Role of the Light‐dark Cycle and Medium Composition on the Production of Coccoliths by Emiliania Huxleyi (Haptophyceae)1

Production of coccoliths by cells of Emiliania huxleyi (Lohmann) Hay and Mohler was measured during exposure of the cells to two diel light‐dark cycles (16:8 h). During the light period about eight coccoliths per cell were formed at a constant rate of one coccolith per 2 h. Cells divided during the first half of the dark period. No coccolith production took place during the dark period. With electron microscopy we found early‐stage, coccolith‐production compartments in cells after mitosis while still in the dark. No calcification was observed in these compartments. Cells grown on enriched seawater (Eppley's medium) tended to produce enough coccoliths to cover the cell in a single layer. When these cells reached the stationary phase coccolith production stopped. Coccolith production was induced by removal of extracellular coccoliths. Cells grown on medium containing 2% of the nitrate and phosphate of Eppley's medium tended to produce coccoliths in the stationary phase. This resulted in the formation of multiple layers of coccoliths. The multiple covering was restored after decalcification of stationary cells. Formation of multiple layers of coccoliths may help the cells reach deeper, nutrient‐rich water by increasing the sinking rate of the cells.