Variable production of transparent exopolymeric particles by haploid and diploid life stages of coccolithophores grown under different CO2 concentrations

The production of transparent exopolymeric particles (TEP) by the coccolithophores, Emiliania huxleyi, Calcidiscus leptoporus and Syracosphaera pulchra was investigated in batch cultures. The abundance, size spectra and carbon content of TEP were examined during the exponential growth phase of both haploid and diploid life stages grown under ambient (400 µatm) and elevated (760 µatm) CO2 partial pressure (pCO2) conditions. Results showed species- and life stage-specific differences in TEP production rate (day−1) derived from abundance and carbon content of TEP. At 400 µatm, TEP production rate was the highest in the diploid stage of S. pulchra and E. huxleyi, while TEP carbon content per cell was the highest in the diploid stage of C. leptoporus. At 760 µatm, TEP production rate increased in almost all species and was closely related to the cell growth rates (except in the diploid stage of C. leptoporus), while the slope values δ of the regression lines between TEP size distribution and concentration decreased. This means that the contribution of smaller size TEP was relatively more important than larger TEP in the high pCO2 treatment. Elevated pCO2 is potentially able to alter TEP size distribution. TEP-C content cell−1 generally decreased with increasing pCO2. TEP-C accounted for 1–24% of the cell particulate organic carbon production and was inversely related to increasing pCO2. TEP production by C. leptoporus and S. pulchra has not previously been documented. The amount of organic carbon released as TEP by these coccolithophores is comparable to and may even exceed TEP production by some diatoms.