Aquaculture and the spread of introduced mussel genes in British Columbia

Abstract

Aquaculture can promote the introduction of non-indigenous species (NIS) into wild marine environments. In addition, NIS aquaculture escapees may hybridize with closely-related native species introducing foreign alleles to their gene pool. To quantify the influence of mussel aquaculture on the native community in British Columbia we sampled mussels from fourteen locations on Vancouver Island. There are two native species in this region, M. trossulus and M. californianus, and two farmed NIS, Mytilus edulis and M. galloprovincialis, both originally from Europe. DNA was extracted from mussel tissue and the mitochondrial cytochrome c oxydase subunit 1 (COI) gene was sequenced. One nuclear locus that exhibits different alleles for M. edulis, M. galloprovincialis and M. trossulus (Glu-5′) was also characterized, using PCR, in order to identify heterozygotes. We found the proportion of NIS introgression depended primarily on farm density. Other habitat traits such as the degree of exposure to the open sea and, to a minor extent, salinity, contributed significantly to explain the distribution of introgressed individuals. Different habitat preference of NIS and native species, and marine currents, provide additional explanations for the distribution of alien and native species along Vancouver Island coasts. As a whole, our results suggest that native M. trossulus populations are more introgressed by M. galloprovincialis genes in open habitats.