Great Barrier Reef losing its ability to recover, scientists warn

Coral bleaching on the Great Barrier Reef earlier this year

Credit: JAMES COOK UNIVERSITY AUSTRALIA/AFP

The Great Barrier Reef is losing its ability to regenerate, scientists have warned, as rising water temperatures stop it from being able to recover. 

Researchers at the ARC Centre of Excellence for Coral Reef Studies in Queensland, Australia, found that numbers were declining across the board. 

Larger coral colonies are essential for reproduction, but their numbers are falling, leading to less new coral, said lead author Andreas Dietzel. 

"Reproduction essentially scales the size of the colony, so if you’re losing all the big ones, that means you have less reproduction going on, and therefore less baby coral," he said. 

For the study, published in the journal Proceedings of the Royal Society B, the team examined colonies across the Great Barrier Reef in 2017 and compared numbers to those seen during a similar survey in 1995. 

Small colonies at the highest point of the reef, known as the "crest", declined by 76 per cent, and on the slope, where the reef drops down towards the seabed, the decline was 57 per cent. 

Overall the number of corals had declined by more than half, with scientists warning that the reef’s ability to bounce back was diminishing. 

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"Our results show the ability of the Great Barrier Reef to recover — its resilience — is compromised compared to the past, because there are fewer babies, and fewer large breeding adults," Mr Dietzel added. 

A study released last year found that the rate at which the reef was adding new coral had fallen by 90 per cent after two bleaching events in 2016 and 2017 in  different areas. Bleaching occurred again this year along the whole length of the reef. 

Bleaching happens when triggers including warmer water causes coral to expel the algae living in its tissues. 

Under normal conditions, photosynthesis from this algae is its source of nutrition. It can recover if the algae reenters but if the conditions which caused the bleaching persist this is less likely to happen.