Thermal challenges reveal low phenotypic plasticity in common shallow water fish

Climate variations in recent decades have led to an increase in ocean temperatures and an escalation in the number, intensity, and duration of marine heatwaves. Species such as Pomatoschistus microps, which inhabit shallow marine environments, are particularly exposed to these environmental extremes. This makes them ideal model species for assessing the impacts of ocean warming in these areas. Thermal tolerance, metabolic rate, and cellular stress response of this species were assessed after exposure to both present-day and projected future summer scenarios, along with their respective heatwaves. The thermal maximum did not appear to vary among the different scenarios tested, suggesting a limited acclimation capacity. Additionally, their metabolic rate remained stable, and there were no significant alterations in the levels of cellular stress response biomarkers. This lack of change suggests that their homeostatic state was not disrupted. Temperature data collected at the sampling site indicates that this species maintains a substantial thermal safety margin, which equips it to withstand thermal challenges not only in the present but also in anticipated future summer and heatwave conditions.