A three-dimensional coupled biogeochemical-circulation numerical model was implemented in the Adriatic Sea. The biogeochemical part of the model is a development of the European Seas Regional Ecosystem Model (ERSEM II), while the circulation model is the Adriatic Sea implementation of the Princeton Ocean Model (POM). The model was run under climatological monthly varying atmospheric and river runoff forcing in order to reproduce seasonal circulation and biochemical processes. Simulated chlorophyll, nutrient, and plankton biomass and distributions were analyzed and compared with the data coming from a historic in situ data set and a newly constructed chlorophyll climatological data set from SeaWiFS. Model reproduction of the chlorophyll seasonal cycle is, at least qualitatively, in good agreement both with the remote sensing and the in situ data. However, larger production than observed is simulated during the late winter and spring, probably due to inadequate knowledge of the nutrient inputs. Comparison between simulated nutrients and observations shows a general underestimation for orthophosphate and orthosilicate, while nitrate is mostly overestimated. The shape of the nutrient-simulated profiles is in qualitatively good agreement with observations in the central and southern part of the basin. The analysis of the ratio between the large (>20 ¿m) and small (<20 ¿m) phytoplankton biomass and between the bacteria and phytoplankton biomass shows that the Western Adriatic Coastal Current is not only a physical frontal structure but also an ecosystem front, where larger phytoplankton grow on the coastal side while smaller ones are present offshore where the microbial loop is the dominant food web.