Modeling of integrated marine ecosystem including the generation-tracing type scallop growth model

The new numerical marine ecosystem model has been developed to establish an optimum management plans for sustainable aquaculture in estuaries. This model was applied to Lake Saroma, which is the third largest brackish lake and one of the major sources of aquacultured scallops in Japan. In this study, the pelagic ecosystem model, the benthic ecosystem model and the scallop growth model were integrated comprehensively. This model is remarkable for two features. Firstly, the farming cycle in this area was considered in detail. This was achieved by dividing the aquacultured scallops into three compartments according to their age; each compartment having two state variables, biomass and number of individuals. This feature, called the Generation-tracing type model, made it possible to evaluate weight changes of scallops for each generation. Consequently, simulated results of scallop weights showed good accordance with the measurements. Secondly, the amount of released nutrients from the sediment was evaluated using a vertical diffusive equation with simultaneous mineralization processes in sediment. To evaluate the amount, the interaction between the pelagic and benthic systems, which is generally a very important factor in enclosed water, was modeled. This structure provided the model with an ability to predict future water quality and production of scallops with sediment changes. At the next stage of the study, we applied this model to compare scenarios for future management. Preliminary results showed that a larger number of cultured scallops would result in a smaller average scallop size and worse water quality because of sediment degradation due to the increased deposit of scallop feces.