Context- and density-dependent effects of introduced oysters on biodiversity
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Pacific oysters, Crassostrea gigas, have been introduced throughout much of the world, become invasive in many locations and can alter native assemblage structure, biodiversity and the distribution and abundance of other species. It is not known, however, to what extent their effects on biodiversity change as their cover increases, and how these effects may differ depending on the environmental context. Experimental plots with increasing cover of oysters were established within two estuaries in two different habitats commonly inhabited by C. gigas, (mussel-beds and mud-flats) and were sampled after 4 and 15 months. Within mud-flat habitats, macroscopic species living on or in the substratum increased in richness, Shannon–Wiener diversity and number of individuals with oyster cover. In mussel-bed habitats, however, these indices were unaffected by the cover of oysters except at one estuary after 15 months when species richness was significantly lower in plots with the greatest cover of oysters. Assemblage structure differed with oyster cover in mud-flats but not in mussel-beds, except at 100 % cover in one location and at one time. Within mud-flats at one location and time (of four total tests), assemblages became more homogenous with increasing cover of oysters leading to a significant decrease in β-diversity. These responses were primarily underpinned by the facilitation of several taxa including a grazing gastropod (Littorina littorea), an invasive barnacle (Austrominius modestus) and a primary producer (Fucus vesiculosus) with increasing cover of oysters. Although there were consistent positive effects of C. gigas on mud-flat biodiversity, effects were weak or negative at higher cover on mussel-beds. This highlights the need for the impacts of invasive species to be investigated at a range of invader abundances within different environmental contexts.
KeywordsInvasive species Biodiversity Ecosystem engineer Environmental context Density-dependent Crassostrea gigas
This research was funded by the project SIMBIOSYS (2007-B-CD-1-S1) as part of the Science, Technology, Research and Innovation for the Environment (STRIVE) Programme, financed by the Irish Government under the National Development Plan 2007–2013, administered on behalf of the Department of the Environment, Heritage and Local Government by the Irish Environmental Protection Agency (EPA). We would also like to thank Bas Boots, the editor Jennifer Ruesink and two anonymous reviewers for helpful comments that helped to improve this manuscript.
- Anderson MJ (2001) A new method for non-parametric multivariate analysis of variance. Austral Ecol 26:32–46Google Scholar
- Anderson MJ, Crist TO, Chase JM, Vellend M, Inouye BD, Freestone AL, Sanders NJ, Cornell HV, Comita LS, Davies KF, Harrison SP, Kraft NJB, Stegen JC, Swenson NG (2011) Navigating the multiple meanings of beta diversity: a roadmap for the practicing ecologist. Ecol Lett 14:19–28PubMedCrossRefGoogle Scholar
- Escapa M, Isacch JP, Daleo P, Alberti J, Iribarne O, Borges M, Dos Santos EP, Gagliardini DA, Lasta M (2004) The distribution and ecological effects of the introduced Pacific oyster Crassostrea gigas (Thunberg, 1793) in northern Patagonia. J Shellfish Res 23:765–772Google Scholar
- Green DS, Rocha C, Crowe TP (2013) Effects of non-indigenous oysters on ecosystem processes vary with abundance and context. Ecosystems doi: 10.1007/s10021-013-9659-y
- Groffman P, Baron J, Blett T, Gold A, Goodman I, Gunderson L, Levinson B, Palmer M, Paerl H, Peterson G, Poff N, Rejeski D, Reynolds J, Turner M, Weathers K, Wiens J (2006) Ecological thresholds: the key to successful environmental management or an important concept with no practical application? Ecosystems 9:1–13Google Scholar
- Hosack G (2003) Effects of Zostera marina and Crassostrea gigas culture on the intertidal communities of Willapa. Bay, Washington. M.Sc. Thesis, University of WashingtonGoogle Scholar
- Little C, Morritt D, Stirling P (1992) Changes in the shore fauna and flora of Lough Hyne. Ir Nat J 24:87–95Google Scholar
- Olden JD, Kennard MJ, Pusey BJ (2008) Species invasions and the changing biogeography of Australian freshwater fishes. Glob Ecol Biogeogr 17:25–37Google Scholar
- Parker IM, Simberloff D, Lonsdale WM, Goodell K, Wonham M, Kareiva PM, Williamson MH, Von Holle B, Moyle PB, Byers JE, Goldwasser L (1999) Impact: toward a framework for understanding the ecological effects of invaders. Biol Invasions 1:3–19Google Scholar
- Underwood AJ (1997) Experiments in ecology: their logical design and interpretation using analysis of variance. Cambridge University Press, Cambridge UKGoogle Scholar