Rapid assessments of Pacific Ocean net coral reef carbonate budgets and net calcification following the 2014-2017 global coral bleaching event

The 2014-2017 global coral bleaching event caused widespread coral mortality; however, its impact on the capacity for coral reefs to maintain calcium carbonate structures has not been determined. Here, we quantified remotely sensed maximum heat stress during the 2014-2017 bleaching event, census-based net carbonate budgets from benthic imagery and fish survey data, and net reef calcification from salinity normalized seawater total alkalinity anomalies collected from 2017-2019 for 56 Pacific coral reef sites (Mariana Islands, Northwestern Hawaiian Islands, Pacific Remote Island Areas, and American Samoa). We incorporated the census-based and chemistry-based metrics to determine a calcification vulnerability index for each site to maintain calcium carbonate balance to provide accessible information to managers and policy makers. Most coral reef sites likely experienced ecologically severe (79%, n = 44) or significant (9%, n = 7) heat stress during the 2014-2017 coral bleaching event. Census-based net carbonate budgets (mean +/- 95% = 2.1 +/- 0.6 kg CaCO3 m(-2) yr(-1)) were positive for 77% of sites (n = 43), neutral for 16% of sites (n = 9), and negative for 7% of sites (n = 4). Chemistry-based relative net reef calcification (mean +/- 95% = 22 +/- 10 mu mol kg(-1)) was positive for 84% of sites (n = 47), neutral for 11% of sites (n = 6), and negative for 5% of sites (n = 3). The calcification vulnerability index suggested the Pacific Ocean reef sites surveyed were of minimal (68%, n = 38) to moderate (32%, n = 18) concern for maintaining calcium carbonate balance following the bleaching event. This suggests that many reefs maintained positive calcium carbonate balance, but that a large number of reefs may be approaching a potential threshold for maintaining their calcium carbonate balance under the climate crisis.