A competition model among mussels (Mytilus galloprovincialis) was developed to predict the environmental impacts of mussels under a coastal floating platform, which is called Mega-Float. The model describes the dynamics of mussels as controlled by competition for space and food availability. The model consists of a physiological growth submodel based on the Dynamic Energy Budget (DEB) model and a competition submodel for space and food. First, the parameter values in the physiological submodel are calibrated by using observations on growth of mussels (Mytilus galloprovincialis) cultivated in the north-west coast of Spain. Then the competition submodel for space and food among mussels is described as a function of the mussel density, and is calibrated by using observations on time variation in the population number of the mussels on the cultivation ropes. The population number of mussels starts with 5,000 individuals per meter and some mussels are shoved to the inner layer of the mussel bank as mussels grow. This undoubtedly leads to food shortage and starvation for them due to their unfavorable position. As a result, some mussels are starved to death and about half of the remaining mussels are inactive in the inner layer of the mussel bank. The competition model can predict well the decrease in the population number of mussels at the cultivation ropes. Finally, the competition model is combined with three-dimensional marine ecosystem model and numerical simulation is conducted to predict the growth of the mussel bank on the under-surface of an imaginary Mega-Float, which is anchored in the head of Tokyo Bay. It was revealed that about two-thirds of mussels are inactive in the inner layer of the mussel bank and do not contribute to food ingestion rate of the mussel bank.

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