Do physical barriers hamper dispersal in the deep sea?

The presence of topographic features, such as mid-ocean ridges, can divide the abyss into basins, which can be interconnected through gaps and potentially affect species distribution and dispersal. Holding endemic and widespread species, nematodes represent ideal organisms to study species-range sizes, dispersal, distribution, and turnover in the deep sea. On board of the RV Sonne to the Vema Fracture Zone (VFZ), our study aimed to investigate if: a) The VFZ represent a barrier to gene flow; b) Genetic differentiation increase with increasing geographic distance; c) Species-range size for nematodes (< 100 km vs. > 1000 km)?. Based on integrative taxonomy (molecular and morphology-based methods) and community analyses, our results suggest no geographical trend, indicating a weak correlation between genetic divergence and geographical distance. Nevertheless, most species were restricted to one area (62.5 – 76 %), while 24 – 37.5 % of the species were shared between areas. These results suggest that the VFZ may not limit dispersal completely, reacting like a sharp boundary, but it might act as a transition zone, restricting dispersal. Additionally, our results bring new insights on species turnover and species-range sizes in the deep sea, which will help to manage and estimate the potential impacts of anthropogenic activities.