We aimed to verify the effects of local environmental hydrodynamics on the individual size of two sand-reef sabellariids (Sabellaria wilsoni and S. nanella) on a tropical intertidal beach in north-east Brazil. We also tested the hypothesis that the richness and abundance of their reef-building associated fauna would be influenced by environmental conditions related to the wind and wave action intensity. Individuals from three distinct intertidal levels at Cabo Branco beach (7o8′46″S 34°47′55″W), João Pessoa, Paraíba, Brazil, were sampled, identified, sexed, measured and the fauna associated with the reef samples was identified and quantified. Our statistical tests indicated that reef builders have distinct organization patterns which are related to environmental conditions. The aggregates exposed to the strongest wave and wind conditions presented reduced density and sabellariids of smaller sizes in comparison with the other aggregates. The associated fauna abundance and composition was also influenced by the local hydrodynamic regime.
