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First published online June 29, 2007
Journal of Experimental Biology 210, 2453-2463 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003343

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Electron and ion microprobe analysis of calcium distribution and transport in coral tissues

Alan T. Marshall^1,*, Peta L. Clode², Robert Russell³, Kathryn Prince³ and Richard Stern^2,

¹ Analytical Electron Microscopy Laboratory, Faculty of Science, Technology and Engineering, La Trobe University, Melbourne, VI 3086, Australia
² Centre for Microscopy, Characterisation and Microanalysis (M010), The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
³ SIMS Laboratory, ANSTO, New Illawara Road, Lucas Heights, NSW 2234, Australia

^* Author for correspondence (e-mail: A.Marshall{at}latrobe.edu.au)

Accepted 24 April 2007

It is shown by x-ray microanalysis that a gradient of total intracellular Ca concentration exists from the outer oral ectoderm to the inner skeletogenic calicoblastic ectoderm in the coral Galaxea fascicularis. This suggests an increase in intracellular Ca stores in relation to calcification. Furthermore, Ca concentration in the fluid-filled space of the extrathecal coelenteron is approximately twice as high as in the surrounding seawater and higher than in the mucus-containing seawater layer on the exterior of the oral ectoderm. This is indicative of active Ca²⁺ transport across the oral epithelium. Polyps were incubated in artificial seawater in which all ⁴⁰Ca was replaced by ⁴⁴Ca. Imaging Ca²⁺ transport across the epithelia by secondary ion mass spectroscopy (SIMS) using ⁴⁴Ca as a tracer showed that Ca²⁺ rapidly entered the cells of the oral epithelium and that ⁴⁴Ca reached higher concentrations in the mesogloea and extrathecal coelenteron than in the external seawater layer. Very little Ca²⁺ was exchanged in the mucocytes, cnidocytes or zooxanthellae. These observations again suggest that Ca²⁺ transport is active and transcellular and also indicate a hitherto unsuspected role in Ca²⁺ transport for the mesogloea.

Key words: biomineralisation, coral, calcium, ion microprobe, SIMS, ion transport, x-ray microanalysis