Biomineralization in Mediterranean Corals: The Role of the Intraskeletal Organic Matrix Michela Reggi, † Simona Fermani, † Valerio Landi, † Francesca Sparla, ‡ Erik Caroselli, § Francesca Gizzi, § Zvy Dubinsky, ∥ Oren Levy, ∥ Jean-Pierre Cuif, ⊥ Yannicke Dauphin, ⊥ Stefano Goffredo,* ,§ and Giuseppe Falini* ,†,# † Dipartimento di Chimica “Giacomo Ciamician”, via Selmi 2, ‡ Dipartimento di Farmacia e Biotecnologie, Via S. Donato 15, § Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione di Biologia, via Selmi 3, Alma Mater Studiorum - Universita ̀ di Bologna, 40100 Bologna, Italy ∥ The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel ⊥ Universite ́ Paris-Sud, Orsay, Bat. 504, UMR IDES, F-91405 Orsay, France # Centro Interdipartimentale di Ricerca per le Scienze Ambientali, Sede di Ravenna - Universita ̀ di Bologna, via S. Alberto 163, 48100 Ravenna, Italy * S Supporting Information ABSTRACT: The precipitation of calcium carbonate was carried out in the presence of the intraskeletal organic matrix (OM) extracted from Mediterranean corals. They were diverse in growth form and trophic strategy, Balanophyllia europaea and Leptopsammia pruvotisolitary corals, only the first zooxanthellate coraland Cladocora caespitosa and Astroides calyculariscolonial corals, only the first zooxanthellate coral. The results showed that, although the OM marked differences among species, the diverse influence over the calcium carbonate precipitation was evident only for B. europaea. This OM was the most prone to favor the precipitation of aragonite in the absence of magnesium ions, according to overgrowth and solution precipitation experiments. In artificial seawater, where magnesium ions were present, this OM, as well the one from A. calycularis, precipitated mainly a form of amorphous calcium carbonate different from that obtained with SOM from L. pruvoti or C. caespitosa. The amorphous calcium carbonate from B. europaea was the most stable upon heating up to 100 °C and was the one that mainly converted into aragonite instead of magnesium calcite after heating at 300 °C. All this indicated a higher control of B. europaea OM over the calcium carbonate polymorphism than the other species. The influence of SOMs over precipitate morphology turned out to be also species related. In conclusion, this comparative study has shown that the influence of OM on in vitro precipitation of calcium carbonate was not related to the coral ecology, solitary vs colonial and zooxanthellate vs nonzooxanthellate, and suggested that the coral control over biomineralization process was species specific and encoded in coral genes. ■ INTRODUCTION Scleractinian corals represent the biggest source of biogenic calcium carbonate 1,2 and are among the fastest marine mineralizing organisms. 3 In corals the calcification process occurs in a biological confined environment, under the control of biological macromolecules. 4 This is confirmed by the observation that, although coral skeleton morphology can be affected by habitat conditions, 5−7 the change always remains within the species-specific “vocabulary” controlled by the DNA of the organism. 8−10 The skeleton of corals is a composite structure with both inorganic (aragonite) and organic components. 11,12 The merging of data from several investigations 13,14 has revealed that the actual growth unit of the skeleton is a few micrometers- thick mineralizing growth layer synchronically increasing the “sclerodermites”, forming a given skeletal unit (e.g., a septum). The mineralizing growth layer simultaneously increases the two distinct mineralizing areas that have been extensively described from a structural point of view. At the growth edge of any structural components (e.g., septal spines) a granular and porous nanocrystalline phase (randomly oriented) forms the initial skeletal framework (also the earliest appearing mineralized elements after larval metamorphosis, according to Vandermeulen and Watabe 15 ). These early mineralizing zones (EMZ), usually called “center of calcification”, are laterally reinforced by deposition of a second structural layer made of dense, large, acicular crystals: the fibers. 16 Organic components, referred to as organic matrix (OM), are involved in biomineral synthesis and become entrapped in the skeleton. 17−20 The composition of coral OM compounds Received: March 13, 2014 Revised: June 9, 2014 Published: July 7, 2014 Article pubs.acs.org/crystal © 2014 American Chemical Society 4310 dx.doi.org/10.1021/cg5003572 | Cryst. Growth Des. 2014, 14, 4310−4320