Zinc Isotope Fingerprints in Juvenile Fishes from Estuarine Nurseries with Different Pollution Histories: Perspectives for Environmental Monitoring and Fish Ecology

Zinc (Zn) isotopes are effective tracers of Zn cycling in marine environments and hold strong potential for ecological applications, yet they remain underexplored. This study analyzes Zn concentrations and isotope compositions (δ⁶⁶Zn) in 96 juvenile European seabass (<i>Dicentrarchus labrax</i>) and common sole (<i>Solea solea</i>) from three French estuarine nurseries─Seine, Loire, and Gironde─each with distinct Zn pollution histories. Seabass from the three estuaries exhibit similar trends in Zn bioaccumulation (body burden) and biodilution (concentration) with an increasing size and age. However, significant δ⁶⁶Zn differences among estuaries indicate that each system "stamps" a unique isotopic fingerprint on local fish populations. Intraestuarine variability among seabass age classes (1-4 years) is smaller than interestuarine differences. Juvenile soles consistently display higher δ⁶⁶Zn values than seabass of similar ages, suggesting that species-specific Zn homeostasis and ecological factors influence isotope compositions. Across estuaries, δ⁶⁶Zn patterns in fish mirror those in sediments, indicating that Zn sources drive the isotope compositions. These results confirm that anthropogenic Zn circulates through local food webs with both environmental and dietary sources influencing fish isotope compositions alongside homeostatic processes. Overall, Zn isotope analysis in juvenile seabass and common sole provides new insights for monitoring anthropogenic Zn bioaccumulation and elucidating dietary niches in fish ecology.