Decline of Coral in Great Barrier Reef

The Great Barrier Reef is the biggest living structure on Earth. This reef is an extraordinary place that’s practically an underwater city: it’s full of wonders at every corner. From sharks that move effortlessly to the anemones that dance under the waves, it’s a place I have wanted to go to for as long as I can remember. In December 2024, I finally had a chance to fulfill this dream, traveling with my family over 20 hours by plane to Australia just to get to this miraculous place. 

I was awed the second I dove into the water, for it was filled with schools of fish and was so clear that I could see the bottom. Looking up I saw the blue water with sunlight piercing through. It was as though I was living in a dream. One thing that seemed rather curious was that the water temperature felt oddly like a hot bathtub.  Shocked, I made my descent to the bottom of the reef. There, I saw that a majority of the coral was fluorescing (which causes it to appear as a striking neon color); though it was beautiful to look at, it is a stage of death in which zooxanthellae (small algae cells) inside the coral are ejected because of the warming water. Other coral were bleaching, showing their skeletons as their skin became pellucid. This saddened me and made me determined to show others exactly what is happening to these beautiful and lively structures. I interviewed Sharlee Correa, an ecologist working as a wildlife educator in the Cairns Aquarium in Cairns, Australia, to learn more. 

“Coral reef systems, they support one-quarter of all creatures in the ocean; one-quarter of them live on the reef, and less than 1 percent of our ocean is covered in reef, and that just blows my mind every time,” said Correa.

I asked Correa about the bleaching and fluorescing that I’d seen when scuba diving. How pervasive is it, and what are its consequences on the marine ecosystem? 

“We do see corals, once they reach a really extreme stress point before the bleaching, they fluoresce,” she said. “And that bright fluorescent color is actually that coral on its last place. It's really trying to protect itself from bleaching... And I have seen quite a bit of bleached corals when I've gone out on the reef. And we've looked at some studies that they've done on the Great Barrier Reef, like the whole length of it, and they found that over 70 percent of the Great Barrier Reef is showing signs of stress and bleach.” 

“One-quarter of all living creatures in the ocean rely on the reef. They live there. That's their home… 70 percent of our oxygen comes from the ocean, and a massive part is caused by the reef as well, and it absorbs carbon dioxide and does what it does best,” added Correa. “And if we lose that, it wouldn't just be the animals, it would be all of us as well.” 

Furthermore, the Great Barrier Reef, along with other reefs around the globe, provides income for many. The U.S. National Oceanic and Atmospheric Administration states, “The National Marine Fisheries Service estimates the commercial value of U.S. fisheries from coral reefs is over $100 million. Local economies also receive billions of dollars from visitors to reefs.” 

Bleaching isn’t only occurring in the Great Barrier Reef; it’s happening around the globe, with the same risks popping up everywhere. The magnitude of these bleaching events is immense. According to a study from One Earth, a non-profit platform with the goal of halting climate change,  “Global coverage of living coral has declined by half since the 1950s.” This is absolutely horrific! Not only is this consequential to the coral, it affects everyone.

Now that we understand just how significant these reefs are, let us dive more into some other causes of the decrease in coral population. Though the key factor in mass bleaching is global warming, another cause of dying coral is the crown-of-thorn sea star. This predator devours coral, and its population is booming. Though predators of the sea star include the Humpheaded Maori Wrasse, Triton Triggerfish, and Triton snails, there are just not enough of them, and they take a long time to mature. Plus, some cultures eat them as delicacies. 

On the other hand, the crown-of-thorn sea star’s population is booming. “So you remove the predators and then the animal, the crown-of-thorn sea star, he's living his best life because he doesn't have any of those natural predators anymore,” said Correa. “Sea stars are really good at making babies. They can reproduce on their own; we've also found that farming runoff has increased algae blooms that the baby juvenile sea star feeds on. So, more food for the babies, less predators for the adults.”

Furthermore, the toxic chemicals oxybenzone and octinoxate in many sunscreens break down the calcium carbonate that makes up the coral skeleton. 

However, there is still hope to protect these complex creatures. Correa’s favorite quote is, “Those who have the privilege to know have the duty to act.” We have to be guardians of the corals. As the world around us is changing, we must act and educate others not only for the benefit of corals, but for the whole world. Everyone needs the Great Barrier Reef and all other reefs in the ocean. As we see the planet getting warmer and warmer, take it as a reminder. 

The first step we can take is by “making sure that we’re talking about it,” said Correa. Let us advocate for a better world, a better ocean.