Plastic pollution is widely recognized as a major threat to marine ecosystems and biodiversity. Although systematic reviews (SRs) and meta-analyses (MAs) on plastic pollution have become increasingly common in the last decades, the conveyed evidence remains fragmented and often leads to contrasting conclusions. To obtain a broader perspective, we conducted the first systematic review of systematic reviews and meta-analyses investigating the effects of plastic pollution across diverse marine taxa at multiple levels of the biological organisation.

A total of 34 SRs/MAs, published between 2018 and 2024 and synthesizing 1176 primary studies, were analysed. We synthesized the reported ecotoxicological, ecophysiological and functional responses, while simultaneously evaluating the overlap among reviews using the Corrected Covered Area (CCA), and assessing their methodological quality through the AMSTAR 2 framework.

Despite the large amount of available evidence, overlap among SRs/MAs was remarkably low (CCA = 1.8%), indicating limited redundancy but strong thematic specialization of research on marine plastic impacts. At the same time, methodological quality was generally poor, with almost three-quarters of the reviews classified as critically low. The overview also highlighted persistent gaps in current synthetized research, including limited ecological realism, scarce attention to higher trophic levels and ecosystem-level processes, and strong methodological heterogeneity mainly due to the predominance of laboratory-based studies focusing on microplastics.

Our results demonstrate that this approach provides insight that cannot be obtained from individual evidence syntheses, through the identification not only of what is known, but also where evidence remains weak or fragmented. More broadly, the overview-of-reviews approach may be particularly valuable in rapidly expanding research fields, such as marine plastic pollution, where multiple systematic reviews and meta-analyses are available.