Eutrophication, driven by excessive nutrient enrichment from sources like agricultural runoff, industrial discharge, and urbanisation, has severely impacted the Black Sea since the 1980s. This study aimed to assess eutrophication dynamics in the Romanian Exclusive Economic Zone from 2020 to 2022 using the Black Sea Eutrophication Assessment Tool (BEAST), an integrated approach to the causes and effects of eutrophication. Data were collected from 68 stations during five oceanographic expeditions, analysing 617 water samples for nutrients, chlorophyll a, zooplankton species Noctiluca scintillans, and dissolved oxygen. Additionally, 179 zoobenthic and 251 phytobenthic community samples were collected. The results indicate that coastal waters exhibit higher nutrient levels and algal blooms compared to offshore waters, necessitating significant reductions in nutrient concentrations to achieve good environmental status. In transitional waters, within the Danube Delta Biosphere Reserve, a 55% reduction in inorganic phosphorus and a 43% reduction in inorganic nitrogen concentrations are required, while coastal waters need reductions of 38% and 37%, respectively. The study highlights the need for improved wastewater treatment, stricter agricultural runoff controls, and continuous monitoring. Effective ecosystem-based management strategies, integrated coastal zone management, and international cooperation are essential to mitigate eutrophication and promote the long-term health of the Black Sea ecosystem.

Marine ecosystems are becoming increasingly vulnerable to cumulative anthropogenic effects and pressures. Therefore, various methodological approaches and tools have been designed to apply cumulative impact appraisal schemes and better assess the dynamics and interactions among pressures affecting marine ecosystems. This study aims to apply the Spatial Cumulative Assessment of Impact Risk for Management (SCAIRM) tool for the Black Sea coastal waters considering human activities, pressures, and effects on different ecosystem components coupled with one management scenario development for actual and new emerging sectors. According to the SCAIRM, the primary pressure on the marine ecosystem was identified as introducing or spreading non-indigenous species from shipping. Additionally, when considering cumulative impact, activities related to coastal defense and flood protection, particularly beach nourishment works, were found to have the highest impact. This is due to the cumulative scores associated with the physical loss from permanent alteration or removal of seabed substrates, and temporary or reversible physical disturbances to the seabed. The scenario development indicated that after shipping, oil and gas exploitation is anticipated to become the second-highest risk sector for additional impact in the Romanian Black Sea. Additionally, the increased military activities related to the war in Ukraine present escalating risks that must be considered in EBM strategies. The results assess the possible effects of human activities and the associated pressures to direct management toward achieving sustainability, biodiversity protection, and the marine ecosystem’s integrity.

In order to analyze how environmental factors affect planktonic organisms along the Romanian Black Sea coast, this study created semi-quantitative models of the causal relationships between phytoplankton, zooplankton, and physicochemical parameters by utilizing user-friendly modeling tools. Eleven years of time-series data (March–September 2008–2018) were used to investigate the relationships between phytoplankton, zooplankton, and environmental factors (such as temperature, salinity, and nutrients). Variables such as marine reporting units and phytoplankton species and classes were used to identify developmental patterns, utilizing the Mental Modeler platform to consider interactions between the physicochemical parameters and phytoplankton, phytoplankton and zooplankton, and zooplankton and physicochemical parameters. Although the increase in the overall number of elements and linkages was uncertain in waters with variable salinity compared to marine ones, the semi-quantitative models created for the three marine reporting units along the Romanian Black Sea coast were comparable in terms of complexity. Across the typical and examined types of phytoplankton proliferation (normal, abundant, and blooms), the number of components and connections in the case of phytoplankton blooms substantially decreased as species- and growth-promoting variables increased.

The paper contributes to the Sustainable Development Goals (SDGs) targeting Life Below Water by introducing user-friendly modeling approaches. It delves into the impact of abiotic factors on the first two trophic levels within the marine ecosystem, both naturally and due to human influence. Specifically, the study examines the connections between environmental parameters (e.g., temperature, salinity, nutrients) and plankton along the Romanian Black Sea coast during the warm season over a decade. The research develops models to forecast zooplankton proliferation using machine learning (ML) algorithms and gathered data. Water temperature significantly affects copepods and “other groups” of zooplankton densities during the warm season. Conversely, no discernible impact is observed on dinoflagellate Noctiluca scintillans blooms. Salinity fluctuations notably influence typical phytoplankton proliferation, with phosphate concentrations primarily driving widespread blooms. The study explores two scenarios for forecasting zooplankton growth: Business as Usual, predicting modest increases in temperature, salinity, and constant nutrient levels, and the Mild scenario, projecting substantial temperature and salinity increases alongside significant nutrient decrease by 2042. The findings underscore high densities of Noctiluca scintillans under both scenarios, particularly pronounced in the second scenario, surpassing the first by around 70%. These findings, indicative of a eutrophic ecosystem, underscore the potential implications of altered abiotic factors on ecosystem health, aligning with SDGs focused on Life Below Water.

SUMMARY: The dinoflagellate family Amphidomataceae includes the genera Azadinium and Amphidoma, several species of which are known producers of lipophilic toxins known as azaspiracids (AZAs). However, the diversity, abundance, and distribution of this important group of nanoplanktonic dinoflagellates in the Black Sea remain poorly understood. To address this knowledge gap, Amphidomataceae were specifically investigated during a PHYCOB research cruise in the western Black Sea in September 2021. The study employed live microscopy observations on board, electron microscopy of field‐collected samples, quantitative assessments of abundance and distribution in preserved samples, and the establishment of clonal strains. Amphidomataceae species were detected at all stations, with abundances ranging from 1.2 to 13.0 × 10³ cells per liter. However, no AZAs were detected in any of the field samples. Light microscopy and subsequent SEM analyses revealed a high diversity of species. Field‐sample‐SEM‐documented records included Azadinium trinitatum, Az. spinosum, Az. luciferelloides, an undescribed Azadinium species, Amphidoma languida, and an undescribed species of Amphidoma. Additionally, two clonal strains were successfully established and are newly described here as Amphidoma pontica. This new species closely resembles Am. languida and Am. fulgens, but is distinguished by the absence of contact between the distalmost apical plate (6′) and the distalmost precingular plate (6″). Molecular phylogenetic analysis based on concatenated ribosomal markers supports its classification as a distinct species. Neither of the Am. pontica strains produced detectable levels of AZAs. This study significantly contributes to a foundational assessment of the species diversity, distribution, and potential toxicity of Amphidomataceae in the Black Sea.

Harmful Algal Blooms (HABs) represent a significant global challenge to human health, economies, and ecosystems, including those of the Black Sea. Despite previous reports of potentially toxic microalgae and phycotoxins in the basin, the taxonomy and occurrence of toxigenic species and their associated toxins remain poorly resolved. During the PHYCOB cruise in September 2021, the diversity and distribution of toxigenic microalgae and phycotoxins were investigated across 23 stations in the western Black Sea, covering Bulgarian and Romanian waters. Numerous potentially toxic microalgal taxa were identified using complementary morphological (light microscopy and scanning electron microscopy) and molecular (DNA metabarcoding) methods. The genus Pseudo-nitzschia was the only representative of potentially toxic diatoms, but no domoic acid was found. Among toxic dinoflagellates, Dinophysis spp., Protoceratium reticulatum, Lingulaulax polyedra, and Gonyaulax spp. were frequently observed, along with the related pectenotoxins and yessotoxins. Species distribution modelling indicated that the western Black Sea provides favorable conditions for Dinophysis spp., L. polyedra, and P. reticulatum. Additionally, several Alexandrium species were identified, including the first record of A. fragae in the basin, along with the detection of the associated phycotoxins (GTX-2/3 and GDA). This study provides the first integrated assessment combining light and scanning electron microscopy, DNA metabarcoding, and chemical analyses of toxigenic microalgae in field samples from the western Black Sea, contributing to an improved understanding of their region-specific profiles.