Simple SummaryThe potential risks posed by microplastics is fully recognised by the scientific community. Because of the multiple pathways that allow microplastics to reach aquatic ecosystems, researchers have focused their work on the ingestion and impact of microplastics on aquatic organisms. However, the main mechanisms through which microplastics shape ecological responses at different levels in the ecological hierarchy remain understudied, and a high degree of data fragmentation exists in the literature. Functional traits, having indirect effects on the three components of individual fitness: growth, reproduction, and survival, represent the main door through which anthropogenic disturbance can enter, impacting the ecological hierarchy, community structure and composition, and ecosystems’ features. In light of this, this meta-analysis aims at using data available in the literature to understand and assess how the impacts from microplastics spread across the ecological hierarchy, from the individual to the ecosystem level, and how and if microplastics pollution is negatively affecting biodiversity, ecosystem functioning, and the provision of ecosystem goods and services. Developing trait-based indicators represents a useful step to investigate the impacts of microplastics on ecosystems, and at the same time, could be used to guide policy makers in the development of adequate management plans capable of safeguarding ecosystems, together with the valuable goods and services they offer.AbstractMicroplastics represent an ever-increasing threat to aquatic organisms. We merged data from two global scale meta-analyses investigating the effect of microplastics on benthic organisms’ and fishes’ functional traits. Results were compared, allowing differences related to vertebrate and invertebrate habitat, life stage, trophic level, and experimental design to be explored. Functional traits of aquatic organisms were negatively affected. Metabolism, growth, and reproduction of benthic organisms were impacted, and fish behaviour was significantly affected. Responses differed by trophic level, suggesting negative effects on trophic interactions and energy transfer through the trophic web. The experimental design was found to have the most significant impact on results. As microplastics impact an organism’s performance, this causes indirect repercussions further up the ecological hierarchy on the ecosystem’s stability and functioning, and its associated goods and services are at risk. Standardized methods to generate salient targets and indicators are urgently needed to better inform policy makers and guide mitigation plans.