eDNA metabarcoding in zooplankton improves the ecological status assessment of aquatic ecosystems

Aquatic ecosystems are monitored worldwide using a range of biological quality elements that are morphologically identified. The environmental DNA (eDNA)-based approach has unprecedented advantages (e.g., high throughput, high efficiency and low cost) for biodiversity surveys in both freshwater and marine ecosystems compared with traditional sampling and image recognition. The use of eDNA has been mostly limited to biodiversity estimation, how to apply the eDNA approach in assessing the ecological health status is largely unexplored. Here, using zooplankton as an example, we examined the application of eDNA monitoring for ecological status assessment in an aquatic ecosystem. The results showed that eDNA monitoring reflected the spatial and temporal variations in zooplankton structure. Both species composition and bio-interactions varied significantly between sampling seasons (dry, normal and wet). A total of 60 different zooplankton indices were calculated based on eDNA monitoring and most of these indices were highly correlated with the level of water pollution, which was indicated by the water quality index in one or all three seasons. Both qualitative and quantitative eDNA-based biological indices were correlated with water quality. The season-dependent eDNA zooplankton integrity index (IZI) reflected the ecological status, and this method improves the timeliness of bioassessment.