Biodiversity (species richness and species diversity) of chydorid Cladocera were examined by weekly sweep net sampling during the ice-free period and through surface sediment assemblages in 9 limnologically different lakes in southern Finland. Species richness in the sweep net samples was low in 2 lakes with recent ecological perturbations and the highest in one oligotrophic lake. Species diversity was the lowest in 2 eutrophicated lakes and generally higher in the oligotrophic lakes. The biodiversity values in sediment assemblages showed trends similar to those in the sweep net samples; the lowest values were observed in one of the eutrophic lakes and the highest in the oligotrophic lakes. It is likely that the observed differences were due to the impact of nutrients on the development of littoral vegetation and consequently chydorid habitats and resources. The role of nutrients as a forcing mechanism on chydorid biodiversity was indicated by high and significant negative correlations between species diversity in both total phosphorus and sweep net and sediment samples. The comparison between biodiversity in the 2 sample types showed that the biodiversity values were almost consistently higher in the surface sediment assemblages than in the sweep net samples, suggesting that surface sediment analysis provides an effective alternative method to living material examination for biodiversity evaluations.
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Vol. 17 • No. 4