1 Evaluating the importanceenvironmental drivers of Species variability and connectivity in the deep sea: evaluating effects of spatial heterogeneity variability in and forand hydrodynamicsfree- living nematode assemblagess in the deep seaalong the Portuguese margin 5 Lidia Lins 1,2 , Frederik Leliaert 1 , Torben Riehl 3 , Sofia Pinto Ramalho 1,4 , Eliana Alfaro Cordova 5 , André Morgado Esteves 2 , Ann Vanreusel 1 1 Marine Biology research group, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium, lidia.linspereira@ugent.be, 10 Tel:+32 (0)9 264 8531 2 Meiofauna Laboratory, Federal University of Pernambuco, Av. Prof Moraes Rego 1235, 50670-901, Cidade Universitária, Brazil 3 CeNak, Center of Natural History, University of Hamburg - Zoological Museum, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany 15 4 Departamento de Biologia & CESAM, Universidade de Aveiro, Campus de Santiago, 3810-193, Aveiro, Portugal 5 Prodelphinus, Jose Galvez 780-E, Lima 18, Peru Correspondence to: Lidia Lins (Lidia.linspereira@ugent.be) Abstract Understanding processes responsible for shaping biodiversity patterns on continental margins is an important requirement for 20 comprehending anthropogenic impacts in these environments. Continental margins perform crucial functions which are mainly structured by hydrodynamic effects and surface primary productivityproductivity and POC flux to the seafloor, but also by heterogeneity in seafloor characteristics. 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 habitat sediment heterogeneityhydrodynamic effects affect nematode alpha and beta diversity at different 25 depths in similar ways. We also examined the potential role of connectednesstivity 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 along the margin. 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. 30 Our study also demonstrated that higher hydrodynamics bottom stress 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)