It is observed that low concentrations of dissolved oxygen (DO) act as natural stressors for deep-sea coral ecosystems. Nonetheless, recent findings are progressively challenging this notion. Here, we describe a surprisingly well-structured megabenthic community found at 780-1000 m deep cliffs in the severe hypoxic waters of Barkley Canyon (NE Pacific). This area is bathed by the NE Pacific Oxygen Minimum Zone (OMZ), spanning across a wide depth range (530-1450 m). Yet, ROV surveys revealed unexpectedly rich and well-preserved benthic assemblages, structurally dominated by the black coral Chrysopathes speciosa and the bubblegum coral Sibogagorgia cauliflora, together with other octocorals and sponges. These cliffs are also inhabited by hundreds of fish individuals mainly represented by Sebastolobus alascanus (shortspine thornyhead) including many juveniles, possibly indicating a nursery area. Preliminary results indicate that the abundance of structuring species decreases away from the canyon axis, suggesting that along-canyon hydrodynamic processes play a role in the maintenance of these ecosystems. Decade-long time-series from Ocean Networks Canada’s NEPTUNE cabled seafloor observatory reveal extremely low average DO values (0.28 ml·L-1), with corresponding low average temperatures (3.6 °C). In-situ Acoustic Doppler Current Profiler measurements revealed the occurrence of semidiurnal internal tides with amplitudes of up to 200 m. We hypothesize that the breaking of internal tide waves on the steep topography of Barkley Coral Cliffs triggers the resuspension of sediments, which are rich in organic matter according to previous studies. Despite the permanent natural stressor of the OMZ’s severe hypoxia, the well-developed black coral communities on the canyon cliffs may be thriving on an abundant and organic-rich suspended particle load provided by local hydrodynamics. Studies focusing on the ecological responses, physiological and metabolic adaptations of black corals to severe hypoxia are currently lacking. The present study will provide insights onto deep-sea ecosystem responses to long-term climate change, in particular in the E and NE Pacific, where OMZs are rapidly expanding due to climate change

6th International Network for Submarine Canyon Investigation and Scientific Exchange (INCISE), 4-7 December 2023, Wellington, New Zealand