Emiliania huxleyi shows identical responses to elevated pCO2 in TA and DIC manipulations

a r t i c l e i n f o With respect to their sensitivity to ocean acidification, calcifiers such as the coccolithophore Emiliania huxleyi have received special attention, as the process of calcification seems to be particularly sensitive to changes in the marine carbonate system. For E. huxleyi, apparently conflicting results regarding its sensitivity to ocean acidification have been published (Iglesias-Rodriguez et al., 2008a; Riebesell et al., 2000). As possible causes for discrepancies, intra-specific variability and different effects of CO 2 manipulation methods, i.e. the manipulation of total alkalinity (TA) or total dissolved inorganic carbon (DIC), have been discussed. While Langer et al. (2009) demonstrate a high degree of intra-specific variability between strains of E. huxleyi, the question whether different CO 2 manipulation methods influence the cellular responses has not been resolved yet. In this study, closed TA as well as open and closed DIC manipulation methods were compared with respect to E. huxleyi's CO 2-dependence in growth rate, POC-and PIC-production. The differences in the carbonate chemistry between TA and DIC manipulations were shown not to cause any differences in response patterns, while the latter differed between open and closed DIC manipulation. The two strains investigated showed different sensitivities to acidification of seawater, RCC1256 being more negatively affected in growth rates and PIC production than NZEH. Since the industrial revolution, anthropogenic activities such as the burning of fossil fuels or changes in land use have increased atmospheric pCO 2 values from about 280 μatm to 385 μatm (Lüthi et al., 2008; Tans, 2009). About one third of the emitted CO 2 has already been taken up by the oceans, leading to increased DIC concentrations in surface waters (Wolf-Gladrow et al., 1999). The subsequent changes in speciation, such as increased CO 2 concentrations [CO 2 ] and decreased CO 3 2-concentrations [CO 3 2-], lead to decreasing oceanic pH values (Broecker et al., 1971). This process, commonly referred to as ocean acidification, has diverse effects on marine organisms, communities and ecosystems (e.g. There have been several studies investigating ocean acidification effects on phytoplankton on the single species and community level (for review see Fabry et al., 2008; Rost et al., 2008). CO 2 perturbation experiments are the prime tools to mimic future CO 2 scenarios and to study organism responses. These experiments can be conducted by i) equilibrating with air of a certain pCO 2 , ii) the addition …