There is increasing evidence that continental slope ecosystems represent one of the major repositories of benthic marine biodiversity. The enhanced levels of biodiversity along slopes are hypothesized to be a source of biodiversity for continental shelves and deeper basins. Continental margins are increasingly altered by human activities, but the consequences of these anthropogenic impacts on benthic biodiversity and ecosystem functioning are almost completely unknown. Thus, there is an urgent need to gather sufficient information to enable us to understand patterns and drivers of deep-sea biodiversity along continental margins. Although the local diversity of some deep open slope ecosystems is moderately well documented, very little is known about the biodiversity of these systems at greater spatial scales. Topographic setting, hydrodynamic forcing, and the biogeochemical characteristics of the deep-sea floor may play key roles in promoting and sustaining high biodiversity along the open slopes of continental margins. HERMES provided the opportunity to acquire a significant volume of information on the biodiversity, trophic conditions, and topographic characteristics of open slopes across European margins, increasing our knowledge of the latitudinal, longitudinal, and bathymetric patterns of benthic biodiversity, and extending our comprehension of the mechanisms driving deep-sea biodiversity and its potential loss. Improved knowledge of these processes is needed to inform policy decisions for promoting sustainable management of open slopes and deep-sea ecosystems along continental margins.

Danovaro, R., M. Canals, C. Gambi, S. Heussner, N. Lampadariou, and A. Vanreusel. 2009. Exploring benthic biodiversity patterns and hotspots on European margin slopes. Oceanography 22(1):16–25, https://doi.org/10.5670/oceanog.2009.02.

Bauer, J.E., and E.R.M. Druffel. 1998. Ocean margins as a significant source of organic matter to the deep open ocean. Nature 392:482–485.

Canals, M., P. Puig, S. Heussner, X. Durrieu de Madron, A. Palanques, and J. Fabres. 2006. Flushing submarine canyons. Nature 444:354–357.

Clarke, A., and A. Crame. 1997. Diversity, latitude and time: Patterns in the shallow sea. Pp. 122–147 in Marine Diversity: Patterns and Processes. R.F. Ormond, J.D. Gage, and M.V. Angel, eds, Cambridge University Press, Cambridge.

Crame, J.A. 2000. Evolution of taxonomic diversity gradient in the marine realm: Evidence from the composition of recent bivalve faunas. Paleobiology 26:188–241.

Culver S.J., and M.A. Buzas. 2000. Global latitudinal species diversity gradient in deep-sea benthic foraminifera. Deep-Sea Research Part I 47:259–275.

Danovaro, R., A. Dinet, G. Duineveld, and A. Tselepides. 1999. Benthic response to particulate fluxes in different trophic environments: A comparison between the Gulf of Lions-Catalan Sea (western Mediterranean) and the Cretan sea (eastern Mediterranean). Progress in Oceanography 44:287–312.

Danovaro, R., C. Gambi, A. Dell’Anno, C. Corinaldesi, S. Fraschetti, A. Vanreusel, M. Vincx, and A.J. Gooday. 2008a. Exponential decline of deep-sea ecosystem functioning linked to benthic biodiversity loss. Current Biology 18:1–8.

Danovaro, R., C. Gambi, N. Lampadariou, and A. Tselepides. 2008b. Deep-sea biodiversity in the Mediterranean Basin: Testing for longitudinal, bathymetric and energetic gradients. Ecography 31:231–244.

Dell’Anno, A., and R. Danovaro. 2005. Extracellular DNA plays a key role in deep-sea ecosystem functioning. Science 309:2,179.

Etter, R.J., and J.F. Grassle. 1992. Patterns of species diversity in the deep sea as a function of sediment particle size diversity. Nature 369:576–578.

Gooday, A.J., B.J. Bett, R. Shires, and P.J.D. Lambshead. 1998. Deep-sea benthic foraminiferal diversity in the NE Atlantic and NW Arabian sea: A synthesis. Deep-Sea Research Part II 45:165–201.

Gray J.S., G.C.B. Poore, K.I. Ugland, R.S. Wilson, F. Olsgard, and Ø. Johannessen. 1997. Coastal and deep-sea benthic diversities compared. Marine Ecology Progress Series 159:97–103.

Gray, J.S. 2000. The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf. Journal of Experimental Marine Biology and Ecology 250:23–49.

Hoste, E., S. Vanhove, I. Schewe, T. Soltwedel, and A. Vanreusel. 2007. Spatial and temporal variations in deep-sea meiofauna assemblages in the Marginal Ice Zone of the Arctic Ocean. Deep-Sea Research Part I 54:109–129.

Jahnke, R. 1996. The global ocean flux of particulate organic carbon, areal distribution and magnitude. Global Biogeochemistry Cycles 10:71–88.

Lambshead, P.J.D., and G. Boucher. 2003. Marine nematode deep-sea biodiversity—hyperdiverse or hype? Journal of Biogeography 30:475–485.

Lambshead, P.J.D., and P. Schalk. 2001. Overview of marine invertebrate biodiversity. Pp. 543–559 in Encyclopaedia of Biodiversity, Volume 3. S. Levin, ed., Academic Press, San Diego, California.

Lambshead, P.J.D., J. Tietjen, T.J. Ferrero, and P. Jensen. 2000. Latitudinal diversity gradients in the deep sea with special reference to North Atlantic nematodes. Marine Ecology Progress Series 194:159–167.

Levin, L.A., and J.D. Gage. 1998. Relationships between oxygen, organic matter and the diversity of bathyal macrofauna. Deep-Sea Research Part I 45:129–163.

Levin, L.A., R.J. Etter, M.A. Rex, A.J. Gooday, C.R. Smith, J. Pineda, C.T. Stuart, R.R. Hessler, and D. Pawson. 2001. Environmental influences on regional deep-sea species diversity. Annual Review of Ecology and Systematics 32:51–93.

Macpherson, E., and C.M. Duarte. 1994. Patterns in species richness, size, and latitudinal range of East Atlantic fishes. Ecography 17:242–248.

McClain, C.R. 2005. Bathymetric patterns of morphological disparity in deep-sea gastropods from the western north Atlantic basin. Evolution 59:1,492–1,499.

McClain, C.R., and R.J. Etter. 2005. Mid-domain models as predictors of species diversity patterns: Bathymetric diversity gradients in the deep sea. Oikos 109:555–566.

Myers, N., R.A. Mittermeier, C.G. Mittermeier, G.A.B. da Fonseca, and J. Kent. 2000. Biodiversity hotspots for conservation priorities. Nature 403:853–858.

Rex, M.A. 1981. Community structure in the deep-sea benthos. Annual Review of Ecology and Systematics 12:331–353.

Rex, M.A., C.R. McClain, N.A. Johnson, R.J. Etter, J.A. Allen, P. Bouchet, and A. Warén. 2005. A source-sink hypothesis for abyssal biodiversity. The American Naturalist 165:163–178.

Rex, M.A., C.T. Stuart, and G. Coyne. 2000. Latitudinal gradients of species richness in the deep-sea benthos of the North Atlantic. Proceedings of the National Academy of Sciences of the United States of America 97:4,082–4,085.

Rex, M.A., C.T. Stuart, R.R. Hessler, J.A. Allen, H.L. Sanders, and G.D.F. Wilson. 1993. Global-scale latitudinal patterns of species diversity in the deep-sea benthos. Nature 365:636–639.

Rex, M.A., R.J., Etter, and C.T., Stuart. 1997. Large-scale patterns of species diversity in the deep-sea benthos. Pp: 94–121 in Marine Biodiversity: Patterns and Processes. R.F.G. Ormond, J.D. Gage, and M.V. Angel, eds, Cambridge University Press, Cambridge.

Ricklefs, R.E., and D. Schluter. 1993. Species Diversity in Ecological Communities: Historical and Geographical Communities. University of Chicago Press, 414 pp.

Rohde, K. 1999. Latitudinal gradients in species diversity and Rapoport’s rule revisited: A review of recent work and what can parasites teach us about the causes of the gradients? Ecography 22(6):593–613.

Rosenzweig, M.L. 1995. Species Diversity in Space and Time. Cambridge University Press, Cambridge, 460 pp.

Roy, K., D. Jablonski, J.W. Valentine, and G. Rosenberg. 1998. Marine latitudinal diversity gradients: Tests of causal hypotheses. Proceeding of the National Academy of Sciences of the United States of America 95:3,699–3,702.

Stuart, C.T., M.A. Rex, and R.J. Etter. 2003. Large spatial and temporal patterns of deep-sea benthic species diversity. Pp. 295–311 in Ecosystems of the World: Ecosystems of Deep Oceans. P.A. Tyler, ed., Elsevier, Amsterdam.

Thomas, E., and A.J. Gooday. 1996. Cenozoic deep-sea benthic foraminifers: Tracers for changes in oceanic productivity? Geology 24:355–358.

Vincx M., B.J. Bett, A. Dinet, T. Ferrero, A.J. Gooday, P.J.D. Lambshead, O. Pfannkuche, T. Soltwedel, and A. Vanreusel. 1994. Meiobenthos of the deep Northeast Atlantic. Advances in Marine Biology 30:2–88.

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.