In the ocean, the availability of N is one of the most influential factors controlling primary productivity. Biological N₂ fixation, i.e., the reduction of atmospheric N₂ gas to biologically available ammonium (NH₄⁺), constitutes the major source of new N for the surface ocean (140 ± 50Tg N yr^-1), significantly larger than riverine and atmospheric inputs. By maintaining a pool of bioavailable N, this process sustains oceanic productivity over broad timescales and space scales. However, a critical question that has been poorly studied is the transfer and fate of diazotroph-derived N (DDN) in the pelagic food webs. The actual flux of DDN that supports the growth of different groups of autotrophic and/or heterotrophic plankton and can be transferred up the trophic chain, remineralized and/or exported from the euphotic zone is unknown. To answer these questions, a triplicate mesocosm (55 000L) experiment was conducted in the southwest Pacific (New Caledonia; 22°29.073 S, 166°26.905 E) in January–February 2013 within the framework of the ANR–INSU–IRD–GOPS-funded VAHINE project. This study, which involved 25 scientists from 7 institutes, yielded a comprehensive data set on community-level responses to a diazotroph bloom and its impact on community changes, biogeochemical cycles and export.