Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Though rotifers play an important role in many pelagic ecosystems, there is a lack for studies on diurnal variations in feeding behaviour. Diurnal feeding rhythms of estuarine populations of <jats:italic>Brachionus plicatilis</jats:italic> and <jats:italic>Keratella cruciformis f. eichwaldi</jats:italic> and a pond population of <jats:italic>K. cochlearis</jats:italic> were investigated using <jats:sup>14</jats:sup>C‐Chlorella and <jats:sup>14</jats:sup>C‐labelled natural bacteria populations, respectively, as a tracer food during <jats:italic>in situ</jats:italic> experiments. A <jats:sup>51</jats:sup>Cr/<jats:sup>14</jats:sup>C double tracer technique was used to determine Assimilation efficiencies.</jats:p><jats:p>All species had about two times higher feeding rates during day than during dark hours. There was a tendency for higher values during the afternoon. No trend was found regarding diurnal changes in assimilation efficiency.</jats:p><jats:p>Diurnally segregated niches between microphagous daytime active rotifers and nighttime active crustacean populations in pelagic ecosystems are demonstrated and their ecological significance with special regard to changes in food quality and predation pressure is discussed.</jats:p>