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Coral Bleaching: Why It’s An Issue and Ways to Stop It

Coral reefs, the “rain forests of the sea,” are a vital part of the biodiversity seen on this planet. Because, these large structures are home to many diverse species who depend on them for survival.

What is Coral Bleaching?

Coral bleaching is the process of coral expelling the symbiotic zooxanthellae (algae) living in their tissues1. Zooxanthellae provide the carbon needed to build the coral’s skeleton and in return the coral provide the zooxanthellae the nutrients they need for photosynthesis. The optimal conditions needed for this relationship are clear and shallow waters and with temperatures between 23o and 29o celsius2. When these conditions aren’t met the relationship is lost, causing the coral to turn white.

Why Does Coral Bleaching Happen?

Coral bleaching happens for a variety of reasons, the main being a rise in greenhouse emissions. This rise causes oceans to warm, overwhelming the coral. It only takes the water warming two degrees farenheit to cause coral bleaching1. Bleaching can also be a result of especially low tides, pollution, or too much sun1

Coral Bleaching in the Great Barrier Reef

photo by Chad Taylor on unsplash

The Great Barrier Reef, located off the coast of Queensland, Australia, is the largest reef system in the world. It is made up of over 2,900 individual reefs and stretches for 2,600 kilometers3. Unfortunately, the reef has suffered from three major bleaching events in the past five years.

photo by Ars Technica

The first bleaching event, which occurred in 2016, saw a 30% loss of coral, compared to 20% in 20174, and 25% in 20205.These back to back bleaching events have scientists afraid the Great Barrier Reef will never fully recover.

Why Coral Bleaching is a Problem

Coral that has been bleached has increased vulnerability to disease and elevated mortality rates6. Bleaching can lower reproductive rates, making it harder for the reefs to survive. Researchers have found that bleaching events have increased from once every 25 to 30 years in the early 80s to once every six years since 20102

According to Reefs at Risk Revisited, “If local and global threats are left unchecked, the percent of threatened reefs will increase to more than 90 percent by 2030 and to nearly all reefs by 2050”7

Bleaching isn’t only an issue for the coral itself. Bleaching can also cause problems for both the marine species and people the reefs support. 

Marine Life

Coral reefs are essential to the survival of multiple marine species such as reptiles, fish, crustaceans, and sea birds. The reefs provide the animals with food, shelter, and nurseries to raise their young1. They also provide protection from predators. Without the reefs these populations could diminish and already dwindling species could go extinct. 


Coral bleaching can also affect a person’s source of income, food security, and safety1. Coral reefs can contribute largely to a society’s economic status. Tourism from coral reefs can bring in billions of dollars. From 2015-2016, the Great Barrier Reef provided $6.4 billion dollars and 64,000 jobs to the Australian economy8.

Fishermen also rely on this ecosystem to provide the fish needed for their income and as a food source. Without the coral reefs, jobs and income are lost and the food reefs provide are no longer accessible. 

Reefs provide people with construction material such as limestone and medicine. In fact, coral is sometimes referred to as the “medicine cabinets of the 21st century9.” Coral is used in the development of new drugs to treat conditions such as cancer, HIV/AIDS, and arthritis. 

Coral reefs act as barriers to storm surges and large waves1. Without this protection, seawalls have to be built. Seawalls tend to be expensive, less effective, and can also cause environmental harm.

Ways to Prevent Coral Bleaching

photo by Q.U.I on unsplash

Given the chance to restore itself, coral bleaching can be reversed and reefs can regain their symbiotic relationships and vibrant colors. This recovery process can take 9-12 years10. Here are some practical steps you can take to make sure coral reefs are allowed to thrive into the future:

Volunteer for a reef cleanup

Floridareef.org holds a Friends of Our Florida Reefs annual cleanup and it takes place every summer.

Find alternatives to herbicides and pesticides 

Limit your herbicide and pesticide pollution. Find natural ways to protect your crops such as essential oils. You can mix citrus essential oils with cayenne pepper and water to spray on your plants or you could use straight eucalyptus oil on the area11.

Realize that corals are living animals

When going snorkeling and diving remember that corals are alive. Keep your hands to yourself because corals are fragile creatures and this could damage or kill them12. If you are a boater, anchor in boat-safe locations such as sandy bottoms and be vigilant of coral.

Use environmentally-friendly transportation

Try to bike, walk, or take public transportation more often13. If you do need a car, try to buy a hybrid or an electric as they help lower greenhouse emissions.

Cut back on sunscreen use

Ingredients in sunscreens can be damaging to coral reefs. Choose products that don’t contain oxybenzone and octinoxate14. You can’t always be 100% sure your sunscreen is coral safe. Alternatively you can opt to wear long sleeves and hats to protect yourself from the sun. 

Support a non-profit organization that helps to rebuild and care for coral reefs

Many organizations throughout Florida dedicate their efforts to restoring and protecting coral reefs. Coral Restoration Foundation is the largest reef restoration non-profit in the world and they operate out of Key Largo, Florida. They focus on restoration in the Florida Reef Tract.

Reef Relief  is a non-profit who works out of Key West. They do a lot of reef education through their camp and K12 school program. 


1.Hancock,Lorin. “Everything You Need to Know about Coral Bleaching- And What We Can Do to Stop It.” World WildLife Fund, https://www.worldwildlife.org/pages/everything-you-need-to-know-about-coral-bleaching-and-how-we-can-stop-it

2.Cho, Renee. “Losing Our Coral Reefs.” Columbia Climate School, 13 June 2011, https://news.climate.columbia.edu/2011/06/13/losing-our-coral-reefs

3. “Great Barrier Reef Facts”. https://greatbarrierreef.org/about-the-reef/great-barrier-reef-facts/

4. Ward, Selina. “How the 2016 Bleaching Altered the Shape of the Northern Great Barrier Reef.” The Conversation, 18 April 2018, https://theconversation.com/how-the-2016-bleaching-altered-the-shape-of-the-northern-great-barrier-reef-95142

5.Alberts, Elizabeth C. “Great Barrier Reef Suffers Biggest Bleaching Event Yet.” MongaBay, 9 April 2020, https://news.mongabay.com/2020/04/great-barrier-reef-suffers-biggest-bleaching-event-yet/

6. “Bleaching Impacts.” Reef Resilience, https://reefresilience.org/stressors/bleaching/bleaching-impacts/

7. “Reefs at Risk Revisited.” World Resources Institute, https://www.wri.org/research/reefs-risk-revisited

9. “What Does Coral Have to Do With Medicine?” National Ocean Service, https://oceanservice.noaa.gov/facts/coral_medicine.html

10. “How Long Does it Take Coral Reefs to Recover From Bleaching?” James Cook University, 20 February 2019, https://www.jcu.edu.au/news/releases/2019/february/how-long-does-it-take-coral-reefs-to-recover-from-bleaching

11.Group, Edward Dr. “10 Homemade Organic Pesticides.” Global healing, 10 April 17, https://explore.globalhealing.com/organic-pesticides/

12. “Coral Etiquette 101.” NOAA Coral Reef Conservation Program, https://coralreef.noaa.gov/aboutcrcp/news/featuredstories/feb15/coraletiquette.html

13. “What You Can Do to Help Protect Coral Reefs.” Environmental Protection Agency, https://epa.gov/coral-reefs/what-you-can-do-help-protect-coral-reefs

14. “Reef_Safe Sunscreen: What You Need to Know.” Chasing Coral, https://www.chasingcoral.com/2018/05/23/reef-safe-sunscreen-need-know/

15. Hughes, Terry and Morgan Prachett. “Great Barrier Reef survey: “What we saw was an utter tragedy.”” Ars Technica, 7 April 2020, https://arstechnica.com/science/2020/04/great-barrier-reef-survey-what-we-saw-was-an-utter-tragedy/

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