Ciliate communities of a large shallow lake: Association with macrophyte beds

We investigated the influence of macrophyte composition on ciliate community structure in a large, shallow, eutrophic Lake Võrtsjärv. We hypothesized that macrophyte composition must have strong influence on the dispersal of ecologically different ciliate groups in a shallow lake and that more diverse macrophyte stands cause also a greater diversity in the ciliate community. In Võrtsjärv macrophyte distribution is spatially strongly polarized both in east-west and north-south directions in relation to abiotic factors. Phragmites australis and Myriophyllum spicatum were the most widespread species occurring in most parts of the lake. Correlation of environmental, macrophyte and planktonic ciliate variables confirmed the suggested spatial gradients. More diverse macrophyte stands supported a high species richness and abundance of epiplanktonic community but showed negative influence on the number and abundance of euplanktonic ciliate taxa. Opposite trends were found relative to the abundance of P. australis. Benthic ciliates showed a similar distribution pattern to euplanktonic taxa being most abundant in sites were the Shannon-Weaver index for macrophytes was low. Strong polarizing effect of the lake's vegetation on planktonic ciliate diversity was reflected in correlations of the number of ciliate taxa as well as the numbers of eu- and epiplanktonic taxa with geographic co-ordinates.