Planktonic Trophic Transitions in the Black Sea: Functional Perspectives and Ecosystem Policy Relevance

Phytoplankton–mesozooplankton interactions play a central role in shaping Black Sea food web dynamics, yet their trophic coupling has been insufficiently investigated in policy-relevant frameworks. This systematic review of 86 peer-reviewed studies (1987–2025) synthesizes research trends, limitations, and knowledge gaps in the field. The analysis reveals a clear dominance of work on plankton community structure (81%), whereas topics such as modeling and scenario analysis (7%), ecosystem assessment (7%), and bloom dynamics and seasonality (5%) remain comparatively underrepresented. Post-2020 publications indicate a promising shift toward scenario-based frameworks, gelatinous zooplankton impacts, and trait-based indicators, although functional integration remains fragmented. Keyword co-occurrence and network analyses revealed a concentration on nutrient–phytoplankton–zooplankton pathways, while other themes—such as bioluminescence and redoxcline dynamics—appeared only marginally represented in the literature we analyzed. To support ecosystem-based management under the Marine Strategy Framework Directive (MSFD), we highlight three priorities: improving NPZD-type models, using trophic efficiency metrics, and standardizing plankton indicators across the region. Strengthening the mechanistic understanding of planktonic trophic linkages is critical for improving food web assessments and adaptive marine governance in the Black Sea.