Science Made Simple – Coral Bleaching

How climate change has affected coral reefs – and how it could destroy whole taxonomical classes in the next 30 years.

A collection of FAQs on corals and bleaching, and all the reasons we have to save them.

What is a coral?

A coral is an animal, just like us. It can contain millions of tiny animals called polyps. The polyps have a symbiotic relationship (mutually beneficial) with photosynthetic algae called zooxanthellae.

The polyps supply shelter and protection for the zooxanthellae. The zooxanthellae provide photosynthetic abilities to produce food for the coral polyps.

Polyps (via Derwent Hunter EcoTour )
Polyps (via Derwent Hunter EcoTour Web

What is coral bleaching?

Coral bleaching is a process that occurs when water temperatures rise above normal. As a result, the polyp begins to expel everything from its system, including the zooxanthellae (much like if a human is ill). Without the algae, the outer “skin” of the coral becomes translucent, and the inner skeleton becomes visible (aka coral bleaching). At this point, it will still be alive.

Without the zooxanthellae, the coral will begin to starve. They will no longer grow or allow the algae to return, and are susceptible to disease. The coral bleaching process can happen in a short period of time (months).

A coral is dead when there is an appearance of thick algae on its surface.

Heron Island Coral Bleaching (Picture via XL Catlin Seaview Survey/Underwater Earth)
Heron Island Coral Bleaching (Picture via XL Catlin Seaview Survey/Underwater Earth)

Why should you care?


  1. Between 500,000,000 to 1,000,000,000 people rely on coral reefs for their main food source or for a primary income.
  2. They protect coastal cities and communities from tropical storms, waves, and erosion by creating a natural barrier.
  3. They host organisms that have the potential to cause medical breakthroughs. Some drugs taken from reef organisms can fight cardiovascular disease, inflammation, ulcers, and even cancer. Read more here: Medicine Chests of the Sea – Coral.Org
  4. Some countries, especially small islands, rely on tourism. Reefs bring tourists from around the globe and allow countries to collect millions of dollars in order to support their economies – and take care of their reefs.
  5. Reefs are the tropical rainforests of the ocean. They boast a vast amount of biodiversity. An estimated 1/4 of all sea life spends at least some of its life on reefs. If that doesn’t seem like a lot to you, consider that there are around 40,000 known species of reef fish and 1000 species of corals…and an estimated 1-8 billion species we have not yet discovered.
Photo by Kelly Coyne

How bad is it? 

Pretty bad. Or at least, it’s projected to be. In the next 30 years, almost all of the world’s corals could be dead. 

Global bleaching events have become more and more frequent. After 2014, annual bleaching has been observed worldwide, destroying corals in the Northern Barrier Reef, Hawaiian Islands, Caribbean Islands, amongst others. After the 2016 bleaching event, 67% of the northern region of the Great Barrier Reef bleached – according the Chasing Coral (film, produced 2017) it was the equivalent of losing most of the trees between Maine and Washington D.C. 

Corals can come back from a bleaching event if given enough time, but with current conditions they are unable to keep up and repair themselves.

Overfishing, pollution, and ocean acidification have also been destructive to reefs.

Hermit Crab at Paiko Reef Flat, Hawaii (Via Reece Kilabey @kilabey)

What would the world look like without coral reefs?

Do you remember the first time you snorkeled or saw a reef on television ? What was it like? Do you remember the colors, the fish and the various corals along the bottom?

If you have only visited a reef in recent years, you might not remember it this way. Right now, we are in the crossroads of what has the potential to become ruins. Without reefs, poor countries will lose economic security, either from loss of catch or decreased tourism. Communities in coastal regions will lose food security. Biodiversity will be destroyed. Algae will cover the ocean floor and less fish will visit the reef. The ocean will be duller. We will see it disappear in our lifetime.

Sea Star at Aquarium of the Bay, San Francisco (via Kelly Coyne)

What can be done? What can YOU do?

If we continue with current trends, corals will suffer and die world wide. It doesn’t have to end like this. The difference is people choosing to take action. Here are some things you can do:

  1. Dedicate time to learn some things about coral reefs. NOAA is a great place to find information on our oceans and the creatures that live in them.
  2. Choose sustainable seafood – this is a great guide
  3. If you go snorkeling or diving, never touch or step on corals. They are alive. Use reef safe sunscreen that doesn’t contain Oxybenzone and Octinoxate,  which cause bleaching (like this Alba Botanica Mineral Sunscreen – $8.99 at Target)
  4. Participate in a beach cleanup – or do one yourself. Bring a bucket the next time you go to the beach. Remember to use less plastic as well.
  5. Do more to reduce your carbon footprint. For example, take public transportation, eat less meat (a big one), and use less energy. Be efficient with what you have.
  6. Urge your government to take action by participating in protests, sending letters, or signing petitions. You can do this through organizations like Greenpeace or Oceana.
  7. Contribute to research. For example, The Ocean Agency is a great company that uses communication to push conservation. They also have created a scientific aspect in 50 Reefs
  8. Be aware and be active. Spread the word. It’s not too late.



All information was taken from memory, education, or from external sources listed in the article or below. Sources below also include valuable sites and information. 

Chasing Coral

NY Times – Without Reefs

NOAA – Corals and Importance

Monterey Bay – Ocean Issues

Smithsonian – Oceans


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