The structure of scleractinian coral skeleton analyzed by neutron diffraction and neutron computed tomography

Abstract

Two analytical methods based on the neutrons high penetrability, i.e. neutron diffraction (ND) and neutron computed tomography (NCT) were used to investigate the structure of the aragonitic skeleton of an exemplar/sample of Dipastraea pallida (Dana 1846), a modern hermatypic coral. ND was used to reconstruct the orientation distribution function (ODF) of the crystalline fibrils which compose the coral skeleton. Accordingly, 684 ND spectra were analyzed using the Rietveld method. The result confirmed the aragonite as the sole mineral component of coral skeleton, allowing to recalculate the ODF of aragonite fibrils and to represent it by means of (100), (010) and (001) crystallographic planes pole figures (PF). Experimental PF showed a remarkable similarity with PF recalculated by considering that all aragonite fibrils are oriented either along the growth axis of polyp cups or perpendicular to this direction. This result confirmed the previous observations based on optical microscopy, proving at the same time the availability of ND for such types of investigations. In turn, NCT evidenced the individual polyp cups, their interlocked 3D rigid porous structure as well as a periodic variation of density which could be attributed to a seasonal influence of the marine environment. Different from the classical X-ray computed tomography, the NCT, in view of neutron high cross-section for hydrogen, demonstrated the presence of a small amount of organic matter, otherwise transparent for X-and gamma rays.

Micro‐CT reconstruction reveals the colony pattern regulations of four dominant reef‐building corals

“…In recent years, computed tomography (CT) has been applied to study reef‐building coral skeletons (Beuck et al, 2007 ; Gutiérrez‐Heredia et al, 2015 ; Knackstedt et al, 2006 ; Kruszyński et al, 2007 ; Kruszynski et al, 2006 ; Pinzón et al, 2014 ). With the development and popularization of high‐resolution micro‐computed tomography (HRCT), research on coral skeletons has revealed the morphological and internal structures of coral branchlets, and also investigated coral skeletal structures (Ivankina et al, 2020 ; Sentoku et al, 2015 ; Sentoku et al, 2015 ; Urushihara et al, 2016 ) and exogenous influences on coral skeletons, including water currents (Chindapol et al, 2013 ), the marine environment (Iwasaki et al, 2016 ), and ocean acidification (Enochs et al, 2016 ; Fordyce et al, 2020 ). However, there are various challenges in studying coral growth patterns regulation using CT sectional slices that are singly dependent on skeleton reconstruction.…”

Polyp-Canal Reconstruction Reveals Evolution Toward Complexity in Corals

“…The construction of evolutionary trees is further challenged by the evolutionary mechanisms of reef-building corals, which include incomplete lineage sorting of shared ancestral polymorphisms and deep divergence [ 17 , 18 ]. Although existing morphological studies provide intuitive structural information of reef-building corals to complement systematic molecular studies [ 19 ], they are limited by their methods and techniques as they fail to obtain several aspects of growth information that are hidden in the opaque skeletons [ 20 ].…”

Quantifying skeletal density at high temporal resolution in massive scleractinian corals by using two-dimensional grid-scanning gamma densitometry

“…However, this method is not easily applicable due to the need of special equipment and handling issues (Carricart-Ganivet and Barnes 2007;Duprey et al 2012). Ivankina et al (2020) have used neutron-computed tomography (NCT) for the investigation of coral skeletons. The application of NCT can penetrate coral samples more intensely in relation to classical X-ray CT and, therefore, enables the visualisation of intra-skeletal structures, which were previously not recognised (Ivankina et al 2020).…”

“…Ivankina et al (2020) have used neutron-computed tomography (NCT) for the investigation of coral skeletons. The application of NCT can penetrate coral samples more intensely in relation to classical X-ray CT and, therefore, enables the visualisation of intra-skeletal structures, which were previously not recognised (Ivankina et al 2020). Barnes and Devereux (1988) reported first results on skeletal density of Porites corals by using gamma densitometry, which shortly after was described in detail by Chalker and Barnes (1990).…”