During the last fifteen years in the northern Adriatic, changes in hydrological regime and exchange of water masses were noticed, as well as an increased frequency of mucilage events. This phenomenon is related to the organic carbon cycle, being favoured when expressed horizontal and vertical gradients occur. Such gradients develop in the frontal zones in the late spring/summer period due to a combination of main frontal forcings: eastward transport of freshened waters formed in the Po delta area and intrusions of high salinity oligotrophic waters from the central Adriatic. The main goal of the project is to investigate the structures and physiology of the microbial communities as well as their connection to the hydrodynamic structure of the frontal zone. It is also presumed that acute structural and physiological changes of the microbial communities are the main cause for the changes of the organic matter flow direction, and therefore key triggers of unusual events. Therefore the research is divided in four topics: a) hydrodynamic structure of the frontal zone; b) structure, biomass and physiological state of the phytoplankton community; c) structure of the active bacterial community; and d) definition and flow within microbial food loop. This research is expected to explain the flow and distribution of the organic matter in the frontal zone by an integration of physical and biological processes as well as to confirm the key role of the frontal zones in the northern Adriatic ecosystem functioning and resilience. Frontal processes can enhance biological production or trigger unusual events, thus greatly influencing biological diversity of the area, feeding, reproductive strategy and migratory patterns for necton, retention for larvae of benthic organisms and establishment of benthic invertebrate communities.