Biodiversity and distributional patterns in deep-sea vulnerable marine ecosystems and associated fish communities of the Seco de los Olivos Bank

Abstract

Seamounts are ubiquitous in the global ocean enhancing locally the biological biodiversity in the deep-sea and hosting multiple Vulnerable Marine Ecosystems (VMEs), like cold-water corals (CWCs) and sponge grounds. In the western Mediterranean basin (Alborán Sea), the Seco de Los Olivos Seamount (Chella Bank) is considered a hotspot of deep-sea biodiversity, being part of the protected marine network in Europe (Natura 2000). While previous studies provided extensive qualitative information about what species and habitats occur in the seamount, there is still a challenge to have accurate quantitative information to better understand the spatial distribution patterns of the megabenthic species and its functional role. Using underwater video transects recorded by a Remotely Operated Vehicle (ROV) during the MEDWAVES survey (EU project ATLAS H2020), we quantitatively characterize the megabenthic communities in the Seco de Los Olivos Seamount. A total of 62 operational taxonomic units (OTUs) grouped into five major assemblages were identified, which were mainly associated with the substrate type. The main groups typifying these assemblages included massive sponges, black corals, sea pens, and ray-finned fishes. In addition, taxonomic diversity was evaluated and the patterns observed were also associated with the substrate type and to the flank orientation in a lesser extent. Besides our ecological findings, we found a variety of human impact evidence (e.g., pieces of fishing lines, glass bottles, and trawl marks). Nonetheless, there is a management plan in progress aiming to regulate different human activities (e.g., fisheries) carried out in this area declared a site of ecological importance. Abundances and densities obtained through this study for the most representatives OTUs represent an important contribution to improve our understanding of the biodiversity, ecological associations and potential threats of deep-sea communities and thus, will help to enhance the spatial management and conservation plans for these vulnerable marine ecosystems.