The Great Barrier Reef is the largest coral reef system on Earth, stretching approximately 2,300 kilometers along the coast of Queensland in northeastern Australia. It covers 344,400 square kilometers of ocean, making it visible from space and roughly comparable in length to the west coast of the United States from Vancouver to the Mexican border. It is a UNESCO World Heritage site, a critical marine ecosystem, and a major economic engine for Australia.
Size and Structure
The reef is not a single continuous structure but a vast mosaic of individual coral reefs, islands, and sandy cays spread across the continental shelf. The entire system sits within the Great Barrier Reef Marine Park, which was established to manage and protect the area. To put its scale in perspective, the park is larger than the United Kingdom, Italy, or the entire state of New Mexico.
The living reef we see today is less than 10,000 years old, though fossil reef structures on the underlying shelf date back several hundred thousand years. Research published in 2018 found that the current reef is just the latest of at least five reef systems that have grown in this region over the past 30,000 years, each one shaped by rising and falling sea levels. At times, the coral grew vertically as fast as 20 meters per thousand years to keep pace with rising water. At other times, sea levels changed too quickly and entire reef generations drowned or were exposed above the waterline and died off.
Why It Matters Economically
The reef contributes over $9 billion annually to the Australian economy and supports 77,000 full-time equivalent jobs, making it the country’s fifth largest employer. Its total estimated value is $95 billion, a 69 percent increase from the $56 billion estimate in 2017. Most of that economic activity comes from tourism, commercial fishing, and recreation. For the communities along the Queensland coast, the reef is not just a natural wonder but a livelihood.
World Heritage and Indigenous Connection
The Great Barrier Reef was inscribed as a World Heritage site in 1981, meeting all four natural criteria the committee uses for designation. Those criteria recognize it as an outstanding example of Earth’s evolutionary history, an active site of significant geological and biological processes, and a place of exceptional natural beauty containing superlative ecosystems.
Long before that formal recognition, the reef held deep significance for Australia’s First Nations peoples. Around 70 Aboriginal Traditional Owner groups hold authority for sea country management within the marine park, and Torres Strait Island Traditional Owner groups are also connected to the reef through cultural knowledge and traditional use spanning thousands of years. These groups are increasingly involved in on-country management, policy, and planning programs, including formal agreements with the Great Barrier Reef Marine Park Authority that recognize their role as stewards of the marine environment.
Current Health and Coral Bleaching
The reef is under serious stress. The most recent large-scale coral survey, covering over 1,080 individual reefs, found that three quarters showed some level of bleaching. On 40 percent of those bleached reefs, more than half the corals had turned white. Coral bleaching happens when water temperatures stay too high for too long, causing corals to expel the algae living in their tissue. Without those algae, corals lose their color and their primary energy source. If conditions don’t improve quickly enough, the coral dies.
The damage has been uneven across the reef’s geography, but the numbers are stark. In the northern section, from Cape York to Cooktown, average coral cover dropped by about a quarter in a single year, falling from 39.8 percent to 30 percent between 2024 and 2025. Near Lizard Island, individual reefs lost up to 70 percent of their coral. The southern reef, from Proserpine to Gladstone, fared even worse in relative terms: coral cover declined by almost a third, dropping from 38.9 percent to 26.9 percent after the highest levels of heat stress ever recorded in that region during the summer of 2024.
The central section, from Cooktown to Proserpine, was the most stable, with some reefs holding steady or even gaining coral. But even there, the region-wide trend was a 14 percent decline, and reefs near Cairns lost between 17 and 60 percent of their 2024 coral cover. The declines in both the north and south were the largest single-year drops in the 39 years since systematic monitoring began.
Threats Beyond Warming Water
Heat stress from climate change is the reef’s most severe and widespread threat, but it is not the only one. Outbreaks of crown-of-thorns starfish, a large predator that feeds directly on coral tissue, remain a persistent problem. These starfish occur naturally on the reef, but in outbreak numbers they can strip reefs bare faster than the coral can recover. Outbreaks on one reef also tend to spread to neighboring reefs if left unchecked.
The Australian government runs a dedicated control program to manage these outbreaks. During the 2024-25 season, the program surveyed 234 target reefs and culled nearly 74,000 starfish across more than 11,700 hectares of reef habitat, logging over 18,000 hours of underwater work. Long-term monitoring has shown that suppressing adult starfish populations on one reef produces benefits that extend well beyond that immediate area. Corals that aren’t simultaneously fighting off starfish predation have more energy to cope with heat stress, storms, and other pressures.
Other ongoing threats include runoff from agricultural land, which carries sediment, fertilizers, and pesticides into reef waters; cyclone damage, which can physically break apart coral structures; and ocean acidification, which makes it harder for corals to build their calcium carbonate skeletons over time.
What Lives There
The reef supports an extraordinary concentration of marine life. It is home to more than 1,500 species of fish, around 400 types of coral, six of the world’s seven species of sea turtle, and significant populations of dugongs, dolphins, and humpback whales that use the reef’s waters as a breeding ground. Hundreds of species of birds nest on the reef’s islands and cays.
This biodiversity is part of what earned the reef its World Heritage listing, but it also makes the ecosystem functionally complex. Coral provides the physical structure that fish, invertebrates, and algae depend on for shelter, food, and breeding habitat. When coral cover declines, the populations of species that rely on it decline too, creating cascading effects throughout the food web.