As the CO2 concentration in Earth's atmosphere increases, so does the acidity of the world's oceans. This phenomenon, called "ocean acidification", threatens the life of shell- and reef-forming organisms in the sea. Coral reefs are highly vulnerable to ocean acidification as it reduces their ability to maintain coral structures and fish habitats. But so far, assessments of the threat from ocean acidification to coral reefs have not considered how some reef areas can locally reduce this risk by decreasing acidity, whereas other areas naturally acidify their water, adding to the ocean acidification stress.

"Overall, CO2 enrichment and ocean acidification is bad news for coral reefs", says Dr Ken Anthony, Research Team Leader for the Climate Change and Ocean Acidification team at AIMS. "But some reef areas take up more CO2 than they produce (through photosynthesis), which can lower the vulnerability of neighbouring reef areas to ocean acidification. On the other hand, reef areas with greater coral cover produce more CO2 than they consume (through calcification and respiration) and that adds locally to the ocean acidification threat".

"If we can start to understand which areas of large reef systems such as the Great Barrier Reef can counteract pH changes locally and which areas cannot, then we are better able to assess the relative risks of ocean acidification", says Dr Joanie Kleypas.

The research was recently published in the international journal Global Change Biology, by a group of scientists from the Australian Institute of Marine Science (Dr Ken Anthony), the National Center for Atmospheric Research in the US (Dr Joanie Kleypas), and from the Centre National de la Recherche Scientifique in France (Prof Jean-Pierre Gattuso).

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