Interactive Effects of CO2, Temperature, and Nutrient Limitation on the Growth and Physiology of the Marine Coccolithophore Emiliania huxleyi (Prymnesiophyceae)

The marine coccolithophore Emiliania huxleyi (strain PnB 272 B10) was grown in a continuous culture system on a 12:12 light:dark cycle at temperatures from 10 °C to 28 °C under either nutrient-replete or nitrate-limited conditions and at either 493 ppmv (low) or 1003 ppmv (high) partial pressures of CO2 (pCO2). The maximum and minimum nutrient-replete growth rates were 0.751 d−1 at 20 °C and 0.365 d−1 at 10 °C, respectively. Ratios of particulate organic carbon (POC) to particulate inorganic carbon (PIC) were independent of pCO2 and of the degree of nitrate limitation but were temperature dependent and lower at 10 °C and 28 °C than at intermediate temperatures. Nutrient-replete growth rates were higher at high versus low pCO2 at 25 °C but did not differ significantly at other temperatures. Ratios of POC to particulate nitrogen (PN) were independent of temperature under nutrient-replete conditions (mean ± standard deviation = 5.07 ± 0.48 g g−1) and under nitrate-limited conditions at half the nutrient-replete growth rates at the same temperature and pCO2 (5.52 ± 0.60 g g−1), but POC/PN ratios were significantly higher at low pCO2 (7.26 ± 0.88 g g−1) versus high pCO2 (5.52 ± 0.59 g g−1). Ratios of POC to chlorophyll a were positively correlated with temperature under nitrate-limited conditions and negatively correlated with temperature under nutrient-replete conditions. The ratio of productivity indices under nitrate-limited and nutrient-replete conditions was positively correlated with temperature and exceeded 1.0 at temperatures of 15 °C or higher. Growth efficiencies were significantly reduced at suboptimal and supraoptimal temperatures and by a transition from nutrient-replete to nitrate-limited conditions, but they were not significantly different under high and low pCO2 conditions. Calcification by this strain of E. huxleyi appeared to be very insensitive to environmental conditions over the range of conditions that we examined.