Preserving the Great Barrier Reef

The battle below the idyllic waters of the Great Barrier Reef is being mediated by an innovative approach to scientific research developed by Malcolm McCulloch and his team.

Peering onto the serene splendour of the Great Barrier Reef from the dry side of a glass-bottomed boat, the hordes of tourists who visit Australia’s  renowned marine wonder are rarely likely to entertain the idea that they are looking into a war zone.

The adventurous ones who bob around in brightly coloured swimwear or don scuba gear to explore the depths won’t be caught in any cross fire, but they have nonetheless strayed onto a battlefield where a struggle for supremacy has been raging for centuries. The two sides in this epic fight are coral and algae, and until European settlement they were evenly matched.

But shortly after Cook’s arrival in Australia, the Europeans formed an unwitting alliance with the algae and the coral has been losing ground ever since.

Keeping your troops supplied is a vital part of any campaign and the tonnes of phosphate-loaded runoff flushing into the sea thanks to farming practices imported from the northern hemisphere have had a knock-on effect, boosting the algae population and putting the reef at a serious disadvantage.

Fortunately in recent years Australians have begun to take notice of the damage their submerged neighbour has sustained, with people like Professor Malcolm McCulloch stepping up to fight in the reef’s corner.

Professor McCulloch and his colleagues have produced the evidence proving the relationship between farm run-off and enhanced nutrients being delivered to the reefs.

Temperature rising

Steps are now being taken to limit run-off, which is vital if the coral is to have any chance of withstanding the seemingly inevitable water temperature rises associated with global warming.

“The Great Barrier Reef is like a person. If it is healthy it can cope with challenges much better than if it is sick. The reef has withstood rises in water temperature before and if it’s in good condition there is no reason why it shouldn’t be able to survive global warming,” he explains.

“But if it continues to suffer these constant attacks from algae and creatures like the crown of thorns starfi sh, it will be too weak to handle the additional burden of warmer seas.”

Steps are now being taken to limit runoff and using Professor McCulloch and his team’s methodology it will be possible to continue to chart the health of the reef and whether these measures are taking effect.

The team was able to detect an influx of fresh water by looking for fluorescence in samples of coral – if it glowed under ultra-violet light that indicated the presence of fresh water.

They then found it was possible to use a substance called barium, which is contained in the clay along with the phosphates, as a ‘proxy’ for the damaging nutrients themselves. Barium leaves a measurable signature on the coral, so by measuring barium levels they had a reliable indicator of the amount of alien nutrients that were present.

Once satisfied of the link between the clay in soil run-off and levels of barium in the reef, they took core samples – three to four metre long cylinders of coral – from the section of the inner reef affected by the Burdekin River. Using laser measuring equipment, they were able to look at each year’s coral growth (much like rings in a tree) and see how barium levels changed with time.

Reef history

The cores told the story of 400 years in the life of the Great Barrier Reef and they had recorded the dramatic changes in living conditions following European settlement and the subsequent importation of farming practices that belonged on the other side of the world.

“Our results showed that before the Europeans came, there were plenty of these major flood events, but no barium discharge,” explains Professor McCulloch.

“There is no doubt that after the Europeans came we see a lot more peaks in barium discharge, which means more sediment discharge.”

The project required the earth scientists to look beyond their core samples and carry out some historical detective work, investigating farming and river level records and learning from economic, social and oral history to piece together the background to their findings.

“In 1974 there was the biggest discharge of freshwater from the Burdekin River into the reef, so it was interesting that this didn’t correspond to the biggest peak in sediment levels.

“When we looked into this we found that following the 1974 flood cattle numbers increased due to increased availability of fodder, introduction of more drought resistant cattle breeds from India and the use of supplementary feeding during droughts. So farmers increased their stock numbers and kept them on the land for a lot longer during droughts – more animals on the land, meant more erosion and therefore a heavier sediment load.

“When we had a very severe drought at the beginning of the 1980s the first drought-breaking rains in 1981 carried an immense amount of sediment into the reef.”

Farmers both fearful of losing valuable topsoil and aware of their esponsibility to the reef are starting to adopt new practices. Cores appear to show changes in conditions have redressed the balance in the underwater struggle between coral and algae, “but we still have a long way to go before we return to the ‘natural’ levels before Europeans came,” McCulloch says.

Complete picture

The model and methodology that Professor McCulloch and his team have developed on the Burdekin River is now being applied elsewhere along the inner Great Barrier Reef to provide a complete picture.

By continuing to apply them over the next two decades and showing the improvement in conditions that correspond to responsible farming, it will become valuable feedback to both graziers and sugar cane farmers about the success or otherwise of more sustainable farm practices and continue to remind people that there is a close link between farming practices and the health of the reef.

“The work that’s being done along the river catchment seems to be making a real difference.

“It may seem obvious that sensible land use, where you don’t have stock stamping all over the river banks, keeps sediment out of the rivers and gives the coral a fighting chance but it’s very hard to quantify the improvement and you need science to support these common sense initiatives.

“Ours is the only quantitative record that shows how sediment discharge changed the reef. In years to come it will prove that what is being done now is hopefully contributing to a healthier reef.”

His work on the Burdekin River, which he is expanding across to the mid and outer reef, is just one of a range of projects that Professor McCulloch hopes will help the beleaguered coral repel attacks from its foes.

He is working on a similar project on the outer reef that will look at how the upwelling of cooler water from the depths of the ocean is affecting the health of the other side of the reef.

He is also analysing the breadth and health of the diversity of coral life that makes up the Great Barrier Reef. Meanwhile, he and colleagues at ANU will have a role in the newly established Centre of Excellence in Innovative Science for Sustainable Management of Coral Reef Biodiversity, which will help protect one of world’s most valuable assets for generations to come.

“Australia is a leader in reef research. The Great Barrier Reef is the most valuable reef in the world and the approach we are taking is a template for other countries to follow.

“It’s great to be able to do this type of research that I see has got direct benefit to society – to be able to say to kids that I’ve done something that’s contributed to future generations and the wellbeing of our coral reefs.

“If you can help protect the Great Barrier Reef, I think you can say, ‘I’ve made a small contribution’.”