Isolation and speciation of tidepool fishes as a consequence of Quaternary sea-level fluctuations

Dispersal is fundamental to the colonization of oceanic islands that were never connected to larger landmasses. For species with limited dispersal capabilities, colonization of remote islands can be followed by isolation and speciation. The tidepool fish community of Trindade Island, 1,160 km off the Brazilian coast at the eastern end of the Vitria-Trindade Chain, is composed of 18 species from 11 families. Four endemics accounted for 48 % of the total number and 10 % of the total fish weight in tidepools. The fact that the five species confirmed to be endemic to Trindade are restricted to intertidal and shallow waters indicate that in the present interglacial period the seamounts of the Vitria-Trindade Chain do not allow dispersal following a stepping-stones model. Thus, seamounts must have been used as stepping-stones when emerged during lower sea-level periods of the Pleistocene, but this connection was definitively interrupted when they became submerged at the end of the last glaciation. This highlights the importance of considering sea level fluctuations as a structuring factor of intertidal and shallow water communities at oceanic localities.