Diversity and Spatial Distribution of Fucalean Forests in the Ustica Island Marine Protected Area (Western Mediterranean, Italy): Historical Records and Current Status

This study investigates the diversity and spatial distribution of Fucalean stands within the Ustica Island Marine Protected Area (MPA). Field surveys were carried out in autumn 2024 and summer 2025 using scuba diving and snorkeling across the three protection zones (A, B, and C). Overall, 20 fucoid taxa at the specific and infraspecific level were recorded: 11 in zone A, 19 in zone B, and 16 in zone C. Comparison with historical data confirmed the persistence of 18 taxa previously recorded for Ustica Island. Notably, two species are reported here for the first time: the expanding non-indigenous Sargassum furcatum and the rare Mediterranean endemic S. trichocarpum. Additionally, the rediscovery of Sargassum cf. hornschuchii after approximately 40 years suggests that the Ustica Island MPA may provide suitable environmental conditions for the persistence of rare and conservation-relevant Fucalean species. Overall, the results indicate a high and comparatively stable Fucalean diversity within the MPA, particularly in zones subject to regulated human activities. These findings highlight the importance of continuing the actions for protection and regular monitoring of Fucalean forests, which represent key ecosystem-engineering habitats in the Mediterranean Sea.