Hybrid Mytilus spp. detected in commercial mussel stocks: implications for aquaculture practices and biosecurity

Marine mussels ( Mytilus spp.) are a key species for aquaculture in Europe, accounting for over a third of the 1.1 million tonnes produced annually. However, species within the Mytilus spp. complex readily hybridise when occurring in sympatry. This has potential impacts for aquaculture, as not all species are equally profitable to cultivate, due to lower meat yield and fragile shells leading to a lower-quality product, shorter shelf life and reduced profit margins. This study presents a comprehensive investigation of Mytilus spp. distribution in a region with intensive bottom-grown mussels, and screens both cultivated and wild populations using qPCR and the most widely applied genetic marker Me15/16. Previously, all Mytilus spp. populations in the region were assumed to be the native Mytilus edulis . However, our findings reveal the presence of the Mytilus galloprovincialis genotype, as well as a Mytilus trossulus hybrid, reported here for the first time. These findings have implications for aquaculture practices, including spat harvesting and the transfer of seed from natural beds.