Shrinking of fishes exacerbates impacts of global ocean changes on marine ecosystems

Changes in temperature, oxygen content and other ocean biogeochemical properties directly affect the ecophysiology of marine water-breathing organisms(1-3). Previous studies suggest that the most prominent biological responses are changes in distribution(4-6), phenology(7,8) and productivity(9). Both theory and empirical observations also support the hypothesis that warming and reduced oxygen will reduce body size of marine fishes(10-12). However, the extent to which such changes would exacerbate the impacts of climate and ocean changes on global marine ecosystems remains unexplored. Here, we employ a model to examine the integrated biological responses of over 600 species of marine fishes due to changes in distribution, abundance and body size. The model has an explicit representation of ecophysiology, dispersal, distribution, and population dynamics(3). We show that assemblage-averaged maximum body weight is expected to shrink by 14-24% globally from 2000 to 2050 under a high-emission scenario. About half of this shrinkage is due to change in distribution and abundance, the remainder to changes in physiology. The tropical and intermediate latitudinal areas will be heavily impacted, with an average reduction of more than 20%. Our results provide a new dimension to understanding the integrated impacts of climate change on marine ecosystems.