Climate change is accelerating ocean acidification, making it essential to understand the adaptive strategies enabling marine species to cope with the changing environment. In this context, natural acidification sites provide a unique opportunity to explore both short- and long-term responses of marine organisms. In this study, we examined, for the first time, the survival strategies of the brown algae Dictyota dichotoma along a natural pH gradient at Fuencaliente (La Palma, Canary Islands). Algal thalli were collected from three sites—acidified, transitional, and control—and analyzed for photosynthetic efficiency, pigment composition, antioxidant capacity, and key functional, anatomical and morphological traits. Additionally, algal cover at each sampling site was measured to assess responses at the population level. Results indicated that photosynthetic efficiency did not vary along the pH gradient, while thallus dry matter content and algal cover increased at acidified site, suggesting a potential benefit under elevated CO₂. In contrast as acidity increased, surface thallus area and total chlorophyll content decreased, and carotenoid concentration and antioxidant capacity increased, indicating a shift in metabolic investment likely associated with stress mitigation under acidification. Anatomical analysis provides first documented evidence of significant thallus thinning, likely due to a decrease in cortical cell thickness. Such structural changes, together with stable photosynthetic efficiency and strong antioxidant response, highlight the significant plasticity of D. dichotoma. Overall, our findings suggest that D. dichotoma have several adaptive traits—functional, structural, and biochemical—that may help its persistence in naturally acidified marine environments. This study contributes to understanding the resilience mechanisms engaged by macroalgae to counteract future ocean acidification scenarios.