Climate and Land-Use Change May Reshape the Biogeography of Freshwater Crabs Across China.

Freshwater biodiversity is increasingly exposed to the synergistic effects of climate forcing and land-use change, yet the regional responses of key invertebrate lineages remain poorly resolved. We employed ensemble species distribution models to assess how future climate-land-use trajectories may reorganize the suitability patterns for two ecologically distinct freshwater crab families in China: the inland Potamidae and the coastal-estuarine Sesarmidae. Utilizing georeferenced occurrences from 2014 to 2024 and seven bioclimatic and land-use predictors, we developed AUC-weighted ensembles of MaxEnt and Random Forest models (AUC 0.91-0.94; TSS 0.75-0.77). Current suitability is concentrated within the humid river basins and coastal systems of southern and eastern China. Potamidae distributions are primarily associated with macro-scale thermal gradients, whereas Sesarmidae suitability reflects a strong interaction between climatic variables and coastal land-use signatures. Future projections (SSP1-2.6 and SSP5-8.5) indicate a systematic increase in mean and median continuous suitability across both families, suggesting a transition toward a more bioclimatically permissive landscape. However, the threshold-defined suitable area contracted sharply, particularly for Sesarmidae, demonstrating that future change is better characterized as a spatial redistribution from concentrated contemporary cores toward broader, more diffuse intermediate-suitability envelopes. While Potamidae exhibits a northward and inland expansion of moderate suitability, Sesarmidae maintains a restricted association with coastal refugia despite broader regional permissiveness. These results indicate that global change may expand environmental envelopes without preserving stable core habitats, underscoring the need to distinguish broad suitability from high-confidence refugia in freshwater biodiversity conservation.