The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep‐sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep‐sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold‐water coral and commercially important deep‐sea fish species under present‐day (1951–2000) environmental conditions and to project changes under severe, high emissions future (2081–2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%–100% in suitable habitat for cold‐water corals and a shift in suitable habitat for deep‐sea fishes of 2.0°–9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%–30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%–42% of present‐day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%–14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep‐sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area‐based planning and management tools.

Deep-sea corals are fragile and long-lived species that provide important habitat for a variety of taxa. The rarity of in situ observations in deep waters off Newfoundland, Canada, motivated the first extensive deep-sea research cruise to that region in 2007. We conducted 7 dives in 3 canyons (Haddock Channel, Halibut Channel, and Desbarres Canyon) with ROPOS (Remotely Operated Platform for Ocean Science). Over 160 000 coral colonies were enumerated and, of the 28 species found, Acanella arbuscula, Pennatula spp., and Flabellum spp. were most frequently observed. The largest coral observed was Keratoisis grayi at over 2 m in height. Corals spanned the entire depth range sampled (351 to 2245 m) and inhabited all bottom types surveyed, but boulder and cobble habitats were most species-rich. Assemblages differed significantly with depth class and bottom type. The unique assemblage at outcrops was strongly driven by the presence of Desmophyllum dianthus. Keratoisis grayi, D. dianthus, and Anthomastus spp. were largely absent in mud-sand habitats. Sea pen meadows covered large tracts of muddy seafloor spanning >1 km. Acanella arbuscula and Flabellum spp. characterised large coral fields with abundant corals but relatively low species richness. These results highlight not only the importance of hard structure in determining patterns of coral distributions, abundances, and assemblages, but also the need to focus conservation efforts on a variety of habitats to ensure protection for the full suite of deep-sea coral species.

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