Rates of Turnover and Net Accretion of Calcium and the Role of Calcium Binding Polysaccharides During Calcification in the Calcareous Alga Halimeda opuntia (L.)

Abstract

AbstractCalcification in the calcareous alga Halimeda opuntia involves Calcium exchange with the seawater. Calcium influx and‐outflux is nearly the same and approximately 300 μg Ca/g alga/min. Calcium net accretion is 3.6 ± 1.1 μg Ca/g alga/min. Calcium outflux alga‐seawater is higher in darkness than in light. Calcium exchange in live algae is 3–6 times faster than in dead algae. Calcium is lost from the seawater at two distinctly different rates and is taken up by watersoluble polysaccharides in the algal mucilage and by the skeleton. These two Calcium pools represent 0.1 and 99.9% of the algal Calcium respectively. Between 0.8–2.0% of the skeletal Calcium is exchangeable. The analysis of the 45Ca specific activity curves suggests that there are more than 2 Calcium pools in the alga. The polysaccharides constitute a small but rapidly exchanging Calcium pool which communicates with the seawater and at least 2 other pools. The Calcium binding polysaccharides are involved in the Calcium metabolism of the alga and may play a role in algal calcification.