title: Biomineralization in newly settled recruits of the scleractinian coral Pocillopora damicornis.
abstract: Calcium carbonate biomineralization of scleractinian coral recruits is fundamental to the construction of reefs and their survival under stress from global and local environmental change. Establishing a baseline for how normal, healthy coral recruits initiate skeletal formation is, therefore, warranted. Here, we present a thorough, multiscale, microscopic and spectroscopic investigation of skeletal elements deposited by Pocillopora damicornis recruits, from 12 h to 22 days after settlement in aquarium on a flat substrate. Six growth stages are defined, primarily based on appearance and morphology of successively deposited skeletal structures, with the following average formation time-scales: A (<24 h), B (24-36 h), C (36-48 h), D (48-72 h), E (72-96 h), and F (>10 days). Raman and energy dispersive X-ray spectroscopy indicate the presence of calcite among the earliest components of the basal plate, which consist of micrometer-sized, rod-shaped crystals with rhomboidal habit. All later CaCO3 skeletal structures are composed exclusively of aragonite. High-resolution scanning electron microscopy reveals that, externally, all CaCO3 deposits consist of <100 nm granular units. Fusiform, dumbbell-like, and semispherulitic structures, 25-35 µm in longest dimension, occur only during the earliest stages (Stages A-C), with morphologies similar to structures formed abiotically or induced by organics in in vitro carbonate crystallization experiments. All other skeletal structures of the basal plate are composed of vertically extending lamellar bundles of granules. From Stage D, straight fibrils, 40-45 nm in width and presumably of organic composition, form bridges between these aragonitic bundles emerging from the growing front of fusing skeletal structures. Our results show a clear evolution in the coral polyp biomineralization process as the carbonate structures develop toward those characterizing the adult skeleton.
authors: Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1009, Lausanne, Switzerland; Center for Advanced Surface Analysis, Institute of Earth Sciences, University of Lausanne, CH-1009, Lausanne, Switzerland.
authors: Melany
authors: M
authors: Gilis
authors: Anders
authors: A
authors: Meibom
authors: Isabelle
authors: I
authors: Domart-Coulon
authors: Olivier
authors: O
authors: Grauby
authors: Jarosław
authors: J
authors: Stolarski
authors: Alain
authors: A
authors: Baronnet
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000033:anatomy & histology* / Q000254:growth & development / Q000502:physiology*; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry*; D057894:Coral Reefs; D003460:Crystallization; D008855:Microscopy, Electron, Scanning
chemical_list: D002119:Calcium Carbonate
keywords: Raman spectroscopy; calcium carbonate; dumbbell; scanning electron microscopy