Mystery behind oysters and ocean acidification revealed

A new study by researchers at Oregon State University (OSU) has determined why oysters are so sensitive to ocean acidification — and it is not necessarily that acidic water dissolves their shells, but rather that water high in carbon dioxide alters shell formation rates, energy usage and thereby growth and survival.

The results were published in the journal Geophysical Research Letters.

“From the time eggs are fertilized, Pacific oyster larvae will precipitate roughly 90 per cent of their body weight as a calcium carbonate shell within 48 hours,” said George Waldbusser, an OSU marine ecologist and lead author of the study. “The young oysters rely solely on the energy they derive from the egg because they have not yet developed feeding organs.”

In increasing carbon dioxide in water, shellfish need more energy to build shell and adult oysters and other bivalves may grow slower, other studies have shown. But larvae in the first two days of life cannot wait.

“They must build their first shell quickly on a limited amount of energy – and along with the shell comes the organ to capture external food more effectively,” said Waldbusser, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “It becomes a death race of sorts. Can the oyster build its shell quickly enough to allow its feeding mechanisms to develop before it runs out of energy from the egg?”

The study is important, scientists say, because it is unprecedented in documenting the connections between shell formation rate, available energy and sensitivity to acidification.

The study’s authors say that the faster the shell forms, the more energy is needed and oyster embryos building their first shell need “to make a lot of shell material on short order.”

Using stable isotopes, the researchers found that on the second day of life, 100 per cent of the larval tissue growth was from egg-derived carbon and the larvae relied on this energy until they were 11 days old.

Waldbusser noted that adult bivalves are well-adapted to grow shell in more acidified conditions, and have evolved several mechanisms for this including use of organic molecules to organise and facilitate the formation of calcium carbonate; pumps that remove acid from the calcifying fluids; and outer shell coatings that protect the mineral.

The discovery could help hatcheries make changes to offset some of the effects of ocean acidification.

“On the energy side, you can make sure that eggs have more energy before they enter the larval stage, so a well-balanced adult diet may help larval oysters cope better with the stress of acidified water,” Waldbusser said.

Breeding for specific traits is another strategy, researchers say.

Natalia Real, FIS Worldnews, 13 June 2013. Article.

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