Oysters at hatcheries in Oregon showing the effects of ocean acidification. (Photo: OSU)
Larval oyster failure linked to carbon dioxide levels
Thursday, April 12, 2012, 22:40 (GMT + 9)
Researchers at Oregon State University (OSU) have definitively linked an increase in ocean acidification to the collapse of oyster seed production at a commercial oyster hatchery in Oregon, where larval growth had declined to a level considered by the owners to be "non-economically viable."
A study by the researchers found that elevated seawater carbon dioxide (CO2) levels, resulting in more corrosive ocean water, inhibited the larval oysters from developing their shells and growing at a pace that would make commercial production cost-effective. As atmospheric CO2 levels continue to rise, this may serve as the proverbial canary in the coal mine for other ocean acidification impacts on shellfish, the scientists say.
Results of the research have just been published in the journal, Limnology and Oceanography.
|Oyster larvae are placed into growing tanks. (Photo: Lynn Ketchum, OSU)
"This is one of the first times that we have been able to show how ocean acidification affects oyster larval development at a critical life stage," said Burke Hales, an OSU chemical oceanographer and co-author on the study. "The predicted rise of atmospheric CO2 in the next two to three decades may push oyster larval growth past the break-even point in terms of production."
The owners of Whiskey Creek Shellfish Hatchery at Oregon's Netarts Bay began experiencing a decline in oyster seed production several years ago, and looked at potential causes including low oxygen and pathogenic bacteria. Alan Barton, who works at the hatchery and is an author on the journal article, was able to eliminate those potential causes and shifted his focus to acidification.
Barton sent samples to OSU and the National Oceanic and Atmospheric Administration's (NOAA) Pacific Marine Environmental Laboratory for analysis. Their ensuing study clearly linked the production failures to the CO2 levels in the water in which the larval oysters are spawned and spend the first 24 hours of their lives, the critical time when they develop from fertilized eggs to swimming larvae, and build their initial shells.
"The early growth stage for oysters is particularly sensitive to the carbonate chemistry of the water," said George Waldbusser, a benthic ecologist in OSU's College of Earth, Ocean and Atmospheric Sciences. "As the water becomes more acidified, it affects the formation of calcium carbonate, the mineral of which the shell material consists. As the CO2 goes up, the mineral stability goes down, ultimately leading to reduced growth or mortality."
Commercial oyster production on the West Coast of North America generates more than USD 100 million in gross sales annually, generating economic activity of some USD 273 million. From 2007 to 2010, major hatcheries supplying the seed for West Coast oyster growers suffered persistent production failures.
The wild stocks of non-hatchery oysters simultaneously showed low recruitment, putting additional strain on limited seed supply.
"In addition to the impact of seasonal upwelling, the water chemistry changes with the tidal cycle, and with the time of day," Hales said.
"The takeaway message here is that the response to poor water quality isn't always immediate," said Waldbusser. "In some cases, it took until three weeks after fertilization for the impact from the acidic water to become apparent. Short-term experiments of just a few days may not detect the damage."