January 7th 2009
Coral warning on grim future for reef
If you can imagine the Great Barrier Reef (GBR) reduced to a chain of featureless mounds of coral rubble, hidden somewhere below a carpet of suffocating green algae, then you are likely to be picturing what has become of our greatest ecological treasure by the year 2050. And, if you think this is something to worry about for the future, then think again: the work of two Magnetic Island-based, Australian Institute of Marine Science (AIMS), scientists: Dr Glenn De'ath and Dr Katharina Fabricius and their colleague, Dr Janice Lough, shows that the changes to the ocean's chemical balance started with the industrial revolution but, since 1990, one critical factor affecting corals and countless other ocean organisms has slumped like Wall Street.
This grim scenario for a future GBR follows the publication, last week, of their study, "Declining coral calcification on the Great Barrier Reef" in Science magazine. It shows that, since the "tipping point" year of 1990, the speed at which corals build their skeletons has slowed by over 14%.
"The causes of this sharp decline remain unknown, but our study suggests that the combination of increasing temperature stress and ocean acidification may be diminishing the ability of GBR corals to deposit calcium carbonate," said Glenn De'ath.
A large Porites coral (Photo: Eric Matson, AIMS)
The report is the most comprehensive to date on calcification rates of GBR corals. It has been widely reported in Australian and international media and was based on a study of the largest coral archive in the world - 329 coral cores of Porites (a common coral species) collected over the past thirty years up and down the length of the Great Barrier Reef by the Australian Institute of Marine Science (AIMS).
A cross-section from a Porites coral used to analyse declining calcification (Photo: Eric Matson, AIMS)
"Some of the cores are from corals reaching back 400 years," said Glenn De'ath.
Katharina Fabricius says, "Since the industrial revolution ocean acidity has increased significantly, due to the oceans absorbing about 30% of the extra CO2 that humans have put into the atmosphere. Without the buffering of the oceans, global warming would be more severe than it already is"
"What happens when corals stop growing is that reefs erode through storms. The fragile corals go quickly, small fish lose their habitat and die off and big fish have nothing to eat. It's a cascading effect," said Glenn De'ath.
It works like this. The amount of CO2 in the air has increased from 280 parts per million, before the industrial revolution, to 387 ppm today. Some of this additional atmospheric CO2 is absorbed by the oceans where it forms carbonic acid which lowers the pH balance and stops corals from calcifying. As increased CO2 in the air also makes the seas hotter, the combined effect leads to corals being unable to maintain their structures.
Katharina Fabricius says, "The current projections are that corals will be really badly affected by mid century unless the global community starts acting now. Our study shows that corals were happy up to 350 ppm (the level of 1990), but present conditions are already getting too high. Most accept 450 ppm as a global long-term target, but levels higher than 700 ppm will be reached later this century in a 'business-as usual' scenario.
"If you extrapolate out to 450 ppm you have a fairly severe reduction in calcification with more algae and less hiding places for fish. The off-shore reefs will become mounds of rubble and the inshore reefs dominated by algae and very few corals.
"Fish need structures. If there is no coral there's no reef and no fish"
Katharina also points out that there is an even bigger problem caused by oceanic acidification. "This can also affect planktonic algae - the absolute basis of the ocean's food chain."
When asked how the federal government's 5% minimum target for the reduction of greenhouse gases, announced recently in its white paper, would affect the calcification process, the scientist put it as politely as, it seemed, she could, "It is important that the government is making a first step but they need to be braver," she said, adding, "At 450 ppm there is still some hope but it's not there at 550ppm. A 20 - 40% reduction in emissions by 2020 is needed to reach the 450 target."
The pair were more comfortable referring to the Government's own Garnaut Report which claims that the longer we put off CO2 reductions the more expensive it will be into the future. Garnaut's projections indicate that a 10% reduction from 2000 CO2 levels by 2020, within a global agreement, would only produce an outcome of 550ppm.
The government's white paper commits to a medium-term national target to reduce Australia's greenhouse gas emissions by between 5 per cent and 15 per cent below 2000 levels by the end 2020.
Story: George Hirst
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