The Great Barrier Reef is a vast coral reef system off northeastern Queensland comprising thousands of individual reefs and hundreds of islands, recognized as the world’s largest coral reef ecosystem and inscribed on the World Heritage List in 1981, covering a World Heritage Area of about 348,000 km² and a Marine Park of about 344,400 km², according to the UNESCO World Heritage Centre and the Australian Reef Authority.

Location and physical characteristics

Extending for more than 2,300 km along Australia’s northeast coast in the Coral Sea, the reef complex spans inshore shallows to outer-shelf waters beyond 2,000 m depth, reflecting cross‑shelf and latitudinal diversity that underpins its Outstanding Universal Value, as detailed by UNESCO.
The World Heritage Area contains more than 3,000 coral reefs and about 1,050 islands and cays, including roughly 600 continental islands, 300 coral cays, and about 150 inshore mangrove islands, according to the Reef Authority.
The Marine Park’s width varies between roughly 60 and 250 km, with inshore waters averaging ~35 m depth and outer-shelf slopes descending to >2,000 m, according to the Reef Authority’s fact summary of key physical parameters (Reef Authority).

Biodiversity and habitats

The property supports exceptional biodiversity, with at least 1,500 species of fishes, about 400 species of hard corals, some 4,000 mollusc species, and around 240 bird species, while also providing critical habitat for threatened species such as dugongs and green turtles, according to the UNESCO World Heritage Centre.
Recent Reef Authority summaries indicate approximately 1,625 fish species and more than 450 hard coral species, alongside extensive mangrove (representing 54% of global mangrove diversity) and ~6,000 km² of seagrass habitats, underscoring the ecosystem’s breadth of flora and fauna (Reef Authority).
Islands within the World Heritage Area—about 1,050 in total—support significant seabird rookeries and turtle nesting beaches, reflecting the reef’s role in regional life cycles (Reef Authority).

Geological and ecological significance

The reef records major stages of Earth’s evolutionary and climatic history through reef-building episodes and sea‑level fluctuations since the last glacial period, which together produced a continuum of reef types from fringing to barrier formations, as recognized in the site’s World Heritage criteria (UNESCO).
Ecologically, the system’s latitudinal span of roughly 14 degrees and cross‑shelf gradients create diverse habitats and ecological processes that underpin high species richness and endemism, a basis for its inscription under all four natural World Heritage criteria (UNESCO).

Governance and protection

The Great Barrier Reef Marine Park was established under the Great Barrier Reef Marine Park Act 1975, which created the Great Barrier Reef Marine Park Authority and provides planning, zoning, permissions, enforcement, and a prohibition on most mining operations in the region, according to the Act and the Authority’s legislative overview (Australian Government legislation; Reef Authority).
Marine Park zoning, including no‑take Marine National Park (Green) Zones defined in the Zoning Plan 2003, separates uses to reduce cumulative impacts while allowing sustainable activities, according to the Authority’s zoning guidance (Reef Authority).
Strategic frameworks such as the Reef 2050 Long‑Term Sustainability Plan and the associated Integrated Monitoring and Reporting Program coordinate Commonwealth‑State actions on threats including water quality, coastal development, and species protection (DCCEEW; Reef Authority RIMReP; Reef Knowledge System).

Traditional Owners and cultural values

Approximately 70 Aboriginal and Torres Strait Islander Traditional Owner groups maintain enduring connections to Sea Country, and co‑management occurs through Traditional Use of Marine Resources Agreements (TUMRAs) accredited under legislation, with 10 TUMRAs now covering more than 43% of the Marine Park coastline, according to the Reef Authority’s Traditional Owner program updates (Reef Authority; Reef Authority news, 2025).
These agreements integrate cultural lore and contemporary science for species management, monitoring, and compliance, reflecting long‑standing custodianship of Sea Country (Reef Authority).

Disturbances and major threats

Climate-driven marine heatwaves have caused repeated mass Coral bleaching events, with landmark research showing that the severity and geographic footprint of the 1998, 2002, and 2016 events were dictated primarily by sea‑surface temperature anomalies, and that local protection conferred little resistance to extreme heat, underscoring the primacy of global warming in driving bleaching risk (Nature).
Long-term analyses documented a multidecadal decline in coral cover from 1985–2012 attributable mainly to tropical cyclones, Crown-of-thorns starfish (Acanthaster cf. solaris) predation, and bleaching, indicating both vulnerability and capacity for recovery in the absence of acute disturbances (PNAS).
During the 2023–24 austral summer, aerial and in‑water surveys by the Australian Institute of Marine Science (AIMS) and the Great Barrier Reef Marine Park Authority recorded the reef’s fifth widespread bleaching since 2016, with bleaching observed on 73% of the 1,000 surveyed reefs within the Marine Park, coincident with cyclones and floods that compounded impacts (AIMS Reef Snapshot, Apr. 17, 2024).
AIMS’ 2025 Long‑Term Monitoring Program summary reports substantial regional coral-cover declines after the 2024 mass bleaching and cyclones, noting the event formed part of a fourth global coral‑bleaching episode confirmed in April 2024 by NOAA and ICRI (AIMS LTMP Annual Summary 2024/25; ICRI/NOAA announcement).
NOAA and ICRI reported that by March 30, 2025, bleaching‑level heat stress had affected about 84% of the world’s coral reefs, making the event the most extensive on record, with the Great Barrier Reef among the heavily impacted systems (ICRI 2025 update; NOAA NESDIS).
Crown‑of‑thorns starfish outbreaks remain a recurrent pressure, and large-scale control programs under the Reef Trust Partnership deploy diver injections (e.g., bile salts or vinegar) to reduce coral mortality on high‑value reefs (Great Barrier Reef Foundation; GBR Foundation COTS facts).
Other chronic stressors include degraded water quality from catchments, extreme weather, disease, and coastal activities, which are targeted in the Reef 2050 Water Quality Improvement Plan and associated monitoring via Paddock‑to‑Reef reporting (Reef 2050 WQIP; DCCEEW Reef 2050 achievements).

Monitoring and research

AIMS’ Long‑Term Monitoring Program has surveyed hundreds of reefs for more than 35 years, producing one of the globe’s most comprehensive coral‑reef status datasets used widely in management and science (AIMS LTMP).
Reef‑wide seasonal condition snapshots, integrated observing, and the Reef 2050 Integrated Monitoring and Reporting Program inform adaptive management and public reporting across ecological, social, and cultural values (Reef Authority RIMReP).

Economy and visitation

Tourism activity is concentrated in a small share of the Marine Park, with 2.13 million total visitor days in 2023 as the sector rebounded from pandemic-era lows, according to the Reef Authority’s Outlook reporting on commercial marine tourism (Reef Authority Outlook—Tourism).
The reef’s annual economic contribution and employment significance have been estimated at A$6.4 billion and over 64,000 jobs (2015–16) in a national assessment, highlighting its role in regional economies and national branding (Great Barrier Reef Foundation—Value of the Reef; Deloitte summary via GBRF).

International status

The Great Barrier Reef remains inscribed on the World Heritage List for all four natural criteria, with repeated reviews focusing on management responses to climate and water‑quality threats and ongoing dialogue over potential “in danger” listing amid recent mass bleaching, as reflected in decisions and monitoring by the UNESCO World Heritage Centre and partners (UNESCO listing).

Climate context

The 2023–25 period forms part of a fourth global coral‑bleaching event linked to unprecedented ocean heat and an El Niño phase, with scientific agencies noting the scale and intensity of thermal stress as exceptional, thereby increasing risks of mortality and reduced recovery intervals on the Great Barrier Reef and elsewhere (Reuters—NOAA announcement; ICRI).

Key institutions

The Great Barrier Reef Marine Park Authority is the statutory manager of the Marine Park, exercising planning, permitting, compliance, and enforcement functions under Commonwealth law, including compulsory pilotage provisions in prescribed shipping areas, as set out in the Marine Park Act and the Authority’s legislative overview (Australian Government legislation; Reef Authority).
The Australian Institute of Marine Science conducts long‑term ecological monitoring and research on bleaching, cyclones, and predators such as crown‑of‑thorns, providing data that underpin regional status assessments and management responses (AIMS LTMP; AIMS bleaching updates 2024).