The Great Barrier Reef is one of those locations that is discussed as a singular entity, like a mountain or a monument. In fact, it is more akin to a large city, one that extends for so long that its characteristics change significantly from its one end to the other. Located off the coast of Queensland in northeast Australia, it is vast in scale, encompassing thousands of distinct reefs and islands. Any attempt to envision it as a continuous entity misses out on its essential nature: It is discontinuous, with lots of holes, channels, lagoons, and different ecological communities. The dominant component of what is colloquially known as “the reef” is the structure built by corals themselves. Coral animals are tiny, but as they grow and die, their hard skeletons are built up over long periods of time. This forms the basis of an ecosystem that is teeming with life: Fish, rays, sharks, sea turtles, clams, sponges, sea stars, and many, many more animals that most people do not even recognize all live in the nooks and crannies of the reef.

It is not simply a scenic backdrop for scuba divers; it is a thriving ecosystem that forages, hides, spawns, and lives in complex ways that are dependent on the architecture and the health of the corals. One of the key aspects of corals that is important to understanding what’s happening with them is that they have a symbiotic relationship with single-celled algae that live within their bodies. The algae help supply them with energy, while the coral provides them a safe home. This symbiosis is one of the reasons that reefs are able to thrive in clear tropical waters that are poor in nutrients. It is an efficient system, but a sensitive one.

When the water gets too hot for too long, the coral gets stressed and ejects the algae. That is what is known as coral bleaching. The coral turns white as the colorful algae are expelled. Bleaching does not necessarily mean that the coral is dead immediately, but it does mean that it is in distress, and successive or severe bleaching can kill it.

There are many factors that shape the Great Barrier Reef, some not immediately apparent from the photographs. Ocean currents transport the larvae of corals from one reef to another like an invisible network of highways. Storms can break corals apart, but the broken fragments can grow into new corals if they settle in a good place. Predators also play a role. The most prominent one is the crown-of-thorns starfish, a spiny predator that eats coral. When conditions are right for it, and its population surges, it can ravage large swaths of living corals, leaving behind a reef that still has its structure intact as seen from a distance but has lost much of its living cover.

Finally, there is the human component. The Great Barrier Reef is an integral part of Australia’s natural heritage, and it is a huge tourist draw. To many of the communities along the Queensland coast where the GBR is a dominant part of the economy, it is not a story of an environmental issue. It is a story about livelihoods, jobs, and small businesses. It is also a multi-use area, including fishing, shipping, tourism, etc. There are things like zoning restrictions to prevent certain types of activities in certain areas. And efforts to control water quality (from land-based activities) because, just like any river, what happens upstream will eventually make its way downstream.

Water quality is a pretty boring topic, until you realize the impact it can have. Heavy rainfall can result in sediment, fertilizer, and pesticides from river catchments making their way into the ocean. Sediment can decrease the amount of light in the water (coral needs light to survive) and excess nutrients can promote the growth of algae, which can out-compete coral. These are not immediate threats like a ship running aground, they are long-term pressures. And when a reef is already under pressure from rising sea temperatures, it has limited scope to cope with other issues.

Climate change is the elephant in the room, that is making all of this harder. A reef can recover from a cyclone, or a localized bloom of coral-eating starfish, as long as the broader conditions for its survival remain in place. Recovery is a big part of the life-cycle of a reef, as they are not a static entity. But the more frequent those heat events become, and the higher the ambient temperature of the ocean becomes, the smaller the window for recovery becomes. It stops being something of a setback, and starts being something of a shove.

Which is why there is so much urgency in the discussion around the GBR. The resilience of the system relies on time, and the warming of the planet is taking that time away. Despite all of this, many of the people who work on the reef still talk about it with a sense of concern, but also a sense of defiant optimism. Some areas have already shown significant signs of recovery. Scientists are monitoring coral cover, species composition, temperature stress, and dozens of other metrics in an effort to understand what is going on, and where intervention may assist.

There are programs underway to restore damaged reefs, to breed or select corals that are more resilient to temperature stress, and to improve local conditions to give the corals the best possible chance. Nobody is under any illusions that these programs are a panacea, but they can provide a stop-gap, and help preserve some of the system, whilst we get on with the more important job of dealing with emissions, and addressing long-term climate trends.

If you ever get the chance to visit, the reef will surprise you because it doesn’t always live up to the brochure. Some areas will be teeming with fish, and look a vibrant, healthy brown color. Others will be quieter, and more rubble-strewn, with fewer branching corals. That juxtaposition is part of what makes it so important. It is not something preserved in a glass case, it is a living, breathing ecosystem that is changing.

Going to see it firsthand can change the way you think about it. It is not just something with a “wonder of the world” tag attached to it. It is a reminder that small things can add up to something truly massive, and that massive things can still be incredibly fragile when the underlying conditions that support them start to get out of kilter.