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

## TL;DR

This study shows that chironomid insect communities in mountain and hilly streams of South-East Europe vary significantly between ecoregions due to environmental factors like temperature and water chemistry.

## Contribution

The study provides new evidence that ecoregions strongly influence chironomid assemblage patterns in South-East European streams.

## Key findings

- Environmental factors like water temperature, oxygen, and pH explained 72.20% of variation in chironomid assemblages.
- The Pannonian Lowland showed the highest chironomid diversity and within-ecoregion similarity.
- Ecoregion was identified as the strongest influence on chironomid community patterns.

## Abstract

South-East Europe, with its diverse geological and climatic settings, is a freshwater biodiversity hotspot, yet studies linking ecoregional environmental conditions to macroinvertebrate assemblages remain limited. This study examines the diversity and structure of chironomid assemblages in hilly and mountainous streams across three ecoregions, the Pannonian Lowland, Dinaric Western Balkans, and Eastern Balkans, based on 130 samples. As one of the most abundant and ecologically versatile freshwater macroinvertebrate groups, Chironomidae serve as key indicators in biological monitoring and are the main focus of this study. The results showed that environmental factors such as water temperature, oxygen content, conductivity, pH, and altitude, explained most regional differences, with the assemblages in the Pannonian Lowland showing the highest diversity and most substantial inter-region similarity. Overall, the findings demonstrate that ecoregions strongly shape chironomid assemblages, producing clear spatial patterns across the study area.

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.