Measurement of DIC acquisition and evidence for a CO2 concentrating mechanism in Gephyrocapsa oceanica (Isochrysidales, Coccolithophyceae)

ABSTRACT The possession of a carbon concentrating mechanism (CCM) by a given phytoplankton species will in part determine its response to changes in the dissolved inorganic carbon concentrations in the global ocean. Earlier work on CCMs in the coccolithophore Emiliania huxleyi suggested that this species did not possess a CCM, though more recent studies indicate that a CCM is indeed present. Here we report work showing that another coccolithophore species, Gephyrocapsa oceanica, also possesses a functioning CCM, implying that increasing CO2 concentrations are unlikely to lead to enhanced growth rates. We discuss the protocol required for working with this species, noting that due to its liths being 10 or more times as massive as of those of Emiliania huxleyi, much lower centrifugation speeds (<400 × g) must be used to avoid damage to the cells.