The main objective of the project is to construct and validate a tractable and reliable 3D biogeochemical model of the Black Sea's basin ecosystem coupled with a benthic model and a hydrodynamical model at mesoscale in order to understand the mesoscale ecodynamics in connection with the spatial and temporal variability of the hydrodynamics and, in particular to assess and predict the response of the ecosystem to changing environmental pressures . In a first step, an ecosystem model containing the required complexity to accurately represent the Black Sea' s ecological processes will be developed. Its conceptualization will be based on a sound understanding of the Black Sea's ecosystem gained from the inspection of data bases and previous modeling studies. This model will be coupled with a biogeochemical benthic model and with a 3D large scale hydrodynamical model. Once validated, the complex ecosystem model will be simplified by aggregating some of its state variables in order to derive a tractable but reliable reduced ecosystem model. An objective method based on the computation of the energy fluxes between the different trophic levels will be used to select the aggregation scheme which simulates best the dynamics of the complex model . Then, the aggregated ecosystem model will be coupled with a hydrodynamical model at mesoscale . The performance of the coupled model will be assessed by comparing model predictions with ocean color images and field observations.