Natural environments are increasingly affected by human activities since the early twentieth century. Both Polar Regions are particularly affected by those climate changes. The Southern Ocean plays a key role in global ocean circulation and global climate. It participated in the thermohaline circulation, which regulates the global climate. 

Marine environments in Kerguelen Islands were relatively little affected by human activities. The isotopic signatures δ13C δ15N of three species of sea urchins harvested in different environments, were analyzed to characterize their food strategies. A mapping of the trophic niche each species was performed by using the SIBER mixing model. This aim to study the trophic plasticity of these organisations and the possible interactions between them. The results show that there is no interaction between species due to their very different diets. However inter-area and inter-species differences have been identified. The isotopic values δ13C and δ15N will be sensitive to the physico-chemical conditions of the environment. A second mixture model is used, SIAR, to characterize the diet of S.diadema at Port Matha (-2m), but also C.nutrix and S.diadema of Ilot des Trois Bergers (-20m). The C.nutrix will favor sponges, S.diadema feed from different sources (sponges, algae, sediment).