Short-term response of the coccolithophore Emiliania huxleyi to abrupt changes in seawater carbon dioxide concentrations

The response of the coccolithophore Emiliania huxleyi to rising CO 2 concentrations is well documented in acclimated cultures where cells are exposed to the CO 2 treatments for several generations prior to the experiment. Extended acclimation times have generally been applied because of the lack of information about time required to reach a 5 new physiological " equilibrium " (acclimation) in response to CO 2-induced changes in seawater carbonate chemistry. Here we show that Emiliania huxleyi's short-term response (hours to 1 day) to increasing CO 2 is similar to that obtained with acclimated cultures under comparable conditions in earlier studies. At CO 2 concentrations ranging from glacial (190 µatm) to projected year 2100 (750 µatm) levels, calcification de-10 creased and organic carbon fixation increased within 8 h after exposing the cultures to the changed CO 2 conditions. This led to a decrease in the ratio of CaCO 3 to organic carbon production. Our results show that Emiliania huxleyi rapidly alters the rates of various essential processes in response to changes in seawater carbonate chemistry, establishing a new physiological (acclimation) " state " within a matter of hours. If this 15 relatively rapid response applies to other phytoplankton species, it may simplify interpretation of studies with natural communities (e.g. mesocosm studies and ship-board incubations), where often it is not feasible to allow for a pre-conditioning phase before starting experimental incubations.