Galápagos coral reef persistence after ENSO warming across an acidification gradient

Anthropogenic CO2 is causing warming and ocean acidification. Coral reefs are being severelyimpacted, yet confusion lingers regarding how reefs will respond to these stressors over this century. Sincethe 1982-1983 El Niño-Southern Oscillation warming event, the persistence of reefs around the GalápagosIslands has differed across an acidification gradient. Reefs disappeared where pH<8.0 and aragonitesaturation state (Ωarag) ≤ 3 and have not recovered, whereas one reef has persisted where pH>8.0 andΩarag>3. Where upwelling is greatest, calcification by massive Porites is higher than predicted by a publishedrelationship with temperature despite high CO2, possibly due to elevated nutrients. However, skeletal P/Ca, aproxy for phosphate exposure, negatively correlates with density (R = -0.822, p<0.0001). We propose thatelevated nutrients have the potential to exacerbate acidification by depressing coral skeletal densities andfurther increasing bioerosion already accelerated by low pH.