Assessment of Taxonomic and Functional Diversity of Mayfly Assemblages Along the Course of a Large European River

Abstract

Large rivers are complex freshwater systems with high habitat heterogeneity providing home and resources for numerous species. Even though they are considered biodiversity hotspots, our knowledge about the ecological requirements of inhabiting biota is still not sufficient. In this study, we investigated mayfly assemblages along the course of a large European river, Sava, with the main aim of identifying their taxonomic and functional diversity patterns along the river's course, as well as their relationship with environmental variables (water parameters and land use). A total of 29 mayfly species were recorded. We observed a downstream decreasing gradient in mayfly taxonomic assemblage metrics, influenced by habitat characteristics and anthropogenic pressures. Mayfly assemblages were highly determined by altitude, distance from the source and water parameters, such as temperature and conductivity. Higher taxa richness and abundance were recorded in colder upstream sections compared to downstream ones, characterized by higher conductivity (and higher anthropogenic impact). However, functional diversity was comparable along the river's course, with distinct traits compensating for each other and maintaining overall functional complementarity. Despite the present human impacts, some rare and sensitive species, such as Ephoron virgo, were recorded in the lower section of the studied river, indicating its conservation value. Hence, our study highlights the need for conservation measures for large rivers and the protection of the rare species they provide habitat for.