MEPS 320:169-176 (2006)  -  doi:10.3354/meps320169

Re-colonisation rate differs between co-existing indigenous and invasive intertidal mussels following major disturbance

Johan Erlandsson1,2, Purba Pal1,3, Christopher D. McQuaid1,*

1Department of Zoology and Entomology, Rhodes University, Grahamstown 6140, South Africa
2Present address: Department of Systems Ecology, University of Stockholm, 10691 Stockholm, Sweden
3Present address: Department of Invertebrate Zoology, Swedish Museum of Natural History, Box 50007, 10405 Stockholm, Sweden
*Corresponding author. Email:

ABSTRACT: The potential of introduced species to become invasive is often linked to their ability to colonise disturbed habitats rapidly. We studied the effects of major disturbance by severe storms on the indigenous mussel Perna perna and the invasive mussel Mytilus galloprovincialis in sympatric intertidal populations on the south coast of South Africa. At the study sites, these species dominate different shore levels and co-exist in the mid mussel zone. We tested the hypotheses that in the mid-zone P. perna would suffer less dislodgment than M. galloprovincialis, because of its greater tenacity, while M. galloprovincialis would respond with a higher re-colonisation rate. We estimated the percent cover of the 2 mussels in the mid-zone from photographs, once before severe storms and 3 times afterwards. M. galloprovincialis showed faster re-colonisation and 3 times more cover than P. perna 1 and 1.5 yr after the storms (when populations had recovered). Storm-driven dislodgment in the mid-zone was highest for the species that initially dominated at each site, conforming to the concept of compensatory mortality. This resulted in similar cover of the 2 species immediately after the storms. Thus, the storm wave forces exceeded the tenacity even of P. perna, while the higher recruitment rate of M. galloprovincialis can explain its greater colonisation ability. We predict that, because of its weaker attachment strength, M. galloprovincialis will be largely excluded from open coast sites where wave action is generally stronger, but that its greater capacity for exploitation competition through re-colonisation will allow it to outcompete P. perna in more sheltered areas (especially in bays) that are periodically disturbed by storms.

KEY WORDS: Invasive species · Spatial co-existence · Exploitation competition · Mytilus · Perna · Recovery · Disturbance

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