Seasonal Dynamics and Heavy Rain Effects on the Diversity of Microeukaryome in the Nakdonggang River

Abstract

Rapid and cost-effective eDNA-based approaches are valuable for understanding biological communities and monitoring the biodiversity of inaccessible areas, such as large rivers and lakes. To determine temporal dynamics and precipitation effects on micro-eukaryotic assemblages, we monitored upstream (SJ) and downstream (MG) sites of the Nakdonggang River, monthly or bimonthly, from March 2019 to April 2021 using an eDNA metabarcoding technique. We observed 775 unique operational taxonomic units during the entire sampling period using the V4 region of the 18S rRNA gene as a marker. In the cluster analysis and non-metric multidimensional scaling analysis based on the relative abundance ratio of the micro-eukaryotic assemblages at the SJ and MG sites, respectively, both regions were classified by four seasons, with dominant taxa for each season being different. Whereas Chlorophyta was relatively abundant in the MG site during summer, diatoms were most abundant at the SJ site during winter. Further, metazoan taxa were relatively abundant at the MG site. Total detection of metazoa, protozoa, and microalgae taxa significantly increased with heavy rainfall. In addition, the indicator taxa representative for heavy rainfall and tolerance ranges of the amount of precipitation were predicted at both sites. As the frequency of drought and heavy rain is expected to increase owing to climate change, efforts to standardize the relation between precipitation and eDNA analysis are required.