Mechanisms of dispersal and establishment drive a stepping stone community assembly on seamounts and oceanic islands

The mechanisms driving the ecology and biodiversity of seamount communities are still unclear. Here we analyzed the distribution and species traits of reef fish species recorded over seamounts, oceanic islands, and the continental shelf of the southwestern Atlantic Ocean to understand the influence of mechanisms of dispersal and establishment in these ecosystems. Species richness did not decrease with distance from the mainland, and community composition was not related to geographic position and geological history of seamounts and oceanic islands. Similarity among sites was explained by habitat heterogeneity, shallowest depth, and distance from mainland. Inter-site isolation had a significant influence on the spatial turnover of species. All species traits related to dispersal and establishment worked as ecological filters driving the composition of communities and distribution of species along seamounts and oceanic islands. We conclude that seamount communities are closely related to those of oceanic islands, with the stepping-stones (inter-site isolation) process being the most important one shaping species composition and distribution. Establishment and dispersal mechanisms, in combination with historical sea-level fluctuations, regulate the persistence of species and the similarity of communities among adjacent and environmentally similar sites.