Trouble on the Half Shell

Baby oysters and carbon dioxide don't mix.
This post is part of the research project: Northwest Ocean Acidification
gautsch.net, flickr

gautsch.net, flickr

Four summers ago, Sue Cudd couldn’t keep a baby oyster alive.

She’d start with hundreds of millions of oyster larvae in the tanks at the Whiskey Creek Shellfish Hatchery in Netarts, Oregon. Only a handful would make it.

Sometimes, they’d swim for a couple of weeks. But they’d stop developing before they grew a critical shell structure, or maybe the foot or eyespot. They’d feed poorly. One day, the larvae would simply die. A hatchery that has supplied seafood businesses for three decades had virtually nothing to sell for months, said Cudd, who owns the hatchery.

They would just sort of fade away…It was really devastating. We’re kind of the independent growers’ hatchery, and we had always been reliable up until that point. People were just shocked. I heard a lot of times how it was ruining people’s businesses.

It’s tough to say with scientific certainty that ocean acidification is the sole cause of the die-offs that have plagued two of the Northwest’s three major oyster hatcheries in the last few years.

But this much seems clear: young oysters have a hard time surviving in conditions that will only become more widespread as carbon dioxide from cars, coal plants and other industries cause the fundamental chemistry of the ocean to become more acidic. (For more on that process, see our earlier posts here, here and here).

Scientists have linked the mass mortalities at Whiskey Creek with seasonal “upwelling” events drawing acidic and corrosive seawater that normally lurks down deep towards our beaches and shorelines. And that kind of water is likely to surface more often along the Pacific Coast as more carbon dioxide is pumped into the atmosphere.

Put simply, carbon dioxide causes seawater to shift towards the acidic end of the pH scale. Calcium carbonate—a basic building block for shells and skeletons—becomes unavailable to creatures like oysters and abalone and sea urchins that need it. And if waters become corrosive enough, those shells simply start to dissolve.

Along with the hatchery problems, wild oysters for the last six years have failed to spawn in Washington’s Willapa Bay, one of the few places where Pacific oysters used to reproduce naturally.

Margaret Barrette, executive director of the Pacific Coast Shellfish Growers Association, said nearly everyone in the industry, whether they grow oysters, geoducks, mussels, or clams, is paying attention to ocean acidification. No one knows how other species may be affected down the road, and the vulnerable oyster crop supports the region’s shellfish infrastructure. Says Barrette:

It’s in their face now—they have no reason to turn a shoulder to it because it’s directly affecting them…These are people’s jobs. Rural economies are fueled by these shellfish farms and without the larvae being successful, nothing can happen. It’s right at the top of our list of things to worry about.

What scientists don’t yet know is just what makes the upwelled water so lethal to baby oysters. Is it the elevated carbon dioxide, the low pH, the lack of calcium carbonate to build shells, some kind of algae or trace metals or bacteria that exist in upwelled water, or some combination of all of the above? Oregon State University researchers are designing laboratory experiments right now to tease apart exactly what is causing the problems. As OSU oceanographer Burke Hales puts it:

I think it’s absolutely clear that high carbon dioxide and baby oysters don’t go well together…But it’s really hard to do experiments when you’re seeing these natural fluctuations and say “yes, this in fact is the thing that’s causing the problem,” as opposed to something else that might happen to correlate with carbon dioxide.

No seeds, no oysters

cswtwo, flickr

In the Northwest, everyone from waterfront homeowners with shellfish gardens to mom and pop oyster growers to multi-million dollar commercial farms rely on oyster hatcheries.

The Pacific Oyster favored by commercial growers is native to Japan and is loathe to spawn in our cooler waters. So most West Coast farms buy tiny oyster “seed”—or larvae—from hatcheries and grow them out to maturity on shellfish beds or in bags or racks.

When the hatcheries have problems, the effects ripple across the $72 million West Coast oyster industry, which pumps more money into the regional economy than farmed clams, mussels, geoduck, and other forms of shellfish combined. It would be like a tomato farmer plowing the ground in spring and getting all ready to plant, only to find he couldn’t get his hands on any tomato seeds.

Eighty percent of those oyster sales are in Washington state, 17 percent in California, and the rest in Oregon and Alaska, according to the Pacific Coast Shellfish Growers Association. Because oysters take several years to grow and harvest, it’s not yet clear how much the recent seed shortages will cost the regional economy. But from 2005 to 2009, West Coast oyster production dropped from 94 million pounds to 73 million pounds, resulting in an $11 million loss in sales.

A recent paper on the potential impact of ocean acidification on fisheries did the math this way: In lab experiments, growth rates for oysters and mussels decrease by about 10 percent and 25 percent in ocean conditions that might be reached by 2060 if we do nothing to control carbon dioxide. If comparable losses occur in nature, the decrease in 2006 shellfish and crustacean harvests across the US would have racked up $200 to $500 million in losses.

In the Northwest, those kind of losses would hit rural counties the hardest. In particular, coastal communities in places like Pacific, Gray’s Harbor, or Mason counties in Washington State are highly dependent on the health of the shellfish industry, Barrette says:

In the economic downturn we’ve experienced as a country, some of these communities have managed to stay pretty solid because these farms are providing family wage jobs and they’re contributing to the economic base of that community. And that’s huge right now, especially where timber production has gone down.

willapalens, flickr

Estimating potential losses for the broader seafood industry is nearly impossible, since it’s not yet clear how many species will be affected by ocean acidification. But just about every ocean creature that might wind up on your dinner plate—from salmon to halibut to scallops to shrimp—either uses calcium carbonate that is vulnerable to more acidic seas or eats something that does.


‘A ticking time bomb’

In 2008 and 2009, the largest US producer of farmed shellfish had its own oyster debacle. Taylor Shellfish Farms relies on its hatchery on Dabob Bay, a finger of Hood Canal, to supply much of the company’s oyster seed. Production plummeted by 60 and 80 percent during those two years, no matter what they tried, said chief hatchery scientist Benoit Eudeline.

It was pretty much massive mortalities in the tanks. You’d do your thing and feed them and grow them and suddenly at a certain stage they’d just die. Like pretty much the whole group. Over and over again.

Then, things turned around. In 2010, and so far this summer, the hatchery has had some of its best years for oyster larvae ever. But that’s largely due to better monitoring equipment and lucky weather.

Federal funding allowed the company to install equipment that allows hatchery operators to monitor the chemistry of the seawater which they use to grow oysters and mussels and geoducks.

In Dabob Bay, there’s a layer of “good” water for rearing oysters that rests near the surface and “bad” water down deeper that’s high in carbon dioxide and low in pH. Some summers, strong winds hopelessly mix the two. But for the last two years, the weather has cooperated and the corrosive water has stayed down deep. The hatchery has been able to avoid the “bad” acidic seawater by only using an intake pipe near the surface.

But running a hatchery is never as easy as following a cookbook, and the information they’re gathering changes all the time, Eudeline said. When he’s tried to grow oyster larvae in the deep corrosive water, for instance, the results have been inconsistent, he says:

I still think we’re sitting on a ticking time bomb…My gut feeling is that if there was an upwelling event right now, we’d see larvae slowing down or dying. But it’s not something I’m eager to find out.

New monitoring systems also alert hatchery operators at Whiskey Creek to high carbon dioxide conditions. They adjust their spawning times to try to avoid it, but the business still isn’t where it used to be. They’ve also had some luck with manipulating the water chemistry once it gets into their tanks, but it’s unclear how economical and practical that will be in the long run. Researchers are also racing to find out if certain families or strains of oysters are less vulnerable.

But as frustrating as her hatchery problems have been, Cudd is even more worried about wild creatures that will have to fend for themselves in more acidic seas. In normal years, they have to clear out barnacles and mussels from their intake pipes every three months. They haven’t seen any of that growth in a while, she says:

That was the thing that was even more surprising. I think the really bigger issue is what’s happening to the natural species in these conditions—stuff we can’t control. I just don’t know what’s going to happen.

In our next post, we’ll talk to others in the seafood industry about what the future may hold.

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