# High Diversity and Spatiotemporal Dynamics of Silica-Scaled Chrysophytes (Class Chrysophyceae) in Reservoirs of the Angara Cascade of Hydroelectric Dams

## TL;DR

This study explores the diversity and seasonal changes of silica-scaled chrysophytes in reservoirs formed by hydroelectric dams on the Angara River.

## Contribution

The study provides new insights into the spatiotemporal dynamics and ecological roles of silica-scaled chrysophytes in human-altered aquatic ecosystems.

## Key findings

- 45 species of silica-scaled chrysophytes were identified in 2024, with a total of 57 species recorded over time.
- Species composition varied significantly between reservoirs and across seasons.
- Approximately 44% of the species were phototrophs, contributing to primary production and the silicon cycle.

## Abstract

One of the human impacts on nature is the construction of hydroelectric dams. As a result, the river expands their channels, the flow slows down, artificial reservoirs are formed, and new or altered habitat conditions for aquatic organisms are created. Using electron microscopy, we examined phytoplankton samples from a vast aquatic system—including the southern part of Lake Baikal, the Angara River flowing from it, and a cascade of four reservoirs—and found a high species richness of silica-scaled chrysophytes. The species composition of these microscopic organisms varied both among reservoirs and between seasons. Our results are important for a better understanding of the processes driving diversity formation and the transformation of aquatic ecosystems under human influence.

The study of aquatic biodiversity in the context of ecosystem sustainability is of urgent research importance, with several existing knowledge gaps. Among the under-studied groups are silica-scaled chrysophytes. Their cells are covered with silica scales and bristles/spines, the species-specific structure of which can be distinguished only by electron microscopy. In June and August 2024, samples were collected from a broad aquatic system comprising the southern part of Lake Baikal and a cascade of four reservoirs formed after the construction of hydroelectric dams on the Angara River flowing from Lake Baikal. Using electron microscopy, we identified 45 species of silica-scaled chrysophytes in phytoplankton in 2024, and the overall checklist was expanded to 57, accounting for interannual differences. Clear differences in species composition and richness were observed both between seasons and among reservoirs. Approximately a quarter of the recorded species were heterotrophs, which do not contribute to primary production, whereas 44% were phototrophs and 31% mixotrophs, both groups contributing to the Si cycle and to primary production. Continuous monitoring of reservoirs is essential for understanding the processes shaping silica-scaled chrysophytes diversity and may serve as an additional criterion for assessing the sustainability and transformation of freshwater ecosystems.