Microplastics in our oceans pose a growing concern to megafauna. Manta rays, whale sharks and some other large marine animals are filter feeders, which means they are at risk of ingesting these tiny pieces of plastic. Microplastics are now found in all oceans, with the Coral Triangle region having one of the highest concentrations of microplastics in the world. Plastics contain, absorb and concentrate toxics that may negatively affect the reproduction abilities of these already threatened species. Using manta rays and whale sharks as model species, the Marine Megafauna Foundation is studying the impacts of microplastics on large filter-feeding elasmobranchs.
In 2016, we investigated the levels of marine debris including microplastics in waters where manta rays are feeding in several locations across Indonesia.
Our preliminary findings based on concentrations of microplastics suggest that mantas could be ingesting 40-90 pieces of plastic per hour of surface feeding in the locations studied. Further work to discern seasonality trends is currently underway.
Additionally, we are examining if manta rays are exposed to plastic-associated toxins and to what levels, by collecting samples of egested material and stomach contents of manta species and their smaller cousins, the devil rays. Future work is also aimed at assessing microplastic concentrations and toxin exposure at feeding aggregation areas for whale sharks.
This project is capitalizing on the importance of healthy manta ray populations for the blue economy and ecotourism of nearby communities, while raising awareness of the impact of microplastics using the manta ray as our flagship species. Having already collected baseline surveys on current waste management attitudes and habits of local community stakeholders, we are planning follow-up surveys and outreach sessions. These insights will be used to inform local governments, organizations and stakeholders in an effort to improve local waste management policies.
Working in collaboration with Murdoch University in Western Australia, this project is currently supported by the Ocean Park Conservation Foundation, Foundation Fortuna, PADI Foundation, and Idea Wild. Additional collaborators are the Udayana University in Indonesia and the Large Marine Vertebrate Project Philippines.