Marine scientist Ross Hill believes there's no question global warming is already impacting on the Great Barrier Reef, but researchers in the UTS Faculty of Science are also seeing encouraging signs that there's some potential for coral species to withstand rising sea temperatures.

"Maybe the Great Barrier Reef won't be dead, but it will be different," Hill said. "It's a pretty grim outlook nevertheless."

Hill, a member of the Aquatic Photosynthesis Laboratory team lead by Associate Professor Peter Ralph, is undertaking PhD research into the processes of coral bleaching – the temperature-triggered breakdown of a crucial symbiotic relationship between the reef-building animal and a plant (microalgae known as zooxanthellae).

The UTS team is leading the field in the assessment of coral health using a new instrument called a Pulse Amplitude Modulated (Imaging-PAM) fluorometer.

"Imaging-PAM measures light wavelengths emitted by the zooxanthellae algae, giving us information about its photosynthetic efficiency – essentially whether the algae is happy or not," Hill said.

"The symbiotic relationship between coral and algae is integral to the survival of the reef. The animal host creates a protective environment for the algae and the zooxanthellae produces compounds through photosynthesis to sustain the animal.

"Bleaching is the outward sign that the algae has been expelled from the coral and the major cause of that is elevated sea temperatures along with high light levels."

However, Hill has found that not all coral species react the same way to bleaching and the zooxanthellae fares differently depending on where it is sited in the coral structure.

"Some coral species are killed outright by bleaching and others demonstrate a greater ability to recover. The zooxanthellae is more vulnerable in exposed tissue, but where the coral takes the form of polyps, the animal has the ability to contract inwards and provide increased protection from intense light.

"Perhaps we will be looking at shift in the reef ecosystem favouring better-protected populations of zooxanthellae that have the potential to withstand more intense environmental conditions."

Associate Professor Ralph said the new technology being used by the UTS researchers had immense potential in the understanding of the physiological processes involved in coral bleaching.

"It is a means of identifying impacts to the animal-algal symbiosis before any visual changes become apparent," he said. "It is a non-intrusive and non-destructive method of investigation which allows for the study of the zooxanthellae in an ecologically meaningful context."