PROFUNDAL MEIOFAUNA IN 2 LARGE LAKES - INFLUENCE OF POLLUTION AND BATHYMETRIC DIFFERENCES

Two sets of meiofauna samples were taken from Lake Paijanne along poll ution gradients, one from the maximum depths and one from the upper pr ofundal zone, and one set of samples from the northern part of Lake La doga. The stations in Lake Paijanne could be grouped on the basis of m eiofauna variables in approximately similar manners for both sets of s amples. The connections between the meiofauna variables and environmen tal variables were examined for L. Paijanne, the meiofauna of the deep est zone being found to be influenced more by environmental factors th an that of the upper part of the profundal zone. Oxygen saturation and phytoplankton biomass were the most important parameters in the deepe st zone and total phosphorus and COD had the strongest influence in th e upper profundal zone. The larger size of L. Ladoga confers a higher tolerance to environmental changes on the meiofauna, whereas the semil otic conditions in L. Paijanne seem to affect the meiofauna very easil y, certain quantitative and diversity values achieving their maxima in a semi-polluted or semi-lotic environment. Ratios calculated using th e quantities of Aeolosomatidae, Naididae, Harpacticoida, benthic Cyclo poida, resting stages of Cyclopoida, benthic Cladocera and meiofauna/m acrofauna biomass were used to assess regional differences in pollutio n, in which species-level identifications greatly improve the possibil ities for using meiofauna. Top-down control seems to be more important in regulating the meiofauna than bottom-up control.