Connectivity in the Clarion-Clipperton Zone: a review

Lara Macheriotou ^1* Sven Rossel ² Massimiliano Molari ³ Pedro Martinez Arbizu ² Saskia Brix ² Magdalini Christodoulou ⁴ Pierre-Antoine Dessandier ⁵ Ana Hilário ⁶ Felix Janssen ⁷ Erik Simon-Lledó ⁸ Lenaick Menot ⁹ Ellen Pape ¹ Gustavo A. Ramírez ¹⁰ Ann Vanreusel ¹

• ¹ Ghent University, Ghent, Belgium
• ² Department of Marine Research, Senckenberg am Meer, Wilhelmshaven, Germany
• ³ Max Planck Institute for Marine Microbiology, Max Planck Society, Bremen, Bremen, Germany
• ⁴ Biologiezentrum, Linz, Austria
• ⁵ Laboratoire d'écologie benthique côtière, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Plouzané, France
• ⁶ Department of Biology, University of Aveiro, Aveiro, Portugal
• ⁷ Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven, Bremen, Germany
• ⁸ National Oceanography Centre, University of Southampton, Southampton, England, United Kingdom
• ⁹ Centre de Bretagne, Institut Français de Recherche pour l'Exploitation de la Mer, Plouzane, France
• ¹⁰ California State University, Northridge, Los Angeles, California, United States

temperature, pressure, oxygen) are absent, meaning that the connectivity of benthic communities could operate across thousands of km. Our understanding of fundamental processes, such as dispersal and connectivity, that regulate biodiversity at such large scales, is severely limited; thus, synthesising our currently available knowledge across all benthic size classes [i.e., microbes (<32 µm), meiofauna (> 32 µm), macrofauna (>300 µm), megafauna (>1 cm)], is critical to guide conservation efforts as well as future research.The umbrella-term "connectivity" is used ubiquitously to refer to (i) genetic, (ii) demographic, (iii) biological, (iv) ecological, (v) structural, and/or (vi) functional connectivity (Selkoe et al., 2016). All seek to describe and understand the continuity of species distributions in space and time via different avenues. Beta diversity, which is defined as the shift in species composition among sites (Whittaker, 1960), can be used as an indirect measure of connectivity between communities and more generally to study biogeography (i.e., distribution of taxa across space and time). The biogeography of organisms is controlled by four fundamental processes: dispersal, ecological drift, selection, and mutation (Hanson et al., 2012). It is thought that the scale, direction, frequency and intensity of species dispersal is most influential for deep-sea connectivity (Baco et al., 2016;Hilário et al., 2015). The interaction of these processes manifests in two major biogeographical patterns: the taxa-area relationship, i.e., the positive relationship between the number of taxa in an area and the size of that area (Arrhenius, 1921); and the distance-decay relationship, i.e., the decline in community similarity over increasing geographical distance (Nekola & White, 1999). Several studies have identified taxa-area and distance-decay relationships in marine microbes, with stronger patterns in heterogeneous and island-like habitats than in continuous ones (Zinger et al., 2011(Zinger et al., , 2014)). Microbial dispersal is shaped by intrinsic taxon-specific traits (e.g., spore formation, morphology, habitat specificity) and extrinsic factors such as population size (