Identifying lineages of cold-tolerant rotifers in a Korean brackish lagoon using eDNA metabarcoding, morphology, and...

Environmental DNA (eDNA) metabarcoding has become a powerful tool for uncovering cryptic biodiversity in brackish ecosystems. However, ecological and physiological characterization of newly detected taxa remains limited. In this study, we combined eDNA-based community profiling, morphological analysis, and in vivo life-parameter experiments to resolve the lineages and cold-adaptive traits of two rotifer strains (H-SL and H-US) collected from Hwajinpo Lagoon, East Sea, Korea. eDNA surveys revealed a rotifer-rich microfaunal community, particularly in Hwajinpo, where unidentified Brachionus taxa were dominant. Targeted isolation and subsequent analyses indicated that H-SL and H-US correspond to large- and small-type Brachionus lineages, respectively, each exhibiting distinct morphological traits and molecular affiliations with known species complexes. Life-parameter experiments revealed that H-SL maintained reproductive activity and population growth under cold conditions (16-20 °C), suggesting cold tolerance and demographic stability, whereas H-US exhibited a warm-adapted, fast-growing strategy with limited persistence. These findings underscore the value of combining eDNA detection with integrative biological characterization to reveal functional diversity in transitional ecosystems and identify candidate strains for cold-water aquaculture.