First evidence of live mesophotic coral reefs on the Benin continental shelf

Mesophotic coral ecosystems (MCE) remain poorly documented along the West African coastline, particularly on the continental shelf of the Gulf of Guinea. Coral reef barriers were reported off the coast of Benin during studies conducted in 1963-1964, but their ecological status remained unknown and they were presumed dead. Between April and December 2025, exploratory marine surveys combining side-scan sonar mapping and underwater video exploration were conducted to re-evaluate these historical data. Over a surveyed west-east extent of approximately 7 km, side-scan sonar data revealed two spatially distinct zones of elevated acoustic backscatter, interpreted as consolidated hard-bottom structures. Visual observations conducted at selected sonar targets documented living coral communities at depths of 54 m on rocky substrate at discrete locations within the surveyed area along the Benin continental shelf. The assemblage was dominated by octocorals, forming a mesophotic coral garden rather than a structuring scleractinian reef. At least six octocoral morphotypes and two black coral taxa, and eight associated reef fish species were observed from imagery. These observations provide the first confirmed visual evidence of living mesophotic coral communities off Benin and, to our knowledge, the first documented occurrence on the Gulf of Guinea continental shelf. More broadly, this study contributes baseline information for a region where mesophotic ecosystems remain largely unexplored and highlights the need for broader acoustic mapping, quantitative surveys, and physical sampling to better understand the extent and ecological significance of these habitats.