Abstract
Abstract. The response of the coccolithophore Emiliania huxleyi to rising CO2 concentrations is well documented for acclimated cultures where cells are exposed to the CO2 treatments for several generations prior to the experiment. The exact number of generations required for acclimation to CO2-induced changes in seawater carbonate chemistry, however, is unknown. Here we show that Emiliania huxleyi's short-term response (26 h) after cultures (grown at 500 μatm) were abruptly exposed to changed CO2 concentrations (~190, 410, 800 and 1500 μatm) is similar to that obtained with acclimated cultures under comparable conditions in earlier studies. Most importantly, from the lower CO2 levels (190 and 410 μatm) to 750 and 1500 μatm calcification decreased and organic carbon fixation increased within the first 8 to 14 h after exposing the cultures to changes in carbonate chemistry. This suggests that Emiliania huxleyi rapidly alters the rates of essential metabolical processes in response to changes in seawater carbonate chemistry, establishing a new physiological "state" (acclimation) within a matter of hours. If this 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.
Highlights
The response of the coccolithophore Emiliania huxleyi to rising CO2 concentrations is well documented for acclimated cultures where cells are exposed to the CO2 treatments for several generations prior to the experiment
From the lower CO2 levels (190 and 410 μatm) to 750 and 1500 μatm calcification decreased and organic carbon fixation increased within the first 8 to 14 h after exposing the cultures to changes in carbonate chemistry. This suggests that Emiliania huxleyi rapidly alters the rates of essential metabolical processes in response to changes in seawater carbonate chemistry, establishing a new physiological “state” within a matter of hours. If this relatively rapid response applies to other phytoplankton species, it may simplify interpretation of studies with natural communities, where often it is not feasible to allow for a pre-conditioning phase before starting experimental incubations
After 8 h of exposure to the experimental CO2 levels cumulative organic carbon fixation in Emiliania huxleyi increased with CO2 concentration (Fig. 1a), with statistical significance (p = 0.0499) and a linear correlation factor (R) of 0.7069
Summary
Particular attention has been given to coccolithophores, a group of calcifying marine phytoplankton which was found to exhibit distinct sensitivity to ocean acidification. Members of this group, which is considered responsible for a significant fraction of the pelagic biogenic carbonate precipitation (Milliman, 1993), responded to CO2 induced seawater acidification by changing cellular calcification rates. The best studied and probably most productive coccolithophore, Emiliania huxleyi, has generally been found to decrease its calcification rate in response to elevated CO2 concentrations under nutrient and light replete conditions (Feng et al, 2008; Riebesell et al, 2000b; Zondervan et al, 2001). Acclimation period here refers to the time necessary for individual cells to establish a new physiological “state” in response to a change in the environmental condition
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