Can the oyster industry survive ocean acidification?

by Brendon Bosworth

For four frustrating months in 2007, Mark Wiegardt and his wife, Sue Cudd, witnessed something unsettling at their Oregon oyster hatchery: tank bottoms littered with dead baby oysters. Usually, the larvae are grown until they're three weeks old and a quarter of a millimeter in size -- 10 million bunched together are roughly the size of a tennis ball. Then they are shipped to 50-some growers in the U.S., Canada and Mexico. But that summer, the oysters died before they were ready to ship. Whiskey Creek Shellfish Hatchery struggled to fill a third of its orders.

"You have good and bad weeks, but this was a blanket kill on everything we tried to do," recalls Wiegardt. "We thought we were going out of business because we couldn't make the larvae grow."

It turned out that "corrosive" seawater, which makes it harder for young oysters to build shells, was largely to blame. Like the atmosphere, the world's seas are burdened by our fossil fuel use and deforestation. The ocean has sponged up a quarter of the carbon dioxide humans have produced since the Industrial Revolution, steadily lowering its pH. Today's seas are 30 percent more acidic than their pre-industrial ancestors. By the turn of the century, scientists anticipate they will be 150 percent more so -- a trend that led National Oceanic and Atmospheric Administration (NOAA) chief Jane Lubchenco to call ocean acidification climate change's "equally evil twin."

Even if manmade carbon emissions ceased tomorrow, the West Coast would face decades of increasingly corrosive water because the ocean is laden with CO2 from decades past and will continue to absorb the CO2 already in the air, slowly changing its chemistry. "The train has already left the station," says Richard Feely, a senior fellow at NOAA's Pacific Marine Environmental Laboratory in Seattle. "If we don't reduce carbon dioxide emissions, we'll (see) conditions that will be corrosive to more species."

Creatures that build shells from calcium carbonate -- pteropods, for example, tiny sea snails that swim with dainty "wings" and nourish the pink salmon that sustain Alaska's fishing industry -- are particularly vulnerable. In water, CO2 becomes carbonic acid, which releases hydrogen ions when it breaks down. The hydrogen ions bond with carbonate ions, stealing them from animals that use them to form calciferous homes. Experiments with non-shelled species have also yielded disturbing results. Clownfish -- the orange-and-white-striped reef dwellers immortalized in Finding Nemo -- seem to go deaf when raised in seawater with CO2 levels predicted to be present by 2050 and 2100.

But for Northwest oyster growers, ocean acidification is no distant threat. The Whiskey Creek die-offs, which continued in 2008, dealt the industry a serious blow, since the hatchery supplies the majority of independent West Coast growers. Production also slumped at Washington's Taylor Shellfish Inc., another major producer, in 2008 and 2009, and acidic water probably played a role. These declines came at an especially vulnerable moment: Larvae growing naturally at Washington's Willapa Bay, a chief source of wild seed, had also been failing, because the water was too cold. Seed shortages contributed to the region's 22 percent drop in production between 2005 and 2009, according to a trade group. "Ocean acidification poses a serious threat to Washington's marine economy, cultures, and environment," concluded a recent report from Washington state, the West Coast oyster industry's hub.

Now, growers are attempting to adapt to the sea's new chemical reality. Experiments are under way at Whiskey Creek and at least one other hatchery, which, owing to their geography, have already experienced what's expected to become the West Coast's norm before too long. These experiments should help the industry answer a pressing question:  Can it survive the inevitable?

Whiskey Creek's three barn-like buildings sit on Netarts Bay, a shallow, tree-fringed estuary whose wide mouth opens onto the azure Pacific. At low tide, the bay drains into the ocean; at high tide it's replenished. Since the bay's water exchanges frequently, it's an almost direct chemical reflection of the adjacent sea. Water conditions vary drastically between April and October, when northwesterly winds push surface water offshore, allowing water 500 to 650 feet below the surface to flow upward into near-shore regions -- a process known as upwelling. When that water hugs the coastline, it surges into Netarts Bay.

The upwelling water is rich with dissolved CO2, thanks in part to microbes that feast on decaying plants and animals in the deep, releasing CO2 as they go. This is a natural process, but CO2 from human activities has increased gas concentrations in upwelled water by about 12 percent, says NOAA's Feely. Together, the manmade and natural CO2 make this water's chemistry similar to what scientists expect to become commonplace along the West Coast by 2050. That's particularly true when it comes to a low availability of carbonate ions, which oysters use to build shells.

Research suggests that in the first two days of their lives, oyster larvae in carbonate-deficient water burn through energy faster than usual because they have to work harder to build shells. This exhausts them, retarding their growth. The oysters' failure to thrive is akin to young children eating lead-paint chips and later, in their teens, scoring miserably on SAT tests, says Burke Hales, a professor of ocean ecology and biogeochemistry at Oregon State University.

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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