Isotopic niches of emperor and Adélie penguins in Adélie Land, Antarctica
Résumé
The emperor and Adélie penguins are the only two species of penguins that co-occur at high-Antarctic latitudes. We Wrst measured and compared their isotopic niches on the same year in Adélie Land in spring, when the two species co-exist. Emperor and Adélie penguins segregated by their blood isotopic signatures, with adult 13C values (¡24.5 § 0.2 and ¡25.4 § 0.2‰, respectively) suggesting that emperor penguins foraged in more neritic waters than Adélie penguins in spring. At that time, diVerence in their 15N values (4.1‰, 12.0 § 0.4 vs. 7.9 § 0.1‰) encompassed more than one trophic level, indicating that emperor penguins preyed mainly upon Wsh (and squids), while Adélie penguins fed exclusively on euphausiids. Second, we compared the food of breeding adults and chicks. The isotopic signatures of adults and chicks of emperor penguins were not statistically diVerent, but 15N value of Adélie penguin chicks was higher than that of adults (10.2 § 0.8 vs. 9.0 § 0.2‰). The diVerence showed that adult Adélie penguins captured higher trophic level prey, i.e. higher-quality food, for their chicks. Third, the isotopic signatures of Adélie penguins breeding in Adélie Land showed that adults fed on Antarctic krill in oceanic waters in spring and shifted to neritic waters in summer where they preyed upon ice krill for themselves and upon Wsh and euphausiids for their chicks. A comparison of isotopic niches revealed large overlaps in both blood 13C and 15N values within the community of Antarctic seabirds and pinnipeds. The continuum in 15N values nevertheless encompassed more than one trophic level (5.2‰) from Adélie penguin and crabeater seal to the Weddell seal. Such a broad continuum emphasizes the fact that all Antarctic seabirds and marine mammals feed on varying proportions of a few crustacean (euphausiids) and Wsh (Antarctic silver-Wsh) species that dominate the intermediate trophic levels of the pelagic neritic and oceanic ecosystems.