Abstract
Distinguishing between environmental and species-specific physiological signals, recorded in coral skeletons, is one of the fundamental challenges in their reliable use as (paleo)climate proxies. To date, characteristic biological bias in skeleton-recorded environmental signatures (vital effect) was shown in shifts in geochemical signatures. Herein, for the first time, we have assessed crystallographic parameters of bio-aragonite to study the response of the reef-building coral Stylophora pistillata to experimental seawater acidification (pH 8.2, 7.6 and 7.3). Skeletons formed under high pCO2 conditions show systematic crystallographic changes such as better constrained crystal orientation and anisotropic distortions of bio-aragonite lattice parameters due to increased amount of intracrystalline organic matrix and water content. These variations in crystallographic features that seem to reflect physiological adjustments of biomineralizing organisms to environmental change, are herein called crystallographic vital effect (CVE). CVE may register those changes in the biomineralization process that may not yet be perceived at the macromorphological skeletal level.
Highlights
Distinguishing between environmental and species-specific physiological signals, recorded in coral skeletons, is one of the fundamental challenges in their reliable use asclimate proxies
The effects of ocean acidification (OA) on coral biomineralization have been identified in natural (Great Barrier Reef in Australia21) and experimental conditions emulating acidification scenarios predicted by the end of the 21st century[22]
Enlargements of the coenosteum show granulated surfaces composed of bundles of fibres (Fig. 1d–e, i–j, n–o) of thickening deposits (TD) and smoother but polycentric rapid accretion deposits (RAD, Fig. 1d,i,n)
Summary
Distinguishing between environmental and species-specific physiological signals, recorded in coral skeletons, is one of the fundamental challenges in their reliable use as (paleo)climate proxies. Skeletons formed under high pCO2 conditions show systematic crystallographic changes such as better constrained crystal orientation and anisotropic distortions of bio-aragonite lattice parameters due to increased amount of intracrystalline organic matrix and water content These variations in crystallographic features that seem to reflect physiological adjustments of biomineralizing organisms to environmental change, are called crystallographic vital effect (CVE). In contrast to inorganically precipitated aragonite, coral bio-aragonite shows several distinct crystallo-chemical properties such as crystal morphology (from nanogranulae to microfibers2–5), controlled textures (microstructural patterns related to phylogenetic position of coral3,6,7), preferential crystallographic orientation[5,8,9,10], and heterogenous biogeochemical composition[11,12,13] These features of the coral biominerals are the outcome of highly variable physiological activity of epithelial cells (i.e., calicoblastic ectoderm) that control: secretion of organic phases into calcification medium; ion transport from external environment; formation of an amorphous phase, a direct substrate for crystallisation via amorphous particle attachment mechanism[14,15,16]. Some corals are capable to adapt to changes[30,31], the combination of acidification and high temperatures typically have a detrimental effect on coral survival[23,32]
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