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

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 midzone 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 midzone 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.

Balancing survival and reproduction: seasonality of wave action, attachment strength and reproductive output in indigenous Perna perna and invasive Mytilus galloprovincialis mussels

“…The major gamete production was more protracted for Perna perna (4 mo) than for Mytilus galloprovincialis (2 mo) and maximum GSI was much greater for the invasive species. It has been shown that M. galloprovincialis has a very high reproductive output (van Erkom Schurink & Griffiths 1991, Harris et al 1998, which, together with fast growth, and the ability to colonise free space very rapidly (Erlandsson et al 2006) could be responsible for allowing it to become the most abundant alien marine species in South Africa (Robinson et al 2005).…”

Changes in an East African social-ecological seagrass system: invertebrate harvesting affecting species composition and local livelihood

“…Also on the east coast of South Africa local people have mainly been harvesting bivalves and gastropods, reducing the intertidal mussel beds there to almost non-existence, with a change in community structure and dramatic declines in biodiversity and ecosystem function (Lasiak 1991;Dye 1992;Lasiak and Field 1995). These mussel beds also have extreme difficulties to recover through natural recruitment, since there are strong adult-recruit relationships and high post-settlement mortality (Erlandsson et al 2006;Erlandsson et al 2008). This is also an example of the classic theory "the tragedy of the commons", which will deplete biological resources and impoverish local people (Hardin 1998).…”

Geographic variation in the trophic ecology of an avian rocky shore predator, the African black oystercatcher, along the southern African coastline

“…The arrival of this invasive species has caused major changes in the structure and functioning of intertidal communities on these rocky shores (Robinson et al 2007). Because of its higher physiological performances, dispersal rates and ability to colonize free space (Branch & Steffani 2004, Erlandsson et al 2006, this invasive species has replaced the indigenous mussels Aulocomya ater and Choromytilus meridionalis as the dominant mussel on the mid and low shores on the west coast (Robinson et al 2007). Moreover M. galloprovincialis outcompetes adult limpets (Scutellastra argenvillei and S. granu laris) for primary space on exposed rocky shores on the west coast (Hockey & van Erkom Schurink 1992, Steffani & Branch 2003.…”