Survey and management of mussel Mytilus species in Scotland

The important ecological role of Mytilus mussels in marine ecosystems, their high abundance in coastal waters and the demand for human consumption has made them a target species for aquaculture. Mussel cultivation is the most important and rapidly growing sector of the Scottish shellfish aquaculture industry and until recently production was considered to be based exclusively on the native species Mytilus edulis. However, the sympatric occurrence of M. edulis, M. trossulus, M. galloprovincialis and their hybrids in cultivation has recently been reported and significant production losses (over 50% at some sites) have been attributed to the presence of fragile-shelled M. trossulus. Given the ecological and economical importance of these species, an urgent need arose for a wider understanding of Mytilus species distribution on Scottish coasts and its implication for the sustainability of the Scottish shellfish industry. Here we present a summary of a 3-year project established within the "ECOsystem approach to SUstainable Management of the Marine Environment and its living Resources" (ECOSUMMER) Marie Curie network to address this need. We developed DNA-based molecular assays for the detection and surveillance of the different Mytilus species in Scotland. Several potential management strategies have been explored, aimed at favouring M. edulis production at mixed-species sites, but these have so far not been found to provide the reliable efficacy necessary for adoption by the industry. Complete eradication of M. trossulus from economically affected areas in Scotland may be unrealistic, especially considering that its introduction and distribution mechanisms in the environment remain uncertain. Area-specific solutions to managing the problem may thus be required, which may or may not involve eradication and fallowing (clearance of mussels from production sites for a given period of time). Nevertheless, the current distribution of M. trossulus is limited and its spread outside its existing range is clearly undesirable. Any management solutions must also be accompanied by an industry wide strategy and awareness, for example, through the development of an industry supported code of good practice.