Adding early-stage engineering species affects advanced-stage organization of shallow-water fouling assemblages

Although commonly overlooked, processes determining early patterns of species assembly may affect community dynamics and diversity at advanced states. In this study, we followed richness and community structure in experimental units pioneered by single or multiple species, within a given functional group-colonial ascidians, arborescent, and encrusting bryozoans. We tested the hypotheses that richness and community structure are positively affected by founder-richness at more advanced stages, and that such effect may depend on the functional traits of founders (more or less prone to facilitate other species). More diverse founding assemblages of arborescent bryozoans led to richer communities after 1 and 5 months of succession, with no effects observed for the other functional groups. Assemblages started by a single species were dominated by space monopolizers (encrusting bryozoans), while the ones founded by two species were characterized by a higher abundance of engineering forms (arborescent bryozoans), which may provide a physically complex substrate suitable to both the attraction and protection of other species recruits. Both effects on advanced-stage richness and community structure reflect the importance of facilitation through founder diversity and functionality in community organization.