Relationship between coccolith length and thickness in the coccolithophore species Emiliania huxleyi and Gephyrocapsa oceanica

by Simen Alexander Linge Johnsen, Jörg Bollmann, Christina Gebuehr, Jens O. Herrle

Coccolith mass is an important parameter for estimating coccolithophore contribution to carbonate sedimentation, organic carbon ballasting and coccolithophore calcification. Single coccolith mass is often estimated based on the k_s model, which assumes that length and thickness increase proportionally. To evaluate this assumption, this study compared coccolith length, thickness, and mass of seven Emiliania huxleyi strains and one Gephyrocapsa oceanica strain grown in 25, 34, and 44 salinity artificial seawater. While coccolith length increased with salinity in four E. huxleyi strains, thickness did not increase significantly with salinity in three of these strains. Only G. oceanica showed a consistent increase in length with salinity that was accompanied by an increase in thickness. Coccolith length and thickness was also not correlated in 14 of 24 individual experiments, and in the experiments in which there was a positive relationship r² was low (<0.4). Because thickness did not increase with length in E. huxleyi, the increase in mass was less than expected from the k_s model, and thus, mass can not be accurately estimated from coccolith length alone.