Combining stable isotope mixing models and a bioenergetics-based approach to spatialize the exploitation efficiency of juvenile demersal fish a coastal nursery
Résumé
Estuarineand coastal ecosystemsare spatially-restricted habitatsfulfillinga nursery function for many demersal fish species. These nursery-dependant species concentrate at the juvenile stage in these habitats, resultingin density-dependent regulationand thuslimiting thegrowthandsurvival.However, the underlying mechanisms are still poorly understood and thelimitation of the food supplyon thejuvenilefishremains a pending issue.The Seineestuarine and coastal ecosystem (Eastern English Channel) is a nursery composed ofa mosaic of habitatsoffering diversefood resources. Over thelast decades,important anthropogenic stresssignificantlyreducedthe surface of mudflats and productive habitats.In this context, the understanding of the trophic contribution and role of each habitat is essential to understand the localtrophicfunctioning and more generally to test the food limitation hypothesisat a finer spatial scale. We used arecently developed bioenergetics-basedapproach to estimate thebenthictrophic capacity of thisnursery. Thisapproach estimatesthe exploitation efficiency (EE), i.e.the part of the production consumed by the juveniles. Theproduction model can be easily spatialized in the different habitats. However, fish mobilitymakes the spatialization of the consumption model,which estimatesthe total energy required by the fish growth,morechallenging. This issue was overcomeby combining the outputs of the consumption model withthose of isotopic mixing models, the latterintegrating isotope compositions of juveniles’ prey from the different habitats.The comparison of the EEassessedwill help identifying trophically-limitedhabitatsfor the juveniles’ production.