Inter- and intraspecific variation of carbon and nitrogen stable isotope ratios in freshwater bivalves
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Freshwater bivalves provide important ecosystem functions and services, yet many of their ecological traits such as feeding mechanisms and resource use are largely ignored. In this study, we aimed to evaluate the potential overlap in resource use by bivalve species living in sympatry in European freshwater ecosystems. This was accomplished by analyzing the stable isotope ratios of carbon (C) and nitrogen (N) values of six bivalve species (five native species plus the invasive species Corbicula fluminea) in six distinct aquatic ecosystems. Results showed significant inter- and intraspecific differences in both stable isotope ratios. The interspecific variability suggests differences in the food sources consumed, which can be related to differences in feeding behavior. At the intraspecific level, there was a gradient in the stable isotope ratios from the oligotrophic River Paiva (15N-depleted and 13C-enriched) to the eutrophic Mira Lagoon (15N-enriched and 13C-depleted), suggesting a change in the resources used from benthic to pelagic food sources, respectively, and/or differences in the stable isotopic baseline in each ecosystem. Thus, flexible feeding strategies combined with size selectivity may decrease the possible competition for food sources by native and invasive species living in sympatry.
KeywordsBivalves Corbicula fluminea Freshwater ecosystems Invasive and native species Stable isotopes
A. Novais was supported by a Ph.D. Grant (SFRH/BD/86463/2012) from the Portuguese Foundation for Science and Technology—FCT through POPH/FSE funds. This study was conducted in the scope of the project ECO-IAS: ecosystem-level impacts of an invasive alien species, funded by FCT and COMPETE funds (contract: PTDC/AAC-AMB/116685/2010). This study was also partially supported by the European Regional Development Fund (ERDF) through the COMPETE, under the project “PEst-C/MAR/LA0015/2011.” Special thanks are addressed to Francisco Carvalho and Ângela Amorim for help in collecting the organisms in the field, to Sofia Gonçalves for assistance in the stable isotope analyses, to Joel C. Hoffman, Beat Oertli, and two anonymous referees for valuable suggestions on an earlier version of the manuscript.
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