Coastal vascular plant diversity of the Danube Delta Biosphere Reserve: Rare plants, vegetation mosaics, and conservation priorities

The coastal margin of the Danube Delta Biosphere Reserve (DDBR) forms a dynamic ecological interface between the delta, the Razim-Sinoe lagoon system, and the Black Sea. We synthesized project-derived floristic, phytocoenological, spatial, and pressure records collected during 2009-2018 from Musura Island to Corbu, including 86.92 km covered during the final detailed mapping stage. The harmonised inventory comprised 661 vascular plant taxa, 47 vegetation associations, and 58 taxa included in Romanian red-list or red-book sources; 42 taxa were prioritised for conservation assessment. Analysis of 1,243 occurrence records representing 111 species profiles in 134 source grid squares showed the greatest profile richness in Natura 2000 habitats 1410 and 1310, with the strongest compositional overlap (Jaccard = 0.806). This overlap indicates conservation interfaces within a fine-scale mosaic of beaches, dunes, saline surfaces, wet depressions, grasslands, and shrub communities, rather than interchangeable habitat units. The most frequently documented pressures were grazing or overgrazing, tourism and development, mechanical beach disturbance, and habitat restriction. Because survey effort was heterogeneous and habitat links were assigned at grid-square level, the results represent a regional historical baseline rather than standardised estimates of occupancy or trend. Conservation should maintain natural coastal dynamics while protecting rare-species microhabitats and regulating mechanical cleaning, vehicle access, tourism, and grazing.