Ocean acidification and its impacts on the marine biodiversity

Ocean acidification is roughly emerged as one of the largest threats to marine organisms and ecosystems. Average global surface ocean pH has already fallen from a pre-industrial value of 8.2 to 8.1, corresponding to an increase in acidity of about 30%. Values of 7.8–7.9 are expected by 2100, representing a doubling of acidity. The ocean has absorbed between 24 and 34% of anthropogenic CO2 emissions during the past 5 decades. The massive input of CO2 generates sweeping changes in the chemistry of seawater, especially on the carbonate system. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Decreases in the availability of carbonate ions force marine organisms to spend more energy building and maintaining their shells or skeletons. For some organisms, spending more energy on shell formation may leave less en¬ergy for other biological processes like growing, reproducing or responding to other stresses. Many shell-forming marine organisms are very sensi¬tive to changes in pH and carbonate ion concentrations; conditions predicted for the coming decades may prove very stressful to these calcifying organisms. Corals, bivalves (such as oysters, clams, and mussels), pteropods (free-swimming snails) and certain phytoplankton species fall into this group. The biological impacts of ocean acidification will vary, because dif¬ferent groups of marine organisms have a wide range of sensitivities to changing seawater chemistry. Impacts from ocean acidification at any life stage can reduce the ability of a population to grow or to recover from losses due to disturbance or stress. Therefore ocean acidification will also impact various economic sectors (eg: fisheries, aquaculture, tourism and coastal communities) and may also have heavy indirect effects on much broader segment of the world economy and production. Ocean acidification represents yet another stress on marine environments that may endanger the flow of goods and services to marine-dependent communities. The atmospheric CO2 can be controlled by avoiding anthropogenic activities such as fossil fuel burning and deforestation. The mitigation approach for ocean acidification includes addition of lime and iron fertilization which could neutralize the acidity and increase the ocean productivity.