment for feeding. The only pelagic protist observed was Uronema, probably because its opportunistic behaviour leads it to exploit enriched environments such as marine snow. Flagellate and ciliate abundances in laboratory-made macroaggregates were much higher than in surrounding water, which indicates that marine snow represents an enhanced habitat for protist growth.