No escape from microplastics: Contamination of reef manta ray feeding areas in a remote, protected archipelago

Remote islands receive plastic debris from elsewhere, ranging from microplastics (>5 mm) to macroplastics, which can further breakdown into microplastics. The ingestion of microplastics by marine species has been linked to decreased fitness. Reef manta rays, Mobula alfredi, are liable to ingest microplastics due to their filter-feeding strategy and habitat overlap with plastic hotspots. Their population is in decline due to unsustainable fishing pressures and a slow life history, with potential additional demographic pressure from plastic pollution. This study investigates the concentration and characteristics of microplastics in the top 0.5 m of the water column in reef manta rays feeding areas around the Chagos Archipelago, a large remote marine protected area that is highly contaminated by macroplastic debris. Across all samples, a mean of 1.1 microparticle/m3 was found, the majority of which were blue and black fibers. Half of the particles were confirmed as synthetic (53.6%, n = 305 out of 569 Fourier transform infrared spectroscopy'd particles), with the main synthetic polymers being polyester (21.1%), polypropylene (8.8%) and nylon (4.6%). Egmont Atoll, an International Union for Conservation of Nature “Important Shark and Ray Area” for its importance to reef manta rays, was the most contaminated atoll around the archipelago (1.6 microparticle/m3). Continued regular beach cleans in important areas for biodiversity are recommended, as well as implementing new methods to reduce local input of microplastics, such as washing machine filters, and ultimately a global continued effort to reduce plastic usage and improve its disposal.