Rhodolith beds are globally widespread biogenic habitats formed by the accumulation of free-living calcareous red algae. They support high biodiversity and provide important ecosystem services, including carbon sequestration. In the Mediterranean Sea, these habitats mainly occur at mesophotic depths (30-100 m), and their distribution, structural complexity, and biodiversity are still poorly known.

This study focuses on four rhodolith beds in the Tyrrhenian Sea (Capri, Sorrento, Ischia, and Cilento), located between 50 and 70 m depth, and investigates their floristic and faunistic composition. In addition to the macrofaunal community, the meiofaunal component was also examined for the first time in Mediterranean rhodolith beds.

The results revealed marked variability in rhodolith cover and bed structural complexity among sites. A high diversity of coralline algae was recorded (>10 taxa). The Cilento rhodolith bed, which showed the highest cover and structural complexity, also exhibited the greatest macrofaunal abundance and species richness. Similar dominance patterns of the main taxonomic groups were observed across all beds, with Polychaeta, Mollusca, Crustacea, and Echinodermata being the most represented. Polychaetes were the most abundant group, while molluscs contributed the highest number of species.

Among trophic guilds, deposit feeders played a key role in shaping community structure, highlighting the importance of rhodolith beds in detrital food webs. Rhodoliths also hosted a distinctive meiofaunal assemblage, mainly represented by copepods and numerous temporary meiofaunal species (juveniles of macrofauna), confirming the nursery role of these habitats.

Overall, these findings confirm the high floristic and faunistic diversity of rhodolith beds and emphasize their crucial role as biodiversity hotspots in the Mediterranean Sea.