MEPS 370:171-183 (2008)  -  DOI: https://doi.org/10.3354/meps07626

ABSTRACT: The Mediterranean mussel Mytilus galloprovincialis is the most widespread marine alien species along the South African coast. Long-term monitoring of the mid-to-low intertidal zone in the Groen-Spoeg area on the west coast between 1988 and 1993 tracked the establishment and expansion of this aggressive invader along a gradient of wave action. Additionally, the effects of M. galloprovincialis on other dominant species were quantified. The rate of increase and abundance of M. galloprovincialis was promoted by exposure to strong wave action. The tube-building polychaete Gunnarea capensis remained the dominant space occupier on sheltered shores but its density was negatively correlated with the M. galloprovincialis expansion on semi-exposed and exposed shores. In contrast, the indigenous mussel Aulacomya ater demonstrated no significant changes in density over time as it simply became incorporated into the spreading M. galloprovincialis beds. Overall abundance of the grazing limpet Scutellastra granularis was positively affected by the M. galloprovincialis invasion, although adults and recruits occupying primary space showed a negative correlation with M. galloprovincialis abundance, the strength of which increased with wave exposure. Conversely, adults and recruits occurring on secondary space were positively affected by M. galloprovincialis beds, which enhanced settlement. Again the strength of the interaction increased with wave action. Patterns observed in the field therefore indicated that abundance of M. galloprovincialis and its effects on other elements of the fauna were linked with the intensity of wave action.

KEY WORDS: Mytilus galloprovincialis · Invasive species · Wave action