Projecting habitat changes in range-restricted endemic freshwater fishes: Species- and scale-dependent outcomes

Climate change is expected to substantially alter the distribution and persistence of freshwater biodiversity, particularly for narrowly distributed endemic species with limited dispersal capacity. We assessed the environmental drivers and projected habitat changes of endemic freshwater fishes across Korean watersheds under future climate scenarios (SSP1-2.6 and SSP5-8.5) using MaxEnt-based species distribution models. Using a multi-scale habitat suitability framework at nationwide, watershed, and sub-basin scales, we evaluated how spatial scale influences projected species responses and conservation inference. Seven species ( Acheilognathus signifer, A. somjinensis, Iksookimia pacifica, Kichulchoia multifasciata, Koreocobitis naktongensis, Pseudopungtungia nigra, and P. tenuicorpa ) inhabited highly restricted watersheds and river basins, and their distributions were closely associated with temperature and precipitation gradients. Projections revealed heterogeneous, species- and scale-dependent responses: some taxa gained climatically suitable habitats at broader watershed scales, whereas many showed habitat contractions within their currently occupied river basins, particularly those confined to lowland or thermally stable environments. These contrasting patterns indicate that reliance on broad-scale projections alone may overestimate species persistence by masking fine-scale habitat losses within occupied river systems. Overall, this study emphasizes the importance of a quantitative, multi-scale and hydrologically informed framework for assessing habitat suitability and guiding climate-resilient conservation of endemic freshwater fishes.