Great Barrier Reef: Coral Spawning, Crown-of-Thorns, and Bleaching

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The Great Barrier Reef stretches over 2,300 kilometers off northeast Australia and covers about 344,400 square kilometers in more than 2,900 reefs and 900 islands, all built by pencil eraser sized coral polyps laying limestone cups. Australia drifting north about seven centimeters a year reached the Coral Sea some 24 million years ago, but the living reef began only about 9,000 years ago as rising seas after the last ice age flooded a coastal plain where Aboriginal Australians had lived for at least 40,000 years. HMS Endeavour ran aground on it on June 11, 1770, and Matthew Flinders mapped and named it in 1802. It hosts 400 coral species, over 1,500 fish species and six of seven sea turtle species.

Corals spawn in mass events cued by water temperature, daylight and the moon. Studies found the reef lost more than half its coral cover between 1985 and 2017 to marine heat waves that make corals expel their zooxanthellae, and acidification is removing aragonite. Over 90 percent of local pollution is farm runoff, and doubling chlorophyll raises crown of thorns starfish larval survival tenfold. Queensland's shark control program killed about 50,000 sharks from 1962 to 2018. Yet in 2022 the Australian Institute of Marine Science recorded the highest coral cover in 36 years in the north and center, led by fast growing Acropora.

• Inner reefs spawn just after the October full moon, outer reefs in November and December.
• The coal carrier Shen Neng 1 ran aground in 2010 and leaked oil onto the reef.
• The 2004 rezoning raised no take zones from about 4.5 percent to over 33 percent.
• The Reef 2050 plan of 2015 has been criticized for lacking binding emissions measures.
• Bird guano under tourist pontoons links to 12 percent coral disease versus 1.1 percent nearby.