Grazing on Bacteria by Zooplankton in Australian Billabongs

Five species of rotifer (Brachionus lyratus, Conochilus dossuaris, Keratella cochlearis, Keratella quadrata and Trichotria tetractis) ingested bacteria at a prey density of 5-7 × 109 cells L.-1, and a sixth (Keratella procurva) did so at a higher bacterial concentration of 4 × 1010 cells L-1. Gastropus minor, Polyarthra vulgaris, Synchaeta pectinata and Trichocerca similis were not bacteriovores. Fluorescent-stained (DATF or acridine orange) bacteria were not suitable for determining which rotifers were potential grazers. However, bacteriovory was detected easily with safranin-red or methylene-blue stained bacteria. Clearance rates for the zooplankton community larger than 51µpm, determined with 3H-thymidine labelled bacteria, varied from 200µm, 90-200µm and 51-90µm fractions: it was impossible to ascribe bacteriovory to discrete taxonomic groups, because zooplankton taxa were not completely separated by these mesh sizes.