Effects of a subtidal macroalgae bed on soft-bottom polychaete assemblages in Arraial do Cabo, Rio de Janeiro, Brazil

A set of sediment samples was collected in a subtidal sandy beach, between 3 to 6 m depth to determine whether the Sargassum furcatum bed influences the species composition and the structure of the polychaete assemblages in adjacent sediments. A total of 274 individuals representing 25 species was found. Aricidea (Allia) albatrossae, Armandia longicaudata and Kinbergonuphis tenuis were the most abundant species. Density varied from 6.67 to 17.67 ind 0.018 m⁻², Shannon diversity (H') from 0.35 to 2.00 and evenness (J') from 0.25 to 0.90. Three associations were identified and were related to depth and the presence of the S. furcatum bed which were found to influence the structure of neighboring soft-bottom assemblages.