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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 μmol 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. [ABSTRACT FROM AUTHOR]

The article focuses on the study that examines how environmental factors drive the distribution of Symbiodinium genotypes. It cites that researchers use time series environmental data in the sampling set of coral hosts across multiple spatial scales and among multiple regions. They surveyed bleaching-susceptible corals in the genus of Acropora which is known as a component of Pacific reefs with species hosting Clades C and D. The researchers assayed clade membership for symbionts of Acropora hyacinthus and Acropora cytherea from American Samoa, Fiji, Philippines, and Palmyra Atoll. Based on the distribution patterns, they conclude that maximum habitat temperatures can drive local scale adaptation of symbiont populations, while other processes can dominate at the regional area.

Recent advances in DNA-sequencing technologies now allow for in-depth characterization of the genomic stress responses of many organisms beyond model taxa. They are especially appropriate for organisms such as reef-building corals, for which dramatic declines in abundance are expected to worsen as anthropogenic climate change intensifies. Different corals differ substantially in physiological resilience to environmental stress, but the molecular mechanisms behind enhanced coral resilience remain unclear. Here, we compare transcriptome-wide gene expression (via RNA-Seq using Illumina sequencing) among conspecific thermally sensitive and thermally resilient corals to identify the molecular pathways contributing to coral resilience. Under simulated bleaching stress, sensitive and resilient corals change expression of hundreds of genes, but the resilient corals had higher expression under control conditions across 60 of these genes. These "frontloaded" transcripts were less up-regulated in resilient corals during heat stress and included thermal tolerance genes such as heat shock proteins and antioxidant enzymes, as well as a broad array of genes involved in apoptosis regulation, tumor suppression, innate immune response, and cell adhesion. We propose that constitutive frontloading enables an individual to maintain physiological resilience during frequently encountered environmental stress, an idea that has strong parallels in model systems such as yeast. Our study provides broad insight into the fundamental cellular processes responsible for enhanced stress tolerances that may enable some organisms to better persist into the future in an era of global climate change.