Abstract
Calcium exchange and differential saturation of algal calcium pools complicate the application of the 45Ca tracer method for the determination of net deposition rates of calcium in calcareous algae. The kinetics of 45Ca uptake is critically reevaluated, and it is shown that incorporation occurs in two stages. A fast stage, saturating the exchangeable calcium pools; and a slow stage, giving rise to net deposition. The reliability of the method much depends on the determination of the second rate constant. Calcium net-deposition rates are obtained from the expression \((\frac{{\Delta y}}{{\Delta x}})_{4^{/S_{SW} } } \), where \((\frac{{\Delta y}}{{\Delta x}})_4 \) represents the second rate constant and S SW the specific activity of the seawater. Calcium exchange and recycling of tracer would lower the second rate constant, hence the method will give rise to minimum values. The application of the method is demonstrated for the following algae: Halimeda incrassata, H. opuntia, Penicillus pyriformis, Udotea flabellum, Cymopolia barbata, Padina sanctae crucis and Amphiroa fragilissima; the results show close agreement of data with independent chemical estimates.
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