title: Morphology, microstructure, crystallography, and chemistry of distinct CaCO3 deposits formed by early recruits of the scleractinian coral Pocillopora damicornis.
abstract: Scleractinian corals begin their biomineralization process shortly after larval settlement with the formation of calcium carbonate (CaCO(3)) structures at the interface between the larval tissues and the substrate. The newly settled larvae exert variable degrees of control over this skeleton formation, providing an opportunity to study a range of biocarbonate structures, some of which are transient and not observed in adult coral skeletons. Here we present a morphological, structural, crystallographic, and chemical comparison between two types of aragonite deposits observed during the skeletal development of 2-days old recruits of Pocillopora damicornis: (1) Primary septum and (2) Abundant, dumbbell-like structures, quasi-randomly distributed between initial deposits of the basal plate and not present in adult corals-At the mesoscale level, initial septa structures are formed by superimposed fan-shaped fasciculi consisting of bundles of fibers, as also observed in adult corals. This organization is not observed in the dumbbell-like structures. However, at the ultrastructural level there is great similarity between septa and dumbbell components. Both are composed of <100 nm granular units arranged into larger single-crystal domains.Chemically, a small difference is observed between the septae with an average Mg/Ca ratio around 11 mmol/mol and the dumbbell-like structures with ca. 7 mmol/mol; Sr/Ca ratios are similar in the two structures at around 8 mmol/mol-Overall, the observed differences in distribution, morphology, and chemistry between septa, which are highly conserved structures fundamental to the architecture of the skeleton, and the transient, dumbbell-like structures, suggest that the latter might be formed through less controlled biomineralization processes. Our observations emphasize the inherent difficulties involved in distinguishing different biomineralization pathways based on ultrastructural and crystallographical observations.
authors.affiliation: Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, CH-1009, Switzerland.|Center for Advanced Surface Analysis, Institute of Earth Sciences, University of Lausanne, Lausanne, CH-1009, Switzerland.
authors.forename: Melany
authors.initials: M
authors.lastname: Gilis
authors.affiliation: Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, CH-1009, Switzerland.|Center for Advanced Surface Analysis, Institute of Earth Sciences, University of Lausanne, Lausanne, CH-1009, Switzerland.
authors.forename: Anders
authors.initials: A
authors.lastname: Meibom
authors.affiliation: Interdisciplinary Centre for Electron Microscopy, Ecole Polytechnique Fédérale de Lausanne, Switzerland.
authors.forename: Duncan
authors.initials: D
authors.lastname: Alexander
authors.affiliation: Aix-Marseille Université and Centre Interdisciplinaire de Nanosciences De Marseille (CINaM), Campus de Luminy, Marseille, 13288, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Grauby
authors.affiliation: Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, Warsaw, PL-00-818, Poland.
authors.forename: Jarosław
authors.initials: J
authors.lastname: Stolarski
authors.affiliation: Aix-Marseille Université and Centre Interdisciplinaire de Nanosciences De Marseille (CINaM), Campus de Luminy, Marseille, 13288, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Baronnet
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000378:metabolism* / Q000648:ultrastructure; D002119:Calcium Carbonate / Q000378:metabolism*
chemical_list: D002119:Calcium Carbonate
keywords: TEM; aragonite; biocalcification; coral recruits; dumbbell; septa