The Black Sea is the largest semi‐closed permanently anoxic basin on our planet with long‐term stratification. The study aimed at describing the Black Sea microbial community taxonomic and functional composition within the range of depths spanning across oxic/anoxic interface, and to uncover the factors behind both their vertical and regional differentiation. 16S rRNA gene MiSeq sequencing was applied to get the data on microbial community taxonomy, and the PICRUSt pipeline was used to infer their functional profile. The normoxic zone was mainly inhabited by primary producers and heterotrophic prokaryotes (e.g.,Flavobacteriaceae,Rhodobacteraceae,Synechococcaceae) whereas the euxinic zone—by heterotrophic and chemoautotrophic taxa (e.g.,MSBL2,Piscirickettsiaceae, andDesulfarculaceae). Assimilatory sulfate reduction and oxygenic photosynthesis were prevailing within the normoxic zone, while the role of nitrification, dissimilatory sulfate reduction, and anoxygenic photosynthesis increased in the oxygen‐depleted water column part. Regional differentiation of microbial communities between the Ukrainian shelf and offshore zone was detected as well, yet it was significantly less pronounced than the vertical one. It is suggested that regional differentiation within a well‐oxygenated zone is driven by the difference in phytoplankton communities providing various substrates for the prokaryotes, whereas redox stratification is the main driving force behind microbial community vertical structure.

Plastic pollution is a global concern that has a significant impact on marine life. Plastic is widely used and has become a pervasive pollutant in marine environments. Plastic contamination has been documented both in marine environments and biota. Plastic contamination in cetacean gastro-intestinal tract (GIT) content has received limited attention, especially in the Black Sea. This study aims to investigate plastic contamination in the GITs of bottlenose dolphins and harbour porpoises, introducing a novel methodology. Given the limited exploration of this issue in the Black Sea, the research predominantly focuses on microplastic contamination. The GITs were sampled through necropsy from stranded and by-caught cetaceans, and content was washed through a multi-sieves tool. The material retained on each sieve was analysed following specific protocols. All (100%) of the GITs contained plastics (meso- and microplastics). In total, 1059 items (fibres, fragments, and beads) ranging from 22.86 µm to 5776 µm were found, suggesting a high contamination level in the Black Sea cetaceans. Future efforts should concentrate on increasing the number of samples and using the results for the implementation of the Marine Strategy Framework Directive (MSFD).

The ability of bacteria to degrade organic pollutants influences their fate in the environment, impact on the other biota and accumulation in the food web. The aim of this study was to evaluate abundance and expression activity of the catabolic genes targeting widespread pollutants, such as polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and hexachloro-cyclohexane (HCH) in the Black Sea water column and sediments. Concentrations of PAHs, PCBs and HCH were determined by gas chromatography (GC) coupled to mass spectrometry (MS) and electron capture (ECD) detectors. bphA1, PAH-RHDα, nahAc, linA and linB that encode biphenyl 2,3 dioxygenase, α-subunits of ring hydroxylating dioxygenases, naphthalene dioxygenase, dehydrochlorinase and halidohydrolase correspondently were quantified by quantitative PCR. More recalcitrant PAHs, PCBs and HCH tended to accumulate in the Black Sea environments. In water samples, 3- and 4-ringed PAHs outnumbered naphthalene, while PAHs with > 4 rings prevailed in the sediments. Congeners with 4-8 chlorines with ortho-position of the substituents were the most abundant among the PCBs. β-HCH was determined at highest concentration in water samples, and total amount of HCH exceeded its legacy Environmental Quality Standard value. bphA1, was the most numerous gene in water layers (10⁵ copies/mL) and sediments (10⁵ copies/mg), followed by linB and PAH-RHDα genes (10³ copies/mL; 10⁵ copies/mg). The least abundant genes were linA (10³ copies/mL; 10⁴ copies/mg) and nahAc (10² copies/mL; 10⁴ copies/mg). The most widely distributed gene bphА1 was one of the least expressed (10^-3-10^-2 copies/mL; 10^-1 copies/mg). The most actively expressed genes were linB (10¹-10² copies/mL; 10³ copies/mg), PAH-RHDα (10¹ copies/mL; 10² copies/mg) and linA (10^-1-10⁰ copies/mL; 10⁰ copies/mg). Interaction of bacteria with PAHs, PCBs and HCH is evidenced by high copy numbers of the catabolic genes that initiate their degradation. More persistent compounds, such as high-molecular weight PAHs or β-HCH are accumulating in the Black Sea water and sediments, albeit microbial activity is directed against them.

Macroalgal cultures are currently of great interest worldwide. Although along the Romanian Black Sea coast, there is no tradition in this sense, currently, a major interest in developing this direction exists, taking into consideration that the overexploitation of wild seaweed resources involves the disturbance of the marine environment, with implications that can sometimes be irreversible. Porphyra and Pyropia species (also known as nori algae) are considered the world’s most valuable mariculture algal products due to their high nutritional value and multiple active principles, considered unique representatives of marine algae. Considering these aspects, attention was focused on the only nori species from the Romanian Black Sea coast, namely, Pyropia leucosticta. The species was cultivated in controlled laboratory conditions for 5.5 months by manipulating its reproductive elements. The aim was to establish a simple, low-cost method by avoiding the complicated conchocelis phase of the species; therefore, reproduction and further species development were achieved by collecting the released neutral spores and isolating them in culture vessels, ensuring, at the same time, proper nutrient conditions, using sterile enriched seawater and mimicking ambient conditions. At the end of the experiment, specimens of almost 80−90 mm were obtained, making this method suitable for obtaining ex situ P. leucosticta blades on the Romanian Black Sea shore.

Microplastics (<5 mm) are an emerging threat to marine ecosystems and organisms, including fish. Recent studies have ranked the Black Sea as one of the most plastic-polluted European seas. Although there is evidence of microplastic ingestion in various fish species in the Black Sea, data for the Romanian sector are still lacking. This study presents the first assessment of microplastic abundance, color, shape, and size in the gastrointestinal tract and gills of Engraulis encrasicolus (European anchovy) collected from different locations along the Romanian coast (NW Black Sea). Ingested plastics were identified using 10% potassium hydroxide (KOH) chemical digestion and analyzed under a stereomicroscope. We observed a high frequency of plastic ingestion, with up to 88% of anchovies containing microplastics (98.5%) and mesoplastics (1.5%), with a mean of 3.03 plastic items/individual, marking the highest reported abundance in the Black Sea. The most common types found were transparent fibers, within the size range of 330 µm–1 mm. Our assessment is the first to demonstrate microplastic contamination in commercial European anchovies from the Romanian coast. Further studies are required to completely understand the extent of microplastic pollution in Black Sea anchovies and its potential impact on both human health and the ecosystem.

Plastic and marine litter is one of the current growing issues worldwide, affecting the unique Black Sea ecosystem as well. Litter is yearly monitored for assessing ecological status across the Romanian beaches. We tested aerial drone-inspection or UAV method versus visual census for efficiency of litter monitoring on two Black Sea beaches, located in the Danube Delta area. The detection probability varied between size-category of items, with 71 – 100% accuracy of visual screening of drone images. Our pilot study showed the successful combination of the traditional visual census method with the new emerging UAV techniques for marine litter monitoring in the selected areas. To the best of our knowledge, this is the first study evaluating the UAV method for fast-screening of not-easily accessible sites at the Romanian coast of the Black Sea.