PCR BASED DETECTION OF MTDNA HAPLOTYPES OF NATIVE AND INVADING MUSSELS ON THE NORTHEASTERN PACIFIC COAST - LATITUDINAL PATTERN OF INVASION

Frequencies of mitochondrial haplotypes characteristic of native Mytil us trossulus and introduced M. galloprovincialis were determined in po pulations along the west coast of North America from San Diego, Califo rnia, to the Aleutian Islands, Alaska. We also identified the haplotyp es of mussels cultured from larvae arriving in Coos Bay, Oregon, durin g 1988 - 1990 from sites in Japan in the seawater ballast of ocean-goi ng ships. All mussels from ballast-water samples were M. galloprovinci alis. We found that sampled populations north of San Francisco Bay, in cluding Coos Bay, were entirely composed of mussels with the M. trossu lus haplotype, while haplotypes of both species were present in all si tes in and south of San Francisco Bay. The presence of M. trossulus in southern sites is contrary to evidence from allozyme studies, and we suggest that mtDNA introgression from M. trossulus to M. galloprovinci alis may explain this discordance. This study demonstrates that, despi te continued transport and release, M. galloprovincialis has not becom e established in northern sites. Failure to invade the north coast of North America may reflect environmental unsuitability for M. galloprov incialis. However, invasion success may be probabilistic, and the cont inuing release of M. galloprovincialis larvae may foreshadow a future successful invasion.