The hidden cold-water coral communities of the Ormonde seamount (Gorringe Bank): a world to explore, a world to discover

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.