The Great Barrier Reef is a thing that people refer to as if it were a discrete structure, like the Great Pyramid or something. It’s really more of a long, messy urban district where all the buildings are alive and it’s so long that its character changes along its length. It’s off the northeast coast of Australia, in the state of Queensland, and it goes on forever, comprising thousands of separate reefs and islands. When you try to think of it as a line, you’re ignoring the complexity: it’s an archipelago, with holes, passages, lagoons, and very different ecosystems juxtaposed.

“The reef” is the coral, which isn’t a plant. The coral is animals, tiny polyps that are easy to miss, but their hard skeletons are slowly stacked up into a frame that supports a teeming ecosystem. It’s home to fish and rays and sharks and sea turtles and clams and sponges and sea stars and all sorts of things that I couldn’t even begin to identify, but which live in the nooks and crannies of the coral’s ridges and valleys. It’s not just pretty for divers, it’s a working ecosystem that relies on the coral for food and shelter and breeding in complex ways that aren’t immediately clear.

The curious and crucial fact here is that corals share an internal home with small algae, which contribute to their host’s energy, while the corals offer the algae a place to live. It’s why reefs are able to thrive in the nutrient-poor clear waters of the tropics. The relationship is efficient and, well, fragile. When temperatures rise for too long, the corals can become stressed and release the algae. This is “coral bleaching.” The corals lose their color as the colorful algae disappear. Bleaching doesn’t necessarily mean instant death for the coral, but it does mean it’s in trouble and repeated or severe bleaching can push it over the edge.

The GBR is affected by processes that you can’t see in photos. Larvae are transported between reefs by currents, sort of like invisible roads. Storms can batter the coral and break it off, but if the pieces settle in the right place, they can start new colonies. Predation is a factor. The one that gets the most attention is the crown-of-thorns starfish, a spiny creature that eats coral. If the conditions are right and its population surges, it can denude big swaths of living coral, resulting in a reef that from afar appears fine but is mostly denuded of its live cover.

Let’s not forget the people. The reef is a symbol of Australia, and it’s a big tourism draw. For a lot of communities, this isn’t just an environmental issue. It’s livelihoods. It’s livelihoods and economies. It’s also not just a nature reserve; you’ve got industries that depend on the reef, like fisheries and shipping. So there’s always this challenge of how you use it and how you protect it. They’ve been trying to set up various zones for different activities over the years, and there’s a lot of work going on to improve the water quality. There’s a lot of pollution that ends up on the reef from the rivers, so they’ve been working to improve that.

Water quality doesn’t sound like a fascinating topic, but everything is linked. Rainfall can wash sediment, fertilisers and pesticides into rivers, which in turn wash it into the sea. The sediment reduces water clarity, and means less light is available for the corals, and too many nutrients can lead to blooms of algae, which compete with the coral. It’s a creeping, invisible threat, not like the attention grabbing image of a ship running aground on a reef, and when you combine it with the background stress from rising temperatures, there’s very little head-room left to deal with the situation.

Climate change is the larger context that makes everything more difficult. A reef can recover from a cyclone, or a small predator plague, as long as the broader context is good. Recovery is a big part of the life of reefs. They’re not fixed things. But if heat events occur more frequently, if the background temperature of the ocean increases, the space between those events decreases. It stops being a hit, and starts being a pressure. Which is why we often talk about the Great Barrier Reef in terms of urgency. The resilience of the system needs time, and climate change is eating time.

Despite all that, however, many who depend on the reef speak of it with a combination of concern and dogged optimism. In some places, the coral has regrown well after impacts. Researchers measure coral cover, species, temperature stress, and dozens of other variables to gauge the state of the reef and identify where action might help. There are programs to restore reefs, breed or choose corals that are more resilient to temperature, and make local environments as healthy as possible for corals. Nobody claims such initiatives are solutions, but they can offer a breathing space and protect parts of the ecosystem as more profound choices are made about emissions and future climate directions.

If you see it, you might be surprised that the reef doesn’t always look like the brochures. Some parts are a riot of fish and life, and some parts are more still, with more rubble and fewer branching corals. That’s the nature of it. It’s not a display in a diorama, a perfect ecosystem preserved for posterity. It’s a living thing, and it’s changing. And when you see it, it can change your perspective. It’s not a “wonder of the world” thing. It’s a reminder that tiny things can make a giant structure, and that giant structures can still be delicate when their circumstances start to get a little out of whack.