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Marine Ecology Progress Series

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

Decoupling of calcification and photosynthesis in the coccolithophore Emiliania huxleyi under steady-state light-limited growth

Balch WM, Fritz J, Fernandez E

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

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