ENVISION aims at examining for the first time the dynamics of B-vitamins and their role in microbial plankton dynamics at adequate spatial and temporal scales in a highly productive region. We followed a multidisciplinary approach including correlation analysis based on physical, chemical and biological field observations micro- and mesocosm experiments and more sophisticated molecular tools such as metatranscriptomic and microautoradiographic analyses to reach the following objectives: (1) To describe the spatial and temporal variability of dissolved B-vitamins (B1, B2, B6, B7, and B12) concentrations in relation to the phytoplankton and bacterioplankton community composition in coastal waters off NW Spain (2) To assess the spatial and temporal variability of the response of phytoplankton and bacterioplankton to the experimental amendment of mineral nutrients, vitamin B1 and B12 (separately and in combination) in coastal waters off NW Spain (3) To study the influence of short-term variability in B-vitamins availability on the succession of microbial plankton species (4) To identify the bacterial groups responsible for B-vitamins synthesis in coastal waters off NW Spain and (5) To determine the role of bacteria as consumers of B1 and B12 vitamins.