Bleaching is a sign of stress, which is caused by several factors, including pollution, silt, changes in salinity, and rising water temperatures. Climate change is expected in any case to raise water temperatures significantly. But this new research suggests that it will affect the coral in another way as well. It shows that when CO2 dissolves in seawater it makes it more acidic. And that affects the way in which the coral forms.
Reefs consist of calcium carbonate, produced by tiny creatures called coral polyps.
The researchers found that as the CO2 dissolves in the water, the increasing acidity it causes slows down the production of calcium carbonate. It does this by lowering the levels of essential carbonate ions in the seawater. CO2 is the chief gas caused by human activities that is contributing to global warming. And climatologists think it will have reached double its pre-industrial level by as early as 2065. If the coral does suffer further damage, places like the Red Sea and Australia's Great Barrier Reef will lose their attraction for tourists.