Biogeosciences, 6, 2637–2646, 2009 www.biogeosciences.net/6/2637/2009/ © Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. Biogeosciences Strain-specific responses of Emiliania huxleyi to changing seawater carbonate chemistry G. Langer 1,2 , G. Nehrke 2 , I. Probert 3 , J. Ly 1,2 , and P. Ziveri 1,4 1 ICTA, Autonomous University of Barcelona (UAB), 08193 Bellaterra, Spain 2 Alfred Wegener Institute for Polar and Marine Research, 27570 Bremerhaven, Germany 3 CNRS/UPMC, Station Biologique de Roscoff, 29682 Roscoff, France 4 FALW, Vrije Universiteit Amsterdam, 1081HV Amsterdam, The Netherlands Received: 27 March 2009 – Published in Biogeosciences Discuss.: 17 April 2009 Revised: 19 October 2009 – Accepted: 4 November 2009 – Published: 24 November 2009 Abstract. Four strains of the coccolithophore E. huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO 2 levels ranging from ∼200 µatm to ∼1200 µatm. Growth rate, particulate or- ganic carbon content, and particulate inorganic carbon con- tent were measured, and organic and inorganic carbon pro- duction calculated. The four strains did not show a uniform response to carbonate chemistry changes in any of the anal- ysed parameters and none of the four strains displayed a re- sponse pattern previously described for this species. We con- clude that the sensitivity of different strains of E. huxleyi to acidification differs substantially and that this likely has a genetic basis. We propose that this can explain apparently contradictory results reported in the literature. 1 Introduction Anthropogenic CO 2 emissions cause a decrease of surface seawater pH, a process termed ocean acidification (Royal Society, 2005). Among the adverse effects of ocean acid- ification on marine organisms, reduction in the capacity of calcifiers to build shells has received special attention be- cause calcium carbonate precipitation in surface waters and its subsequent export to the sediments play important roles in the global carbon cycle (Van Cappellen, 2003). In terms of calcite export to sediments, the coccolithophores, unicel- lular haptophyte algae that cover the cell surface with minute intracellularly-produced calcite platelets (the coccoliths), are one of the most important groups of calcifiers in today’s oceans (Baumann et al., 2004). The question of how coccolithophores will respond to ocean acidification has attracted increasing attention over the last decade. To date, the majority of evidence stems Correspondence to: G. Langer (gerald.langer@awi.de) from laboratory culture experiments. Following the semi- nal study by Riebesell et al. (2000), the first widely adopted notion was that coccolithophores decrease their calcifica- tion rate with increasing CO 2 concentration (decreasing pH) in a linear fashion (see also Zondervan et al., 2001). These studies were conducted on one culture strain of each of two closely related species, E. huxleyi and Gephyro- capsa oceanica, both gephyrocapsid coccolithophores that are relatively small (≤ 8 µm), but numerically dominant in coccolithophore assemblages in modern oceans. A subse- quent study showed that one culture strain of each of the two larger, heavily calcifying coccolithophores Calcidiscus lep- toporus and Coccolithus braarudii, did not follow the re- sponse pattern previously reported for E. huxleyi (Langer et al., 2006). While C. leptoporus displayed an optimum curve, C. braarudii was insensitive over the CO 2 (pH) range tested. This clearly demonstrated that there is no uniform response of coccolithophores to acidification. For E. huxleyi, apparently conflicting results have been reported. In direct contrast to the results of Riebesell et al. (2000), a recent study reported that E. huxleyi increases its calcification rate in response to increasing CO 2 concentra- tion under light saturation (Iglesias-Rodriguez et al., 2008a). Despite an active debate on the subject (Riebesell et al., 2008; Iglesias-Rodriguez et al., 2008b), it is presently un- known why apparently contradictory results have been ob- tained in different studies on E. huxleyi. One striking fact is that in every study a different culture strain of this species has been used. Bearing in mind that different species of coc- colithophore have been shown to exhibit different responses to carbonate chemistry changes, it can be hypothesized that intra-specific responses also exist. To test this, we cultured four strains of E. huxleyi under light saturation and four dif- ferent CO 2 concentrations, and measured, inter alia, calcifi- cation rate. Published by Copernicus Publications on behalf of the European Geosciences Union.