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Ocean acidification poses a threat to coral skeleton formation via reductions in the saturation state of aragonite (Ω_Ar) in seawater. Given that corals precipitate their skeletons from a calcifying fluid supplied by seawater, reductions in seawater Ω_Arshould, in theory, confound calcification. Here, we reconstruct up to 200 years of coral calcifying fluid Ω_Ar, using Raman spectroscopy techniques, at approximately monthly resolution in twoPoritessp. skeletal cores from the Coral Sea region to investigate (i) the regulation of coral calcifying fluid Ω_Arand (ii) the skeletal calcification response to industrial-era ocean acidification. Our results reveal a significant increase in calcifying fluid Ω_Ar, suggesting that some corals may adjust to the pace of acidification in the wild more effectively than suggested by short-term laboratory studies. 

Abstract We present CoralCT, a software application for analysis of annual extension, density, and calcification in coral skeletal cores. CoralCT can be used to analyze computed tomography (CT) scans or X‐ray images of skeletal cores through a process in which observers interact with images of a core to define the locations of annual density bands. The application streamlines this process by organizing the observer‐defined banding patterns and automatically measuring growth parameters. Analyses can be conducted in two or three dimensions, and observers have the option to utilize an automatic band‐detection feature. CoralCT is linked to a server that stores the raw CT and X‐ray image data, as well as output growth rate data for hundreds of cores. Overall, this server‐based system enables broad collaborations on coral core analysis with standardized methods and—crucially—creates a pathway for implementing multiobserver analysis. We assess the method by comparing multiple techniques for measuring annual extension and density, including a corallite‐tracing approach, medical imaging software, two‐dimensional vs. three‐dimensional analyses, and between multiple observers. We recommend that CoralCT be used not only as a measurement tool but also as a platform for data archiving and conducting open, collaborative science. 

Abstract: Data and R code used in generating the figures (both main text and supporting information) included in the article "Comparison of red (785 nm) and blue (457 nm) excitation lasers for Raman analysis of synthetic and natural calcium carbonate samples", to be submitted to the Journal of Raman Spectroscopy.  Data folders are organized by figure number. Within the R code, please set the working directory accordingly with your own computer's folders, file paths, etc. Please also carefully refer to the commented lines for directions on setting up the various plotting code templates for specific figure types.  Version 2 update (9/1/25) includes new axis titles and new supporting information figure added during manuscript review. 

Climate change is imposing multiple stressors on marine life, leading to a restructuring of ecological communities as species exhibit differential sensitivities to these stressors. With the ocean warming and wind patterns shifting, processes that drive thermal variations in coastal regions, such as marine heatwaves and upwelling events, can change in frequency, timing, duration, and severity. These changes in environmental parameters can physiologically impact organisms residing in these habitats. Here, we investigate the synchrony of coral and reef fish responses to environmental disturbance in the Red Sea, including an unprecedented combination of heat stress and upwelling that led to mass coral bleaching in 2015. We developed cross-dated growth chronologies from otoliths of 156 individuals of two planktivorous damselfish species,Pomacentrus sulfureusandAmblyglyphidodon flavilatus, and from skeletal cores of 48Poritesspp. coral colonies. During and immediately after the 2015 upwelling and bleaching event, damselfishes exhibited a positive growth anomaly but corals displayed reduced growth. Yet, after 2015–2016, these patterns were reversed with damselfishes showing a decline in growth and corals rebounding to pre-disturbance growth rates. Our results reveal an asynchronous response between corals and reef fish, with corals succumbing to the direct effects of heat stress, and then quickly recovering when the heat stress subsided—at least, for those corals that survived the bleaching event. Conversely, damselfish growth temporarily benefited from the events of 2015, potentially due to the increased metabolic demand from increased temperature and increased food supply from the upwelling event, before declining over four years, possibly related to indirect effects associated with habitat degradation following coral mortality. Overall, our study highlights the increasingly complex, often asynchronous, ecological ramifications of climate extremes on the diverse species assemblages of coral reefs. 

Abstract As mass bleaching events decimate stony coral populations, production of calcium carbonate is diminished on reefs, dampening their capacity to keep pace with rising sea levels. However, perturbations to the calcification process of surviving wild corals during bleaching are poorly constrained, owing to the lack of suitable techniques to retroactively extract this information from coral skeletons at sufficient resolution. Here, we use novel Raman spectrometry techniques to test the biogeochemical response of long‐lived corals before, during, and after bleaching. Maintenance of high aragonite saturation state (Ω Ar ) in the coral calcifying fluid is key to driving rapid skeletal growth but would be expected to decrease when corals become energetically depleted without their symbionts. Contrary to this expectation, our results demonstrate that corals upregulate calcifying fluid Ω Ar during bleaching and for at least 2 yr after recovery. This indicates that the calcification process of coral‐bleaching survivors is unexpectedly resilient. 

ABSTRACT Raman spectroscopy has become a prominent analytical technique in calcium carbonate geochemistry, crystallography, and mineralogy. Many Raman‐based calcium carbonate studies have commonly utilized the 785‐nm (near‐infrared or “red”) excitation laser for its relatively high scattering intensities (peak intensities) and low background fluorescence. Although the 457‐nm (blue) laser has a theoretically higher spatial resolution due to its lower wavelength and experiences relatively less background fluorescence compared to the 532‐nm (green) laser, it remains largely unused and untested for Raman analyses of calcium carbonate crystals. Here, we performed comparative Raman analyses (area mapping and vertical profiling) on various abiogenic and biogenic aragonite and calcite samples to assess spatial resolution differences in acquired Raman spectral data (ν₁full width at half maximum or FWHM, Raman shift, and peak intensity) between the red and blue excitation laser settings. Area maps and vertical profiles demonstrate that analyses with the blue laser provide higher lateral and vertical spatial resolution than those with the red laser, likely due to the smaller lateral spot size and depth penetration of the blue laser. We also performed spot measurements on precipitated aragonite samples from previous studies, which generated distinct trend lines between ν₁FWHM and aragonite saturation state (Ω_Arag) for specific excitation laser wavelengths and instrument models. Blue excitation lasers provide a mode of producing higher quality Raman area maps, which will be useful for high‐resolution spatial analyses on natural and synthetic calcium carbonate samples known to contain crystallographic and structural heterogeneity. 

Abstract. As science fields enter the Big Data revolution, open-access repositories are essential for addressing larger-scale questions than are possible for single researchers by making data findable, accessible, interoperable, and reusable (FAIR). Furthermore, transparent data and code are increasingly important for reproducible research, especially for data types that inherently require subjective human interpretations. These ideas are applicable to coral sclerochronology, as the field has long been characterized by individual researchers collecting and analyzing coral skeletal cores from their study sites without substantial data sharing or archiving of the core images to meet FAIR principles. Here, we present CoralCache, a virtual coral core repository that not only archives image datasets (i.e., digitized X-rays and computed tomography scans), but also observer interpretations of the density banding patterns. CoralCache is linked to a graphical user interface, CoralCT, which together offer a way forward for coral growth rate analysis that is reproducible and collaborative. The data organization systems presented here could also be readily applied to related archives such as tree rings or bivalve shells. 

Abstract Ocean warming is increasing the frequency, extent, and severity of tropical-coral bleaching and mortality. During 2014–2017, marine heatwaves caused the Third Global Coral Bleaching Event. We analyze data from 15,066 reef surveys globally during 2014–2017. Across all surveyed reefs, 80% and 35% experienced moderate or greater (affecting >10% of corals) bleaching and mortality, respectively. We assess the global extent of coral bleaching and mortality by applying bleaching response curves calibrated from surveyed reefs to predict bleaching globally, based on comprehensive remote-sensing of heat stress. These models predict that 51% and 15% of the world’s coral reefs suffered moderate or greater bleaching and mortality, respectively, during one or multiple years, surpassing damage from any prior global coral bleaching event. Our findings demonstrate that the impacts of ocean warming on coral reefs are accelerating, with the near certainty that ongoing warming will cause large-scale, possibly irreversible, degradation of these essential ecosystems. With heat stress levels during this event surpassing those observed previously, the National Oceanic and Atmospheric Administration developed more extreme Bleaching Alert levels that are now being used during the ongoing Fourth Global Coral Bleaching Event. 

Abstract Corals nucleate and grow aragonite crystals, organizing them into intricate skeletal structures that ultimately build the world’s coral reefs. Crystallography and chemistry have profound influence on the material properties of these skeletal building blocks, yet gaps remain in our knowledge about coral aragonite on the atomic scale. Across a broad diversity of shallow-water and deep-sea scleractinian corals from vastly different environments, coral aragonites are remarkably similar to one another, confirming that corals exert control on the carbonate chemistry of the calcifying space relative to the surrounding seawater. Nuances in coral aragonite structures relate most closely to trace element chemistry and aragonite saturation state, suggesting the primary controls on aragonite structure are ionic strength and trace element chemistry, with growth rate playing a secondary role. We also show how coral aragonites are crystallographically indistinguishable from synthetic abiogenic aragonite analogs precipitated from seawater under conditions mimicking coral calcifying fluid. In contrast, coral aragonites are distinct from geologically formed aragonites, a synthetic aragonite precipitated from a freshwater solution, and mollusk aragonites. Crystallographic signatures have future applications in understanding the material properties of coral aragonite and predicting the persistence of coral reefs in a rapidly changing ocean.