Biomineralization in Newly Settled Recruits of the Scleractinian Coral Pocillopora damicornis

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 (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