Calcium localisation by X-ray microanalysis and fluorescence microscopy in larvae of zooxanthellate and azooxanthellate corals

X-ray microanalysis and fluorescence microscopy (Calcium Orange(TM)) was used to determine the distribution of intracellular calcium (I-Ca), in the form of total and ionic calcium respectively, in planulae and settled larvae of a zooxanthellate coral. The distribution of total calcium only was determined in larvae of an azooxanthellate coral. In azooxanthellate planulae and settled larvae, total I-Ca concentration in the oral ectoderm was high and similar to that in seawater (SW). Calcium concentration did not vary (P > 0.05) between planulae and settled larvae. However, settled larvae accumulated large amounts of calcium in gastrodermal lipid-containing cells. In contrast, zooxanthellate planulae possessed significantly (P < 0.01) lower concentrations of total I-Ca within ectodermal cells in comparison to settled larvae. In addition, in settled zooxanthellate larvae total calcium concentration in the mesogloea and coelenteron was significantly (P < 0.05) higher than in the oral ectodermal and gastrodermal cells, respectively. Total I-Ca concentrations in the oral ectoderm of settled larvae were also significantly (P < 0.01) lower than that of the calicoblastic ectoderm. In zooxanthellate settled larvae, ionic I-Ca levels in the aboral epithelium surrounding rapidly growing septa were high. These levels increased significantly (P < 0.05) within the tissue surrounding growing septa after incubation in high-calcium SW. (C) 2004 Elsevier Ltd. All rights reserved.