This dataset presents a comprehensive study conducted in the southeastern Bay of Biscay over a span of 30 years. It encompasses detailed information regarding surveyed sites, macroalgal species identification, and assessments of morphofunctional groups. The surveys, conducted in 1991, 2008, 2013, and 2021, aimed to discern temporal and spatial variations within the macroalgal community. Furthermore, Species Temperature Index (STI, °C) were determined for all identified species, enabling the calculation of the Community Temperature Index (CTI, °C) for each site and year under study. This dataset serves as a valuable resource for understanding long-term trends and dynamics within the macroalgal ecosystem of the southeastern Bay of Biscay