coral bleaching
Education,  Learning Resources

Coral Bleaching: The Basics You Need to Know

Returning to your favorite snorkel spot, you stumble upon decaying white coral—a devastating result of coral bleaching. What used to be a radiant reef full of colorful coral and fish is now washed out, depleted, and lonely. No fish in sight anymore.

But, what exactly is coral bleaching? And, what causes it? Most importantly, how can we prevent this from happening?

For many, corals are one of the most awe-inspiring and majestic aspects of the ocean. When I was younger, snorkeling along the coral reefs in Hawai’i greatly impacted my decision to be a marine biologist. Full of life, coral reefs teem with biodiversity, beauty, and fascinating discoveries.

To learn about the fundamentals of coral bleaching, read this beginner’s guide. Not only will you grow a greater fondness for coral, but you will also wield greater knowledge to protect ocean ecosystems from mortality events, like coral bleaching. 

coral bleaching
Photo by Francesco Ungaro

Coral Basics

Firstly, we need to define what a coral is. Sometimes confused for plants, corals are actually animals. According to the Smithsonian, corals are closely related to sea anemones and consist of polyps, mineral skeleton, tentacles with stinging cells called nematocysts, and algae called zooxanthellae. To eat, corals use their tentacles to attack and pull in passing organisms. Additionally, corals share a symbiotic relationship with zooxanthellae, and the zooxanthellae produce food for the coral through photosynthesis.

At the end of the day, corals play a massive role in keeping the ocean and people healthy and thriving. For example, coral reefs support over a quarter of all species in the ocean. Furthermore, corals are essential to the well-being of humans. For instance, corals sustain our fisheries, prevent coastal erosion, and provide countless ecotourism opportunities. Money-wise, corals are worth between 30 and 172 billion US dollars annually.

Fun Fact: Corals have a lengthy history. For example, corals originated over 240 million years ago. And, the coral reefs alive today are often 5,000 to 10,000 years old.

coral bleaching
Photo by Hiroko Yoshii

Coral Bleaching 101

Perhaps, you’ve never heard of coral bleaching. A rising concern, coral bleaching poses detrimental consequences to the future of our oceans and society. For the sake of our oceans, it’s imperative to understand how coral bleaching works and what it means for the future.

According to NOAA, coral bleaching is a process where stressed corals release zooxanthellae from their tissues. When the corals release these algae, they not only lose their bright color but also lose their primary source of food. However, once bleaching occurs, not all corals will die—at least not immediately. Sadly, bleaching puts coral in a vulnerable circumstance where disease and the slightest environmental changes can kill it.

For my scuba diving friends, have you come across bleached coral? Oftentimes, these corals take on a haunting white color.

If you’d like to learn more about how coral bleaching works, watch the video below.

Causes of Coral Bleaching

Coral bleaching occurs for a variety of reasons. For instance, the World Wildlife Fund cites dramatic swings in temperature, tidal abnormalities, over-exposure to sunlight, and pollution as major causes of coral bleaching. Overall, climate change plays the most significant role in coral bleaching. With a temperature shift of only 2 degrees Fahrenheit, corals can bleach.

To truly understand the effects of bleaching, think about this. In a recent news article, the BBC reported on a research study that found, since 1995, the Great Barrier Reef has lost over half of its coral population. Scientists concluded that the main driver of this coral bleaching has been warmer water conditions due to climate change. Furthermore, the BBC highlighted how, as of now, the UN postulates that only a 1.5 degree Celsius increase in water temperature will kill 90% of all corals.

When people think about climate change, they often think about fuzzy polar bears in the arctic. However, climate change affects everything and everyone, even sea creatures like coral. At the rate things are going, the ocean and its coral ecosystems will face severe challenges in the coming years.

To see coral bleaching in real time, give this video a watch.

How to Prevent Coral Bleaching

Thankfully, there is hope for coral reefs. For example, organizations, like the Great Barrier Reef Foundation, are innovating promising coral reef recovery programs. To combat coral bleaching, the Great Barrier Reef Foundation has projects in place, such as a coral propagating project using Coral IVF,  a coral bleaching forecasting project called eReefs, and a project distributing coral probiotics to at-risk corals. Other projects involve reef-freezing technology called cryopreservation, coral stress tests, and biodegradable shields for coral sun protection.

So, what are some ways you can help protect corals? According to the US EPA, there are a variety of ways individuals can promote healthy coral reef ecosystems. For instance, when you’re at the beach, refrain from anchoring your boat near coral reefs, don’t touch corals when you’re in the water, and always use reef-friendly sunscreens. Lastly, you can keep corals healthy even when you’re away from the beach by limiting the amount of fertilizer you use on your lawn, only using energy when you need it, and opting to bike or walk instead of drive.

If you’re looking for a film that addresses coral science and bleaching in a comprehensive, inspiring fashion, take a look at this Netflix feature.

Next time you’re out snorkeling, soak in the ambiance and appreciate the coral reefs we do have. As the oceans tackle environmental challenges, such as ocean warming, be mindful of your actions and do your part to protect corals at risk. In this way, we can help future generations enjoy and treasure all the incredible things corals do.

We all play a part in climate change, which means we all have a responsibility to mitigate climate change. Start with the simple things, like replacing disposable items in your house with reusable items, driving your car less, gardening, composting, etc…

If you’d like to support aquariums and their conservation efforts, give this blog post a read. Perhaps all this snorkel talk has you interested in trying snorkeling? In that case, take a peek at this blog post.

Hi, I’m a San Diego-based blogger who's passionate about marine biology, finance, and science communication. Having recently graduated from UC San Diego with a bachelor's in marine biology, I am now working on a certificate in science communication. Over the years, I’ve worked in laboratory research and science outreach at aquariums, zoos, and environmental research centers. When I’m not writing, you can find me home brewing, tide pooling, skydiving, playing DnD, or hanging out with my two adopted guinea pigs. Reach out to me anytime, and follow Sand Dollar Wallet!


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