The plight of Moss Landing’s Olympia oysters


MOSS LANDING — In the past three years, thousands of Olympia oysters have been raised in a laboratory and planted in the Elkhorn Slough in an ambitious effort to fend off local extinction. And the iconic creatures seem happy, hale and hearty in their new home.

But they’re not making enough babies.

The scientists working with the Olympia oysters, affectionately dubbed “Olys”  — the West Coast’s only native species of oysters — are puzzled, particularly because the shellfish being planted in the muddy slough have a good survival rate compared with other oyster restoration sites.

In the past decade, researchers have discovered new baby Olys in the slough in only two of those years — and only a handful of them at that.

“We don’t know what the problem has been,” said Kerstin Wasson, a UC Santa Cruz adjunct professor and the research coordinator at the Elkhorn Slough National Estuarine Research Reserve.

With the support of universities,  environmental groups and government agencies, researchers at nearly 40 West Coast sites are trying to reestablish Olympia oysters in places where they have historically thrived. The San Francisco Bay Area has several sites, including Crissy Field in San Francisco, China Camp State Park in Marin County and Point Pinole Regional Shoreline in Richmond.

One big reason for the restoration projects, scientists say, is that oysters are an essential part of the ecosystems of estuaries, often called the “nurseries of the sea.” Oysters filter out pollutants from the water and protect other species by creating crevices for fish and invertebrates.

“They provide a habitat for a lot of different animals, including baby fish that grow up to be fish that we eat,” said Jacob Harris, a San Jose State University graduate student at Moss Landing Marine Laboratories who studies Olympia oysters.

Here are three of the 600 or so adult oysters used to create thousands of Olympia baby oysters in Moss Landing Marine Lab. In early December, a research team and volunteers planted the baby oysters into Elkhorn Slough. (Photo by Brian Phan) 

Researchers say the beloved bivalves could also help protect California shorelines from wave erosion, a problem that is expected to worsen with climate change. Creating reefs of oysters, marine scientists say, can reduce erosion by acting as natural breakwaters.

Olympia oysters are named after Washington state’s capital, the city of Olympia at the southern end of Puget Sound, where most of the West Coast’s oysters are still farmed.

Olys are the only native species of oysters on the West Coast. They have lived here for at least 10,000 years and were a part of the diets of California’s Indigenous people.

Demand for the oysters exploded during the Gold Rush in the mid-1800s. Popular with miners, the Hangtown Fry quickly became Northern California’s most pricey breakfast. Containing bacon, Common Murre eggs from the Farallon Islands and oysters from San Francisco Bay, the meal cost roughly $6, about $165 in today’s currency.

Some historians say that the miners’ expensive tastes led to the overharvesting of the Olympia oysters all along the West Coast. That, coupled with the rapid decline of water quality in San Francisco Bay caused by hydraulic mining upstream — triggered the collapse of the native oyster populations, historians have concluded.

Juvenile Olympia oysters growing on old clamshells are tied to stakes for placement in the mudflats at Elkhorn Slough. (Karl Mondon/Bay Area News Group) 

In recent years, however, some scientists and California historians have called the miners’ role in the Olys’ decline an exaggeration because no one really knows how many Olympia oysters were in San Francisco Bay before the Gold Rush.

Because of the high demand for their product, West Coast oyster farmers introduced the Atlantic oyster from the East Coast and the Pacific oyster from Japan to the West Coast to replace the tinier, slow-growing native oyster — famed for its sweet, briny and almost metallic flavor.

The Atlantic oyster, however, failed to establish itself in many estuaries. So the Pacific oyster eventually became the West Coast’s dominant oyster species.

Oyster farming was so successful in Elkhorn Slough that it once supplied 16% of California’s total annual harvest. In 1931 alone, West Coast Oyster Farms planted 15 million baby Pacific oysters in Elkhorn Slough on floating rafts.

Since the 1970s, though, researchers have not spotted any significant populations of Pacific oysters in the slough. And the Olys are on life support.

By 2007, researchers estimated there were only 5,000 Olympias in Elkhorn Slough, where once there were millions. And by 2018, that figure fell to fewer than 1,000, prompting scientists to put 2,500 lab-produced baby oysters into the slough.

Most of the oysters survived, but they had no offspring. So in early June, scientists stepped up their efforts and took about 600 adult oysters from the slough and placed them into rows and rows of containers at Moss Landing Marine Lab.

Juvenile Olympia oysters growing on old clamshells are tied to stakes for placement in the mudflats at Elkhorn Slough Reserve by Monique Fountain (front) and Kerstin Wasson in Moss Landing. (Karl Mondon/Bay Area News Group) 

Researchers heated the water in the containers to between 60 and 64 degrees Fahrenheit, hoping that love would soon be in the water. In the wild, those ideal temperatures for fertilization occur only one or two times a year.

“Olympias are different than other oysters because they do internal fertilization,” Harris said. “The females collect the sperm and fertilize their eggs in their mantle cavity. Then after about two weeks of brooding, the females release live larvae.”

After one to two weeks in the warm water, Harris said, microscopic baby oyster larvae were swimming free. He and his colleagues then filtered them into different containers containing hard shells and ceramic tiles in the hopes that the larvae would find a hard surface to attach themselves to so they could grow into oysters.

At the two-month mark, about 9,000 baby oysters were the size of a Sharpie dot. After four months, they were the size of dimes.

In early December, the research team and dozens of eager volunteers arrived at the slough in knee-high boots, chest waders and wetsuits to trek through the sulfur-rich mud during low tide.

The shells and tiles were then hung with zip ties connected to poles stuck in the mud, allowing the young oysters to stay off the mucky bottom of the slough.

Kerstin Wasson carries stakes holding juvenile Olympia oysters to the mudflats at Elkhorn Slough in Moss Landing, Calif. The native oysters have been in decline for decades but are now the focus of an intensive restoration project. (Karl Mondon/Bay Area News Group) 

“I was mainly thinking of setting the oysters at the right height because if they’re too low they suffocate in the mud,” said Rikke Jeppesen, an estuarine ecologist at the Elkhorn Slough Reserve. “And if they’re too high, they get overgrown by nonnative species.”

No one really knows what’s going wrong at Elkhorn. But researchers do have their guesses.

One possibility, Harris said, is that the oysters are focusing too much of their energy on survival rather than reproducing.

Oysters filter water, but they don’t digest everything they filter, Harris explained. The particles that they don’t absorb in their tissues are excreted as pseudofeces, tiny mucus packages deposited onto the slough floor. The process forces the oysters to expend energy that might have been used to make babies.

But determining if this is the reason for the lack of newborn oysters will be difficult because such a large number of factors affect the production of pseudofeces — everything from the salinity of the slough water to the amount of microscopic solids floating in it. Harris is now working on a project aimed at determining whether the age of the oysters and the temperature of the water could be affecting pseudofeces production.

To give Olympia oysters a fighting chance in Elkhorn Slough, Wasson and her team plan to grow 50,000 more oysters next year and plant them in different locations throughout the slough to see if they are more successful.

Chela Zabin, an ecologist at the Smithsonian Environmental Research Center in Tiburon, said oyster restoration projects as a whole face an uphill climb.

“For the future, there’s definitely a lot of concerns,” she said. “They mostly have to do with climate change.”



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