Enhanced calcification in the coccolithophorid Emiliania huxleyi (Haptophyceae) under phosphorus limitation

The effect of phosphorus limitation on calcification in the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler was investigated by chemical Ca and C analyses, as well as in short-term 14C uptake experiments. The latter made use of a newly developed microdiffusion method to separate 14C in coccolith carbonate from photosynthetically assimilated 14C. In comparison with exponentially growing cells in a nutrient-replete medium, cells grown in P-limited chemostats at half the maximum growth rate produced c. 60% more CaCO3 relative to organic carbon. In the short-term incubations, cells from P-limited chemostats showed a relative increase in the capacity for calcification under reduced irradiance and in the dark. Nutrient effects on calcification are of potential interest in considerations of the impact of E. huxleyi blooms on the sea-air CO2 interchange, and they deserve further study.