Earth’s biggest reef keeps bleaching—and sometimes bouncing back
Queensland’s Great Barrier Reef strings more than 2,900 reefs and 900 islands across 2,300-plus kilometres and about 344,400 square kilometres of Coral Sea. Marine parks blunt some harm, yet heat-driven bleaching keeps rewriting the outlook every few years.
Aboriginal and Torres Strait Islander peoples have long known and used the reef, which runs from Bramble Cay in Torres Strait to Lady Elliot Island in the south. Cook’s Endeavour struck a shoal near modern Cooktown on 11 June 1770 and spent seven weeks under repair, and Matthew Flinders gave the reef its name after surveys from 1802. More than 20 ships were lost there between 1791 and 1850, prompting surveys by Phillip Parker King, Francis Blackwood, and Owen Stanley.
Its foundation is a coastal plain of sediment eroded from the Great Dividing Range. Coral skeleton deposits date back half a million years, and managers put the first complete reef structures at 600,000 years ago. As seas rose between 20,000 and 6,000 years ago, corals climbed the drowned hills; by 13,000 years ago the ocean stood only 60 metres below today’s level. Reefs grow only in sunlit water shallower than about 150 metres, while Australia itself drifts north roughly 7 cm a year.
Managers divide the World Heritage Area into 70 bioregions, 30 of them reefs. Ribbon and deltaic reefs occur only in the north, fringing reefs cluster around high southern islands such as the Whitsundays, and seafloor springs called wonky holes release fresh, sometimes nutrient-laden water. Thirty species of whales and dolphins have been recorded, along with large dugong herds and more than 1,500 fish species.
Under the 1975 Marine Park Act, Outlook reports every five years track its health. Mass bleaching struck in 2016 and again in March 2022, yet that year the Australian Institute of Marine Science recorded the strongest recovery in 36 years, driven by fast-growing Acropora corals. Polluted runoff, dredging, and warming seas remain the main threats.
Source: Great Barrier Reef
