SUCCESSION OF BACTERIVOROUS PROTISTS ON LABORATORY-MADE MARINE SNOW

Colonization and succession over time by bacterivorous protists on lab oratory-made marine snow were analysed in five assays during 1994. Mar ine snow was made from natural seawater using rolling tanks. In all ex periments, the macroaggregates were stable in size and consistency aft er the fourth day, and the colonization and succession processes were similar. Newly formed macroaggregates became colonized by heterotrophi c nanoflagellates on the fourth day, most of them kinetoplastids (Bodo designis and Rhynchomonas nasuta) and bicosoecids (Pseudobodo tremula ns and Bicosoeca sp.). Sarcodines and ciliates appeared 1 day later. A mong the former, the most abundant genus was Vannella sp., while scuti cociliates (Uronema marinum) and hypotrichs (Euplotes vannus and Aspid isca steini) were the most abundant ciliates. Most of the species obse rved in the study were more common to benthic habitats than to pelagic ones. The planktonic existence of the genera Bodo, Rhynchomonas, Bico soeca, Euplotes and Aspidisca depends on the presence of surfaces beca use they are poor swimmers or immotile, and Pseudobodo and Vannella ne ed attachment for feeding. The only pelagic protist observed was Urone ma, probably because its opportunistic behaviour leads it to exploit e nriched environments such as marine snow. Flagellate and ciliate abund ances in laboratory-made macroaggregates were much higher than in surr ounding water, which indicates that marine snow represents an enhanced habitat for protist growth.