Examining the life cycle of coccolithophores

Coccolithophores are abundant marine phytoplankton that are characterized by their ability to form a covering of calcium carbonate plates or coccoliths. Calcification by coccolithophorid algae plays an important role in the global carbon cycle, contributing to the export of carbon from the surface ocean. Despite their importance to global biogeochemical cycles, many aspects of coccolithophore biology remain poorly understood. For example, coccolithophores exist in two distinct life cycle stages (haploid and diploid), but we do not understand the ecological and physiological significance of this.

The two life cycles stages are distinct, as only the diploid stage possess the characteristic heavily calcified heterococcoliths. The haploid stage of some species can also be calcified, but to a much lower extent, producing simple holococcoliths. There is some evidence indicating that haploid and diploid forms of each coccolithophore species are found in distinct marine environments, such as different depths or nutrient regimes. This suggests that the differing life cycle stages may allow coccolithophores to exploit alternative ecological niches. A greater understanding of the differing physiologies of these life cycle stages is required to help us understand their environmental distribution and their ecological role.

This project will examine the physiological differences between coccolithophore life cycle stages, focusing on species such as Coccolithus braarudii and Calcidiscus leptoporus that are abundant in Atlantic Ocean but are currently poorly characterized. In addition to these laboratory studies, the project will also explore the distribution of the life cycle stages in the environment, via examination of samples obtained on research cruises and from the MBA's weekly sampling regime in the Western English Channel (Western Channel Observatory). The final aspect of the research will be to examine in more detail the mechanisms of calcification between life cycle stages to better understand the physiological and ecological roles of the different forms of coccolith. The findings will provide a broader insight into the ecology of coccolithophores and their role in ecosystem function.