BULLETIN OF MARINE SCIENCE, 67(1): 321–335, 2000 321 THE EARLY ESTABLISHMENT AND DEVELOPMENT OF A POLYCHAETE COMMUNITY SETTLED ON ARTIFICIAL SUBSTRATA AT TODOS SANTOS BAY, BAJA CALIFORNIA, MEXICO Victoria Díaz-Castañeda ABSTRACT The polychaete colonization process was studied in Todos Santos Bay, Baja California, by suspending 39 plates in April 1997 and recovering replicates at 14–45 d intervals over a year. A total of 3579 polychaetes representing 13 families and 38 species was collected during this period. Composition and structure of the community were studied. A ‘lag- period of 48 d was observed before settlement of polychaetes. First macrofauna coloniz- ers were barnacles (Balanus amphitrite) and amphipods (Caprella californica, Corophium sp., Erithonius brasiliensis). The best represented polychaete families were: Serpulidae (59.5%), Spionidae (11.1%) and Opheliidae (8%). The main trophic groups were filter- feeders (59.8%) and deposit-feeders (27.6%). The early stages were dominated by spe- cies belonging to the Nereididae and Serpulidae, whereas the last 3 mo were dominated by the Polynoidae, Phyllodocidae, Terebellidae, Syllidae, Opheliidae, and Serpulidae. Abundance, number of species, and diversity increased progressively, with a peak of 292 polychaetes, 23 species per plate and, 3.914 bits ind −1 on the last plates collected after 378 d of immersion. Czekanowski and Jaccard’s coefficients separated five groups of plates, depending on their ‘immersion age’, and six groups of species in relation to their abun- dance and the period in which they were present. The multivariate analysis (FCA) re- vealed the existence of a colonization pattern linking an opportunistic/pioneer commu- nity to a more mature and organized community, there was a separation between the first and second half of the study, in which abundance, number of species, diversity, equitability, and dominance presented different values. The development of epibenthic communities on hard substrates in the marine environ- ment has been the subject of numerous investigations (Reish, 1965; Osman, 1977; Greene et al., 1983; Breitburg, 1985; Goren, 1985; Bailey-Brock, 1987; Wendt et al., 1989; Nandakumar, 1996). However, polychaete studies have received less attention (Hutchings and Murray, 1982; Hutchings, 1983; Hutchings et al., 1992; Díaz-Castañeda and Marsden, 1994). Recruitment is fundamental to community structure because it becomes the foundation upon which all subsequent interactions will take place (Woodin, 1991). Community struc- ture is controlled by the successful settlement of species which may then become domi- nant. Maintenance of benthic communities also depends critically on larval recruitment success. The often substantial variation in success of recruitment can profoundly influ- ence the dynamics of adult benthic populations. Polychaetes represent a dominant component of the benthic fauna in coastal environ- ments and in particular on artificial substrata (Zajac and Whitlatch, 1982; Gravina et al., 1989) with regard to number of species, density, and biomass. Also they present a great variety of reproductive strategies and occupy a great number of trophic niches (Gambi and Giangrande, 1986).