Acidifying Oceans Damaging To Coral Reefs
According to new findings, seas off Papua New Guinea suggest that acidifying oceans will severely hit coral reefs by the end of the century.
Carbon dioxide bubbles into the water from the slopes of a dormant volcano there, making it more acidic.
Coral is badly affected and not growing at all in the CO2-rich zone.
The scientists say this "lab" mimics conditions that will be widespread if CO2 emissions continue.
The oceans absorb some of the carbon dioxide that human activities are putting into the atmosphere.
This action is making seawater around the world slightly more acidic.
This reduces the capacity of corals and other marine animals to form hard structures like shells.
Projections of rising greenhouse gas emissions suggest the process will accelerate.
"This is the most realistic experiment done to date on this issue," Chris Langdon, a coral specialist from the Rosenstiel School of Marine and Atmospheric Science in Miami, US, told BBC.
"So I don’t have any qualms about believing that what we found will apply in other parts of the world."
The water becomes progressively more acidic closer to the vents that are bubbling CO2.
This allows researchers to study the impacts on coral at different levels of acidity.
Seawater has an average pH of about 8.1, which is already about 0.1 lower than before the industrial age.
The Intergovernmental Panel on Climate Change (IPCC) projects that by the end of the century, emissions may have risen so much that pH may fall to 7.8.
At the Papua New Guinea site, few types of coral grew at pH 7.8.
"We saw only a few species of coral, and none of the structurally complex ones that provide a lot of cover for fish," Professor Langdon told BBC News.
"The much simpler forms support many fewer species, and theory suggests they create an environment that would be very vulnerable to other stresses."
The scientists said that in an even more acidic part of the study site, "reef development has ceased."
The study site offers a snapshot of the future that might be applicable to the world’s tropical coral hotspots.
"The results are complex, but their implications chilling," Alex Rogers from the University of Oxford, who was not part of the study team, told BBC.
"Some may see this as a comforting study in that coral cover is maintained, but this is a false perception; the levels of seawater pH associated with a 4C warming completely change the face of reefs."
"We will see the collapse of many reefs long before the end of the century."
The team behind the new research suggests the picture from PNG may underplay the threat.
Reefs in the acidic zones of the study site receive regular doses of larvae floating in from nearby healthy corals, replenishing damaged stocks.
A major survey published earlier this year found that about 75 percent of the world’s reefs are at risk, with exploitative and destructive fishing being the biggest immediate threat.
The study titled "Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations," was published in the June issue of the journal Nature Climate Change. The paper’s co-authors include Katharina Fabricius Sven Uthicke, Craig Humphrey, Sam Noonan, Glenn De’ath and Janice Lough from the Australian Institute of Marine Science and Martin Glas from Max-Planck Institute for Marine Microbiology. The research was funded by the Australian Institute of Marine Science, the University of Miami, and the Max-Planck Institute of Marine Microbiology through the Bioacid Project (03F0608C).
Image Caption: A new study of Papua New Guinea’s "champagne reefs" in Nature Climate Change by the University of Miami, the Australian Institute of Marine Science and the Max-Planck Institute for Marine Microbiology in Germany concludes that ocean acidification, along with increased ocean temperatures, will likely severely reduce the diversity and resilience of coral reef ecosystems within this century. These reefs provide sobering illustrations of how coral reefs may look in 100 years if ocean acidification conditions continue to worsen. Credit: Katharina Fabricius/Australian Institute of Marine Science
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