Macroalgae can be used to indicate biological and physical disturbances in the environment. In this study, the phyto-benthic community structure served to characterise the Cairuçú Protected Area. Six sampling sites represented a variety of environmental conditions inside Parati Bay, RJ. The most wave-exposed site was Ponta da Cajaíba followed by moderately exposed Praia da Conceição, and all the other sites were sheltered. Quali- and quantitative sampling of macroalgae were carried out four times a year. Algal cover was estimated within functional-form groups in the sublittoral zone using 10 m transects, each one with 10-30 random quadrats of 0.04 m². Density of herbivorous sea urchins was estimated within 10 areas of 0.25 m². There were 15 taxa added to the marine flora of Parati district, making a total of 136 taxa. Comparing local floras in southern areas of Rio de Janeiro State, Parati was similar to both Sepetiba Bay and the remaining of Ilha Grande Bay. Ilha Comprida, Saco da Velha, Praia Vermelha and Ponta do Buraco were dominated by corticated, coriaceous and articulated calcareous erect algae showing a lower cover of crustose calcareous algae. Sargassum dominated in more stable environmental conditions being replaced by smaller rhodophytes after its senescent phase, suggesting competition for stratum space. Places more exposed to waves and/or herbivores (Praia da Conceição and Ponta da Cajaíba) were dominated by crustose and small erect algae, in agreement with algae abundance patterns predicted by form and function models dependent on degrees of physical and biological disturbance.
APA Cairuçú; distribution; functional-form groups; macroalgae; physical and biological disturbances