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Acid Oceans Threaten Billion-Dollar Oyster Business

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By Tim Radford, Climate News Network

LONDON  − Bad news for American gourmets: the commercial oyster industry in the Pacific Northwest has been failing for several years, and may go on failing as increasingly acid oceans put the larvae of the bivalve Crassostrea gigas seriously at risk.

The good news is that U.S. scientists now know exactly why things are going wrong in the oyster beds, which opens up the possibility of commercial hatcheries finding ways to get round the problem.

Rare treat: commercial harvests of Pacific oysters have been failing for several years.
Credit: flickr/Guido

First, the facts: as carbon dioxide levels in the atmosphere rise inexorably, so the gas dissolves in water and falls as a very weak carbonic acid rain, with a subtle but measurable change in the pH values of the planet’s oceans.

There have always been dissolved gases in rainwater, but as long as pH levels remain stable, the ocean’s corals and mollusks not only adapt, they subtly exploit the water chemistry to build stronger bones and shells.

Sensitive to change

Oysters seem unusually sensitive to changes in pH, but marine biologist George Waldbusser and research colleagues at Oregon State University report in Geophysical Research Letters that the failure of the oyster harvest isn’t a simple case of acid waters dissolving calcium carbonate shells.

Instead, water high in dissolved carbon dioxide tends to alter the shell formation rates, the energy usage and, ultimately, the growth and survival of young oysters.

Females tend to produce eggs by the million as water temperatures reach around 20°C. Once fertilized and hatched, the embryos have about two days to start building a shell. Raised carbon dioxide levels in the water impose an extra energy cost for the little shell-builders.

Mature oysters can take their time and assemble calcium carbonate production more slowly, but larvae don’t have the time. Their only energy supply is the nourishment in the egg.

Water high in dissolved carbon dioxide tends to alter the shell formation rates, the energy usage and, ultimately, the growth and survival of young oysters.
Credit: flickr/Min Lee

“From the time eggs are fertilized, Pacific oyster larvae precipitate roughly 90 percent of their bodyweight as calcium carbonate shell within 48 hours,” Dr. Waldbusser says. “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.”

Death race

“It becomes a death race of sorts. Can the oyster build its shell quickly enough to allow its feeding mechanism to develop before it runs out of energy from the egg?”

Armed with this insight into oyster bed ecology, the scientists say, there are interventions that can be introduced at hatcheries that may offset some of the effects of ocean acidification. Some hatcheries have started to “buffer” the water supplies in commercial hatcheries that supply the marine and estuary oyster beds − essentially, adding antacids to incoming waters.

However, what may be hopeful news for fish farmers may not be such good news for the wild oyster, which will no doubt experience more stress in its native waters as carbon dioxide levels go on rising.

The research matters at one level because Pacific oyster farming is now a billion-dollar business, and at another because it exposes something of the intricate connection between sea-dwelling creatures and the chemistry of the sea.

It is also a reminder that any creature faces different hazards at every stage of its life cycle. The report’s authors say: “We suggest that the predictions of winners and losers in a high CO² world may be better informed by calcium carbonate kinetics, bioenergetics, ontogeny, and life-history characteristics than by shell mineralogy alone.” 

Tim Radford is a reporter for Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.

Comments

By Charles Hollahan (Pasadena, Ca)
on June 30th, 2013

There have been efforts before to restore native oysters in Oregon, Ostrea conchaphila, has had programs to restore them. I assume they have been successful and I know that some oyster growers in the PNW grow native oysters. There’s a paper online about a NOAA program to restore them in Oregon but the paper won’t open so I cannot report on it further.

One of the biggest problems is the harvest of the oysters reduces alkalinity in the places where they are cultured and harvested. It would be helpful if local users would save the shells and they were returned to the waters so they could provide calcium carbonate for new growth as well as cultch for new settlement. Local sources or fossil sources are necessary to prevent diseases from being introduced.

Species other than oysters which use calcium carbonate will be impacted as well. The rivers in Washington and Oregon provide a near constant source of calcium but the problem is associated with turnover by wind during the Summer months when the wind blows plus there’s Vibrio spp. which kill the planktonic stage as well.

It would not be too difficult to culture the wild shellfish, then release them after they have settled - the same method that the growers use. I’m an experienced shellfish aquaculturist and I would be interested in projects like this. Government isn’t going to get the funds in these days of partisan gridlock so private parties will have to step forward.

If others find this approach to be interesting, then they may contact me via email. My address is charleshollahan@gmail.com   Thanks, Charles

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