Morphology and density of mussels on natural and aquaculture structure habitats: implications for sea duck predators

We compared density and morphology of wild mussels Mytilus trossulus growing naturally on shellfish farming structures to that of mussels from nearby intertidal areas, and considered the relevance to molluscivorous sea ducks. Mussel density on aquaculture structures greatly exceeded that of intertidal areas and farm mussels were larger, had lower shell mass, and had weaker byssal attachments. Differences in environmental conditions and predation regimes throughout the summer growing season were likely responsible for these differences. These morphological and density differences, in turn, have important implications for their primary winter predators, sea ducks, including surf scoters Melanitta perspicillata and Barrow's goldeneyes Bucephala islandica. Higher levels of mussel depletion in farm habitats and strong associations of ducks with shellfish farms indicate that sea ducks responded to this novel, profitable prey resource. Our results support recent research that indicates that artificial structures introduced into coastal areas create novel marine habitats that can support unique communities of epibiota. That sea ducks appear to profit from the introduction of aquaculture structures is evidence of a positive effect of anthropogenic modifications in a coastal environment.