Climate change and freshwater biodiversity refuges in the Chilean Mediterranean Ecoregion

Climate change represents a major threat to biodiversity in Mediterranean ecosystems; however, its specific impacts on freshwater systems remain poorly understood. To address this gap, we developed species distribution models for 51 species from three taxonomic groups (fish, macrophytes, and macroinvertebrates) and projected their responses to intermediate (SSP245) and extreme (SSP585) climate scenarios for 2050 and 2070 the Chilean Mediterranean Ecoregion, South America. We assessed changes in habitat suitability and species richness under restricted colonization and non-colonization assumptions, identifying zones of habitat loss, gain, and stability, and from these identified potential climate refuges. Our results indicated that, by 2070 under the most extreme scenario (SSP585), average habitat loss for freshwater biodiversity could reach up to 33 %. Freshwater fish was the most vulnerable group, experiencing a 40 % loss, while macrophytes and macroinvertebrates showed comparatively greater persistence, with 26 % and 33 % loss, respectively. Nine fish species, six macroinvertebrates, and two macrophytes are projected to lose more than 50 % of their suitable habitat by 2070. Conversely, some species, particularly fish and macrophytes, could gain new areas of potentially suitable habitats, though colonization of these areas remains uncertain. Biodiversity hotspots are projected to shift to higher elevations and latitudes, depending on species' dispersal capacities. We identified three priority climate refuges in central Chile: the Nahuelbuta Range, the Valdivia Coastal Range, and a smaller area near Llanquihue. Only 14 % of these refuges currently overlap with existing protected areas. Our findings highlight the crucial need to incorporate climate refuges into the national network of protected areas. These areas offer key opportunities to mitigate biodiversity loss and support climate change adaptation. Prioritizing their protection and restoration, along with efforts to improve habitat connectivity, will be essential to maintaining freshwater biodiversity in this region under future climate conditions.