Scientists warn for acid oceans - could erode Great Barrier Reef

The world’s oceans are becoming more acid, with potentially devastating consequences for corals and the marine organisms that build reefs and provide much of the Earth’s breathable oxygen. The acidity is caused by the gradual buildup of carbon dioxide (CO2) in the atmosphere, dissolving into the oceans. Scientists fear it could be lethal for animals with chalky skeletons which make up more than a third of the planet’s marine life.

Acid oceans will be among the issues explored by Australia’s leading coral scientists at a national public forum at the Shine Dome in Canberra tomorrow. The Coral Reef Futures 07 Forum is on October 18-19, 2007 and is hosted by the ARC Centre of Excellence for Coral Reef Studies (CoECRS).

Recent research into corals using boron isotopes indicates the ocean has become about one third of a pH unit more acid over the past fifty years. This is still early days for the research, and the trend is not uniform, but it certainly looks as if marine acidity is building up. - Professor Malcolm McCulloch of CoECRS and the Australian National University

It appears this acidification is now taking place over decades, rather than centuries as originally predicted. It is happening even faster in the cooler waters of the Southern Ocean than in the tropics (previous post). It is starting to look like a very serious issue, warns McCulloch.

Corals and plankton with chalky skeletons are at the base of the marine food web. They rely on sea water saturated with calcium carbonate to form their skeletons. However, as acidity intensifies, the saturation declines, making it harder for the animals to form their skeletal structures (calcify).

Analysis of coral cores shows a steady drop in calcification over the last 20 years. There’s not much debate about how it happens: put more CO2 into the air above and it dissolves into the oceans. When CO2 levels in the atmosphere reach about 500 parts per million, you put calcification out of business in the oceans. [Atmospheric CO2 levels are presently 385 ppm, up from 305 in 1960.] - Professor Ove Hoegh-Guldberg of CoECRS and the University of Queensland

It isn’t just the coral reefs which are affected – a large part of the plankton in the Southern Ocean, the coccolithophorids, are also affected. These drive ocean productivity and are the base of the food web which supports krill, whales, tuna and fisheries. They also play a vital role in removing carbon dioxide from the atmosphere, which could break down.

Professor Hoegh-Guldberg said an experiment at Heron Island, in which CO2 levels were increased in the air of tanks containing corals, had showed it caused some corals to cease forming skeletons. More alarmingly, red calcareous algae – the ‘glue’ that holds the edges of coral reefs together in turbulent water – actually began to dissolve:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: greenhouse gas emissions :: carbon dioxide :: ocean acidification :: marine life :: coral :: Australia ::

The risk is that this may begin to erode the Barrier of the Great Barrier Reef at a grand scale, he says. As an issue it’s a bit of a sleeper. Global warming is incredibly serious, but ocean acidification could be even more so.

Other issues to be explored at the forum include:

• the latest science on coral bleaching
• the rising plague of coral disease
• managing Australia’s coral reefs under climate change
• managing resilience in coral reefs
• protecting sea water quality from activities on land
• are ‘green zones’ helping to replenish fish stocks on the GBR?
• the plight of reef sharks and other top predators

The forum will feature a public discussion hosted by ABC Science Show host Dr Robyn Williams on the future of Australia’s coral reefs, at 6 PM on Thursday, October 18, at the Shine Dome, Canberra.

Australia’s coral reefs, particularly the Great Barrier Reef, Ningaloo Reef, and Lord Howe Island World Heritage Area are national icons, of great economic, social, and aesthetic value. Tourism on the Great Barrier Reef alone contributes approximately $5 billion annually to the nation’s economy. Income from recreational and commercial fishing on Australia’s tropical reefs contributes a further $400 million annually. Consequently, science-based management of coral reefs is a national priority.

Globally, the welfare of 500 million people is closely linked to the goods and services provided by coral reef biodiversity. Uniquely among tropical and sub-tropical nations, Australia has extensive coral reefs, a small population of relatively wealthy and well-educated citizens, and well developed infrastructure. Coral reef research is one area where Australia has the capability, indeed the obligation, to claim world-leadership.

Picture: Bleached coral wih damsel fish. Bleached coral reefs cannot support populations of fish which feed specifically on corals. Courtesy: Great Barrier Reef Marine Park Authority Images.

References:
Australian Research Council Center of Excellence - Coral Reef Studies: Acid Oceans Warning - October 17, 2007.

Coral Reef Futures Forum program.

Biopact: Southern Ocean carbon sink weakens - May 18, 2007