Mesophotic banks of Dendrophyllia ramea offshore Marzamemi (Sicily, Ionian Sea): a habitat classification model

The occurrence and distribution of mesophotic autogenic habitat engineers are critical for the effective management and conservation of marine resources, as well as for regulating human activities. Recent deep-sea explorations in the Mediterranean Sea have revealed the occurrence of algal reefs (coralligenous), alongside notable contributions from invertebrates in creating reefs. As part of the CRESCIBLUREEF project, we investigated a sector offshore Marzamemi (Ionian Sea), at depths between 30 and 100 m, using integrated acoustic surveys and underwater videos. This study presents a detailed characterization of the acoustic facies associated with a dense population of Dendrophyllia ramea, a vulnerable arborescent scleractinian coral included in the cold-water coral group and recognized as habitat-former. Found between 65 and 90 m of depth in a muddy-sandy sedimentary environment, D. ramea forms small reef-like banks with patchily distributed colonies ranging in size from less than 10 cm to over 50 cm, generally on buried biogenic hard substrates, occupying an area of approximately 0.42 km2. D. ramea functions as an autogenic habitat engineer, supporting rich epibenthic assemblages including abundant Neopycnodonte cochlear at the base of the colonies. However, evidence of marine litter, particularly abandoned ropes entangling the corals, indicates anthropogenic impacts, likely from fishing activities. By identifying the acoustic signature of D. ramea and validating it with in situ observations, this study successfully maps previously undocumented mesophotic coral banks in the Marzamemi area. Our findings underscore the ecological relevance and vulnerability of D. ramea habitats, highlighting the need for their inclusion in marine spatial planning and conservation strategies.