The meeting was a coming-out party of sorts for scientists interested in the biological implications of the chemical changes occurring as the oceans absorb huge and growing amounts of atmospheric carbon dioxide. Just 8 years ago, an inaugural symposium on the topic in Paris drew only 125 researchers from 20 nations; this year, more than 550 scientists from 40 nations showed up. The field is getting “much bigger and more competitive,” Gattuso says.
Acidification researchers are also shifting their focus. To date, many experiments have involved simply plopping sea creatures into laboratory tanks full of acidified water for a few days or months to see how they respond. Many species suffer, researchers reported. Fish and shellfish larvae exposed to more acidic waters, for example, often fail to thrive: They don’t grow as big or live as long as those born in more alkaline waters. But some species show substantial resilience, reported biologist Sam Dupont of the University of Gothenburg, Kristineberg, in Sweden. After he used acidic water to completely dissolve the shells of developing sea urchins, for instance, the urchins were able to regrow them and live normally once they were returned to normal seawater.
Such limited studies, however, “can’t really tell you whether a species has the capacity to adapt to acidification, or how pH changes affect a larger ecosystem,” says marine scientist Gretchen Hofmann of the University of California, Santa Barbara.
Coccolithophore fossils might help forecast how future pH changes will affect ocean phytoplankton. CREDIT: PAUL BOWN/UNIVERSITY COLLEGE LONDON/SAMANTHA GIBBS/UNIVERSITY OF SOUTHAMPTON
One approach to leaping those limitations is to go back to the future, by looking for times in the fossil record when ocean ecosystems experienced similarly dramatic carbon dioxide–driven changes. One popular candidate, known as the Paleocene-Eocene Thermal Maximum (PETM), occurred 55 million years ago during rapid global warming (Science, 18 June 2010, p. 1500). Increasingly corrosive bottom waters appear to have helped drive many bottom-dwelling species extinct during the PETM, reported paleontologist Paul Bown of University College London. But what happened at the ocean’s surface is less clear. The fossil record suggests that many species of phytoplankton—the tiny plants at the base of the marine food chain—also disappeared but were replaced by other species, with little change in overall diversity.
But such coarse measures can’t tell you how ancient acidification might have affected reproduction or growth patterns in these marine communities, Bown says. To get that more detailed view, Bown and his colleagues have been analyzing some exquisitely preserved fossils of PETM phytoplankton called coccolithophores, which surround themselves with shieldlike plates of shell. By studying some closely related living species, the researchers found that they could estimate ancient coccolith growth and reproduction patterns by painstakingly counting the plates on individual fossils. (The number increases as the organisms grow.) So far, preliminary studies haven’t found deformed shells or other dramatic signs of lower pH, but Bown cautions against taking that as a sign that modern acidification won’t be a problem. Change in the PETM moved “much, much slower than today,” he says.
Read the full article: Science 5 October 2012: Vol. 338 no. 6103 pp. 27-28, DOI: 10.1126/science.338.6103.27
A rare find of stunningly intact fossils of prehistoric plankton will allow researchers to study how the tiny marine organisms cope with rising acidity in the oceans.
Finding such intact specimens of coccolithophores, micrometre-sized marine plankton encased in discs of calcium carbonate, is a real coup — searching for fossils of calcified single-celled organisms often yields only skeletal bits that have fallen to the ocean floor.
Scanning electron microscope image of rock surfaces collected from the Bass River core in New Jersey. Image Credit: Paul Bown
“Breaking open undisturbed 56-million-year-old sediment samples, we can image coccolithophores — right down to their intracellular vesicles — using a scanning electron microscope,” said Paul Bown, a palaeoceanographer at University College London, who this week presented images of the fossils at the Third International Symposium on the Ocean in a High CO2 World in Monterey, California.
A growing concern among scientists is that ocean acidification, driven by climate change, will reduce the abundance of calcium carbonate in the seas, making it difficult for algae to form their microscopic plating, essential for their survival. With intact fossils in hand, researchers can compare the sizes, shapes, thickness and growth rates of ancient and modern coccolithophores.
Read the full article: Nature doi:10.1038/nature.2012.11500
