title: Isotopic investigation of contemporary and historic changes in penguin trophic niches and carrying capacity of the southern Indian ocean.
abstract: A temperature-defined regime shift occurred in the 1970s in the southern Indian Ocean, with simultaneous severe decreases in many predator populations. We tested a possible biological link between the regime shift and predator declines by measuring historic and contemporary feather isotopic signatures of seven penguin species with contrasted foraging strategies and inhabiting a large latitudinal range. We first showed that contemporary penguin isotopic variations and chlorophyll a concentration were positively correlated, suggesting the usefulness of predator δ¹³C values to track temporal changes in the ecosystem carrying capacity and its associated coupling to consumers. Having controlled for the Suess effect and for increase CO₂ in seawater, δ¹³C values of Antarctic penguins and of king penguins did not change over time, while δ¹³C of other subantarctic and subtropical species were lower in the 1970s. The data therefore suggest a decrease in ecosystem carrying capacity of the southern Indian Ocean during the temperature regime-shift in subtropical and subantarctic waters but not in the vicinity of the Polar Front and in southward high-Antarctic waters. The resulting lower secondary productivity could be the main driving force explaining the decline of subtropical and subantarctic (but not Antarctic) penguins that occurred in the 1970s. Feather δ¹⁵N values did not show a consistent temporal trend among species, suggesting no major change in penguins' diet. This study highlights the usefulness of developing long-term tissue sampling and data bases on isotopic signature of key marine organisms to track potential changes in their isotopic niches and in the carrying capacity of the environment.
authors.affiliation: Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, Villiers-en-Bois, France. audrey.jaeger@gmail.com
authors.forename: Audrey
authors.initials: A
authors.lastname: Jaeger
authors.forename: Yves
authors.initials: Y
authors.lastname: Cherel
mesh_terms: D025041:Animal Migration / Q000502:physiology; D000818:Animals; D000864:Antarctic Regions; D003247:Conservation of Natural Resources; D017753:Ecosystem; D005241:Feathers / Q000737:chemistry / Q000378:metabolism; D049673:History, 20th Century; D049674:History, 21st Century; D019156:Indian Ocean; D007553:Isotope Labeling / Q000379:methods; D009587:Nitrogen Isotopes / Q000493:pharmacokinetics; D011157:Population Dynamics / Q000266:history; D046429:Spheniscidae / Q000378:metabolism / Q000502:physiology; D013696:Temperature; D013997:Time Factors
chemical_list: D009587:Nitrogen Isotopes