This dataset originates from a standardized benthic survey conducted during 2020 and 2021 at multiple coastal locations around São Miguel Island, Azores (Northeast Atlantic), within the scope of the MIMAR project (Monitoring, Control and Mitigation of Marine Organism Proliferations Associated with Human Disturbances and Climate Change in the Macaronesian Region). The primary objective of the sampling campaign was to characterize the composition and spatial variability of shallow subtidal macroalgal assemblages across representative benthic habitats of the island. Using consistent field methodologies, the survey generated a robust baseline of macroalgal community data, enabling comparisons among sites and supporting assessments of benthic biodiversity patterns at local and regional scales. The dataset provides reference information relevant for ecological assessment and long-term monitoring, including the evaluation of environmental variability, anthropogenic pressures, and potential changes in community structure over time, such as those associated with climate-driven shifts and the introduction or spread of non-indigenous species in coastal ecosystems.