How does El Nino specifically threaten the Great Barrier Reef?

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El Nino Poses a High Risk of Severe Bleaching and Ecosystem Collapse to the Great Barrier Reef

The Great Barrier Reef is facing a significant threat of extreme and widespread coral bleaching, potentially leading to "ecosystem collapse," directly linked to the current El Nino weather phenomenon. This year's El Nino is notable for its anticipated strength, which is warming surface temperatures in the Pacific Ocean and consequently altering global weather patterns, including wind, pressure, and rainfall. Scientists project a high probability of severe, large-scale mass bleaching events occurring on the reef.
El Nino's Impact on Ocean Temperatures

The current El Nino event is expected to be exceptionally strong, leading to record-breaking warmth in the central and eastern equatorial Pacific Ocean. This warming trend directly impacts marine environments by increasing sea surface temperatures. When these temperatures rise above a certain threshold for an extended period, they stress corals, initiating the process of bleaching.
The Mechanism of Coral Bleaching

Coral bleaching occurs when corals, under environmental stress such as elevated water temperatures, expel the symbiotic algae (zooxanthellae) living in their tissues. These algae provide corals with their vibrant colours and are a primary source of nutrition through photosynthesis. Without these algae, the coral turns white, a phenomenon known as bleaching. While corals can recover from mild or short-lived bleaching events, prolonged or severe bleaching can lead to coral mortality.
Consequences for the Great Barrier Reef Ecosystem

The Great Barrier Reef has already experienced significant declines in hard coral cover, with the current event marking its sixth mass bleaching since 2016. Scientists warn that the severity of this El Nino could result in localized species extinctions and a widespread collapse of the reef's ecosystem. Beyond the direct impact of bleaching, the reef faces compounding pressures from extreme weather events, land-based runoff, coastal development, and predation by the Crown of Thorns starfish, all of which exacerbate its vulnerability.

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How does El Nino specifically threaten the Great Barrier Reef?

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