The recovery of Northern California’s once-great kelp forest may come down to dropping bricks to the bottom of the ocean.

Earlier this month, Bay Area researchers did just that: They made baby kelp grow on twine in a lab, then wrapped the twine around clay bricks and deposited them into Drakes Bay, a part of Point Reyes National Seashore that was once dense with the golden, towering strands of seaweed.

“The hope is that they’ll stay in one place long enough for the kelp to grow up and be able to produce its own spores,” said Rietta Hohman, the kelp restoration project manager at the Greater Farallones National Marine Sanctuary, who wore an orange life vest on the deck of the sanctuary’s research vessel. 

The bricks are an attempt to revive lush underwater habitats — often compared to giant redwood groves but with nourishment for an even greater diversity of life, from shellfish to seals  — in Northern California waters where the rocky sea bottom is now dominated by purple sea urchins and little else. 

Restoration has become increasingly urgent: The kelp forest declined by more than 90% during the past decade along the Sonoma and Mendocino county coasts, thanks to a cascade of environmental catastrophes including the insatiable sea urchin. 

Scientists, divers and nonprofits have been trying to revive it, and the new program at Drakes Bay is part of the sanctuary’s effort to restore 27 acres of kelp forest along Sonoma County. It is the most ambitious to date, due to receive close to $9 million in state and federal funding and involving at least five universities.

And, it’s the first to use algae-covered bricks.

“We’ve seen a global loss of kelp forests,” said Hohman, who also works for the nonprofit Greater Farallones Association and hopes the program can be a model for scientists working on the same problem worldwide. “The scale of loss is tremendous.”

The restoration will take place within the marine sanctuary, 3,300 square miles of protected waters from Marin County to Mendocino County where about 80 miles of coastline have lost kelp forest and with it opportunities for recreational abalone diving.

“Kelp forests are incredibly amazing ecosystems,” said Kristen Elsmore, who leads kelp management for the California Department of Fish and Wildlife, which is involved with the project. “They support so many species, but also the connection with humans and how people engage with those ecosystems is very important, particularly to the North Coast community.”

Restoration will be twofold: The bricks will be one of several methods they’ll try for planting new kelp, and professional divers will remove purple sea urchins from specific areas. The urchins, which completely took over the environment after their main predator, the sunflower sea star, died off from disease starting in 2013, are one of the major reasons the kelp forest hasn’t come back.

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“Obviously, we can’t remove urchins from that entire stretch of the coastline. That’s millions and millions and millions of pounds of urchins,” said Hohman. 

Instead, the team has identified areas in Sonoma County where they think restoration will stick, based in part on kelp’s past abundance: Fort Ross, Timber Cove, Stillwater Cove and Ocean Cove, all located north of Jenner, while Drakes Bay will be used for experimentation. Bull kelp, the type that grows on the North Coast, is an annual plant that grows each spring and dies off in winter. The hope is that once it is re-established in those areas, it will release more spores and naturally reproduce on its own. 

They chose Drakes Bay for the pilot project because it has similar conditions to the restoration spots in Sonoma County but is easier to access. The downside is that divers won’t remove urchins there because of the danger of encountering white sharks.

Early on June 8, the sanctuary’s research vessel left Sausalito as the sunrise lit up the San Francisco skyline and tinted the sky orange-silver. The boat approached a part of the bay called Double Point, where jutting land creates a small inlet. With seabird breeding season in full swing, common murres perched on a floating log like shipwreck survivors and nested on guano-covered sea rocks alongside cormorants and sea gulls. 

During the previous two days Hohman’s research team had dropped 140 bricks wrapped with kelp-covered twine into specific areas of the bay. The weight of the bricks is seen as a plus in the rugged northern coast.

The technique was developed by Brent Hughes, assistant professor at Sonoma State University. Hughes talked about the importance of the kelp forest at a Bodega Bay meeting last month focused on returning the California sea otter to the Sonoma coast.  The otter, a sea urchin predator, was hunted to extinction in the area. “Right now we’re trying to protect that last 10%,” of the kelp forest, he said.

To inoculate the twine with kelp, researchers gather spores from bull kelp and put them in a swirl tank of water until they become what are called gametophytes. Those fertilize each other and become sporophytes, basically mini kelps. Finally, they allow the microscopic sporophytes to grow on the twine before wrapping it around the bricks. 

On June 8, researchers replaced sensors on a mooring in the bay that keeps track of environmental factors like salinity, temperature and dissolved oxygen so they can see if certain conditions may be more or less beneficial for kelp.

They also deployed a remotely operated vehicle — an underwater robot about the size of a laptop — to look for bricks they planted last fall and signs of kelp. Hohman’s colleagues gathered around her phone as the video showed the drone bouncing along the rocky sea floor, past sea stars, anemone and purple urchin, but no bull kelp — or bricks. But that didn’t mean they were not there somewhere. It’s a big bay.  

Later this summer, they’ll start urchin removal and kelp planting in Fort Ross and Timber Cove, and return to Drakes Bay in September for planting and more underwater and drone aerial surveys to see where the canopy grows.

Future experiments will involve other planting methods — including dropping mesh bags full of spores to the sea floor.   

Other recent attempts to save the kelp forest in California have included targeted volunteer efforts to cull urchins with hammers and even suck them up with vacuums. In 2021, density of kelp increased significantly in a small area in Monterey Bay called Tanker Reef after volunteers culled a half million urchins.

But just removing urchins alone does not appear to be the answer for year-over-year restoration, said Tristin McHugh, kelp project director at the Nature Conservancy, which recently began working with partners to plant kelp on the sea floor after years of urchin removal efforts in Mendocino County, where a kelp uptick did occur in 2021.

The goal, she said, is finding a way to “catalyze the resurgence of the forest — give it that little boost it needs to tip the ecosystem from an urchin barren into a kelp forest.” 

Fortunately, Hohman said, urchins go through boom and bust cycles. 

“Eventually there will be a bust of some sort. But we can’t really wait around for that because we’re going to lose our local bull kelp populations, and with that the whole ecosystem,” she said. “The option of doing nothing is not an option.”

Source:

Tara Duggan at San Francisco Chronicle

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