The number of new corals on the Great Barrier Reef in Australia has dropped 89% since unprecedented bleaching events in 2016 and 2017, scientists said.
The events, which damaged two-thirds of the world's largest reef system, are now blamed for the collapse of the resumption of coral growth last year.
"Dead corals do not make babies," said lead author Professor Terry Hughes of Queensland's James Cook University.
Scientists attribute the problem to rising sea temperatures.
The research, published Thursday in the journal Nature, was conducted by a group of scientists last year.
It measured the number of adult corals along the reef that had survived after mass bleaching and the number of new corals produced.
"Across the length of the Great Barrier Reef, there has been an average decline of 90% over the past [1990s] recruitment levels, "the BBC co-author, Professor Andrew Baird, told the BBC.
& # 39; There is nothing left to restore the reef & # 39;
Professor Baird said the "rather extraordinary" decline was unexpected. It was probably the first problem of re-growth of the reef on a large scale, he added.
"Babies can travel long distances and if a reef is knocked out, there are usually plenty of adults in another reef to provide juveniles," said Professor Baird.
However, bleaching in 2016 and 2017 affected 1,500 km (900 miles) of reef.
"Now the magnitude of the mortality is such that there is nothing left to replenish the reef," said Professor Baird.
The study also revealed that the mixture of baby coral species had changed. He found a 93% drop in Acropora, a species that usually dominates a healthy reef and provides habitat for thousands of other species.
The researchers said coral rebuilding could recover over the next five to 10 years if there were no future bleaching.
However, given current estimates, this probability was "almost inconceivable," said Professor Baird.
"We are now at the point where local solutions to the reef are almost useless – the only thing that matters is the action on climate change," said Professor Baird.
The reef – an expansive collection of thousands of smaller coral reefs extending from the northern tip of Queensland to the city of Bundaberg in the south of the state – has been listed as a World Heritage Site. UNESCO in 1981.
The UN says that it is "the richest in diversity" of all World Heritage sites and that it is "of enormous scientific and intrinsic importance".