The major cause of ocean acidification is not the total amount of CO2 entering the oceans but the unprecedentedly short time over which this uptake is occurring. Atmospheric CO2 concentration is now increasing by more than 2 ppm per year. This rate exceeds that predicted by the Intergovernmental Panel on Climate Change (IPCC) under a “worst case scenario”1 and is nearly 100 times greater than any historical, naturally induced increase. Rapid acidification is expected to continue to the extent that in 50 years’ time the oceans are predicted to have a lower pH than at any time in the past 20, and likely 55, million years.
If ocean acidification continues to proceed as currently predicted, many commercial interests, from commercial and recreational fishing to tourism, as well as ecosystem services are likely to be impacted. Therefore, ocean acidification has the potential to change the way humans feed themselves, earn their livings, run their communities, and live their lives.
Impacts on biodiversity
Marine organisms possess a number of behavioural and physiological tools to deal with the stress of living in a highly changeable environment. These include tools for dealing with changes in seawater pH and elevated levels of dissolved CO2. However, using these tools comes at an energetic cost and as the environmental stress associated with ocean acidification increases so does the energetic cost of living under these new conditions. The efficiency and manner to which organisms manage their energy budget, relative to their competitors, predators or prey, will determine which species are able to cope with ocean acidification and those which are not.
A growing body of research has demonstrated that the biological impacts of acidification are intrinsically linked to those of warming, at a physiological level. The likelihood that a species will be lost from an area as a result of increased environmental stress could be determined by both its phylogeny and its ecology. Due to the complex interactions between marine species in the food web, it is not easy to predict which species could be potential winners in the changing marine environment. Some animals will tolerate higher acidity; some may even thrive on it; but there will probably be fewer species overall, and the mix of species in a given locale will almost certainly change.
Impacts on fisheries and aquaculture
The impacts of ocean acidification on marine organisms could have knock on effects for both fisheries and aquaculture. A laboratory study has shown that when marine snails are exposed to acidified seawater their shells are seen to dissolve. As these organisms are the primary food for Alaska’s juvenile pink salmon, the fishery could be at risk if the salmon are unable to switch to another food source.
Along the NW coast of the US the combined effects of strong upwelling and acidification have been observed to accelerate the movement of corrosive “acidified” water onto the continental shelf. Since 2005, there has been a progressive decline in the oyster industry as larvae have failed to survive. Oyster larvae are particularly susceptible to ocean acidification as their early shells are made from an easily eroded form of calcium carbonate. It is feared that the acidic seawater that rises from the deep Pacific Ocean which is getting pumped into seaside hatcheries may be corrosive enough to kill oyster larvae.
Some hope for the aquaculture industry may lie in selective breeding. There is some evidence that aquaculture populations may actually show some adaptive tolerance to ocean acidification. However, it is also important to note that warmer more acidic ocean conditions appear to be favouring smaller phytoplankton species such as dinoflagellates. This could therefore increase the occurrence of harmful algal blooms and impact upon shell fisheries.