The use of models is essential for the MSFD as a tool that can support monitoring activities, the setup of indicators and make scenarios for reaching the ecological goals in MSFD. However, models are never better than the data for their calibration. In this respect, it is 14 essential to calibrate and validate the models to rate measurements and not just standing stocks. In Danish waters the primary production is the only rate measured regularly. We have therefore optimized the biogeochemical ERGOM model for primary production using the thousands of primary production measurements available for the Kattegat/Belt Sea area and experimental data. ERGOM was also modified to be valid for both the North Sea – Baltic Sea by adding silicate, modifying zooplankton grazing impact and adjusting light parameterizations and is one of the few models that are validated for both areas. ERGOM is coupled to the 3d circulation model HBM (Hiromb-BOOS model) with a fine two-way nested grid in the Kattegat to Arkona Basin.