What is Coral Bleaching?

Hi, everybody! For those of you who don't know, my name is Daisy, and I'm a Purple Sea Urchin! Today, I want to talk to you about coral bleaching. To understand how coral bleaching works and how it affects you, we first need to learn about corals themselves! Coral reefs are without a doubt some of the most beautiful things nature has to offer. Just look at all the different colors and shapes in the photos below:

Getting to know coral.

These photos might have you thinking that corals are naturally very colorful plants. Well, that's actually wrong in more ways than one. First off, corals are animals, not plants. They do not photosynthesize the way plants do - meaning they don't use the sun, water, and carbon dioxide to feed themselves. Corals are also naturally white. So where does all that beautiful color come from? And, more importantly, how do corals feed themselves?

The answer: algae.

Corals and algae have what's called a symbiotic relationship - meaning both the coral and the algae benefit by working together! The algae, which gives coral its color, does photosynthesize, and it provides the coral with up to 90% of the energy it needs. The other 10% of the coral's energy comes from passing by plankton being captured by the coral. While the algae provides the coral with energy, the coral provides the algae with a safe place to stay, away from deeper, colder waters. This relationship is what allows coral to grow so fast and form giant reef systems - like the Great Barrier Reef which can be seen from space!

Daisy and Otto learning about coral bleaching

So, what is coral bleaching?

Coral bleaching is what happens when this relationship breaks down. The algae is very sensitive to changes in water temperature, pollution, and even heavy storms. If the water temperature rises too high for too long, the algae begins to heat stress. It stops photosynthesizing, and instead of producing food, it begins to release waste products that are toxic to the coral. The coral will then kick out the algae, which causes the coral to lose its color and turn white. This is where we get the term "bleaching". Pollution or heavy storms (in which rain water decreases the level of salt in the ocean) can also cause the algae to stress and the bleaching process to begin.

Surviving coral bleaching.

Daisy and Otto teaching kids coral bleaching

A bleached coral is not a dead coral. Corals are capable of catching their own food. Like I mentioned earlier, coral can feed on plankton that happens to be passing through the water around it, but if the coral is unable to catch enough plankton, it will die. However, if water temperatures, salt levels, and cleanliness return to normal quickly enough, the coral will regain its algae and return to normal.

Coral reefs are home to a lot of ocean species, including sea urchins, clams, fish, eels, sharks, and so many more! In fact, coral reefs are like the big cities of the ocean - think New York or Los Angeles. There is so much life in our coral reefs. It's no wonder it's a favorite spot for divers and photographers. 

Daisy and Otto teaching kids about coral bleaching

Divers and photographers aren't the only people who benefit from coral reefs. We all do. Coral reefs provide shelter, food, and spawning grounds for species that live on and off the reef. Without coral reefs, the ocean's food chain could be thrown out of balance, disrupting the entire ocean. Coral reefs also provide food and even medicine to humans. The disappearance of our coral reefs would be bad for everybody, sea creature and human creature alike.