Hypoxia traits imprinted in otolith δ¹³C from individual to global scales

Hypoxia tolerance and its variation with temperature, activity, and body mass, are critical ecophysiological traits through which climate impacts marine ectotherms. To date, experimental determination of these traits is limited to a small subset of modern species. We leverage the close coupling of carbon and oxygen in animal metabolism to mechanistically relate these traits to the carbon isotopes in fish otoliths (δ¹³C_oto). The model reproduces the major empirical patterns in δ¹³C_oto at individual to global scales. The weak dependence on body size and strong, non-linear, dependence on temperature reflect the same balance between metabolism and ventilatory gas exchange that underlies organisms' hypoxia tolerance. The global relationship between temperature and δ¹³C_oto records both the fractionation by aragonite precipitation and the variation in hypoxia traits across ocean biomes. Because hypoxia tolerance is imprinted on both otolith geochemistry and species biogeography, the model allows the aerobic limits of species geographic ranges to be predicted from fish δ¹³C_oto. This physiologically grounded model provides a foundation for the use of otolith chemistry to reconstruct modern spatial patterns and paleoceanographic changes in key traits that shape aerobic habitat of aquatic species.