UC Santa Cruz

Studies on the ecology and biogeography of seamounts and oceanic islands have advanced substantially in the last 60 years. However, few seamounts have been scientifically characterized, with basic aspects of their biodiversity still unknown and many hypotheses not empirically tested. Consequently, the role of seamounts in the evolution for marine species is still unclear. In the south Atlantic, the Vitória-Trindade Chain (VTC) extends ca. 1,200 km offshore the Brazilian coast. For a long time, most of the biological information available was limited to the emergent islands, where a high richness and endemism is found. The seamount chain, situated between the islands and the mainland, is thought to contribute importantly to the regional biodiversity, and has been suggested as stepping-stones, repositories and museums for coral reef species. The goal of this dissertation is to characterize the biogeographic patterns of reef fishes that inhabit the VTC and test hypotheses to explain those patterns. The results reveal large mesophotic reefs sheltering a very high biodiversity, where new records, depth range extensions and new species were reported. The regional biogeography is very complex; species richness does not decrease with distance from the mainland and it is related instead to seamount and island environmental characteristics and ecological traits of the species. Speciation is not only resulted from the islands isolation, as many endemics are widely distributed along the seamounts, and selection and adaptation are stronger drivers of genomic differentiation than is isolation. In conclusion, oceanic islands would unlikely exhibit the biogeographic patterns we observe today in the absence of seamounts as intermittent stepping-stones, reservoirs of coral reef biodiversity.