Species variability and connectivity in the deep sea: evaluating effects of spatial heterogeneity and hydrodynamics

Understanding processes responsible for shaping biodiversity patterns on continental margins is an important requirement for comprehending anthropogenic impacts in these environments. Continental margins perform crucial functions which are mainly structured by hydrodynamic effects and surface primary productivity. However, to what extent these processes control benthic local and regional biodiversity remains unclear. In this study, we focused on two isobathic parallel transects to test if food resources arriving at the seafloor and hydrodynamic effects affect alpha and beta diversity at different depths in similar ways. 20 We also examined the potential role of connectivity between both depths as a result of dispersal. This is the first study applying integrative approaches using molecular and morphological techniques in combination with environmental factors to unravel spatial variability and connectivity in relation to depth in the deep sea. Results revealed that high variability in resource availability is directly linked to high alpha diversity and spatial heterogeneity, and that communities dwelling in deeper regions are able to use resources complementarily promoting species coexistence. Our study also demonstrated that higher 25 hydrodynamics at the shallower habitats near the shelf break, as inferred from the high sediment heterogeneity, promoted variation in community structure across stations (higher beta diversity) compared to the deeper area. In addition, phylogenetic relationships revealed no evidence for depth-endemic lineages or isolation per habitat, indicating regular species interchanges across different depths.