Inter- and intraspecific variation of carbon and nitrogen stable isotope ratios in freshwater bivalves

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.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.’’info:eu-repo/semantics/publishedVersio

Temporal changes in the trophic ecology of the asymbiotic gorgonian Leptogorgia virgulata

Gorgonians are widespread sub-littoral benthic suspension feeders in the world oceans. However, data on their trophic ecology and role in benthic–pelagic coupling and biogeochemical cycles remain limited. This study assesses the trophic ecology of Leptogorgia virgulata in the Skidaway River estuary, USA (31.9896N, 81.0242W) by analysing carbon and nitrogen isotopic signatures of its soft tissue and different-sized fractions of particulate organic matter (POM) in its environment. Samples were taken in 5 April, 2 August, and 15 October 2012 and 11 January 2013. Results support a distinct temporal shift in the diet of L. virgulata from the POM fraction <10 µm (i.e. pico- and nanoplankton) to the 10–63-µm fraction (i.e. microplankton). This trophic regime is likely associated with the natural abundance of prey items within these size classes, thus suggesting that L. virgulata may be an opportunistic feeder, and seasonal shifts in food availability in the water column affect its diet. As such small prey items affect the bioenergetics of L. virgulata, it is important to understand the implications of changes in food availability associated with environmental drivers on the physiology and population dynamics of this dominant species in the western Atlantic Ocean