Oysters on Acid

The life of an oyster on the West Coast is not an easy one.

Due to considerably low water temperatures, there are few places Pacific oysters can actually spawn and have their larvae grow into adulthood.

After that, oysters face small and narrow estuaries, which can cause the oyster to get swept out to sea.

To make matters worse, oysters face a new threat: ocean acidification.

The molluscan broodstock program — based at Oregon State University’s Hatfield Marine Science Center in Newport — has been studying oyster breeding since 1996.

In 2005, scientists in the laboratories encountered the inexplicable issue of oysters dying off.

A year later, oyster larvae at the Whiskey Creek Shellfish Hatchery in Tillamook, just up the road from the scientists’ laboratories, strangely began dying.

Sue Cudd, who owns and manages the hatchery, called OSU scientists for help to explain the sudden poor survival and slow growth rates of the larvae.

Scientists thought the issue might be attributed to bacterial pathogens or water chemistry, but at that time, the researchers didn’t have the tools to test what the issue could be, according to Chris Langdon, director of the molluscan broodstock program.

Upwelling, a phenomenon that occurs as north winds push warmer surface water away from the shoreline and out to sea and replaces it with cold water from offshore, was also considered a possible cause to the oyster deaths.

The result of upwelling is acidified seawater. This water had been drawn into the hatchery, thereby lowering the pH level and the aragonite saturation state within the oysters.

Aragonite, the crystal form of calcium carbonate, is the main component of the oyster shell in the larvae.

If there is a saturation state that is less than one, the shell starts to dissolve.

The collaboration between OSU scientists and Whiskey Creek fostered a greater production capacity within the hatchery, and scientists discovered the correlation between upwelling and poor oyster larvae production, according to Langdon.

Sometimes, the saturation state dropped to one or a little less than one, creating a problem for the larvae toward producing a shell.

OSU researchers and Whiskey Creek started adding sodium carbonate to the seawater to buffer the acidified water, in order to increase the aragonite saturation state.

“And that’s worked pretty well,” Langdon said. “The hatcheries seem to be functioning now. There’s still something not quite right with this upwelling of water and we’re working hard to figure it out.”

The oyster industry on the West Coast of the United States is substantial, with production in the realm of $17 million per year in product. The shellfish industry as a whole, if clams and mussels are included, produces around $25 million, which supports approximately 3,500 people along the West Coast.

West Coast oysters travel all around the world.

Oysters are shipped abroad to places like Korea, China, New York and Chicago, and others are consumed within the state or up and down the West Coast.

Digging deeper into the mortality of oysters, OSU scientists George Waldbusser, Burke Hales and Brian Haley in OSU’s College of Earth, Oceanic and Atmospheric Sciences, and Langdon of the Hatfield Marine Science Center, began running experiments to find the threshold at which oysters, clams and mussels are harmed by acidification. They are funded by a four-year grant that began in 2010.

Researchers are now manipulating water chemistry to try to find out what parameters and components of acidified water is detrimental to the larvae.

Hales, one of the world’s leading scientists in ocean carbonate chemistry, formulated an assortment of different seawater types from which researchers are able to tease the oyster growth issue apart.

And the answer for researchers is that in most species there seems to be an aragonite saturation state.

“It seems to be affecting the shell formation particularly in the very early larval stages,” Langdon said. “As the egg develops, it has to lay down a lot of shell very quickly.”

This very rapid shell formation seems to be extremely sensitive to the effects of aragonite saturation state.

OSU researchers have now established a program in which they are testing different species and different water types to try and find out which species vary in their sensitivity to upwelling and which component of the acidified seawater is detrimental.

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