Barnacles as emerging sentinels of microplastic contamination: A global synthesis and analytical framing

Barnacles are filter-feeders of promising performance as sentinels of microplastic contamination, yet their use remains limited. Here, we synthesize field-based evidence on microplastic in barnacles worldwide, proposing analytical standardization to enable their use in environmental monitoring. Fourteen field studies across seven countries reveal pronounced spatiotemporal variability. Fibers and fragments dominated, with polyethylene and cellophane as the prevalent polymers, reflecting distinct regional contamination profiles. Barnacles consistently reflected environmental microplastic conditions, capturing both elevated and low contamination regimes. Reaching 184.1 particles g −1 , Japan and Iran are potential hotspots. However, a global overview of barnacle-based assessments remains limited due to analytical heterogeneity and geographical monitoring gaps. Key methodological priorities for future research include standardizing rigorous quality control, biometrics, digestion, filtration, and multi-matrix integration. Barnacles may be robust sentinels, capable of enhancing the spatiotemporal and ecological representativeness of global microplastic monitoring frameworks. • Barnacles reflect microplastic contamination levels in contrasting environments. • Barnacles accurately reflect polymer type, size, shape and color patterns. • Contamination hotspots emerging despite limited geographic coverage. • Expand monitoring and homogenizing methodology is crucial to comparability. • Barnacles may be able to integrate global microplastic monitoring networks.