The more humanity acidifies and warms the world’s oceans with carbon emissions, the harder will be the job of saving the reefs. That’s the message from a new study, which finds that ocean acidification and global warming combine with local impacts like over fishing and nutrient runoff, to weaken the world’s coral reefs as they struggle to survive.
A team led by Dr Ken Anthony of the ARC Centre of Excellence for Coral Reef Studies and the University of Queensland’s Global Change Institute, in the first study to integrate global scale processes with local factors such as over fishing and runoff, to assess their combined impact on coral reefs, has found that over fished reefs and those affected by land runoff are more vulnerable to increasing CO2 in the atmosphere as a result of carbon emissions.
Warmer water causes periodic mass coral death by bleaching; acidifying seawater weakens corals by interfering with calcification, making them more vulnerable to storm impacts. If corals are also affected by nutrient runoff from the land fertilizing algae, along with the loss of parrot fishes and other species that keep reefs clear of weed, then corals can struggle to re-establish after a setback and the reef can become overgrown by algae.
(Photo courtesy of Guillermo Diaz-Pulido)
As CO2 levels are expected to rise to 450-500 parts per million by 2050, how well fishing and runoff are managed will become critical to the survival of coral reefs, to prevent their being overgrown by algae.
The team’s modelling, said to be on the conservative side, has implications for the preservation of well-managed reefs such as the Great Barrier Reef, let alone reefs in developing countries. Coral reefs in developing nations, where most of the world’s reefs exist, are particularly vulnerable, highlighting the need to develop greater reef management capacity across SE Asia.
A failure to rapidly stabilize and reduce the concentration of CO2 in the Earth’s atmosphere is likely to lead to significant loss of key reef builders such as Acropora, irrespective of the effectiveness of local management, however local reef management to maintain grazing fish populations and prevent runoff of silt, fertilisers and sewage will play a critical role in maintaining coral resilience while CO2 concentrations are stabilized.
Ahead of the Greenhouse 2011 conference on climate change, taking place in Cairns, Queensland, Australia, Professor Ove Hoegh Guldberg has issued the warning that the Great Barrier Reef will be lost unless there’s dramatic action to cut greenhouse gasses over the next 10 years.
Healthy reef, Lady Elliot Island
(Photo courtesy of Paul Marshall)
Professor Guldberg, a leading coral biologist whose study focuses on the impact of global warming and climate change on coral reefs and the director of the Global Change Institute, said that coral bleaching events are becoming more frequent due to rising sea temperatures and that the Great Barrier Reef could be gone within four decades unless carbon emissions are cut. “If we go another 10 years of pumping two parts per million or more CO2 into the atmosphere, we’ll pass a point at which we won’t be able to constrain further temperature increases and greenhouse gas concentrations that will allow reefs to persist,” he said.
He went on to say, “If we actually act today we can save the Great Barrier Reef and reefs around the world”. But, he continued, it would take a concerted, global effort; with current climate modelling showing sea temperatures and ocean acidification would soon rise to levels that could not sustain coral reefs.
“Ocean acidification and warming will lower coral reef resilience” by Kenneth R Anthony, Jeffery A Maynard, Guillermo Diaz-Pulido, Peter J Mumby, Paul A Marshall, Long Cao and Ove Hoegh-Guldberg. Global Change Biology (2011).