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Previous studies have found a higher proportion of alien plant species along the coastal area of the Black Sea. The goals of the present study were to assess the role of two harbours as gateways and reservoirs for alien plant species, to compare the structure and invasion pattern of the alien plants recorded there, and test methods useful for effective monitoring programs. We inventoried 12 sites along the western Black Sea coast from the harbour of Sulina in the north to Cape Kaliakra in the south. Each site was visited at least three times each. A more intensive survey was done in the two harbours targeted by our study: Constanţa and Sulina. The proportion of neophytes was higher in the harbours (representing about one third of the total plant species) and lower in coastal protected areas (with an average proportion of 6.7%). Species accumulation curves and estimators of species richness indicated that while the plant inventory was not complete, invasive alien species (IAS) were adequately inventoried. Harbours act not only as gateways for IAS but also as reservoirs, facilitating their acclimatization and naturalization. The use of species accumulation curves and estimators of species richness are useful tools in designing and evaluating simple monitoring programs based on repeated inventories. Our study has stressed the importance of monitoring not only coastal waters but also green areas in harbours for the early detection of IAS.

Biological invasions are one of the main drivers of modern human-induced species losses. Research on the distribution of alien species and their pathways of introduction is essential for understanding and tackling the invasion process. A comprehensive overview on invasive alien plant (IAP) species in Romania is lacking. With this paper, we aim to contribute to filling this gap and to provide a visualization of national patterns regarding plant species invasions, geographical origins and pathways of introductions. Based on plant species occurrence records in the published literature and herbaria we compiled a national database of 102 invasive and potentially invasive alien plant species. We georeferenced 42776 IAP species occurrences and performed an analysis of their spatial patterns. The spatial analyses revealed a biased sampling, with clear hotspots of increased sampling efforts around urban areas. We used chord diagrams to visualize the pathway of introduction and geographical origins of the IAP species, which revealed that species in Romania originate mainly in North and Central America, while the dominant pathway of plant introduction was horticulture. Our results provide an important baseline in drafting management and action plans, as invasive alien plant species represent a priority for the European Union through the Biodiversity Strategy for 2030, and a good starting point for various analyses as the database is further developed and regularly updated.