BRAUNS (M.), GARCIA (X.F.), PUSCH (M.) 2007.- Potential effects of water level fluctuations on littoral invertebrates in lowland lakes. Hydrobiologia (in press).
Lakes in the lowlands of East-Germany are highly susceptible to climatic changes, as most of lakes are fed by groundwater, and the annual precipitation is already low. As a significant decrease of precipitation at least during summer is forecasted, a substantial reduction of their water levels can be expected. It is assumed that increased dynamics of the water level will predominantly affect the eulittoral zone, and submerged roots of alder (Alnus glutinosa) as the most important habitat type for eulittoral invertebrates in East-German lowland lakes will disappear. The effects of water level fluctuations on natural lowland lakes have rarely been described since most studies focused on reservoirs or human regulated lakes. Hence, we aimed to examine the potential effects of the loss of the root habitat and whether this loss could be substituted by habitat types of the infralittoral zone. For that purpose, we compared benthic invertebrate species richness, community composition, major taxonomic groups, and functional feeding groups of eulittoral root habitats with that of the four major infralittoral habitat types from six East-German lowland lakes. Species richness did not significantly differ between eulittoral roots and the infralittoral habitat types. Community composition of roots significantly differed from those of coarse woody debris (CWD), sand and stones but not from the community of the reed habitat. The densities of Trichoptera, Odonata, Coleoptera and the densities of all but the filterer and collector/gatherer were significantly lower on sand than on roots. Our results suggest that the loss of the root habitat in the eulittoral zone will cause a significant alteration of the invertebrate community composition. However, this effect is mitigated if unimpaired reed habitats are available in the infralittoral zone which may serve as a refuge for most species typical for root habitats. The results need to be verified by direct observations especially because the amplitude of future water level fluctuations is currently not appreciable and might be more severe than presented here.