The Distribution and Trends of Marine Alien Macroalgae in Italian Marine Protected Areas: An Overview

Non-indigenous species (NIS) pose a severe threat to Mediterranean biodiversity, health, and economy. Although marine protected areas (MPAs) are key conservation tools, they remain vulnerable to biological invasions, whose impacts are still poorly understood. This study provides an updated literature-based overview of non-indigenous macroalgae in Italian MPAs and adjacent non-protected areas. For this analysis, we used a dataset derived from the inventory of Wesselmann, updated with the most recent scientific literature up to 2026. In particular, we consulted the library of the Laboratory of Phycology at the University of Catania, and the browsers Google Scholar and PubMed. Overall, non-protected areas accounted for a higher number of records (1001) than MPAs (280). Among the protected areas, the highest numbers of non-indigenous macroalgal records were observed in the MPA Secche della Meloria (48 records), the MPA Isole Pelagie (42 records), and the Tuscan Archipelago National Park (42 records). In terms of species richness, the MPAs harboring the highest number of non-indigenous taxa were the Tuscan Archipelago National Park (15 taxa), followed by MPA Isole Ciclopi (14 taxa), MPA Isole Egadi (12 taxa), and the MPAs Isole Pelagie and Isole Tremiti (both with 10 non-indigenous macroalgal taxa). Notably, data remain lacking for many regions and MPAs; the observed differences in records and species numbers among MPAs are essentially linked to their geographical location, accessibility, and varying degrees of scientific interest or sampling effort. To address these gaps, future efforts must prioritize early detection and regular monitoring of non-indigenous macroalgae across all areas, particularly within MPAs.