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

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°59S, 02°35W) and Robertskollen (71°28S, 03°15W) 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 ¹³C value of –23.9±0.7 (range: –24.7 to –22.9; n=9) and a mean ¹⁵N 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 ¹³C 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 ¹³C 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 ¹³C values in their body tissues than animals foraging farther out over the open ocean. However, the high ¹³C of snow petrel collagen is possibly more likely to be related to the correspondingly high ¹⁵N values found in this tissue, and hence caused by snow petrels including offal from high trophic level Antarctic mammals and birds in their diet.