Zooplankton communities in mountain reservoirs of the Eastern Alps

Due to global changes, ski lift operators are increasingly dependent on artificial snow. The snowmaking process requires large amounts of water, leading to the construction of mountain reservoirs throughout the Alps. While these reservoirs can have a negative impact on the mountain ecosystem and landscape structure, they also provide a potential new habitat for aquatic organisms such as zooplankton. In addition to the harsh conditions in alpine regions, species inhabiting these water bodies must also cope with fluctuations in water levels. Our study aimed to identify the zooplankton species inhabiting mountain reservoirs, to determine whether these communities show similarities to those of natural alpine lakes, and to identify the ecological factors related to their abundance. Samples were collected from eleven reservoirs located in the Eastern Alps twice during the ice-free period. Depth profiles were obtained for temperature, dissolved oxygen, electrical conductivity and pH, and samples were taken for water chemistry, chlorophyll a, bacteria, ciliates and zooplankton. The results show that all reservoirs contained zooplankton (22 taxa in total, 1-11 taxa per reservoir, 7 taxa on average). The species composition was similar to that of nearby natural lakes. Furthermore, reservoirs located in close proximity displayed similarities in zooplankton composition. A wide range of abundance was observed (summer: 0.09-168.74 Ind per litre; autumn: 0.04-1092.78 Ind per litre), which was significantly related to environmental factors, including elevation, DOC, chlorophyll a, pH, K⁺, total phosphorus, and Ca²⁺. While rotifers were numerically dominant in the reservoirs, the zooplankton biomass was dominated by crustaceans. Our data suggest that local factors have a greater effect than regional factors on these rapidly changing systems. The findings contribute to our understanding of the distribution of zooplankton in remote regions, despite the artificial nature of these systems.