Effects of cadmium and low magnesium on cell division and calcification in the marine coccolithophorid Cricosphaera (Hymenomonas) carterae

Cadmium (Cd) added to normal media and to magnesium (Mg)-deficient media produced inhibitory effects on cell division and cell calcification in the marine coccolithophorid alga Cricosphaera (Hymenomonas) carterae. Compared with controls in normal media (with 25 mM Mg), cell growth decreased progressively with Cd at concentrations of 5–20 M. In Mg-deficient media (with 6 mM and 0.08 mM Mg) the inhibitory effects were more pronounced with complete arrest of cell division at 20 M Cd. The greatest Cd inhibition occurred in media with the lowest Mg concentration (0.08 mM). Cadmium (5–40 M) also decreased recalcification (coccolith formation) in cells previoasly decalcified with CO₂ with complete inhibition at 40 M Cd. Inhibition of recalcification in various Cd concentrations (5–40 M) was more pronounced in low-Mg medium (with 6 mM and 0.08 mM Mg) compared with normal medium (25 mM Mg). Partial or complete reversal of the inhibitory effects of Cd and low Mg media on cell division and calcification occurred following a wash and resuspension of the cells in normal control medium (25 mM Mg).