GROWTH-RATES OF DOMINANT PLANKTONIC CILIATES IN 2 FRESH-WATER BODIES OF DIFFERENT TROPHIC DEGREE

The in situ growth rates of dominant ciliate species were studied duri ng and shortly after phytoplankton peaks in two water bodies: the eutr ophic Rimov Reservoir (South Bohemia, Czech Republic) and the oligo-me sotrophic Piburger See (Tyrol, Austria). Growth rate estimates based o n changes in ciliate abundances in incubated pre-screened samples (E(N )) were compared with those derived from the ciliate cell volume and a mbient temperatures (E(T)). The values of E(N) were always rather lowe r than those of E(T). During the studies, the food supply limited the ciliate growth depending on the ciliate feeding mode. An ecological gr ouping into filter feeding versus raptorial feeding ('hunting') specie s, on the one hand, and attached/crawling (browsing) versus free swimm ing species, on the other hand, clearly affected experimental estimati on. Both fine filter feeders (namely attached) and browsers exhibited a calculated E(N) closer to the theoretical (maximum) E(T) than did hu nters and coarse filter feeders. It was apparent, for example, compari ng E(N) and E(T) (day(-1)) of the following species: filter feeders Ha lteria grandinella (E(N) = 0.42; E(T) >1.4), Strobilidium hexakinetum (0.34; >1.9), Pelagohalteria viridis (0.27; >0.9), Vorticella aquadulc is complex (0.75; >1.0); raptorial Balanion planctonicum (0.65; >1.5), Urotricha furcata (in Rimov Reservoir 0.65; >2.1; in Piburger See 0.2 0; >1.5), Rhabdoaskenasia minima (0.22; >1.0), Askenasia acrostomia (0 .12; >0.6); opportunistic Cyrtolophosis mucicola (0.42: >1.6) and Cine tochilum margaritaceum (0.86; >1.4). Predation by rotifers apparently affected measurements in several samples containing similar to 400 rot ifers 1(-1); however, it seemed to be of little importance in the wate r column.