In ocean acidification, the pH of ocean water becomes more and more acidic as carbon dioxide from the atmosphere is absorbed. One of the many problems this causes is inhibition of calcification. Many marine animals, such as snails and clams, use this process to incorporate calcium from the water into their shells. New research just published in the Journal of Limnology and Oceanography shows that at least one species, the Olympia oyster, may have a strategy to deal with this issue.
Olympia oysters used to be very common on the Pacific Northwest coast. Over-harvesting wiped many of them out and loss of suitable habitat meant the population struggled to recover. Researchers at Ohio State University compared the calcification rates of these oysters to those of a common commercially-raised species, the Pacific oyster. They found that while Pacific oysters begin developing their calcium carbonate shells right away, Olympia oysters wait until a few days after fertilization, when they’ve developed a bit more. In addition, Olympia oysters build the shell at a much slower rate, over several days. The more common Pacific oysters have a very small window of opportunity to build their shells, about six hours. This means that, for the Pacific oyster, poor water conditions during that time period can result in a weaker shell. Even if they manage to properly build their shell, the extra energy required from the process might kill them soon after.
Olympia oysters take a much less risky approach. By spacing out the calcification steps over several days, they can deal with occasional acidic water conditions. They use much less energy per day, helping them survive after the process is complete. This is significant because it’s the first recorded instance of an animal having a built-in strategy to deal with ocean acidification.
The researchers did note that Pacific oysters can possibly make up for poor water conditions by producing many more offspring. Pacific oysters are capable of releasing more eggs than Olympia oysters and these eggs are also much smaller. This won’t matter, however, if none of the oysters are able to properly build their calcium shells due to changing ocean pH.
The Olympia oyster’s slow and steady strategy may allow the species to cope with acidic water attributed to increasing levels of carbon dioxide in the atmosphere. Importantly, this research shows that there may be other organisms with similar strategies, allowing them to survive climate change.
George G. Waldbusser et al, Slow shell building, a possible trait for resistance to the effects of acute ocean acidification, Limnology and Oceanography (2016).