Galápagos coral reef persistence after ENSO warming across an acidification gradient

Abstract:

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