Invasion of an indigenous Perna perna mussel bed on the south coast of South Africa by an alien mussel Mytilus galloprovincialis and its effect on the associated fauna.

Abstract  The introduced mussel Mytilus galloprovincialis is progressively increasing in abundance along the south coast of South Africa. Quantitative 0.1 m2 samples were collected in the mid-zone of an indigenous Perna perna mussel bed in the 1980s prior to the arrival M. galloprovincialis (12) and in the 2000s during the M. galloprovincialis invasion (16). In addition, in situ counts of M. galloprovincialis were done on eight occasions between 1993 and 2005, and in the low- and high-zones on four occasions. In the mid-zone M. galloprovincialis was absent until 1987, its mean densities were low (2) between 1993 and 1996, but thereafter increased steadily, peaking in 2004 (at 721 individuals/0.1 m2), before declining in 2005 (331 individuals/0.1 m2). The greatest densities of M. galloprovincialis were recorded at the high-zone (1121 individuals/0.1 m2) and the smallest in the low-zone. As M. galloprovincialis numbers increased, there was an associated, but smaller decline in P. perna numbers and the overall density of mussels increased significantly (P P. perna. The density of associated fauna differed significantly (P Chthamalus dentatus appeared to be the only associated faunal species that was directly affected by the M. galloprovincialis invasion, experiencing a significantly (P ≤ 0.05), but temporary decline in density and biomass values. [ABSTRACT FROM AUTHOR]