Concern and awareness are spreading about the visible danger that plastic waste poses to life in the oceans. But there is another, invisible side to the problem.

While videos and social media images often showcase animals drowning from entanglement in plastic fishing nets or lines, or washing ashore with their stomachs full of plastic garbage,  the lesser known threat is the amount of micro-plastic pollution in the oceans. Tiny-sized bits of plastic, some of it the result of the breakdown of plastic as waste, but some of it purposely manufactured that way as additives to consumer products, pose a particular risk to ocean health.

A manta ray feeds in Indonesian waters. Photo by Lillian Ellevog.

The waters of Southeast Asia are some of the most biologically diverse marine regions on the planet. They are also among the most severely affected by plastic waste. In Indonesia, for example, up to 40 percent of disposed-of plastic garbage enters the marine environment. As waste of this kind is exposed to water it gradually dissolves into smaller pieces. [Editor’s note: see Olga Mironenko’s blog for an eyewitness account of how this process happens.]

Plastics are also purposefully manufactured to be microscopic in size for use in products such as facial scrubs and cosmetics, which eventually enter the oceans through sewers and water management systems. Some synthetic fabrics, such as the fleece fabrics popular in casual and outdoor sports clothing, shed microscopic fibers when laundered, and those too end up in seas and oceans.

Microplastics accumulate in marine organisms of all sizes. Photo courtesy Elitza Germanov.

As plastic pieces decrease in size, the likelihood of their being ingested by animals increases. Micro-plastics have been found in the respiratory and digestive systems of smaller animals such as crabs, and extremely small pieces have even been observe in plankton and algae. (See this BBC video of a micro-plastic fiber being ingested by a small plankton.)

Filter feeders, like the manta ray and whale shark, which inhabit the Southeast Asia region, coast along the ocean surface to feed on zooplankton. These species face a severe risk of ingesting micro-plastics, because the tiny particles and fibers get mixed in with the tiny animals they feed upon. Plastic accumulation can be detrimental to the digestive tracts of these animals and limit their ability to absorb nutrients. Micro-plastics also contain and absorb chemical toxins from the surrounding water, which can leach into the animals and affect other biological functions, such as their reproductive capacity.

Taking samples of plastic, while a manta ray feeds. Photo courtesy Elitza Germanov.

To better understand the consequences that these animals face from consuming micro-plastics, researcher Elitza Germanov  of Australia’s Murdoch University launched a four-year project in 2015 to measure the levels of micro-plastics in feeding grounds in Australia, Indonesia and the Philippines, as well as in the bodies, of manta rays and whale sharks. Germanov also aims to establish how levels of toxins such as pesticides and industrial chemicals may be building up in the animals’ bodies.

So far, the research in Indonesia has shown that manta rays ingest approximately 40-90 pieces of micro-plastic per hour while consuming zooplankton. The majority of these pieces came from the breakdown of shopping bags, food and household wrappers, and single use plastic items such as straws and bottle caps.

Germanov’s research project is supported by Marine Megafauna Foundation, a conservation NGO focusing on protection of large sea animals such as sharks, rays, marine mammals and turtles.