This paper aimed to describe the biological structure of Sargassum beds along the coasts of Rio de Janeiro and São Paulo states. Sixteen rocky shore communities were sampled at random (50 x 50 cm quadrats) during 1991-92. These communities presented populations of distinct Sargassum species. They were chosen because they were subjected to different degrees of wave action and emersion. Seven infrageneric taxa of this genus were studied. The Sargassum dry mass varied from 37 g.m-2 to 587 g.m-2; the highest values were found in moderate and protected sites. The cluster analysis of these communities, considering the dry mass of 75 groups of macroalgae and macroinvertebrates, indicated three structural patterns characterized by the most abundant group of organisms: 1) Sargassum, in places not exposed to direct wave action, frequent emersion nor recent disturbances; 2) calcareous algae (Corallinaceae), mainly in exposed places, with Phragmatopoma lapidosa (tube worm) and/ or Perna perna (mussels); 3) other groups of non-calcareous algae, such as Dictyopteris delicatula, representative in intermediate situations. These patterns may be usefull to study the exploitation potentiality of Sargassum and other organisms, like mussels, in the Brazilian coast.
Sargassum; Corallinaceae; dry mass; structural patterns