Ecological and biogeographic implications of Siderastrea symbiotic relationship with Symbiodinium sp. C46 in Sal Island (Cape Verde, East Atlantic Ocean)

The relative abundance of the genus Siderastrea and its relationship with temperature and irradiance was assessed around Sal Island (Cape Verde). In some of the surveyed sites, these corals accounted for 80–90 % of the living cover, making it a biotope-dominant organism. Unlike Siderastrea corals from West Atlantic and Caribbean locations, genetic analyses of the dinoflagellate symbiotic partner revealed high specificity between Siderastrea sp. in Cape Verde and the Symbiodinium type C46. Biotope restriction of the ecological success of Siderastrea in Cape Verde may be explained in part by this host–symbiont partnership, resulting locally in a small optimum ecological niche with specific light intensity regimes. Distinctively, West Atlantic and Caribbean Siderastrea associates with a much broader range of Symbiodinium diversity, suggesting that these symbioses exhibit some flexibility under differing environmental conditions where these corals occupy a wider range of ecological niches. Geographic isolation and/or long-standing environmental conditions are probably responsible for such adaptions and coral–dinoflagellate symbioses. Additional genetic analyses on Clade C Symbiodinium associated with Siderastrea were conducted with the hyper-variable plastid psbA minicircle to resolve phylogeographic patterns that indicate the relative connectivity and/or isolation of these symbionts throughout the tropical Atlantic.