In search of suitable habitats for water beetles (Insecta: Coleoptera) within a heavily transformed river system

Abstract

The Odra is a large, regulated river, along which many groynes have been built. There are few publications examining how groynes affect the functioning of a river. We investigated the effect of these hydro-engineering structures on the water beetle fauna of a river subject to strong human pressure. The species composition, assemblages, functional and ecological groups of these beetles in groyne fields were compared with those of oxbows in the Odra valley. We demonstrated that the groyne fields were highly beneficial for water beetle development, offering highly suitable alternative habitats to oxbows which, though natural, are sensitive and endangered habitats in river valleys. The numerically dominant species in the groyne fields were rheophiles, which are typical of weakly eutrophic, well-oxygenated oxbows. Species-wise, eurytopes were the most important beetle assemblage. Macrophytes and organic matter were the factors governing the occurrence of saprophages and polyphages, which provide plentiful food resources for the predominating predators in these habitats. Either the pH, visibility, temperature, hardness and O2 both the vegetation, water depth, breadth of the littoral of the two habitat types were key to the beetles' distribution. The presence of groyne fields has rendered the species richness of the Odra's water beetles comparable with that of large, natural rivers, which amply demonstrates that not all anthropogenic transformations of habitats are inherently negative.