Global seafloor connectivity over evolutionary time

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. In 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 North Atlantic and
Southern Australia, on the opposite sides of the globe. 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.