The Tricky Art of Growing Oysters in the Lab So They Can Survive in the Field

On July 1, a foggy morning, Moss Landing Marine Lab researchers along with the Amah Mutsun Tribal Band, Amah Mutsun Land Trust and The Nature Conservancy, prepare to plant baby oysters in Elkhorn Slough’s Oak Marsh near Santa Cruz. This “outplanting” session is one of many that have happened over the years as part of a restoration project started in 2018.  The goal is to eventually plant 10 million oysters, a whole hectare, in the Slough.  As a photojournalist I’m tagging along to document this ambitious effort for KneeDeep. 

Conception begins at the Moss Landing Marine Labs aquaculture facility in Monterey County, where Olympia oysters broodstock are spawned. Eventually, millions of these oysters will be outplanted in the Elkhorn Slough, a winding estuary that extends inland from Monterey Bay. Pictured above is a controlled system where food for developing oysters is carefully grown. 

Growing oyster food — microalgae — is a delicate science. “The hardest part about growing oysters is growing the food for them,” says Luke Gardner, an aquaculture specialist at Moss Landing Marine Labs. Gardner compares growing microalgae to cultivating a garden. One has to manage a mix of environmental factors to keep weeds and unwanted organisms from taking over. They closely monitor the type of algae they’re using, the culture, what they’re cleaning the tanks with — all to make sure it has the right amount of nutrients to thrive, but not so much that the algae grows dense enough to turn the water too alkaline, where the pH is so high that the algae dies. 

Similar to how seaweeds have red, brown, and green species, so do microalgae. Here, researchers experiment with a variety of them representing different nutrient portfolios. One might have more protein, another might have a better amino acid — researchers experiment with a range of species to see which kind of food is taken up best by the oysters at different parts of their life cycle.   

Microalgae are the foundation of aquatic food webs. In an aquaculture setting, they need many of the same conditions found in the wild: light, proper nutrients like nitrogen and phosphorus, carbon dioxide, and the right temperature and salinity. But the plants also need a variety of wavelengths, represented by the different colors of light inside the photo bioreactor to create an optimal growing environment and prevent dense algae cultures from shading one another.

Gardner pulls out one of the adult oysters from a group resting on trays in the water. These oysters will eventually be responsible for breeding the next generation of babies to be planted at the Elkhorn Slough. The time for the oysters to breed is a bit of an unknown. The bivalves tend to start breeding when they’re “really happy or really unhappy,” Gardner says.

Olympia oysters are alternating hermaphrodites, meaning they change sexes throughout their adult lives. When they breed, one of these tubs will have millions of larvae; the successful ones get piped out into another tub and fed various types of microalgae as they grow and settle on a substrate.

On the foggy July morning, about a dozen people prepare to outplant the baby oysters in Elkhorn Slough’s Oak Marsh as part of a  continuing effort to regrow the local population. When famed marine biologist George MacGinitie began studying Olympic oysters and the other invertebrates in the estuary in the 1920s, he documented an oyster population that was flourishing, abundantly found throughout the estuary. Known as the only oyster native to the West Coast, the bivalve had sustained indigenous people for millennia. But a decade after MacGinitie arrived, their numbers had already greatly diminished as they were highly sought after by oystermen from the San Francisco Bay. Eventually, they became so rare that, for decades, they were not detected in surveys. 

The group walks along a path to the slough, where Indigenous archeological sites suggest that native Olympia oysters once lived in dense aggregations from the mouth of the estuary to its upper reaches for most of the past 7,000 years. Today, poor water quality from agricultural inputs, stagnant water in diked wetlands, and sediment from decades of decaying algal mats all post challenges to oyster survival in the estuary.

The group heads out during an especially low tide, ideal for planting the juvenile oysters in the mud. During king tides, the water will rise high enough to cover the levee. The Elkhorn Slough Reserve is gradually removing the levees throughout the estuary and is currently exploring whether some could be deconstructed and repurposed as oyster habitat.

Kerstin Wasson, research coordinator at the Elkhorn Slough National Estuarine Research Reserve in Moss Landing, explains how native oyster beds — which once stretched along the California coast — have largely vanished. Large, continuous oyster reefs are now absent from California, a loss that researchers with Moss Landing Marine Laboratories and its partners hope to reverse. Wasson likens oyster reefs to coral reefs, saying they provide critical habitat for numerous species and play an essential role in maintaining healthy coastal ecosystems.

Amah Mutsun Tribal Band members and other partners assemble the baby oysters before outplanting. In this case, clam shells were used as the substrate for which the baby oysters cemented themselves in clusters. The babies are gregarious settlers, explains Wasson, in that the oysters prefer to settle close to other existing oysters.

With fewer than 1,000 oysters, the native population remaining in the Elkhorn Slough in 2018 was so low it was nearing extinction, prompting the Native Olympia Oyster Restoration project. Moss Landing Marine Laboratories’ goal is to restore self-sustaining native oyster populations in the estuary. Oysters are ecosystem builders: individuals group together to create structures that help clean the water, stabilize sediments, and provide shelter for thousands of fish, crabs, and other marine life. 

Through their collaboration, project partners have developed guidance for achieving Olympia oyster restoration goals over the next 50 years in one of the state’s largest and most ecologically diverse salt marshes.

Before the oysters are outplanted, researchers collect baseline data from each “unit” — a tagged set of oyster shells attached to a line. They count the live oysters on each shell, measure the largest oyster and tag three shells covered with juvenile oysters. The information provides a baseline for comparing oyster survival and growth after outplanting.

Measuring tools and outplanting materials sit off to the side while the group gets ready to outplant. The morning began at 7 a.m. to coincide with peak low tide, and tribal members started with a short ceremony. The partnership is collaborative by design, leveraging science-based experimentation and community engagement to drive restoration.

Each “unit” clusters three clam shells covered in baby oysters and tagged for identification. The tiny specks of blue and green on the clam shells are the baby oysters that have taken root. A fun fact Wasson shares with the group is that oysters spend the first two weeks or so of their lives “swimming,” propelling themselves in the water with tiny hairs known as cilia, before choosing a place to cement themselves.

At the water’s edge at Oak Marsh, group members firmly press the stake attached to the clam shells into the sand. As the water rises, they will remain fully submerged except for during peak low tide.

Olympia oysters are the only native oyster on the West Coast of the United States. In response to the loss of this species, The Nature Conservancy formed “The Alluring World of Olympia Oysters,” a working group that includes the San Francisco Estuary Partnership, Hog Island Oyster Company, and other partners, to increase awareness of important species and scale restoration efforts in estuaries across the Bay Area.

The Amah Mutsun Tribal Band, whose lands, known as Popeloutchom, included the Elkhorn Slough area (along with other tribes that call this area home), is a leader among California tribes in reconnecting to estuarine habitats and engaging in shellfish restoration. Recently, it reinstated a robust tribal stewardship program through the Amah Mutsun Land Trust to restore oyster populations using cultural knowledge and community engagement. 

On the July day of the oyster planting, half a dozen members of the tribe joined others in shepherding the tiny oysters from indoors to out. The way Gardner explains it, there is a happy medium that has to be established in not only growing the oysters in the lab, but seeing survivorship in the field. Oysters that are too small may not be strong enough to survive the elements, while oysters that are larger require a lot more time and investment in the lab. “During summer, there’s more sun, the water’s warmer, so their food, the microalgae is going to be more dense,” he explains. “When you put them out in winter, you run the risk of big freshwater influxes coming down from the rain. Oysters are pretty good at dealing with that until there’s a lot of it.”

The group picks up a striped shore crab, plucked out of the levee. A variety of crab species have set up shop here, taking a liking to the gaps and spaces in the levee, partially caused by erosion and naturally occurring from old oyster shells and crab casings that litter the marsh. The initiative has increased the number of oysters from 1,000 in 2018 to more than 50,000 today, a boon for local estuary habitat.

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