CLEARANCE RATES OF BACTERIA BY THE ROTIFER FILINIA-LONGISETA (EHRB) MEASURED USING 3 TRACERS

The clearance rates (CRs) of bacteria by Filinia longiseta were measur ed at 19-degrees-C, both in situ in Lake Loosdrecht and in the laborat ory during summer. The tracer particles used in the field were: (1) 0. 51 mum fluorescent microspheres, and (2) fluorescently labelled bacter ia (FLB). A third type of tracer particle, natural [methyl-H-3]-thymid ine-labelled bacteria (< 1.2 mum), were used as a radiotracer in a lab oratory experiment. The uptake of the first two tracer-particle types was measured by microscopic examination of the rotifer guts. In the th ird case, the uptake of radioactivity was determined by liquid scintil lation counting. The rate of uptake of the microspheres decreased 10 m in after the start of the experiment, probably because the gut passage time was exceeded. Using a 5 min feeding time, the rate of uptake of microspheres was higher than that of the FLB, though the variation in the uptake in both cases was high. The ingestion rates and CRs of bact eria by F. longiseta based on the fluorescent tracers were: microspher es, 5115 bact.ind-1 h-1 and 0.368 mul ind-1 h-1; FLB, 2252 bact.ind-1 h-1 and 0.162 mul ind-1 h-1. The mean CR using the thymidine-labelled natural bacteria and a 10 min feeding time was 0.179 mul ind-1 h-1. Th us, the CR based on the microsphere method was twice as high as for th e other two methods.