Climate change is rapidly altering Mediterranean benthic ecosystems, with marine heatwaves posing a major threat to long-lived habitat-forming species such as the gorgonian Eunicella singularis. This study investigates how seasonal thermal stress affects the eco-physiological performance and ecosystem functioning of E. singularis forests in a coralligenous habitat of the central Mediterranean Sea (Capo Gallo and Isola delle Femmine MPA, Sicily, Italy). An integrated in situ approach was used, combining benthic chamber incubations to quantify respiration and photosynthetic oxygen production, pulse-amplitude modulated fluorometry (Fv/Fm) to assess symbiont photophysiology, antioxidant enzyme assays (SOD, CAT, GR) as biomarkers of oxidative stress, and measurements of total and organic suspended matter to evaluate particle dynamics in the water column. Sampling was conducted before and after the summer warming period in forests with contrasting gorgonian density. The results showed a marked seasonal variation in metabolic activity, with a post-summer decrease in respiratory functions. The photosynthetic efficiency of the symbionts (Fv/Fm) was higher after the summer warming period compared to the pre-summer phase. Oxidative stress biomarkers revealed enhanced antioxidant activity after summer warming, with increases in superoxide dismutase (SOD) and glutathione reductase (GR), indicating activation of cellular defense mechanisms against reactive oxygen species. This pattern, together with the observed physiological changes, indicates the activation of cellular stress-response mechanisms under thermal stress conditions. Although no mass tissue mortality was observed, the physiological signal suggests sublethal effects associated with summer warming. Overall, these findings suggest that Eunicella singularis forests exhibit physiological resilience to seasonal warming; however, the detected sublethal effects may represent early warning signals of potential vulnerability to recurrent extreme thermal events, with possible implications for the functioning and resilience of Mediterranean coralligenous ecosystems.