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Two Thirds of Great Barrier Reef Now Suffering from Coral Bleaching

Back-to-back severe bleaching events have affected two-thirds of Australia’s Great Barrier Reef, new aerial surveys have found.

The findings have caused alarm among scientists, who say the proximity of the 2016 and 2017 bleaching events is unprecedented for the reef, and will give damaged coral little chance to recover.

Scientists with the Australian Research Council’s Centre of Excellence for Coral Reef Studies last week completed aerial surveys of the world’s largest living structure, scoring bleaching at 800 individual coral reefs across 8,000km.

The results show the two consecutive mass bleaching events have affected a 1,500km stretch, leaving only the reef’s southern third unscathed.

Where last year’s bleaching was concentrated in the reef’s northern third, the 2017 event spread further south, and was most intense in the middle section of the Great Barrier Reef. This year’s mass bleaching, second in severity only to 2016, has occurred even in the absence of an El Niño event.


  • From Wikipedia, this is what bleaching is for anyone who hasn't read about it:

    Bleaching occurs when the conditions necessary to sustain the coral's zooxanthellae cannot be maintained.[5] The corals that form the structure of the great reef ecosystems of tropical seas depend upon a symbiotic relationship with algae-like unicellular flagellate protozoa that are photosynthetic and live within their tissues. Zooxanthellae give coral its coloration, with the specific color depending on the particular clade. Any environmental trigger that affects the coral's ability to supply the zooxanthellae with nutrients for photosynthesis (carbon dioxide, ammonium) will lead to expulsion.[5] This process is a "downward spiral", whereby the coral's failure to prevent the division of zooxanthellae leads to ever-greater amounts of the photosynthesis-derived carbon to be diverted into the algae rather than the coral. This makes the energy balance required for the coral to continue sustaining its algae more fragile, and hence the coral loses the ability to maintain its parasitic control on its zooxanthellae.[5] Bleaching has been attributed to a defense mechanism in corals; this is called the "adaptive bleaching hypothesis", from a 1993 paper by Robert Buddemeier and Daphne Fautin.[6]

    Some scientists consider bleaching a poorly-understood type of "stress" related to high irradiance; environmental factors like sediments, harmful chemicals, and freshwater; and high or low water temperatures.[1] But as corals in very remote and clear areas of the Great Barrier Reef have also shown widespread bleaching in 2017, rising sea water temperatures have been identified as the main cause of "stress" for corals.[7] This "stress" causes corals to expel their zooxanthellae, which leads to a lighter or completely white appearance, hence the term "bleached".[8]

    Physiologically the lipid composition of the symbiont thylakoid membrane affects their structural integrity when there is a change in temperature, which combined with increased nitric acid results in damage to photosystem II. As a result of accumulated oxidative stress and the damage to the thylakoid of chloroplasts, there is an increase in degradation of the symbiosis and the symbionts will eventually abandon their host.

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