Growth rate over time of Emiliania huxleyi during laboratory experiments

Emiliania huxleyi was incubated for two years (2015-11-20 to 2017-12-01) under two conditions: present-day subantarctic water during summer (11°C and pH 8.1; Now), and projected conditions for subantarctic water by 2100 (14°C and pH 7.8; Future; Law et al. 2018). The pH was reduced by 0.3 units by bubbling 10% CO₂ through the medium prior to the addition of coccolithophore cells and confirmed using a spectrophotometric method (DOE 1994). One culture of each treatment was maintained in a semi-batch style to ensure the cells remained in exponential growth, with cell concentration maintained at low levels (<80000 cells ml⁻¹) to maintain pH at the target value. The pH of the medium after cell growth was checked periodically using a spectrophotometric method (DOE 1994) and was always found to be at the target pH. The in vivo fluorescence of the cultures was measured with a Turner 10-AU fluorometer and the growth rate of the cultures was calculated from the least squares regression of the natural logarithm of in vivo fluorescence, versus time during exponential growth (Strzepek et al. 2011).