Modelling the environmental Impacts of suspended Mussel (Mytilus edulis L.) farming.

The potential impacts of marine aquaculture operations on the environment arereviewed. The reported effects of suspended mussel farms on the benthicenvironment are examined and the potential impacts discussed. A framework toassess the impacts of suspended mussel farms is presented.The use of simulation models to predict the impact of fish farm wastes on the benthicenvironment is discussed and the mathematical theory supporting such models ispresented. The applicability of these models to mussel farming is discussed and thedata required to undertake such modelling identified.The effect of increased sedimentation on the macrobenthic community, physicalstructure and biogeochemistry of the surficial sediment around three suspendedmussel farms are examined. At one site, the benthic community was subjected to bulksedimentation, organic enrichment and reduced macrobenthic infaunal diversity.Elevated levels of organic carbon were recorded close to the farm. At the remainingtwo sites, benthic impacts were less clear and not demonstrably due to the musselfarms.The settling velocity of mussel faeces and pseudofaeces was required to enablemodelling of particles ejected from the farm sites. An experiment was devised tomeasure this parameter.- The settling velocity of mussel faeces (~0.5 cms-I) was lessthan pseudofaeces (~1 cms-I). Differences in these settling velocities were attributedto the organic content and particle size of the excreted matter.The particle tracking model DEPOMOD (Cromey et at., 2000a) was used as aplatform from which to develop a simulation model predicting the benthic impact ofsuspended mussel farms. Parameters within the model were modified to be representa mussel farming scenario. Data from the three sites surveyed were applied to themodel. Although the model results compared favourably with the field data, themodel tended to overestimate the benthic impact as measured by the Infaunal TrophicIndex.The results of the model are discussed and improvements and further experiments areidentified