Low temperature stimulates cell enlargement and intracellular calcification of coccolithophorids

Temperature effect on growth, cell size, calcium uptake activity, coccolith production was studied in coccolith-producing haptophytes, Emiliania huxleyi (Lohmann) Hay & Mohler (strain EH2) and Gephyrocapsa oceanica Kamptner (strain GO1) (Coccolithophorales, Prymnesiophyceae). E. huxleyi grew at a wider temperature range (10 degrees-25 degrees C), while G. oceanica growth was limited to warmer temperatures (20 degrees-25 degrees C). Cell size was inversely correlated with temperature. At low temperature, the enlargement of chloroplasts and cells and the stimulation of coccolith production were morphologically confirmed under fluorescent and polarization microscopes, respectively. 45Ca uptake by E. huxleyi at 10 degrees C was greatly increased after a 5-day lag and exceeded that at 20 degrees C. These results clearly showed that low temperature suppressed coccolithophorid growth but induced cell enlargement and as stimulated the intracellular calcification that produces coccoliths.