The world heritage site currently has its greatest coral cover in decades.
However, experts cautioned that the regrowth was made up largely of a common, fast-growing but weak genus known as acropora that could easily be lost – and one expert said “more needs to be done”.
Acropora is renowned for its branching colonies that resemble staghorns and can grow in thickets covering large areas in a variety of colours.
It also plays a key role in reef-building, providing much of the calcium carbonate structure, and is tied to the popular images of the Great Barrier Reef.
However, it is vulnerable to storms and crown-of-thorns starfish, which feed on coral, and often grows in “boom and bust” cycles.
The reef, which stretches for nearly 2,400km along the coast of Queensland, has been badly impacted by climate change in recent years and suffered a series of “mass bleaching” events, where stressed coral turns white.
However, scientists revealed that the northern and central parts of the reef now have the highest amount of coral cover since monitoring began 36 years ago.
A question mark remains over the exact reason for the reef’s sudden recovery, which suggests the ecosystem has much greater resilience and ability to recover than previously understood.
It may have been helped by a quiet period in terms of cyclones and crown-of-thorns starfish, which means the progress could be undone by further disturbances.
Dr Mike Emslie, of the Australian Institute of Marine Science, said the results were “good news”, but there were still major worries about the reef’s health.
Professor Terry Hughes, a marine scientist, said replacing the large, old, slow-growing corals that had defined the reef was probably “no longer possible”, adding: “Instead, we’re seeing partial reassembly of fast-growing weedy corals before the next disturbance.”
Dr Paul Hardisty, chief executive of the Australian Institute of Marine Science, said: “These latest results demonstrate the reef can still recover in periods free of intense disturbances.”
He also warned that the increased frequency of mass coral bleaching caused by climate change was “uncharted territory” for the reef, and that a bleaching event earlier this year was the first to occur during a La Niña weather pattern.
Dr Maxine Newlands, a political scientist from James Cook University in Queensland, said the reef’s survival depended on a delicate balancing act.
“Politicians and policy- makers cannot see this as a sign of a recovered reef, but as an indicator that more needs to be done,” she said.
The reef has been on Unesco’s World Heritage list since 1981 because of its scientific significance as one of the planet’s most diverse ecosystems.
However, Unesco officials, who inspected the reef earlier this year, have accused Australian authorities of not doing enough to protect it.
Telegraph Media Group Limited