Biogeography of tropical reef fishes: the South Atlantic puzzle

Aim To reveal underlying distributional mechanisms of tropical reef fishes in the South Atlantic. Location The tropical South Atlantic, with emphasis on the Brazilian province. Methods The disjunct distributions of thirty-five reef fish species occurring in the Brazilian Province were analysed to allow a better understanding of present biogeographical patterns. To avoid potential bias because of taxonomic problems or misidentification, we only included families taxonomically well documented, with conspicuous species, and relatively easy to identify. Results The low-level differentiation between Caribbean and Brazilian species/populations, as well as the presence of restricted populations of a few northern or southern species on the opposite side of the Amazon River, clearly indicate that this barrier to dispersion can be occasionally bridged. Transoceanic dispersal appears to be frequent and to occur along three routes: from the Caribbean to North East Atlantic, from northern Brazil to the Gulf of Guinea, and from Africa to southern Brazil. Intermediate stepping-stones are apparently not required along transatlantic routes because of the rarity of consecutive colonizations. However, intermediate stopovers are persistently used along short routes. In all cases, the long-term success of colonists, i.e. the establishment of stable local populations, appears to depend upon ecological factors. Main conclusions The puzzling patterns of distribution found in the South Atlantic seem primarily the outcome of allopatric speciation and of the interaction of long distance dispersal abilities and ecological processes. Successfulness of the colonization of remote sites appears to be less dependent from dispersal ability than upon persistence ability or settlement preferences.