Ocean acidification : marine ecosystem under threat

The ocean is becoming more acidic, but what does that really mean? On a pH scale of 1 – 14, 1.0 is strongly acidic and 14.0 is strongly alkaline or basic; typically ocean waters are slightly alkaline and fall around 8.0-8.1 on this scale. Over the past hundred years, the pH of seawater has decreased, dropping 0.1 pH units. This is due to ocean acidification, a process that occurs when seawater absorbs carbon dioxide (CO2) from the air.

Ocean acidification research till date has looked at the effects of elevated CO2 and reduced pH on those organisms that form calcium carbonate (CaCO3) shells and skeletons, such as corals, molluscs, and coralline algae.More than a quarter of the carbon dioxide we release by burning fossil fuels is absorbed by the ocean where it reduces ocean pH and alters seawater carbonate chemistry. If we do not act to reduce our carbon dioxide emissions, these changes in ocean chemistry could have a devastating impact on many shell-forming organisms, such as corals and some planktons, and marine ecosystems as a whole.

Ocean acidification represents a key threat to coral reefs by reducing the calcification rate of framework builders. In addition, acidification is likely to affect the relationship between corals and their symbiotic dinoflagellates and the productivity of this association. However, little is known about how acidification impacts on the physiology of reef builders and how acidification interacts with warming.

So what can be done about ocean acidification? The obvious solution is to slow and eventually eliminate carbon emissions from burning fossil fuels and to develop approaches for removing carbon dioxide from the atmosphere. Unless there is a dramatic change in our fossil fuel use, projected human-driven ocean acidification during this century will be larger and more rapid than anything experienced by marine life for tens of millions of years. And the problem will be with us for a long time because it takes centuries to thousands of years for natural processes, primarily mixing into the deep-sea and increased dissolution of marine carbonate sediments, to remove excess carbon dioxide from the air.

Although there will be biological winners as well as biological losers, it is likely that the ocean of the future under high carbon dioxide levels will look quite different within the lifetimes of today’s children if we continue on our current course.

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