Few studies of natural populations of the red algae Hypnea musciformis have been conducted. To enhance our knowledge, it would be helpful to define methodologies that explore the species' adaptability to different environments and seasons. Tetrasporophyte is the most frequent reproductive stage in this species. A case study of 2 populations in the Brazilian tropics allowed us to define a fertility index based on the meiotic count of tetrasporangia. Significant differences were found in the production of tetrasporangia among microhabitats and between the dry and rainy seasons. The analysis of this index in red algae may constitute an important tool for understanding the biology and ecology of this algal group.

Hypnea musciformis ocorre amplamente na costa nordeste do Brasil, sendo uma das mais importantes fontes naturais de k-carrageenana que é utilizado nas indústrias alimentícia e cosmética. Apesar do potencial de explotação, pouco se sabe sobre sua ecologia. O objetivo deste estudo foi conhecer a biologia e ecologia de H. musciformis no Brasil através da análise do estoque de biomassa e da flora acompanhante. Duas populações de H. musciformis foram analisadas nas praias de Stella Maris e Itacimirim (Bahia, Brasil). Oito amostragens foram realizadas entre 2007 e 2009, durante as estações seca e chuvosa. As algas foram coletadas ao longo de transectos (20 m) utilizando quadrados (0,04 m²) em três diferentes regiões hidrodinâmicas dos recifes (TP, PRR e FRR). t-Test, Teste de Dunn e ANOVA paramétrica e não-paramétrica foram utilizados para a análise estatística. Foram identificadas 17 espécies hospedeiras e 41 espécies associadas. O maior estoque de biomassa foi observado durante a estação seca. Em Stella Maris, a região com maior estoque de biomassa foi FRR, e em Itacimirim, TP apresentou biomassa maior. Este estudo permite supor que sazonalidade, microhabitats, hidrodinamismo e fatores em microescala contribuem para a variação no estoque de biomassa em populações de H. musciformis.

Hypnea musciformis occurs widely in the northeast coast of Brazil, and it is one of the most important natural sources of k-carrageenan, which is used in food and cosmetic industries. Despite its potential for exploitation little is known about its ecology. The aim of this study was to investigate the biology and ecology of H. musciformis in Brazil through analyses of biomass stock and accompanying flora. Two populations of H. musciformis were analyzed: those on the beaches of Stella Maris and Itacimirim (Bahia, Brazil). Eight samplings were conducted between 2007 and 2009 during the dry and rainy seasons. The algae were sampled along transects (20 m) using quadrats (0.04 m²) in three different hydrodynamic regions of the reefs (TP, PRR and FRR). The t-Test, Dunn's Test and parametric and nonparametric ANOVA were used for statistical analyses. 17 host species and 41 associated species were identified. The highest biomass stock was observed during the dry season. On Stella Maris, the region with the highest biomass stock was FRR; on Itacimirim, TP had the highest biomass value. This study permits the assumption that seasonality, microhabitat, hydrodynamic and micro scale factors contribute to variation in biomass stock in H. musciformis populations.