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.