MEPS 142:87-97 (1996)  -  doi:10.3354/meps142087

Carbon fixation of Emiliania huxleyi was studied in light-limited, steady-state, continuous cultures. Six growth rates were examined ranging from 0.24 to 1.0 d^-1 although the lowest may have been carbon-limited. Cell-specific and chlorophyll-specific rates of photosynthesis and calcification increased as a function of growth rate. The ratio of calcification to photosynthesis (C/P) increased from about 0.2 to 0.7 as the growth rate increased (from 0.24 to 0.75 d^-1), then the C/P ratio decreased slightly as the growth rate approached washout at 1 d^-1. Extrapolation of the regression data at low growth rates suggested that there should be zero calcification at a growth rate of about 0.1 d^-1. Cells were also given a 30 s acidification/neutralization treatment to dissolve their coccoliths, and then carbon fixation was measured. Photosynthesis and calcification at all growth rates increased by about 0.1 pg C cell^-1 h^-1 following this treatment. Carbon fixation per unit chlorophyll a was predicted by multiplying the total carbon:chlorophyll a ratio by the respective culture dilution rate. These predictions were almost identical to ¹⁴C measurements of carbon fixation per unit chlorophyll. Nevertheless, if only total carbon incorporation data are available for a coccolithophore population, accurate predictions of just photosynthesis or calcification will require the function (presented in this paper) which relates the C/P ratio to growth rate. This function suggests a decoupling of photosynthesis from calcification as growth becomes progressively more light-limited.

Coccolithophores · Calcification · Photosynthesis · Coccoliths · Growth rate