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Acidification of ocean's adversely impacting sea animals' health

Washington, August 26 : Biologists have claimed that acidification of our oceans could change the ecosystems of our seas even by the end of this century.


In a new study, biologists at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), compiled and analysed all available data on the reaction of marine animals to ocean acidification.

The scientists found that whilst the majority of animal species investigated are affected by ocean acidification, the respective impacts are very specific.

The oceans absorb more than 25 percent anthropogenic carbon dioxide emitted to the atmosphere and form a natural store without which the Earth would now be a good deal warmer.

But their storage capacities are limited and the absorption of carbon dioxide is not without consequence. Carbon dioxide dissolves in water, forms carbonic acid and causes the pH value of the oceans to drop - which affects many sea dwellers. In recent years much research has therefore been conducted on how individual species react to the carbon dioxide enrichment and the acidifying water.

In order to gain an initial overview, Dr. Astrid Wittmann and Prof. Hans-Otto Portner from the Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI), surveyed all studies so far conducted which dealt with the consequences of ocean acidification for marine species from five animal taxa: corals, crustaceans, molluscs, vertebrates such as fishes and echinoderms such as starfish und sea urchins.

By the end they had compiled a total of 167 studies with the data from over 150 different species. In order to classify these results they used emission scenarios for carbon dioxide on which the world climate report is also based. These scenarios allow to forecast the impacts of different carbon dioxide concentrations in the atmosphere far into the future.

Wittmann said that the study showed that all animal groups we considered are affected negatively by higher carbon dioxide concentrations. Corals, echinoderms and molluscs above all react very sensitively to a decline in the pH value.

Some echinoderms like brittle stars have lower prospects of survival in carbon dioxide values predicted for the year 2100. By contrast, only higher concentrations of carbon dioxide would appear to have an impact on crustaceans such as the Atlantic spider crab or edible crab. However, the sensitivity of the animals to a declining pH value may increase if the sea temperature rises simultaneously.

Scientists from the Alfred Wegener Institute determined the consequences of ocean acidification on the fitness of the individual species using physiological features.

The reason for different taxa reacting differently to ocean acidification is that they differ fundamentally in terms of their bodily functions. Whilst fish, for example, are physically very active and are able to balance any initial fall in the pH value very well in their blood, this is more difficult for corals.

They spend their entire life in one place and cannot compensate as well for a higher carbon dioxide level in their bodies because they lack efficient physiological mechanisms. Failure to compensate the pH value in the body fluids can result for example in lower coral calcification, i.e. its calcareous skeleton does not protect against erosion and it cannot be repaired or developed as well.

The study has been published in scientific journal Nature Climate Change.

--ANI (Posted on 26-08-2013)

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