Can stable isotope (δ13C and δ15N) measurements of little auk (Alle alle) adults and chicks be used to track changes in high-Arctic marine foodwebs?
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The little auk (Alle alle), a small and abundant planktivorous seabird that breeds in the high Arctic, has the potential to be used as a monitor of the composition and abundance of lower trophic-level zooplankton. We investigated age- and sex-related sources of variation in diet and stable isotope (δ13C and δ15N) values of little auks breeding in Spitsbergen during the summer of 2002 to evaluate this possibility. Stable isotope profiles of both adult and chick blood changed over the breeding season, with blood δ15N values increasing and δ13C values decreasing. This could represent a switch to higher trophic-level prey derived from more pelagic sources. However, while chick blood δ13C values followed those values in their meals, this was not the case for blood δ15N values, suggesting additional physiological mechanisms influencing blood δ15N values in growing chicks. Chicks had consistently lower δ15N values than their parents, which may indicate they were being fed on lower trophic-level prey items or may alternatively reflect complexities in chick blood δ15N values through the growth period. These results have several important implications for use of stable isotope analysis as a tool to detect changes in seabird diet and availability of lower trophic-level prey in high-Arctic marine environments. Until physiological aspects of stable isotope discrimination are well understood, we caution against using chicks of this seabird as any form of isotopic monitor.
KeywordsPrey Item Stable Isotope Analysis Late Incubation Chick Diet Tufted Puffin
We thank Magda Owczarek for her long hours helping with fieldwork; the captains and crews of the vessels Lance, Oceania and Norbjørn for transport; Jan Marcin Węsławski and Lech Stempniewicz for advice, support and collaboration; and John Piatt for his support throughout. Special thanks to Tomasz Moczadłowski (Polish Polar Station) for logistical help, and we are grateful to Lucjan Nowosielski (Station leader) and all our friends at the Polish Polar Station for hospitality and support. Blanca Mora Alvarez assisted with preparation of samples for stable isotope measurements. M. Stocki conducted analyses at the Department of Soil Sciences, University of Saskatchewan. Many thanks to three anonymous referees for their thoughtful reviews. This study was funded by the Institute of Geophysics (Polish Academy of Sciences), the Atlantic Seabird Group, the Gino Watkins Memorial Fund, the Augustine Courtauld Trust, and Alaska Pacific University, and was supported by USGS-Alaska Science Center. All birds were handled under the permission of the Norwegian Animal Research Authority and the Governor of Svalbard.
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