Isotopic values of Antarctic Krill in relation to foraging habitat of penguins

Abstract

Antarctic Krill Euphausia superba is a key component of the Antarctic coastal marine ecosystem. Investigations into stable isotopic values of krill in predation hotspots are important in facilitating our understanding of the feeding environments of krill in a local coastal ecosystem. In this study we investigated stable isotopic values and maturity and size composition of krill at a small spatial scale, by logging GPS tracks of five Chinstrap Pygoscelis antarcticus and seven Gentoo P. papua penguins, and analyzing their stomach contents. The study was conducted at a penguin colony on Barton Peninsula, King George Island, Antarctica. The main food item of both species was Antarctic Krill (>98% wet mass). One Chinstrap and four Gentoo penguin foraging trips were classified as "on-shelf" trips, and four Chinstrap and three Gentoo Penguin foraging trips were classified as "off-shelf" trips. Krill collected from off-shelf trips had higher δ15N (4.22±0.28‰) values than those from on-shelf trips (3.78±0.29‰). The δ13C of the krill samples did not differ between the two penguin species or between trip types. The proportion of juvenile krill taken was higher for Chinstrap (13.04±4.97%) than Gentoo penguins (3.33±2.43%). Our results suggest that the main food source of the krill in our sample originated as non benthic planktonic/suspended organic matter, and that krill in off-shelf habitat may occasionally consume higher trophic level prey compared to those in on-shelf habitats.