Ghost Reefs: The Global Coral Bleaching Crisis
Coral bleaching worldwide has surged as ocean temperatures rise. Corals rely on microscopic algae called zooxanthellae inside their tissues. These algae provide up to 90% of a coral’s energy and give reefs their color. When water temperatures stay 1 to 2°F above normal for weeks, this partnership breaks down. Corals expel the algae, losing their main energy source and turning white. If cooler water returns within weeks, algae can repopulate the coral and recovery may take months. If heat persists 1 to 3 months, corals starve and often die.
Global bleaching events have become more frequent. Since 1998, there have been four major cycles. The current event, starting in 2023, affected about 84% of reefs by 2025, including roughly 80% of the Great Barrier Reef, making it the most extensive on record. Earlier peaks reached roughly 21% in 1998, 35% in 2010, and 56% during 2014–2017. Recovery periods that once lasted decades have shortened to about 5 years, leaving reefs stressed before the next heat wave. Scientists estimate that more than 50 nations with coral reefs have experienced significant bleaching events during this period.
Between 2009 and 2018, the world lost about 14% of coral cover, larger than the Great Barrier Reef. Australia alone has lost roughly 30% of its coral cover since 1995, and U.S. reefs have lost about 20% in the same period. Localized mortality can reach 70% in some areas.
Scientists are cultivating heat-tolerant corals, reintroducing larvae, and using probiotics to boost survival. Programs in Australia, the Caribbean, and Southeast Asia aim to increase coral cover 25–30% and create artificial structures to stabilize reefs.
Despite losses, coral reefs continue to support a significant portion of marine life and ecosystems. They remain critical habitats for about 25% of all marine species, provide shelter for juvenile fish, and maintain biodiversity across the oceans.
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