Photo by Jonathan MacKay.

The birth of the California Current Acidification Network

When oyster larvae started dying in record numbers, California Sea Grant jumped into action

Tomales Bay, a serenely beautiful inlet an hour north of San Francisco, has been home to shellfish cultures for centuries. In 1983, Terry Sawyer too joined two partners in tending a five-acre oyster lease in the inlet’s sheltered water in the hours after his then-day job as an aquarist at the Monterey Bay Aquarium. By the mid-2000s, their Hog Island Oyster Company had grown into a thriving business that included an oyster bar in San Francisco’s historic Ferry Building.

Then, abruptly, Sawyer couldn’t find any more baby oysters to grow. He’d long bought tiny seed oysters from commercial hatcheries along the Pacific Coast, which produced billions of larvae in a typical year. Suddenly, most of these larvae were dying. “The hatcheries were experiencing unusually high mortalities,” says Sawyer. “At the critical moment, when we needed to plant our seed oysters, none were available.”

Sawyer wasn’t the only one who noticed that something was amiss. Elsewhere on the coast, sea urchin diver Bruce Steele started to realize that the ocean was changing and that this threatened shellfish such as oysters and urchins. Steele’s wife, Diane Pleschner-Steele, then the executive director of the California Wetfish Producers Association alerted California Sea Grant. “We saw this as a serious problem and acted quickly,” says Russ Moll, director of California Sea Grant at the time. 

Spurred by the concerns of Steele and the shellfish industry, California Sea Grant coordinated a series of meetings that culminated in a workshop held in Costa Mesa, California, in July 2010, which proved to be pivotal. The workshop brought together an unusually broad coalition of shellfish farmers, scientists and government representatives. Jointly, they not only locked down the cause for the mass deaths of the baby oysters but also laid the groundwork for an extraordinary partnership called the California Current Acidification Network or C-CAN , which would shelter the West Coast’s billion-dollar shellfish industry from the new threat.


“We walked out of that meeting 100% convinced.”

Initially, even the experts didn’t understand why the oyster larvae were dying. Some thought this could be a bacteria problem. 

At the workshop, various groups that usually work in isolation — the shellfish growers tending to their cultures, the biologists conducting experiments in the lab, the chemists studying the ocean’s properties — compared notes. Afterward, “we walked out of that meeting 100% convinced that the problem was ocean acidification,” says Steve Weisberg, the director of the Southern California Coastal Water Research Project (SCCWRP), which hosted the workshop.

Scientists had already known that the ocean was turning more acidic as it absorbed increasingly large amounts of the carbon dioxide (CO2) that human-centered fossil fuel use deposits into the atmosphere. As the gas dissolves into the sea, it forms a weak acid. But hardly anybody had expected this to pose a problem for another 50 years or so.

What the assembled experts realized was that this acid was, at times, already dissolving so much of the ocean’s minerals — including calcium carbonate, the substance that oysters and other mollusk use to build their shells — that it had become a threat to the animals. “It was, ‘Oh, wow, climate change is starting to affect the biology,’” says Weisberg. And thanks to its geography, the West Coast’s shellfish industry found itself at the epicenter of the crisis.

Baby oysters in hand. Courtesy of Priya Shukla.
A grown oyster can reach four to six inches in diameter. But these baby oysters are still tiny and particularly vulnerable to ocean acidification. Courtesy of Priya Shukla.

Winds on the West Coast often blow from land to sea and push ocean surface waters away from the shore. As this happens, colder and nutrient-rich water from the deep rises to replace it. These upwellings make the waters along the West Coast some of the most biologically productive and ecologically diverse in the world. But the water that rises from the deep is also naturally more acidic because as dead marine life sinks into the deep, then decomposes, it produces CO2. 

When the already CO2-enriched upwelling deep sea rises to the surface and encounters even more carbon dioxide from the atmosphere, it turns “corrosive,” says former California Sea Grant director Moll.

This hits shellfish hatchlings particularly hard. Oyster larvae build their first protective shells within six hours after emerging from the egg. The shells protect the larvae as they float in the water column, where they’ll remain until they’re large enough to attach to rocks or other substrates. 

If calcium carbonate is scarce on the day of hatching because the wind has caused mineral-dissolving deep water to well up, the effort of building the shell can easily overwhelm young oysters. Those that don’t die outright become highly susceptible to disease and predators. If any survive at all, they grow unusually slowly.


A solution is born

But figuring out the “why” didn’t by itself help the growers, who at the time couldn’t even be sure when conditions were bad. Back then, only a few stations monitored the Pacific’s pH level (or water acidity), and those were located on the open ocean. 

Conditions in the shallow shore estuaries, where the aquafarmers culture their bivalves, tend to be vastly different. Plus, they can fluctuate wildly from day to day as the tides, sunlight, algae photosynthesis and freshwater coming in from the rivers change the water’s chemistry. Not knowing when this happened, the growers were flying blind—only realizing that the water had turned corrosive as they fished thousands of dead hatchlings from their cultures. 

Person in water holding oyster bag. Courtesy of Hog Island Oyster Co.
Getting up-to-date information on the oceans’s fluctuating acidity allows growers to counteract an erosive pH by adding minerals to the water. Courtesy of Hog Island Oyster Co.

With the Costa Mesa workshop came a solution. “Everybody said, ‘It’s such a good thing how we brought people together and it developed into an ongoing relationship between the scientists and industry,” says Weisberg. “One of the focal points became monitoring.” From this, the California Current Acidification Network was born.

C-CAN, as the network is known, deployed sensors at the shellfish farms. While the workers flipped oyster racks and sorted through floating bins full of seedlings, the sensors measured things such as the amount of calcium carbonate minerals in the water. Scientists then analyzed the data. “We turned the headlights on” ocean acidification, says Sawyer.

It became a game changer. Having up-to-date information on the water’s fluctuating acidity allowed growers to let their oysters hatch when the conditions were benign. They can also add minerals to the hatcheries’ water that neutralize the ocean’s surplus acidity. 

“We now buffer the water constantly,” says Sawyer, whose company hatches its own shellfish these days. ”It's worked very well for us.


Looking ahead

Soon, there were half a dozen Coastal Acidification Networks around the country that adopted C-CAN’s principles. But eventually, even C-CAN won’t be enough. As carbon  emissions keep climbing, ocean acidification continues to worsen. The average pH of the surface ocean has dropped by 0.1 units since the start of the industrial era, which translates to about a 30% increase in ocean acidity. 

By the turn of the next century, it is projected to fall an additional 0.4 to 0.5 units. Even adult shellfish are now starting to be affected.

Sawyer, whose company now leases 160 acres in Tomales Bay plus 120 acres in Humboldt Bay, is trying to develop brood stock more resistant to acidification. But he foresees a time when growers might have to retreat. “Shellfish farming will probably become an on-land culture with completely modified water,” he says.

He is getting frustrated trying to get more attention to the issue from policymakers and regulators. “As a society, we are not facing the truth and moving at a glacial pace." There are still things we can do, he says. “But we need to take care of the ocean. Then everything else falls into place. It may sound simplistic, but it's the truth.

About California Sea Grant

NOAA’s California Sea Grant College Program funds marine research, education and outreach throughout California. Headquartered at Scripps Institution of Oceanography at the University of California San Diego, California Sea Grant is one of 34 Sea Grant programs in the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce.