Decline of a Native Mussel Masked by Sibling Species Invasion

Abstract: The European blue mussel (  Mytilus galloprovincialis ) has extensively invaded southern California, whereas a native species, M. trossulus , is abundant in northern California and further north. In this study, a portion of the 16S ribosomal RNA gene was sequenced from mussels collected in southern and central California in the nineteenth century. I aligned these sequences with 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 continuously present in this region since the time these mussels were collected, these data indicate that M. trossulus were present during the initial invasion of M. galloprovincialis , but, due to the morphological similarity of the two species, declined without notice.