Since kelp forests began disappearing from the California coast in the mid-2010s when a sea heat wave and voracious native sea urchins decimated them, people have tried to remedy the problem.
Today, one project is showing signs of success.
At a site called Tanker Reef in Monterey, just off the tourist shops and restaurants of Old Fisherman’s Wharf, the kelp forest has rebounded after volunteer divers killed more than half a million sea urchins since the spring 2021. The underwater area has slowly transformed from a so-called sea urchin barren, areas where the spiny purple creatures eat any remaining kelp, back to a leafy forest full of life.
It’s “really just a day and night difference. As if you were diving there in 2021, it was just rocks and sea urchins, truly devoid of life and diversity,” said Dan Abbott, director of the kelp forests program at project partner Reef Check. largely volunteer, who said it was the most successful so far in California. “Now you go and it looks totally different.”
Data collected at the site indicate that kelp density, measured by the number of individual plants called stipes attached to the ocean floor with multiple blades, increased from nearly zero to 1.5 per square meter, when voracious predators decreased from 8 to 1 sea urchin per square meter on a 2.5 acre site.
“It’s very encouraging to see such positive results,” Abbott said, referring to the first year of data from a three-year project.
The non-profit group Giant Kelp Restoration organized the volunteers who completed 1,070 dives and spent 800 hours culling sea urchins, working with state and federal agencies on the experimental project.
“When I was first scouting there, you could count the fish on two hands,” said Keith Rootsaert, founder of Giant Kelp Restoration. Then, “we started to see all these little fish coming, and then we saw bigger fish coming and eating the little fish.”
Rootsaert, who has a day job as a building systems engineer, has personally participated in around 200 of the dives. There are 150 volunteers in the group, all trained by local dive shops.
The kelp forests that covered hundreds of miles of coastline provided vital habitat for young fish, crabs and other creatures as well as the marine mammals and seabirds that ate them. In Sonoma and Mendocino counties, the size of the kelp forest decreased by 95% between 2014 and 2019, according to a UC Santa Cruz analysis. The Monterey Peninsula has not been studied extensively, but Abbott estimates that the size of its kelp forest is shrinking by about two-thirds over a similar period.
There are two main reasons, both related to climate change. The 2014-2016 marine heatwave reduced kelp growth, which depends on nutrients that accompany upwelling, when winds push warm water offshore and bring cool water from the depths. The warmer water also likely increased the severity of a disease that killed off one of the native purple sea urchin’s top predators, the sunflower starfish.
In March, the Biden administration awarded the Greater Farallones National Marine Sanctuary $2 million for kelp restoration on the Sonoma and Mendocino Coast, and the state’s Ocean Protection Council funded earlier projects. . The Tanker Reef project received very little funding, Abbott said.
While the North Shore has bull kelp, an annual plant that grows in the spring and dies during winter storms, Tanker Reef and the rest of the Monterey Peninsula have giant kelp, a perennial plant. Monterey also has sea otters, which eat purple sea urchins, but only if they contain meat – and most of them don’t because food is so scarce in the sea urchin barrens.
Giant Giant Kelp Restoration received permission from the state Fish and Game Commission to use small hand tools to destroy sea urchins at Tanker Reef during the project. Other restoration projects have collected sea urchins and then disposed of them or tried to find a use for them.
Rootsaert finds this too time-consuming. Additionally, leaving dead sea urchins in the ocean has the added benefit of providing food for fish, snails, and other marine animals.
After the project began, the volunteers began to notice that a large proportion of the invertebrates were under 1 inch or 1 year old, which meant the animals were still reproducing despite the starvation conditions. Also, there was no way to prevent sea urchins from infiltrating other areas.
“There’s this big area that’s full of sea urchins. And as we remove them from the reef, they keep coming back,” Rootsaert said. “We’re basically shoveling water.”
Eventually, however, progress was made in several passes. Part of the ongoing process will be to see how often divers need to return to maintain the site.
“The hope is that once the kelp grows, it stays there and stands on its own,” Abbott said. “If you have to sustain it, that kind of effort is much less scalable.”
Abbott and Rootsaert meet every two weeks with officials from the state Department of Fish and Wildlife and the National Oceanic and Atmospheric Administration to discuss the project.
Rootsaert said the hope is to expand to other more popular areas for diving. There is a backlog of more than 400 people who want to be trained to remove sea urchins, Rootsaert said.
“I couldn’t be prouder of all the work we’ve done,” Rootsaert said. “It’s about ocean stewardship. It’s about bringing in volunteers who love the ocean, who want to protect the ocean and give them a way to do what they can, before they can’t.
Tara Duggan (her) is a staff writer for the San Francisco Chronicle. Email: [email protected] Twitter: @taraduggan