Records of Normanellidae Lang, 1944 (Copepoda, Harpacticoida) from Madeira island support the hypothetical role of seamounts and oceanic islands as “stepping stones” in the dispersal of marine meiofauna

Abstract

Many meiofauna species show a wide and even amphioceanic distribution with populations separated by thousands of kilometres of oceanic deep sea despite their apparently limited dispersal potential (the “meiofauna paradox”). Several studies have attempted to explain this contradiction. One hypothesis is that seamounts act as “stepping stones” in the dispersal of meiofauna, supporting the colonisation of remote habitats by chance dispersal. This would be confirmed if meiofauna species were found on oceanic elevations located between apparently fragmented populations. To test this hypothesis we studied the littoral Normanellidae (Copepoda, Harpacticoida) of the Portuguese islands Madeira and Porto Santo and reviewed their known geographical distribution. All three species of Normanellidae recorded on Madeira were already described from other inshore shallow-water habitats. Furthermore, we also recovered one of these species, Normanella pallaresae, formerly only known from the Argentinian coast, on the summit of Seine Seamount, in the adjacent deep sea of Sedlo Seamount and in a Mediterranean cave. The presence of this species on the Atlantic elevations provides a link in its amphiatlantic distribution and faunistic evidence for the “stepping stone” hypothesis. A re-description of Normanella pallaresae is also provided.