Calcification response of Emiliania huxleyi under calcite and aragonite sea

Abstract

The magnesium/calcium ratio of seawater has oscillated throughout the geological time between aragonite seas (>2) and calcite seas (<2), which strongly influenced coccolithophores biocalcification, along with the variation of ocean temperature and pH. Here we proposed to analyze in a concomitant way the effect of temperature and pH together with Mg/Ca on coccolithophores. In this study, we cultured Emiliania huxleyi (RCC963) under a range of Mg/Ca ratios (Mg/Ca: 0.2, 1, 5), temperature (15℃, 21.5℃, 28℃) and pH (7.4, 7.8, 8.2) to evaluate the cell adaption and calcification sensitivity by measuring the growth rate(μ), Photosystem Ⅱ efficiency (Fv/Fm), calcification rate and coccolith morphology. We have found that in the calcite sea, E. huxleyi is more vulnerable to changes of temperature and pH than it is in the aragonite sea. The coccolith morphology also supports the different response to the Mg/Ca ratio variation where more malformed and incomplete coccoliths were observed with the decreasing of temperature and pH. Further exploration is needed to understand the multi-changes in environmental parameters in the distribution of Mg in coccoliths of E. huxleyi and morphogenesis.