Shells turn brittle

By Supriya Singh
Published: Friday 15 May 2009

Carbon emissions harm marine organisms

studies linking an increase in the levels of atmospheric carbon dioxide to the acidification of oceans are widely reported and accepted. The effects of acidification on marine life are not well understood. A team showed a direct link between ocean acidification and decrease in the weights of calcareous shells of microplanktons.

Scientists from the Antarctic Climate and Ecosystem Cooperative Research Centre, Tasmania, compared weights of modern forams (single-celled calcite-secreting marine animals) collected from sediment traps in the Southern Ocean with weights of shells preserved in the underlying Holocene-aged (Holocene is the geological era that began 11,700 years ago) sediments. The modern forams weighed 30-35 per cent less than the older ones. The shells of these microplanktons form a significant sink for calcium carbonate in the oceans. A subsequent decrease in the number of the microplanktons would impact the structural and functional organization of the marine ecosystem. The study, reported in the March 8 issue of Nature Geoscience, said monitoring changes in calcium carbonate production by the forams will reveal effects of climate change on the marine food chain.

Marine organisms like corals and molluscs also have calcium carbonate skeletons. "Reduced rate of skeleton formation will make them less strong and prone to predators," explained M W M Wafar, National Institute of Oceanography, Goa.

There is lower pH near the coast due to industrial and domestic pollution, which is reversible. Acidification of seawater at deeper levels is different. Its reversal could take decades and by then the marine ecosystems could significantly destabilize. "To isolate changes effected by acidification on marine life, oceans need to be monitored continuously," said T Balasubramanian, centre for advanced studies in marine biology, Annamalai University, Tamil Nadu.

A related study, in the April 12 issue of Nature Geoscience, described a mussel species, Bathymodiolus brevior, that survived acidic marine conditions around the Northwest Eifuku volcano, Japan, for many decades. Their shell weights were half of those growing in normal conditions, suggesting metabolic impairment. Their survival is attributed to lack of predators, like crabs, in the highly acidic environment. But their vulnerability is likely to increase in a future ocean with low pH.

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