Effects of eutrophication, morphological alteration and habitat characteristics on the spatial distribution of littoral macroinvertebrate communities in natural Mediterranean lakes

Introduction. The relative strength of different factors in shaping the spatial distribution of lake littoral invertebrate assemblages in Mediterranean lakes are largely unknown. In this paper we quantified the effects of habitat heterogeneity and 2 of the major anthropogenic pressures (eutrophication and morphological alterations) on littoral invertebrates. Materials and methods. Within the framework of the EU funded WISER project, we collected macroinvertebrate samples in 15 natural Mediterranean lakes, characterized by diverse degree of anthropogenic pressures. We selected 9 sites per lake according to different levels of alteration of the shores and kick sampled macroinvertebrates with a 500 μm hand net in all the mesohabitats present at each site for an amount of time proportional to their areal extent. We used spatial analysis techniques along with variable selection procedures to partition the variance among environmental variables at different scales and the pure spatial components. Results. About half of the explained community variance (49%) was due to the pure spatial component. Of the remaining community variance, a large fraction was explained by morphological alterations (27%), while eutrophication explained 3%, and habitat characteristics less than 1% of variance. The remaining variance fraction was explained by interactions among variable groups. Among the eutrophication related stressors, TP was the most significant explanatory variable, while site land use (natural/seminatural, agricultural, urban), percentage of modified shoreline, percentage of natural/seminatural, urban and agricultural land use in the 200 m belt around the lake were significant stressors related to morphological alteration. Finally percentage of site macrophyte cover, number of littoral mesohabitats, substrate texture groups resulted significant habitat habitat-related factors. Conclusion. The spatial structure of littoral invertebrate communities of Mediterranean lakes are mostly constrained by morphological alteration while eutrophication and habitat characteristics seem to have only marginal effects.