The diversity of algal banks composed of species out the genera Gracilaria Greville and Hypnea J.V. Lamouroux have been impacted by commercial exploitation and coastal eutrophication. The present study sought to construct dynamic models based on algal physiology to simulate seasonal variations in the biomasses of Gracilaria and Hypnea an intertidal reef at Piedade Beach in Jaboatão dos Guararapes, Pernambuco State, Brazil. Five 20 × 20 cm plots in a reef pool on a midlittoral reef platform were randomly sampled during April, June, August, October, and December/2009 and in January and March/2010. Water temperature, pH, irradiance, oxygen and salinity levels as well as the concentrations of ammonia, nitrate and phosphate were measured at the sampling site. Forcing functions were employed in the model to represent abiotic factors, and algal decay was simulated with a dispersal function. Algal growth was modeled using a logistic function and was found to be sensitive to temperature and salinity. Maximum absorption rates of ammonia and phosphate were higher in Hypnea than in Gracilaria, indicating that the former takes up nutrients more efficiently at higher concentrations. Gracilaria biomass peaked at approximately 120 g (dry weight m-2) in March/2010 and was significantly lower in August/2009; Hypnea biomasses, on the other hand, did not show any significant variations among the different months, indicating that resource competition may influence the productivity of these algae.

Este trabalho apresenta o levantamento florístico e alguns aspectos ecológicos das algas vermelhas do Arquipélago de São Pedro e São Paulo (00º56'N; 29º22'W - 00º 55'N; 29º 20'W). O material foi coletado durante as marés baixas em seis estações, nas zonas entre-marés e infralitoral no mês de outubro de 2003 (estação seca) e abril de 2005 (estação chuvosa). Foram registradas 24 espécies, distribuídas entre as ordens Bonnemaisoniales (uma espécie), Ceramiales (12 espécies), Corallinales (seis espécies), Erythropeltidales (uma espécie), Gelidiales (uma espécie), Rhodymeniales (duas espécies) e Stylonematales (uma espécie). Foram feitos 15 novos registros de rodofíceas à flora do Arquipélago e quatro novas adições para as ilhas oceânicas brasileiras: Ceramium brevizonatum var. caraibicum H. E. Petersen & Börgesen, Ceramium tenerrimum (G. Martens) Okamura, Jania prolifera A. B. Joly e Stylonema alsidii (Zanardini) K. M. Drew. Foram registradas algas vermelhas em apenas três estações. A maior riqueza de táxons (16 taxa) ocorreu na Estação 01 (Enseada) e no período chuvoso (23 taxa). A similaridade florística, com base no índice de Sørensen, em relação à profundidade, variou de 0 a 0.66%.

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%.