## 1 Introduction  
Toxicity tests are key tools for biomonitoring and assessing the risk of chemical substances released into the environment. Protocols for organism culture and bioassays with species from various trophic levels and taxonomic groups are essential for understanding the potential impacts of environmental pollution. Thus, improving standardization and developing new standardized protocols for bioassays with ecologically relevant species are key priorities in ecotoxicology [1]. Identifying model species in marine ecotoxicological studies is particularly important. These species should be abundant, widely distributed, ecologically relevant, and experimentally manageable in the laboratory. They should aid in elucidating pollutants' acute, chronic, and developmental toxicity. Copepods fulfill all these criteria, and their potential in ecotoxicology has long been recognized [2]. An increased understanding of copepod physiology, monitored through endpoints such as survival, development, growth, fecundity, respiration, and swimming behavior, is essential. This knowledge can help predict how natural copep populations will respond to environmental changes in the context of oil and gas exploration and production [3; 4]. _Acartia tonsa_ was selected as the model species for this study due to its extensive usage in ecotoxicological research, ecological importance, and high sensitivity to environmental pollutants. Widely utilized in ecotoxicology, it offers a strong foundation of scientific literature and standardized protocols, enabling reliable comparisons across studies [5]. Ecologically, _A. tonsa_ plays a crucial role in marine and estuarine ecosystems as a primary consumer, influencing the food web and serving as an indicator of ecosystem health [6; 7; 8]. Its high sensitivity to pollutants, even at low concentrations, makes it an ideal species for detecting and assessing toxic effects in aquatic environments, providing early warning signals of ecological disturbances [3; 9]. These factors collectively make _A. tonsa_ a critical species for environmental research and the assessment of ecological risks [1]. The Black Sea is a unique marine environment characterized by specific climatic conditions and distinct ocean currents, contributing to its ecological sensitivity [10]. The region experiences limited water exchange with other seas, leading to a stratified water column where the deeper layers are often oxygen-deprived [11; 10; 12]. This stratification, combined with the sea's semi-enclosed nature, makes the Black Sea particularly vulnerable to ecological disturbances [13; 14]. The ecosystem is highly sensitive to changes, and even minor environmental shifts can have significant consequences for marine life [15; 16; 17]. Potential environmental stressors in the Black Sea include pollution from agricultural runoff, industrial discharges, and heavy maritime traffic, all of which pose substantial risks to the balance of this ecosystem [18; 19]. These factors make the Black Sea an area of concern for environmental research, necessitating careful monitoring and assessment to protect its ecological integrity. In recent years, the interest and development in oil and gas exploration and production have increased significantly in the Romanian Black Sea region [20; 21]. Covering 22,000 square kilometers and reaching depths beyond 1000 m, the Romanian offshore area is divided into various perimeters [22]. Some of these perimeters have been allocated to operators for exploration, development, and production activities [21; 22]. While current exploration primarily targets shallower waters (up to 1000 m deep), there is also a focus on developing new plays represented by slope and basin-floor fans located further offshore [21; 23]. As a result, there is a growing concern about the potential environmental impact of chemicals discharged during oil and gas production on the Black Sea [21].