Individual and interacting effects of pCO2 and temperature on Emiliania huxleyi calcification: study of the calcite production, the coccolith morphology and the coccosphere size
The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO 2 (180 ppmV CO 2 , 380 ppmV CO 2 and 750 ppmV CO 2 corresponding to past, present and future CO 2 conditions, respectively) and temperature (13 • C and 18 • C) during the exponential growth phase of the coccolithophore E. huxleyi using batch culture experiments.
... lture experiments. We showed that cellular production rate of Particulate Organic Carbon (POC) increased from the present to the future CO 2 treatments at 13 • C. A significant effect of pCO 2 and of temperature on calcification was found, manifesting itself in a lower cellular production rate of Particulate Inorganic Carbon (PIC) as well as a lower PIC:POC ratio at future CO 2 levels and at 18 • C. Coccosphere-sized particles showed a size reduction with both increasing temperature and CO 2 concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO 2 while temperature did not have a significant impact on coccolith morphology. No interacting effects of pCO 2 and temperature were observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming.