How Plastics Affect Coral Reefs

Also referred to as the rainforest of the sea, coral reefs are these beautiful underwater ecosystems found in various oceans around the globe. Home to over 4,000 species of fish, the reefs play an important role to a thriving underwater life.

coral reefs

And as pretty as these coral reefs are, they are now at great risk. Plastics are finding their way into reef ecosystems. And what we often labelled as “just one straw” or “just one water bottle” when we toss it into the ocean or leave it by the shore, sink below the surface, and contaminate the corals. This is when the problem begins.


Tune in to WAKEcup and Smell the Coffee podcast to learn more about how coral reefs help us and how we can help make a difference in their future.

Our Plastic Waste in Numbers

In the UK, we produce about 2.2 million metric tons of plastic package waste each year. We use about 13 billion plastic bottles each year and while recycling efforts are increasing, only 7.5 billion are recycled. That’s 5.5 billion plastic bottles ending up in landfills and incinerators annually. According to a 2019 report, The River Mersey is considered the most polluted with microplastics in the UK. The environmental organisation Greenpeace says it's “proportionally more polluted than the Great Barrier Reef patch.” And this is just a river - imagine the amount of plastic in the vast ocean waters.

plastic in ocean

In the US, over 300 million tons of plastic are produced annually and it is estimated that 50% of this is for single-use purposes. In Asia, plastic demand continues to rise, as much as 16% in 2019 and it’s estimated that 359 million tonnes of plastic were produced in 2018. According to scientific online publication Our World in Data, China has the highest share of mismanaged plastic waste with around 28% of the global total. This is followed by Indonesia at 10%, and Philippines and Vietnam at both 6%. Unfortunately, less than 10% of plastic was recycled in Asia. And these numbers are the very reason why reducing plastic waste is important.

How Plastics Affect Coral Reefs

The UK’s water is home to coral reefs that are about 8,000 years old. And Asia contains about 38,600 square miles of coral reefs. That’s almost 34% of the world’s total. These reefs and more are at risk with the amount of plastic waste going into the oceans. Because plastics damage corals in more than one way.

plastic waste

“Over the past 7 years of working in the dive industry, I have seen first hand the effects of plastic pollution and even more worryingly, I have seen an increasing amount of it in places that I visit regularly. Even in the most far away and remote Pacific Islands, I have collected plastic waste which has travelled thousands of miles on ocean currents from all corners of the globe,” says Grant Thomas.

Thomas is a multi-awarded underwater photographer whose work gives us a glimpse of how beautiful our great waters are. Thomas shares that “plastic pollution affects the entire ecosystem and when it comes to the ocean, this can be extremely detrimental as many organisms rely on one another to survive,” adding that “when one single component of this fragile system is disturbed it has a knock-on effect for everything else.”

Unable to photosynthesise

Corals practically have their own food system. Zooxanthellae is a type of algae living within the coral polyps. This algae needs sunlight to make sugar for energy which is then transferred to the polyps.

coral reefs

But when coloured plastics reach the reefs, “it will prevent light from reaching the zooxanthellae embedded on the tissues of the corals and prevent these symbionts from photosynthesizing and depriving the coral its food,” explains Vincent Hilomen Ph.D., an associate professor at the Institute of Biological Sciences at the University of Los Baños in the Philippines. He added that when they settle in reefs, plastics can “smother coral colonies and prevent polyps from extending tentacles to feed.” Over time, colonies covered by plastic, according to Hilomen, can die.

Increasing chances of disease

Yes, plastics can cause disease in coral reefs. In fact, reports say that the likelihood of disease “increases from 4% to 89% when corals are in contact with plastic.” Our oceans have all sorts of bacteria and when corals come in contact with plastic items, they get abraded. This means bacteria from the water could easily find its way into the corals. It’s kind of like the plastics are tearing and opening the skin of the corals.

It Affects Other Animals, Organisms, and Us

coral reefs

Thousands of fish species depend on coral reefs. “This is commonly referred to as symbiosis - the interaction between two different organisms living in close, physical association, typically to the advantage of both,” says Thomas. Fish depend on coral reefs for food and shelter. Some are commercially important species. Thus, when plastics damage the reefs, it could reduce the fish occupying that ecosystem. Not to mention that when plastics disintegrate into small bits called microplastics, it will find its way to our food. As Hilomen puts it, “the stage when plastics become microplastics is scariest because plastic that small can literally enter tissues of fish and other living organisms. This is when plastics can enter our food chain.”

When fishes consume microplastics, it may also disrupt how they affect the corals. “Parrotfish are important ‘grazers’ for reef systems, keeping them healthy” says Thomas. And when a parrotfish ingests microplastics, they could be poisoned.

What Can We Do

There’s so much to learn about the beauty of coral reefs, its relation to other animals and organisms, and how plastic can disrupt it. Equally, there’s so much we can do to make sure we don’t worsen the situation.

By being mindful of our plastic usage, we are essentially training our minds to keep track of how much plastic we use. It’s not easy to shift from a lifestyle of ease to one that is more beneficial to the planet. Especially that undeniably, plastic products do add ease to our lives, and we’ve been so used to it. Making this shift takes time and practice. But even the simplest act such as bringing a water bottle with you all the time so you won’t have to purchase those in plastic bottles can serve as a good start.

Studies also help push those in position to act. In the Philippines, Hilomen shares that a small study was conducted by a group of teachers in Negros Oriental. “When they sampled tissues of rabbitfishes, they found significant amounts of plastic in the intestines and flesh of the fish. Many locals eat the intestines of this fish,” he noted, adding that this study “triggered the provincial government to ban single-use plastics in the province.”

coral reefs

There’s a lot we can do and there’s a lot to do. Nobody will clean the oceans for us but us. And most certainly, nobody will be ultimately affected by the damage in reefs and oceans caused by plastics but us. “The surface of our planet is covered by 70% water meaning that this is a global issue and one which affects all of us,” says Thomas.


Tune in to WAKEcup and Smell the Coffee podcast to learn more about how coral reefs help us and how we can help make a difference in their future.

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