Getting a Good Start in Life? A Comparative Analysis of the Quality of Lagoons as Juvenile Habitats for the Gilthead Seabream Sparus aurata in the Gulf of Lions

Temperate coastal lagoons are considered key habitats for several highly prized marine fishes, which colonise them as nurseries. Lagoons can, however, exhibit diverse abiotic and biotic conditions, with potential consequences for their quality as habitats. To investigate this, we compared size, body condition (Fulton’s condition factor K and lipid classes), past growth rate (from otoliths) and sources of food web organic matter (OM), among group 0 juveniles of the gilthead sea bream Sparus aurata L. 1758, captured at the end of their first summer of residence in four lagoons of the Gulf of Lions in the NW Mediterranean (Mauguio, Thau, Bages and Salses-Leucate). These lagoons have different environmental conditions and freshwater inputs. Although age was similar for all lagoons, juveniles from Mauguio and Bages were significantly larger and heavier than those from Thau and Salses-Leucate. They were also in better condition, with higher white muscle triacylglycerol/sterol ratio (mean ± SD 35.7 ± 20.1 in Mauguio and 23.2 ± 9.8 in Bages versus 15.1 ± 15.2 in Thau and 7.4 ± 7.9 in Salses-Leucate). All exhibited similar otolith growth rates for their larval marine phase (2.8 ± 0.4 μm day⁻¹), but significant differences were found for the lagoon phase, with higher values in Mauguio and Bages (10.1 ± 0.9 and 9.7 ± 1.0 μm day⁻¹, respectively) than those in Thau and Salses-Leucate (8.4 ± 1.2 and 8.9 ± 0.8 μm day⁻¹, respectively). White muscle stable isotope analysis revealed that terrestrial carbon use by the juveniles was >33 % in Mauguio and