BASICS will identify the most important prokaryotic organisms associated with the carbon and sulphur cycling biogeochemical function of the sea through the development of single-cell analysis techniques applied to pelagic microbes. We will first describe bacterial richness diversity in the coasts of different European seas, describe their role in the biogeochernical cycling of carbon and nitrogen, and develop, fine-tune and tests several single-cell analysis methods that will allow as to identify key bacterial organisms in the function of the marine ecosystem. We will profit from that knowledge to model and study how resilient the link is between the bacterial diversity and the bacterially mediated ecosystem biogeochemical functioning, in the face of the most important global environmental changes expected in European coastal waters.