Scleractinian diversity in the upper mesophotic zone of Ludao (Taiwan): a museum collection with new records from Taiwanese waters

Taiwan’s shallow coral reef habitats (0–30 m) and their scleractinian fauna are well-studied but its mesophotic zone (30–90 m) remains underexamined. This study documents mesophotic (38–60 m) habitat and species diversity at Ludao, Taiwan. In northern and southern Ludao, mesophotic habitats display low-grade slopes (< 30°) dominated by a mixture of sand/rubble and small to large patches of hard substrates. Specimen collection and in situ photography yielded records of 102 scleractinian coral species (among 350 specimens collected) encompassing 15 families and 49 genera (plus two non-scleractinian reef-building species, e.g., Heliopora sp. and Millepora sp.). Thirty-seven percent of species found at shallow depths also populated the mesophotic zone of Ludao, implying that the ecological refuge hypothesis of the mesophotic zone could apply to less than half of the scleractinian coral community at the island. We predict that species overlap, and endemic species richness will increase with additional sampling efforts, especially for the families Acroporidae, Fungiidae, Lobophylliidae, and Poritidae. A large number of scleractinian corals were found in sandy or rubbly habitats, partly forming small rhodolith beds, suggesting that both stable and unstable substrates should be targeted for diversity surveys at mesophotic depths. Aside from providing a museum collection (with skeletons and tissue samples) and enhancing our knowledge of the regional stony coral distribution, this study highlights Ludao as a possible ecological refuge and evolutionary refugium for stony corals.