Can Ecosystem Transformations by Non-Indigenous Mussel Introductions Inform Shellfish Reef Restoration?

Shellfish reefs were once common features in temperate coastal waters and estuaries. However, anthropogenic impacts have resulted in significant declines in these ecosystems globally. Whilst a growing body of scientific literature and restoration projects have demonstrated the success of restoration using oysters, at both local and ecosystem-wide scales, restoration initiatives using mussels are relatively new. Due to the lack of long-term data on the ecological impact of restored mussel reefs, information to assist restoration practitioners in identifying potential positive and negative outcomes is limited. However, introductions of mussels have occurred on every continent, and detailed documentation exists on their impacts on local ecosystems. Such information is thus invaluable as these long-term studies can contribute knowledge on predicting ecosystem changes following mussel introductions. Through compiling information derived from 318 published articles, unplanned mussel introductions were found to have both positive and negative impacts, and these were context- and species-specific. In eutrophic water bodies, the impacts were typically considered positive, particularly on shallow-water benthic communities. It was also found, however, that mussels can reduce zooplankton biomass, impact native mussels and were occasionally implicated in increasing cyanobacteria concentrations. Despite these instances, this review presented multiple lines of evidence that mussel introductions, when undertaken intentionally at suitable locations, would have a considerable positive impact at the ecosystem-wide scale.