Long-term monitoring of subtidal benthic macroalgae at São Miguel Island (Azores, Portugal)

The dataset was compiled to investigate long-term changes in the structure, composition, biomass, and diversity of macroalgal-dominated rocky reef communities over a period exceeding 20 years. The dataset combines a historical survey conducted between 1993 and 1995 at São Roque with contemporary surveys conducted between 2016 and 2018 at São Roque, Lagoa, and Caloura.

Sampling was performed at 5 m and 15 m depth in rocky subtidal habitats representative of coastal ecosystems throughout the Azores. Macroalgal assemblages were sampled using standardized quadrat-based methods, and all macroalgae were identified to species level and quantified through dry biomass measurements.