Abstract
The skeleton of scleractinian corals is commonly believed to be composed entirely of aragonite due to the current Mg/Ca molar ratio of seawater, which thermodynamically favours the deposition of this polymorph of calcium carbonate (CaCO 3). However, some studies have shown that other forms of CaCO 3 such as calcite can be present in significant amount (1-20%) inside tropical coral skeletons, significantly impacting paleo-reconstructions of SST or other environmental parameters based on geochemical proxies. This study aims at investigating for the first time, (1) the skeletal composition of two Mediterranean solitary corals, the azooxanthellate Leptopsammia pruvoti and the zooxanthellate Balanophyllia europaea, across their life cycle, (2) the distribution of the different CaCO 3 forms inside skeletons, and (3) their implications in paleoclimatology. The origin of the different forms of CaCO 3 observed inside studied coral skeletons and their relationships with the species' habitat and ecological strategies are also discussed. CaCO 3 composition of L. pruvoti and B. europaea was investigated at six sites located along the Italian coasts. Skeleton composition was studied by means of X-ray powder diffraction and Fourier transform infrared spectroscopy. A significant amount of calcite (1-23%) was found in more than 90% of the studied coral skeletons, in addition to aragonite. This calcite was preferentially located in the basal and intermediate areas than at the oral pole of coral skeletons. Calcite was also mainly located in the epitheca that covered the exposed parts of the coral in its aboral region. Interestingly in B. europaea, the calcite content was negatively correlated with skeleton size (age). The presence of calcite in scleractinian corals may result from different mechanisms: (1) corals may biologically precipitate calcite crystals at their early stages in order to insure their settlement on the substrate of fixation, especially in surgy environments; (2) calcite presence may result from skeletons of other calcifying organisms such as crustose coralline algae; and/or (3) calcite may result from the infilling of galleries of boring microorganisms which are known to colonize coral skeletons. We suggest that more than one of the above mentioned processes are involved.
Original language | English |
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Pages (from-to) | 187-199 |
Number of pages | 13 |
Journal | Geochimica et Cosmochimica Acta |
Volume | 85 |
DOIs | |
State | Published - 15 May 2012 |
Bibliographical note
Funding Information:This study is part of the FP7 IDEAS EU-Research Project “CoralWarm” (Grant Agreement no. 249930 ). We thank L. Bortolazzi, A. Comini, M. Cova, G. Gasparini, P. Bonzi, M. Ghelia, G. Neto, and L. Tomesani for their underwater assistance in collecting the samples. The diving centres Centro Immersioni Pantelleria, Il Pesciolino, Polo Sub, and Sub Maldive supplied logistic assistance in the field. The Bologna Scuba Team (BST) and the Scientific Diving School (SDS) collaborated in the underwater activities. The Marine Science Group ( http://www.marinesciencegroup.org ) supplied scientific, technical, and logistical support. This research was financed by the Ministry of Education, University and Research (MIUR), the Ministry of Tourism of the Arab Republic of Egypt, the Associazione dei Tour Operator Italiani (ASTOI), the Project AWARE Foundation, the Scuba Nitrox Safety International (SNSI), the Scuba Schools International (SSI), the Underwater Life Project (ULP), the Marine & Freshwater Science Group Association, and the Consorzio Interuniversitario di Ricerca della Chimica dei Metalli nei Sistemi Biologici. The experiments complied with current Italian law.
Funding
This study is part of the FP7 IDEAS EU-Research Project “CoralWarm” (Grant Agreement no. 249930 ). We thank L. Bortolazzi, A. Comini, M. Cova, G. Gasparini, P. Bonzi, M. Ghelia, G. Neto, and L. Tomesani for their underwater assistance in collecting the samples. The diving centres Centro Immersioni Pantelleria, Il Pesciolino, Polo Sub, and Sub Maldive supplied logistic assistance in the field. The Bologna Scuba Team (BST) and the Scientific Diving School (SDS) collaborated in the underwater activities. The Marine Science Group ( http://www.marinesciencegroup.org ) supplied scientific, technical, and logistical support. This research was financed by the Ministry of Education, University and Research (MIUR), the Ministry of Tourism of the Arab Republic of Egypt, the Associazione dei Tour Operator Italiani (ASTOI), the Project AWARE Foundation, the Scuba Nitrox Safety International (SNSI), the Scuba Schools International (SSI), the Underwater Life Project (ULP), the Marine & Freshwater Science Group Association, and the Consorzio Interuniversitario di Ricerca della Chimica dei Metalli nei Sistemi Biologici. The experiments complied with current Italian law.
Funders | Funder number |
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AWARE Foundation | |
Associazione dei Tour Operator Italiani | |
Consorzio Interuniversitario di Ricerca della Chimica dei Metalli nei Sistemi Biologici | |
Ministry of Tourism of the Arab Republic of Egypt | |
Scuba Nitrox Safety International | |
Scuba Schools International | |
Seventh Framework Programme | 249930 |
Ministero dell’Istruzione, dell’Università e della Ricerca | |
Statens Serum Institut |