Highest levels of coral cover in the Great Barrier Reef in 36 years but the ecosystem remains vulnerable

Scientists at the Australian Institute of Marine Sciences (AIMS) have stated that the coral cover in Australia’s Great Barrier Reef is the highest ever recorded, since records began 36 years ago, but the ecosystem remains vulnerable. 

The Great Barrier Reef on the eastern coast of Australia is the world’s largest natural reef system of over 2,900 individual reefs and 900 islands over 2,300 kilometres (1,400 miles) long. It was listed as a UNESCO World Heritage Site in 1981 and labelled one of the seven natural wonders of the world in 1997. 

AIMS scientists have been monitoring the levels of coral coverage in the reef to determine its health. They publish their findings annually. 

The scientists measure the amount of hard corals (rather than soft corals), because hard coral can re-build itself. Hard corals, such as staghorn corals, have hard calcium carbonate skeletons and form colonies that fish and marine animals live in.

Based upon long-term surveys of the reef, scientists consider the reef to be healthy if the coverage of hard corals is more than 30%.

This year, in 2022, AIMS scientists recorded the highest levels of coral cover on parts of the Great Barrier Reef since records began 36 years ago in 1985. However, this is only in parts of the reef.

In the northern region of the reef, average hard coral cover grew to 36% in 2022, while in the central region, hard coral cover increased to 33% – the highest levels for both regions since 1985.

But in the southern region, which generally has higher levels of hard coral cover than the other two regions, the cover reduced to 34% in 2022 – from 38% in 2021. The scientists think that the decrease was caused by an outbreak of Crown-of-Thorns (Acanthaster planci), a sea star in the Acanthasteridae family that preys on hard or stony coral polyps (Scleractinia).

In early 2022, there was mass coral bleaching (whitening of the coral) which is a negative occurance. It occurred during La Nina, a natural climate cycle that typically brings cooler temperatures to the tropical waters that allows the coral to recover or rebound. It was the fourth mass coral bleaching in seven years.

Dr Paul Hardisty, AIMS chief executive, said ‘In our 36 years of monitoring the condition of the Great Barrier Reef, we have not seen bleaching events so close together.’ Mass bleaching events are occurring more frequently due to human activity warming the oceans, sayd the AIMS 2022 annual report.

AIMS scientists are concerned that this year’s positive rebound in coral cover could be undone by future mass bleaching events, which critically threaten the health of the reef. 

Although the Great Barrier Reef is a resilent ecosystem that seemingly can recover from disturbances, the AIMS monitoring program leader Mike Emslie said that the frequency of these disturbances is increasing and longer-lasting, particular mass coral bleaching events. He warned that future disturbances could reverse the positive recovery in a short period of time.

Photographer: Martina Nicolls


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