Optical processes have been incorporated into an ecosystem model for the equatorial Pacific region. The bio-optical model is able to reproduce many measured optical properties and key biogeochemical processes in the region. In order to achieve such good agreement between data and model results, however, key model parameters, for which no field measurements are available, have to be constrained. Coupling explicit optics to ecosystem models provides advantages in generating: (1) a more accurate subsurface light-field, which is important for light regulation on biogeochemical processes, (2) additional constraints on model parameters that help to reduce uncertainties in ecosystem model simulations, and (3) model results which are comparable to basic remotely-sensed properties. Sensitivity analysis of the model results to optical parameters reveals a significant role played by colored dissolved organic matter through its influence on the quantity and quality of the ambient light. In addition, the coupling of biogeochemical models and optics paves the road for future assimilation of ocean color and in-situ measured optical properties into the models.