In Marin, driving along the 101, it’s not surprising to glance out the window and spy a great blue heron fishing or a black-necked stilt wading through eelgrass. They are reminders that our coastline was once mostly tidal marshes.
For centuries, we’ve reclaimed wetlands for development. “When you look at what’s been filled — all the way from the hills to the bay, well…” said Barbara Salzman, president of the Marin Audubon Society. “It’s important to keep the little pieces we have left.”
Ironically, climate change is stepping in to determine the fate of Marin’s marshes, too. One foot higher oceans, which may occur as soon as 2050, could restore wetlands to historic levels of the 1850s. And as the sea rises, stronger waves will change the shore edge, driving animals and plant species inland. And if we don’t make room, our natural world will degrade further.
That’s why county leaders and planners agree that the threat of sea level rise is an opportunity to improve our coastal environment.
Adapting To Higher Seas
What will be dry land and what will be marsh? A first adaptation step is deciding where to draw the “resilient edge,” the line between land and water. Then it’s a question of how the changes under consideration will affect the habitat. “You have to weave together a lot of different things,” said Chris Choo, assistant director of the Marin County Community Development Agency. “We have to map a way forward.”
Planners agree on four main adaptation strategies: raising buildings and infrastructure like roads; hardening the edge where water encroaches on development; reducing the impact of wave action with nature-based solutions; and floating architecture where there’s no way to avoid the incoming sea.
Two of the strategies — elevating and floating homes and buildings — already exist in Marin. Many structures are on pilings in tidal communities. The Sausalito houseboat marinas have raised parking lots, and the newest dock rises and falls with the tides, keeping utilities safe from saltwater.
Hardening the land-water edge usually involves building a seawall, a solution that’s often chosen when there isn’t much space. “A wetland can’t be just plopped down,” Choo said, adding that in an urban area like San Rafael there isn’t room for a sloping marsh.
But seawalls disturb where the water goes, and marine life experience what’s called a “coastal squeeze,” losing places to feed and spawn and thrive.
Instead, there’s good science to back green solutions.
Bringing Back Oysters
“Oyster reefs are just as effective, if not more, as those highly engineered solutions we often see, like riprap and seawalls,” said Katharyn Boyer, professor at San Francisco State and director of the Estuary and Ocean Science Center. “And, they provide habitat.”
Oysters are the heroes of the sea. Olympia oysters slow erosion by catching sediment and filtering out pollutants as they feed, such as those that cause algal blooms. One oyster purifies eight to 12 gallons of water per day. Female oysters disperse fertilized oysters in a plankton-like form, which swims around for two weeks, then settles on sheltered estuaries, which is why it’s vital to provide reefs in tidal zones.
In 2012, Boyer, an expert in the restoration and conservation of coastal habitats in a changing climate, led the first Living Shorelines Project in San Rafael at Spinnaker Point. Her team created a series of manmade oyster reefs with and without eelgrass plantings. They used shell bag mounds to see if these reefs would attract oysters, reduce the flow of water and accumulate sediment.
“It was wildly successful — there are millions of oysters out there,” she said, noting that despite flaws in the design, the reefs did accumulate sediment and slow wave action.
Building on that first success, they built new modular and more lightweight reefs. In 2020, they installed them in three areas in Marin: in the same location in San Rafael; at the north end of the Estuary and Ocean Science Center, between Tiburon and Corte Madera; and at Dunphy Park, in Sausalito.
All three succeeded, with especially ideal conditions in Sausalito. “The biggest Olympia oysters anyone has seen are at Dunphy Park,” Boyer said. They have found individual oysters in the 40–50 millimeter range (1.5–2 inches). That’s about 10 millimeters larger than what’s normally found in San Francisco Bay.
Restoring Marshes
It turns out the protected shoreward sides of oyster reefs are also ideal for eelgrass. Eelgrass, a native flowering plant, forms beds above ground and their rhizomes help keep sediment in place. They provide essential spawning space for herring and other fish as well as benefits for the planet.
“Eelgrass is a climate powerhouse,” Boyer said. “They capture carbon and they can raise the pH of the water to counter the acidification of the ocean.” More acidic oceans are bad news for shellfish, and their decline would impact the whole ocean ecosystem.
Bothin Marsh in Mill Valley, stretching from Blithedale Avenue to Route One, is one place where bringing back a healthy wetland will encourage eelgrass growth. The multiuse path that divides the marsh is going to be moved to the perimeter, close to the shops and restaurants in Tam Junction. “We can give up a little and gain a lot,” Choo said. The restored 1200-acre marsh will be rebuilt to reduce flood risk and provide saltwater at the right depth for the plants to get sunlight and live. The terrain will become varied in height, enabling animals to hide at high tide from predators and rising water. The approved project is expected to be completed in 2030.
In San Rafael, the rehabilitation of Tiscornia Marsh is already underway. The Marin Audubon Society teamed up with the Multicultural Center of Marin with a grant from the Marin Community Foundation to fix this critical habitat near the Canal. “The existing marsh was eroding,” Salzman said. The project will open the diked marsh to tidal action, providing transition zone habitat for wildlife and flood control.
The Marin Audubon Society also worked to restore wetlands in Bahia near Novato. “The marsh was basically barren,” she said. “The most difficult part is dealing with the invasives.” Volunteers helped plant natives, which needed watering for a few summers until becoming established.
Living With Water
Supervisor Stephanie Moulton-Peters is optimistic that Marin will make choices that will simultaneously prepare the county for a higher sea and enhance the environment. “There are many examples of communities living with water,” she said. “People around the world have figured it out, and we can, too.”
We don’t need to look further than Larkspur to imagine a future where people and wildlife can co-exist. Near the ferry terminal, 48 homes rest on pilings above the tidal marsh.
Walking the half-mile Greenbrae Boardwalk to and from their car is not a problem for local Wanden Treanor and her partner. “It keeps us active, and it’s good for our mental health,” she said.
Although some of the homes will need to be raised higher, and safeguards need to be added to reduce wave action from the larger ferries, the community happily coexists with the snowy egrets and herons.
“We’ve lived here for four decades,” Treanor added. “It’s home.”
Feature image by @aeg7photography
