Lipid Biomarker Diversity in the Coccolithophoridemiliania Huxleyi(prymnesiophyceae) and the Related Speciesgephyrocapsa Oceanica1

Twenty‐four strains ofEmiliania huxleyiand two strains ofGephyrocapsa oceanicawere grown at 15°C under identical culture conditions to assess genetic variability in key lipid biomarker profiles (C37‐C39alkenones, C36and C37alkyl alkenoates, and C31‐C38alkenes). Under our culture conditions, little divergence an biomarker composition was detected betweenE. huxleyistrains from different oceanic regions or betweenE. huxleyiandG. oceanicaeven though the strains originated from biogeographical regions as diverse as the subpolar North Atlantic and subtropical Western Pacific. The major differences observed were in tetraunsaturated alkenone abundance and alkene profiles, which tended to separate neritic from open ocean strains. Different strains from the same locality were as different as strains originating from widely separated ocean basins, indicating extreme genotypic diversity within a population. Replicate cultures of the same strain showed significant variability in their biomarker profiles even though the culture temperature varied by only ±0.3°C, indicating that their synthesis ratios are influenced by environmental and/or physiological variable(s), as yet unidentified, in addition to temperature. Strong covariance in C37and C38methyl alkenone unsaturation ratios (Uk37and Uk38Mρrespectively) and, in coastal strains, C33, alkene and alkenone unsaturation ratios indicates that these compounds are biochemically linked.