Growth rates of dominant planktonic ciliates in two freshwater bodies of different trophic degree

The in situ growth rates of dominant ciliate species were studiedduring and shortly after phytoplankton peaks in two water bodies:the eutrophic Rímov Reservoir (South Bohemia, Czech Republic)and the oligo-mesotrophic Piburger See (Tyrol, Austria). Growthrate estimates based on changes in ciliate abundances in incubatedpre-screened samples (E_N) were compared with those derived fromthe ciliate cell volume and ambient temperatures (E_T). The valuesof E_N were always rather lower than those of E_T. During thestudies, the food supply limited the ciliate growth dependingon the ciliate feeding mode. An ecological grouping into filterfeeding versus raptorial feeding (‘hunting’) species,on the one hand, and attached/crawling (browsing) versus freeswimming species, on the other hand, clearly affected experimentalestimation. Both fine filter feeders (namely attached) and browsersexhibited a calculated E_N closer to the theoretical (maximum)E_T than did hunters and coarse filter feeders. It was apparent,for example, comparing E_N and E_T (day^–1) of the followingspecies: filter feeders Halteria grandinella (E_N = 0.42; E_T>1.4), Strobilidium hexakinetum (0.34;>1.9), Pelagohalteriaviridis (0.27;>0.9), Vorticella aquadulcis complex (0.75;>1.0);raptorial Balanion planctonicum (0.65;>1.5), Urotricha furcata(in Rímov Reservoir 0.65;>2.1; in Piburger See 0.20;>1.5),Rhabdoaskenasia minima (0.22;>1.0), Askenasia acrostomia(0.12;>0.6); opportunistic Cyrtolophosis mucicola (0.42;>1.6)and Cinetochilum margaritaceum (0.86;>1.4). Predation byrotifers apparently affected measurements in several samplescontaining {small tilde}400 rotifers l^–1 however, it seemedto be of little importance in the water column.