A comparison of the fish assemblages on natural and artificial reefs off Sal Island (Cape Verde)

Tourism is a growing activity in Cape Verde, which can lead to more intensive and uncontrolled fishing and diving activities, affecting the quality of marine habitats. To mitigate this biodiversity problem, a private diving operator, supported by the local authorities, decided to deploy the first artificial reefs (ARs) in the Archipelago just off Santa Maria Bay (Sal Island). To evaluate the ARs capacity to promote marine fish biodiversity in Santa Maria Bay, the fish assemblages were compared to those from nearby natural reefs (NRs), located at the same depth (10 and 28 m depth), by means of visual census. All study sites were surveyed by visual census in August 2009. A total of 64 species were recorded, mostly consisting of sedentary and/or benthophagous demersal species, followed by highly-sedentary benthic cryptic species. 'Tchuklassa' NR showed the highest species richness (58 species), while the lowest was recorded at 'Santo Antao' AR (48 species). An overall positive relationship was observed between habitat rugosity and mean species richness. The results showed a high percentage of common species on both reef types. Higher mean values of community descriptors (number of species, Shannon-Weaver diversity index, Simpson dominance index and equitability) and fish density were found on the ARs, with slightly higher densities recorded on the deeper reefs. These results suggest that ARs can have an important role promoting the local fish biodiversity and supporting local sustainable development of diving tourism.