[en] Trace elements are among the most common contaminants in the marine ecosystem. Beyond critical thresholds, all trace elements present a potential danger that can lead to disturbances at the cellular and individual level, but also at the population or ecosystem level. In the Mediterranean Sea, Corsica Island has long been considered an area of low anthropic pressure. Due to its ecological characteristics, its high tolerance to contaminants and its ability to bioaccumulate trace elements, the sea urchin Paracentrotus lividus (Lamarck, 1816) is recognized as a bioindicator. The aim of this thesis was to better understand the variations of trace element contamination in Corsica and their effects on an emblematic organism, Paracentrotus lividus. An assessment of the contamination of classical and emerging trace elements was conducted on sea urchin gonads. In this context, several samples were collected in order to determine the main trace elements susceptible to be bioaccumulated by the adult sea urchin and the spatio-temporal variations of these contaminants. This research has highlighted areas in Corsica with higher trace element concentrations due to geochemical backgrounds associated with anthropogenic pressures. Seasonal variations were also identified with lower concentrations during the summer season. These variations are mainly due to the reproduction cycle of the sea urchin and show the importance of biotic factors in the evaluation of contamination levels. Biochemical analyses of adult sea urchins suggest that the oxidative stress induced by the measured contaminations has no direct impact on their health. Bioassays performed on larval stages of sea urchins were used to evaluate the effects of several trace element contaminations. These contaminations induced malformations and a slowing of the development. In addition, research on the stress responses of the different larval stages has highlighted the high capacity of larvae to respond to oxidative stress, but also the importance of spawners in studies using sea urchin larvae. These innovative experiments are the first to investigate the effects of such important combinations of trace elements on the entire larval cycle of the sea urchin. This present work could strengthen other tools for diagnosing and monitoring coastal water quality in order to improve the ecological quality of marine waters.
