Characterization of communities and habitats in submarine canyons. The case study of the Avilés canyon system, southern Bay of Biscay

To assess the presence of vulnerable marine ecosystems and map their spatial distribution for conservation purposes, we conducted high resolution studies of macrobenthic species aggregations and habitats in the southern Bay of Biscay. The study area covers three submarine canyons and a rocky outcrop, and was sampled using non-invasive photogrammetric techniques. To study the community structure, we analyzed the aggregations of sessile macrobenthic species using hierarchical cluster analysis based on Bray-Curtis similarity index. The main groups obtained were cold-water corals accompanied by hexactinellid sponges, brisingids and black corals; aggregations of demosponges; a sedimentary habitat dominated by pennatulids; and two lower bathyal habitats, one dominated by Acanthogorgia armata and Thouarella (Euthouarella) grasshoffi , and another by the foraminifera Syringammina aff. Fragilissima . To obtain their spatial distribution, we developed two-part hurdle models for each group by combining binomial presence–absence predictions with negative binomial density models of key species, identified by a similarity percentage analysis. Results indicated high densities of cold-water corals along the canyon walls and in deep biogenic and geogenic zones; sponge aggregations on shallow hard substrates, and high density of pennatulids, mainly Kophobelemnon stelliferum , in sedimentary areas. These findings provide an essential baseline knowledge for the implementation of on ecosystem-based management plans and conservation strategies. • Non-invasive sampling techniques are fundamental for characterizing biological communities in the complex context of submarine canyons. • The combination of presence/absence spatial distribution models with the densities of key species are powerful tools for the study of interaction with fisheries. • Submarine canyons outstand for being one of the most important biodiversity hotspots in the bathyal zone. • Submarine canyons host important hard bottom habitats, including biogenic reefs and geogenic rocky outcrops, which support high densities of species indicative of vulnerable marine ecosystems (VME).