Impact of port conditions and acclimation capacity of common two-banded seabream juveniles in the bay of Toulon: implications for nursery rehabilitation efforts

Ports are heavily anthropized coastal environments characterized by intense pollution and habitat alterations, creating challenging living conditions for marine organisms, particularly juvenile fish that rely on these areas as nurseries. While recent rehabilitation efforts of the nursery function in ports have focused on structural modifications, the impacts of port chemical and physical pollution are currently disregarded. Using field sampling and caging experiments, we examined the physiological (growth, lipid content, CYP1A-dependent biotransformation activity) and molecular (RNA-seq) responses of juvenile two-banded sea bream ( Diplodus vulgaris ) by comparing one port site with two adjacent sites from outside of the port, assessing their potential for short-term acclimation to port conditions. Results from individuals sampled in the field revealed distinct physiological and transcriptomic profiles in port juveniles, indicating specific responses to this environment. Notably, alterations related to lipid accumulation, detoxification, hypoxia, and circadian regulation were observed. After one month of caging all the individuals from different locations in the port, juveniles originating from outside the port exhibited stronger transcriptional responses compared to individuals that grew within the port, with higher expression of genes involved in detoxification and lipid metabolism, and a strong overexpression of oncogenes, while individuals originating from the port upregulated genes involved in energy metabolism, suggesting some capacity for short-term acclimation in port-resident juvenile fish. These findings highlight the potential impact of port conditions on juvenile fish health, with implications for the effectiveness of rehabilitation efforts. This study emphasizes the need for further research to inform nursery rehabilitation strategies in polluted ports.