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Low temperature X-ray microanalysis of calcium in a scleractinian coral: evidence of active transport mechanisms

Peta L. Clode and Alan T. Marshall^*

Analytical Electron Microscopy Laboratory, Department of Zoology, La Trobe University, Bundoora, Melbourne. Victoria, 3083, Australia

View larger version (46K): [in a new window]   Fig. 1. Schematic diagram of a transverse section through a Galaxea fascicularis polyp, detailing the regions analysed by X-ray microanalysis, using selected area analyses. See text for details.

View larger version (222K): [in a new window]   Fig. 2. Scanning electron micrograph of a typical fracture surface of the oral epithelium of a frozen-hydrated and superficially etched Galaxea fascicularis polyp prepared for selected area analyses. The external seawater layer (EXT), oral ectoderm (OE), mesogloea (Mg), oral gastrodermis (OG), zooxanthellae (Zx), mucus granules (M) and extrathecal coelenteron (ETC) are clearly distinguishable. Scale bar, 10 µm.

View larger version (197K): [in a new window]   Fig. 3. Scanning electron micrograph of a typical fracture surface of the aboral epithelium of a frozen-hydrated and superficially etched Galaxea fascicularis polyp prepared for selected area analyses. The skeleton (Sk), calicoblastic ectoderm (CE), mesogloea (Mg), aboral gastrodermis (AG) and extrathecal coelenteron (ETC) are visible. Scale bar, 10 µm.

View larger version (198K): [in a new window]   Fig. 4. Transmission electron micrograph showing the mucus layer (ML) located within the external seawater layer at the outer surface of oral ectodermal cells (OE), in a freeze-substituted, sectioned Galaxea fascicularis polyp. Abundant mucocytes (M) within the oral ectoderm are also visible. Scale bar, 2 µm.

View larger version (21K): [in a new window]   Fig. 5. Concentrations of elements present in standard seawater (SW) (N=17), and the external SW layer (N=33), extrathecal coelenteron SW (N=38) and internal coelenteron SW (N=18) of bulk, frozen-hydrated Galaxea fascicularis polyps sampled during daytime. Values are means ± S.E.M. All results were standardised to 546 mmol kg-1 Cl. See Results for significant differences. ^Not detectable.

View larger version (12K): [in a new window]   Fig. 6. Raw Ca X-ray counts (mean ± S.E.M.) for the external (EXT; N=6), extrathecal (ETC; N=5) and internal (INT; N=3) seawater compartments, obtained from a single Galaxea fascicularis polyp. Different letters denote statistical significance (P<0.05; ANOVA).

View larger version (19K): [in a new window]   Fig. 7. Comparison of element concentrations (mean ± S.E.M.) within seawater (SW) compartments obtained from bulk, frozen-hydrated Galaxea fascicularis polyps sampled during daytime and night time. (A) External SW; (B) extrathecal coelenteron SW; (C) internal coelenteron SW. All results were standardised to 546 mmol kg-1 Cl. *P<0.05 (Wilcoxon). ^Not detectable.

View larger version (17K): [in a new window]   Fig. 8. Ratios (% of S, mean ± S.E.M.) of the primary elements present in mucocytes of the oral ectoderm (OE; N=45), oral gastrodermis (OG; N=43), aboral gastrodermis (AG; N=36) and calicoblastic ectoderm (CE; N=11), of bulk, frozen-hydrated Galaxea fascicularis polyps. See Results for significant differences.

View larger version (54K): [in a new window]   Fig. 9. (A) Fracture surface of a bulk, frozen-hydrated Galaxea fascicularis skeleton infiltrated with a NaCl-PVP solution. The interface between the skeleton (Sk) and the NaCl-PVP solution (NaCl) is depicted by a thin line. The position of the line scan across this interface is depicted by the broad line. Scale bar, 10 µm. (B) Peak to background X-ray counts (P/B; 0-2500 full scale) for Ca along the line scan shown in A.