Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

Background Sooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management. Methodology/Principal Findings Tracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters. Conclusions/Significance The shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem

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