Beyond bleaching: collapse of net coral reef carbonate budgets in the Tropical Eastern Pacific after the fourth global coral bleaching event

The increasing frequency and severity of marine heatwaves are driving unprecedented ecological changes in coral reefs. Although mass coral bleaching events and subsequent declines in live coral cover are well documented in scientific literature, the consequences of these disturbances for reef functionality and calcium carbonate production remain less well understood. Here, we investigate the effects of the fourth global bleaching event on CaCO3 production in coral reefs of the Tropical Eastern Pacific. Using a combination of field surveys, carbonate production models and thermal stress analyses, we show that prolonged sea surface temperature anomalies peaked at 2.24°C in August 2023, with degree heating weeks reaching a record-breaking 16, far surpassing established bleaching and mortality thresholds. This extreme thermal event led to regional coral mortality exceeding 76%, with some reefs experiencing complete loss of live coral cover. Consequently, these reefs shifted from highly productive carbonate states (4.25 ± 2.13 kg CaCO3 m⁻² yr⁻¹) to net erosional states (-2.67 ± 2.82 kg CaCO3 m⁻² yr⁻¹). Furthermore, we observed significant disruptions in the mechanisms underlying both carbonate production and erosion. Our findings underscore the vulnerability of reef structural functionality to climate change-induced thermal stress and provide crucial insights into the potential status of coral reefs affected by the fourth global coral bleaching event.