This study deals with the associated fauna of Sabellaria alveolata (Annelida: Polychaeta) colonies on the central coast of Portugal. Samples were collected on two shores, Magoito and Avencas and a total of 137 taxa were found on both shores. In qualitative terms, χ2-test shows significant differences between shores. In Magoito crustaceans are the most abundant associated fauna while in Avencas polychaetes are the most abundant. Relative biomass and abundance per kg of sediment is much higher in eroded colonies than in developed ones and diversity seems to increase with reduced wave action.