Mineralogy of Deep-Sea Coral Aragonites as a Function of Aragonite Saturation State

Abstract

In an ocean with rapidly changing chemistry, studies have assessed coral skeletal health under projected ocean acidification (OA) scenarios by characterizing morphological distortions in skeletal architecture and measuring bulk properties, such as net calcification and dissolution. Few studies offer more detailed information on skeletal mineralogy. Since aragonite crystallography will at least partially govern the material properties of coral skeletons, such as solubility and strength, it is important to understand how it is influenced by environmental stressors. Here, we take a mineralogical approach using micro X-ray diffraction (XRD) and whole pattern Rietveld refinement analysis to track crystallographic shifts in deep-sea coral Lophelia pertusa samples collected along a natural seawater aragonite saturation state gradient ( sw = 1.15-1.44) in the Gulf of Mexico. Our results reveal statistically significant linear relationships between rising sw and increasing unit cell volume driven by an anisotropic lengthening along the b-axis. These structural changes are similarly observed in synthetic aragonites precipitated under various saturation states, indicating that these changes are inherent to the crystallography of aragonite. Increased crystallographic disorder via widening of the full width at half maximum of the main (111) XRD peaks trend with increased Ba substitutions for Ca, however, trace substitutions by Ba, Sr, and Mg do not trend with crystal lattice parameters in our samples. Instead, we observe a significant trend of increasing calcite content as a function of both decreasing unit cell parameters as well as decreasing sw . This may make calcite incorporation an important factor to consider in coral crystallography, especially under varying aragonite saturation states ( Ar ). Finally, by defining crystallography-based linear relationships between Ar of synthetic aragonite analogs and lattice parameters, we predict internal calcifying fluid saturation state ( cf = 11.1-17.3 calculated from b-axis lengths; 15.2-25.2 calculated from unit cell volumes) for L. pertusa, which may allow this species to calcify despite the local seawater conditions. This study will ideally pave the way for future studies to utilize quantitative XRD in exploring the impact of physical and chemical stressors on biominerals.

The Incorporation of Marine Coral Microparticles into Collagen-Based Scaffolds Promotes Osteogenesis of Human Mesenchymal Stromal Cells via Calcium Ion Signalling

“…Coral are marine invertebrates which have been proposed to offer the potential to act as natural bioceramic scaffolds for bone repair. The XRD analysis carried out in this study confirmed the coral skeleton to be composed of calcium carbonate, primarily aragonite but also containing traces of calcite, which tallies well with other studies in the field that have examined the mineral composition of marine corals [25,26]. Upon the incorporation of coral microparticles into a collagen-based slurry, the subsequent freeze-dried collagen/coral scaffold was shown to have a crystalline calcium ethanoate structure.…”

Crumbling Reefs and Cold-Water Coral Habitat Loss in a Future Ocean: Evidence of “Coralporosis” as an Indicator of Habitat Integrity

“…In instances where calcite (1%) was observed in recently dead coral skeletons, it is possible that calcite incorporation is linked to aragonite precipitation (Farfan et al, 2018). While changes in Electron Backscatter Diffraction (EBSD) results here were driven by changes in crystal size rather than type, recent work (Farfan et al, 2018) has also shown that in some cases the incorporation of calcite in L. pertusa can be up to 3%, with highest values found in dead samples from deep sites. The decrease in crystal size in corals from below the ASH is consistent with observations (Hennige et al, 2015a), where L. pertusa samples were incubated in mesocosms of projected future conditions.…”

Electrochemical Approach for Isolation of Chitin from the Skeleton of the Black Coral Cirrhipathes sp. (Antipatharia)

“…Black corals (Hexacorallia: Antipatharia) are a taxonomic group that appear worldwide in all the oceans and exhibit a wide depth distribution, ranging between coastal shallows and abyssal depths [63][64][65]. To date, the order Antipatharia comprises about 247 valid species, and they are most abundant in tropical and subtropical seas, in deep waters (≥50 m) beneath the photic zone [63,66,67].…”