Export de carbone par les poissons lagunaires à l'interface mer-continent: caractérisation et quantification. – LAGUNEX

Lagoons contribute highly to marine coastal zones' productivity. Their positioning at the sea-continent interface explains their richness but exposes them to numerous climatic and anthropic constraints. The amplification of these constraints threatens lagoon ecosystems' functioning. Therefore, it is essential to identify the ecological and biological services provided by coastal lagoons and estimate their importance for marine organisms in order to assess the factors responsible for species survival and biogeochemical process preservation in the coastal zone. Temperate lagoons are used by numerous marine euryhaline fish species, mainly during their early life history. This phase of their life cycle and its consequences for population dynamics and ecosystem functioning are poorly known. This can bias greatly our perception of lagoons' importance for coastal zones' productivity. Hence, fish can play a key role in lagoon ecosystems functioning, mainly through their ability to regulate benthos abundance and composition as top predators. In marine euryhaline fish, individuals are furthermore likely to participate to organic matter export to the sea when they move back offshore after a few months to a few years of lagoon life. This project aims to determine (1) the extent of lagoon use in marine euryhaline fish and (2) the origin (marine, terrestrial) of the carbon sustaining fish growth in the lagoons, in order to estimate the potential trapping and export of terrestrial carbon by this highly mobile biological compartment. These questions will be answered through the study of (1) fish lifetime sea-lagoons movements and (2) fish lagoon food webs in 2 representative species: the common sole and the sea bream. This multidisciplinary study, based on the use of state-of-the-art methods in aquatic ecology (otolith microchemistry, stable isotopes), should significantly expand the research themes of the ECOLAG laboratory (UMR CNRS-UM2 5119), mainly towards the study of fish trophic role in the lagoons and organic matter fate at the sea-continent interface. Its successful completion should help understanding the origin of coastal zone productivity and how to preserve it in spite of the current increase in environmental constraints. This is crucial for maintenance of coastal resources and preservation of the economical activities they sustain.