New health update for Great Barrier Reef coral

A new report has revealed new findings on the health of coral on the Great Barrier Reef, but experts are saying it should be read with caution.

Coral on the Great Barrier Reef was flourishing at record levels in two of three regions at the onset of summer, the latest report into the health of the 2300-kilometre natural wonder has found.

But two cyclones over summer and a lengthy marine heatwave – leading to a record spread of coral bleaching – points to the extremely fragile nature of the reef, scientists said.

The Australian Institute of Marine Science (AIMS) has been studying the reef in extreme close-up since the late 1980s, with trained divers being cable-towed over individual coral outcrops to determine their size and health.

In the latest Long Term Monitoring Study, released publicly on Wednesday, the AIMS team found hard coral coverage in the northern region (north of Cooktown) was at 39.5 per cent and in the central region (between Proserpine and Cooktown) it was at 34 per cent.

Both were record highs.

Trained divers being cable-towed over individual coral outcrops to determine their size and health. Picture: Australian Institute of Marine Science

In the southern region, south of Proserpine, growth was also observed, with coral coverage estimated at 39.1 per cent. This was the highest level observed since the 1990s, but not a record breaker.

“It’s awesome news that we have these high coral cover levels, but I would caution that with the knowledge that major disturbance events, like the 2024 mass bleaching event, are becoming more frequent,” said Dr Mike Emslie, head of the monitoring program at AIMS.

While the bleaching events were becoming more frequent – almost biennial in the past decade, according to Dr Emslie – they’re also becoming more widespread.

In another study conducted by AIMS and the Great Barrier Reef Marine Park Authority – conducted from the air rather than by divers, at the end of summer and not part of Wednesday’s report – scientists detected a wider spread of bleaching than ever before.

Scientists have detected a wider spread of bleaching than ever before. Picture: Australian Institute of Marine Science

Nearly one in three surveyed reefs were identified as having levels of bleaching that were either extreme (7 per cent) or very high (25 per cent).

Only about one in five reefs (21 per cent) had no evidence of bleaching.

While the extent of the bleaching is of concern, what the scientists do not know as yet is what proportion of the coral affected will die as a result.

“Some types of corals can remain bleached for months, remaining on a knife edge between survival and death,” Dr Emslie said.

“This is why returning and repeating surveys of the reefs in this vast, complex and dynamic system is so important.”

AIMS Research Program Director Dr David Wachenfeld. Picture: Supplied

AIMS Research Program Director Dr David Wachenfeld said almost half of the 3000 or so reefs within the Great Barrier Reef Marine Park experienced more heat stress than

ever before over the summer.

“We are only one large scale disturbance event away from a reversal of the recent recovery,” he said.

Dr Wachenfeld said the reef had some “lucky escapes” in recent years, with some cyclones and bleaching events not leading to as much coral mortality as initially feared, but the full extent of the recent marine heatwave would not be known for a few months.

“The frequency and intensity of bleaching events is unprecedented, and that is only forecast to escalate under climate change, alongside the persistent threat of crown-of-thorns starfish outbreaks and tropical cyclones,” he said.

The AIMS report showed the reef’s southern region had the most Crown of Thorns starfish activity, with three outbreaks – one listed as severe, one as established and another as potential.