Spatiotemporal dynamics of migratory shorebird populations in Korean coastal wetlands within the East Asian–Australasian Flyway

Shorebirds migrate long-distances along the East Asian–Australasian Flyway (EAAF), exhibiting distinct spatiotemporal fluctuations in population dynamics. Because of habitat degradation and population declines at key stopover sites along the EAAF, the South Korea's coastal wetlands have gained increasing attention for their ecological value. This study analyzed the shorebird population dynamics across 35 coastal wetlands in South Korea from 2016 to 2024 using data from the National Marine Ecosystem Monitoring Program. For the time-series analysis, we employed three indicators: seasonal changes in abundance, short-term fluctuations (Fi), and long-term trends, assessed using the TRends and Indices for Monitoring data (TRIM) model. Abundance, species richness, and Shannon diversity indices were assessed across the regions during spring and autumn. The TRIM results revealed significant population increases in both seasons (“Strong increase” in spring and “Moderate increase” in autumn). Species-level trends indicated notable increases in large-bodied shorebirds, including globally threatened species such as the Far Eastern Curlew (Numenius madagascariensis), Eurasian Curlew (N. arquata), and Eurasian Oystercatcher (Haematopus ostralegus), whereas other species showed variable responses. The Yellow Sea region (Gyeonggi, Chungcheong, and Western Jeolla) showed high biodiversity indices in spring, which may be associated with time-minimization strategies, whereas autumn patterns were characterized by more flexible and selective stopover use, possibly related to energy-minimization strategies. The East Coast and Jeju regions showed the lowest biodiversity indices. Furthermore, community-level analyses using Non-metric Multidimensional Scaling (NMDS) and PERMANOVA revealed distinct clustering of bird assemblages by macro-region and season, confirming significant spatial differentiation in community composition. These findings contrast with the broader declining trends reported across the EAAF and suggest that South Korea's coastal wetlands may serve as stable alternative stopover habitats, potentially supporting the redistribution or recovery of some species. This study highlights the importance of transboundary cooperation and region-specific habitat management that reflects local ecological contexts for effective conservation.