Oz boffins reveal working of coral reefs engine

Australian scientists have revealed the workings of the Symbiodinium, the microscopic algae that feed the corals, providing the primary energy source for the entire reef.

Sydney, Aug 31 : Australian scientists have revealed the workings of the Symbiodinium, the microscopic algae that feed the corals, providing the primary energy source for the entire reef.

"Symbiodinium uses sunlight to convert CO2 into carbohydrates for the corals to feed on. At the same time there's evidence the corals control its output, suggesting that they are farming their captive plants," said Professor David Yellowlees.

"But these microscopic algae are quite weird and unlike any other life form. They have different photosynthetic machinery from all other light-harvesting organisms. They have 100 times more DNA than we do and we have no idea why such a small organism needs so much. They really are like no other living creature we know," he said.

Co-researcher, Dr Bill Leggat said the team focused particularly on understanding the biochemical relationship between Symbiodinium and corals when they are stressed by heat, light, increased CO2 levels and pollutants from land run-off.

These stressful conditions cause corals to 'bleach' by expelling the Symbiodinium and - if they do not recover them within a few days - the corals die. Large-scale bleaching struck half of the Great Barrier Reef in 2002, and eight major bleaching episodes have been reported worldwide in the last 30 years due to warming seawater."Our aim is to identify the genes that make the symbiotic plants susceptible to these stresses, and lead to the coral expelling them," said Dr Leggat.

In experiments at Heron Island Research Station, the team of scientists from the ARC Centre of Excellence for Coral Reef Studies, James Cook University and the University of Queensland, exposed corals to various stresses associated with climate change and then analysed the gene composition in the symbiotic algae.

Another team analysed the effects in corals.

Working together and using the powerful micro-array technology, the scientists now hope to assemble a picture of the 'chemical conversation' that goes on between the corals and their symbiotic plants that leads to a breakdown in the relationship, a divorce - and the corals starving themselves to death.

"An example of the challenge we face is the gene which is expressed the most when Symbiodinium is stressed. It's obviously important - but at this stage we have no idea what it does. It is even stranger when you consider that this gene was originally acquired from a bacterium," said Prof Yellowlees.

So far, the team has identified about 4500 genes in Symbiodinium, compiling them into the world's first gene expression library for this symbiotic organism.

The team hopes this will have value for understanding other symbiotic relationships in nature.

ANI