Manta rays and whale shark are guzzling down pieces of plastic at a startling rate while feeding in the waters of Indonesia, a new study has revealed.

The study, published in the journal Frontiers in Marine Science, has investigated how the feeding behavior of manta rays (Mobula alfredi) and whale sharks (Rhincodon typus) is being affected by plastic pollution in three coastal locations around Indonesia's Coral Triangle, known as the “Amazon of the seas" due to its rich biodiversity. 

From tiny flecks of plastic formed from broken down carrier bags to fishing nets and candy bar wrappers, they found that these marine giants were indiscriminately hoovering vast amounts of plastic while attempting to filter feed on plankton.

At certain times of the year, they estimated whale sharks could be swallowing up to 137 pieces of plastic per hour, while manta rays swallowed up to 63 per hour.

The international research team reached these figures by working out the concentrations of plastics in the marine areas based on trawl samples and visual surveys, the volume of water these animals swallow while filter-feeding, and how often they feed.

The abundance of plastic varied massively, with visual surveys suggesting there could be between 210 to 40,844 pieces per square kilometer depending on the area. The researchers took into account how the concentration of plastic varies depending on the season, with plastic abundance becoming 44 times higher during the rainy season. This meant in the dry season, manta rays would consume around 4.4 pieces an hour, however, that would rise to 62.7 pieces per hour during the wet season.

Indonesia’s waters have a notorious plastic problem. The southeast Asian nation is the second-biggest producer of plastic trash after China, responsible for around 10 percent of the planet’s mismanaged plastic waste. Unfortunately, the area is also a gold mine of biodiversity. The Coral Triangle is home to over 75 percent of the world’s coral species, six of the world's seven marine turtle species, and a bunch of different marine mammals, including dolphins, porpoises, blue whales, and the endangered dugong.

Despite being found everywhere – from human poop to Arctic snow – researchers know relatively little about the health effect of microplastics on wildlife. However, as you can imagine, it’s fairly clear that ingesting larger pieces of plastic can cause huge problems for marine mammals, fish, and seabirds. 

Just last year, a dead sperm whale washed ashore on the coast of Indonesia with a stomach full of 5.9 kilograms (13 pounds) of plastic trash, including at least four plastic bottles, 25 plastic bags, two pairs of plastic flip-flops, and over 100 plastic cups.

Worse still, a Cuvier's beaked whale was recently discovered in the neighboring country of the Philippines with over 40 kilograms (88 pounds) of plastic trash in its guts.