Environmental controls on planktonic community variability and ecosystem responses in the Romanian Black Sea

This study examines the structure, distribution, and environmental influences on planktonic communities in the Romanian Black Sea, based on data collected from Black Sea national monitoring stations in June 2023. We assessed the qualitative and quantitative composition of phytoplankton, microzooplankton, mesozooplankton, macrozooplankton, and ichthyoplankton, alongside key environmental factors such as temperature, salinity, dissolved oxygen, and nutrient concentrations (nitrite, nitrate, ammonium, phosphate, and silicate). The results highlight the dominance of dinoflagellates within the phytoplankton community, while copepods constitute the most abundant mesozooplankton group. Species from the Codonellidae family mainly represent microzooplankton diversity, while macrozooplankton is largely dominated by the scyphozoan Aurelia aurita. Ichthyoplankton diversity peaks in coastal waters, with Engraulis encrasicolus and Scorpaena porcus as the most abundant species. Environmental analyses indicated strong correlations between plankton distribution and salinity gradients, nutrient availability, and oxygen levels, with nutrients playing a significant role in shaping community structure. Principal component analysis further reveals spatial variability driven by nutrient enrichment in coastal and transitional waters, influencing primary production and trophic interactions. These findings provide essential insights into the ecological functioning of the Black Sea ecosystem, offering valuable data for marine biodiversity conservation, climate impact assessments, and sustainable resource management strategies.