Profundal meiofauna in two large lakes: Influence of pollution and bathymetric differences

Abstract

Two sets of meiofauna samples were taken from Lake Paijanne along pollution gradients, one from the maximum depths and one from the upper profundal zone, and one set of samples from the northern part of Lake Ladoga. The stations in Lake Paijanne could be grouped on the basis of meiofauna variables in approximately similar manners for both sets of samples. The connections between the meiofauna variables and environmental variables were examined for L. Paijanne, the meiofauna of the deepest zone being found to be influenced more by environmental factors than that of the upper part of the profundal zone. Oxygen saturation and phytoplankton biomass were the most important parameters in the deepest zone and total phosphorus and COD had the strongest influence in the upper profundal zone. The larger size of L. Ladoga confers a higher tolerance to environmental changes on the meiofauna, whereas the semilotic conditions in L. Paijane seem to affect the meiofauna very easily, certain quantitative and diversity values achieving their maxima in a semi-polluted or semilotic environment. Ratios calculated using the quantities of Aeolosomatidae, Naididae, Harpacticoida, benthic Cyclopoida, resting stages of Cyclopoida, benthic Cladocera and meiofauna/macrofauna biomass were used to assess regional differences in pollution, in which species-level identifications greatly improve the possibilities for using meiofauna. Top-down control seems to be more important in regulating the meiofauna than bottom-up control