In the framework of the Italian project CO2 Monitor, two culture experiments were carried out in vertical closed photobioreactors with Pleurochrysis cf. pseudoroscoffensis Gayral & Fresnel 1983, a coccolithophore isolated from the Gulf of Trieste (North Adriatic Sea).The aim of this study was to investigate the effects induced by pH variations due to CO2 emissions on its growth and morphology.Two experiments were carried out with two different CO2 concentrations (1 and 2%) relatively to the total volume of insufflated air. Growth and cell size in light microscopy, morphology and coccolith size in scanning electron microscopy, particulate nitrogen (PN) and particulate inorganic and organic carbon (PIC and POC) content of the coccolithophore were investigated during the light and dark phases. Dissolved inorganic nutrient (nitrate and phosphate) concentrations and pH of the medium and the presence of heterotrophic prokaryotes (HP) were monitored as well.

Slight changes in morphology of coccoliths resulted from analysis of scanning electron micrographs. Coccoliths particularly showed thinner inner tubes and a lower number of nodes compared to the control in the experiment with 1% CO2.