Trophic ecology of marine migratory fishes in Mediterranean coastal lagoons

Fish trophic ecology may change among coastal lagoons because of their natural characteristics and the intensity and type of human activities, which can alter the eutrophication level. The diet, trophic niche and position of the Sparidae Sparus aurata and Diplodus sargus and of Mugilidae were investigated during their residence in 3 lagoons along the French Mediterranean coast. These lagoons differ in environmental characteristics and degrees of human activities. Analyses of bulk δ13C and δ15N were done on both fish muscle and bone collagen because these tissues have different turnover rates and inform of diet changes within a different time frame. For S. aurata we also analysed δ13C and δ15N of amino acids in bone collagen to further explore the origin of baseline food sources and the trophic position without an external baseline. In the least impacted of the 3 lagoons, fishes occupied a higher trophic position. Sparidae showed the most specialised diet and Mugilidae the most generalist one. Bone collagen showed, instead, no variation in trophic position or diet, likely because it integrates signals over fish growth and is more conservative than muscle. However, the similar δ 15 N patterns observed between tissues across the three lagoons indicate that eutrophication imprints both short- and long-term dietary signals, highlighting the potential of fish bone collagen as a proxy for reconstructing long-term eutrophication patterns in coastal lagoons. Highlights : • The δ15N values of muscle and collagen tissues indicated differences among lagoons in the level of nutrient load derived from human activities. • Based on muscle tissue, isotopic niches and TP varied according to the level of human impacts. However, bone collagen analyses showed little variation. • Human impact may affect fish trophic ecology differently during their growth and muscle tissue seems to be more appropriate for evaluating these changes due to its faster turnover rate.