Credit: Corbis
TWENTY-FIVE KILOMETRES out to sea from Port Douglas and Four Mile Beach are the Low Isles, and it's here, in the last days of my trip, that I spend some time snorkelling, seeing the reef up close. These islands are coral cays vegetated with mangroves and palm trees, and the reefs offshore are famous as the location of one of the first detailed ecological studies of coral reefs ever attempted – an expedition mounted by Britain's Royal Geographical Society between 1928 and 1929.
As I paddle around, I am dumbfounded by the variety of species: an array of brightly coloured fish, hard and soft corals, giant clams, anemones and even a turtle. I see as much life here, just below the surface, as I had scuba diving in deeper waters elsewhere in the tropics, which is testament of the incredible diversity of the Great Barrier Reef.
Even here though, in a seemingly pristine spot, damage to the reef is evident. While I'd been out on the Southern Surveyor, Prime Minister Kevin Rudd and the Minister for Climate Change, Penny Wong, had been taken out to the Low Isles by researchers to see examples of healthy reefs and those that have been heavily damaged by bleaching.
Reefs worldwide have had a tough time in recent years: overfishing, pollution and the warming effect of climate change have all taken a heavy toll. Bleaching, a stress response to warm water (whereby a coral ejects the symbiotic algae that it needs to survive, and often dies) is one of the most immediate problems.
An Australian study published in the journal Ecology Letters in 2006 provided compelling evidence that coral reefs have suffered more damage between the 1970s and today than at any other time in the last 220,000 years. If the reefs are already struggling so much, what hope do they have in coming years as acidification accelerates?
Chris Langdon runs the Corals and Climate Change Laboratory at the University of Miami in Florida, and worked alongside Kleypas in the early days to impress the severity of the problem on other experts. He predicts that – though they can live for 300 years – as coral colonies die, they will not be replaced by new recruits at the rate needed to sustain them.
"The latest results are showing that the growth rate of baby corals in the first days of their lives are strongly impacted by ocean acidification, such that they develop more slowly, prolonging their time at a highly vulnerable stage," he says.
Unfortunately, because ocean acidification is such a new problem, much of the fieldwork that will help us predict the effects has yet to be completed. But the research that does exist is not encouraging.
A study published in the Proceedings of the National Academy of Sciences in July 2008 looked at an area of the Pacific Ocean off Central America where there is a natural upwelling of CO2-rich waters from the sea bed. It found that there is little of the calcium carbonate cement that holds reefs together, and that reefs here grow slowly and erode rapidly.
Studies of the communities around shallow volcanic vents in the Mediterranean Sea provide more evidence. The water here is cool, rich in CO2 and has a pH of about 7.5, so it provides some clue as to what life may be like in a more acidic ocean. Around these vents, "you don't get many organisms with calcium carbonate skeletons; you get a lot of algae and seagrass growing," says Tilbrook. "This is probably an indication of what might happen in the extreme."
Towards the end of the century, Tilbrook envisages a reef structure that is severely weakened, easily damaged by storms and with few new corals growing on it. "It might be dominated by algae, we really don't know, but there are likely to be some pretty significant changes," he says. "The picture is: no reef as we know it, a completely changed habitat."
"In 50 years time, the Great Barrier Reef will probably be severely affected by coral bleaching and the coral diseases that seem to follow," Kleypas tells me. "At these levels, ocean acidification won't cause their death, but it will already be affecting the ability of corals and coralline algae to grow and compete for space."
She points to research showing that some algae and seagrasses are more successful in high CO2 conditions, meaning that ocean acidification will give them an advantage over the corals and coralline algae that cement the reef together.
