Rapid spatiotemporal monitoring of beach microplastics in the Galápagos Islands

Understanding the environmental fate and behaviour of microplastics across space and time is challenging, especially in remote locations such as the Galápagos Islands. Citizen science can support plastic monitoring by extending geographic and temporal coverage, though concerns persist around data validation. This study evaluated a simple citizen science methodology, aided by a near-infrared portable spectrometer (PlasTell), for the rapid monitoring of beach microplastics (>1 mm) to investigate spatiotemporal accumulation patterns on Tortuga Bay, Santa Cruz Island, Galápagos. A total of 3377 suspected microplastics were collected by citizen scientists between 2020 and 2025. ATR-FTIR spectroscopy verified that 92.77% of particles had been correctly identified as plastic, primarily low-density polyethylene (72.51%) and polypropylene (22.44%) fragments. The mean microplastic concentration on Tortuga Bay was 145.29 ± 23.57 particles m^-2, which increased significantly in 2024 (290.88 ± 73.76 particles m^-2), coinciding with the El Niño-Southern Oscillation in the Pacific Ocean. Accumulation gradients both parallel and perpendicular to the waterline were observed, with four-fold higher concentrations and elevated pre-production pellet ('nurdle') composition at the turtle nesting zone at the back of the beach (234.59 ± 42.25 particles m^-2, 22.54% respectively). Despite more limited characterisation potential, PlasTell identified 89.24% of microplastics in <1 s with no false positives, overcoming the analytical bottleneck of microplastics for researchers and enabling timely data validation. Subsequently, this study demonstrates how technology aided citizen science methodologies can fill major regional knowledge gaps on microplastic accumulation, compensating for climatic complexity and environmental variability, to support plastics monitoring efforts in remote island systems.