26 September 2023

Parrotfish prove surprise reef saviours

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Australian Institute of Marine Science (AIMS) researchers have revealed that reef-dwelling parrotfish populations are booming in the wake of severe coral bleaching of the Great Barrier Reef.

The surprise finding came when researchers, led by AIMS’ Dr Brett Taylor, looked at fish populations in severely bleached areas of two reefs 8,000 kilometres apart – the Great Barrier Reef and the Chagos Archipelago in the Indian Ocean.

“Warming oceans place enormous pressure on reefs and if the temperatures remain high for too long the coral will die,” Dr Taylor said.

“The more frequently this occurs there is less time for coral reefs to recover.”

“In the damaged areas of the reefs, the study found that parrotfish populations increased in number by between two and eight times, and individual fish were about 20 per cent larger than those in unbleached sections,” Dr Taylor said.

He said almost every other species of fish was in sharp decline in the bleached areas.

“Parrotfish, named because of their tightly packed teeth in a beak formation, use their teeth to scrape microorganisms off coral, and their presence in large numbers on damaged reefs very likely helps the process of repair,” Dr Taylor said.

The researchers concluded that the coral and the parrotfish constituted a ‘feedback loop’, slowly bringing each other into balance.

“When reefs are damaged, parrotfish numbers swell,” Dr Taylor said.

“This results in low levels of scunge, giving the coral the best chance to recover. As the reef then returns to health, parrotfish numbers decline again.”

“The fact that plump parrotfish were found in large numbers on both reefs indicates the feedback loop is an inherent part of reef ecology and not caused by local factors,” he said.

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