Aggregations of free-living corals facilitate reef expansion at upper mesophotic depth off Poivre Island, Seychelles

Abstract Free-living corals on unconsolidated substrates, such as sand and coral rubble, can play a key role in the outward expansion of coral reefs, yet their ecological significance at mesophotic depths remains poorly studied. Here, we present the first detailed documentation of aggregations of free-living corals at mesophotic depths (30–40 m) off Poivre Island, Seychelles, western Indian Ocean. Using manned submersibles and qualitative analysis of high-resolution video transects, we identified different benthic communites. Some of these communities were dominated by assemblages of free-living corals consisting of fungiids and a poritid, with a total of 13 species recorded. These free-living corals contributed substantially to live coral cover (estimated up to 75%) and provided new substrate for reef organisms, facilitating reef growth on unconsolidated sediments. Our findings offer the first direct evidence that free-living coral assemblages can enhance habitat complexity and live coral cover at upper mesophotic depths in the region. Although documented from a single site, our observations highlight the underappreciated ecological importance of free-living corals in deep reef environments and underscore the need for further quantitative research on their role in reef development and resilience.