Coastal ecosystems are impacted by numerous sources of degradation (coastal urbanisation, chemical pollution, climate change). It is essential to understand how coastal organisms survive the combined action of these stressors. At IRL EARLY, RNA sequencing, used to measure the expression level of all genes in an organism, is employed to describe how fish acclimate to their environment. This project focuses on an emblematic species of Okinawa, the Sapphire Devil Chrysiptera cyanea, which can be found from isolated beaches to urbanised river mouths. Over consecutive years, field sampling campaigns and aquarium experiments are conducted to characterise the effects of urbanisation, chemical pollution (notably PFAS exposure), food availability, and heatwaves on gene expression in the species. This project contributes to a better understanding of the links between fish state and local conditions, and aims to establish the use of RNA sequencing as a resource for coastal monitoring.