ABSTRACT Freshwater habitats are globally threatened by various anthropogenic pressures, resulting in reduced habitat quality and diminished biodiversity. Due to their sensitivity to environmental change, mayflies are commonly used in biomonitoring programs worldwide. We investigated how mayfly assemblages in anthropogenically impacted habitats (hydropower plant reservoirs, drainage ditches, tailrace canals, old river channels) of the Drava River are affected by habitat type, physical and chemical water parameters and fish assemblages. Overall, the reservoirs had the lowest mayfly taxa richness, taxonomic and functional diversity, due to substantially altered habitat hydromorphology. Similarly, reservoirs and tailrace canals had significantly lower mayfly abundance compared to drainage ditches, most natural habitats and old river channels. Water quality parameters had only a minor influence in shaping mayfly assemblages, as species were primarily driven by hydromorphological habitat traits rather than by any single water quality parameter. Furthermore, our results indicate an important influence of predators, such as fish, in shaping mayfly assemblages in the studied river system, as a negative correlation was observed between fish assemblages and mayfly assemblage metrics. Our results confirm that hydromorphological habitat alterations (dams and river impoundments), combined with high fish occurrence, exert a strong negative influence on mayfly assemblages.
Vilenica et al. (Fri,) studied this question.