Abstract: Kelp ecosystems which are present throughout the world are biodiversity hot-spots. These ecosystems which are poorly studied especially in antarctic and sub-antarctic regions are however sensitive to climate change. The point of this study is therefore to describe this type of ecosystem. For this, stable isotopes of carbon, nitrogen and sulfur were used and measured for different carbon sources as well as several species of consumers. The contribution of these food sources were then estimated using the mixing model simmr. Two models were studied, the first including values of carbon nitrogen and sulfur and the second including only carbon and nitrogen values. Results showed that the use of sulfur isotopes in association with carbon and nitrogen allows for a better distinction between food sources and therefore a better estimation of their contribution to consumers diets. The results also showed that the kelp Macrocystis pyrifera which is the most abundant carbon source contributes little to primary consumers diets. Indeed, the consumers seem to prefer Ulva sp. and suspended organic matter.