Two morphotypes of Emiliania huxleyi (Lohmann 1902) Hay et al. 1967, types A and B, known to be unequally distributed in the oceans, were grown in dilution cultures at a range of photon flux densities (PFDs) (1.5–155 μmol photons·m−2·s−1) and two temperatures (10° and 15° C). Calcite carbon and organic carbon content of the cells as well as instantaneous growth rate, cell size, chlorophyll fluorescence, and light‐scatter properties clearly depended on growth conditions and differed considerably for the two morphotypes. The ratio between calcite carbon and organic carbon production showed an optimum of 0.65 in E. huxleyi type A cells at PFD = 17.5. The ratio increased slightly with a temperature increase from 10° to 15°C but remained < 1.0 at both temperatures in light‐limited cells. In contrast, calcite carbon production exceeded organic carbon production (ratio: 1.4–2.2) in phosphate‐deprived cultures. Emiliania huxleyi type B generally showed a higher calcite carbon/organic carbon ratio than E. huxleyi type A, but the relation with PFD was similar.
The content of calcite carbon and organic carbon as well as the instantaneous growth rate, cell size, chlorophyll fluorescence, and light‐scatter properties showed large diel variations that were closely related to the division cycle. Our results show the importance of mapping the structure of any sampled cell population with respect to the phase in the cell division cycle, as this largely determines the outcome of not only “per cell” measurements but also short time (less than 24 h) flux measurements. For instance, dark production of calcite by E. huxleyi was negatively affected by cell division. Slowly growing (phosphate‐stressed) cultures produced calcite in the light and in the dark. In contrast, rapidly growing cultures at 10°C produced calcite only in the light, whereas in the dark there was a significant loss of calcite due to dissolution.
Culture strains of Emiliania huxleyi (Lohmann 1902) Hay et al. 1967 were placed into two groups designated E. huxleyi type A and type B on the basis of coccolith morphology and immunological properties of the coccolith polysaccharide. We studied the distribution of these types in the North Atlantic region using an indirect immunofluorescence assay with antisera directed against the coccolith polysaccharide of E. huxleyi type A and type B and epifluorescence microscopy. In field samples taken in the Northeast Atlantic Ocean, E. huxleyi type A was found exclusively. In contrast, type B was dominant in the North Sea. Scanning electron microscopy of the samples revealed the same unequal distribution of the two types as found with the immunofluorescent‐labelling assay.
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