Abstract:

Aims: The Chishui River basin in the upper reaches of the Yangtze River harbors a rich array of macroinvertebrate diversity. While the area’s importance has been acknowledged and is included in the National Rare and Endemic Fish Nature Reserve, our understanding of its macroinvertebrate diversity and dynamics remains limited. Importantly, continuous, seasonal macroinvertebrate surveys of the entire Chishui River basin have not been undertaken. To address this shortcoming, we conducted a comprehensive analysis of species diversity in this system and updated the species list based on the combined datasets of 2019-2021 seasonal investigations.
Methods: Macroinvertebrates were sampled from the main stream and tributaries in autumn (October 2019), winter (December 2019), summer (July 2020) and spring (March 2021). One-way ANOVA was used to examine the differences of abundance, biomass and ecological indices between different reaches and different seasons. Principal co-ordinates analysis (PCoA) and PERMANOVA were adopted to test the variation of community structures among different reaches and seasons. Redundancy analysis was applied to identify the key environmental factors and spatial factors that significantly influence the community structure of macroinvertebrates. The potential drivers of observed community patterns and proposed protective strategies and actions were subsequently identified.
Results: A total of 209 species of 186 genera and 86 families in 22 orders and 5 phyla were recorded with the exclusively dominant species being aquatic insects: Ephemera sp., Heptagenia sp., Polamanthus sp., Baetis sp., Naucoridae sp. and Polypedilum sp. Indexes of species richness, abundance and measures of diversity (Shannon-Wiener diversity index, Simpson dominance index, Pielou evenness index) revealed substantial spatial-temporal differences, with the largest in spring and in the upstream region. PCoA showed that the macroinvertebrate community structure varied significantly between seasons and sections of the river. Redundancy analysis (RDA) showed that five environmental (substrate, altitude, velocity, dissolved oxygen, NH₄⁺-N) and four large-scale spatial factors (PCNM1, PCNM2, PCNM3, PCNM6) were the key drivers underpinning community variation. Variation partitioning analysis indicated that environmental filtering had a stronger effect on community variation than spatial structuring.
Conclusion: To rehabilitate and protect the river’s macroinvertebrate diversity, we recommend the implementation of multiple protective strategies and preventive actions. These include at the very least, the introduction of a ten-year fishing ban, continuous afforestation practices, and regulation of illegal mining and liquor-making industries to promote recovery of the natural hydrological rhythm and riparian zones. State-of-the-art methods to prevent and control invasive alien species, and the establishment of effective prediction and risk evaluation mechanisms are also recommended.

Key words: Chishui River, macrobenthos, community structure, biodiversity, redundancy analysis