Oceanic barriers as indicated by scombrid fishes and their parasites

Four genera of scombrid fishes (26 species) and their copepod (32 species) and monogenean ectoparasites (25 species) were used to test the hypothesis that the East Pacific Barrier is responsible for the most pronounced break in the circum-tropical warm water fauna of the continental shelves, and not the New World Barrier. Analysis at the species level showed that there is a primary centre of diversity in the West Pacific, and a secondary centre in the West Atlantic. The former, almost entirely, shares its species of the largely coastal Scomberomorus and Grammatorcynus and their parasites with seas located to the west. Only four parasites (all copepods) are shared by the East and West Pacific, and they are circum-tropical. In contrast, the West Pacific shares species of the more pelagic Scomber and their parasites with seas both to the east and west, although at the genus level, only two circum-tropical monogenean genera are shared by the E and W Pacific. We conclude that the East Pacific Barrier has been a 100% or almost 100% effective barrier to dispersal of species of Scomberomorus, Grammatorcynus and their parasites, whereas for species of Scomber and their parasites, the East Pacific has been a less effective barrier.