Description and quantification of the deep-sea megabenthic communities in Ormonde seamount (Gorringe Bank, NE Atlantic) using video analysis

The Gorringe Bank is a seamounts complex located at the eastern tip of the Azores-Gibraltar plate boundary separating Eurasia and Africa. Despite its early discovery at the end of the XIX century, the knowledge of the benthic communities and other associated fauna is still very scarce in this region, particularly in the deep areas below 200 m. The Ormonde seamount is one of the two main summits of Gorringe Bank, which rises from 5000 m to 33 m depth. In this study, we characterised the deep-sea communities in the Ormonde seamount from 900 to 2000 m depth by analysing underwater videos recorded by remotely operated vehicle (ROV) during the MEDWAVES survey (EU H2020 project ATLAS). We provided for the first time, detailed and quantitative information on species composition, densities, spatial distribution and state of conservation compared to other well studied seamounts. The surveyed areas were strongly dominated by sponges, but the presence of patches of cold-water corals were also notable and some other vulnerable marine ecosystems (VMEs) were identified. Spatial patterns in the deep-sea communities were also analysed as a result of the different water masses that bathed the area, exhibiting higher biodiversity in the presence of the Mediterranean Outflow Water (MOW). Studies of deep-sea ecosystems not only improve our knowledge of the deep ocean but also are essential defining an appropriate management plan and conservation measures

Community characterization of two Atlantic seamounts. First steps into addressing the influence of the Mediterranean Outflow Water (MOW)

An important goal of the ATLAS project is to improve our understanding of the ocean transport pathways and connectivity of water masses at basin and regional scales relevant for benthic marine ecosystems. The MEDWAVES cruise (21st September-26th October, 2016) aimed to better understand the characteristics of the Mediterranean Outflow Water (MOW) and its potential influence in the occurrence, composition and distribution of deep-sea benthic communities from the Mediterranean to the Azores. Among the geomorphological features targeted in MEDWAVES, two Atlantic seamounts were included: Ormonde (Portuguese continental shelf) and Formigas Bank (close to the Azores Archipelago). During MEDWAVES, the geomorphology and oceanography of the areas was characterised. Further submarine video transects were conducted by means of a Remotely Operated Vehicle (ROV). The transects were performed in the different flanks of the seamounts aiming to characterise the benthic communities considering different geographical orientations and the influence of water masses. The characteristics of the video transects allowed to perform a methodology for video analysis based on still images. The images were taken directly from the video recordings at regular length intervals based on the positioning of the ROV, generating a set of images that allowed for comparisons between different areas. To make such comparisons robust, a thorough filtering was carried out based on the position of the parallel laser beams on screen. Only images that had a similar area observed were selected, in which all megabenthic organisms are currently being identified to the lowest possible taxon. It is expected that this protocol can be used for the video processing in all benthic communities surveyed during MEDWAVES. Some examples of coral garden habitats and sponge grounds identified in these areas are presented. This proposed methodology and preliminary results represent the first steps in a larger study that aims to: (1) characterise the megabenthic communities, the species diversity and their distribution in Ormonde Seamount and Formigas Bank, (2) evaluate the influence of substrate type, flank orientation and the characteristics of the water masses in the patterns observed, and (3) do a comparison between both seamounts to determine differences in their biological composition

Variability of deep-sea megabenthic assemblages along the western pathway of the Mediterranean outflow water

The presence of different water masses in depth may influence the species distribution and community structure in deep-sea benthic ecosystems. In the North Atlantic, the Mediterranean Outflow Water (MOW) represents an important forcing water mass, whose influence on the distribution of cold-water corals in the northern European margins has been particularly investigated. However, the MOW also spreads westwards into the central North Atlantic bathing several seamounts and seafloor elevations, whose deep-sea benthic communities are still poorly known. In this study, we provide a local to large-scale comprehensive description of deep-sea megabenthic assemblages along the western branch of the MOW, from its origin in the western Mediterranean Sea to the Central North Atlantic close to the Azores archipelago. For some of the studied seafloor elevations, such as Ormonde (Gorringe bank, offshore SW Portugal margin) and Formigas seamounts (SE Azores archipelago), this is the first time these assemblages have been characterized and quantified. The results indicate a strong effect of substrate type in the structure and diversity of the assemblages at local scales; but the effect of water masses becomes more relevant when a large bathymetrical gradient is considered. The results also suggest a potential role of the MOW for biodiversity and biogeographic patterns at the North Atlantic basin, suggesting a potential enhancement of the biodiversity of some deep-sea megabenthic assemblages. Understanding water masses as an integrative tool to delineate biodiversity and biogeographic patterns from local to large scale will contribute to identify different megabenthic assemblages, including vulnerable marine ecosystems, as well as potential regions of refugia under future climate change conditions.En prensa2,42

Preliminary characterization of Vulnerable Marine Ecosystems and associated communities of Chella Bank (Alboran Sea, W Mediterranean)

Poster presentation at ATLAS 3rd General Assembly. Seamounts may promote the presence of vulnerable marine ecosystems (VMEs) worldwide. In the Alboran Sea (W Mediterranean Sea), the Chella Bank (locally known as “Seco de los Olivos”) is a seamount that covers ca. 100 km2 and is under the influence of different water masses in this important Atlanto-Mediterranean biogeographical transition zone. During the MEDWAVES expedition (September-October 2016) within the frame of the H2020 ATLAS project, biological and sediment samples collected with Van Veen dredge and ROV underwater videos were obtained in sedimentary and coral rubble bottoms of Chella Bank. The analyses have revealed a diverse invertebrate community associated with these bottoms containing abundant cold-water coral (CWC) remains (mainly Madrepora oculata and Lophelia pertusa), which provide complex heterogeneous microhabitats to many different taxa. The community associated with the coral rubble bottoms is mainly composed of different genera of bivalves (Mendicula, Limopsis, Asperarca), gastropods (Gibberula, Epitonium), small crustaceans (class Malacostraca), polychaetes (Eunice), ophiuroideans (Ophiothrix), bryozoans (order Cyclostomata), hydrozoans (Cryptolaria), poriferans (Terpios, Haliclona) and brachiopods (Megathiris, Megerlia), among other taxa. Furthermore, the megafauna include cnidarians (Bebryce, Acanthogorgia, Dendrophyllia), sponges (Pachastrella) and dense shoals of the carangid fish Caranx rhonchus. Unlike coral rubble bottoms, macro- and micro-fauna inhabiting close sandy, muddy or hemipelagic muddy habitats seems less diverse (up to four times in terms of abundance and species richness). These communities are mainly composed of polychaetes, small crustaceans and bivalves (Abra, Ennucula, Yoldiella), together with shoals of the ammodytid fish Gymnammodytes cicerelus. Coral rubble bottoms of Chella Bank may therefore represent an interesting habitat for conservation, harboring a good representation of the biodiversity linked to CWC communities. This study increases the scarce information on biodiversity and biogeography (WP3) for this area that probably favors the connectivity of CWC associated fauna (WP4) between the Atlantic and Mediterranean basins