MOSS LANDING – Over the past three years, thousands of Olympia oysters have been bred in a lab and planted on Elkhorn Slough in an ambitious effort to combat local extinction. And the iconic creatures seem happy, vigorous and warm in their new home.
But they don’t make enough babies.
Scientists working with Olympia oysters, affectionately nicknamed “Olys” – the only oyster species native to the West Coast – are puzzled, particularly because the shells placed in the muddy quagmire have a good survival rate compared to others. oyster restoration sites.
Over the past decade, researchers have discovered new baby Olys in the quagmire in just two of those years – and only a handful of them.
“We don’t know what the problem was,” said Kerstin Wasson, assistant professor at UC Santa Cruz and research coordinator at the Elkhorn Slough Estuarine National Research Preserve.
With support from universities, environmental groups and government agencies, researchers at nearly 40 West Coast sites are trying to restore Olympia oysters to places where they have always thrived.
One of the main reasons for these efforts, scientists say, is that oysters are an essential part of estuarine ecosystems, often referred to as the “nurseries of the sea.” Oysters filter pollutants from the water and provide protection for other species by creating crevices for fish and invertebrates.
“They provide habitat for many different animals, including baby fish that become 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’s coastlines from wave erosion, a problem that is expected to worsen with climate change. Creating oyster reefs, marine scientists say, can reduce erosion by acting as natural breakwaters.
Olys are the only native species of oyster on the west coast. They have lived here for at least 10,000 years and were part of the diet of the native people of California.
Demand for oysters skyrocketed during the Gold Rush in the mid-1800s. Popular with miners, the Hangtown Fry quickly became Northern California’s most expensive breakfast. Containing bacon, common guillemot eggs from the Farallon Islands and oysters from the San Francisco Bay, it costs around $6, or about $165 in today’s currency.
To meet demand, oyster farmers introduced the East Coast Atlantic oyster and the Japanese Pacific oyster to the West Coast to replace the smaller, slow-growing native oyster famous for its sweet flavor. , brackish and almost metallic.
The Atlantic oyster, however, has failed to establish itself in many estuaries. Thus, the Pacific oyster eventually became the dominant oyster species on the West Coast. In 1931 alone, an oyster company planted 15 million baby Pacific oysters in Elkhorn Slough on floating rafts.
Since the 1970s, however, researchers have not spotted significant populations of Pacific oysters in the swamp. And the Olys are on life support.
In 2007, researchers estimated that there were only 5,000 Olympias at Elkhorn Slough. And in 2018, that number dropped to less than 1,000, prompting scientists to place 2,500 lab-produced baby oysters in the swamp.
Most of the oysters survived, but they had no offspring. So, in early June, scientists stepped up their efforts and removed about 600 adult oysters from the swamp and placed them in rows of containers at the Moss Landing Marine Lab.
The researchers heated the water in the containers to between 60 and 64 degrees Fahrenheit, hoping love would soon be in the water. In nature, these ideal temperatures for fertilization only occur once or twice a year.
“Olympias are different from other oysters because they perform internal fertilization,” Harris said. “Females collect sperm and fertilize their eggs in their pallial cavity. Then after about two weeks of brooding, the females release live larvae.
After one to two weeks in the warm water, Harris said, the microscopic baby oyster larvae were free-swimming. He and his colleagues then strained them into different containers containing hard shells and ceramic tiles in the hope that the larvae would find a hard surface to attach themselves to so they could turn into oysters.
After two months, about 9,000 baby oysters were the size of a Sharpie point. After four months, they were the size of a dime.
In early December, the search team and dozens of enthusiastic volunteers arrived at the swamp in knee-high boots, waders and wetsuits to wade through the sulfur-rich mud at 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 clear of the muddy bottom of the quagmire.
“I was mainly thinking about placing the oysters at the right height because if they are too low, they suffocate in the mud,” explains Rikke Jeppesen, estuarine ecologist at the Elkhorn Slough reserve. “And if they’re too high, they get overrun by non-native species.”
No one really knows what’s wrong with Elkhorn. But researchers have their guesses.
One possibility, Harris said, is that oysters focus their energy too much on survival rather than reproduction.
Oysters filter water, but they don’t digest everything they filter, Harris explained. Particles that they do not absorb into their tissues are excreted as pseudo-feces, tiny mucus packets deposited on the mud floor. The process forces the oysters to expend energy that could have been used to make babies.
But determining whether this is the primary reason for the lack of hatchling oysters will be difficult because so many factors affect the production of pseudofeces – everything from the salinity of swamp water to the amount of microscopic solids floating there.
To give the Olympia oysters a fighting chance at Elkhorn Slough, Wasson and his team plan to grow 50,000 more oysters and plant them in different spots in the swamp to see if they have more success.
Chela Zabin, an ecologist at the Smithsonian Environmental Research Center in Tiburon, said oyster restoration projects face a tough climb.
Intense heat waves triggered in part by climate change, when combined with low tides, can lead to mass kills of intertidal animals such as mussels, clams and oysters. That’s what happened in British Columbia last year and in Bodega Bay in 2019.
Despite the worrying signs, California scientists say they will remain deeply committed to the return of native oysters.
“I consider them a pretty iconic species,” Zabin said. “Oysters are part of what makes the West Coast West Coast.”
Plus, she added, “they’re cool animals.”
All about Olys
• Nicknamed Olys, Olympia oysters are West Coast natives that live in bays, estuaries and tidal pools.
• They are sequential hermaphrodites, beginning life as males and becoming females for spawning. They can change sex throughout their life.
• Oysters are named after the town 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 are 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