Microplastic pollution along the Ningaloo Coast World Heritage Area: Local source contributions within a remote marine protected area.

This study provides the first quantitative assessment of microplastic (MP) contamination on beaches along the Ningaloo Coast World Heritage Area (NCWHA; Western Australia), a remote Marine Protected Area of multiple use, including tourism. Sediment collected across seven remote and urbanised beaches were processed using elutriation and density floatation separation, with putative MPs analysed by stereomicroscopy and Fourier transform infrared spectroscopy. Microplastics were detected at all sites and in 88% of samples, but at relatively low levels (0-8.5 MPs L-1) compared to many urbanised coastlines. Concentrations significantly differed among sites, indicating spatially heterogeneous accumulation. This was explained by proximity to boat ramps, distance to townships and beach aspect, with higher concentrations of MPs on north-west facing beaches. Polyethylene terephthalate (PET; 38.2%) and polypropylene (PP; 20.2%) dominated polymer composition, with manufactured fibres (72.4%) the most common shape across all sites. Consequently, no relationship was found between polymer or shape and site-specific predictors. Despite its remoteness and protected status, the NCWHA remains vulnerable to MP inputs, potentially from local human activities with dispersion influenced by natural processes. This baseline provides a critical foundation for future monitoring efforts and evaluation of targeted management interventions at high-use access points.