Ecological refugia in the deep: insights from the canyon Dohrn in the Gulf of Naples (Central Tyrrhenian Sea)

Deep-sea ecosystems represent the largest biome on Earth, their steep topography, substrates and ability to enhance transport and retain organic matter and CO2, create environmental conditions that support rich assemblages of suspension feeders, cold-water corals, and associated fauna. In the Mediterranean Sea, these systems were observed to have unique features and might play an important ecological role, potentially functioning as biodiversity hotspots and ecological refugia for many species. This study focuses on the Dohrn Canyon in the Gulf of Naples (Central Tyrrhenian Sea), which is recognized for its structurally complex habitats dominated by cold-water coral assemblages. The analysis was based on 22 ROV transects from 5 oceanographic campaigns, for each of them, video footages were examined to identify benthic and demersal species, while spatial information were processed using QGIS. Particular attention was given to habitat-forming species such as the cold-water corals (CWCs) Madrepora oculata and Desmophyllum pertusum, whose colony size structure was analyzed to better understand their presence in the area. The results reveal a diverse assemblage, specifically, CWCs dominated communities were recorded, with D. pertusum and M. oculata acting as key bioconstructors. The presence of N. zibrowii, A. excavata and Protanthea simplex was also recorded further highlighting the ecological importance of the canyon’s ecosystem. The main objective of this work was to provide a preliminary quantitative ecological characterization of benthic and demersal communities in the explored areas and to evaluate if the observed ecological patterns could help to support the hypothesis that the system may function as a deep-sea ecological refugium. Overall, this study provides baseline ecological information on the benthic communities of the Dohrn Canyon and contributes to the total knowledge on Mediterranean deep-sea ecosystems underlining the conservation value of this system.