PARTICLE-SIZE DEPENDENT FEEDING BY THE ROTIFER BRACHIONUS-PLICATILIS

Size selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0. 3-3.5 mum) and mono-disperse latex beads (0.3-3 .0 mum) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter greater-than-or-equa l-to 2 mum, but particles with diameter down to 0.3 mum were also inge sted. The clearance rate of bacteria was 15-55% of that obtained for o ptimal sized particles (greater-than-or-equal-to 2 mum), and was relat ed to particle size. The relative reduction in retention of particles with diameter < 2 mum was more pronounced for latex beads than for nat ural food particles, suggesting other mechanisms than size to be impor tant for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i .e. rotifers with low maximum clearance rate. This may reflect a strat egy to optimize energy utilization by reducing locomotion costs and in creasing energy intake. The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high pop ulation densities, such as in live feed cultures, the rotifer may, how ever, efficiently remove bacteria from the culture.