Great Barrier Reef has lost half its coral since studies began

The animals of the Australian Great Barrier Reef is rapidly running out of habitat. Photo / Cindy Chan, Unsplash

A study of the Great Barrier Reef has concluded that the complex forest of corals has shrunk by half in the past three decades.

It's no secret that the largest living structure on Earth is no longer as big as it used to be. Bleaching and erosion from warming oceans is well documented. However, the rate at which it is shrinking is a new and alarming discovery.

"We found the number of small, medium and large corals on the Great Barrier Reef has declined by more than 50 per cent since the 1990s" said professor Terry Hughes, one of the authors.

Hughes says that while certain species such as the table-shaped corals were particularly affected by "record-breaking temperatures that triggered mass bleaching in 2016 and 2017," the damage has been happening for decades and across "virtually all species".

The study by the Australian Research Centre of Excellence is led by Dr Andy Dietzel, who started documenting the breeding cycles and size coral colony populations in 1995. It was the first of its kind on the reef.

Mass coral bleaching captured by the study. Photo / Andreas Dietzel, ARCCE Supplied

"We measured changes in colony sizes because population studies are important for understanding demography and the corals' capacity to breed," said Dietzel about his findings.

Part of the study into coral breeding has shown periods of recovery, but the overall trend is one of decline.

"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," says Dietzel.

The coral structures provide a base layer for the tropical reef's abundant ecosystem. With its diminished size so diminishes the habitat and abundance of fish and species supported by the reef.

Hughes said that when they started the study the opinion was that the reef was "protected by its sheer size —but our results show that even the world's largest and relatively well-protected reef system is increasingly compromised and in decline."

There is fear that a marine heatwave over summer could produce another mass bleaching event in 2020. There are plenty of places across the coast of Tropical North Queensland, where coral colonies are still vibrant draws for sea life and tourism.

However, if there is no action taken to combat rising temperatures there we will pass a point of no return.

"There is no time to lose," conclude the study's authors.

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