Characterization and mapping of bathyal benthic communities of Cabo Verde (NW Africa)

Benthic communities, such as those dominated by cold-water corals (CWC) and sponges, contribute to the habitat complexity and diversity of deep-sea ecosystems, with characteristic taxa serving as indicators of Vulnerable Marine Ecosystems (VMEs). Many areas on the West African margin remain under-surveyed for the presence of deep-sea benthic communities and, hence, VMEs, limiting the implementation of marine spatial plans. In this study, the benthic communities of SW Cabo Verde (NW Africa), in particular Cadamosto Seamount (SW Brava Island) and the slopes of the islands of Fogo and Brava, were characterized and mapped, providing an assessment of the potential differences in benthic community composition between the two systems (seamount vs island slopes). We employed machine learning approaches (multivariate regression trees and a Random Forest classification) using data on morphospecies composition and densities retrieved from Remotely Operated Vehicle (ROV) video data collected from 2,100 to 1,450 m depth, as well as environmental data on substrate type, terrain, and water column parameters. Ten different benthic communities were identified in the study area, with cnidarians, porifera, and echinoderms as the dominant taxa. Higher densities of CWCs and communities with higher species richness were observed on the seamount compared to the adjacent island slopes. Depth, substrate type, pH and dissolved oxygen were identified as the key environmental variables driving habitat heterogeneity. Additionally, communities composed of characteristic taxa with VME attributes were observed, including (i) sponge aggregations, (ii) scleractinian, (iii) octocoral and black CWC gardens, and (iv) sea pen fields. Despite the apparent low impact of fishing activities in the study area, lost fishing gear was noted in areas where CWCs were observed in higher densities. This study provides important information for the implementation of area-based conservation measures in Cabo Verde, following the application of the precautionary principle.