Copepod-associated microbiome responses to organophosphate ester plasticizers and other bioaccumulative organic pollutants in the ocean

• Oceanic copepod-associate microbiomes responded to bioaccumulative pollutant exposures. • Enterobacterales tracked OPEs, PAHs, and PFAA levels across an Atlantic transect. • OPE exposure reduced copepod egg production and changed microbiome composition. • Potential use of host-associated microbiomes as pollutant biosensors is suggested Organic pollutants pose a growing threat to ocean ecosystems, largely due to their persistence, bioaccumulation potential, and toxicity. Yet, directly measuring the full spectrum of pollutants in situ remains unfeasible, and thus there is a dearth of alternative indicators of exposure. Host-associated microbiomes offer a promising but underexplored approach to fill this gap. Along a latitudinal transect of the Atlantic Ocean (40°N – 52°S), we observed significant correlations between the relative abundance of Enterobacterales in copepod-associated bacterial communities and seawater concentrations of organophosphate esters (OPEs), polycyclic aromatic hydrocarbons (PAHs) and with some perfluoroalkyl acids (PFAAs). All these chemicals bioaccumulate in marine zooplankton. Laboratory exposures of the copepod Paracartia grani to environmentally relevant OPE concentrations revealed similar microbiome composition shifts and decreased fecundity, revealing active depuration processes, including microbial degradation and fecal pellet production. These findings establish the basis for exploring host-associated microbiomes as sensitive indicators of bioaccumulative contaminant exposure in marine ecosystems, offering a novel avenue for large-scale pollution monitoring.