Effect of carbon dioxide concentration on calcification in the red coralline alga Bossiella orbigniana

The relationship between various experimental concentrations of CO₂ and calcification in Bossiella orbigniana (Decaisne) was studied by measuring Ca-45 incorporation into the crystalline matrix. Air containing CO₂ at partial pressures (P_{CO 2}) of 0.04 to 5.5% was bubbled through synthetic seawater in incubation vessels. The resultant pH values in the presence of plants ranged from 6.5 to 8.7. The maximum calcification rate appears to lie between 0.11 and 1.05% P_{CO 2}. The data suggest that calcification is controlled by a biological process that may be sensitive to pH and/or to the relative bicarbonate concentration. The data also suggest that a severalfold increase in CO₂ over the present atmospheric level might lead to increased calcification in this marine alga.