BRAUNS (M.), GARCIA (X.F.), PUSCH (M.), WALZ (N.) 2006.- The effect of trophic state on the eulittoral invertebrate community in lowland lakes. In: G. Nützmann (Ed.), Annual Report 2005, Leibniz-Institute für Gewässerökologie und Binnenfischerei, 23/2006, 89-100.
Urban and agricultural land use still cause inputs of phosphorus and nitrogen compounds into lakes, resulting in a substantial increase of the trophic state. While the effects of trophic state on pelagic and profundal invertebrates are well known, there have been relatively few attempts to relate the composition of the eulittoral invertebrate community to the trophic state. In order to test whether the trophic state affects the eulittoral invertebrate community and whether potential effects differed between the habitat types, eulittoral invertebrate communities in five distinct habitat types of 38 North German lowland lakes were investigated. A lake-specific analysis revealed that invertebrate community composition was significantly correlated to the percentage of forest in the catchment, the percentage of coarse woody debris (CWD) and root habitats, lake water conductivity, and to total phosphorous (TP) concentration. A habitat-specific analysis revealed that TP did not affect the invertebrate community composition of reed and stone habitats, and hardly affected the community of sand habitats. Instead, community composition was determined by wind exposure (reed, stones) and by the presence of coarse debris (sand). In hypertrophic riverine lakes, CWD and root habitats were dominated by invasive species. This interrelation of invasive species' dominance and high trophic state made it difficult to separate the potential effects of trophic state and biotic interactions on the invertebrate community. Overall, we demonstrated that TP concentration explained only a part of the observed differences of the eulittoral invertebrate community composition, while catchment land use, habitat availability and wind exposure were shown to be similarly or even more important. Thus, it seems that invertebrate assemblages in the eulittoral zone are much less impacted by high trophic states than in the profundal zone. Conversely, eulittoral invertebrate assemblages are highly susceptible to land use practices that adversely affect the structural complexity of the eulittoral zone as well as to the immigration of invasive species.