The uptake of CO2 by oceans initiates a series of chemical reactions that increase acidity and decrease carbonate ion concentration in seawater. Corals and other marine organisms (e.g. some species of plankton and mollusks) use carbonate ions to build their skeletons or shells. Model projections indicate that by 2100, only 30 percent of cold-water reefs will still be in waters supersaturated with aragonite. With fewer carbonate ions available, there could be a dramatic reduction in the growth of both the corals and marine plankton species that make their shells from aragonite. As the oceans become more acidic, corals are expected to build weaker skeletons, a process similar to osteoporosis in humans.
Cold-water corals provide habitat for many commercially important fish species and harbor several species of sponges that produce chemicals with anti-cancer and other medicinal uses. Unfortunately, says Guinotte, just as scientists are finding out how diverse and important cold-water corals are, they are being threatened by a one-two punch.
"First, bottom trawlers smash them to bits. Then, ocean acidification will probably slow the skeletal growth and/or lead to weaker skeletons of those that remain. Ocean acidification will likely have serious and wide-reaching impacts, not only for coral ecosystems but for all life in the oceans. Many species of marine plankton use carbonate ions and occupy the base of most marine food webs, so a reduction in their numbers could lead to harmful effects throughout marine ecosystems."
Only a decrease in the burning of fossil fuels is likely to slow this trend, say Guinotte and colleagues.