Did you know that oysters can swim? At least, for a part of their lives.
Katie Rodriguez here, after an early, brisk morning spent in Elkhorn Slough’s Oak Marsh, where I learned a very fun fact: Baby oysters spend their first couple of weeks propelling themselves through the water column, beating tiny hairs called cilia before cementing themselves.
“The larvae are gregarious settlers,” says Kerstin Wasson, researcher coordinator at Elkhorn Slough National Estuarine Research Reserve. “They like to settle where there's existing oysters, so by putting these out, we should be attracting more settlements to the area.”
She’s holding clam shells speckled with tiny oysters that look like delicate fingernails with a gorgeous aqua blue sheen. She, alongside stewards with the Amah Mutsun Tribal Band, Amah Mutsun Land Trust and The Nature Conservancy, let me tag along to see an oyster outplanting project that’s been years in the making.
In the past, estuaries across California used to have dense oyster reefs, or vast aggregations of oysters layered on top of one another forming complex underwater structures. Today, that critical habitat has disappeared.
“There are no large extensive oyster beds in California today,” she says. “Oyster beds were to temperate waters what coral reefs are to tropical waters: really important.”
These beds once sheltered species like fish and crabs, filtered water, stabilized shorelines, recycled nutrients, and were a valuable food supply. Over time, Elkhorn Slough and other estuaries lost so many oysters there wasn’t enough to make babies.
Today, the Slough’s oyster population is around 50,000—up from 1,000 in 2018, largely thanks to this restoration project. The goal is 10 million.
“We’ve done studies of what season to put them out, what size, what affects mortality,” says Luke Gardner of The Nature Conservancy. “You need to find that happy medium between survivorship and the actual cost or effort that goes into it.”
The baby oysters are raised at Moss Landing Marine Laboratories before being outplanted along the shoreline at Oak Marsh. Tribal stewards and researchers take all kinds of measurements of the oyster clusters before they’re planted, and periodically go back to track their growth.
The Amah Mutsun Tribal Band, whose ancestral lands include Elkhorn Slough alongside those of neighboring Ohlone people, have been central to this effort. The tribe is considered a leader in reconnecting to estuarine habitats and shellfish restoration. Oyster restoration, alongside broader habitat restoration, is a huge part of their oral history and cultural knowledge.
“My father would take us to the rivers and we would take out invasive plants,” says Catherine Rodriguez, an Amah Mutsun elder. “We were in relationship with the river at all times. It’s a constant relationship with all species, and then the next generation goes in and that knowledge is handed down.”