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

Abstract

X-ray microanalysis and fluorescence microscopy (Calcium Orange™) 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.