This paper presents a floristic survey of the red algae and some ecological aspects of the São Pedro and São Paulo Archipelago (00º56'N; 29º22'W - 00º55'N; 29º 20'W). Collections were carried out during low tide in six stations located in the intertidal and infralittoral zones, in October 2003 (dry season) and April 2005 (rainy season). It was registered 24 infrageneric taxa distributed among the orders Bonnemaisoniales (1 specie), Ceramiales (12 species), Corallinales (6 species), Erythropeltidales (1 specie), Gelidiales (1 specie), Rhodymeniales (2 species) and Stylonematales (1 specie). Fifteen taxa are new records to the Archipelago flora. It was also registered four new records to the Brazilian oceanic islands: Ceramium brevizonatum var. caraibicum H. E. Petersen & Börgesen, Ceramium tenerrimum (G. Martens) Okamura, Jania prolifera A. B. Joly and Stylonema alsidii (Zanardini) K. M. Drew. The red algae were registered only in three stations. The highest specific diversity (16) occurred to Station 01 (Enseada) and to the rainy season (23 species). The Søresen floristic similarity in relation to depth varied from 0 to 0.66%.
Seaweed; Rhodophyta; Archipelago; Brazil
