First characterization of upper mesophotic coral assemblages in Santo Antão (Cabo Verde, East Atlantic Ocean): Demographic and community approaches provide baseline ecological data

Preserving healthy marine ecosystems is crucial for human societies, especially in resource-dependent locations like Santo Antão, the most northwestern island of Cabo Verde (East Atlantic Ocean). However, effective conservation requires baseline ecological knowledge on target ecosystems, which is often lacking. This study provides the first ecological characterization of upper mesophotic coral assemblages (i.e., at depths of 30–40 m) in Santo Antão. We focused on density, size structure, and conservation status of canopy-forming coral species in two assemblages types: i) a mixed coral assemblage dominated by black corals (e.g., Stichopathes luetkeni; Brook, 1889, Tanacetipathes spinescens; Gray, 1857, or Tanacetipathes wirtzi; Opresko, 2001) and gorgonians (e.g., Leptogorgia capverdensis; Grasshoff, 1986, Leptogorgia gaini; Stiasny, 1940, Eunicella granulata; Grasshoff, 1992, or Eunicella papillifera; Milne Edwards & Haime, 1857), and ii) monospecific black coral assemblages dominated by Antipathella wollastoni (Gray, 1857) and T. spinescens, respectively. Additionally, we used a trait-based approach to characterize the functional community structure of the mixed assemblage and quantified the abundance of its main morpho-functional groups. Our results show that these assemblages are structurally complex, functionally diverse, and well-preserved. Notably, they harbor some of the densest black coral populations reported to date, with mean densities exceeding 20 colonies/m² for some species. This suggest that the studied assemblages provide important ecosystem services to local communities, such as increasing fish biomass for artisanal fishing and enhancing aesthetic value for a sustainable diving tourism. However, further surveys at other sites are needed to assess the generalizability of these findings and support future conservation planning.