Influence of tributaries on the species richness of silica-scaled chrysophytes in the Angara River (Russia, Eastern Siberia)

The escalating impact of climate change requires comprehensive monitoring of aquatic microeukaryotic communities. Specifically, it is essential to study their successional dynamics under natural thermal fluctuations and identify organisms particularly sensitive to these changes. During the hydrological spring (early June), the watercourses of the Angara region differ in the intensity of water warming and can serve as promising model systems for studying such variations. Chrysophytes, which form siliceous scaled shells, serve as indicators of water temperature changes. In this study, we analyzed the influence of the main tributaries in the upper reaches of the Angara River–Irkut, Kuda, Kitoy, Belaya, and Ida–on the species richness of silica-scaled chrysophytes in the river channel, which is mainly affected by the cold, oligotrophic waters of Lake Baikal. During research performed in June 2024, a total of 57 silica-scaled chrysophytes species were identified in the study area using scanning and transmission electron microscopy. Among these, 11 species are potentially new to science, while one rare species Paraphysomonas capreolata and the form Synura petersenii f. columnata were recorded for the first time in Russian water bodies. The analysis demonstrated a positive correlation between the species diversity of silica-scaled chrysophytes and both water temperature and silicon concentration, alongside a negative correlation with pH levels. Statistical analysis of silica-scaled chrysophytes occurrence revealed two main profile groups: those from the main channel of the Angara River and those from its tributaries. Thus, it was determined that tributaries considerably increase the species richness of silica-scaled chrysophytes communities in the large river system, thereby increasing the overall stability of the aquatic ecosystem. This research is important for understanding the underlying mechanisms of the formation of biodiversity in freshwater ecosystems.