A STUDY OF FEEDING IN PREDACIOUS CILIATES USING PREY CILIATES LABELED WITH FLUORESCENT MICROSPHERES

Feeding in predacious estuarine ciliates was investigated in a series of laboratory experiments using a new method of prey labeling which facilitates microscopic indentification of ingested prey items. Ingestion rates of Mesodinium pulex, Euplotes vannus and E. woodruffi were estimated using the appearance, inside the predator, of bacteriovorous ciliates (Metanophrys sp., Cyclidium sp. and Pleuronema sp.) labeled with fluorescent microspheres. Prey remain motile and have presumably unaltered surface characteristics. Ingestion rates of log-growth phase predators increased with prey density. Mesodinium pulex ingested 0.15-0.32 cells h-1 over a prey concentration of 60-2300 ml-1. Maximum ingestion rates of E. woodruffi and E. vannus were 4.5 and 3.4 cells h-1 respectively, estimated at prey abundances of 75 and 172 cells ml-1 respectively. Comparisons of feeding rates on prey of different sizes, and the effects of starvation, indicated that ingestion is likely limited by different factors in 'raptorial' (M. pulex) and 'filter feeding' (Euplotes spp.) predators.