Coccolithophores are an important group of unicellular calcifying algae that impact ocean biogeochemistry and global climate. Importantly, they display complex sexual haplodiplontic life cycles comprising diploid and haploid phases that can multiply independently by mitosis and that are markedly distinct in terms of morphology and eco-physiological properties. Life cycle transitions in coccolithophore are poorly understood, but may act as a stress response system to environmental variations and promote the growth of the better adapted life phase. Thus, in order to expand our understanding of the ecological role of coccolithophores and the triggers for life cycle transitions we survey the seasonal dynamics of different life phases across species in relation to environmental physicochemical parameters in the Northern Red Sea, Eastern Mediterranean Sea, and the Gulf of Naples.

See our recent publications on the topic:

• Keuter, S., et al (2022). Deep-Sea Research 1. https://doi.org/10.1016/j.dsr.2022.103919

• Keuter, S., et al. (2022). Marine Micropaleontology. https://doi.org/10.1016/j.marmicro.2022.102153

• Keuter, S., et al. (2021). Journal of Micropaleontology. https://doi.org/10.5194/jm-40-75-2021

• Keuter, S., et al. (2019). Marine Micropaleontology. https://doi.org/10.1016/j.marmicro.2019.03.007.

• Frada, M.J., et al. (2019). Perspectives in Phycology. doi: 10.1127/pip/2018/0083.

The cosmopolitan coccolithophore Emiliania huxleyi is responsible for the formation of dense blooms (>10,000 cells per mL) that annually cover thousands of square kilometers in the oceans during spring. High cell densities during blooms promote high contact rates with specific large lytic coccolithoviruses (E. huxleyi virus, EhV) leading to the decay of E. huxleyi populations. Little is however known about this host-virus dynamic interplay at low densities. In order to understand the impact of EhV during non-blooms scenarios we explore the E. huxleyi-EhV dynamic interplay in dilute oligotrophic systems in the Northern Red Sea and Eastern Mediterranean Sea, and during pre and post-bloom seasons in the English Chanel*.

Emiliania huxleyi blooms appear to be largely dominated by diploid (2N) calcifying cells that are sensitive to specific lytic viruses (EhV) that drive the termination of blooms. During its life cycle E. huxleyi can form non-calcified biflagellate haploid (1N) cells and non-calcified biflagellate 2N cells, both of which appear to be insensitive to EhV (Frada et al. 2017). Interestingly, biflagellate-2N cells can be formed during infections, which enables a few 2N cells to escape EhV. We are both interested to assess the extent of cellular and physiological differences between the 3 life phases, the mechanism prompting life phase transition, and the mechanisms of viral resistance of flagellate cells. As a first step, we are performing a comparative transcriptome analyses of the 3 life phases, which will unveil the underlying basis for the cellular and physiological complexity of this important marine phytoplankter.