Some species tolerate ocean acidification

Increasing carbon dioxide levels lead to rising ocean acidity, which can harm corals and many other species of ocean life. Acidification causes calcium carbonate, which corals usually need to build skeletons, to dissolve. “Every day, ocean acidification is taking up the weight of 6 million midsize cars’ worth of carbon, said Nina Keul, a graduate student at the Alfred Wegener Institute for Polar and Marine Research in Germany during a 7 December press conference at the AGU Fall Meeting.

Somewhat surprising, though, is that some species are more tolerant of acidic conditions than scientists had expected. For instance, Keul exposed a species of foraminifera, Ammonia tepida, to seawater with varying acidity and varying carbonate ion concentrations. Previous studies had found that foraminifera growth declined with decreasing carbonate levels, but Keul’s foraminifera continued to grow in the acidic conditions. She said that the mechanism that allows this species to tolerate the low carbonate conditions is as yet unknown.

Another study reported at the Fall Meeting found that some species of corals are able to withstand acidic conditions. Adina Paytan, a researcher with the University of California, Santa Cruz observed natural submarine springs of acidic water in the Caribbean off the coast of Mexico’s Yucatán Peninsula. While many experiments on organisms’ tolerance to acidity are done in controlled laboratory conditions, the naturally occurring acidic springs made it possible to observe high acid conditions in the natural environment. “To our surprise, some corals were able to grow at these low pH conditions,” Paytan said. The researchers found three species of coral that were able to survive high acid conditions. However, she notes, these species are solitary corals, not the kinds of corals that build reefs. A much greater variety of coral species lives farther away from the acidic springs.

Ernie Balcerak, 2011. Eos, Transactions American Geophysical Union 92 (51): 481. Article (subscription required).

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