The alien species Macrobrachium nipponense (De Haan, 1849), known as the oriental river prawn, has been identified in the Bulgarian part of the Lower Danube for the first time, based on morphological characteristics and DNA barcoding. Four specimens were caught in October 2023 in the Danube River near Pozharevo island (422.2 rkm). The diagnosis of the species was based on the number of the teeth on the dorsal and ventral side of the rostrum, the large size of the second pair of pereopods, and the presence of the hepatic spine. A fragment of cytochrome c oxidase subunit I (COI) gene of mitochondrial DNA was sequenced to supplement species identification. Phylogenetic analysis has revealed a high genetic similarity (over 99%) between the Bulgarian sample and samples from various geographic locations (Ukraine, China, Bangladesh, Iran, Iraq, and Russia). The record of the oriental river prawn confirms its expansion and successful naturalization in the Lower Danube region. The invasion of the species will probably affect the structure of benthic macroinvertebrate communities and represent a high risk to native species, which necessitates long-term monitoring of species’ impact on Danube River ecosystems.

The Dalmatian pelican Pelecanus crispus is a Near Threatened species of waterbird with populations in the wetlands of the Lower Danube River. Breeding populations declined due to habitat loss and wetland drainage and conservation efforts have focused on bringing breeding Dalmatian pelicans back to their former wetland sites in Bulgaria. Since 2008, conservation efforts have focused on building artificial nesting platforms at marshes along the Lower Danube River. These efforts resulted in considerable growth of the population in the country. Between 2011 and 2021, four wooden platforms were installed at the Belene Island wetland complex (Pechina and Martvo Marshes) and the Kalimok wetland complex. All four platforms were used successfully by pelicans, resulting in the formation of two new breeding colonies and a total of 91 pairs in 2021. The majority, 88 pairs, were recorded at the Belene Island marshes, with the remainder at the Kalimok colony. The average annual breeding success was 1.17 young per pair at Peschina Marsh (occupied from 2016-2021), 0.90 at Martvo Marsh (2020-2021), and 1.33 at Kalimok (2021). The average across all three colonies was 1.14 young per pair. By 2021, the breeding population of Dalmatian pelicans in Bulgaria had grown to 131-150 breeding pairs at three locations.

The present study aimed to assess the pollution of Bulgarian brackish lakes based on their ability to accumulate the heavy metals Cd, Zn and Ni. Physicochemical parameters, including pH, electrical conductivity and salinity of the waters, were determined by potentiometric methods. The heavy metal content of the water and crustacean samples was determined by atomic absorption spectrophotometry. The highest pH in the investigated lakes (Atanasovsko Lake, Poda and Pomorie Lake) in the period May–September 2021 was found in the month of September, in the waters of Atanasovsko Lake (8.84). The concentrations of Cd measured in Atanasovsko Lake in the fall were in the order of 0.0125 µg/L—the highest value recorded for all the studied water bodies. The concentrations of zinc and nickel in the waters did not exceed the norms in Bulgarian legislation. The dynamics of biogenic elements (Zn and Ni) in crustaceans were inversely proportional to those found in the waters. The levels of the toxicant cadmium as well as the metals zinc and nickel in the species Gammarus spp. and Atremia spp., inhabiting all analyzed water bodies, were significantly lower than those specified in the Bulgarian and European legislation. The pH and electrical conductivity parameters of the tested waters, as well as the concentrations of the heavy metals, cadmium, zinc and nickel, were within the recommended values. High positive correlations were determined between the content of nickel, on the one hand, and cadmium and zinc, on the other, in the organism of the investigated crustaceans. A longer period of research is needed to accurately determine the degree of contamination of these waters.

(1) Background: To date, data concerning the population of Alosa immaculata and Alosa tanaica from the marine waters of Bulgaria are rather scarce. In the range of a project for mapping the Bulgarian marine protected sites from the network NATURA 2000, we provide an intense investigation of the biology and distribution of both Alosa species. (2) Methods: A trawling survey was carried out within 102 predefined sampling plots of 10 × 10 km grid cells (93 cells on the continental shelf, up to 100 m depth, and 9 offshore cells). In some coastal regions, sampling was conducted with gill nets of different mesh sizes (28 mm to 36 mm). Analysis of the suitability of the occupied habitat of both species was carried out using the MAXENT v 3.4.0 software application. The status of the populations was studied based on the parameters abundance (ind./km⁻²), biomass (kg/km⁻²), size, sex structure, maturity, and food spectrum. (3) Results: Out of 102 transects studied, A. immaculata was found in 12 transects and A. tanaica in 13. A total of 408 fish specimens were captured, out of which 313 were A. immaculata and 95 were A. tanaica. Both species were distributed along Bulgaria’s entire Black Sea coast, with a numerical prevalence of the catches in the southern part. The population size of A. immaculata for the number of individuals on a biographical level in the Marine Black Sea Biographic Region (MBLS) was a minimum of 100,255 individuals and a maximum of 526,408 individuals (the average was 313,286). The population size for A. tanaica was a minimum of 28,183 individuals and a maximum of 449,549 individuals (an average of 238,866). The current population density of A. immaculata in the MBLS was 25.98 ind./km⁻², and for A. tanaica, it was 19.00 ind./km⁻². The current biomass of the population of A. immaculata in the MBLS was 3.44 kg/km⁻², and the population of A. tanaica was 0.53 kg/km⁻². The sex ratio for A. immaculata was 1 male:2.6 females, and for A. tanaica, 1 male:3.8 females. Both shad species were feeding with less intensity or not feeding during the winter. The diversity in the food spectrum of A. tanaica was more limited compared to that of A. immaculata. (4) Conclusions: Key parameters for the Bulgarian Black Sea Exclusive Economic Zone indicate current stability in the resources of A. immaculata and A. tanaica and more favorable conditions for the populations in the Natura 2000 sites compared to that outside the Natura 2000. The results of this study should be used to develop management plans for marine protected areas, and future monitoring projects should follow the sampling protocol.

The aim of the present study was to evaluate the bioavailability and associated bioactivity of p-coumaric (p-COA), caffeic (CA), and ferulic (FA) hydroxycinnamic acids (HCAs) isolated from an aqueous extract of plant material. An aqueous extract is more applicable in practice because this form is the most commonly used for oral administration. The p-COA, CA, and FA acids were evaluated for their behavior in the processes of absorption, distribution, metabolism, and excretion (ADME) using modern methods for assessing their functional groups according to Lipinski’s Rule of Five and the Rule of Nines. Given the available data on extensive metabolism of hydroxycinnamic acids during the first pass through the liver, it is necessary to consider an alternative route of administration, namely the sublingual route. Sublingual delivery of exogenous molecules obtained from plant material by extraction may represent a preferable alternative to oral administration, as first-pass hepatic metabolism is bypassed when dosage forms are administered sublingually.