The time for oysters

 

Next time you find yourself in the San Francisco Bay Area, which for your own sake will be soon, I hope, there are a few things you ought to do. Walk across the Golden Gate, go one of the Thursday “NightLife” events at the Academy of Sciences and drive north to Tomales Bay and feast on fresh oysters from one of the local hatcheries.

T

he bridge may be a touristy stop, but it’s a beautiful one that no one regrets. The museum after dark is hottest ticket in town -- all the cool kids will be there, loving on science and displaying fashionable shoes. And the oyster feast is something to enjoy sooner rather than later, for oysters, and shellfish at large, may be on their way out.

The ocean’s acidity is increasing, fast enough to affect shellfish, so fast they may not be able to adapt and keep up.

Since the late 1950s geochemists have been concerned about climate-caused ocean acidity. However, a study published this April purports to be the first conclusive link that massive die offs in Pacific Northwest Oyster hatcheries have been due, at least in part, to climate-caused changes in ocean chemistry.

 

In contrast with many environmental problems, the chemistry of ocean acidification is simple and essentially without controversy. As nicely explained by Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, the chemistry of the ocean is driven by the chemistry of the atmosphere; more carbon dioxide in the air leads to more carbon dioxide dissolved in the water; these changes spell trouble for animals with shells made of calcium. The dissolved CO2 becomes carbonic acid -- a corrosive (just pop some chalk in a glassful of  soda and see what happens). And there is something else at play.

“The early growth stage for oysters is particularly sensitive to the carbonate chemistry of the water,” said George Waldbusser in a release from Oregon State University. Waldbusser is a benthic ecologist in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “As the water becomes more acidified, it affects the formation of calcium carbonate, the mineral of which the shell material consists. As the CO2 goes up, the mineral stability goes down, ultimately leading to reduced growth or mortality.”

The larval oysters were at times so impaired, so slow to grow at the study site, a commercial hatchery in Oregon’s Netarts Bay, rearing them commercially would not be cost-effective. Noticing die-offs several years ago, the Whiskey Creek Shellfish Hatchery suspected low oxygen or bacterial infections. Instead, by rearing oysters in different samples of ocean water, they saw oysters fail in low-pH water that had been taken during seasonal upwellings, when cold, deep, CO2-rich waters flooded the bay.

While this pushed the larval oysters over the edge, this is a bigger, longer-term problem for shellfish around the globe. The oceans absorb about a third of the carbon that humans put into the atmosphere. Since the start of the Industrial Revolution, they’ve become roughly 30 percent more acidic.

The Whiskey Creek hatchery, fortunately, is not out of business. Hatchery operators have been able to adjust, taking in water during times of the day when quality is at its highest.

While the news is good in the short-term, the longer view is a sobering one. Previous research by one of the study’s authors found that the water upwelled off the Oregon coast was last in contact with the surface 50 years ago, when atmospheric carbon was much lower. “Since atmospheric CO2 levels have risen significantly in the past half-century, it means that the water that will be upwelled in the future will become increasingly be more corrosive,” said Burke Hales, in the OSU release.

The oysters of Tomales are currently holding steady. A distributed partnership known as C-CAN operates a monitoring program, and hasn’t noticed any dramatic die-offs yet.

When I’m in my 80s, however, any oyster larvae left along the coast will be contending with the carbon dioxide dissolving in the ocean today. That’s true even if we are then spewing less carbon into the atmosphere. So I’ve pretty much given up hope of taking my grandkids to Tomales Bay oyster feasts.

Let’s just hope, at that point, I can still walk across the Golden Gate Bridge. And, if I’m very lucky, maybe those grandkids will take me to NightLife at the CalAcademy. We can visit the oysters preserved in alcohol, I’ll tell them how they used to taste: tangy, full of minerals, best eaten raw on the half shell with a squeeze of lemon, chased down with a lager.

Danielle Venton is a former High Country News intern and reporter for KRCB 91-FM in Sonoma County, California.  

Image(s): 1) Golden Gate Bridge, Brandi Korte/Flickr; 2) Tomales Bay Oyster Co., Dave Schumaker/Flickr.