Potential effects of water-level fluctuations on littoral invertebrates in lowland lakes

Abstract

East-German lowland lakes are highly susceptible to climatic changes, as most lakes are groundwater fed and strongly dependent on the balance of precipitation and evapotranspiration in their catchments. As a significant decrease of precipitation at least during summer is forecasted, a substantial and permanent reduction of lake water levels can be expected. Water-level fluctuations will predominantly affect the eulittoral zone where submerged tree roots form an important habitat type in lowland lakes that will become unavailable for eulittoral invertebrates. Hence, we compared the invertebrate community from eulittoral root habitats with those of infralittoral habitats to test which components of the invertebrate community would be potentially affected by the loss of root habitats, and whether infralittoral habitat types could mitigate these effects. Species richness did not significantly differ between eulittoral roots and the infralittoral habitat types. Community composition of roots significantly differed from that of coarse woody debris, sand and stones but not from reed habitats. Abundances of Coleoptera, Trichoptera and abundances of piercer, predator, shredder and xylophagous species were significantly lower on sand than on roots. Conversely, there were no significant differences in community measures between reed and root habitats except abundances of Coleoptera. Our results suggest that the loss of eulittoral root habitats will cause a significant alteration of the littoral invertebrate community. This could be mitigated if unimpaired reed habitats are available in the infralittoral zone which may serve as a refuge for most species typical for root habitats. Our results need to be verified by direct observations, especially as the extent of future water-level fluctuations is currently not assessable and might be more severe than assumed.