The present study characterizes the seaweed assemblages growing on trunks of mangrove trees in two rivers of the Serra do Mar State Park - Núcleo Picinguaba (Ubatuba County, São Paulo State) evaluating composition, abundance, temporal and spatial distribution variations and reproductive phases of seaweeds. Ten samples were randomly collected on four collecting events at three different mangrove sampling sites along the rivers Picinguaba and Fazenda, and 16 seaweed taxa were reported. The more expressive species in terms of frequency and biomass were Bostrychia calliptera, Bostrychia moritziana and Bostrychia radicans. The highest values were observed on samples from site B at the River Fazenda in September (160.17 ± 75.51 g.m-2), while the lowest values were found on samples from site C at the River Picinguaba in March (24.85 ± 23.80 g.m-2). No clear pattern in the distribution of the species was found. The obtained results indicate that both rivers are under similar environmental conditions for the growth of the "Bostrychietum" species, probabily due to the high water volume of both rivers combined with the lack of a dry season along the year.
mangrove; seaweeds; conservation unit