PS 37-18 - Seasonal dynamics of eukaryotic and fish communities in Yangyang Namdae Stream using environmental DNA metabarcoding

Abstract: Yangyang Namdae Stream in Korea is a notable river that flows into the East Sea, with a significant presence of cold-water fish species and brackish water organisms. It has great ecological importance due to its high biodiversity and dynamic population characteristics, particularly in relation to the migration of diadromous species among domestic rivers. This study aimed to identify the composition of eukaryotic and fish species in Yangyang Namdae Stream using environmental DNA over a period of four years. Freshwater samples were collected from seven sites, including one tributary, from the brackish coast to the upstream, and a total of five surveys were conducted between 2019 and 2022. eDNA metabarcoding analysis was performed using universal primers targeting nuclear 18S rRNA V9 and mitochondrial DNA 12S rRNA regions as markers for eukaryotes and fish, respectively.

The metabarcoding analysis generated 6,541,377 merged reads for eukaryotes and 5,338,452 merged reads for fish, identifying 46 phyla and 97 species, respectively. The eukaryote communities in Yangyang Namdae Stream showed distinct characteristics based on watershed location (brackish water/lower stream/mid-upper stream), with the August community being particularly noteworthy irrespective of the watershed and year. Paracalanidae and Chaetocerotaceae were identified as the most abundant taxa in brackish waters, and representative algae such as Chrysophyceae, Scenedesmaceae, and Dunaliellaceae were found in August. The fish communities also displayed distinct characteristics based on their location in the stream (brackish water/downstream/upstream), with seasonal dynamics of anadromous Salmonidae species (Oncorhynchus keta and Oncorhynchus mykiss) being evident in March and November. In addition, we were able to identify the spawning evidence of Plecoglossus altivelis from August to October and the spawning and migration characteristics of Tribolodon hakonensis in March. This study indicated that environmental DNA (eDNA) metabarcoding is a promising tool for monitoring the distribution of eukaryotes and fish in dynamic river systems and for elucidating seasonal variations in biodiversity and community structure.