Australasian Science: Australia's authority on science since 1938

Setting the Record Straight on Coral Bleaching

By Russell Reichelt

The mass bleaching on the Great Barrier Reef this summer is the most damaging recorded.

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Over the past 12 months, corals in most tropical regions across the world have experienced the most severe mass coral bleaching ever recorded. By June this year, 22% of coral died on the 3000 reefs of the Great Barrier Reef, with most of the mortality occurring in the far north above Cooktown.

Coral bleaching occurs in hard and soft corals, and is triggered by prolonged heat stress that causes corals to expel the colourful, symbiotic organisms that live inside their tissue. These organisms, called zooxanthellae, normally mask the underlying white skeleton. Giant clams and sea anemones also have these symbionts, and consequently also turn white when under heat stress.

Under the presence of a strong El Niño, sea temperatures from February to May over much of the Reef were a degree or more over their long-term monthly averages, exceeding all previous temperature records. The El Niño came on top of an underlying trend of ocean warming caused by human-induced climate change – since 1871 the average temperature on the Reef has risen by 0.67°C.

The physiology of corals is adapted to their local region, and they thrive in waters close to their thermal tolerance limits, which can vary by 5–6°C across the full geographic range of tropical corals.

The mass bleaching on the Great Barrier Reef this summer is the most damaging ever recorded. To date, surveys...

The full text of this article can be purchased from Informit.