A trait-based index shows a south-to-north decline in the intrinsic adaptive capacity of reef fishes to climate change

Climate change is reshaping marine communities and altering reef fish assemblages across coastal ecosystems. To predict these shifts, we developed an adaptive capacity index (ACI) to assess the potential of reef fish communities in the Tropical Eastern Pacific (Gulf of California and Mexican Pacific coast) to cope with ocean warming. Using life-history traits compiled from an extensive literature review, we evaluated the adaptive potential of 710 reef-associated fish species. Fourteen variables were initially considered, and a principal component analysis (PCA) identified 7 variables as the most informative predictors of adaptive capacity: individual growth rate, age at first maturity, generation time, intrinsic rate of population growth, natural mortality rate, latitudinal range and longitudinal range. The ACI was calculated as the mean of standardized ( z -score) values for these traits. Species with slow life histories and narrow ranges, such as species in the family Sebastidae, showed the lowest adaptive capacity, whereas small-bodied, fast-reproducing species displayed higher values. The community-level ACI for 19 reef localities between 15° and 30°N revealed a latitudinal gradient, with southern communities showing higher adaptive capacity than northern ones, mirroring broader global trends observed at higher spatial resolutions. In addition, the ACI developed here provides a straightforward approach to estimate the adaptive potential of marine fishes using accessible species traits, facilitating the identification of species and regions with lower intrinsic adaptive capacity under climate change.