Biogeographically Derived Metabolic Index: a Data-Poor Approach to Understand the Impacts of Warming and Deoxygenation on Marine Organisms

Ocean warming and deoxygenation are affecting the physiological performance of marine ectotherms by increasing their metabolic oxygen demand while reducing oxygen supply. Under such conditions, growth and reproduction are impacted at the individual level, in turn affecting population level and macroecological dynamics - such as shifts in biogeographic ranges. Previous studies have developed metabolic indices that integrate physiological, biogeographic and climatic data to quantify the effect of warming and deoxygenation on marine organisms. However, these methods generally require physiological data obtained from laboratory experiments typically available only for a limited number of well-studied (mostly temperate) species. To enable the analysis of the effects of ocean warming and deoxygenation on global marine biodiversity and fisheries, we develop a biogeographically-derived metabolic index (B-dMI) applicable in data-poor situations. We validate this method by comparing results between a published metabolic index and B-dMI for four study species (cod, squid, seabream, and Atlantic rock crab) using temperature and oxygen projections from simulations of a fully coupled Earth system model (GFDL ESM2M). Both metabolic indices show similar spatial patterns in and magnitude of losses of suitable habitat by the end of the 21^st century relative to 1971-2000 under a high emission scenario RCP8.5, with differences of 0.46% - 2.67%. Index values were found to be significantly and positively correlated (R² > 0.97). These results support the broad applicability and use of B-dMI to study the impacts of ocean warming and deoxygenation across a wide range of fishes and invertebrates. This index will facilitate the understanding of climate-driven warming and deoxygenation impacts on global marine fisheries resources and biodiversity.