TESTING THE EFFECTS OF ELEVATED PCO2 ON COCCOLITHOPHORES (PRYMNESIOPHYCEAE): COMPARISON BETWEEN HAPLOID AND DIPLOID LIFE STAGES1

The response of Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler, Calcidiscus leptoporus (G. Murray et V. H. Blackman) J. Schiller, and Syracosphaera pulchra Lohmann to elevated partial pressure of carbon dioxide (pCO₂) was investigated in batch cultures. We reported on the response of both haploid and diploid life stages of these three species. Growth rate, cell size, particulate inorganic carbon (PIC), and particulate organic carbon (POC) of both life stages were measured at two different pCO₂ (400 and 760 parts per million ppm]), and their organic and inorganic carbon production were calculated. The two life stages within the same species generally exhibited a similar response to elevated pCO₂, the response of the haploid stage being often more pronounced than that of the diploid stage. The growth rate was consistently higher at elevated pCO₂, but the response of other processes varied among species. Calcification rate of C. leptoporus and of S. pulchra did not change at elevated pCO₂, whereas it increased in E. huxleyi. POC production and cell size of both life stages of S. pulchra and of the haploid stage of E. huxleyi markedly decreased at elevated pCO₂. It remained unaltered in the diploid stage of E. huxleyi and C. leptoporus and increased in the haploid stage of the latter. The PIC:POC ratio increased in E. huxleyi and was constant in C. leptoporus and S. pulchra. Elevated pCO₂ has a significant effect on these three coccolithophore species, the haploid stage being more sensitive. This effect must be taken into account when predicting the fate of coccolithophores in the future ocean.