Microplastics & Megafauna

Starting in 2016, we investigated the levels of marine debris including microplastics in waters where manta rays and whale sharks are feeding in several locations across Indonesia.

We estimated the abundance of microplastics in surface waters where manta rays and whale sharks feed. Our findings suggest that manta rays could be ingesting around 60 pieces of plastic per hour of surface feeding at some of the sites studied. For whale sharks, it is more than double, at roughly 140 pieces per hour. Plastic was up to 44 times more abundant in the wet season than in the dry season, with the largest seasonal swing at Nusa Penida — so filter-feeders face a far higher risk of plastic ingestion at particular times of year. More than three-quarters of the plastic we found was smaller than 5 mm: fragments and films, not recognizable objects.

We confirmed that plastic ingestion by manta rays occurs by collecting samples of egested material — the first direct evidence that manta rays swallow plastic. We have since characterized what that plastic is: analysis of hundreds of pieces collected from a critical manta ray feeding ground at Nusa Penida found that almost all of it was polyethylene and polypropylene, broken down from larger items rather than manufactured at that size. Those two polymers are among the less hazardous plastics in themselves, but the chemicals they carry — additives absorbed from the surrounding water, and the microbial films that grow on them — remain a concern. Our current work is assessing whether these plastic-associated chemicals are accumulating in manta ray tissues, and whether they are passed from mothers to their pups.

This project is capitalizing on the importance of healthy manta ray populations for the blue economy and ecotourism to nearby communities while raising awareness of the impacts of microplastics. We have surveyed local community stakeholders to establish a baseline on their current waste management attitudes and habits, provided outreach session about our findings so far, and followed up our surveys to understand changes in attitudes and perceptions of waste management. These insights will be used to inform local governments, organizations, and stakeholders in an effort to improve local waste management policies.