1.Toinvestigate the role of fish ecology in controlling terrestrial particulate organicmatter (POM) uptake by benthic fish species and population responses to changes incontinental inputs to coastal areas, depth distribution, diet and stable isotope (δ13C andδ15N) data from the juveniles and adults of five important flatfish species (Arnoglossuslaterna, Buglossidium luteum, Citharus linguatula, Solea lascarisand S.solea) werecompared off the Rhone River delta (NW Mediterranean).2.In moderate river discharge, isotopic signatures differed with fish species and benthiclife stage, suggesting intra- and interspecific differences in trophic levels and food sources.Food web analysis indicated terrestrial POM uptake in all life stages of S.soleaandA. laterna (δ13C = −20·1 to −20·0‰ and −18·9 to −18·2‰, respectively), in the adults ofB.luteum (δ13C = −19·0‰) and in the juveniles of S.lascaris (δ13C = −18·7‰), whereas all life stages of C.linguatula (δ13C = −17·6‰), S.lascarisadults (δ13C = −16·9‰) andB. luteum juveniles (δ13C = −17·5‰) exploited marine POM almost exclusively.3.Fish diet and depth distribution accounted fully for the intra- and interspecificdifferences in terrestrial POM uptake observed. Greater terrestrial signatures wereobserved in fish eating larger quantities of deposit-feeding polychaetes (the main preyexploiting terrestrial POM for growth) and occurring mainly in the 30 – 50 m depth zone(where river POM sedimentation and its uptake by the benthos were the highest). Dueto intra- and interspecific differences in fish depth distribution and diet, Rhone Riverfloods were predicted to have little effect on C.linguatulapopulations but to increase theother four species’ local stocks for several years, with a maximum impact on S. solea.4.This study shows that the ability of benthic fish to exploit terrestrial POM inputs to thecoastal zone depends strongly on their ecology. As this parameter will determine fishpopulations’ reactions to river floods, it must be assessed carefully before making hypothesesabout the consequences of variations in river discharge on coastal fisheries’ production.