The west coast of Spitsbergen is one of the most impacted area in the world due to global warming, as Atlantic, Arctic and glacial waters converge and mix there. As a result, the Kongsfjorden is a very relevant ecosystem to better assess and predict what will be the fate of polar coastal ecosystems in the near future. A high production of macroalgae (i.e. kelps) occurs in such ecosystems but most of this production is not used as fresh by consumers. This organic matter may therefore be exported to other habitats like subtidal mudflats, where it can be trapped into the sediment. Aim of this project is to determine to which extent subtidal mudflats can act as storage areas for detrital matter of macroalgae origin and what is the fate of this organic matter in these habitats at two seasons: summer, when primary production (i.e. macroalgae, phytoplankton) is high, and winter, when primary production is very low, suggesting that consumers have to rely on detrital food sources. In this aim, we will determine and compare the community structure of the benthic fauna at these two seasons and determine the role of macroalgae detrital matter in the functioning of subtidal mudflats using trophic markers (i.e. stable isotopes, fatty acids). Our results will thus provide information about the connectivity between two major habitats of polar coastal ecosystems: kelp belts and subtidal mudflats.