Feeding ecology of chinstrap penguins Pygoscelis antarctica at Livingston Island (Antarctic)

摘要

Antarctic and Southern Ocean marine ecosystems have been changing for the past 30 years, along with the global climate change. The most evident changes are on the Western Antarctic Peninsula, which is warming four times faster than the average rate of Earth‘s overall warming. Within the Antarctic Peninsula region, one of the penguin species used to monitor Southern Ocean food web changes is the chinstrap penguin (Pygoscelis antarctica). The main objective of this study is to assess the feeding ecology of chinstrap penguins in Livingston Island. This is done by comparing the diets from adult chinstrap penguins (through fecal samples; scats) and chicks (through stomach contents from naturally died chicks). To complement these analyses, different tissues (i.e. feathers, blood, flesh and nails) were collected from adult penguins and dead chicks and used for stable isotope analyses of 15N and 13C. Also a snapshot of the marine food web around Livingston Island is provided, in order to assess chinstrap penguin trophic level in comparison with other organisms through the stable isotopic analyses of typical, key organisms found in Livingston Island (i.e. algae, krill, seabirds, seals). Crustaceans, specifically Antarctic krill comprised the diet 100% by frequency of occurrence, by mass and by number of both adults and chicks chinstrap penguins. This confirmed that Antarctic krill dominates the diet of chinstrap penguins at least during the breeding period. The mean size of collected Antarctic krill was 38.66 ± 2.56 mm for adults and 39.87 ± 2.69 mm for chicks. Different tissues reflect different time scales of stable isotope incorporation. For adults, feathers were more enriched in stable isotope ratios of nitrogen and carbon than blood, and reflect the diet form the previous year after the breeding season, while blood reflects the most recent diet. High significant differences were found between these two tissues, indicating different feeding habits during breeding and non-breeding periods. In the case of chicks of chinstrap penguins there were two metabolically inactive tissues – feathers and nails, and metabolically active flesh. The chicks were 2-3 weeks old when they died, thus for this short period the sampled tissues should accumulate isotopes at the same rates. However, no correlation was found between these tissues, and high significant differences for δ15N were recorded between feathers and all other tissues, which confirm that different tissues accumulate the same isotopes at different ratios. Regarding the δ13C values significant differences between active and inactive tissues (flesh and nails; flesh and feathers) refer to different foraging habitats during incubation and during chick-growing period. Also, it was possible to compare stable isotope ratios of feathers between adult and chicks. Chick feathers indirectly reflect mother‘s diet, while adult feathers reflect the period after the previous breeding season. Expectedly, differences in carbon values indicate changed feeding habitat in summer and in winter, while nitrogen comparison shows that they remain foraging at the same trophic level. Analyses of δ15N and δ13C of other organisms revealed three main groups in the marine food web of Livingston Island - higher order predators such as elephant seal, brown skua, kelp gull and southern giant petrel were at the top of the food chain, while penguins had increased levels of nitrogen and carbon isotope signatures compared to their prey – Antarctic krill. The food chain length for Livingston Island marine food web calculated is 4.7, and it is inside the range calculated for other marine pelagic ecosystems across the planet. This study is particularly relevant for monitoring programs under CCAMLR. It showed that it is possible to contribute to the future monitoring of chinstrap penguin diets in alternative ways (i.e. not invasive for penguins). In general this kind of study can contribute to the conservation of this species through protecting their food resources and feeding habitats and in understanding their future population processes.