Abstract: The Kerguelen Islands (40°S, 70°E) contain freshwater ecosystems among the most isolated from
human activities in the world. The aim of this work was to study the bio-ecological factors influencing
levels of chemical bioaccumulation in Kergueln salmonids tissue (brown trout, Salmo trutta and brook
trout, Salvelinus fontinalis) and their potential toxic effects. Our work demonstrated that the hepatic
and muscular Cu and Cd levels, and also, the muscular PCB levels were hight and similar to those of
salmonids from impacted areas. Moreover, differences in contamination according to species, season
and morphotype (lake, river and base) were noted. Histological analysis of trouts livers showed clear
damage of liver (fibrosis, infiltration of immune cells, development centers mélanomacrophagiques)
and of hepatocytes (necrosis, nuclear alteration) in all studied fish traducing an important level of
stress consistently with the high concentration of toxicant in this organ. On the other hand, antioxidant
defenses biomarkers revealed differences between the studied morphotypes. Moreover, analysis of
serum lysozyme activity showed that these salmonids were characterized by reduced immune
competences. Kerguelen Islands constitute a workshop site for ecotoxicological studies. The long-term
monitoring should improve the knowledge of changes in eco-physiological responses of freshwater
fish populations dealing with the global chemical pressure.

Abstract: The lithosphere of Antarctica reacts to both the stress variations due to the dynamics of the mantle and the variation of the glacial load due to changes in climate. These two factors act on the dynamics of the glacial mass, on the evolution of the continent's topography and on the plate seismicity. This means that the knowledge of spatial variations in lithospheric thickness is needed to comprehend of the processes that involve interactions between climate and the geosphere. The main aim of this work is to produce a tomographic model of the continent. The classic data source for tomographic studies is a set of seismic signals produced by earthquakes. In this work I use a different technique: information is extracted by correlating the ambient seismic noise recorded in different locations. Instead of a the classic cross-correlation, this work uses the phase cross correlation technique, which appears to be more robust in our use case. Signal phases are used even to improve the correlogram stacks, by weighting the stack samples according to the correlograms' coherence. In Antarctica, the 30s Rayleigh wave group velocity map shows lower velocities in East Antarctica, and higher velocities in West Antarctica, coherently with expectations related to a thicker cratonic crust in the East, and thinner extending crust in the West. Deeper sensitivity of longer periods make the color pattern switch for the 80s map, sensing the upper mantle and consequently higher velocity at the cold roots of cratonic East Antarctica and lower velocity in the tectonically active West. I also contributed to the maintenance and development of the seismic observational infrastructure in Antarctica. This thesis recaps the activities I carried out during my participation to the 31st campaign of the Italian National Antarctic Research Program, to which I participated during the PhD course.

Abstract: Global warming is now hardly a disputable matter. The rapid changes in climate are unequivocal and foreseen to continue drastically within the next centuries, profoundly affecting the biological component of our planet. As the 6th mass extinction crisis is looming,
it is becoming urgently necessary to increase our understanding of ecosystems and their responses to climate change. This is especially true for the poorly known yet important marine ecosystems. Covering most of the Earth’s surface, oceans are indeed key actors in climate regulation, and the responses of their ecosystems to climate change have been insufficiently studied. In particular, due to its geographical location at high latitudes which makes it strongly prone to the effects of climate, and due to its connectivity with all the other major oceans of the Earth, understanding how climate change might affect the remote Southern Ocean is a scientific priority. In this thesis, we investigated the effects of climate on Southern Ocean ecosystems through the monitoring of their emblematic top predators: the penguins. As top-predators, penguins are considered good indicators of their environment as they integrate the effects of climate which occur at every level of the food chain. The present work relied on data collected over several years on three penguin species (little penguins, king penguins and Adélie penguins) using automatic monitoring systems based on Radio-Frequency- IDentification, that we suggest to be a relatively harm-free method for monitoring individual penguins over the long-term. We found juvenile survival in king penguins to be higher than previously thought and close to adult survival rate. Surprisingly, it increased in years of high sea surface temperature (SST), indicating contrasted effects of climate on king penguins depending on the life-history trait considered. SST has also been shown to possibly bias the sex ratio of king penguin fledglings, which may affect in return the population dynamics. The study of different species enabled us to highlight the importance of the time-scale at which the effect of climate is investigated and the necessity of adapting it to the species biology. For instance, in little penguins chick mortality was concentrated on some weeks, underlining the dependence of reproductive success on punctual conditions, probably due to the low reserves accumulated by the chicks. Finally, we also show the importance of taking into account individual heterogeneity and quality, leading to consistent differences in parental effort in little penguins and in the ability to face different sea-ice conditions in Adélie penguins. Such inter-individual differences along with the flexibility exhibited in some behaviour (such as foraging in little penguins) may help penguins to adapt to new environmental pressures through phenotypic plasticity, though the rapidity and strength of climate change under these latitudes leave little hope for these long-lived animals.

Abstract: Life history theory predicts that long-lived species should firstly favour their survival at young ages since their chances to engage in future reproductive attempts is high, and then progressively favour their reproduction when growing old. This theory has received much support from experimental and field data as reproductive success often increases with age until the individual reaches senescence. One explanation of age-dependent reproductive performance could be the improvement in foraging efficiency with age and acquisition of experience. We examined age and experience effects on foraging behaviour in a long-lived seabird, the king penguin (Aptenodytes patagonicus).
We highlighted that, with increasing age and experience, king penguin in Crozet Archipelago conduct strategies that aim at reducing the foraging effort, such as diving optimization or age-specific choice of prey. The extra foraging effort of first breeders had an impact on their breeding success. Nevertheless, we found no differences in hunting efficiency according to age and/or experience. Our results suggest that foraging efficiency of breeders could be more linked to physiological processes, such as cellular ageing, than to age or experience.