Unusual Micrometric Calcite-Aragonite Interface in the Abalone Shell Haliotis (Mollusca, Gastropoda)

Species of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which calcite and aragonite coexist at a microscale with small patches of aragonite embedded in larger calcitic zones. A detailed examination of the boundary between calcite and aragonite using analytical microscopies shows that the organic contents of calcite and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a calcitic zone suggests the occurrence of very fast physiological changes in these tax

Structural, mineralogical, and biochemical diversity in the lower part of the pearl layer of cultivated seawater pearls from Polynesia

A series of Polynesian pearls has been investigated with particular attention to the structural and compositional patterns of the early developmental stages of the pearl layer. These initial steps in pearl formation bear witness of the metabolic changes that have occurred during the pearl-sac formation. The resulting structurally and biochemically complex structures have been investigated using a variety of techniques that provide us with information concerning both mineral phases and the organic components. Results are discussed with respect to our understanding of the biomineralization mechanisms, as well as for the grafting process

From visible light to X-ray microscopy: major steps in the evolution of developmental models for calcification of invertebrate skeletons

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From visible light to X-ray microscopy: major steps in the evolution of developmental models for calcification of invertebrate skeletons

The calcareous skeletons built by invertebrate organisms share a paradoxical property. Although growing outside the mineralizing cell layers the crystal-like skeleton units exhibit morphologies and three-dimensional arrangements that imply an efficient link between crystallization process and taxonomy. Almost two centuries of investigation led to a series of developmental models in which biological and physical or chemical influences are variously balanced. Recent innovative methods allow for their re-examination. From control of the overall shape of the shell to photo-spectroscopic evidence at the atomic level, influence of the biological processes on mineral properties may be a widely shared specificity of the calcareous biomineralization mechanism

Gains and losses of coral skeletal porosity changes with ocean acidification acclimation

Ocean acidi\ufb01cation is predicted to impact ecosystems reliant on calcifying organisms, potentially reducing the socioeconomic bene\ufb01ts these habitats provide. Here we investigate the acclimation potential of stony corals living along a pH gradient caused by a Mediterranean CO2 vent that serves as a natural long-term experimental setting. We show that in response to reduced skeletal mineralization at lower pH, corals increase their skeletal macroporosity (features >10 micrometers) in order to maintain constant linear extension rate, an important criterion for reproductive output. At the nanoscale, the coral skeleton\u2019s structural features are not altered. However, higher skeletal porosity, and reduced bulk density and stiffness may contribute to reduce population density and increase damage susceptibility under low pH conditions. Based on these observations, the almost universally employed measure of coral biomineralization, the rate of linear extension, might not be a reliable metric for assessing coral health and resilience in a warming and acidifying ocean

Synchrotron-Based HR-Fluorescence and Mineralogical Mapping of the Initial Growth Stages of Polynesian Cultivated Pearls Disprove the ‘Reversed Shell’ Concept

In a series of Polynesian pearls collected after short cultivation periods, early post-grafting mineral deposits were characterized by high resolution synchrotron-based X-ray fluorescence with unprecedented accuracy. Morphological patterns and elemental composition are correlated through simultaneous imaging processes. Evidence that aragonite and calcite occur in neighboring units during the earliest biomineralization stages reveals that the grafting process can result in a greater degradation than usually admitted in the widely shared ‘reversed shell’ concept. Compared with ultrastructure of the pristine nacreous tablets, this method enables a precise evaluation of the possible biological changes in the biomineralization mechanism during grafting

Variation of geochemical signals in coral skeletons: Environmental changes or biological processes?

Corals are widely distributed throughout a long stretch of geological time and can provide highresolution histories of climatic variabilities in the tropics, which play a key role in understanding the Earth's climate system. Geochemical approaches to corals have been widely used for reconstructing palaeoclimates because the geochemistry of the skeleton is believed to vary as a function of several environmental conditions. However, large variations that cannot be ascribed to a single environmental factor have been observed among and/or within calibrations of coral-based proxies. Two main unsolved factors could lead to these large discrepancies: unexpected environmental changes in reefs and unknown biological processes occurring at coral biomineralization sites. In this review, we show the recent progress in dealing with this question by application of coral culture technique and micro analytical methods to skeletal geochemistry in corals and discuss on how the degree of geochemical variation could be affected by environmental changes and how by biological processes during the skeleton's calcification. The next challenge will be to perform high-resolution analysis on cultured corals growing under controlled and/or constant environmental conditions. Such efforts hold the promise of yielding important new insights into the various biomineralization processes that may affect the chemical and isotopic composition of the skeletons, with the goal of understanding how environmental changes express themselves in geochemical variability