This training proposal is aimed at acquiring competences in methods used to investigate the relationship between marine microbes and the environment in which they live. Sampling at sea using research vessels will be part of the training. In addition, the student will learn how to use a flow cytometer to count and estimate optical properties of picoplankton, unicellular organisms driving the functioning of the ocean. These microorganisms, which include bacteria and eukaryotic algae, are the base of the trophic food web and indicators of trophic state of any marine ecosystem. We investigate their diversity, also using molecular methods (sequencing), they abundance and their adaptation to changing ecological conditions. The student will also learn how to plot the data and to represent them graphically, elaborating statistical tests in order to support the conclusions drawn from the observations.