Biogeographic Spread of the Non-Indigenous Copepod Pseudodiaptomus marinus in Italian Waters—Insights by the Marine Strategy Framework Directive Surveys

Aim This research investigates the distribution of the non-indigenous calanoid copepod Pseudodiaptomus marinus Sato, 1913 in Italian coastal waters as retrieved by the data collected in the Marine Strategy Framework Directive (MSFD) programme in the 2015–2023 time window. Location Italian marine coastal waters, Mediterranean Sea. Taxon Pseudodiaptom marinus Sato, 1913 (Copepoda, Calanoida). Methods The occurrence of P. marinus along the Italian coasts was checked in the Italian MSFD database, focusing on Descriptor 1 (D1: marine biodiversity) and Descriptor 2 (D2: non-indigenous species). The temporal and seasonal patterns at a key site (port of Civitavecchia) were also examined. Results The MSFD records account for a ~15% increase in the number of P. marinus occurrences in Italian waters, expanding the documented range of this species. Records were more abundant in ports and coastal sites, and copepodites dominated the observations. In addition, the seasonal analysis at the port of Civitavecchia showed late-summer peaks, indicating recurrent recruitment and establishment. Main Conclusions These findings demonstrate the ongoing expansion and successful establishment of P. marinus along the Italian coasts and confirm the role of coastal infrastructures as primary introduction pathways. This study highlights the importance of constant monitoring of the coastal areas to assess the introduction and establishment of non-indigenous species, and underlines the pivotal role of broad-scale initiatives like the MSFD to solicit transnational initiatives.