Smaller fish species dominate warmer, oxygen-poor oceans

Fossil fish bones in marine sediments off Peru suggest that smaller fish species will dominate the oceans of a warmer Earth. The findings reveal new insights into the ecological and economic impacts of our rapidly warming climate. Warming oceans under climate change are expected to result in ecosystems dominated by smaller fishes, largely due to increased temperatures and reduced oxygen availability. However, while it’s been shown that smaller fish maintain high activity in warm, oxygen-poor water, the impact of future climate change on fish abundance isn’t well understood and difficult to predict. To better understand these potential shifts, Renato Salvatteci and colleagues look back to fish populations during the last global warm, or interglacial, period. Salvatteci et al. evaluated fossil fish vertebrae in marine sediments that have recorded the Humboldt Current system off the coast of Peru for the last 130,000 years. According to the findings, previous warm periods were dominated by small, goby-like fishes rather than the larger, anchovy-like species that dominate the current ecosystem and drive the region’s incredibly productive modern fishery. The authors suggest that this shift was most likely due to the lower oxygen content of the warmer water rather than changes in food supply. Not only would a similar shift in the future have profound effects on marine biodiversity, warming oceans also pose a threat to fisheries worldwide. “The findings of Salvatteci et al. are the latest addition to the emerging evidence that a warmer future will alter ecological communities in tropical oceans, which disproportionately affect developing countries, where reliance on small-scale fishing is especially high,” write Moriaki Yasuhara and Curtis Deutsch in a related Perspective.