Decline of a native mussel masked by sibling species invasion

The European blue mussel (Mytilus galloprovincialis) has extensively invade d southern California, whereas a native species, M. trossulus, is abundant in northern California and further north. In this study, a portion of the 1 6S ribosomal RNA gene was sequenced from mussels collected in southern and central California in the nineteenth century. I aligned these sequences wit h 22 sequences representing modern M. galloprovincialis, M. edulis, and M. trossulus. Phylogenetic analysis using parsimony identified the nineteenth- century mussels as M. trossulus. Because mussel populations have been conti nuously present in this region since the time these mussels were collected, these data indicate that M. trossulus were present during the initial inva sion of M. galloprovincialis, but, due to the morphological similarity of t he two species, declined without notice.