This paper presents the 2024 research results from the Danube Delta Biosphere Reserve (DDBR), including reed bed mapping and typology for fire management, assessment of sustainable use of vegetal resources, conservation status of invertebrates, fish, reptiles, amphibians, colonial waterbirds, and mammals of Community interest, evaluation of species invasiveness under climate change, and studies on human well-being and ecotourism within a sustainable development framework.

Deltas are highly susceptible to biological invasions because of strong hydrological connectivity, frequent disturbance, and intense human use. Here, we synthesise coordinated monitoring observations and literature evidence on invasive alien plant species (IAS) recorded in four Black Sea riparian protected areas located across five countries, surveyed under the IASON/IASON+ initiatives (Danube Delta, Nestos Delta and Lake Vistonida, Kızılırmak Delta, Chorokhi Delta and Kolkheti National Park). Across the study sites, 17 IAS were documented, mainly represented by taxa native to North America and characterised by high propagule production and/or strong vegetative regeneration. Woody riparian invaders (e.g., Amorpha fruticosa, Robinia pseudoacacia, Acer negundo, Gleditsia triacanthos and Ailanthus altissima) exploited nutrient-rich floodplain soils and disturbances. In contrast, annual weeds (e.g., Ambrosia artemisiifolia, Sicyos angulatus and Xanthium orientale) remained associated with disturbed habitat edges. Aquatic dominance was confined to the Danube Delta, where Elodea nuttallii and Elodea canadensis formed dense submerged stands. Species were assigned to broad range expansion categories (slowly, moderately and rapidly spreading species) based on project observations and supporting records. We discuss shared invasion syndromes linked to reproductive and dispersal traits and outline management implications for Black Sea deltas, emphasising pathway prevention, early detection and rapid response for localised taxa, and sustained control combined with restoration for dominant invaders.

This paper presents the 2024 research results from the Danube Delta Biosphere Reserve (DDBR), including reed bed mapping and typology for fire management, assessment of sustainable vegetal resource use, conservation status of invertebrates, fish, reptiles, amphibians, colonial waterbirds, and mammals of Community interest, evaluation of species invasiveness under climate change, and studies on human well-being and ecotourism within a sustainable development framework.

Long-term outcomes of reconstructed floodplain wetlands remain poorly documented in Romania and the lower Danube region. We combined dated records from 2012-2016 with aquatic-vegetation surveys from 2018, 2023 and 2026, hydrochemistry, bathymetric context, repeat photography and calibrated Sentinel-2 classifications. Previous evidence documented a shift from a reed-dominated polder, following dredging and reed removal in 2015, to rapid recolonisation by submerged, floating and pioneer wetland plants in 2016. Mean richness increased from 6.5 taxa per relevé in 2018 to 10.7 in 2023 and 17.6 in 2026. This pattern remained significant after observations were aggregated within eight repeatedly sampled plots (Friedman Q = 16.0, p < 0.001; Holm-adjusted paired p = 0.023). Floristic composition also differed among years in a blocked sampling plot PERMANOVA (R² = 0.356, p < 0.001). Two principal components summarised 85.8% of plot-mean hydrochemical variance, and exploratory redundancy analysis related 43.6% of 2026 floristic variance to these axes (adjusted R² = 0.210, p = 0.017; n = 8). Across a common 136.94 ha cover, calibrated estimates indicated that open water decreased from 25.0 ha in 2018 to 3.2 ha in 2026, while reed increased from 31.7 to 49.7 ha and dense reed, shrubs, and trees increased from 20.2 to 34.2 ha. At Zaghen, local plant richness increased even as open water and submerged vegetation habitats declined and emergent and woody vegetation expanded across the wetland. Reconstruction success should be evaluated through both local diversity and the persistence of a heterogeneous habitat mosaic.

Aquatic macrophytes with invasive or range-expanding behaviour are a growing ecological concern, especially in vulnerable wetland habitats under pressure from climate change. The present study analyses the phytocoenological preferences and climate-influenced expansion potential of three macrophyte species in the Danube Delta Biosphere Reserve: two alien invasive species, Azolla filiculoides and Elodea nuttallii , and one non-native range-expanding macrophyte, Vallisneria spiralis . The study was conducted during 2024–2025, in selected lakes from the Danube Delta Biosphere Reserve, Romania. For vegetation analysis, phytocoenological relevés were carried out, subsequently processed by cluster analysis and DCA ordering, in order to highlight floristic groupings and gradients of vegetation variation. Species presence data and environmental variables were used for spatial modelling. The three aquatic species studied differed clearly in their current distribution, the factors controlling their occurrence and their response to future climate scenarios. Azolla filiculoides showed the highest current suitability and a generally stable to expanding trend under SSP3-7.0, although a reduction was projected under SSP5-8.5 by 2071–2100. Elodea nuttallii showed a reduction under most scenarios, but a late-century increase in suitable area was projected under SSP5-8.5. Vallisneria spiralis was more stable overall, although the models indicated an initial increase in suitable area, followed by a decline towards the end of the century, more pronounced under SSP5-8.5. Cluster analysis showed that each species was mainly linked to its characteristic vegetation type, while DCA revealed moderate to relatively strong floristic gradients between relevés. In conclusion, climate change may increase the risk of invasion of some aquatic macrophytes in the Danube Delta, but the magnitude and direction of change differ depending on the species. Azolla filiculoides appears to benefit most from future conditions, E. nuttallii may become more restricted, and V. spiralis appears comparatively more stable. This species-specific response highlights the need for targeted monitoring and adaptive management in vulnerable wetland habitats. The qualitative hydromorphological assessment further indicates that differences in lake connectivity, water exchange and transparency may contribute to the ecological variation observed among the studied lakes and should be considered in future monitoring of submerged macrophyte development.