Do the Ecoregions Support Distinct Hilly and Mountain Stream Chironomid Assemblages in South-East Europe?

The region of South-East Europe, located in geologically and climatically diverse areas, hosts a wide range of freshwater habitats. However, comprehensive studies of macroinvertebrate communities are limited, and research on Chironomidae (Diptera) is particularly scarce. We present data on the diversity and structure of chironomid assemblages in hilly and mountainous streams across three ecoregions: the Pannonian Lowland (Ecoregion 11), the Dinaric Western Balkans (Ecoregion 5), and the Eastern Balkans (Ecoregion 7) and provide a comparative overview of their community patterns based on 130 samples. According to the CCA results and Monte Carlo permutation tests, water temperature, dissolved oxygen, conductivity, pH, and altitude were identified as statistically significant parameters influencing Chironomidae assemblages across the ecoregions, collectively explaining 72.20% of the variation. The higher diversity indices were recorded in each season in the Pannonian Lowland and the highest within-ecoregion similarity. Dissimilarity was highest between ER11 and ER7 and lowest between ER5 and ER7. These results demonstrate that the ecoregion was the strongest influence of the studied environmental variables on Chironomidae assemblages, with community patterns closely reflecting their spatial distribution across distinct ecoregional settings.