Impact of ocean acidification on Corallium rubrum (L. 1758): an experimental approach

6    1. Introduction 1.1. Ocean acidification Over the past 250 years, atmospheric carbon dioxide (CO 2 ) levels increased by nearly 40%, from pre-industrial levels of approximately 280 ppm (parts per million) to nearly 384 ppm in 2007 (Solomon et al. 2007). This rate of increase, driven by human fossil fuel combustion and deforestation, is at least an order of magnitude faster than that occurred for millions of years (Doney & Schimel 2007), and the current concentration is higher than experienced on Earth for at least the past 800,000 years (Luthi et al. 2008). Rising atmospheric CO 2 is tempered by oceanic uptake, which accounts for nearly a third of anthropogenic carbon added to the atmosphere (Sabine et al. 2004), and without which atmospheric CO 2 would be approximately 450 ppm today: a level of CO 2 that would have led to even greater climate change than that presently experienced. Ocean CO 2 uptake, however, is not benign; it causes pH reductions and alterations in fundamental chemical balances that together are commonly referred to as ‘ocean acidification’. Since climate change and ocean acidification are both caused by increasing atmospheric CO 2 , acidification is commonly referred to as the ‘other CO 2 problem’ (Doney et al. 2009). Ocean acidification is a predictable consequence of rising atmospheric CO 2 and does not suffer from uncertainties associated with climate change forecasts. Absorption of anthropogenic CO 2 , reduced pH, and lower calcium carbonate (CaCO 3 ) saturation in surface waters are well predicted by models and verified by hydrographical surveys and time series data (Caldeira & Wickett 2003, Caldeira & Wickett 2005, Orr et al. 2005, Solomon et al. 2007, Feely et al. 2009). At the Hawaii Ocean Time-Series (HOT) station ALOHA the growth rates of surface