Diversity inhibits colonization in early successional fouling communities

Early successional diversity can inhibit the success of later colonizers, but most studies focus on how the biodiversity of early successional assemblages affects individual colonizers rather than subsequent patterns of the community as a whole. We tested whether initial species richness in subtidal fouling communities inhibits the establishment of all subsequent colonizers during early succession. Using settlement panels deployed at 2 locations in Humboldt Bay, California, USA, we established low-, mid-, and high-richness communities and tracked the percent cover, diversity, and composition of all new colonizers over 10 wk. Panels with higher initial richness consistently exhibited lower cover of newly colonizing species, indicating stronger successional inhibition. This effect emerged within 2 wk and was consistent across locations despite variation in water motion, larval settlement rates, and predator abundance. Inhibition was strongest in communities containing the ascidian Diplosoma listerianum , suggesting that this dominant space-holding species may be driving diversity-mediated inhibition via a sampling effect. By the end of the experiment, all treatments converged in species composition, dominated by D. listerianum and Bugula spp., reflecting the transient nature of diversity-driven inhibition in these dynamic systems. Our results demonstrate that increased initial richness inhibits the establishment of new settlers at the community level, but that this inhibition is temporary and contingent on the identity of early colonists—initial diversity can delay, but not prevent, colonization in early successional fouling communities. These findings highlight the importance of both species richness and identity in shaping community assembly and inhibition of colonization.