Zooplankton community structure as determinant of toxic substances content along the European coast.

Zooplankton are the key components of marine food webs, mediating the transfer of energy and substances between phytoplankton and higher trophic levels. Due to their short life cycles, high surface-to-volume ratios, and position in the food chain, zooplankton may also be highly efficient vectors of toxic compounds, including mercury (Hg) and endocrine-disrupting chemicals (EDCs), such as bisphenol A (BPA), 4-nonylphenol (4-NP), and 4-tert-octylphenol (4-tOP). This study investigated the influence of zooplankton community composition on the accumulation of these toxic substances along the European coast during a research cruise from the Baltic Sea to the Gulf of Cádiz, during which zooplankton and environmental data were collected from 11 coastal and one open-sea site. The use of multivariate statistics allowed to identify salinity as the dominant environmental driver shaping zooplankton community, explaining over 35 % of its variation. Community composition, in turn, was significantly related to the concentrations of Hg and EDCs. Elevated pollutant concentrations were associated with specific taxa, particularly meroplanktonic larvae of Polychaeta and Decapoda, and gelatinous forms e.g., Sagitta sp., and Oikopleura sp., likely due to their morphology and high sorption capacity. Spatial patterns of contamination also reflected anthropogenic inputs, with the highest pollutant levels observed near industrialized coasts and shipping lanes (e.g., Mecklenburg and Eckernförde Bays). Our findings suggest that both biological (taxonomic composition) and environmental (pollution sources, salinity) factors synergistically influence the accumulation and potential trophic transfer of toxic substances. Zooplankton community composition should therefore be considered an important factor in marine ecotoxicological assessments and pollution monitoring programs.