Seasonal Dynamics of the Silica-Scaled Chrysophytes as Potential Markers of Climate Change in Natural Model: Deep Cold Lake–Shallow Warmer Reservoir

In the context of global climate changes, it is important to assess the sustainability perspective of aquatic ecosystems based on marker organisms. In this work, we analyzed seasonal dynamics of silica-scaled chrysophytes in freshwater communicating environments which have considerable differences in water temperature between two ecosystems: the deep and cold oligotrophic Lake Baikal versus the shallower and warmer downstream Irkutsk Reservoir having mesotrophic features. During three seasons of the open water period of 2023, 38 species of silica-scaled chrysophytes were observed at 17 stations using scanning and transmission microscopy. The distribution of silica-scaled chrysophytes was shown to correlate with the water temperature. The greatest species richness was observed in the spring season in a large bay of the Irkutsk Reservoir (23 species), the smallest in the cold spring waters of Southern Baikal (up to 7 species). Widespread species living in Southern Baikal continued to grow in warmer waters of the reservoir. Using the example of silica-scaled chrysophytes, the stability of the high-latitudinal freshwater ecosystems affected by climate change is discussed. Continuous increment of the water temperature can lead to an increased abundance of widespread species and the displacement of psychrophilic species, affecting the overall biodiversity in such ecosystems.