Spatial Patterns of the Marine Alien Gastropod Rapana venosa Invasion Across the Black Sea, Mediterranean, and Atlantic Europe

The invasion of the marine alien gastropod Rapana venosa (Valenciennes, 1846) across different basins is investigated through a spatiotemporal analysis of distribution patterns, aggregation processes, and spatial structure. Occurrence data from scientific literature and citizen science were integrated with GIS-based spatial statistics to compare invasion dynamics in the Black Sea, the Mediterranean Sea, and Northwest Europe. The Black Sea represents the most advanced invasion stage, characterized by extensive distribution, multiple aggregation zones, and strong associations with brackish, nutrient-rich areas influenced by major river outflows. In the Mediterranean, the invasion has progressed from a prolonged establishment phase to a recent acceleration, with the Adriatic Sea acting as the historical core of expansion. Here, persistent populations are concentrated near the Po River delta and lagoon systems, where reduced salinity and high nutrient loads favor both settlement and long-term persistence. In Northwest Europe, R. venosa remains in the establishment phase, forming a compact and localized nucleus along the French Atlantic coast without evidence of broad spatial expansion. Our analyses suggest that environmental factors, particularly salinity gradients and riverine inputs, are possibly related to the observed invasion patterns. Transitional coastal environments emerge as important areas for establishment and subsequent spread, suggesting that monitoring efforts should prioritize these environments.