Can the oyster industry survive ocean acidification?

  • Jeremy Coleman, left, and James Roberts, right, harvest mussels for Taylor Shellfish Farms near Shelton, Washington, in 2011.

    AP Photo/Ted S. Warren
  • Discarded oyster shells at Taylor Shellfish Inc. The hatchery now treats its water to raise pH levels when needed, with mixed results.

    Sarah Gilman
 

Page 2

To stop larvae from munching metaphorical paint chips, Wiegardt and his production manager, Alan Barton, use laptops to monitor the chemistry of water in the bay, and calculate what is known as "aragonite saturation state." Aragonite is a mineral oysters produce using carbonate and calcium in the water that they use to build shells. When they get a reading of 2.0 -- the "magic number" -- or higher, they crank the pumps, flushing the hatchery's tanks with new estuary water. But since the hatchery needs to flush its tanks every 48 hours, that's not enough to solve the problem. When the water falls below the magic number, as it frequently does during summer upwelling periods, they run a series of treatments, which include aerating the water to remove some of the CO2 and injecting it with soda ash to neutralize it -- like using antacids.

Tiny marine plants called phytoplankton, along with eel-grass, assist Barton's doctoring efforts. When the sun is shining, they photosynthesize, sucking CO2 from the water. At night, they release it. So it's better for the hatchery to flush its tanks in the afternoon, once plants have scrubbed some CO2 from the estuary. During severe upwelling episodes, however, the plants are little help.

The careful planning for flushing the tanks and water treatments have helped resurrect Whiskey Creek's production. But cured water is no substitute for the real thing; the hatchery is still only producing 60 to 70 percent of what it once did. "Good water from the ocean is better than good water we produce artificially in the hatchery," says Barton. "We're not that good at it." And in the long term, the windows for pumping good water will shrink because more acidic water will flush the bay more frequently. By mid-century water with aragonite saturations above 1.5 -- lower than Barton's magic number -- will have "largely disappeared," along the West Coast according to a paper published in Science this year.

Whether this will destroy the Pacific Northwest's oyster industry or just change how it operates remains uncertain. But a more acidic sea could impact the survival of oysters beyond the larval stage, which would harm growers who raise the shellfish outdoors where they can't manipulate water chemistry, says Oregon State fisheries professor Chris Langdon. They might be better off farming species that are more resilient to corrosive water, such as clams. Scientists are also experimenting with rearing Pacific Oyster larvae that cope better with more acidic water.

Shellfish farmers may also seek friendlier waters. After struggling to obtain larvae from Whiskey Creek and learning about ocean acidification, Dave Nisbet of Goose Point Oysters in Willapa Bay decided not to gamble on the mercuric local supply. Instead, he built his own hatchery in Keaau, Hawaii, where warmer, saltier water takes up less C02 and is more alkaline. He then ships seed back to Washington, where he rears oysters to adulthood.

Complicating everything is the fact that corrosive water alone can't be blamed for recent slumps. Unlike Whiskey Creek, Taylor Shellfish's hatchery is on a deep bay called Dabob in Washington's Puget Sound. Its water is split into two layers: The upper 60 feet is generally lower in CO2 because sea plants consume it as they photosynthesize; the lower layer is higher in CO2 due to a combination of microbial activity and upwelled water that travels down the Strait of Juan de Fuca, and pours into the bottom of the bay. In summer, northerly winds can bring this water to the surface, creating poor hatchery conditions.  Taylor treats its water as Whiskey Creek does, and has seen some benefit. But the company has suffered even when water chemistry is favorable.  This year, despite chemical conditions similar to last year -- when larval production was robust -- Taylor's numbers are down, and baby oysters are not reaching full size. Production manager Benoit Eudeline suspects it may involve the quality of algae the hatchery raises to feed its baby oysters. "I'm not convinced that at times it's purely high CO2 and low pH," he says. "It has an impact, don't get me wrong, but it's complicated."

To untangle these complicating factors, scientists are studying how bacteria interact with corrosive water to hinder larvae and researching the effects of different chemical conditions on adult oysters used to spawn larvae.

Despite the unknowns, Langdon, the fisheries professor, is optimistic that improved water management at hatcheries and research on more resilient oysters should help the industry cope -- at least in the "near future." What happens after 2050 is a question that remains to be answered.

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