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The Madeira archipelago has a unique underwater landscape that is characterised by narrow shelves, steep slopes and a large submarine tributary system that boosts primary productivity in oligotrophic waters and thus offers a potential for hotspots of biodiversity. Despite this, there have been limited deep-water exploration activities with less than five expeditions since the 1960s. Here, we investigated the seabed on the southern side of the Madeira-Desertas Ridge using a manned submersible along a 3.8 km long transect starting at 366 m depth up the ridge shelf until its top at 73 m. Benthic habitats and community composition were documented with video along a depth gradient from mesophotic to deep sea. Six distinct biotopes were recognised (three deeper, and three shallower than 115 m depth). Our results showed a rich biodiversity with deep biotopes characterised by sponges and non-reef-building corals (e.g., Pachastrella monilifera, Viminella flagellum, Eunicella verrucosa) and shallow biotopes comprising macroalgae and the gorgonian Paramuricea cf. grayi. The pronounced benthic zonation reflects the steep environmental gradient that includes high topographic variation, heterogeneous substrates, and bidirectional regular wave-motion at the shallow mesophotic part. Together with biotic factors, such as low density of sea urchins and presence of predatory fish, this environment with unusual deep light penetration, a mesoscale cyclonic eddy, and deep wave-motion, has allowed the establishment of a mature deep-water kelp population of Laminaria ochroleuca in the plateau (max. >100 individuals p/100 m2). At the same time, a conspicuous coral fauna was observed on a wide range of soft to hard bottoms with several species taking advantage of the favourable hydrodynamic regime and seawater properties together with substratum availability to create coral gardens. These habitats were previously not known from Madeira, and their newfound discovery in the archipelago merit further investigation and protection.

The presence of the opal chimaera, Chimaera opalescens, is reported for the first time in the deep waters of the Azores, with the capture of four specimens by fishermen and the video recording of an additional five individuals. Species identification was supported by the 646 bp sequenced fragment of the mitochondrial gene cytochrome oxidase subunit I. Because C. opalescens is a recently recognised species that had been recurrently misidentified as rabbitfish, Chimaera monstrosa, the historical data of C. monstrosa in the Azores were reviewed to assess the possible presence of both Chimaera species in the region. Although several authors have reported the occurrence of C. monstrosa in the Azorean waters since the 1800s, the majority of these are based on only three specimens caught during the late 1800s. The investigation performed using literature and examination of the museum specimens still available concluded that the most likely scenario is that C. monstrosa is absent from the Azores and past records of that species in the region are most likely misidentifications of C. opalescens.

During a 950 m depth submarine-dive South of Pico Island (Azores) an adult Trachipterus arcticus (Brünnich, 1788) was observed for about 50 seconds. Additionally, a small specimen of the same species with some larval characters was observed near to the surface in the harbour of Horta (Faial Island, Azores). This specimen was caught and observed for 45 minutes in an aquarium. We are reporting here the respective observations on live colouration, external characters, swimming and luring behaviour.

This report describes the DeepWalls survey aimed to characterize and map the distribution of deep-sea megafaunal communities associated with vertical walls in the Azores by means of the submarine LULA1000 of the Rebikoff-Niggeler Foundation (FRN). The primary target areas for the submersible dives were the South of Pico and São Jorge Islands, where the existence of communities of interest in vertical walls had already been identified during exploratory dives performed by FRN based on the information compiled in the database (Deliverable 1.1). Five submersible dives were undertaken in 2020 in the vertical walls down to 1000 m depth around the islands of Pico and São Jorge. In addition to these dives, in August 2019, the DeepWalls team coordinated two dives on seamount ridge Baixo de São Mateus, located south of Pico Island. Theses dives, financed by Oceano Azul Foundation, collected information for the DeepWalls project and to support the process of identifying new areas of interest for conservation in the Azores EEZ under the Blue Azores program, in partnership with the Oceano Azul Foundation (FOA).