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Coral spawning on Great Barrier Reef

25 November 2013 Last updated at 07:16 GMT

For a few days each year, a vast area off Australia's eastern coast becomes the location for coral spawning.

It happens at night when the plankton feeders are asleep and the sea temperature is just right.

Divers and scientists gather annually to witness this spectacle.

Phil Mercer reports from Sydney.

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