Why are Coral Reefs DYING? What is Coral Bleaching?

Coral reefs are the basis for ocean life. A quarter of the ocean’s inhabitants depends on them—and so do millions and millions of humans. But with the warming ocean waters and more extreme weather events, coral reefs are struggling. The corals bleach. But what is coral bleaching?

Coral reefs are cities underwater. About a quarter of marine life depends on coral reefs at some point in their life cycle. Well, plus half a billion people and some land animals. Yet, our reefs are dying.

If you really want to know about all of this, there are a few things you should watch instead of my video, and I’ll recommend all of them. But as I am aware that not everyone has the hours to dedicate, I will give you a small overview in this segment.

Netflix has made a few of its best documentaries available on Youtube for free. I don’t know if this is an image stunt because people keep mentioning streaming as a huge source of greenhouse gas emissions or if someone actually gives a shit, but the result is the same and we should take advantage. Chasing Coral is the best documentary about coral bleaching I have ever seen. It is available on Youtube for everyone. Our Planet by David Attenborough is one of the best documentaries on the subject of humans destroying the planet. It is available on Youtube, as well. And then there’s Blue Planet II which is still not available in most places. I had to buy it in the end to be able to watch it but it was worth every penny and I’ll be rewatching every episode with my two best friends as soon as possible. I could geek out for hours about all the cool things I learned through those three documentaries alone. Then, if you still haven’t learned enough, read as much of the National Geographic website as you can—or the magazine if that’s more your style.

But, I will give you the best overview I know to give:

As we discussed in the first segments of the Biodiversity Basics about corals, corals are animals or rather a colony of many anemone-like animals. That thing that looks like a plant is many animals working together. To make things more complicated, they take up a small symbiotic host (well, two of them, but one is newly discovered and we don’t know much yet) a photosynthetic algae called zooxanthellae which provides the corals with food during the day in return for living space.

Some coral build skeletons underneath themselves that grow into huge structures we know as coral reefs. Corals aren’t the only species on reefs, obviously, but they are the foundation, much like the Giant Kelp in California is the foundation for much of the local life there.

When the ocean warms, as it has exponentially since the Industrial Revolution, all kinds of organisms get effected. From plankton to the largest organisms, everyone gets affected by the warmer temperatures, just like we humans are during a heat wave.

Corals build the basis of the reef cities. They are the house and home for a lot of other organisms. They are the foundation for sponges and other sessile organisms that need to attach to rock or coral to exist. So, we’ll focus on how corals react to warming temperatures.

I still think you should watch Chasing Coral. It shows the struggle of coral reefs so perfectly by documenting the struggles of the camera team trying to document the bleaching event. Anyway, I’ll try.

When things get too hot for corals, they kinda lose their collective mind and expel the zooxanthellae. The hypothesis is that they can only detect that something is wrong and then take the wrong steps to solve it. When they feel that things are wrong, they panic and kick out their little helpers, a major food source. Without the zooxanthellae, they lose the photosynthesis they offer and the nutrients that photosynthesis provides them with. They lose a good chunk of their food supply. So now they are hot, confused, and hungry.

Without the zooxanthellae, the coral doesn’t have any color. The expelled their pigment and what’s left is a white skeleton or translucent hull. If you see coral in this condition, things aren’t lost yet, though there is little you can do to help.

If you are lucky, you’ll see the coral recover. But if the temperatures don’t drop quickly enough and conditions don’t return to a comfortable level very quickly, you’ll watch helplessly as algae covers the coral, covering them with a slimy brown goo. Over time, the underlying tissues will die in something called RTN or rapid tissue necrosis. The coral cannot be saved anymore.

So now that the corals are gone, everything the provided from food to shelter is gone as well. Time lapse footage of dying reefs can be found in many documents on the topic by now, but the work of the Chasing Coral team was breath-taking. For months, they suffered to make something happen that the best technology couldn’t. If you don’t have the time to watch the documentary, I suggest at least having a look at the time lapse summary I will link in the show notes.

As I said, it is not just coral that gets affected by the warming oceans. Organisms grow differently, act differently, reproduce differently. And then there’s the actual ocean which is made of water—duh. And water expands with rising temperature. Most people know about sea levels rising because of melting ice caps but never stop to think about how much water there is in the ocean to expand with every rise in temperature.

I would usually tell you what you can do at this point, but I think the best thing for you to do is to follow my original advice and learn as much as possible about the topic. And then tell everyone else. Everyone. Ignorance will be the end of humanity if we let that happen. Too many powers that be fight for humanity’s ignorance, so we need to fight against it. I’d much rather be insulted as an insufferable know-it-all or a Hermione than risk losing the battle of knowledge that I believe will determine the outcome of this all.

I don’t think it is money that makes the world go round but knowledge. Or at least knowledge will be what keeps the movement going.

Learn more, know more, teach more.

Mentioned in this episode:

Chasing Coral timelapse summary: