Calcification trends in long-lived corals across the Indo-Pacific during the industrial era

Skeletal cores from massive, long-lived coral colonies provide a unique approach to investigating the chronic effects of climate change on coral calcification across decadal to centennial timescales. Here, we show an overall decline in calcification rates during the industrial era, broadly consistent with other studies, based on 148 skeletal cores from ten reef locations throughout the Indo-Pacific. However, these declines are region-specific, modulated by the opposing influences of density and linear extension (the product of which equals calcification), and superimposed on multi-decadal oscillations. The main drivers of declines in calcification were recent marine heatwaves that induced reductions in linear extension, rather than decreasing skeletal density. Our findings contrast with some regional studies that show growth declines beginning only in recent decades, which in some cases may be the most recent troughs of multi-decadal oscillations in calcification. Calcification rates of reef-building corals have decreased across the Indo-Pacific since 1900 due to recent marine heatwaves, according to analyses of coral core samples.