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Journal articles on the topic 'Coral aragonite'
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1
Wendt, J. "The first aragonitic rugose coral." Journal of Paleontology 64, no. 3 (1990): 335–40. http://dx.doi.org/10.1017/s0022336000018539.
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Microstructural and compositional data support the view that the skeletons of rugose corals consisted of (probably high-Mg) calcite, unlike the skeletons of scleractinian corals which are predominantly aragonitic. Total transformation of a late Permian rugose coral skeleton into neomorphic calcite and a significant trace element composition, however, show that aragonite was present in some Rugosa shortly prior to the extinction of this order. This finding sheds new light on the possible phylogenetic relationship between Rugosa and Scleractinia, which still possess a different mode of septal insertion and remain separated by an as yet coral-free interval in the Lower Triassic.
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DeCarlo, Thomas M., Michael Holcomb, and Malcolm T. McCulloch. "Reviews and syntheses: Revisiting the boron systematics of aragonite and their application to coral calcification." Biogeosciences 15, no. 9 (2018): 2819–34. http://dx.doi.org/10.5194/bg-15-2819-2018.
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Abstract. The isotopic and elemental systematics of boron in aragonitic coral skeletons have recently been developed as a proxy for the carbonate chemistry of the coral extracellular calcifying fluid. With knowledge of the boron isotopic fractionation in seawater and the B∕Ca partition coefficient (KD) between aragonite and seawater, measurements of coral skeleton δ11B and B∕Ca can potentially constrain the full carbonate system. Two sets of abiogenic aragonite precipitation experiments designed to quantify KD have recently made possible the application of this proxy system. However, while different KD formulations have been proposed, there has not yet been a comprehensive analysis that considers both experimental datasets and explores the implications for interpreting coral skeletons. Here, we evaluate four potential KD formulations: three previously presented in the literature and one newly developed. We assess how well each formulation reconstructs the known fluid carbonate chemistry from the abiogenic experiments, and we evaluate the implications for deriving the carbonate chemistry of coral calcifying fluid. Three of the KD formulations performed similarly when applied to abiogenic aragonites precipitated from seawater and to coral skeletons. Critically, we find that some uncertainty remains in understanding the mechanism of boron elemental partitioning between aragonite and seawater, and addressing this question should be a target of additional abiogenic precipitation experiments. Despite this, boron systematics can already be applied to quantify the coral calcifying fluid carbonate system, although uncertainties associated with the proxy system should be carefully considered for each application. Finally, we present a user-friendly computer code that calculates coral calcifying fluid carbonate chemistry, including propagation of uncertainties, given inputs of boron systematics measured in coral skeleton.
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Perrin, Christine. "Early diagenesis of carbonate biocrystals : isomineralogical changes in aragonite coral skeletons." Bulletin de la Société Géologique de France 175, no. 2 (2004): 95–106. http://dx.doi.org/10.2113/175.2.95.
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Abstract Early diagenetic changes occurring in aragonite coral skeletons were characterized at the micro- and ultra-structural scales in living and fossil scleractinian colonies, the latter of Pleistocene age. The skeleton of scleractinian corals, like all biomineralized structures, is a composite material formed by the intimate association of inorganic aragonite crystallites and organic matrices. In addition to its organo-mineral duality, the scleractinian skeleton is formed by the three-dimensional arrangement of two clearly distinct basic structural features, the centers of calcification and the fibers. The latter are typically characterized by a transverse micron-scale zonation revealing their incremental growth process. The size, geometry and three-dimensional arrangement of calcification centers and fibers are taxon-specific. The earliest diagenetic modifications of these skeletons have been clearly recognized in the older parts of living colonies. The first steps of diagenesis therefore take place only a few years after the skeleton had been secreted by the living polyps, and in the same environmental conditions. Comparisons with the uppermost living parts of the coral colonies clearly show that these first diagenetic changes are driven by the biological ultrastructural characteristics of these skeletons and are conditioned by the presence of organic envelopes interbedded with and surrounding aragonite crystallites. These first diagenetic processes induce the development of thin fringes of fibrous aragonite cements growing syntaxially on the aragonitic coral fibers, an alteration of the incremental zonation of coral fibers and also preferential diagenetic changes in the calcification centers, including dissolution of their minute internal crystals. Diagenetic patterns observed in Pleistocene coral colonies typically involve the same processes already recognized in the older skeletal parts of living colonies, suggesting that diagenesis occurs through continuous processes instead of clearly differentiated stages. Selective dissolution affects calcification centers and some growth increments of coral fibers. Alteration of the initial transverse zonation of coral fibers also occur through the development of micro-inclusions clearly seen in ultra-thin sections. Although usually thicker than those observed in the ancient skeletal parts of living colonies, syntaxial aragonite cements commonly occur in these fossil skeletons. These cements are often associated with gradual textural modifications of the underlying coral fibers, in particular the loss of the transverse micron-scale zonation. This suggests that the coral skeleton forming the substratum of diagenetic cements is progressively recrystallized in secondary aragonite. This recrystallization of coral aragonite begins at the external margin of the skeleton, just below the diagenetic cements and gradually moves towards the internal skeletal parts. Recrystallization takes place through concomitant fine-scale dissolution-precipitation processes and occurs with textural changes but no mineralogical change. The process of recrystallization is likely initiated by a biological degradation of organic skeletal matrices and can be also driven by thermodynamical constraints involving the lowering of surface free energies resulting from changes in crystal size. Alteration of skeletal organic matrix, textural changes in coral biocrystals through recrystallization and precipitation of secondary diagenetic aragonite may bias the original geochemical characteristics of coral skeletons. Although more work is needed to establish the influence of these early diagenetic processes on the geochemical signatures, it is already well known that the breakdown of organic skeletal envelopes and early recrystallization of shallow-water carbonates alter the stable isotopic composition. The widespread use of coral skeletons as environmental and climatic proxies makes strongly necessary a better understanding of these early diagenetic mechanisms and a precise characterization of the fine-scale diagenetic patterns of specimens for the optimization of geochemical interpretations. In particular, it cannot be assumed that an entire aragonitic composition can guarantee that there is no or slight diagenetic alteration.
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Foster, T., and P. L. Clode. "Skeletal mineralogy of coral recruits under high temperature and <i>p</i>CO<sub>2</sub>." Biogeosciences 13, no. 5 (2016): 1717–22. http://dx.doi.org/10.5194/bg-13-1717-2016.
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Abstract. Aragonite, which is the polymorph of CaCO3 precipitated by modern corals during skeletal formation, has a higher solubility than the more stable polymorph calcite. This higher solubility may leave animals that produce aragonitic skeletons more vulnerable to anthropogenic ocean acidification. It is therefore important to determine whether scleractinian corals have the plasticity to adapt and produce calcite in their skeletons in response to changing environmental conditions. Both high pCO2 and lower Mg ∕ Ca ratios in seawater are thought to have driven changes in the skeletal mineralogy of major marine calcifiers in the past ∼ 540 Ma. Experimentally reduced Mg ∕ Ca ratios in ambient seawater have been shown to induce some calcite precipitation in both adult and newly settled modern corals; however, the impact of high pCO2 on the mineralogy of recruits is unknown. Here we determined the skeletal mineralogy of 1-month-old Acropora spicifera coral recruits grown under high temperature (+3 °C) and pCO2 (∼ 900 µatm) conditions, using X-ray diffraction and Raman spectroscopy. We found that newly settled coral recruits produced entirely aragonitic skeletons regardless of the treatment. Our results show that elevated pCO2 alone is unlikely to drive changes in the skeletal mineralogy of young corals. Not having an ability to switch from aragonite to calcite precipitation may leave corals and ultimately coral reef ecosystems more susceptible to predicted ocean acidification. An important area for prospective research would be the investigation of the combined impact of high pCO2 and reduced Mg ∕ Ca ratio on coral skeletal mineralogy.
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Foster, T., and P. L. Clode. "Skeletal mineralogy of coral recruits under high temperature and <i>p</i>CO<sub>2</sub>." Biogeosciences Discussions 12, no. 15 (2015): 12485–500. http://dx.doi.org/10.5194/bgd-12-12485-2015.
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Abstract. Aragonite, which is the polymorph of CaCO3 precipitated by modern corals during skeletal formation, has a higher solubility than the more stable polymorph calcite. This higher solubility leaves animals that produce aragonitic skeletons more vulnerable to anthropogenic ocean acidification. It is therefore, important to determine whether scleractinian corals have the plasticity to adapt and produce calcite in their skeletons in response to changing environmental conditions. Both high pCO2 and lower Mg / Ca ratios in seawater are thought to have driven changes in the skeletal mineralogy of major marine calcifiers in the past ∼540 myr. Experimentally reduced Mg / Ca ratios in ambient seawater have been shown to induce some calcite precipitation in both adult and newly settled modern corals, however, the impact of high pCO2 on the mineralogy of recruits is unknown. Here we determined the skeletal mineralogy of one-month old Acropora spicifera coral recruits grown under high temperature (+3 °C) and pCO2 (∼900 μatm) conditions, using X-ray diffraction and Raman spectroscopy. We found that newly settled coral recruits produced entirely aragonitic skeletons regardless of the treatment. Our results show that elevated pCO2 alone is unlikely to drive changes in the skeletal mineralogy of young corals. Not having an ability to switch from aragonite to calcite precipitation may leave corals and ultimately coral reef ecosystems more susceptible to predicted ocean acidification. An important area for prospective research would be to investigate the combined impact of high pCO2 and reduced Mg / Ca ratio on coral skeletal mineralogy.
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Yuyama, Ikuko, and Tomihiko Higuchi. "Differential gene expression in skeletal organic matrix proteins of scleractinian corals associated with mixed aragonite/calcite skeletons under low mMg/Ca conditions." PeerJ 7 (July 15, 2019): e7241. http://dx.doi.org/10.7717/peerj.7241.
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Although coral skeletons generally comprise aragonite crystals, changes in the molar Mg/Ca ratio (mMg/Ca) in seawater result in the incorporation of calcite crystals. The formation mechanism of aragonite and calcite crystals in the scleractinian coral Acropora tenuis was therefore investigated by RNA-seq analysis, using early growth stage calcite (mMg/Ca = 0.5) and aragonite (mMg/Ca = 5.2)-based corals. As a result, 1,287 genes were up-regulated and 748 down-regulated in calcite-based corals. In particular, sixty-eight skeletogenesis-related genes, such as ectin, galaxin, and skeletal aspartic acid-rich protein, were detected as up-regulated, and six genes, such as uncharacterized skeletal organic matrix protein 5, down-regulated, in low-Mg/Ca conditions. Since the number of down-regulated genes associated with the skeletal organic matrix of aragonite skeletons was much lower than that of up-regulated genes, it is thought that corals actively initiate construction of an aragonite skeleton by the skeletal organic matrix in low-Mg/Ca conditions. In addition, different types of skeletal organic matrix proteins, extracellular matrix proteins and calcium ion binding proteins appeared to change their expression in both calcite-formed and normal corals, suggesting that the composition of these proteins could be a key factor in the selective formation of aragonite or calcite CaCO3.
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Morad, Tzachy, Roni Mina Hendler, Eyal Canji, et al. "Aragonite-Polylysine: Neuro-Regenerative Scaffolds with Diverse Effects on Astrogliosis." Polymers 12, no. 12 (2020): 2850. http://dx.doi.org/10.3390/polym12122850.
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Biomaterials, especially when coated with adhesive polymers, are a key tool for restorative medicine, being biocompatible and supportive for cell adherence, growth, and function. Aragonite skeletons of corals are biomaterials that support survival and growth of a range of cell types, including neurons and glia. However, it is not known if this scaffold affects neural cell migration or elongation of neuronal and astrocytic processes, prerequisites for initiating repair of damage in the nervous system. To address this, hippocampal cells were aggregated into neurospheres and cultivated on aragonite skeleton of the coral Trachyphyllia geoffroyi (Coral Skeleton (CS)), on naturally occurring aragonite (Geological Aragonite (GA)), and on glass, all pre-coated with the oligomer poly-D-lysine (PDL). The two aragonite matrices promoted equally strong cell migration (4.8 and 4.3-fold above glass-PDL, respectively) and axonal sprouting (1.96 and 1.95-fold above glass-PDL, respectively). However, CS-PDL had a stronger effect than GA-PDL on the promotion of astrocytic processes elongation (1.7 vs. 1.2-fold above glass-PDL, respectively) and expression of the glial fibrillary acidic protein (3.8 vs. and 1.8-fold above glass-PDL, respectively). These differences are likely to emerge from a reaction of astrocytes to the degree of roughness of the surface of the scaffold, which is higher on CS than on GA. Hence, CS-PDL and GA-PDL are scaffolds of strong capacity to derive neural cell movements and growth required for regeneration, while controlling the extent of astrocytic involvement. As such, implants of PDL-aragonites have significant potential as tools for damage repair and the reduction of scar formation in the brain following trauma or disease.
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Conci, Nicola, Martin Lehmann, Sergio Vargas, and Gert Wörheide. "Comparative Proteomics of Octocoral and Scleractinian Skeletomes and the Evolution of Coral Calcification." Genome Biology and Evolution 12, no. 9 (2020): 1623–35. http://dx.doi.org/10.1093/gbe/evaa162.
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Abstract Corals are the ecosystem engineers of coral reefs, one of the most biodiverse marine ecosystems. The ability of corals to form reefs depends on the precipitation of calcium carbonate (CaCO3) under biological control. However, several mechanisms underlying coral biomineralization remain elusive, for example, whether corals employ different molecular machineries to deposit different CaCO3 polymorphs (i.e., aragonite or calcite). Here, we used tandem mass spectrometry (MS/MS) to compare the proteins occluded in the skeleton of three octocoral and one scleractinian species: Tubipora musica and Sinularia cf. cruciata (calcite sclerites), the blue coral Heliopora coerulea (aragonitic skeleton), and the scleractinian aragonitic Montipora digitata. Reciprocal Blast analysis revealed extremely low overlap between aragonitic and calcitic species, while a core set of proteins is shared between octocorals producing calcite sclerites. However, the carbonic anhydrase CruCA4 is present in the skeletons of both polymorphs. Phylogenetic analysis highlighted several possible instances of protein co-option in octocorals. These include acidic proteins and scleritin, which appear to have been secondarily recruited for calcification and likely derive from proteins playing different functions. Similarities between octocorals and scleractinians included presence of a galaxin-related protein, carbonic anhydrases, and one hephaestin-like protein. Although the first two appear to have been independently recruited, the third appear to share a common origin. This work represents the first attempt to identify and compare proteins associated with coral skeleton polymorph diversity, providing several new research targets and enabling both future functional and evolutionary studies aimed at elucidating the origin and evolution of coral biomineralization.
9
Greegor, R. B. "Strontianite in Coral Skeletal Aragonite." Science 275, no. 5305 (1997): 1452–54. http://dx.doi.org/10.1126/science.275.5305.1452.
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Stolarski, J., R. Przeniosło, M. Mazur, and M. Brunelli. "High-resolution synchrotron radiation studies on natural and thermally annealed scleractinian coral biominerals." Journal of Applied Crystallography 40, no. 1 (2007): 2–9. http://dx.doi.org/10.1107/s002188980604489x.
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The structural phase transition from aragonite to calcite in biogenic samples extracted from the skeletons of selected scleractinian corals has been studied by synchrotron radiation diffraction. Biogenic aragonite samples were extracteden blocwithout pulverization from two ecologically different scleractinian taxa:Desmophyllum(deep-water, solitary and azooxanthellate) andFavia(shallow-water, colonial, zooxanthellate). It was found that natural (not pulverized) samples contribute to narrow Bragg peaks with Δd/dvalues as low as 1 × 10−3, which allows the exploitation of the high resolution of synchrotron radiation diffraction. A precise determination of the lattice parameters of biogenic scleractinian coral aragonite shows the same type of changes of thea,b,clattice parameter ratios as that reported for aragonite extracted from other invertebrates [Pokroy, Quintana, Caspi, Berner & Zolotoyabko (2004).Nat. Mater.3, 900–902]. It is believed that the crystal structure of biogenic samples is influenced by interactions with organic molecules that are initially present in the biomineralization hydrogel. The calcite phase obtained by annealing the coral samples has a considerably different unit-cell volume and lattice parameter ratioc/aas compared with reference geological calcite and annealed synthetic aragonite. The internal strain in the calcite structure obtained by thermal annealing of the biomineral samples is about two times larger than that found in the natural aragonite structure. This effect is observed despite slow heating and cooling of the sample.
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Mass, Tali, Anthony J. Giuffre, Chang-Yu Sun, et al. "Amorphous calcium carbonate particles form coral skeletons." Proceedings of the National Academy of Sciences 114, no. 37 (2017): E7670—E7678. http://dx.doi.org/10.1073/pnas.1707890114.
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Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed “vital effects,” that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene–Eocene Thermal Maximum that occurred 56 Mya.
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Yamamoto, S., H. Kayanne, M. Terai, et al. "Threshold of carbonate saturation state determined by CO<sub>2</sub> control experiment." Biogeosciences 9, no. 4 (2012): 1441–50. http://dx.doi.org/10.5194/bg-9-1441-2012.
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Abstract. Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies have suggested that carbonate dissolution will occur in polar regions and in the deep sea where saturation state with respect to carbonate minerals (Ω) will be <1 by 2100. Recent reports demonstrate nocturnal carbonate dissolution of reefs, despite a Ωa (aragonite saturation state) value of >1. This is probably related to the dissolution of reef carbonate (Mg-calcite), which is more soluble than aragonite. However, the threshold of Ω for the dissolution of natural sediments has not been clearly determined. We designed an experimental dissolution system with conditions mimicking those of a natural coral reef, and measured the dissolution rates of aragonite in corals, and of Mg-calcite excreted by other marine organisms, under conditions of Ωa > 1, with controlled seawater pCO2. The experimental data show that dissolution of bulk carbonate sediments sampled from a coral reef occurs at Ωa values of 3.7 to 3.8. Mg-calcite derived from foraminifera and coralline algae dissolves at Ωa values between 3.0 and 3.2, and coralline aragonite starts to dissolve when Ωa = 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminiferans and coralline algae in reef sediments.
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Ahmad Zubir, Ahmad Annuar, Yusri Yusof, and Mohd Al Amin Muhamad Nor. "Physical and Chemical Characteristics of Corals from Bidong Island, Terengganu, Malaysia." Advanced Materials Research 1112 (July 2015): 555–58. http://dx.doi.org/10.4028/www.scientific.net/amr.1112.555.
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Coral and converted coralline hydroxyapatites have been widely used in biomedical application as orbital implant and bone graft substitute. The aim of this study was to characterize the physical and chemical properties of various corals found in Bidong Island and determines their potential for development of bone graft substitute. Five species of coral which is commonly found in Bidong Island, Terengganu was collected and identified. The physical properties of corals such as density and porosity were determined using the Archimedes Principle, whereas a mechanical strength was determined using a universal testing machine. The structure of corals such as pore sizes and shape, distribution and pore connectivity was observed using Scanning Electron Microscope (SEM). Chemical properties of corals were characterized using X-ray diffraction (XRD), and energy dispersive x-ray (SEM-EDX). Five species of coral were identified as Leptoria, Porites, Platygyra, Acropora and Pocillopora. The densities of corals range from 2.00 to 19.00 g/cm3 while the porosity range from 15 to 60%. The corals structure consists of interconnected open pores with mean pore sizes in range of 100 to 600μm. Their compressive strengths are in the range of 4.92 to 27 MPa, which is higher than the reported strength for cancellous bone. SEM-EDX analysis shows the elements calcium carbonate (C, O and Ca) found in Platygyra. This result was supported by XRD analysis, which shows the calcium carbonate phase in form of aragonite presence in Platygyra. Aragonite phase was suitable for transforming coral to hydroxyapatite via hydrothermal treatment. Based on this finding, coral species in Bidong Island, Terengganu has been great potential to be used as bone graft substitutes.
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Sun, Chang-Yu, Cayla A. Stifler, Rajesh V. Chopdekar, et al. "From particle attachment to space-filling coral skeletons." Proceedings of the National Academy of Sciences 117, no. 48 (2020): 30159–70. http://dx.doi.org/10.1073/pnas.2012025117.
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Reef-building corals and their aragonite (CaCO3) skeletons support entire reef ecosystems, yet their formation mechanism is poorly understood. Here we used synchrotron spectromicroscopy to observe the nanoscale mineralogy of fresh, forming skeletons from six species spanning all reef-forming coral morphologies: Branching, encrusting, massive, and table. In all species, hydrated and anhydrous amorphous calcium carbonate nanoparticles were precursors for skeletal growth, as previously observed in a single species. The amorphous precursors here were observed in tissue, between tissue and skeleton, and at growth fronts of the skeleton, within a low-density nano- or microporous layer varying in thickness from 7 to 20 µm. Brunauer-Emmett-Teller measurements, however, indicated that the mature skeletons at the microscale were space-filling, comparable to single crystals of geologic aragonite. Nanoparticles alone can never fill space completely, thus ion-by-ion filling must be invoked to fill interstitial pores. Such ion-by-ion diffusion and attachment may occur from the supersaturated calcifying fluid known to exist in corals, or from a dense liquid precursor, observed in synthetic systems but never in biogenic ones. Concomitant particle attachment and ion-by-ion filling was previously observed in synthetic calcite rhombohedra, but never in aragonite pseudohexagonal prisms, synthetic or biogenic, as observed here. Models for biomineral growth, isotope incorporation, and coral skeletons’ resilience to ocean warming and acidification must take into account the dual formation mechanism, including particle attachment and ion-by-ion space filling.
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Kimball, Justine, Robert Eagle, and Robert Dunbar. "Carbonate “clumped” isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals." Biogeosciences 13, no. 23 (2016): 6487–505. http://dx.doi.org/10.5194/bg-13-6487-2016.
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Abstract. Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop “clumped” isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures, and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ47–temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ47–temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between calcite and aragonite although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect high-Mg and aragonite crystals attaining nominal mineral equilibrium clumped isotope signatures due to conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing crystals. We also cannot rule out a component of a biological “vital effect” influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological vital effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, calcite, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.
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Auscavitch, Steven R., Jay J. Lunden, Alexandria Barkman, Andrea M. Quattrini, Amanda W. J. Demopoulos, and Erik E. Cordes. "Distribution of deep-water scleractinian and stylasterid corals across abiotic environmental gradients on three seamounts in the Anegada Passage." PeerJ 8 (July 31, 2020): e9523. http://dx.doi.org/10.7717/peerj.9523.
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In the Caribbean Basin the distribution and diversity patterns of deep-sea scleractinian corals and stylasterid hydrocorals are poorly known compared to their shallow-water relatives. In this study, we examined species distribution and community assembly patterns of scleractinian and stylasterid corals on three high-profile seamounts within the Anegada Passage, a deep-water throughway linking the Caribbean Sea and western North Atlantic. Using remotely operated vehicle surveys conducted on the E/V Nautilus by the ROV Hercules in 2014, we characterized coral assemblages and seawater environmental variables between 162 and 2,157 m on Dog Seamount, Conrad Seamount, and Noroît Seamount. In all, 13 morphospecies of scleractinian and stylasterid corals were identified from video with stylasterids being numerically more abundant than both colonial and solitary scleractinians. Cosmopolitan framework-forming species including Madrepora oculata and Solenosmilia variabilis were present but occurred in patchy distributions among the three seamounts. Framework-forming species occurred at or above the depth of the aragonite saturation horizon with stylasterid hydrocorals being the only coral taxon observed below Ωarag values of 1. Coral assemblage variation was found to be strongly associated with depth and aragonite saturation state, while other environmental variables exerted less influence. This study enhances our understanding of the factors that regulate scleractinian and stylasterid coral distribution in an underreported marginal sea and establishes a baseline for monitoring future environmental changes due to ocean acidification and deoxygenation in the tropical western Atlantic.
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Kaushal, Nikita, Liudongqing Yang, Jani T. I. Tanzil, Jen Nie Lee, Nathalie F. Goodkin, and Patrick Martin. "Sub-annual fluorescence measurements of coral skeleton: relationship between skeletal luminescence and terrestrial humic-like substances." Coral Reefs 39, no. 5 (2020): 1257–72. http://dx.doi.org/10.1007/s00338-020-01959-x.
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Abstract Some massive coral core slices reveal luminescent bands under ultraviolet light, which have been attributed to terrestrial humic acids in the skeleton. Coral luminescence has therefore been used to reconstruct past climate and hydrological variability. However, it has remained unresolved how closely coral luminescence at sub-annual resolution is related to terrestrial humic acid concentrations. This study presents a solution-based fluorescence method to quantify terrestrial humic substances in less than 4 mg of coral powder. The results show that in corals from Malaysia and Singapore, the luminescence green-to-blue ratio is correlated with skeletal concentrations of terrestrial humic substances (R2 > 0.40, p < 0.001) at two sites that are exposed to terrestrial dissolved organic matter from peatlands on Sumatra. In contrast, coral cores from two other sites located far from major terrestrial organic matter sources show lower green-to-blue values and no convincing correlation with fluorescence intensity of terrestrial humic substances in the skeleton. Abiogenic aragonite precipitation experiments with both terrestrial and marine organic matter sources confirmed that terrestrial humic substances are readily incorporated into aragonite, but not fluorescent organic matter from marine sources. The results of this study suggest that in coral cores with high luminescence green-to-blue ratios (> 0.6) and large downcore variability (range of ≥ 0.05), the green-to-blue ratio is strongly linked to variation in terrestrial humic substances. Coral cores therefore have the potential to reconstruct past variation in terrigenous dissolved organic carbon fluxes.
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Pasquini, Luca, Alan Molinari, Paola Fantazzini, et al. "Isotropic microscale mechanical properties of coral skeletons." Journal of The Royal Society Interface 12, no. 106 (2015): 20150168. http://dx.doi.org/10.1098/rsif.2015.0168.
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Scleractinian corals are a major source of biogenic calcium carbonate, yet the relationship between their skeletal microstructure and mechanical properties has been scarcely studied. In this work, the skeletons of two coral species: solitary Balanophyllia europaea and colonial Stylophora pistillata , were investigated by nanoindentation. The hardness H IT and Young's modulus E IT were determined from the analysis of several load–depth data on two perpendicular sections of the skeletons: longitudinal (parallel to the main growth axis) and transverse. Within the experimental and statistical uncertainty, the average values of the mechanical parameters are independent on the section's orientation. The hydration state of the skeletons did not affect the mechanical properties. The measured values, E IT in the 76–77 GPa range, and H IT in the 4.9–5.1 GPa range, are close to the ones expected for polycrystalline pure aragonite. Notably, a small difference in H IT is observed between the species. Different from corals, single-crystal aragonite and the nacreous layer of the seashell Atrina rigida exhibit clearly orientation-dependent mechanical properties. The homogeneous and isotropic mechanical behaviour of the coral skeletons at the microscale is correlated with the microstructure, observed by electron microscopy and atomic force microscopy, and with the X-ray diffraction patterns of the longitudinal and transverse sections.
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DeCarlo, Thomas M., Juan P. D'Olivo, Taryn Foster, Michael Holcomb, Thomas Becker, and Malcolm T. McCulloch. "Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy." Biogeosciences 14, no. 22 (2017): 5253–69. http://dx.doi.org/10.5194/bg-14-5253-2017.
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Abstract. Quantifying the saturation state of aragonite (ΩAr) within the calcifying fluid of corals is critical for understanding their biomineralization process and sensitivity to environmental changes including ocean acidification. Recent advances in microscopy, microprobes, and isotope geochemistry enable the determination of calcifying fluid pH and [CO32−], but direct quantification of ΩAr (where ΩAr = [CO32−][Ca2+]∕Ksp) has proved elusive. Here we test a new technique for deriving ΩAr based on Raman spectroscopy. First, we analysed abiogenic aragonite crystals precipitated under a range of ΩAr from 10 to 34, and we found a strong dependence of Raman peak width on ΩAr with no significant effects of other factors including pH, Mg∕Ca partitioning, and temperature. Validation of our Raman technique for corals is difficult because there are presently no direct measurements of calcifying fluid ΩAr available for comparison. However, Raman analysis of the international coral standard JCp-1 produced ΩAr of 12.3 ± 0.3, which we demonstrate is consistent with published skeletal Mg∕Ca, Sr∕Ca, B∕Ca, δ11B, and δ44Ca data. Raman measurements are rapid ( ≤ 1 s), high-resolution ( ≤ 1 µm), precise (derived ΩAr ± 1 to 2 per spectrum depending on instrument configuration), accurate ( ±2 if ΩAr < 20), and require minimal sample preparation, making the technique well suited for testing the sensitivity of coral calcifying fluid ΩAr to ocean acidification and warming using samples from natural and laboratory settings. To demonstrate this, we also show a high-resolution time series of ΩAr over multiple years of growth in a Porites skeleton from the Great Barrier Reef, and we evaluate the response of ΩAr in juvenile Acropora cultured under elevated CO2 and temperature.
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Yamamoto, S., H. Kayanne, M. Terai, et al. "Threshold of carbonate saturation state determined by a CO<sub>2</sub> control experiment." Biogeosciences Discussions 8, no. 4 (2011): 8619–44. http://dx.doi.org/10.5194/bgd-8-8619-2011.
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Abstract. Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies suggest that carbonate dissolution will occur in polar regions and in the deep-sea oceans where saturation state with respect to carbonate minerals (Ω) will be <1 by 2100. However, carbonate in coral reefs distributed in tropical zones will not dissolve because the major carbonate in such reefs is aragonite, and the saturation state with respect to aragonite (Ω_a) is >1. Recent reports demonstrated nocturnal carbonate dissolution reefs, despite Ω_a > 1, probably relate to the dissolution of the minor reef carbonate (Mg-calcite), which is more soluble than aragonite. However, the threshold of Ω for the dissolution of natural sediments has not been clearly determined, and it is unknown whether these dissolution processes actually occur under natural conditions. This work describes the measurement of the dissolution rates of coral aragonite and Mg calcite excreted by marine organisms under conditions of Ω_a > 1 with controlled seawater pCO2. Laboratory experimental data of the present study show that bulk carbonate sediments sampled from a coral reef start to dissolve when Ω_a = 3.7, and dissolution rates increase with falling Ω_a. Mg-calcite derived from foraminifera and coralline algae dissolved when Ω_a reached 3.4, whereas coralline aragonite started to dissolve when Ω_a was almost 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminifera and coralline algae in reef sediment.
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Brachert, T. C., M. Reuter, S. Krüger, J. S. Klaus, K. Helmle, and J. M. Lough. "Low Florida coral calcification rates in the Plio-Pleistocene." Biogeosciences Discussions 12, no. 24 (2015): 20515–55. http://dx.doi.org/10.5194/bgd-12-20515-2015.
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Abstract. In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands may be retained allowing for reconstructions of annual extension (= growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. Here we report the first data of calcification rates of fossil reef corals which escaped diagenetic alteration. The corals derive from unlithified shallow water carbonates of the Florida platform (southeastern USA), which formed during four interglacial sea level highstands dated 3.2, 2.9, 1.8, and 1.2 Ma in the mid Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, dissolution is minor along centers of calcification. Mean extension rates were 0.44 ± 0.19 cm yr−1 (range 0.16 to 0.86 cm yr−1) and mean bulk density was 0.86 ± 0.36 g cm−3 (range 0.55 to 1.22 g cm−3). Correspondingly, calcification rates ranged from 0.18 to 0.82 g cm−2 yr−1 (mean 0.38 ± 0.16 g cm−2 yr−1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification with modern zooxanthellate-coral (z-coral) rates from the Western Atlantic (WA) and Indo-Pacific (IP) calibrated against sea surface temperature (SST). In the fossil data, we found an analogous relationship with SST in z-corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the environment of coral growth, stable isotope proxy data from the fossil corals and the overall structure of the ancient shallow marine communities are consistent with a well-mixed, open marine environment similar to the present-day Florida Reef Tract, but variably affected by intermittent upwelling. Upwelling along the platform may explain low rates of reef coral calcification and inorganic cementation, but is too localized to account for low extension rates of Pliocene z-corals recorded throughout the tropical Caribbean in the western Atlantic region. Low aragonite saturation on a more global scale in response to rapid glacial/interglacial CO2 cyclicity is also a potential factor, but Plio-Pleistocene atmospheric pCO2 is believed to have been broadly similar to the present-day. Heat stress related to globally high interglacial SST, only episodically moderated by intermittent upwelling affecting the Florida platform seems to be the most likely reason for low calcification rates. From these observations we suggest some present coral reef systems to be endangered from future ocean warming.
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Pingitore, Nicholas E., and Ted Pogue. "Precise X-Ray Microfluorescence Measurements of Sr/Ca Ratios In Corals For Paleotemperature Analysis." Microscopy and Microanalysis 4, S2 (1998): 366–67. http://dx.doi.org/10.1017/s1431927600021954.
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Coral aragonite encodes a rich, complex record of ambient environmental conditions (including temperature, salinity, pollutants) during skeletogenesis. Annual growth banding in appropriate species provides an internal calendar, and the rapidity of skeletal growth permits temporal sampling to at least a sub-monthly basis. The longevity of reef coral colonies can provide continuous centuries-long environmental records. The presence of well-dated Pleistocene coral reefs at sites across the world ocean extends this record into the more distant past. Thus corals are a remarkable resource for the investigation of environmental conditions over perhaps 7 orders of magnitude of time.The past few years have seen considerable use of Sr/Ca ratios in scleractinian corals to reconstruct sea surface temperatures (SSTs) to document global change. The detailed correlation between Sr/Ca ratios in living corals and measured ambient water temperature is often remarkable, as is the match in older corals between Sr/Ca ratios and such other SST temperature proxies as 18O /16O ratios.
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Brachert, Thomas C., Markus Reuter, Stefan Krüger, James S. Klaus, Kevin Helmle, and Janice M. Lough. "Low Florida coral calcification rates in the Plio-Pleistocene." Biogeosciences 13, no. 15 (2016): 4513–32. http://dx.doi.org/10.5194/bg-13-4513-2016.
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Abstract. In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands often allow for reconstructions of annual extension ( = growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. This report presents the bulk density, extension rates and calcification rates of fossil reef corals which underwent minor diagenetic alteration only. The corals derive from unlithified shallow water carbonates of the Florida platform (south-eastern USA), which formed during four interglacial sea level highstands dated approximately 3.2, 2.9, 1.8, and 1.2 Ma in the mid-Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, voids are commonly present along centres of calcification which lack secondary cements. Mean extension rates were 0.44 ± 0.19 cm yr−1 (range 0.16 to 0.86 cm yr−1), mean bulk density was 0.96 ± 0.36 g cm−3 (range 0.55 to 1.83 g cm−3) and calcification rates ranged from 0.18 to 0.82 g cm−2 yr−1 (mean 0.38 ± 0.16 g cm−2 yr−1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification rates with those of modern zooxanthellate corals (z corals) from the Western Atlantic (WA) and Indo-Pacific calibrated against sea surface temperature (SST). In the fossil data, we found a widely analogous relationship with SST in z corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the environment of coral growth, stable isotope proxy data from the fossil corals and the overall structure of the ancient shallow marine communities are consistent with a well-mixed, open marine environment similar to the present-day Florida Reef Tract, but variably affected by intermittent upwelling. Upwelling along the platform may explain low rates of reef coral calcification and inorganic cementation, but is too localised to account also for low extension rates of Pliocene z corals throughout the tropical WA region. Low aragonite saturation on a more global scale in response to rapid glacial–interglacial CO2 cyclicity is also a potential factor, but Plio-Pleistocene atmospheric pCO2 is generally believed to have been broadly similar to the present day. Heat stress related to globally high interglacial SST only episodically moderated by intermittent upwelling affecting the Florida platform seems to be another likely reason for low calcification rates. From these observations we suggest some present coral reef systems to be endangered from future ocean warming.
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Silva, Cosmelina Gonçalves Da, Dang Dan Nguyen, Alaric Zanibellato, et al. "Artificial coral reefs, electrochemistry and calcium carbonate: electrodeposited coral-like aragonite." Acta Crystallographica Section A Foundations and Advances 71, a1 (2015): s534. http://dx.doi.org/10.1107/s2053273315092116.
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D'Olivo, J. P., M. T. McCulloch, S. M. Eggins, and J. Trotter. "Coral records of reef-water pH across the central Great Barrier Reef, Australia: assessing the influence of river runoff on inshore reefs." Biogeosciences 12, no. 4 (2015): 1223–36. http://dx.doi.org/10.5194/bg-12-1223-2015.
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Abstract. The boron isotopic (δ11Bcarb) compositions of long-lived Porites coral are used to reconstruct reef-water pH across the central Great Barrier Reef (GBR) and assess the impact of river runoff on inshore reefs. For the period from 1940 to 2009, corals from both inner- and mid-shelf sites exhibit the same overall decrease in δ11Bcarb of 0.086 ± 0.033‰ per decade, equivalent to a decline in seawater pH (pHsw) of ~0.017 ± 0.007 pH units per decade. This decline is consistent with the long-term effects of ocean acidification based on estimates of CO2 uptake by surface waters due to rising atmospheric levels. We also find that, compared to the mid-shelf corals, the δ11Bcarb compositions of inner-shelf corals subject to river discharge events have higher and more variable values, and hence higher inferred pHsw values. These higher δ11Bcarb values of inner-shelf corals are particularly evident during wet years, despite river waters having lower pH. The main effect of river discharge on reef-water carbonate chemistry thus appears to be from reduced aragonite saturation state and higher nutrients driving increased phytoplankton productivity, resulting in the drawdown of pCO2 and increase in pHsw. Increased primary production therefore has the potential to counter the more transient effects of low-pH river water (pHrw) discharged into near-shore environments. Importantly, however, inshore reefs also show a consistent pattern of sharply declining coral growth that coincides with periods of high river discharge. This occurs despite these reefs having higher pHsw, demonstrating the overriding importance of local reef-water quality and reduced aragonite saturation state on coral reef health.
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Conci, Nicola, Gert Wörheide, and Sergio Vargas. "New Non-Bilaterian Transcriptomes Provide Novel Insights into the Evolution of Coral Skeletomes." Genome Biology and Evolution 11, no. 11 (2019): 3068–81. http://dx.doi.org/10.1093/gbe/evz199.
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Abstract A general trend observed in animal skeletomes—the proteins occluded in animal skeletons—is the copresence of taxonomically widespread and lineage-specific proteins that actively regulate the biomineralization process. Among cnidarians, the skeletomes of scleractinian corals have been shown to follow this trend. However, distributions and phylogenetic analyses of biomineralization-related genes are often based on only a few species, with other anthozoan calcifiers such as octocorals (soft corals), not being fully considered. We de novo assembled the transcriptomes of four soft-coral species characterized by different calcification strategies (aragonite skeleton vs. calcitic sclerites) and data-mined published nonbilaterian transcriptome resources to construct a taxonomically comprehensive sequence database to map the distribution of scleractinian and octocoral skeletome components. Cnidaria shared no skeletome proteins with Placozoa or Ctenophora, but did share some skeletome proteins with Porifera, such as galaxin-related proteins. Within Scleractinia and Octocorallia, we expanded the distribution for several taxonomically restricted genes such as secreted acidic proteins, scleritin, and carbonic anhydrases, and propose an early, single biomineralization-recruitment event for galaxin sensu stricto. Additionally, we show that the enrichment of acidic residues within skeletogenic proteins did not occur at the Corallimorpharia–Scleractinia transition, but appears to be associated with protein secretion into the organic matrix. Finally, the distribution of octocoral calcification-related proteins appears independent of skeleton mineralogy (i.e., aragonite/calcite) with no differences in the proportion of shared skeletogenic proteins between scleractinians and aragonitic or calcitic octocorals. This points to skeletome homogeneity within but not between groups of calcifying cnidarians, although some proteins such as galaxins and SCRiP-3a could represent instances of commonality.
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Kimball, J., R. E. Tripati, and R. Dunbar. "Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals." Biogeosciences Discussions 12, no. 23 (2015): 19115–65. http://dx.doi.org/10.5194/bgd-12-19115-2015.
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Abstract. Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near constant temperature, salinity and pH, and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly-substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and calcitic gorgonian (Isididae and Coralliidae) deep-sea corals, and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than calcitic gorgonian corals and the two groups of coral produce statistically different relationship between Δ47-temperature calibrations. These data are significant in the interpretation of all carbonate "clumped" isotope calibration data as they show that distinct Δ47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between calcite and aragonite, although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect that crystals may attain nominal mineral equilibrium clumped isotope signatures only under conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing crystals. We also cannot rule out a component of a biological "vital-effect" influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological "vital" effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, calcite, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.
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Gómez, Carlos E., Leslie Wickes, Dan Deegan, Peter J. Etnoyer, and Erik E. Cordes. "Growth and feeding of deep-sea coral Lophelia pertusa from the California margin under simulated ocean acidification conditions." PeerJ 6 (September 27, 2018): e5671. http://dx.doi.org/10.7717/peerj.5671.
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The global decrease in seawater pH known as ocean acidification has important ecological consequences and is an imminent threat for numerous marine organisms. Even though the deep sea is generally considered to be a stable environment, it can be dynamic and vulnerable to anthropogenic disturbances including increasing temperature, deoxygenation, ocean acidification and pollution. Lophelia pertusa is among the better-studied cold-water corals but was only recently documented along the US West Coast, growing in acidified conditions. In the present study, coral fragments were collected at ∼300 m depth along the southern California margin and kept in recirculating tanks simulating conditions normally found in the natural environment for this species. At the collection site, waters exhibited persistently low pH and aragonite saturation states (Ωarag) with average values for pH of 7.66 ± 0.01 and Ωarag of 0.81 ± 0.07. In the laboratory, fragments were grown for three weeks in “favorable” pH/Ωarag of 7.9/1.47 (aragonite saturated) and “unfavorable” pH/Ωarag of 7.6/0.84 (aragonite undersaturated) conditions. There was a highly significant treatment effect (P < 0.001) with an average% net calcification for favorable conditions of 0.023 ± 0.009% d−1 and net dissolution of −0.010 ± 0.014% d-1 for unfavorable conditions. We did not find any treatment effect on feeding rates, which suggests that corals did not depress feeding in low pH/ Ωarag in an attempt to conserve energy. However, these results suggest that the suboptimal conditions for L. pertusa from the California margin could potentially threaten the persistence of this cold-water coral with negative consequences for the future stability of this already fragile ecosystem.
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TANAKA, KENTARO, and SHIGERU OHDE. "Fluoride in coral aragonite related to seawater carbonate." GEOCHEMICAL JOURNAL 44, no. 5 (2010): 371–78. http://dx.doi.org/10.2343/geochemj.1.0079.
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Mansur, Herman S., Alexandra A. P. Mansur, and Marivalda Pereira. "XRD, SEM/EDX and FTIR Characterization of Brazilian Natural Coral." Key Engineering Materials 284-286 (April 2005): 43–46. http://dx.doi.org/10.4028/www.scientific.net/kem.284-286.43.
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In the present work, natural coral from Brazilian reefs were studied according to their crystallography by X-ray diffraction and microstructure by Scanning Electron Microscopy (SEM/EDX). FTIR spectroscopy was also used to evaluate the chemical functionalities and major components present in the material. The SEM morphology results have shown a tri-dimensional coral structure with porous ranging from 50 to 200 µm. Aragonite was identified as the major crystalline phase through XRD analysis and FTIR spectroscopy. Strontium calcium carbonate, (Sr,Ca)CO3, was also identified by XRD analysis. After sintering at 900º/1h, the conversion from aragonite to CaO and calcite was observed. These results have endorsed the high potential application of natural coral materials as 3D scaffolds for biomedical application, because of calcium carbonate compounds can be converted to HA by hydrothermal and biomimetic coating processes.
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Sevilgen, Duygu S., Alexander A. Venn, Marian Y. Hu, et al. "Full in vivo characterization of carbonate chemistry at the site of calcification in corals." Science Advances 5, no. 1 (2019): eaau7447. http://dx.doi.org/10.1126/sciadv.aau7447.
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Reef-building corals form their calcium carbonate skeletons within an extracellular calcifying medium (ECM). Despite the critical role of the ECM in coral calcification, ECM carbonate chemistry is poorly constrained in vivo, and full ECM carbonate chemistry has never been characterized based solely on direct in vivo measurements. Here, we measure pHECMin the growing edge ofStylophora pistillataby simultaneously using microsensors and the fluorescent dye SNARF-1, showing that, when measured at the same time and place, the results agree. We then conduct microscope-guided microsensor measurements of pH, [Ca2+], and [CO32−] in the ECM and, from this, determine [DIC]ECMand aragonite saturation state (Ωarag), showing that all parameters are elevated with respect to the surrounding seawater. Our study provides the most complete in vivo characterization of ECM carbonate chemistry parameters in a coral species to date, pointing to the key role of calcium- and carbon-concentrating mechanisms in coral calcification.
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Watanabe, Tsuyoshi, Masao Minagawa, Tadamichi Oba, and Amos Winter. "Pretreatment of coral aragonite for Mg and Sr analysis: Implications for coral thermometers." GEOCHEMICAL JOURNAL 35, no. 4 (2001): 265–69. http://dx.doi.org/10.2343/geochemj.35.265.
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Wooldridge, S. "A new conceptual model of coral biomineralisation: hypoxia as the physiological driver of skeletal extension." Biogeosciences 10, no. 5 (2013): 2867–84. http://dx.doi.org/10.5194/bg-10-2867-2013.
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Abstract. That corals skeletons are built of aragonite crystals with taxonomy-linked ultrastructure has been well understood since the 19th century. Yet, the way by which corals control this crystallization process remains an unsolved question. Here, I outline a new conceptual model of coral biomineralisation that endeavours to relate known skeletal features with homeostatic functions beyond traditional growth (structural) determinants. In particular, I propose that the dominant physiological driver of skeletal extension is night-time hypoxia, which is exacerbated by the respiratory oxygen demands of the coral's algal symbionts (= zooxanthellae). The model thus provides a new narrative to explain the high growth rate of symbiotic corals, by equating skeletal deposition with the "work-rate" of the coral host needed to maintain a stable and beneficial symbiosis. In this way, coral skeletons are interpreted as a continuous (long-run) recording unit of the stability and functioning of the coral–algae endosymbiosis. After providing supportive evidence for the model across multiple scales of observation, I use coral core data from the Great Barrier Reef (Australia) to highlight the disturbed nature of the symbiosis in recent decades, but suggest that its onset is consistent with a trajectory that has been followed since at least the start of the 1900s. In concluding, I outline how the proposed capacity of cnidarians (which includes modern reef corals) to overcome the metabolic limitation of hypoxia via skeletogenesis also provides a new hypothesis to explain the sudden appearance in the fossil record of calcified skeletons at the Precambrian–Cambrian transition – and the ensuing rapid appearance of most major animal phyla.
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Wooldridge, S. A. "A new conceptual model of coral biomineralisation: hypoxia as the physiological driver of skeletal extension." Biogeosciences Discussions 9, no. 9 (2012): 12627–66. http://dx.doi.org/10.5194/bgd-9-12627-2012.
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Abstract. That corals skeletons are built of aragonite crystals with taxonomy-linked ultrastructure has been well understood since the 19th century. Yet, the way by which corals control this crystallization process remains an unsolved question. Here, I outline a new conceptual model of coral biominerationsation that endeavours to relate known skeletal features with homeostatic functions beyond traditional growth (structural) determinants. In particular, I propose that the dominant physiological driver of skeletal extension is night-time hypoxia, which is exacerbated by the respiratory oxygen demands of the coral's algal symbionts (= zooxanthellae). The model thus provides a new narrative to explain the high growth rate of symbiotic corals, by equating skeletal deposition with the "work-rate" of the coral host needed to maintain a stable and beneficial symbiosis. In this way, coral skeletons are interpreted as a continuous (long-run) recording unit of the stability and functioning of the coral-algae endosymbiosis. After providing supportive evidence for the model across multiple scales of observation, I use coral core data from the Great Barrier Reef (Australia) to highlight the disturbed nature of the symbiosis in recent decades, but suggest that its onset is consistent with a trajectory that has been followed since at least the start of the 1900's. In concluding, I explain how the evolved capacity of the cnidarians (which now includes modern reef corals) to overcome the metabolic limitation of hypoxia via skeletogenesis, may underpin the sudden appearance in the fossil record of calcified skeletons at the Precambrian-Cambrian transition – and the ensuing rapid appearance of most major animal phyla.
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Greiner, Martina, Lurdes Férnandez-Díaz, Erika Griesshaber, et al. "Biomineral Reactivity: The Kinetics of the Replacement Reaction of Biological Aragonite to Apatite." Minerals 8, no. 8 (2018): 315. http://dx.doi.org/10.3390/min8080315.
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We present results of bioaragonite to apatite conversion in bivalve, coral and cuttlebone skeletons, biological hard materials distinguished by specific microstructures, skeletal densities, original porosities and biopolymer contents. The most profound conversion occurs in the cuttlebone of the cephalopod Sepia officinalis, the least effect is observed for the nacreous shell portion of the bivalve Hyriopsis cumingii. The shell of the bivalve Arctica islandica consists of cross-lamellar aragonite, is dense at its innermost and porous at the seaward pointing shell layers. Increased porosity facilitates infiltration of the reaction fluid and renders large surface areas for the dissolution of aragonite and conversion to apatite. Skeletal microstructures of the coral Porites sp. and prismatic H. cumingii allow considerable conversion to apatite. Even though the surface area in Porites sp. is significantly larger in comparison to that of prismatic H. cumingii, the coral skeleton consists of clusters of dense, acicular aragonite. Conversion in the latter is sluggish at first as most apatite precipitates only onto its surface area. However, the process is accelerated when, in addition, fluids enter the hard tissue at centers of calcification. The prismatic shell portion of H. cumingii is readily transformed to apatite as we find here an increased porosity between prisms as well as within the membranes encasing the prisms. In conclusion, we observe distinct differences in bioaragonite to apatite conversion rates and kinetics depending on the feasibility of the reaction fluid to access aragonite crystallites. The latter is dependent on the content of biopolymers within the hard tissue, their feasibility to be decomposed, the extent of newly formed mineral surface area and the specific biogenic ultra- and microstructures.
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Sadło, Jarosław, Anna Bugaj, Grażyna Strzelczak, Marcin Sterniczuk, and Zbigniew Jaegermann. "Multifrequency EPR study on radiation induced centers in calcium carbonates labeled with 13C." Nukleonika 60, no. 3 (2015): 429–34. http://dx.doi.org/10.1515/nuka-2015-0076.
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AbstractIn calcite and aragonite, γ-irradiated at 77 K, several paramagnetic centers were generated and detected by EPR spectroscopy; in calcite, CO3−(orthorhombic symmetry, bulk and bonded to surface), CO33−, NO32−, O3−, and in aragonite CO2−(isotropic and orthorhombic symmetry) depending on the type of calcium carbonate used. For calcium carbonates enriched with13C more detailed information about the formed radicals was possible to be obtained. In both natural (white coral) and synthetic aragonite the same radicals were identified with main differences in the properties of CO2−radicals. An application of Q-band EPR allowed to avoid the signals overlap giving the characteristics of radical anisotropy.
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Guillermic, Maxence, Louise P. Cameron, Ilian De Corte, et al. "Thermal stress reduces pocilloporid coral resilience to ocean acidification by impairing control over calcifying fluid chemistry." Science Advances 7, no. 2 (2021): eaba9958. http://dx.doi.org/10.1126/sciadv.aba9958.
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The combination of thermal stress and ocean acidification (OA) can more negatively affect coral calcification than an individual stressors, but the mechanism behind this interaction is unknown. We used two independent methods (microelectrode and boron geochemistry) to measure calcifying fluid pH (pHcf) and carbonate chemistry of the corals Pocillopora damicornis and Stylophora pistillata grown under various temperature and pCO2 conditions. Although these approaches demonstrate that they record pHcf over different time scales, they reveal that both species can cope with OA under optimal temperatures (28°C) by elevating pHcf and aragonite saturation state (Ωcf) in support of calcification. At 31°C, neither species elevated these parameters as they did at 28°C and, likewise, could not maintain substantially positive calcification rates under any pH treatment. These results reveal a previously uncharacterized influence of temperature on coral pHcf regulation—the apparent mechanism behind the negative interaction between thermal stress and OA on coral calcification.
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Ivanov, Volodymyr, and Viktor Stabnikov. "Calcite/aragonite-biocoated artificial coral reefs for marine parks." AIMS Environmental Science 4, no. 4 (2017): 586–95. http://dx.doi.org/10.3934/environsci.2017.4.586.
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Njegić Džakula, Branka, Simona Fermani, Zvy Dubinsky, Stefano Goffredo, Giuseppe Falini, and Damir Kralj. "In Vitro Coral Biomineralization under Relevant Aragonite Supersaturation Conditions." Chemistry – A European Journal 25, no. 45 (2019): 10616–24. http://dx.doi.org/10.1002/chem.201900691.
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Mass, Tali, Jeana L. Drake, Liti Haramaty, et al. "Aragonite Precipitation by “Proto-Polyps” in Coral Cell Cultures." PLoS ONE 7, no. 4 (2012): e35049. http://dx.doi.org/10.1371/journal.pone.0035049.
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Lauridsen, Bodil Wesenberg, Finn Surlyk, and Morten Bjerager. "The middle Danian Faxe Formation – new lithostratigraphic unit and a rare taphonomic window into the Danian of Denmark." Bulletin Volume 60 – 2012 60 (October 2, 2012): 47–60. http://dx.doi.org/10.37570/bgsd-2012-60-04.
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The new middle Danian Faxe Formation is defined on the basis of the succession exposed in the large Faxe quarry in eastern Denmark. The formation is defined as a distinct mappable ithostratigraphic unit of interfingering coral and bryozoan limestone passing laterally into bryozoan limestones of the Stevns Klint Formation. The Baunekule facies is recognized in the upper part of the coral mound complex of the Faxe Formation, where it forms isolated lensoidal bodies in the flanks of some of the coral mounds. It is characterised by a high diversity invertebrate fauna with both calcite and originally aragonite-shelled benthic invertebrates set in weakly consolidated coral-dominated floatstone to rudstone. The diagenesis of the Baunekule facies is of special significance because a high proportion of the originally aragonite-shelled fauna is preserved by recrystallization to calcite during early burial diagenesis. More than 80% of the species from the Baunekule facies are unknown from other parts of the Faxe Formation. The carbonate mud matrix is only slightly consolidated and the invertebrate fossils are accordingly easy to prepare in contrast to the fossils from the lithified parts of the Faxe Formation, which are commonly only preserved as moulds or casts. The facies therefore presents an exceptional taphonomic window into a cold-water coral mound fauna, giving an unusually complete picture of the diversity and density of the shelly invertebrate fauna.
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Kadi, Achmad. "Karakteristik Makro Algae Berzat Kapur di Perairan Tanjung Sira Lombok-Barat." Biosfera 32, no. 1 (2015): 51. http://dx.doi.org/10.20884/1.mib.2015.32.1.295.
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Coastal waters of Tanjung Sira has calcareousalgae of the genus Halimeda limestone, Padina, Amphiroa, Galaxaura, Corallina, Hydrolithon, Mesophyllum, Peysonallia, Porolithon and Sporolithon. The substrate that used as habitat are sand, coarse sand, rocks and dead coral rubble. Calcium carbonate contained on calcareous algae fungsioning as adhesive and encrusting dead coral, shells of mollusks that have decayed and massive objects in the waters of the sea. The research aims was to determine the growth characteristics of calcareousalgae in the reef flats, local distribution, calcium carbonate contain and its contribution as a frame work coastal reef waters. The research method using transect (Buckland et al., 1993). Identification of the type of aragonite and calcite according to Cordero (1977). Analysis of calcium carbonate according to Hillis (1980). The results showed that the green and brown calcareousalgae found in the reef flats, has thallus and tubers. Red calcareousalgae grew as encrusting on dead reefs and massif substrate. There are 16 species of calcareous algae that found in reseach area, 10 species containing aragonite mineral and 6 species containing calcite mineral. The content of calcium carbonate on each species obtained 100-450 g/m² consists of aragonite and calcite minerals. Calcareousalgae contribute in the new formation of coral reef ecosystems. The other benefit of calcareaousalgae in the coastal waters is an additional food for herbivorous fish. The content of calcium carbonate on calcareousalgae species is used in pharmaceutical field as drug ingredients and supplements for humans.
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Hohn, S., and A. Merico. "Effects of seawater <i>p</i>CO<sub>2</sub> changes on the calcifying fluid of scleractinian corals." Biogeosciences Discussions 9, no. 3 (2012): 2655–89. http://dx.doi.org/10.5194/bgd-9-2655-2012.
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Abstract. Rising atmospheric CO2 concentrations due to anthropogenic emissions induce changes in the ocean carbonate chemistry and a drop in ocean pH. This acidification process is expected to harm calcifying organisms like coccolithophores, molluscs, echinoderms, and corals. A severe decline in coral abundance is, for example, expected by the end of this century with associated disastrous effects on reef ecosystems. Despite the growing importance of the topic, little progress has been made with respect to modelling the impact of acidification on coral calcification. Here we present a model for a coral polyp that simulates the carbonate system in four different compartments: the seawater, the polyp tissue, the coelenteron, and the calicoblastic layer. Precipitation of calcium carbonate takes place in the metabolically controlled calicoblastic layer beneath the polyp tissue. The model is adjusted to a state of activity as observed by direct microsensor measurements in the calcifying fluid. Simulated CO2 perturbation experiments reveal decreasing calcification rates under elevated pCO2 despite strong metabolic control of the calcifying fluid. Diffusion of CO2 through the tissue into the calicoblastic layer increases with increasing seawater pCO2 leading to decreased aragonite saturation in the calcifying fluid of the coral polyp. Our modelling study provides important insights into the complexity of the calcification process at the organism level and helps to quantify the effect of ocean acidification on corals.
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Martinez, Ana, Elizabeth D. Crook, Daniel J. Barshis, et al. "Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring." Proceedings of the Royal Society B: Biological Sciences 286, no. 1905 (2019): 20190572. http://dx.doi.org/10.1098/rspb.2019.0572.
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Coral calcification is expected to decline as atmospheric carbon dioxide concentration increases. We assessed the potential of Porites astreoides , Siderastrea siderea and Porites porites to survive and calcify under acidified conditions in a 2-year field transplant experiment around low pH, low aragonite saturation (Ω arag ) submarine springs. Slow-growing S. siderea had the highest post-transplantation survival and showed increases in concentrations of Symbiodiniaceae, chlorophyll a and protein at the low Ω arag site. Nubbins of P. astreoides had 20% lower survival and higher chlorophyll a concentration at the low Ω arag site. Only 33% of P. porites nubbins survived at low Ω arag and their linear extension and calcification rates were reduced. The density of skeletons deposited after transplantation at the low Ω arag spring was 15–30% lower for all species. These results suggest that corals with slow calcification rates and high Symbiodiniaceae, chlorophyll a and protein concentrations may be less susceptible to ocean acidification, albeit with reduced skeletal density. We postulate that corals in the springs are responding to greater energy demands for overcoming larger differences in carbonate chemistry between the calcifying medium and the external environment. The differential mortality, growth rates and physiological changes may impact future coral species assemblages and the reef framework robustness.
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Ross, Claire L., Verena Schoepf, Thomas M. DeCarlo, and Malcolm T. McCulloch. "Mechanisms and seasonal drivers of calcification in the temperate coral Turbinaria reniformis at its latitudinal limits." Proceedings of the Royal Society B: Biological Sciences 285, no. 1879 (2018): 20180215. http://dx.doi.org/10.1098/rspb.2018.0215.
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High-latitude coral reefs provide natural laboratories for investigating the mechanisms and limits of coral calcification. While the calcification processes of tropical corals have been studied intensively, little is known about how their temperate counterparts grow under much lower temperature and light conditions. Here, we report the results of a long-term (2-year) study of seasonal changes in calcification rates, photo-physiology and calcifying fluid (cf) chemistry (using boron isotope systematics and Raman spectroscopy) for the coral Turbinaria reniformis growing near its latitudinal limits (34.5° S) along the southern coast of Western Australia. In contrast with tropical corals, calcification rates were found to be threefold higher during winter (16 to 17° C) compared with summer (approx. 21° C), and negatively correlated with light, but lacking any correlation with temperature. These unexpected findings are attributed to a combination of higher chlorophyll a, and hence increased heterotrophy during winter compared with summer, together with the corals' ability to seasonally modulate pH cf , with carbonate ion concentration being the main controller of calcification rates. Conversely, calcium ion concentration [Ca 2+ ] cf declined with increasing calcification rates, resulting in aragonite saturation states Ω cf that were stable yet elevated fourfold above seawater values. Our results show that corals growing near their latitudinal limits exert strong physiological control over their cf in order to maintain year-round calcification rates that are insensitive to the unfavourable temperature regimes typical of high-latitude reefs.
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Koga, Nobuyoshi, and Kazuyuki Nishikawa. "Mutual Relationship between Solid-State Aragonite–Calcite Transformation and Thermal Dehydration of Included Water in Coral Aragonite." Crystal Growth & Design 14, no. 2 (2014): 879–87. http://dx.doi.org/10.1021/cg4018689.
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Maier, C., J. Hegeman, M. G. Weinbauer, and J. P. Gattuso. "Calcification of the cold-water coral <i>Lophelia pertusa,</i> under ambient and reduced pH." Biogeosciences 6, no. 8 (2009): 1671–80. http://dx.doi.org/10.5194/bg-6-1671-2009.
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Abstract. The cold-water coral Lophelia pertusa is one of the few species able to build reef-like structures and a 3-dimensional coral framework in the deep oceans. Furthermore, deep cold-water coral bioherms may be among the first marine ecosystems to be affected by ocean acidification. Colonies of L. pertusa were collected during a cruise in 2006 to cold-water coral bioherms of the Mingulay reef complex (Hebrides, North Atlantic). Shortly after sample collection onboard these corals were labelled with calcium-45. The same experimental approach was used to assess calcification rates and how those changed due to reduced pH during a cruise to the Skagerrak (North Sea) in 2007. The highest calcification rates were found in youngest polyps with up to 1% d−1 new skeletal growth and average rates of 0.11±0.02% d−1±S.E.). Lowering pH by 0.15 and 0.3 units relative to the ambient level resulted in calcification being reduced by 30 and 56%. Lower pH reduced calcification more in fast growing, young polyps (59% reduction) than in older polyps (40% reduction). Thus skeletal growth of young and fast calcifying corallites suffered more from ocean acidification. Nevertheless, L. pertusa exhibited positive net calcification (as measured by 45Ca incorporation) even at an aragonite saturation state (Ωa) below 1.
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Barnhill, Kelsey Archer, Nadia Jogee, Colleen Brown, et al. "Acclimatization Drives Differences in Reef-Building Coral Calcification Rates." Diversity 12, no. 9 (2020): 347. http://dx.doi.org/10.3390/d12090347.
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Coral reefs are susceptible to climate change, anthropogenic influence, and environmental stressors. However, corals in Kāneʻohe Bay, Hawaiʻi have repeatedly shown resilience and acclimatization to anthropogenically-induced rising temperatures and increased frequencies of bleaching events. Variations in coral and algae cover at two sites—just 600 m apart—at Malaukaʻa fringing reef suggest genetic or environmental differences in coral resilience between sites. A reciprocal transplant experiment was conducted to determine if calcification (linear extension and dry skeletal weight) for dominant reef-building species, Montipora capitata and Porites compressa, varied between the two sites and whether or not parent colony or environmental factors were responsible for the differences. Despite the two sites representing distinct environmental conditions with significant differences between temperature, salinity, and aragonite saturation, M. capitata growth rates remained the same between sites and treatments. However, dry skeletal weight increases in P. compressa were significantly different between sites, but not across treatments, with linear mixed effects model results suggesting heterogeneity driven by environmental differences between sites and the parent colonies. These results provide evidence of resilience and acclimatization for M. capitata and P. compressa. Variability of resilience may be driven by local adaptations at a small, reef-level scale for P. compressa in Kāneʻohe Bay.
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Finch, Adrian A., and Nicola Allison. "Strontium in coral aragonite: 2. Sr coordination and the long-term stability of coral environmental records." Geochimica et Cosmochimica Acta 67, no. 23 (2003): 4519–27. http://dx.doi.org/10.1016/s0016-7037(03)00410-1.
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Steinacher, M., F. Joos, T. L. Frölicher, G. K. Plattner, and S. C. Doney. "Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model." Biogeosciences 6, no. 4 (2009): 515–33. http://dx.doi.org/10.5194/bg-6-515-2009.
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Abstract. Ocean acidification from the uptake of anthropogenic carbon is simulated for the industrial period and IPCC SRES emission scenarios A2 and B1 with a global coupled carbon cycle-climate model. Earlier studies identified seawater saturation state with respect to aragonite, a mineral phase of calcium carbonate, as a key variable governing impacts on corals and other shell-forming organisms. Globally in the A2 scenario, water saturated by more than 300%, considered suitable for coral growth, vanishes by 2070 AD (CO2≈630 ppm), and the ocean volume fraction occupied by saturated water decreases from 42% to 25% over this century. The largest simulated pH changes worldwide occur in Arctic surface waters, where hydrogen ion concentration increases by up to 185% (ΔpH=−0.45). Projected climate change amplifies the decrease in Arctic surface mean saturation and pH by more than 20%, mainly due to freshening and increased carbon uptake in response to sea ice retreat. Modeled saturation compares well with observation-based estimates along an Arctic transect and simulated changes have been corrected for remaining model-data differences in this region. Aragonite undersaturation in Arctic surface waters is projected to occur locally within a decade and to become more widespread as atmospheric CO2 continues to grow. The results imply that surface waters in the Arctic Ocean will become corrosive to aragonite, with potentially large implications for the marine ecosystem, if anthropogenic carbon emissions are not reduced and atmospheric CO2 not kept below 450 ppm.