Since the beginning of the industrial revolution the release of carbon dioxide (CO2) from our industrial and agricultural activities has resulted in atmospheric CO2 concentrations that have increased from approximately 280 to 387 parts per million (ppm). The atmospheric concentration of CO2 is now higher than experienced on Earth for at least the last ca. 25 million years and is expected to continue to rise at an increasing rate. The ocean has absorbed about 430 billion tons of CO2 from the atmosphere, or about one-third of anthropogenic carbon emissions2. This absorption has benefited humankind by significantly reducing greenhouse gas levels in the atmosphere, thereby minimising global warming. However, the pH (the measure of acidity) of ocean surface waters has already decreased by about 0.1 units, from an average of about 8.2 to 8.1 since the beginning of the industrial revolution3. By the middle of this century atmospheric CO2 levels could reach more than 500 ppm, and by 2100 they could be well over 800 ppm (IPCC scenario B2, 2007). This would result in an additional mean surface water pH decrease of approximately 0.3-0.4 pH units by 2100, implying that the ocean would be about 100-150% more acidic than at the beginning of the industrial revolution.