Facilitative effects of introduced Pacific oysters on native macroalgae are limited by a secondary invader,the seaweed Sargassum muticum |
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| Authors: | Anne C Lang Christian Buschbaum |
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| Institution: | 1. Department of Environmental Science and Policy, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA;2. Coastal and Marine Institute Laboratory and Department of Biology, San Diego State University, San Diego, CA 92182, USA;3. Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark;4. Nordic Center for Earth Evolution, University of Southern Denmark, 5230 Odense M, Denmark;5. Scottish Association for Marine Science, Oban PA37 1QA, UK;6. Arctic Research Centre, University of Aarhus, 8000 Aarhus C, Denmark;1. ISPRA, Italian National Institute for Environmental Protection and Research, Laboratory of Milazzo, via dei Mille 44, 98057 Milazzo (ME), Italy;2. Dept. of Ecology, University of Palermo, Via delle Scienze, Ed. 16, I-90128 Palermo, Italy;3. Consorzio Plemmirio, Via Gaetano Abela, 2, 96100, Siracusa, Italy;4. ISPRA, Italian National Institute for Environmental Protection and Research, c/o Residence Marbela, via Salvatore Puglisi 9, 90143 Palermo, Italy;1. School of Biology and Environmental Science, Science Centre West, University College Dublin, Belfield, Dublin 4, Ireland;2. Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft für Naturforschung (SGN), Goethe-University (GU), Senckenberganlage 25, 60325 Frankfurt am Main, Germany;1. Laboratorio de Biología Marina, Dpto. Zoología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41012 Sevilla, Spain;2. IFAPA-Agua del Pino, Carretera Punta Umbría — Cartaya, s/n. Cartaya, Spain;3. IFAPA-El Toruño, Camino Tiro Pichón s/n. El Puerto de Santa María, Cádiz, Spain;1. Departamento de Ecología y Biología Animal, Facultad de Ciencias del Mar, Universidad de Vigo, Campus Universitario Lagoas-Marcosende, 36310 Vigo, Pontevedra, Spain;2. Departamento de Biología (Zoología), Facultad de Ciencias, Universidad Autónoma de Madrid, C/ Darwin 2, 28049 Cantoblanco, Madrid, Spain |
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| Abstract: | Introduced habitat-providing organisms such as epibenthic bivalves may facilitate the invasion and expansion of further non-native species which may modify the effects of the primary invader on the native system. In the sedimentary intertidal Wadden Sea (south-eastern North Sea) introduced Pacific oysters (Crassostrea gigas) have overgrown native blue mussel beds (Mytilus edulis). These oyster beds are now providing the major attachment substratum for macroalgae. Recently, oysters have expanded their distribution into the shallow subtidal zone of the Wadden Sea, and there support a rich associated species community including the Japanese seaweed Sargassum muticum, which has been presumably introduced together with the oysters. With a block designed field experiment, we explored the effects of S. muticum on the associated community of soft-bottom C. gigas beds in the shallow subtidal. Replicated oyster plots of 1 m2 were arranged with a density of 0, 7, 15 or 45 S. muticum m? 2, respectively. We found no effects of different S. muticum densities on associated epi- and endobenthic community compositions associated to the oyster plots. However, the overall coverage of sessile organisms settling on the oyster shells was significantly reduced at high S. muticum densities. The occurrence of abundant native macro-algal species such as Polysiphonia nigrescens, Antithamnion plumula and Elachista fucicola decreased with increasing S. muticum densities. Sessile invertebrates, by contrast, were only marginally affected and we found no effects of S. muticum canopy on diversity and abundance of endofauna organisms. We conclude that increasing densities of S. muticum on C. gigas beds in the shallow subtidal zone of the Wadden Sea limit the occurrence of native macroalgae which otherwise would benefit from the additional hard substratum provided by the oysters. Thus, a secondary invader may abolish the effects of the primary invader for native species by occupying the new formed niche. |
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