Continuous monitoring of marine metazoan diversity using sediment trap eDNA metabarcoding in the Ulleung Basin, East Sea, off the Korean Peninsula

Sediment trap environmental DNA (ST-eDNA) metabarcoding provides long-term, fine-scale monitoring of marine biodiversity, ideal for open-ocean regions where repeated sampling is challenging. By continuously collecting sinking particulate matter, ST-eDNA detects both persistent and transient species over time. Here, we used ST-eDNA metabarcoding to investigate fine-scale temporal changes in marine metazoan diversity in the Ulleung Basin, a pelagic region of the East Sea off the Korean Peninsula. Weekly sediment trap samples were collected at depths of 300 and 500 m between March and September 2019, leading to the identification of 178 species across 10 phyla and 23 classes. Arthropoda, Chordata, Mollusca, and Cnidaria were the dominant phyla. The mean number of species detected per week ranged from 10 to 71, with arthropods, chordates, and cnidarians showing peak occurrences in May. Species were categorized into (i) resident species, detected in ≥13 weekly samples, indicating persistent presence, and (ii) seasonal species, detected in 4–9 weekly samples, suggesting periodic occurrence. Approximately 50% of the species detected using ST-eDNA overlapped with those detected in Bulk-DNA (net-collected) and eDNA (seawater-filtered) surveys, while others were unique to ST-eDNA. These findings underscore the complementary role of ST-eDNA in capturing hidden and dynamic patterns of marine biodiversity.