Coral is heated with coloured light and
temperature micro-sensors measure
the effect of flow on the temperature
of coral tissue at a very fine scale.

University of Technology Sydney (UTS) researchers are hopeful that a study showing differences in the surface temperatures of corals will assist with the management of coral reefs around the world as sea temperatures rise.

The UTS study, in collaboration with the University of Copenhagen, Denmark, and the University of Sydney, shows for the first time that their size and shape has an impact on the heat budget and thermal micro-environment of shallow-water corals.

UTS International Postgraduate Research Student Isabel Jimenez, who has obtained the first detailed measurement of the thermal micro-environment of corals, said hemispherical corals had higher surface temperatures than branching corals and yet seemed more robust at avoiding coral bleaching.

"Our data will lead to the development of predictive models that can be used with satellite images to understand global coral bleaching patterns," Isabel said.

Coral bleaching is the breakdown of the symbiotic relationship between the coral host (tiny anemone-like animals) and the zooxanthellae (single-celled plants) that live within the host. Mass coral die-offs are occurring more frequently and on a bigger scale. The phenomenon can have devastating global environmental, economic and social impacts.

Scientists have observed before that branching corals are more susceptible to bleaching. Data from Ms Jimenez’s research show for the first time that heat transfer differs between the two types of coral.

"Our data lead us to speculate that hemispherical corals may have adapted to a wider range of temperature exposures. It opens up new areas of research,” Isabel said.

Isabel kept coral species from Heron Island Lagoon on the Great Barrier Reef in specially designed flow chambers. Temperature microsensors measuring 50 micrometers (half the width of an average human hair), were inserted into coral tissue or into the mouth of a polyp, using a dissecting microscope. Variables such as sunlight and water flow were used to investigate the mechanisms and processes of heat transfer.

Head of the UTS Aquatic Photosynthesis Group and co-supervisor of the study, Associate Professor Peter Ralph, said the research added significant new data to the global knowledge bank on coral bleaching at a time when some of Australia's most important natural ecosystems where threatened.

"The team has also been able to obtain the first direct measurement of the thin boundary layer of coral tissue," Professor Ralph said. "This is important because it proves that temperature is ultimately controlled by the presence of this layer and how water flows around it.

"On a number of levels the team’s work has produced breakthrough science".