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by Twenty5Degrees Team September 25, 2020 3 min read

By Shinsaku Takakawa



What are corals?

Corals look like any other plant amidst the ocean. They choose a spot to grow on and stay there for the rest of their lives. Plants or animals that are fixed to one place are called sessile. Coral is a structure covered in tiny flower like creatures called polyps.


These polyps are made up of a mouth and a stomach. The petal-like tentacles eat whatever they can catch. But there isn't a lot of food for polyps to eat in a reef, so the polyps have developed a symbiotic relationship with an algae called zooxanthellae (zo-UH-zan-thuh-lay) which live inside the polyps. The zooxanthellae use photosynthesis to produce sugars which feed both themselves and the polyps they live inside of. 


Why is coral so important?

These polyps are essential to our coral reef's life. Corals are very sensitive to change, and when stressed they let go of the algae that live inside them. This causes the coral to become white which is known as  coral bleaching. 


Coral bleaching can be caused by changes in water temperature, pollution, or overexposure to sunlight and air.


Coral live in a narrow temperature margin, and even a change of 2℃ can cause bleaching events. Water temperature changes are caused by the increasing amount of heat being produced, and the oceans absorb 93% of the heat we produce. Because of the burning of fossil fuels, we have seen an increase in ocean temperatures by 1℃ on average during this century. Last year, 2019 was the hottest year on record for our oceans.

There are many sources of marine pollution, and they damage the ocean’s ecosystems. Marine pollution can be anything ranging from mining operations, fishing practices, sewage disposal, runoff from land, using seawater as a coolant, and human garbage and waste. 

Exposure to sunlight and air can happen during low tide events of shallow coral reefs.


Corals can survive bleaching events if they are able to recover within a certain period of time, but they are more prone to stress, disease and death.

An infamous example of a bleaching event is the Great Barrier Reef, which is on the northeast coast of Australia. In the summers of 1998 and 2002, about 42%-54% of reefs were affected by coral bleaching, according to the Arc Centre of Excellence for Coral Reef Studies. 2002 might seem like a far away time, but coral bleaching is still happening today in 2020. Corals used to take 10-15 years to recover from bleaching events, but we are not giving them the chance to do so. 


How does coral bleaching affect me?

Coral bleaching might seem like something that wouldn’t affect us, but the loss of reefs would leave many species of fish no place to live. These fish would either have to migrate or die off. Even a small disruption in nature’s ecosystem will cause huge impacts on the rest. This would cause shockwaves that affect humans as well. Fishers will have no source of income and look for a new job, many tourism industries would collapse and there would be less coastal protection and food altogether. 


If we want to save all of our reefs and oceans, we must promote more effective ways of protecting nature and fighting pollution to our government leaders. 

For further reading:

ABC Science, director.What Exactly Is Coral?, 5 Oct. 2017,

Borunda, Alejandra.Ocean Warming, Explained. 14 Aug. 2019,

Cave, Damien. “Great Barrier Reef Is Bleaching Again. It's Getting More Widespread.”The New York Times, The New York Times, 6 Apr. 2020,

Cho, Renee. “Losing Our Coral Reefs.”State of the Planet, Columbia University, 13 June 2011,

“Coral Bleaching and the Great Barrier Reef.”Coral Reef Studies,

Fondriest Environmental Learning Center.Water Temperature. 23 Jan. 2019,

Jason, Buchheim.Coral Reef Bleaching,

Living Oceans Foundation, Khaled bin Sultan, director.What Are Corals?, 25 Mar. 2015,

NOAA. “A Smooth Trunkfish.” Unsplash, 18 Sept. 2019, Accessed 16 Sept. 2020.

NOAA. “Red Soft Coral with Polyps Extended.”Unsplash, 18 Sept. 2019,

NOAA. “Reef Scene.”Unsplash,

Reef Resilience Network. “Bleaching Impacts.”Reef Resilience,

US Department of Commerce, National Oceanic and Atmospheric Administration. “Are Corals Animals or Plants?”NOAA's National Ocean Service, 29 Oct. 2018,

US Department of Commerce, National Oceanic and Atmospheric Administration. “What Is Coral Bleaching?”NOAA's National Ocean Service, 15 Mar. 2010,

World Wildlife. “Everything You Need to Know about Coral Bleaching-And How We Can Stop It.”WWF, World Wildlife Fund,

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