The importance of predation and predator size on the development and structure of a subtropical fouling community

Predation plays a fundamental role in shaping marine fouling communities. However, its consequences for species diversity and community organization depend on several intrinsic properties of predators and prey. To evaluate how predators of different sizes affect the organization of sessile communities during their development, we deployed an experiment in which PVC plates were assigned to one of four predation exclusion treatments: partial exclusion cage (2.4 cm mesh), total exclusion cage (0.5 cm mesh), and two respective controls. We evaluated community richness and structure after 30, 90, and 150 days. Regardless of size, predation did not affect total species richness. After 30 days, communities on plates protected against all predators had less free space than any other treatments, but their structure was similar to those protected to large predators only. Therefore, the addition of predators smaller than 2.4 cm to the pool of consumers may intensify predation effects rather than change species dominance and composition. After 90 days, intensified consumption by smaller predators had no longer measurable effects. Our data suggest that the removal of dominant species by predation does not increase species richness but modulates the interaction among species. The removal of ascidians seems to facilitate the dominance of predator-resistant bryozoans.