Virgulinella fragilis in the North Adriatic Coastal Sediments: A New Non-Indigenous Benthic Foraminiferal Taxon?

The Mediterranean Sea is considered a hotspot for bioinvaders. Nonetheless, information on non-indigenous benthic foraminifera is still fragmented. This study documents for the first time the presence along the northwestern Adriatic coast of the non-indigenous benthic foraminifera species Virgulinella fragilis, Grindell and Collen (1976). Due to the low abundance recorded in the study area, the presence of this species may represent an early colonization phase. We discuss the temporal and spatial patterns of V. fragilis arrival in the Mediterranean and Adriatic Seas, and we hypothesize stowaway transport (via ship fouling or ballast water) as the main introduction pathway. Morphological test analyses suggest that V. fragilis prefers a low oxygen content, consistent with the ecological requirements reported for this taxon in the literature. The application of Maximum Entropy (MaxEnt) modeling indicates that the key factor influencing the presence of V. fragilis in the Mediterranean basin is the bacterial concentration expressed as NO3. Projections under future climate scenarios (RCP 4.5) point to a decline of habitat suitability conditions, making widespread invasion unlikely in the Mediterranean. We emphasize the importance of continuous biomonitoring for early detection of alien species, improving our understanding of invasion dynamics and enabling prompt conservation actions, especially in regions impacted by anthropogenic activities.