Storage reservoirs beyond a lake district as secondary habitats for caddisflies (Insecta: Trichoptera) in an area of karst origin (SE Poland)

Shallow and vegetation-rich storage reservoirs can be a very important element of a hydrological network supporting specific fauna. However, their ecological potential for many insect groups is often neglected in hydrobiological studies in contrast to lakes. Therefore, caddisfly fauna was studied at different levels of its organization as well as environmental drivers of the species' distribution across three reservoirs (SE Poland). The species' composition and assemblages distinguishingly showed close relationships with the caddisfly fauna of meso- and eutrophic lakes. Quantitative naturalness index (Wns) of caddisfly fauna in all reservoirs was higher in comparison to this value obtained for regional lakes. Oxygen reduction potential, temperature, electrical conductivity (physical and chemical variables of water), shading, elodeids (structural variables of reservoirs) and the average distance to the nearest water bodies (landscape variables in buffer zones of reservoirs) were all significant for caddisflies in CCA models. Analysis of functional groups revealed two characteristic features of these habitats: the lack of rheophiles and an evenly balanced trophic structure. Shallow reservoirs, despite their origin and human intervention, can provide important secondary habitats for specific invertebrate fauna. Practical guidelines are also given concerning management practices favourable to aquatic biota.