MUSMOD ©, a production model for bottom culture of the blue mussel, Mytilus edulis L.

Abstract

A mussel production model, MUSMOD © was developed to seed bottom culture lease sites in Maine to their carrying capacity. The process of model development is demonstrated with three models: (a) an initial conceptual model, (b) an aggregated model driven by the tidal exchange of food particles and (c) MUSMOD ©, the final model driven by food supplied in the tidal flow of water across a site. The final model predicts mussel production using the concentrations of phytoplankton and detritus in the surface water, detritus quality, tidal current speed, water depth and temperature. Field measurements of several quantities (e.g., clearance, respiration, growth rates for shell and meat, food concentration gradient, and temporal feeding pattern, (Newell et al., 1997, Development of the mussel aquaculture lease site model, MUSMOD ©: a field program to calibrate model formulations, J. Exp. Mar. Biol. Ecol., this volume) were obtained to evaluate and calibrate the final model. Model refinement using iterations of modeling and field work demonstrated the importance of food quantity and quality in explaining the observed patterns of mussel growth. Food quantity explained the first-order growth pattern, but it was necessary to account for the quality of the food to explain the second-order details of growth. Vertical mixing supplied the majority of new food particles, however, particles settling over the mussel bed during slack water accounted for 33% of the phytoplankton and 45% of the detritus entering the feeding layer from above. A sensitivity analysis of the effects of seed density on mussel growth using MUSMOD © identified the optimum carrying capacity for three Maine lease sites. Seeding mussels during the optimum time period (May to early July) resulted in the harvest of marketable mussels from 40 mm seed in 8 months for a high food year and in 13 months when the food supply was low. Characterizing the food supply using particulate organic matter, POM, alone was not sufficient to explain mussel growth in the detail necessary to answer many farm management questions.