MOSS LANDING — In the past three years, thousands of Olympia oysters have been raised in a laboratory and planted in 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 placed 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.
One big reason for the efforts, 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 provide protection for 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.
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.
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, it cost roughly $6, about $165 in today’s currency.
To meet the demand, 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. In 1931 alone, one oyster company 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. And by 2018, that figure fell to fewer than 1,000, prompting scientists to place 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 of containers at Moss Landing Marine Lab.
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.
“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 main 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.
To give Olympia oysters a fighting chance in Elkhorn Slough, Wasson and her team plan to grow 50,000 more oysters 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 face an uphill climb.
Intense heatwaves triggered in part by climate change, when combined with low tides, can cause massive die-offs of intertidal animals such as mussels, clams and oysters. That’s what happened in British Columbia last year and Bodega Bay in 2019.
Despite the ominous signs, California scientists say they will remain deeply committed to the return of the native oysters.
“I consider them a pretty iconic species,” Zabin said. “The oysters are part of what makes the West Coast the West Coast.”
Besides, she added, “they are cool animals.”
All about Olys
• Nicknamed Olys, Olympia oysters are West Coast natives that live in bays, estuaries and tidal pools.
• They’re sequential hermaphrodites, beginning their lives as males and becoming females for spawning. They can switch sexes throughout their lives.
• The oysters are named after the city of Olympia, Washington, at the southern end of Puget Sound.
• Their shells range from white to dark purple, sometimes with yellow or brown stripes.
• They’re the smallest oysters in North America, reaching a maximum size of 3 inches in length.
• Predators include birds, crabs and rays.
Source: California Sea Grant
Source: www.mercurynews.com