PHYSIOLOGICAL SELECTIVITY OF EARLY MESOZOIC OCEAN ACIDIFICATION EVENTS: COMPARISON OF FISH AND INVERTEBRATE EXTINCTIONS

The end-Permian, end-Triassic and Toarcian extinctions coincided with flood basalt eruptions that would have released large quantities of carbon dioxide into the atmosphere, likely leading to ocean acidification. Direct proxy evidence, for example from calcium isotopes and plant stomata, support high atmospheric carbon dioxide levels and reduced ocean pH during the end-Permian and end-Triassic crises. These extinction events provide analogues for anthropogenic CO₂ emissions and can help us understand which taxonomic groups will be threatened by ocean acidification. Fish have cellular mechanisms to buffer extracellular pH changes from exercise-induced metabolic CO₂ production, which also prove advantageous in buffering against changes in seawater pH. Assessing the extinction of fish during CO₂-driven extinctions will test the hypothesis that active fish are less vulnerable than sessile marine invertebrates. We compiled a database of fossil fish occurrences from the Pennsylvanian to the Middle Jurassic, using the Paleobiology Database, to quantify fish extinction rates during background and mass extinctions. Extinction rates among fish were lower than marine invertebrates in these extinctions, consistent with the expectation based on the physiology of the groups. These results will provide information on what physiological adaptations are advantageous and which taxa will be more threatened in future climate projections.