This study investigates how environmental gradients shape the structure and interactions of coastal biotic assemblages in the Romanian Black Sea. A multi-trophic analysis was conducted across a network of stations in June 2023, integrating phytoplankton, microzooplankton, mesozooplankton, macrozooplankton, ichthyoplankton, and macrozoobenthos with key physico-chemical parameters. Principal component analysis revealed strong north–south contrasts: the northern sector was characterized by nutrient enrichment (nitrate, ammonium, and silicate) supporting phytoplankton blooms and microzooplankton peaks, while the southern sector showed more saline conditions and extended trophic coupling from phytoplankton through mesozooplankton to ichthyoplankton. The central sector appeared transitional, with community structure more closely related to oxygen and phosphate levels. In the north and south, plankton dynamics were strongly linked to nutrient availability, while macrozooplankton consistently aligned with salinity and silicate, reflecting their preference for more marine waters and partial decoupling from nutrient-driven pathways. Fuzzy Cognitive Map analysis indicated combined bottom-up and top-down control, with phytoplankton supporting mesozooplankton and macrozooplankton exerting strong negative pressure. Phytoplankton functioned as the main network driver, with mesozooplankton as the central mediator, and the persistent negative macrozooplankton effect suggests direct biological regulation beyond salinity influence. These findings highlight the dual structuring of Black Sea food webs and provide an integrative, multi-trophic baseline for ecosystem-based management and Marine Strategy Framework Directive Descriptor 4 (Food webs) implementation.

"The paper aims to develop and test a semi-quantitative method that generates scenarios for the zooplankton community development under salinity and nutrients fluctuations. First, we identified the relationships between the mesozooplankton component and the environmental factors by analyzing data (N=2566) collected within the warm season (May-September) of a decade (2008-2018). The biotic and abiotic parameters were investigated at 37 stations within the monitoring network of the Romanian Black Sea waters, covering all three marine reporting units (waters with variable salinity, coastal and marine) according to Marine Strategy Framework Directive (MSFD). We identified 32 mesozooplankton species belonging to ten taxonomic classes, copepods representing the bulk of the community. In waters with variable salinity and coastal waters, the fodder component of the mesozooplanktonic community was dominant, while in marine waters the nonfodder component was better and exclusively represented by Noctiluca scintillans. Physicochemical parameters that showed significant correlations with the mesozooplankton species were S (salinity) and nutrients - NO2- (nitrite), NO3-(nitrate), PO43-(phosphate) and NH4+(ammonium). The number of species significantly correlated with the physicochemical parameters showed variations generally correlated with the increasing salinity gradient: in waters with variable salinity nine species being correlated, in coastal waters ten species, and in marine waters five species. Key-Words: mesozooplankton, fodder, nonfodder, correlations, physicochemical "

This paper focuses on the dynamics of four jellyfish species, Aurelia aurita, Beroe ovata, Mnemiopsis leidyi and Pleurobrachia pileus, from the Black Sea. The samples were taken in time of two expeditions in 2021 (May-June and August-September). Aurelia aurita species was dominant in terms of biomass due to its large size, The density of the species Pleurobrachia pileus recorded high values, in the north, but also between the isobaths of 40-80 m. The density of the species Mnemiopsis leidyi was higher in the southern and central area of the Romanian Black Sea. Because jellyfish feed on zooplankton organisms, the eggs and larvae of commercially important fish, high densities of jellyfish can produce direct decreases in the trophic chain by reducing the biomass of zooplankton, and fish eggs and larvae.

As copepods are an important food source for most fish larvae, there is a continuing interest in developing techniques for culturing marine copepods as live food in aquaculture. Studies have shown that several species of calanoid copepods can be used successfully in aquaculture, acclimatized and grown in the laboratory over several generations and serve as testing organisms in acute toxicity tests. However, significant difficulties in cultivating calanoid copepods in high quantities were reported. They are related to their low tolerance to changes in water quality and reduced production capacity compared to other taxonomic groups. Therefore, working methods for obtaining viable cultures of calanoid copepods are dependent highly on the local environmental context. Until now, such a method has not been implemented for calanoid species from the Romanian Black Sea coast. This paper details the methodology we adapted and used for achieving a viable Acartia (Acartiura) clausi (Giesbrecht, 1889) culture using specimens collected along the Romania Black Sea coast Reproduction and egg hatching occurred under laboratory-controlled conditions, and viable individuals of A. clausi were obtained. Our results open the possibility of integrating this species in toxicity tests and food production for the marine aquaculture industry.