Spatiotemporal faunal connectivity across global sea floors.

Our knowledge of biogeographic patterns and processes in the deep sea has been limited by the lack of integrated datasets that cover its vast extent. Here we analyse a new global dataset of genomic DNA sequences, spanning an entire taxonomic class of benthic invertebrates (Ophiuroidea), to obtain a broad understanding of phylogenetic divergence and biotic movement across all oceans, from coastal margins down to the abyssal plains. We show that regional faunas on the continental shelf are phylogenetically divergent, particularly at temperate and tropical latitudes. By contrast, assemblages in the deep sea are much more connected. Many temperate deep-sea lineages have achieved distribution ranges across the planet, including over the Quaternary period. A close relationship exists between deep-sea faunas of the northern Atlantic and, on the opposite side of the globe, southern Australia. Bathymetric interchange is not only reliant on vertical migration through isothermal polar waters but also occurs across the thermal depth gradients of tropical regions. The connected nature of deep-sea life should be an important consideration in marine conservation assessments.