As you probably already know, the Great Barrier Reef is in big trouble. About 50 percent of the reef's coral cover has already been lost, and the generally agreed-upon estimate is that it all could be gone by 2050 unless major action is taken.

The clock is ticking, and unprecedented coral-bleaching events in 2016 and 2017 only demonstrate how precarious — and urgent — the situation is.

The thin silver lining is that, because the reef's plight is so dire, it's receiving a surge of attention in the form of research and rehab. The Australian national and Queensland state governments together spend about 200 million Australian dollars ($150 million) every year to protect the reef's health, and in April 2018, Australia's environment ministry announced that 500 million Australian dollars ($378 million) would be set aside for reef preservation, reportedly the largest-ever single investment for that purpose. While many experts say this still isn't enough, the efforts are ongoing.

Here's a closer look at what makes the Great Barrier Reef great, why that greatness is at risk and how people are trying to save this natural wonder before it's too late:

Why the reef is so important

A view of the Great Barrier Reef from space, captured by NASA's Terra satellite. (Photo: Jacques Descloitres/NASA/GSFC)

The Great Barrier Reef is called "great" for good reason. The superlative refers partly to the reef's immense size: It can be seen from space, stretching over 1,600 miles (2,575 kilometers), which is similar to the distance from Boston to Miami, and covering 133,000 square miles (344,000 square kilometers).

But this massive area isn't just ocean with some coral here and there. It includes a remarkable diversity of habitats and life. According to the World Wildlife Fund: "The Reef is composed of 3,000 individual reef systems, 600 tropical islands and about 300 coral cays. This complex maze of habitats provides refuge for an astounding variety of marine plants and animals — from ancient sea turtles, reef fish and 134 species of sharks and rays, to 400 different hard and soft corals and a plethora of seaweeds."

Of course, these sea creatures deserve to exist for their own sake, but their existence — and the health of the reef — benefits humans, too. The reef acts as nursery and sanctuary for a fishing industry that feeds hundreds of thousands of people, and tourists flock to the reef to experience its incredibly beauty — to the tune of 6 billion Australian dollars ($4.5 billion) a year. And that combined supports almost 70,000 Australian jobs.

What are the threats to the reef?

The coral of the Great Barrier Reef has struggled to survive assaults from climate change and coral bleaching. (Photo: William West/AFP/Getty Images)

There is action being taken on a number of fronts to protect the reef. Solving the problem of coral die-off is expensive and complex because there are at least four main threats to the reef's health, and all have to be dealt with to help the coral.

The Reef 2050 Long-Term Sustainability Plan is the grand plan for protecting the Great Barrier Reef through 2050, and it's how the Australian government answered the UNESCO World Heritage Committee's concerns that would have otherwise put the reef on its list of “world heritage in danger," which would have been an embarrassment for Australia. UNESCO regularly assesses the conservation status of World Heritage sites included on its list. The Reef 2050 plan began in 2015, but some government experts say it is already unachievable due to climate-change impacts.

What is coral bleaching?

High ocean temperatures have triggered major coral-bleaching events at the Great Barrier Reef in recent years. (Photo: Darkydoors/Shutterstock)

Coral bleaching events are a reaction by coral to environmental stress. A bleaching event is a visible SOS by coral, indicating that something is going very wrong.

Bleaching doesn't directly kill coral, but it weakens them severely, often later leading to death as they become more vulnerable to disease. Coral, as you may remember from science class, are animals that live in a symbiotic relationship with certain photosynthetic algae, called zooxanthellae. The coral provide the algae with a safe environment and compounds needed for photosynthesis, while the algae reciprocate with food, oxygen and waste removal (along with their vibrant colors).

This relationship can break down, however, due to environmental stress — namely high seawater temperatures, the risk of which are rising due to human-induced climate change. This thermal stress can force the coral to eject their zooxanthellae, which is initially helpful since heat can cause the algae to produce corrosive substances. If the water remains too hot for too long, however, corals can gradually starve as they turn white due to a lack of zooxanthellae (hence the name "bleaching").

On top of this danger to corals themselves, whose fates tend to foreshadow broader trends, here are some of the greatest threats to the reef ecosystem overall:

Climate change and the reef

Climate change is the largest threat to the reef, because it affects the following:

Ocean acidification: Since the 1700s, about 30 percent of the extra carbon dioxide that humans have pumped into the atmosphere has been absorbed by the oceans. This has changed the oceans' chemistry, making them more acidic — a process known as ocean acidification — which makes it harder for corals (and many other marine animals) to build their calcium-based skeletal structures.

Cyclones: Climate change also favors the development of more powerful tropical cyclones, which can cause significant damage to shallow coral reefs. In addition, during cyclones or other strong storm events, more freshwater and sediments (which essentially smother corals) can make their way into the reef.

Rising sea levels and sea temperatures: The fast-moving changes caused by climate change mean that shoreline plants and animals don't have time to adapt to changes in sea level or temperature. While sea level has risen and fallen over thousands of years, climate change means it happens much faster, so life isn't able to adjust quickly enough.

Migration: Warming ocean temperatures are causing the Great Barrier Reef to move south away from the equator, according to 2019 research. However, scientists believe that the reef will not “migrate” off the coast of Brisbane, because other factors could stop it before it gets too far south.

Climate change is not directly addressed in the Reef 2050 plan, which some experts on the Reef 2050 advisory committee have called out as a huge problem. Considering the severity of the reef's health, some of those experts are calling for a plan to simply maintain the ecological function of the reef, saying it's already too late to restore its former glory.

Local impacts affecting the reef

There are things affecting the reef health that are easier for the Australian and Queensland governments to do something about, since they are issues that can be addressed regionally. None of these is as impactful as climate change, but they can help corals on the margins stay alive versus dying out.

Overfishing

Protected areas around the Great Barrier Reef tend to have richer biodiversity. (Photo: Ryan McMinds/Flickr)

When more fish are caught than an ecosystem can sustain over time, that's overfishing. On the Great Barrier Reef, that happens due to sport and commercial fishing of certain kinds of large, predator fish like coral trout and snapper. When you overfish at the top of the food chain, it causes significant changes all the way down. A less diverse reef is a less resilient reef, and that affects coral health.

“Predatory fish are extremely important for maintaining a balanced ecosystem on the reef, yet predators such as coral trout, snapper and emperor fish remain the main target for both recreational and commercial fishers,” April Boaden, a Ph.D. student who studied fish populations at the ARC Centre of Excellence for Coral Reef Studies, said in a release. In her 2015 paper, Boaden looked at areas where fishing was allowed versus areas where fishing was banned (green zones) and found a significant difference. In areas that allowed commercial and sport fishing, the number of predator fish was lower, as was diversity.

Illegal fishing in those "no-fishing" zones is on the rise. "People are intentionally breaking the law and intentionally going into the [green] zones and fishing; both commercial and recreational fishers," acting general manager of the Great Barrier Reef Marine Park Authority (GBRMPA), Richard Quincey told the Australian Broadcasting Company. "One of the reasons for that is they know there are more fish in there. There can be two or more times higher [fish numbers] as a minimum in protected, closed zones and therefore it becomes an attractive proposition."

The good news is that managing fishing is one of the easier ways to protect the reef ecosystem, and patrols and fines for people fishing in green zones have been stepped up. A new fisheries management plan is still being worked through, with many in the commercial fishing industry opposing it.

Ship traffic

Fuel oil leaks from the Shen Neng 1, a Chinese-registered bulk coal carrier that ran aground on a shoal in the Great Barrier Reef Marine Park in April 2010. (Photo: Maritime Safety Queensland/Getty Images)

Large ships filled with materials mined by Australia's extractive industries — often sent to China — also threaten the reef with physical damage if they experience an accident, as a disaster in 2010 proved. That year, a Chinese ship called Shen Neng 1 ran aground on the reef, gashing an almost 2-mile scar into the reef and dumping tons of toxic fuel oil onto the fragile corals. If that wasn't bad enough, cleanup took more than six years as a legal battle against the Chinese company that caused the damage wended its way through the courts. The government didn't have funds available to restore the reef and collect later because it only had money set aside for damage caused by oil spills and other pollutants, not crashes.

“With the number of ships travelling through the reef only increasing, especially if the port of Abbot Point is expanded to ship coal from the proposed Carmichael mine straight through the reef, the next Shen Neng disaster is not a question of ‘if’ but a question of ‘when’," Russell Reichelt, the chairman of the Great Barrier Reef Marine Park Authority, told the Guardian.

Coastal pollution

Probably the most work done to protect the reef has been in the area of reducing runoff of toxic chemicals and particulate matter, which smothers and sickens the coral on the reef — much of it from the agricultural areas adjacent to the Queensland coast. By working to restore stream- and river-side vegetation (which keeps as much sediment from running into rivers and out into the sea), monitoring aquaculture operations, and minimizing development near the coast, some of these impacts have been reduced by 10 or 15 percent over just a few years.

But it might not matter. During the most recent coral-bleaching events in 2016 and 2017, "reefs in muddy water were just as fried as those in pristine water," Terry P. Hughes, the director of a center for coral reef studies at James Cook University, told the New York Times. "That's not good news in terms of what you can do locally to prevent bleaching — the answer to that is not very much at all. You have to address climate change directly."

Crown-of-thorns starfish

The crown-of-thorns starfish has become a major threat to the Great Barrier Reef ecosystem. (Photo: Shutterstock)

Over the past three decades, 40 percent of the loss of corals is due to the crown-of-thorns starfish (COTS), a native coral-eating species that can be part of a balanced reef ecosystem. Unfortunately, COTS populations can abruptly explode into outbreaks — and those outbreaks seem to be growing more frequent in recent decades. That may be due to excess nitrogen from agricultural runoff, which can boost the plankton that feed COTS larvae.

"Nitrogen run-off from farms leads to algal blooms in Reef waters," explains the World Wildlife Fund. "This algae is a prime food source for starfish larvae, producing population explosions that decimate corals. The current outbreak, which has been building for five years, will further damage the Reef’s coral systems."

Agricultural fields stretch across the landscape in North Queensland, Australia. (Photo: Aerometrex/Shutterstock)

A program that would pay people to remove the starfish and kill them was implemented to deal with outbreaks of these starfish. A robot was even developed to kill the starfish more efficiently. However, an investigation by the Australian National Audit Office concluded in November 2016 that the government was unable to provide any evidence the culling program worked or was a smart use of money.

“It may, in fact, be contributing to the development of more chronic and persistent starfish outbreaks,” Udo Engelhardt, a leading researcher and head of the research consultancy Reefcare International told the Guardian.

The future of the Great Barrier Reef

A coral reef surrounding Green Island, near Cairns, North Queensland, Australia. (Photo: AustralianCamera/Shutterstock)

What comes next for the Great Barrier Reef remains a big question. Many organizations are working hard to minimize a wide range of dangers, and the good news is that at least some of those efforts seem to be working.

In September 2018, Tourism and Events Queensland announced a "positive update" that some affected areas of the Great Barrier Reef showed "significant signs of improvement," reported Bloomberg.

"When a reef is reported as 'bleached' in the media, that often leaves out a critical detail on how severe that bleaching is, at what depth the bleaching has occurred and if it’s going to cause permanent damage to the coral at that site," said Sheriden Morris, The Reef and Rainforest Research Center managing director, in a statement to Bloomberg, and the reef "has significant capacity to recover from health impacts like bleaching events."

Morris did note that the recovery is contingent on environmental conditions and another major bleaching event could still occur if ocean temperatures continue to rise.

It’s clear we need to act quickly to prevent this natural wonder from fading away. And for anyone who has gazed upon that turquoise water and its rich array of wildlife, even if only in pictures, there's no doubt this place is worth fighting for.