Seasonal and Spatiotemporal Dynamics of Plankton Communities Using eDNA Metabarcoding in Singal Reservoir

Understanding environmental drivers of plankton community assembly is critical for predicting ecosystem responses to environmental change in reservoir systems. This study employed environmental DNA (eDNA) metabarcoding to examine how temperature, dissolved oxygen, and spatial gradients structure plankton communities in Singal Reservoir, South Korea, across seasonal and spatial scales from 2021-2022. Water samples were collected from inflow, middle, and outflow zones during spring and autumn, with multi-depth sampling at the central site. The V9 region of 18S rRNA was amplified and sequenced to characterize eukaryotic plankton communities. PERMANOVA analysis revealed that environmental factors explained 39.72% of phytoplankton and 38.62% of zooplankton community variation, with total nitrogen showing the strongest statistical relationship (p = 0.03 for phytoplankton), while temperature and dissolved oxygen patterns revealed important ecological gradients. Phytoplankton communities (130 genera, 5 phyla) showed pronounced seasonal patterns, with autumn exhibiting significantly higher species richness (103 genera) than spring (48 genera) (PERMANOVA: F = 9.52, p = 0.001). Zooplankton communities (43 genera, 2 phyla) displayed similar seasonal trends (F = 7.06, p = 0.001). Spatial analysis demonstrated that sampling location explained 16.7% of zooplankton variance compared to only 1.2% for depth effects, contrasting with expectations about depth effects in shallow reservoirs. Temperature-dissolved oxygen interactions created distinct environmental niches: diatoms preferred high temperature-high oxygen conditions, while dinoflagellates were most common in high temperature-low oxygen environments. Spearman correlations showed environmental preferences, with taxa like Eudiaptomus showing preference for low nutrient conditions (rs = -0.860, p < 0.001 for electrical conductivity). These findings show that environmental selection, especially temperature and dissolved oxygen gradients, are the primary drivers of plankton community structure in reservoir ecosystems, with help predict community responses to climate change and guiding management decisions.