The Gulf of Custonaci, in western Sicily, is characterized by volcanic seabeds with a variety of shapes and landscapes, including submerged crags, rocky slopes, and beaches. The submerged area is covered by an extensive meadow of Posidonia oceanica, a priority habitat for marine biodiversity. Naturalistic highlights include the sidewalk “a vermeti” and the band of orange coral (Astroides calycularis), a thermophilic endangered species. Submerged caves and karst formations contribute to the richness of endolithic fauna. The area is of significant biological and environmental interest and it shows several animal species which are included in the lists of species that have to be protected.