| Summary: | The Antarctic Sea is the largest protected biodiversity hotspot area in the world and plays an important role in the Southern Ocean ecosystem. The structure and dynamics of the Ross Sea ice coverage have a fundamental role in production processes. During the Antarctic Winter, temperature decreases, and the sea ice coverage increases. The later phenomenon limits the availability of food resources for the entire community. With the onset of the Antarctic Summer, the sea ice extension and thickness decrease, resulting in an increase of trophic resources availability (phytoplankton, diatoms, cryptophytes, and krill), supporting large populations of upper-trophic levels. The Emperor (Aptenodytes forsteri) and Adélie (Pygoscelis adeliae) Penguins are two meso-predators, which represent key species in the Antarctic food web. The objectives of this thesis are to determine how the spatial and temporal changes of the sea ice coverage in Ross Sea coastline affect the trophic ecology of penguin species during a year and to compare these changes over two consecutive breeding and moulting periods. The results of the Carbon and Nitrogen stable isotopes analysis show that fish are the most important component of the Emperor Penguin both in Winter and Summer diets. Krill, instead, represent the dominant food resource for the Adélie Penguin in Summer. In Summer 2016-17 I found that Adèlie colonies at highest latitude, foraged more on krill than on fish. Emperor penguins fish consumption in the pre-moulting period decrease significantly from 2016-17 to the following year. The 2016 year, with the lowest atmospheric pressure, highest wind speed, and temperature over the past thirty years had the lowest ice expansion. Based on these conditions, adult krill abundance, which had dependence life cycle on the ice expansion, decreased in 2016 Summer. This decrease in krill availability determined a shift from krill-based diet towards fish-based diet during the Adèlie pre-breeding (Summer), and pre-moulting (Winter) seasons.
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