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The Great Barrier Reef, visible from space, is the largest living structure on Earth, formed over hundreds of thousands of years with over 3,800 individual reefs.
While the reef is widely recognized, many of its most intriguing features remain unknown. Its most remote areas continue to reveal both astonishing and small-scale surprises. Let’s uncover some of these mysteries.
10. A Significant Portion of the Reef Has Died
Ecologist Katharina Fabricius has been studying the Great Barrier Reef since 1988. By 2012, her research revealed that the reef had lost half of its coral. This alarming loss was determined after Fabricius analyzed over 2,000 surveys, showing an annual decline of 3.4 percent over the previous 27 years.
The primary culprit behind the damage was a single species—the crown-of-thorns starfish. While cyclones and climate-induced bleaching also played roles, this destructive starfish was responsible for destroying 42 percent of the 50 percent damaged coral.
The crown-of-thorns starfish doesn’t match the familiar shape most people associate with sea stars. It can grow up to 0.9 meters (3 feet) and is covered in poisonous spines, with 21 arms spread across its body.
Their population thrives because agricultural runoff provides the nutrients that young starfish need. This influx of food has led to a population explosion, causing massive coral destruction. Removing these spiny invaders is challenging but essential.
Fabricius' research showed that if the starfish population decreases, the reef could recover. Even if cyclones and bleaching persist, the reef might fully regenerate within three decades.
9. Astonishingly Deep Coral
While most divers typically explore coral at depths of 30 meters (100 feet), a remarkable discovery was made in 2013. Scientists found coral thriving at an astonishing depth of 125 meters (410 feet).
Normally, polyps, the small creatures that build coral, can't survive in darkness, as they depend on sunlight for nourishment through algae. However, when a submersible explored the dark depths near the Australian continental shelf, it discovered a coral species, Leptoseris, that usually resides no deeper than 100 meters (330 feet).
At these extreme depths, sunlight is scarce, and sponges and sea fans dominate. The submersible also uncovered Staghorn Acropora, the most widespread coral in the world. While the presence of sponges and fans can be explained by their ability to grow without light, the survival of Leptoseris and Staghorn in this seemingly inhospitable environment remains an enigma.
8. The Floating Fan Initiative
While it may sound outlandish, the idea of using giant fans to cool the reef actually has scientific merit. The $2.2 million project aims to address bleaching, which occurs due to heat stress, turning once vibrant areas into stark, white wastelands. During the devastating bleaching events of 2016 and 2017, half of the coral in the Great Barrier Reef perished.
In response, the federal government approved a plan to cool the reef using large floating fans. As part of a trial, eight such fans will be placed off the coast of North Queensland, cooling an area of 1 square kilometer (0.39 mi) near Cairns over a three-year period.
These solar-powered turbines may work slowly, but they can generate cold water currents. During the 2016–2017 bleaching events, scientists found that bleaching was less severe in areas with cool currents, and coral in those regions recovered more rapidly.
Since heat stress is just one of many threats facing the reef, the fans alone won’t be enough to preserve it. The primary goal of the project for now is to safeguard popular tourist areas and the 64,000 jobs that rely on the industry.
7. An Ancient Landslide
In 2017, researchers conducted an expedition along the north Queensland coast, working on a 3-D map of the deep-sea floor. During the process, an unexpected discovery was made: scans revealed an ancient landslide near the Great Barrier Reef.
This massive underwater event scattered debris across a large area within the reef. Among the first findings were eight previously unidentified hills in the Queensland Trough, believed to be relatively flat. Some of these hills, known as Gloria Knolls, rise up to 100 meters (328 feet) and stretch over 3 kilometers (1.9 miles).
The so-called hills are actually the remnants of the landslide. The total volume that shifted is estimated at 32 cubic kilometers (8 miles), and scattered debris was found as far as 30 kilometers (19 miles) beyond the Gloria Knolls.
The Gloria Knolls provided the oldest coral fossil, dating back 302,000 years. Since the knoll itself was beneath the fossil, this suggests the landslide occurred even earlier. This discovery, along with the unique cold-water ecosystem found in the area, helps clarify the region's true geological history.
6. The Blue Hole
Often called the ocean's time capsules, blue holes are submerged sinkholes. Inside, sediment accumulates over millennia, shielded from disturbances like storms and currents. This makes blue holes invaluable to researchers studying the past.
In 2017, marine biologists confirmed the existence of a blue hole in a remote section of the Great Barrier Reef. Situated 200 kilometers (124 miles) from Daydream Island, the hole revealed a delightful surprise. It was home to turtles and fish swimming through the massive circular formation, but the true highlight was the thriving, healthy coral colonies.
Birdsnest and Staghorn corals grew in unusual, intricate shapes, free from the disruption of waves or currents. These corals formed some of the largest and most detailed colonies divers had ever seen. The bottom, around 20 meters (65 feet) deep, sloped towards the center. Geologists suggest that this rare site may be older than its famous counterpart, the Great Blue Hole in Belize.
5. The Starfish-Eliminating Robot
While floating fans may help cool the reef, they don't address the starfish issue. To combat this pest, scientists developed a robotic solution. Named COTSbot, this yellow tube-shaped device uses artificial intelligence to locate and target crown-of-thorns starfish.
Trained with thousands of images and videos, COTSbot can now identify its target with precision. Once it confirms that it’s staring at a crown-of-thorns starfish, and not a particularly spiky octopus, it moves in for the kill. A robotic arm extends, delivering a lethal dose of bile salts.
COTSbot was built to operate autonomously. However, the world's first starfish-killing robot still hesitates in some situations. If it is unsure about an object, it takes a photo and waits for a human to provide an answer. A “yes” will activate the arm, and the encounter will be stored in COTSbot’s memory. Over time, it will learn to make decisions independently without human intervention.
In late 2015, COTSbot began its sea trials, but without the deadly brine injections. Once fully independent, it will be able to patrol the reef for eight hours, delivering over 200 injections during each shift.
4. Source Reefs
In 2017, researchers made an extraordinary discovery: the presence of “source reefs.” These coral nurseries have the ability to replenish more distant and damaged sections of the Great Barrier Reef.
The researchers actively searched for such areas, and when they found them, they uncovered the incredible interconnectedness between reefs. For an area to be classified as a source reef, it must exhibit resistance to bleaching and starfish, and it must remain connected to other reefs through currents. Only 112 such reefs were discovered, making up about 3 percent of the vast, Italy-sized Great Barrier Reef.
Despite their limited number, these source reefs are connected to nearly half of the Great Barrier Reef through ocean currents. Approximately 208 networks are active, which scientists have compared to a cardiovascular system. The fact that these source reefs can send fertilized eggs to more vulnerable areas demonstrates that the Great Barrier Reef has the potential to heal itself in an extraordinary way.
However, this life-support system is not invincible. Researchers are still unsure about how effective it truly is and why so few source reefs are found in the northern regions. Additionally, the source reefs themselves remain vulnerable to the impacts of climate change.
3. The 3-D Printed Reef
If there were an award for the most innovative way to preserve the reef, the University of Sydney would certainly take the top prize. In 2017, researchers began printing precise 3-D replicas of the Great Barrier Reef. The project began with the digital mapping of the coral fields, which were then analyzed for accurate measurements before being transformed into three-dimensional models.
The prosthetic corals, which are exact replicas of the originals, serve multiple purposes. Once installed on the reef, they will provide shelter for fish that eat coral-damaging algae and act as a foundation for living coral. These replicas will facilitate new growth, helping to stabilize the reef as it recovers from storms and bleaching events.
While artificial reefs are not a new concept, this project represents the first attempt to create a natural-looking environment, rather than simply sinking a ship and hoping marine life will follow. The Great Barrier Reef's excellent connectivity allows larvae from source reefs to populate these artificial sanctuaries.
Although prosthetic coral colonies offer valuable assistance, they can only provide temporary relief. Addressing climate change, which drives stronger storms and bleaching events, is essential for the reef’s long-term survival.
2. The Reef Almost Drowned
It may sound strange, but a coral reef can 'drown' if sea levels rise too high. The Great Barrier Reef we know today is the latest in a series of reefs that stretch back through history. Scientists studied a previous reef layer from the Last Interglacial period to understand what happened during that time.
Around 125,000 years ago, this ancient reef thrived in a world with higher sea levels and temperatures than we experience today. It painted a picture of a future Earth, one where unchecked CO2 emissions cause dramatic shifts. The findings gave scientists a rare look at what might happen if pollution continues to escalate.
The situation was dire. Rising sea levels caused by melting ice caps and glaciers put the reef on the brink of total collapse. Yet, the reef’s resilience shone through. Once water levels leveled off, the coral began to recover and grow once more.
Although the fossil reef managed to endure, the future for the Great Barrier Reef is far more uncertain. If a major melting event occurs, sea levels could rise just as much as they did during the Last Interglacial period. Already stressed, the reef could be completely submerged under the weight of a 6-meter (19 ft) rise in water levels.
1. Plastic-Eating Coral
Among the many dangers the reef faces, one of the oddest is the corals’ growing attraction to microplastics. Initially, scientists assumed the polyps consumed plastic because it looked like food. However, laboratory experiments revealed that the coral actually seems to enjoy the taste, likely due to a chemical compound found in the plastic.
The same study discovered that after consuming the plastic, the coral realized it was not nutritious. Within a few hours, up to 92 percent of the plastic was expelled, yet disturbingly, about 10 percent remained inside the polyps’ stomachs.
The plastic was discovered deep within the coral's gut, wrapped in digestive tissue. This could give the coral a false sense of fullness when it is actually starving. Typically, plankton would be the preferred meal, but the corals appear to favor the synthetic substitute instead. Microplastics are not in short supply either, with an estimated 13,000 pieces scattered across every 1 square kilometer (0.39 mi) of ocean.
