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In September-October 2016 the oceanographic cruise MEDWAVES was conducted (in the frame of the ATLAS project H2020), in order to follow the path of the Mediterranean Outflow Water (MOW) in the Atlantic from Cádiz to the Azores. MEDWAVES aimed to investigate the influence of the MOW in the community composition of benthic assemblages in several Atlantic geomorphological features. One of the targeted areas was the Ormonde seamount in the Atlantic Ocean, 160 nautical miles SW off Cape St. Vincent, Portugal. This seamount, together with the Gettysburg seamount, is part of a volcanic ridge named Gorringe that rises from 5,000 m to less than 80m depth, respectively representing the abyssal plain until the photic zone. Its panoply of marine life and environments increased the demand for conservation measures. Consequently, Gorringe bank is currently protected by the Habitats Directive and part of Natura 2000 network since 2015. Other protective measures include the intention to designate the Gorringe Bank,as part of the seamount complex Madeira-Tore, as new Portuguese MPA of large dimensions delimited in deep oceanic areas, under the Marine Strategy Framework Directive implementation. Given its ecological importance and location through the pass of the MOW, the Ormonde seamount was selected as one of the main target areas during the MEDWAVES cruise. Six ROV dives were conducted with the Remotely Operated Vehicle (ROV) “Liropus” (IEO), covering the Northeast and North flanks of the seamount between 1,950 and 600 meters depth. As expected, the depth gradient revealed different benthic communities in the distinct depth zones. Ormonde seems to be a flourishing area for deep-sea sponges (e.g. Asconema sp.), present in high densities along with high species diversity. Scleractinian corals (e.g. Solenosmillia variabilis) as well as gorgonians (e.g. Viminella sp., Corallium tricolor) and black corals (e.g. Stichopathes sp.) were also present in the area displaying varying density patterns in the different flanks of the seamount. The depth gradient is also related with a vertical variation of the water masses, among others, the MOW, located between 500 and 1,400 m depth, with salinities from 35.6 to 36.4 and temperatures between 10 and 12°C. In this work we present the first characterization of the deep benthic megafauna communities of Ormonde and its potential relation to depth, substrate type and water masses.

Mercator mud volcano has been explored by direct visual observations using a ROV at 350 to 370 m depth. Underwater images, taken mainly at the summit, have allowed characterizing the fluid venting environment, where different microforms, habitats and associated biota, with typical seepage components have been identified. Chemosynthetic bacterial communities were detected and sampled at the northeastern side of the summit at 350 m, next to pockmark-like depressions with diameters ranging 1 to 3 m, bioturbation marks, sediment mounds and authigenic carbonates of different sizes (0.1-5m length). Chemosynthesis-based communities were mainly composed by bacterial mats (patch diameter 10-30 cm), however some remains of cold seep chemosymbiotic bivalves (Lucinoma asapheus) were also found on the sediment. Habitat types at Mercator MV are influenced by oceanographic and sedimentation processes deposition and favouring fauna colonizing diverse substrate types, such as large sponges on slabs and sea-pens and annelids on soft bottoms.

In March 2014, the Spanish R/V Sarmiento de Gamboa equipped with the Portuguese multi-operational Remotely Operated Vehicle (ROV) "Luso 6000" explored and sampled five mud volcanoes of the Gulf of Cádiz during SUBVENT2 expedition. The explored mud volcanoes were Mercator, Yuma, Algacel, Mvseis and Madrid located offshore Moroccan Atlantic margin at water depths between 350 and 1650 meters. In addition, bathymetric data were acquired using the Atlas Hydrosweep DS multibeam echo-sounder and were processed with CARIS HIPS & SIPS yielding a bathymetric grid resolution of 15 m. The characterization of habitats and associated biota was based on high resolution videos and captured photographic material with MAGIX software as well as samples collected with the ROV. The observation was done during scanning the sea floor by TV camera at the altitude of 1-5 meters above the seafloor at low velocity of approximately 0.2-0.5m/s. Digital data analyses and their cartographical representation were performed with ArcMap 10.3.1 and Fledermaus. Underwater images allowed to characterize the occurrence of cold seeps with different seafloor micro-features, habitats and associated biota. Chemosynthetic bacterial communities, mainly occurring as bacterial mats (e.g., sulfate-oxidizing cf. Beggiatoa sp.), were detected, sampled and related to active bubbling seeps in pockmark-like depressions of different sizes. Sediment mounds and authigenic carbonates of different sizes (0.1-5 m length) were also detected in vent sites. Six different species of chemosymbiotic bivalves, including Lucinoma asapheus, Acharax gadirae, Solemya elarraichensis, Thyasira vulcoluatre, Isorropodon megadesmus and the deep water mussel Bathymodiulus mauritanicus displayed populations in the studied mud volcanoes. Hard bottoms with exhumated carbonate slabs seem to display a wider biodiversity and complexity, including large size sponges (e.g. Geodia, Phakellia), scleractinians (e.g. Caryophillia, Corallium, Madrepora), gorgonians (e.g. Bebryce, Chelidonisis) and antipatharians (e.g. Stichopathes) as well as different mobile associated species.. Habitat types of these mud volcanoes may be influenced by different oceanographic, sedimentation and venting processes resulting then in a broad biodiversity. SUBVENT project (CGL2012-39524-C02, MINECO, Spain), ATLAS project (EU, Horizon 2020) and EMEPC (Portugal)

The Madeira Island lower slope has been build-up mostly by along slope-processes associated with mass movement deposits as seen in GEBCO bathymetry, multibeam bathymetry, Parasound echosounder profiles and multichannel seismic reflection profiles. A plastered contourite drift (Madeira Drift) developed on this lower slope, being composed of seismic units D1, D2 and D3. The most probable water mass responsible for its deposition is the Antarctica Bottom Water (AABW). The youngest sediments of seismic units D2 and D3 are affected by gravity-driven processes, probably slumps and debris flows, which moved downslope towards west. Parasound profiles show evidences of such mass movements on present-day seabottom (e.g. diffraction hyperbolae echoes) but also of past-events buried within the contourite sediments. These older debris flows are recognized by semitransparent/transparent acoustic facies and lenticular shape. Versión del editor

The Madeira Island lower slope has been build-up mostly by along slope-processes associated with mass movement deposits as seen in GEBCO bathymetry, multibeam bathymetry, Parasound echosounder profiles and multichannel seismic reflection profiles. A plastered contourite drift (Madeira Drift) developed on this lower slope, being composed of seismic units D1, D2 and D3. The most probable water mass responsible for its deposition is the Antarctica Bottom Water (AABW). The youngest sediments of seismic units D2 and D3 are affected by gravity-driven processes, probably slumps and debris flows, which moved downslope towards west. Parasound profiles show evidences of such mass movements on present-day seabottom (e.g. diffraction hyperbolae echoes) but also of past-events buried within the contourite sediments. These older debris flows are recognized by semitransparent/transparent acoustic facies and lenticular shape.