030 | The Piroscafo Torino shipwreck as a biodiversity hotspot in a sandy-bottom habitat (Ionian sea)

In addition to their historical relevance, shipwrecks can serve as secondary habitats for marine biodiversity, particularly when located in mobile seabed environments. By providing structural complexity, refuge availability and altered hydrodynamic conditions, these submerged structures may significantly influence the composition and organization of local marine communities. Despite increasing interest in their ecological role, detailed ecological characterizations of shallow historical archaeological sites remain limited. This study presents the first comprehensive characterization of the benthic and nektonic communities associated with the wreck of the Piroscafo Torino (Melito di Porto Salvo, Ionian Sea), a mixed-propulsion vessel that sank in August 1860 and officially recognized in 2020 as a site of high historical value. The research is based on two seasonal sampling campaigns conducted in February and August 2023, aimed at assessing the composition, abundance and structural features of the communities inhabiting the wreck in comparison with the surrounding sandy bottom-habitat. Nektonic and vagile benthic taxa were surveyed through underwater visual censuses using two linear transects (20 × 4 m), with six replicates per season: one transect was positioned inside the wreck structure and one on the adjacent natural substrate. This design allowed the evaluation of habitat-related differences in taxonomic diversity, abundance patterns and individual size structure. The sessile benthic community was investigated exclusively on the wreck using randomly positioned photo-quadrats (40×40 cm), with 30 replicates per season. Overall, 51 taxa were identified, of which 48 occurred on the wreck and 35 exclusively found within the wreck structure. In both sampling periods, the interior of the wreck consistently exhibited higher values of species richness and abundance compared to the adjacent sandy seabed, suggesting the occurrence of a refuge effect. The fish assemblage was primarily dominated by representatives of the families Labridae, Sparidae and Scaridae, reflecting the suitability of the wreck structure for reef-associated and benthic-linked taxa. The presence of juvenile individuals suggests a potential nursery function, while the detection of Epinephelus marginatus, a species listed as endangered on the IUCN Red List, indicates that the wreck may also act as a refuge for sensitive and conservation-priority species. Due to the shallow depth of the site, the sessile assemblage was largely dominated by algal turf; nevertheless, a diversified epibenthic community was observed, including ascidians, sponges (mainly Irciniidae), serpulids polychaetes and bryozoans, highlighting the capacity of the wreck to support structurally and functionally diverse assemblages despite strong light exposure. These results underline the relevance of shallow historical wrecks as localized biodiversity hotspots in otherwise homogeneous sandy environments. Furthermore, this baseline will support future surveys specifically designed to assess potential changes in community structure.