Is sandy beach of the lake an ecotone? Psammon Rotifera in a mesotrophic Lake Kuc [Masurian Lakeland, Northern Poland

Is inshore, 2-cm layer of wet sand an ecotone? An attempt of this study is to answer the question by analysing characteristic patterns of a structure of rotifer communities inhabiting the psammolitoral zone. Psammon was sampled from sandy shore of a mesotrophic Lake Kuc (Masurian Lakeland, Poland), weekly from May to November 1996 and on one occasion in May 1998. Despite of extremely unfavourable conditions of their abiotic habitat, psammon rotifers of Lake Kuc were reaching occasionally extremely high densities. Seasonal dynamics of numbers and structure of psammon rotifer communities reflected variable character of their habitat. A course of the changes was similar in less variable higropsammon and extremely variable eupsammon. Patterns formed in psammolittoral - when illustrated with qualitative and quantitative features of psammon rotifer communities - fit definitions of an ecosystem, an ecotone, a part of a land/water ecotone, a microlayer in the ecosystem or a specific boundary zone in the lake ecosystem.