A flow field is paid less attention as important factors in an ecological model although it is considered that the detailed circulation for ecosystem is important. Therefore, this study examined the effect of a detailed flow field for a model accuracy of water quality in an ecological model. It is found that it is important to reproduce or predict the detailed flow field by using non-hydrostatic model.
　As a water quality index, Chlorophyll-a was used in the inner Tokyo Bay. First, the characteristics of water quality in Tokyo Bay were determined by the observation results. It reveals that there is a great 0dependency among nutrient, Chlorophyll-a and salinity. It is confirmed that the importance of exact modelling of the detailed flow field to determine the salinity distribution in detail.
　To propose a simple ecological model, the characteristics of diatom, dinoflagelate and zooplankton were investigated. Comparisons between hydrostatic and non-hydrostatic flow model characteristics were carried out to get a good reproduction of salinity transfer mechanisms.
　As a result, it is found that the hydrostatic model gives a wider distributed area of Chlorophyll-a than the area predicted by the non-hydrostatic model because of the difference of the salinity diffusion around the fresh-water front induced by a river plume. It reflects on the model accuracy for a repreduction of a Chlorophyll-a distribution.