Ocean Plastic Pollution and Its Deadly Effect on Manta Rays

by | Nov 24, 2021 | How to Protect Manta Rays, Ocean Advocacy

Our oceans are heavily polluted by plastic. According to Conservation International, the numbers are staggering:

  • Every day, around 8 million pieces of plastic enter the oceans.
  • Every year, 8 million tons of plastic make their way into the oceans.
  • Currently, it is estimated that 150 million tons of plastic are in our oceans.
  • By 2050, the amount of plastic in the ocean will outweigh all of the fish.

Manta rays are victims of plastic pollution because their eating habits cause them to ingest plastic, which has harmful effects.

8 Million Tons of plankton end up in our ocean every year

Microplastics in the Ocean

Microplastics are very small plastics that are less than 5 mm – which is about the size of a sesame seed. They come from larger pieces of plastic that break down into smaller pieces, as well as from microbeads.

Microbeads are tiny pieces of manufactured polyethylene plastic that are added as exfoliants in some beauty products, cleansers, and toothpastes. They are so small that they can pass through filtration systems, which is how they end up in oceans and other bodies of water.

Primary vs Secondary Microplastics

According to National Geographic, “primary microplastics are tiny particles designed for commercial use, such as cosmetics, as well as microfibers shed from clothing and other textiles, such as fishing nets.” They enter the water through product use, unintentionally due to spills, or even from washing clothing.

The same article says that “secondary microplastics are particles that result from the breakdown of larger plastic items, such as water bottles.” The breakdown is typically caused by waves, wind, and the sun’s radiation. Straws, and other single-use plastic items, are the primary source of secondary microplastics.

Issues with Plastics

There are many issues with plastics. First, standard water treatment facilities cannot remove all traces of microplastics.

In addition, plastics are not biodegradable – they don’t break down into harmless molecules. Instead, they take hundreds or thousands of years to decompose.

Furthermore, microplastics in the ocean can bind with other harmful chemicals – and are then ingested by marine life.

Where Microplastics are Found

We know that microplastics are in the oceans and other bodies of water – as well as in marine animals.

Microplastics have also been found in seafood, drinking water, beer, table salt, snow and ice, and even in the air and rain.

In fact, Nature.com reports that there is a level of exposure in most, if not all, species. It’s possible that people ingest up to 100,000 microplastic specks each day – it’s time to put a stop to plastic pollution!

How Manta Rays Eat Plastics While Feeding

Manta rays eat zooplankton – and a lot of it. They have a variety of feeding techniques based on the type of manta ray, where they are feeding, and if they are feeding individually or with a group.

Manta rays are filter feeders: that means they take in the plankton along with other organisms, and then filter out the nutritious bits – and poop or vomit out the rest.

Along with the plankton they need to survive, manta rays ingest a lot of plastics. A study in Frontiers in Marine Science found that in some areas, manta rays may ingest up to 63 pieces of plastic per hour of feeding.

How Plastic Pollution is Hurting Manta Rays

Plastics are further reducing the population of manta rays, which is already considered a globally threatened species.

Direct Effects of Ingesting Plastics while Feeding

When manta rays and other aquatic species consume microplastics, they don’t eat as much of the food that they need for energy to carry out life functions, and to survive.

The toxic chemicals and pollutants found in plastics enter the manta ray’s digestive system, which may prevent the digestion of actual food. Moreover, according to the Marine Megafauna Foundation, this exposure alters hormones that regulate manta rays’ metabolism, growth and development, and reproductive functions.

Larger plastics can be even more harmful because aside from blocking nutrient absorption, they can also damage the digestive tract.

Long Term Effects of Plastics on Manta Rays

Microplastics have been found in zooplankton, the main food source for manta rays. Zooplankton that are exposed to microplastics produce half the number of larvae and the adults are smaller in size. So, as the levels of zooplankton decrease, there may not be enough food for manta rays.

Additionally, due to the altered hormones caused by plastics, manta rays have even lower rates of reproduction.

How to Help Improve the Plastic Problem for Manta Rays

According to Britannica, scientists are currently investigating the use of microorganisms to break down synthetic microplastic polymers. But, the amount of plastic in the ocean is skyrocketing, so we need to take action now!

Legislation to Protect Manta Rays

Over 30 countries and 8 states have banned the use of single-use plastics.

In 2015, President Obama banned the use of microbeads in cosmetics and personal care products through the Microbead-Free Waters Act of 2015.

The Clean Water Act and Trash-Free Waters provides regulatory tools that are used to keep trash out of waterways. However, these tools are not mandated. Instead, these tools can be used in conjunction with other non-regulatory measures to reduce trash in the water.

This is a great start – but there is more work to do!

Ways Everyone Can Help Manta Rays

Manta rays need our help – and there are really simple things we all can do to reduce plastic pollution and save this beautiful species:


Please join us in protecting manta rays from plastic pollution!


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