West Coast shellfish farms impacted by ocean acidification

West Coast shellfish growers have learned to work around upwellings of corrosive waters and save the lives of their bivalve stocks.

Increased levels of carbon dioxide, or CO2, in the atmosphere are changing the chemistry of the oceans, making it more acidic. The CO2 surge stems mostly from coal and, to a lesser degree, oil-fired power plants. The resulting off kilter acidity reduces carbonate, the mineral building block of shells, skeletons and corals.

In 2005, oystermen first noticed failures in natural sets in Willipa Bay in southern Puget Sound, followed by failures at two of four of the region’s major shellfish hatcheries.

“In 2008 our oyster larvae production was off 60 percent, and 80 percent in 2009,” said Bill Dewey, director of public policy and communications for Taylor Shellfish Farms in Shelton, Wash., the nation’s largest producer of farmed oysters, clams, mussels and geoducks.

At first, the growers believed the killer was a lethal, naturally occurring bacterium, but expensive filtration did nothing to stop the larval die offs. Then ocean acidification blipped onto the radar screen, Dewey said, and new testing equipment proved it was the culprit.

“It became very telling very quickly that when the oyster larvae were dying en masse, it was because we were bringing in very corrosive water. The oyster is still growing a shell; it’s just that it is dissolving from the outside faster than they can grow it. So eventually they lose that race and they die,” he said.

Growers credit Washington Sen. Maria Cantwell for acting fast to get funding for monitoring equipment last year to help the $110 million industry adapt to the corrosive seawater.

“Now we can see what’s going on with the sea water chemistry and deal with it in real time,” Dewey said. “We have learned how to essentially dodge it and produce our larvae around those corrosive events.”

Wind direction provides the biggest warning when to plug intake pipes to the shellfish holding tanks. At the Whiskey Creek Hatchery, for example, growers have learned when the wind shifts from the south to the north, they have a 24 hour window before corrosive water shows up at their intake pipe. Other growers also have learned to fill shellfish tanks late in the day instead of mornings, and to use water intakes at different depths.

Research has also shown that bivalves use three different types of calcium carbonate to build their shells in stages, and not all shellfish are equally prone to corrosion. Unfortunately, Pacific oysters turn out to be one of the most vulnerable, Dewey said.

Meanwhile, early detection and gentle south winds have allowed Taylor Shellfish to rebound to record production for oyster larvae this year. Dewey said he is confident that the farmed shellfish industry, at least, will be able to thrive.

“I think we will survive and figure out a way through this,” Dewey said. “But I don’t think it bodes well for other species in the ocean and fishing interests that rely totally on natural production.”

Understanding the impacts of ocean acidification on food webs and ecosystems is a focus of Robert Foy, director of the NOAA Fisheries Science Center in Kodiak. He points to tiny snail-like pteropods, which comprise nearly half of the diet for pink salmon.

“Their physiology will be affected, they’re not going to be able to grow,” Foy repeats in his awareness efforts. “A 10 percent drop in pteropod production would lead to about a 20 percent drop in pink salmon body weight. The loss of that diet source would be extremely detrimental to pink salmon populations.”

A new article in the journal Nature Climate Change says, “the fish are OK,” belief ignores an important knowledge gap – the possible effects of CO2 during the early development of fish eggs and larvae.

Laine Welch, Alaska Journal of Commerce, 25 December 2011. Article.

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