Stable isotope ratios of Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) bone collagen |
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Authors: | W. K. Steele |
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Affiliation: | (1) Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Private Bag, Rondebosch 7700, South Africa;(2) Present address: Rivers & Drainage Group, Melbourne Water, PO Box 4342, Melbourne, Victoria 3001, Australia |
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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 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. |
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