The impact of plastic pollution in the Indian Ocean on filter-feeding megafauna, particularly reef manta rays (Mobula alfredi)

Plastic is ubiquitous in the environment and is known to have major negative impacts on marine ecosystems. Marine organisms can entangle in discarded fishing gear, ingest plastic debris, and accumulate leached toxic chemicals in their systems. The reef manta ray (Mobula alfredi), a large charismatic filter-feeding elasmobranch, is exposed to the risks of plastic pollution, due to its low trophic level and its habitat overlap with areas of plastic accumulation. The central Indian Ocean is home to many reef manta ray populations, but little is known about plastic pollution in that region, and its impacts on reef manta rays is unclear.
This project firstly aims to assess the global exposure of reef manta rays to plastic pollution, by overlapping their habitat range, movement patterns and feeding grounds with plastic distribution maps, to allow the identification of ingestion and entanglement risk hotspots. To validate the risk assessment, the project then explores the presence of microplastic in reef manta ray feeding grounds in the Chagos Archipelago and evidence of entanglement injury from Photo ID pictures. Finally, the project will investigate the origins of plastic pollution in the Chagos Archipelago, including the proportion of debris stemming from shipping lanes and fishing activities.
We hope this project will allow us to translate plastic pollution exposure to actual risk and impact on a species that is highly important for tourism and livelihoods in the region and is already threatened by other anthropogenic stressors. We also hope the project will enable targeted action to reduce plastic pollution at its source and mitigate its impacts in key habitats for reef manta rays. This is especially important in the context of the current negotiations of the UN Global Plastics Treaty.