Stable isotope ratios of Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) bone collagen

Abstract

This study investigated the trophic hierarchy status of the Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) within the Southern Ocean food-web off Dronning Maud Land, Antarctica. During 1991/92 ten Antarctic petrel and ten snow petrel carcasses were collected from Jekselen (71°59′S, 02°35′W) and Robertskollen (71°28′S, 03°15′W) respectively, in the northern Ahlmannryggen, Dronning Maud Land. Collagen from the dense bone of the humeri of these carcasses was extracted and the stable carbon and nitrogen isotope ratios of these samples determined. The snow petrel bone collagen samples displayed a mean δ13C value of −23.9±0.7 (range: −24.7 to −22.9; n=9) and a mean δ15N value of 15.2±1.6 (range: 12.9 to 18.4; n=10). The corresponding values for Antarctic petrel bone collagen were −24.8±1.0 (range: −26.2 to −22.8; n=9) and 13.2±0.6 (range: 12.5 to 13.9; n=8) respectively. The difference between the species’ δ13C values may indicate differences in their foraging habitat. It has previously been suggested that the snow petrel has a higher wing loading than other Procellariiforme species, making the snow petrel less adapted to pelagic foraging than related species and more likely to forage close to the sea ice edge. Algae growing under sea ice apparently can have comparatively high δ13C values, possibly due to growing under carbon dioxide limited conditions. If so, animals foraging close to the sea ice edge might be expected to show higher δ13C values in their body tissues than animals foraging farther out over the open ocean. However, the high δ13C of snow petrel collagen is possibly more likely to be related to the correspondingly high δ15N values found in this tissue, and hence caused by snow petrels including offal from high trophic level Antarctic mammals and birds in their diet.