July 25, 2019

What the Heck is Coral Bleaching and Why Does it Matter?

Hawaii has always been a special place for our family—my late paternal grandfather was born on Oahu and was living at the Pearl Harbor military base on the fateful day of December 7, 1941. Years later, he met my grandmother while living in Hawaii—she was an artist and he had been recruited to play baseball for the navy (talk about a cool position!). We return every couple of years to explore those roots and discover all the enchantment the islands have to offer. Even without these ties, it’s easy to understand why so many people flock to the Paradise of the Pacific and why others choose to live there permanently.

Hawaii is a land of plenty: sunshine, surf, seemingly endless views of the ocean and all its majesty. However, a big problem is brewing.

The coral reefs are dying.

The thing is, it’s not just a Hawaii-centric problem—it’s a major issue spreading all around the world in coastal environments. Why? Well, climate change is a huge factor, for one. But there’s another thing that’s having a major impact on the reefs and it’s causing a serious case of coral bleaching. And it’s something we have control over: sunscreen.

The chemical sunscreens we’re using are killing the reefs around the world!

Hawaii Reef Turtle collage

What is Coral Bleaching?

When chemical-loaded sunscreen washes off your skin and saturates the ocean, it contributes to coral bleaching. Not familiar with coral bleaching? Essentially these chemicals choke the oxygen. They also cause damage to the DNA in both larval and adult coral, limiting their ability to grow and reproduce.

And it’s not just the coral that’s being impacted—there’s a symbiotic relationship to take into account. Oxybenzone, one of the most common ingredients found in popular sunscreens, is a hormone disruptor. It can change male fish to female, which obviously hinders their reproduction. If the fish can’t reproduce then the fish counts are down and if the fish counts are down, they aren’t pooping enough to feed the coral, and the coral can’t feed the fish.

It’s truly an ugly cycle.

However, there’s something we can do about it! A number of reef-friendly sunscreens are popping up in order to combat the issue.

healthy coral vs bleach coral

What’s Happening to Coral Reefs?

Get ready for some really cool biology, courtesy of our resident biologist, Dave. 🙂

Ocean water temperatures have increased over the last 100 years by about 0.13C per decade, with predictions of a 1-4C average increase in ocean water globally. Though this change might seem insignificant, rising seawater temperatures (along with increasing atmospheric CO2) can have drastic effects on sea life.

Think about it this way: when you’ve got a fever your body temperature rises by just a couple degrees, but those couple degrees make all the difference!

Coral Reef Great Barrier Reef Dive

Corals are marine invertebrates that are more broadly placed in a group of animals known as Cnidarians which include corals, sea anemones, and sea jellies. Corals often form a symbiosis with zooxanthellae, a small, single-celled, symbiotic dinoflagellate (Symbiodinium) that provide corals with sugars made through photosynthesis.

A number of experiments (reviewed by Brown 1997) have shown that warming temperatures cause the loss of zooxanthellae (or the algal photosynthetic pigment) and result in a pale coloring of the coral. This stressed state can make corals susceptible to disease, which can ultimately result in death. What’s left? A ghostly calcium carbonate endoskeleton from the coral is left behind that can be especially obvious when bleaching occurs over a large area. As you travel, ask dedicated divers—they can tell you what they’ve observed over the years!

maui coral reef

What Can We Do to Avoid Stressing Corals?

On a high-level, don’t use sunscreens containing oxybenzone or octinoxate.

Dr. Craig Downs, a toxicologist based in Maui, identified oxybenzone and octinoxate as “two chemicals that can lower the resiliency of coral reefs to bleaching. They can affect the development and endocrine systems of fish. And, the risk of spreading the chemicals in the ocean is not only when sunscreen-wearing swimmers are in the water, but also when they go home and use the shower or the toilet” (Maui News).

What Other Chemicals Should I Avoid?

We learned that while there are many other chemicals in sunscreens that can be harmful to the environment (and to humans!), but oxybenzone was the best one to target as it’s easy to identify for consumers. That said, when looking at sunscreen ingredients, it may say oxybenzone-free, but you’ll want to take a look and see if you can pronounce the other ingredients in it.

If you can’t, there’s a good chance it’s actually not that great for the environment.

Curious about what those other main toxic chemicals are? Here’s a snippet of the list from EWG.org: octinoxate/octyl methoxycinnamate, homosalate, octisalate, octocrylene. 

Uv Filter High Toxicity Concerns Reef Chemicals Sunscreen

What Kind of Sunscreen Should I Be Looking For?

We’d suggest opting for mineral-based ones with titanium dioxide or zinc oxide.

While research is ongoing, in July 2018, Hawaii passed a law prohibiting future sales of sunscreens with oxybenzone (also known as benzophenone-3) and octinoxate. This law passed in part due to Susan Varsames, the founder of mama KULEANA reef-safe sunscreen.

While we were in Maui, we met up with Susan and she graciously invited us into her home so we could learn more about the work she does and measures we can take to save the coral reefs! Head over to this post—Taking Responsibility with Reef-Safe Sunscreen for the lowdown.

Let Us Know Your Thoughts



Culture Shoque is digital destination and channel designed to cultivate relationships in your community and while traveling. By breaking down barriers and xenophobia through the exploration of customs and food, the pursuit of joy, and environmental conservation, the goal is to show that at the core, we aren’t all that different. In fact, we all stem from similar roots. It’s time to nourish them and grow together. 

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