Geographic distribution and molecular identification of a metapopulation of blue mussels (genus Mytilus) in northeastern New Zealand

Abstract

We report here on the abundance and distribution of a metapopulation of smooth-shelled blue mussels (genus Mytilus) from northeastern New Zealand (NZ), in the latitudinal range 37–35°S. Site surveys revealed the presence of blue mussels at 12 of 20 locations on the east coast of the Northland Peninsula, in the Hauraki Gulf and into the Bay of Islands region. Additional material was collected subsequently from three sites, including an estuary location in Auckland, which is the southern-most record of blue mussels in this northern region. This new record of an extensive, but patchily distributed metapopulation in northeastern NZ identifies the existence of a pronounced geographic discontinuity between 37°S and 41°S in the distribution of Mytilus throughout NZ. Based on its geographic isolation, we suggest that the northeastern metapopulation is genetically isolated from other more southerly distributed blue mussels in NZ. Molecular identification of the mussels was carried out by both nuclear and mitochondrial DNA RFLP assays. While the majority of mussels were identified as native Southern hemisphere M. galloprovincialis, a substantial number of individuals with a nonnative (Northern hemisphere) M. galloprovincialis mitotype were also identified. The identification of this new metapopulation composed of both northern and southern lineage M. galloprovincialis has challenging biosecurity and conservation implications. Because of the pronounced geographic break in the distribution of blue mussels in NZ it may be possible to minimize further spread of the northern lineage mitotype to the rest of the country using an internal borders containment approach. However, based on introductions of (Northern hemisphere) M. galloprovincialis elsewhere in the world, we believe that the most likely outcome in NZ of this bioincursion is extensive interbreeding and introgression between the northern and southern lineages of M. galloprovincialis.