Microplastics as potential vectors of diatom oxylipins and possible effects on copepods

Microplastic (MP) pollution is a critical planetary boundary threat. Once released into aquatic environments, MPs become rapidly colonized by microbial assemblages forming biofilm communities collectively known as the “plastisphere”. Diatoms are early colonizers and often outcompete other primary producers onto MPs. Although diatoms drive synthesis of many different bioactive secondary metabolites, such as oxylipins, little is known about how diatom-derived chemicals could affect MP-associated community dynamics or even responses of organisms ingesting MPs. Copepods, pivotal components of pelagic ecosystems, can passively entrain MPs into their feeding currents and thus ingest the particles overlapping in size with natural preys such as diatoms, dinoflagellates and ciliates. Ingestion of MPs can alter copepod feeding behavior, reproductive output, hatching success, and finally disrupt carbon export through modified fecal pellet production. Interestingly, these effects largely resemble those historically described after exposure of adult copepod females to oxylipin-producing diatoms. Considering that several diatom genera colonizing MPs are also reported as oxylipin producers, our review proposes a conceptual framework in which MPs not only may cause physical and nutritional stress to copepods but also mediate chemical stress through their epiplastic diatoms. Potential oxylipin synthesis following ingestion of diatom-colonized MPs could multiply the negative impacts of MPs on copepod fitness, with cascading effects at the population level possibly extending to trophic dynamics and carbon cycling. Future research should focus on quantifying oxylipin production in epiplastic biofilms, and on experimental assays comparing copepod responses to sterile versus diatom-colonized MPs to clarify the ecological relevance of these combined stressors.