From Micronutrients to Contaminants: Missing Links Between Trace Metal Bioavailability, Zooplankton Responses, and Food Web Transfer in the Black Sea

Marine zooplankton (ZPK) connect basal pelagic compartments with fish and can mediate trace metal (TM) exposure through dissolved, dietary and particle-associated pathways. Their role in Black Sea (BS) metal cycling, ecological effects and food-web transfer remains poorly understood. This critical narrative review drawns on global TM–ZPK research to identify mechanisms and methods relevant to the BS and translates them into six benchmarks: chemical bioavailability and upstream pathways; uptake and retention; biological resolution; trophic transfer; environmental modifiers; and functional or community-level effects. Black Sea studies identified through a structured regional search were assessed against these benchmarks, and were classified as supported, partly supported, suggestive or untested. Global evidence shows that total TM concentrations in water or bulk plankton cannot elucidate exposure routes, internally retained burdens, ecological effects or trophic transfer. In the BS, although metal fractionation, particle pathways and ZPK ecology are relatively well documented, only a few heterogeneous studies confirm the occurrence of TM in pooled zooplankton. Available metal fractions have not been linked directly to ZPK uptake. The contribution of dissolved and dietary exposure, taxon- and trait-specific accumulation and elimination remain unresolved, whileZPK-mediated trophic transfer is only suggestive. Relevant environmental gradients and functional assays are available, but metal-by-environment interactions and links between internal burdens and population- or community-level effects remain untested. The central regional gap is the lack of matched studies linking bioavailable TM fractions, burdens in individual ZPK taxa, functional effects and transfer to predators. Global research indicates that coordinated sampling of connected compartmentsoffers the clearest path toward ecologically relevant BS pollution monitoring, biodiversity assessment and food-web evaluation.