Predicting the carrying capacity of bivalve shellfish culture using a steady, linear food web model

An investigation into the potential carrying capacity of suspended bivalve culture was undertaken using a linear food web model. The investigation involved configuring the model for the present state using all available information, and then perturbing the food web by introducing the bivalve culture until pre-determined carrying capacity limits were achieved. These carrying capacity trigger levels were defined by the production carrying capacity and the ecological carrying capacity. The production carrying capacity represents the theoretical maximum bivalve culture that could be supported in the embayment. This is defined as when the ecosystem collapses down to a nutrient-phytoplankton-culture-detritus dominated system. This level of culture was found to be a yield of bivalve culture of 310 t km−2 year−1 averaged across the bays in question. By contrast, the ecological carrying capacity was defined as the level of culture that could be introduced without significantly changing the major energy fluxes or structure of the food web. This limit was found to correspond to a bivalve culture yield of 65 t km−2 year−1 averaged across the bays. Introducing the large-scale bivalve culture resulted in a decrease in the mean trophic level of the ecosystem, an increase in the total yield, throughput and efficiency, and the bivalves replaced zooplankton as the major grazers in the modelled system.