Coral calcification: autoradiography of a scleractinian coral Galaxeafascicularis after incubation in 45Ca and 14C |
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Authors: | A T Marshall A Wright |
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Institution: | (1) Analytical Electron Microscopy Laboratory, School of Zoology, La Trobe University, Bundoora (Melbourne), Victoria 3083, Australia e-mail: zooam@zoom. latrobe.edu.au, AU |
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Abstract: | The uptake of 45Ca and/or 14C by the skeleton of coral colonies has been commonly used to investigate the processes of calcification. This study reports
the differential uptake of these tracers within different regions of the skeleton and tissues of individual corallites and
polyps of the hermatypic coral Galaxea fascicularis. Incubation in 45Ca in the light resulted in 80 percent of the 45Ca taken up being deposited in the skeleton. Autoradiography of transverse and longitudinal slices of freeze-substituted polyps
and corallites showed that in the light 45Ca was incorporated into the exsert septa, the outside of the thecal walls of the corallite and the inner edges of the septa.
Incorporation did not occur in the costae. The radioactivity in the skeleton was considerably greater than in the tissues.
In the dark, or in the presence of the photosynthetic inhibitor Diuron, 45Ca was taken up by the exsert septa and was patchily distributed in the corallite walls which suggests that it was not a result
of isotopic exchange. The differential incorporation of 45Ca onto the exsert septa was confirmed by scintillation counting. Negligible radioactivity remained in the extrathecal coelenteron
after a brief 5 min rinse in non-radioactive seawater. Only 0.1% of 14C taken up in the light was incorporated into the skeleton and this was confirmed by autoradiography. In the presence of Diuron
or in the dark, very little 14C was incorporated into tissues or skeleton and in autoradiographs was either not evident in the skeleton or the distribution
was similar to that seen in autoradiographs of 45Ca uptake. These results show that the deposition of 45Ca, and therefore calcium carbonate, occurs at specific loci on the skeleton of a corallite. In the dark, deposition occurs
specifically at the growing points of the corallite. Differential deposition of calcium carbonate within individual corallites
has not been previously reported.
Accepted: 27 May 1997 |
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Keywords: | Coral Calcification Biomineralisation Autoradiography Freeze-substitution |
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