Temperature Modulates Coccolithophorid Sensitivity of Growth, Photosynthesis and Calcification to Increasing Seawater pCO2

摘要

Increasing atmospheric CO2 concentrations are expected to impact pelagic ecosystem functioning in the near future by\uddriving ocean warming and acidification. While numerous studies have investigated impacts of rising temperature and\udseawater acidification on planktonic organisms separately, little is presently known on their combined effects. To test for\udpossible synergistic effects we exposed two coccolithophore species, Emiliania huxleyi and Gephyrocapsa oceanica, to a CO2\udgradient ranging from ,0.5–250 mmol kg21 (i.e. ,20–6000 matm pCO2) at three different temperatures (i.e. 10, 15, 20uC for\udE. huxleyi and 15, 20, 25uC for G. oceanica). Both species showed CO2-dependent optimum-curve responses for growth,\udphotosynthesis and calcification rates at all temperatures. Increased temperature generally enhanced growth and\udproduction rates and modified sensitivities of metabolic processes to increasing CO2. CO2 optimum concentrations for\udgrowth, calcification, and organic carbon fixation rates were only marginally influenced from low to intermediate\udtemperatures. However, there was a clear optimum shift towards higher CO2 concentrations from intermediate to high\udtemperatures in both species. Our results demonstrate that the CO2 concentration where optimum growth, calcification and\udcarbon fixation rates occur is modulated by temperature. Thus, the response of a coccolithophore strain to ocean\udacidification at a given temperature can be negative, neutral or positive depending on that strain’s temperature optimum.\udThis emphasizes that the cellular responses of coccolithophores to ocean acidification can only be judged accurately when\udinterpreted in the proper eco-physiological context of a given strain or species. Addressing the synergistic effects of\udchanging carbonate chemistry and temperature is an essential step when assessing the success of coccolithophores in the\udfuture ocean.