Mussels belonging to the Mytilus edulis species complex have been the focus of numerous studies exploring the systematics and origin of this commercially and ecologically important genus. Species have wide geographical ranges and hybridise where their distributions overlap, making identification difficult. Several molecular markers have been used to distinguish between the species within the M. edulis species complex; however, no single marker system has been found to be completely diagnostic, and a combination of markers are used. Here, we used a combination of three nuclear genes and a mitochondrial gene region to assess the species composition of Mytilus mussels collected across its geographical range in Australia. Our results show that the majority (98.5%) of individuals sampled from Australian populations are Mytilus galloprovincialis, with 56.2% of them displaying a southern hemisphere haplotype, 10.3% displaying a putatively northern hemisphere haplotype, and 32% having M. galloprovincialis genotypes consistent with either northern or southern hemisphere M. galloprovincialis lineages. The taxonomic origin of the remaining 1.5% of samples (n = 3) could not be conclusively determined. Our results suggest that there have been significant introductions of non-native M. galloprovincialis lineages into both southern and northern hemisphere populations.

Australian blue mussels (Mytilus spp.) are an increasingly important sustainable product of the Australian aquaculture industry. Although important for commercial fisheries, aquaculture may have adverse environmental and ecological impacts. This study assessed the impact of standard hatchery-imposed selection practices on the genetic diversity of farmed blue mussels. Using microsatellite markers, relatedness and genetic structure analyses showed that hatchery-reared larvae have high levels of genetic diversity without a significant decline as they move through the hatchery rearing process. Selection and/or genetic drift does appear to be operating during the hatchery rearing process, however, evidenced by an increase in relatedness among larvae over time. Significant shifts in allele frequency as well as genetic clusters provides further evidence that selection is acting on larvae due to the selection practice applied at the hatchery. Comparison of the level of genetic diversity and genetic differentiation of adults from wild and farmed populations provided no evidence that farmed mussels have lower diversity, or that they are genetically swamping local natural populations. The data suggest that careful design and implementation of mussel breeding programs can maintain high genetic diversity among larvae that does not lead to genetic swamping of natural mussel populations in the surrounding area.