Are community composition and abundance of psammon Rotifera related to grain-size structure of beach sand in lakes?

The aim of the study was top test the hypothesis that the size distribution of sand grains in lake beach should affect the species composition, densities and body-size structure of psammon communities of Rotifera. Studies were carried out in hydro-, hydro- and euarenal zones of 38 beaches (5 to 50 m long and 1 to 10 m wide) in 16 lakes of different trophic status and morphometry (Masurian Lakeland, Poland). Porosity has no impact on psammon rotifer numbers as well as body-size of animals does not seem to play a significant role in species preference to different size classes of sand grains. However, the significant correlations were found between the rotifer numbers and the share of grain size fraction 0.25 - 1.00 mm (positive) and the share of the largest (i.e. > 1 mm) fraction (negative). The psammobionts generally are more related to the grain size ffraction 0.5-1.0 mm than the psammoxenes and psammophiles. Although particular rotifer species prefer different grain size fractions, bdelloids arre the only grroup of Rotifera preferring the smallest (<0.125 mm) grain fraction.