Human CO2 emissions are critically poisoning the earth's climate. However, sedimentation by marine primary producers contributes greatly to carbon sequestration, with coccolithophores, unicellular marine algae with cell envelopes composed of CaCO3, being the key contributors. Nevertheless, the extent of the biogeochemical impact of coccolithophores is largely unknown. They have a dual life cycle and can grow as both haploids and diploids, but past research has focused mainly on the diploid phase. Moreover, knowledge of coccolithophores is almost exclusively limited to a single species that is distributed worldwide, and can form blooms visible from space. However, this species is peculiar in many biological aspects and does not calcify in the haploid phase, therefore we need to develop more model organisms to represent impact of coccolithophores on the carbon cycle. In this action, my objective is to understand how the physiological acclimations of the coccolithophore life cycle phases allow them to inhabit different ecological niches. I will implement a multidisciplinary approach to investigate two levels of complexity: how environmental factors influence physiology and which genes contribute to distinct genetic programs. To this end, I will work on a widespread coccolithophore species that calcifies at both life cycle phases. I will characterize for the first time how photosynthesis (light-driven CO2 fixation) and photoprotection (dissipation of excess energy) differ between the two phases, and determine which environmental conditions trigger ploidy transitions. To investigate the underlying genetic factors, I will then sequence the genome and, in both phases, the transcriptome. Overall, the ambition of the Cocco-Next project is to provide important insights into the interplay between life cycles, ecological niches, and biological CO2 sequestration and beyond, create novel, interconnected and open datasets that will be invaluable to the oceanographic community.