Not only do corals have a smell, but that smell can tell scientists how much heat stress they are experiencing.

Researchers from the University of Technology Sydney, the University of Sydney and Southern Cross University made the discovery while investigating coral species on Heron Island in the southern Great Barrier Reef.

Their findings were published on Tuesday in the Global Change Biology journal.

An organism's smell is determined by a mixture of volatile gases that the organism releases.

The Australian study - the first to look at the smell of healthy and stressed corals - found that during times of heat stress, the abundance and chemical diversity of corals' gas emissions is dramatically decreased.

The scientists believe the compound gases released by reef-building corals may play important roles in maintaining the health of reefs.

On land, some of the compounds help plants deal with drought conditions.

A decrease in the chemical diversity and functional potential of the compound gases due to heat stress "could further impact the capacity of corals to cope with increasing temperatures," lead researcher, Dr Caitlin Lawson, said in a statement.

Heat stress has caused recent mass bleaching events in the Great Barrier Reef.

In the past 25 years, 50 per cent of the reef's corals have been lost. Some scientists suggest the reef will bleach again in 2021.

Studying the gases further may help scientists identify what corals are experiencing and if they are communicating by their smells.

"I get really excited about the signalling that could be happening between different species of corals, or whether they have certain smells that they'll release that might attract grazing fish if there's too much algae," said Dr Lawson.

"Is there a certain smell that indicates corals are more vulnerable?"

Senior author, Associate Professor David Suggett, said the work showed that smells played a critical role in coral reef diversity.

"The discovery of a loss of these smells under heat stress driven by ocean warming is yet more evidence reefs will change as we know them unless we urgently tackle climate change," he said.

Australian Associated Press