The deep-sea component of the OceanX 2023 expedition revealed that banks and seamounts heavily exploited by bottom longline fishing are still home deep-sea benthic communities with a high natural and ecological value.

1. During the OXR 2023 we visited 7 different areas, and mapped 3,840 km2 of seabed, of which 630 km2 is new information to be included in official Portuguese databases. We were able to participate in 8 manned submarine dives and 12 remotely operated vehicle dives, which produced 84:30 hours of deep sea video, over 19 km of bottom, and 268 biological samples. We also performed 27 stations for analysis of water masses, in which 157 samples were collected for analysis of environmental DNA and other parameters.
2. We observed big basalt outcrops at around 800 m depth that were densely colonized by many colonies of the black coral Leiopathes expansa. Most of the colonies observed were visually healthy, particularly large, probably older than 1.000 years, and with a lot of associated biodiversity. It is possible that before demersal fishing exploited this bank, these arborescent black corals, vulnerable to fishing, were even much more abundant, larger and older. These corals are very slow growing and can live for thousands of years.
3. We also discovered one of the few (and small) hard coral reefs known in the Azores composed by the lace corals Lophelia pertusa and Madrepora occulata. This small reef was observed at around 850 m depth in the Capelinhos area, west of Faial. Hard coral reefs play an important role in the biogeochemical cycles of the deep sea, but are very vulnerable to ocean acidification. Some portions of this reef were not alive, forming a compact coral framework to which many other associated species were attached. A better understanding of their distribution and their susceptibility to climate change are priority lines of research for the future.
4. We also discovered one of the largest and densest coral garden dominated by the primnoid Callogoria verticillata found in the Azores. This gorgonian forest, found on the Dom João de Castro seamount, is characterized by fan-shaped colonies whose feathery branches resemble palm leaves. Most of the colonies observed were smaller than usual, but this was possibly the densest aggregation of this species observed in the Azores so far.
5. We observed dense aggregations of the largest species of sponges that inhabit the deep sea of the Azores (e.g., Characella pachastrelloides, Haliclona magna), on the Princesa Alice bank. Sponges play a structuring role in the deep sea, increasing ecosystem productivity and creating habitat for other species.
6. In one of the areas explored with multibeam, an unknown canyon (or gorge) of about 15 km long, 340 m wide and with cliffs about 100 m high was found. The canyons and gorges of the Azores are fairly unknown habitats where unique ecosystems can be found.
7. The OceanX 2023 expedition made it possible to identify that a large part of the benthic communities, including corals and sponges, observed in one of the Azores' main demersal fishing grounds are still in good environmental condition and have a high natural and ecological value. However, some long-lived coral colonies with visible fishing impacts were observed. These in situ observations corroborate the conclusions of previous studies which suggest that well-regulated deep-sea fishing based on hook-and-line gear (preferably handlines) could contribute to a sustainable exploitation of the deep sea.
8. Using the sophisticated deep-sea exploration equipment available on the RV OceanXplorer, from manned submarines to an ROV, we were able to collect 268 biological samples belonging to approximately 197 different morphotypes. It is likely that this sampling effort will help solving about 100 taxonomic questions, and some samples could even reveal new species to science.