LOW CONTEXT INDEPENDENT IMPACT OF CRASSOSTREA GIGAS ON INTERTIDAL ASSEMBLAGE STRUCTURE AND BIODIVERSITY REVEALED IN INVADED COMMUNITIES ACROSS EUROPE
Nadescha Zwerschke1, Philip R. Hollyman1, Romy Wild1, Robin Strigner1, John R. Turner1, Jonathan W. King2
1School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey, LL59 5AB, UK
2Centre for Applied Marine Sciences, Bangor University, Menai Bridge, Anglesey, LL59 5AB, UK
e-mail: nzwerschke01@qub.ac.uk
Accelerating spread of invasive species is associated with loss of diversity and alteration of ecosystem services. Impacts of invasive species, however, are context dependent and intrinsically linked to the ecosystem they occur within. In order to broaden the understanding of the impact of a globally widespread invasive oyster, Crassostrea gigas, intertidal surveys were carried out at 15 different sites in Ireland, the UK and France.
The impact of C. gigas on macro- and epifaunal benthic communities and α and β diversity was assessed and compared to those associated with the native flat oyster Ostrea edulis, if present on the shore. Whilst abundance of C. gigas altered benthic community structures, epifaunal communities associated with O. edulis and C. gigas did not differ and changes in benthic assemblage structure were therefore attributed to the presence of oyster shells. α diversity of macrofaunal assemblages increased with oyster cover in muddy habitats, and α diversity of epifaunal assemblages only decreased at great densities of C. gigas. The presence of C. gigas did not cause homogenisation of species assemblages between affected shores. This study assessed the impact of C. gigas over different habitat types and environmental conditions, and enabled more context independent predictions of the impact of C. gigas on native communities, which were found to be low to negligible. Furthermore, C. gigas may be able to replace the ecosystem functions of the declining native oyster in terms of biodiversity facilitation. We encourage a reconsideration of the ecological status of C. gigas within north-west Europe.