Trophic ecology of fur seals and sea lions from northern Patagonia and their food webs through time

VALES, DAMIÁN GUSTAVO; NEWSOME, SETH DARNABY; CARDONA, LUIS; BORELLA, FLORENCIA; POLITIS, GUSTAVO; BAYÓN, CRISTINA; ALDAZÁBAL, VERÓNICA; FRONTINI, ROMINA

Viña del Mar

Conferencia; 11th ISOECOL, International Conference on Applications of Stable Isotope Techniques to Ecological Studies; 2018

Universidad Andrés Bello

High trophic level predators can integrate the biogeochemical characteristics of their habitat through diet, thus serving as ecosystem indicators. Here, we used carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone collagen from ancient and modern South American fur seals (Arctocephalus australis) and sea lions (Otaria flavescens) as proxies of potential changes in a regional marine food web through time. Modern samples come from individuals stranded in northern Patagonia during the period 1990-2007, whereas ancient samples come from coastal archaeological sites from southern Buenos Aires (~7000 14C YBP) and northern Patagonia (3500?800 14C YBP). Bulk bone collagen isotope analysis shows that fur seals and sea lions displayed a steady resource partitioning through time with some overlap in δ13C vs δ15N space over the three periods under study. In agreement with previous work, fur seals had lower δ13C and δ15N values in comparison with sea lions, indicating that fur seals largely forage on pelagic resources, whereas sea lions primarily consume benthic prey. Mean δ13C and δ15N values of fur seals remained stable over time. In contrast, sea lions had lower δ13C values ~7000 years ago than in subsequent periods, suggesting a more pelagic diet. Despite this shift, sea lions showed little overlap with the isotopic niche of Middle Holocene fur seals. Nevertheless, potential temporal shifts in the isotopic baseline of pelagic and coastal (benthic) food webs prevent us from robustly assessing changes in pinniped resource and habitat use. Currently, δ13C and δ15N analysis of individual amino acids (AAs) are in progress, and we anticipate this approach will provide us with data on how baseline (essential AAs) δ13C and (source AAs) δ15N values have changed over time in this ecosystem. In addition, offsets between source and trophic amino acid δ15N values will provide a measure of pinniped trophic level and potential changes in food chain length in response to the development of industrial whaling, sealing, and fishing activities in this region over the past three centuries.