Do Rotifers show "avoidance of the shore"?

The term "avoidance of shore" was used in literature to describe the observation that pelagic crustacea are in general absent near the shore. Experiments in the field show, that Rotifers-which form, together with crustaceans, the main mass of zooplankton-can also be divided not only by morphological criteria but also as a result of their horizontal distribution into inhabitants of either the littoral or the pelagic zone of a lake.These differences of horizontal distribution can be explained by a typical behavioral difference between the littoral rotifer Euchlanis dilatata and the pelagic Asplanchna priodonta: when exposed in the shore zone, Asplanchna wanders in the direction of the pelagic zone, while Euchlanis on the contrary does not prefer any particular direction under the same conditions. Experiments at different lakes with other pelagic rotifers confirm that the "avoidance of shore" shown by Asplanchna is a general phenomenon.The influence of the analyzed behavior on the horizontal distribution patterns of rotifers and the factors which cause and determine the direction of the migration are discussed.