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The Great Barrier Reef (GBR), the world’s largest living structure and a UNESCO World Heritage Site (1981), has recorded its steepest decline in hard coral cover in nearly four decades, according to the Australian Institute of Marine Science (AIMS) 2025 survey. The reef, spread over 2,000 km along Australia’s northeast coast and covering ~350,000 sq. km, accounts for nearly 10% of global coral reef ecosystems and hosts extraordinary biodiversity, including 400 coral species, 1,500 fish species, 4,000 mollusk species, six of seven turtle species, dugongs, and numerous seabirds.

The 2024–25 Mass Bleaching Event

• The 2024 bleaching, the fifth since 2016, coincided with record ocean heat stress, cyclones, flooding, and crown-of-thorns starfish outbreaks.
• AIMS’ long-term monitoring across 124 reefs (Aug 2024–May 2025) revealed:
  • 48% reefs showed a decline in coral cover,
  • 42% reefs showed no change,
  • Only 10% reefs recorded recovery.
• Some areas, especially in the northern GBR (around Lizard Island), lost over 70% of hard coral cover, the sharpest decline since monitoring began in 1986.

Regional Breakdown of Coral Loss (2024–25)

• Northern GBR: Coral cover dropped from 39.8% to 30% (–24.8%), driven by record heat stress, cyclones, and freshwater inundation.
• Central GBR: Cover fell by 13.9% to 28.6%, with Cairns sector reefs losing 6–60% due to Cyclone Jasper (2023) and flooding.
• Southern GBR: Sharpest relative loss, down from 38.9% to 26.9% (–30.6%), largely due to extreme heat stress in the Capricorn-Bunker sector, storm damage, and coral disease.

Drivers of Decline

1. Climate change-induced heat stress – primary driver of bleaching.
2. Cyclones & floods – physical damage and sedimentation.
3. Crown-of-thorns starfish – venomous predators that feed on corals.
4. Coral disease – post-bleaching infections weaken recovery.

Oscillating Ecosystem Under Stress

• Acropora corals, fast-growing and heat-resilient species that helped reef recovery (2017–24), were worst hit.
• Scientists warn of increasing volatility in coral cover, shifting between record highs and lows within short periods.
• Before the 1990s, mass bleaching was rare (first major event: 1998). Since 2020, GBR has faced bleaching in 2020, 2022, 2024, and 2025, with two consecutive years of mass bleaching for the second time in a decade.

Global Perspective

According to the US NOAA, between Jan 2023 and May 2025, 83.9% of global coral reef area experienced bleaching-level heat stress, with mass bleaching reported in at least 83 countries and territories.

Conservation & Outlook

The GBR, managed largely under the Great Barrier Reef Marine Park Authority, remains one of the most studied ecosystems. However, repeated bleaching events are leaving insufficient recovery time, pushing the ecosystem toward collapse. Scientists warn the window to save the GBR is rapidly closing without urgent global climate action.