Integrative taxonomy of living encrusting coralline algae on columnar coralligenous bioconstructions offshore Marzamemi

Mediterranean coralligenous bioconstructions represent hotspots of biodiversity and play key ecological roles in rocky reef systems, yet many of their components, particularly calcareous algae, remain poorly characterized at the species level. In this study, we focus on the living encrusting coralline algae covering three columnar coralligenous constructions collected by scuba divers offshore Marzamemi, Sicily, along a depth gradient from approximately 35 to 95 meters. The coralligenous bioconstructions are part of a broader field of discrete columnar structures distributed along the Hyblean Plateau, a geologically complex sector of the African foreland, which was mapped during the “CresciBluReef: New technologies for knowledge and conservation of Mediterranean reefs” project. This project produced a 17 km² high-resolution bathymetric map using a R2Sonic 2022 multibeam echosounder, ground-truthed by ROV observations, allowing precise selection of coralligenous samples. The sampled columns were covered by dense canopies of fleshy algae and colonies of erect bryozoans, which were manually removed before processing. For taxonomic identification, we combined molecular analyses targeting the rbcL and psbA genes with detailed morphological characterization using scanning electron microscopy, aiming to apply an integrative taxonomy approach to describe the living encrusting coralline algae communities. While the phylogenetic analyses are ongoing, preliminary observations indicate high diversity and variable dominance of coralline taxa along the depth gradient. These findings contribute to a better understanding of the biodiversity of Mediterranean coralligenous bioconstructions and provide baseline information that can inform conservation strategies. By integrating molecular and morphological data, this work highlights the importance of detailed species-level studies in revealing cryptic diversity and understanding ecological processes shaping coralligenous communities. Ultimately, this study underscores the role of coralligenous bioconstructions as biodiversity reservoirs in Mediterranean reefs and demonstrates how targeted sampling combined with integrative taxonomy can support both fundamental research and applied conservation efforts.