Deep beneath the ocean’s surface, in the darkness far below sunlight’s reach, lie hidden forests of cold-water corals (CWCs). Unlike their tropical counterparts, these corals survive without sunlight and can colonize the vertical walls of submarine canyons, fjords, and marine troughs (Orejas et al., 2009; Huvenne et al., 2011; Robert et al., 2020; Cote et al., 2023). These vertical habitats are biodiversity hotspots, offering shelter, feeding grounds, and nursery spaces for a wide range of marine life (Orejas et al., 2009; Huvenne et al., 2011; Robert et al., 2020). In essence, they act as underwater skyscrapers, concentrating species and biomass in an otherwise sparse deep-sea environment.

The unique vertical orientation of these habitats gives them ecological advantages over flatter seafloor areas. Research indicates that wall reefs on canyon slopes can support up to five times more biomass than adjacent flat regions (Greiffenhagen et al., 2024), while also hosting higher species diversity and denser populations (Robert et al., 2020; Morris et al., 2013; Lo Iacono et al., 2018; Robert et al., 2015). These steep structures create a variety of microhabitats — from ledges to crevices — where fish, invertebrates, and the corals themselves can thrive. In this way, vertical CWC habitats play a critical role in maintaining healthy and resilient deep-sea ecosystems (Costello et al., 2005; Baillon et al., 2012).

Despite their importance, CWCs grow extremely slowly and cannot move, which makes them highly sensitive to human impacts. Bottom trawling, deep-sea mining, and ocean acidification all pose serious threats (Roberts et al., 2000; Thrush & Dayton, 2002; Turley et al., 2007). Studies indicate that some deep-sea corals grow only 33–75 micrometers per year (Sherwood & Edinger, 2009) and show little to no recovery even over a decade in disturbed areas (Huvenne et al., 2016). Fortunately, vertical walls may offer some natural protection from trawling and can even act as sources for recolonizing nearby damaged habitats (Robert et al., 2020).

Studying these habitats has long been challenging because of their depth and remote locations. Traditional trawl surveys cannot reach many canyon walls, and steep vertical terrain is difficult to sample (Rideout & Ings, 2018). Remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) have become essential tools for exploring these environments (Cote et al., 2023; Edinger et al., 2011; Auster et al., 2013; Brooke & Ross, 2014; Buhl-Mortensen et al., 2017; Miles, 2018). Although these technologies are not new, their improving capabilities allow researchers to pair them with detailed environmental measurements — such as high-resolution bathymetry, water temperature, current patterns, and sediment composition — to build predictive models that identify where coral habitats are most likely to occur (Kinlan et al., 2020). These models help guide future surveys, reveal previously unknown ecosystems, and deepen scientific understanding of how vertical coral communities form and persist.

As industrial activity in the deep sea grows, the need to understand and protect these ecosystems becomes more urgent. Oil and gas exploration, increased marine traffic, and climate-driven changes threaten the delicate balance of these habitats. Effective conservation and management rely on accurate knowledge of where CWCs occur, how they function, and which species depend on them.

Protecting deep-sea corals is not only a task for scientists and policymakers; everyday actions help safeguard the oceans. Reducing pollution, properly disposing of chemicals, supporting sustainable seafood choices, and backing organizations that protect marine environments all contribute to healthier oceans. Even small steps on land ripple outward, helping maintain the health of distant deep-sea ecosystems.

Vertical cold-water coral habitats may be hidden from view, but they are crucial to life in the deep ocean. By protecting these underwater skyscrapers, we preserve the biodiversity they support — and in doing so, ensure the continued vitality of the oceans that sustain our planet.

References

Auster, P. J., Kilgour, M., Packer, D., Waller, R., Auscavitch, S., & Watling, L. (2013). Octocoral gardens in the Gulf of Maine (NW Atlantic). Biodiversity, 14(4), 193–194. https://doi.org/10.1080/14888386.2013.850446

Baillon, S., Hamel, J. F., Wareham, V. E., & Mercier, A. (2012). Deep cold-water corals as nurseries for fish larvae. Frontiers in Ecology and the Environment, 10(7), 351–356. https://doi.org/10.1890/120022

Brooke, S., & Ross, S. W. (2014). First observations of the cold-water coral Lophelia pertusa in mid-Atlantic canyons of the USA. Deep-Sea Research Part II: Topical Studies in Oceanography, 104, 245–251. https://doi.org/10.1016/j.dsr2.2013.06.011

Buhl-Mortensen, P., Gordon, Jr. D. C., Buhl-Mortensen, L., & Kulka, D. W. (2017). First description of a Lophelia pertusa reef complex in Atlantic Canada. Deep Sea Research Part I: Oceanographic Research Papers, 126, 21–30. https://doi.org/10.1016/j.dsr.2017.05.009

Cote, D., Neves, B. M., Angnatok, J., Bartlett, W., Edinger, E. N., Gullage, L., Laing, R., Normandeau, A., Hayes, V. E., Sherwood, O. A., & Geoffroy, M. (2023). Local ecological knowledge and multidisciplinary approach lead to discovery of hidden biodiversity in the deep ocean of Labrador, Canada. Ecology and Society, 28(4). https://doi.org/10.5751/ES-14325-280404

Costello, M. J., McCrea, M., Freiwald, A., Lundälv, T., Jonsson, L., Bett, B. J., van Weering, T. C. E., de Haas, H., Roberts, J. M., & Allen, D. (2005). Role of cold-water Lophelia pertusa coral reefs as fish habitat in the NE Atlantic (pp. 771–805). Springer Berlin Heidelberg. https://doi.org/10.1007/3-540-27673-4_41

Edinger, E. N., Sherwood, O. A., Piper, D. J. W., Wareham, V. E., Baker, K. D., Gilkinson, K. D., & Scott, D. B. (2011). Geological features supporting deep-sea coral habitat in Atlantic Canada. Continental Shelf Research, 31(2, supplement), S69–S84. https://doi.org/10.1016/j.csr.2010.07.004

Greiffenhagen, L., Kutti, T., Maier, S. R., & De Clippele, L. H. (2024). Biomass mapping of fjordic cold-water coral reefs reveals distinct functional role of vertical wall habitat. Deep-Sea Research Part I: Oceanographic Research Papers, 211. https://doi.org/10.1016/j.dsr.2024.104350

Huvenne, V. A. I., Bett, B. J., Masson, D. G., Le Bas, T. P., & Wheeler, A. J. (2016). Effectiveness of a deep-sea cold-water coral Marine Protected Area, following eight years of fisheries closure. Biological Conservation, 200, 60–69. https://doi.org/10.1016/j.biocon.2016.05.030

Huvenne, V. A. I., Tyler, P. A., Masson, D. G., Fisher, E. H., Hauton, C., Hühnerbach, V., Bas, T. P., & Wolff, G. A. (2011). A picture on the wall: Innovative mapping reveals cold-water coral refuge in submarine canyon. PLoS ONE, 6(12). https://doi.org/10.1371/journal.pone.0028755

Kinlan, B. P., Poti, M., Drohan, A. F., Packer, D. B., Dorfman, D. S., & Nizinski, M. S. (2020). Predictive modeling of suitable habitat for deep-sea corals offshore the Northeast United States. Deep Sea Research Part I: Oceanographic Research Papers, 158, 103229. https://doi.org/10.1016/j.dsr.2020.103229