Are marine organisms able to adapt to ocean acidification?
An international group of researchers under leadership of the Alfred Wegener Institute for Polar and Marine Research demands a stronger consideration of evolutionary adaptations in predictive models. For shell-forming marine algae the scientists compared laboratory experiments with fossil collections. Coccolithophorids - unicellular planktonic algae of only a few thousandths of millimetres - developed malformations of their calcium carbonate skeleton when grown experimentally in seawater of varying acidity. In contrast, fossils of the same species dating back to periods of various carbon dioxide concentrations had intact skeletons. The researchers conclude that the organisms' ability to adapt to changing environmental conditions is greater than previously acknowledged in prediction models.
Greenhouse gases in the oceans impede growth
Almost half of the carbon dioxide released through the burning of fossil fuels is re-absorbed in the oceans. This means that marine systems become increasingly acidic, impeding organisms in their formation of calcium carbonate skeletons. Over the past years, a reduced chance of survival through ocean acidification has already been detected for marine organisms such as corals and snails. Laboratory studies on minute marine algae, so-called Coccolithophories, now give similar results. "In our laboratory experiments, we demonstrated that one of the two species investigated produced less calcium carbonate with both reduced or increased carbon dioxide concentrations in seawater", explains biologist Gerald Langer of the Alfred Wegener Institute. "In addition to reduced calcium carbonate production, the Coccolithophorids show malformations of their lime skeletons."
Due to their high abundance, coccolithophorids are among the most significant primary producers in the world's oceans and they are located at the basis of food chain. Occurring in enormous numbers, Coccolithophorids influence the global carbon cycle ,the global weather, and climate systems. The disappearance of these organisms following acidification of the oceans would have profound consequences.
However, extinction is not inevitable. This, researchers have concluded from rock deposits, such as the chalk cliffs of Rügen, consisting nearly 100 percent of fossil coccolithophores. "Some of the Coccolithophorids in the chalk cliffs were deposited under much elevated carbon dioxide concentrations in the ocean. Other than in our laboratory experiments, we did not find any construction abnormalities in the fossil calcium carbonate skeletons", explains Markus Geisen of the Alfred Wegener Institute. "And also sediment cores from the past ice age - with lower carbon dioxide levels than today - show no skeletal deformations in the same species that we tested in the laboratory."
From the scientists' point of view, the discrepancy between laboratory tests and fossil records can be explained by the species' evolutionary adaptability. Even without human influences, environmental conditions undergo continual changes. In order to escape extinctions, organisms must adapt to these changes. "In the past, Coccolithophorids have been able to adjust to changing carbon dioxide concentrations. Why should they not continue to do so in the future? However, they will need time", comments Gerald Langer. In a next step, the researchers will address the question of how much time is needed for such adaptations in Coccolithophorids and other shelled marine organisms. The scientists already agree that evolutionary adaptations have not been sufficiently considered in predictions about the consequences of climate change.
Other than the Alfred Wegener Institute, scientists of the Leibniz Institute for Marine Sciences at the University of Kiel (IFM Geomar) and the Natural History Museum in London have contributed to the results of the studies that will be published shortly in the journal Geochemistry, Geophysics and Geosystems.
Bremerhaven, September 19, 2006
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The Alfred Wegener Institute (AWI) conducts research in the Arctic, Antarctic and in oceans of temperate and high latitudes. The AWI coordinates polar research in Germany, and provides important infrastructure, such as the research icebreaker 'Polarstern', for international scientific enterprises in the Arctic and Antarctic. The AWI is one of 15 research centres of the 'Helmholtz-Gemeinschaft' (Helmholtz Association), the largest scientific organisation in Germany.
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