Kelp once formed “underwater rainforests” on the California coast, but these fragile ecosystems have largely disappeared. At a marine lab near the Bay Area, scientists are trying to bring them back.
By Carly Nairn, Courthouse News Service
On a rainy day in September along a craggy slice of California shore, some young bull kelp floated around in a cement tub as if enjoying a bubble bath.
Unlike some of their kin elsewhere at this marine laboratory, ecologists had collected these specimens earlier that day. The scientists working here at UC Davis Bodega Marine Laboratory hope the kelp will grow, reproduce and eventually spore — an essential step for restoring the kelp forests that once flourished off the coast of Northern California.
This species — Nereocystis luetkeana, commonly known as bull kelp — is the foundational species in kelp forests, an ecosystem that provides habitat and food for countless other marine animals and plants.
An algae, it only lives for a year but can grow up to a foot per day and reach heights of nearly 100 feet. That’s taller than many trees.
Sadly, California’s kelp forests are in what researchers call “massive decline” as climate change disrupts natural processes in the Pacific Ocean. In around the past 10 years, they estimate more than 90% of these ecosystems have disappeared.
Although it’s normal for kelp forests to rise and fall in response to changing conditions, the past decade has gone well beyond a normal period of decline, said Rachel Karm, a research technician with Sonoma State University who’s now involved in restoration efforts.
“That’s why human intervention was so necessary,” she said. “It wasn’t coming back on its own.”
Although it’s unclear when California kelp forests fell into terminal decline, many researchers point to 2014 — the year a mass of unusually warm water known as “The Blob” was first detected in the North Pacific Ocean.
The Blob coincided with other ecological changes. Kelp-eating Pacific purple sea urchins proliferated. The sea star, a predator that should have kept urchin populations in check, was devastated by disease.
By 2018, Northern California’s coastal kelp forests were looking sparse — and ecologists were at a loss.
“At that point, there was no playbook,” said Brent Hughes, an associate professor of ecology at Sonoma State University. “Nobody had any clue on how you restore a kelp forest.”
Hughes has a long history with kelp. In the early 2000s, he was studying seagrass when he got curious about bull kelp’s life stages. Working with advisor Michael Graham at Moss Landing Marine Labs, they started trying to culture the species.
“I’m like, ‘Can I restore kelp?’” Hughes recalled in an interview in his office at Sonoma State. Through years of trial and error, they started seeing results. “Oh my gosh, how amazing.”
Hughes is now one of a few people in the world who has successfully cultivated kelp in a lab.
In 2018, he became a professor at Sonoma State and pivoted his attention to kelp full time.
He’s now working with scientists from various institutions on the Kelp Restoration Program, a multi-organizational push to revitalize Northern California kelp forests. Collecting specimens from the sea and nurturing them through their unique life cycle, they’re working to restore the forests one acre at a time.
Since the start of culturing and restoration, Hughes and his team have planted nearly ten hectares of bull kelp.
“That is what we’ve been doing,” Hughes said. “My lab in particular is writing that playbook.”
Bull kelp’s various names — mermaid’s bladder, ribbon kelp and bladderwrack — hint at the species’ charisma, suggesting a mythical entity that lives and dies by the sea’s moods. And yet the species begins its life so small that it can’t be seen with the naked eye.
A spore sloughs off of its parent’s “sorus,” a dark patch of tissue. It falls to the sea floor, attaching to hard surfaces like rocks to anchor itself against the ocean’s currents. It then begins to grow.
Bull kelp gets its energy from photosynthesis. A gas-filled pneumatocyst organ or “air bladder” creates buoyancy, allowing the algae to reach upward toward the sun.
As temperatures cool and the kelp reaches maturity, it grows sorus and produces spores, beginning the process again. By winter, storms wipe out mature kelp.
At the Marine Lab, scientists are collecting wild kelp spores, then carefully caring for the algae through its juvenile life stages, when it’s most vulnerable.
As the kelp reaches reproductive age, it produces sori and begins to release spores of its own. Under these carefully controlled conditions, the life cycle takes two years instead of one.
Scientists are still figuring out how best to care for the growing kelp in a lab setting.
One technique they’re trying involves adhering the sori to bits of twine, just as gardeners on land might use stakes and trellises to help a plant steady itself. That gives the kelp something to hold onto as it begins its life.
“Another method that we’re testing is something called spore bags,” said Karm, the research technician with Sonoma State. “We literally take the sori and we just put it in a bag as close to the bottom [of the ocean] as possible and hope that it then releases all of its spores and settles in that area.”
As kelp at Bodega Marine Laboratory grow and mature, scientists move them from petri dishes to jugs. They keep the light dim, mimicking low-light conditions found on the ocean floor.
Things get trickier past that. Kelp see more and more sunlight as they grow taller, and maintaining the right light levels in a lab is a fickle process.
Like with humans, kelp adolescence is a tumultuous phase.
“Just getting them from juvenile to adulthood, they get a little cranky,” said Julieta Gómez, a kelp restoration specialist with the Greater Farallones Association. “I think that’s when they’re the neediest, and that’s when there’s a lot of tears on both ends, from us and the kelp probably.”
Finally, as the kelp reach adulthood, researchers move them outside to large tanks of cool, gurgling sea water. While enjoying the conditions, the kelp’s reproductive sori turns into dark patches along the center of the blades and detaches with ease.
“Once they release all of their sori, there’s no purpose for them anymore,” Karm said as she stood by a tank. She held up a lengthy piece of kelp with a large hole in the middle where a sorus used to be.
It’s a circular process in nature and at this lab, as researchers shepherd the kelp through their life stages from microscopic spore to reproductive adult, then begin again with the next generation.
Besides storing kelp of various ages, they’re also trying to collect spores from various places. “We know that kelp in California is pretty much the same population,” Karm said, “but we just want to make sure that we are collecting as close to where we are out-planting.”
What’s happening in Bodega Bay is just one piece of a complex natural process. Even if researchers can keep bull kelp alive until it’s old enough to reproduce, they must also ensure that the waters off California are a place where they can thrive.
Once kelp are back in the wild, researchers are still figuring out what factors determine whether a kelp forest flourishes or dies. And much of that work revolves around understanding bull kelp’s fiercest predator, the sea urchin.
Pacific purple sea urchins are voracious eaters of kelp. Although the species is native to the West Coast, they can cause massive ecological damage when their population grows unchecked.
That’s just what’s happened in recent years: Urchin numbers have exploded, turning once-lush kelp forests into desert-like “urchin barrens.”
The scientific term for this is “overabundance,” and it happens on land too.
Yellowstone National Park offers one famous example. Without adequate numbers of predators, even native species like elk grew out of control, literally changing the landscape and throwing the whole ecosystem out of whack. Only when wolves were reintroduced in the mid-1990s did Yellowstone begin to return to its natural state.
If urchins are the elk of kelp forests, sea stars are the wolves that are supposed to keep them at bay. But their numbers have dwindled due to a devastating illness.
Sea star wasting disease affects an estimated 26 sea star species and seems to ramp up in the summer, when water temperatures are higher.
The disease has sky-high death rates. Of the critically endangered sunflower sea stars that catch it, about 90% die.
Recently, researchers in British Columbia have ID’ed the bacteria responsible for the disease. Although there is still no known cure, scientists hope that in the coming years, further breakthroughs will begin to help stabilize sea star populations.
Sea stars are a main predator of purple sea urchins. If scientists can find a way to help the creatures rebound, they say it would provide a major boon for kelp forests.
In a paper last year, scientists said sea stars reduced kelp-grazing not just by eating urchins, but by scaring them away. Just the presence of sea stars caused urchins to eat half as much kelp.
“It’s not necessarily direct predation that keeps urchin populations in check, but sunflower stars create what they’re calling this landscape of fear,” said Melanie Prentice, a research associate at the University of British Columbia who has helped study sea star wasting disease.
For Prentice, the importance of sea stars in a thriving kelp ecosystem cannot be understated. Sea stars protect kelp — and kelp, she said, “forms the basis of an entire ecosystem that is really, really important for coastal communities.”
“The impacts are beyond just sea stars and beyond just kelp, but the hundreds of species that are affected by kelp,” she said. “That goes all the way to gray whales that use kelp forest, or fish that hunt or breed.” As a result, she said kelp was important for everything from absorbing carbon dioxide and supporting biodiversity to “to just the food web of the ocean.”
Sea stars are just one part of the picture.
“There’s a big missing component to all this, which is [the] sea otter,” Hughes said.
Sea otters were hunted to local extinction about 150 years ago. There’s now a big debate over whether they should be reintroduced. The Northern California shellfish industry is wary for the same reason that researchers like Hughes are hopeful: Sea otters can eat a lot of invertebrates.
“You talk about a predator that can clean out urchins,” he said. “I mean, a sunflower star can eat an urchin, maybe two urchins an hour or something like that, whereas a sea otter can easily eat 30 to 40 in an hour and will just eat for six hours straight.”
As Hughes and other researchers continue their work to put lab-grown kelp back in the water, they’re still learning lots about what makes the species tick.
In a recent paper in the journal Ecology, scientists at the Marine Lab noted that bull kelp seem to flourish in places where there is a flow of freshwater — for example, due to a river emptying into the ocean.
Although they’re not sure exactly why, they theorize that lower salinity in an area might reduce urchins’ appetite for kelp. These are delicate ecosystems, which can make it difficult to parse out exactly which factors cause what outcomes.
“Kelp’s ecology and history have constantly ebbed and flowed throughout decades of research,” Karm said.
Even so, scientists say it’s not magical thinking to imagine a future where the long flowing blades of healthy kelp forests once again flutter in the tides along Northern California’s coastline. And if these forests do bounce back, it will be a testament to the efforts of ecologists like Hughes.
Recently, Hughes said he’s started to see more rockfish and surf perch — a sign that fragile kelp forests are starting to recover. He wonders what these places could look like in their natural state.
“Do you get more fish? Do you get more abalone? Do you get more seed cucumbers? These are the questions we’re trying to explore right now,” he said. “We don’t really have the answer to everything yet, but we are working on it.”
