At the edge of the ocean, a dazzling ecosystem is changing fast

Vox

01-04-2025

is a senior producer and reporter on Unexplainable, Vox's science podcast. She covers everything scientists don't yet know but are trying to figure out, so her work explores everything from the inner workings of the human body to the distant edges of the universe
In just a few hours, the world I'm walking into will disappear beneath the waves.
I'm at Pillar Point Harbor, a 40-minute drive from San Francisco, near low tide. And because this is one of the lowest tides this August, the water has drawn back like a curtain to expose an ecosystem that's normally hidden away — a place called the rocky intertidal, or, because the receding water leaves little pools behind in the rocks, 'the tidepools.'
Dawn has just broken, pods of pelicans fly overhead, and sea lions bark from the nearby harbor. But I'm more focused on following my guide, a zoologist named Rebecca Johnson, as she picks her way out into these seaweed-covered rocks, pointing out species as she goes. These smooth green strands are surfgrass. Those fat bladders of air that look kind of like puffed-up gloves are called 'seasack.' This dark brown frond Johnson is draping over her shoulders is the aptly named 'feather boa kelp.'
' They're like wildflowers,' Johnson says, 'But it's seaweed.'
Rebecca Johnson wears a feather boa kelp like a feather boa. Byrd Pinkerton/Vox
As we make our way deeper, she points out odd creatures that only the ocean could dream up. A boring clam (which is far from boring, but does bore into rock) puffs itself up like a fierce fleshy ball before squirting a jet of water directly into the air to fend off our threatening vibes. A pale white brittle star, like a flexible daddy longlegs, dances for us across some algae. And rows of fat green anemones wear bits of shells like tiny hats.
' The theory is that…they're protecting themselves from the sun, like a sunscreen,' Johnson tells me.
We crouch together at the edge of a deep pool and see first one, then two — then three, four, five, six! — species of nudibranchs, the sea slugs that Johnson specializes in. One is hot pink and spiky. Another is an aggressive shade of orange. There's a pale lemon one, a ghostly white one. Johnson even finds one covered in orange polka dots, like a marine clown. Some of these species, she tells me, bubbling with enthusiasm, eat anemones and steal their stinging cells, repurposing them as their own defenses.
An orange polka-dotted nudibranch, known as a 'sea clown.' Byrd Pinkerton/Vox
This kind of diversity is wild to witness, but it isn't unusual for these tidepools.
'It's one of the places in the world that you can see species of invertebrates all really, really concentrated,' Johnson told me.
We wander further out, exploring this alien landscape together, until the tide begins to come back in and cover it over, bit by bit, hiding this weird world away again in a slow disappearing act.
' It's extra magical that you can only see it at certain times,' Johnson told me before we came out here, 'You get this little peek, this little window. And that's one of the things I love the most about it.'
Johnson has been coming to this exact spot off Pillar Point for almost three decades now, and in her role as director for the Center for Biodiversity and Community Science for the California Academy of Sciences, she spends time with volunteers monitoring tidepools up and down the California coasts. But she's still enchanted with them.
I'm not surprised. I fell in love with tidepools myself 20 years ago, when I first got to explore them as a kid at a summer camp in Mendocino. The odd, colorful creatures in them made me feel like magic was a little bit real, that science could feel like fantasy. It's part of the reason I'm a science reporter today.
But Johnson is worried about the future of these tidepools she loves so much. She's worried that, like so many ecosystems around the world, they may be heading toward a much more dramatic, much more permanent disappearing act.
So she, along with many, many collaborators all across the state of California and beyond, is doing what many scientists are trying to do for the ecosystems they study: to figure out — first, what's actually happening to them, and second, what, if anything, we can do to save them.
The sun rises over tide pools in Fort Bragg, California. Byrd Pinkerton/Vox
How did we get here?
For Rebecca Johnson, the troubles really began around the arrival of 'The Blob': a marine heatwave. By 2014, it had warmed waters significantly along the West Coast of the United States. Johnson was hearing concerning things from participants in the programs she organized through Cal Academy to get people to go into the tidepools and make observations.
'They started seeing an increase in this really beautiful pink nudibranch called the Hopkins Rose nudibranch,' she says.
Ruby Ash for Vox
Historically, the Hopkins Rose nudibranch has lived in Southern California — and ventured up to Johnson's more northern tidepools mostly during El Niño years. But as the temperatures shifted for the Blob, the spiky pink balls were showing up in huge numbers.
'It became the most common thing,' Johnson remembers.
She was also hearing disturbing reports about another animal — the sea star, known more colloquially as the starfish.
As early as 2013, before The Blob really hit, divers and researchers had started noticing that sea stars were, quite literally, wasting away.
'They were seeing white lesions on starfishes. And they were seeing the starfish kind of disintegrate in front of them,' she says, '[They would] see it one day with these lesions. They'd come back the next day and it was like almost dissolved and then almost gone.'
Sea star wasting also isn't unheard of, but in this instance, the wasting hit species after species of sea stars — at least 20 species in all. Also, as an evolutionary ecologist who studied this outbreak, Lauren Schiebelhut, told me, wasting normally happens on a more local scale — isolated to a single bay, for example.
'For it to spread across the entire West Coast here, that was something we had not seen before,' Schiebelhut says.
'[The Blob] certainly seemed to exacerbate it,' Schiebelhut says.
At one point, Johnson went down to her favorite tidepooling spot, Pillar Point, with a colleague, just to 'see what they could see,' and they saw almost no sea stars.
'It was just like the most bizarre feeling,' she remembers, 'I was still at this place that was spectacularly beautiful, covered with algae. All these other invertebrates are there. But there's just something kind of off about it.'
Byrd Pinkerton/Vox
It was like, she says, going into your room, only to realize that someone has moved all your stuff very slightly.
'And you're like, 'What's wrong with this room?' It had that disconcerting, unsettling feeling.'
This place Johnson knew so well — had been documenting and sharing with people for decades — suddenly felt unfamiliar. And at that moment, she felt a deep, deep uncertainty about its future.
'Like, there might not be starfish, like ever,' she remembers thinking, 'What does that mean?'
What it would mean to lose so many sea stars
The reason that Johnson was so worried about sea stars was not just that the tidepools at Pillar Point looked different. She was worried about the role sea stars play in the tidepools ecosystem. To us, they might seem like pretty creatures that come in a fun shape, but to many of the ocean animals they interact with, they are voracious predators that help keep their ecosystems in balance — chowing down on everything from mussels and barnacles to snails.
To understand why this is so important, let's journey a little beyond the tidepools, a little further offshore, into the California kelp forests. These are underwater forests of algae that are home to a huge diversity of animals, from fish and octopi to abalone. Kelp forests also provide a buffer for the coast against erosion, and they absorb and store large amounts of carbon dioxide, which benefits all of us as we try to stave off climate change. So they're amazing ecosystems.
But, like any forest, California's coastal kelp forest has grazers — basically the marine equivalent of deer. In this case, these are animals like the purple sea urchin, a spiky purple pincushion that chows down enthusiastically on kelp.
Ruby Ash for Vox
Normally, Peter Roopnarine, a paleontologist at the California Academy of Sciences who has studied kelp forests tells me, sea urchins are content to eat the bits of detritus that the kelp shed naturally. But if there isn't enough kelp detritus to go around, urchins can start feeding on the living kelp itself.
' That will happen if, for example, there are not enough predators around to keep their population in control, to keep them hiding,' Roopnarine says, ' Pretty soon they kill the kelp, and what you're left with is what we call an urchin barren, which are these stretches of seafloor that are covered with urchins. And nothing else.'
Sea otters are one of the predators — one of the wolves, to continue the metaphor, to our urchin deer — keeping urchins in check along some parts of the coast. Sea otters were hunted aggressively by European settlers, and have not returned along the northern part of the coast, but have made a comeback in central California.
Another important wolf for these kelp forests, though, is a sea star known as Pycnopodia helianthoides, or the 'sunflower sea star.' Sunflower sea stars are beautiful, often purple or pink, and kind of squishy. But they are also, at least as sea stars go, big. They can have twenty arms, and grow to the size of a dinner plate or larger. (As a kid, when we found them in the tidepools, we used to have to hold them in two hands.) And researchers have increasingly found that they, too, did a lot of work to keep urchins in check.
This is why it was such a big deal when the sea star wasting syndrome hit and wiped out so many sea stars, sunflower sea stars very much included.
After the sickness, a lot of sea star species did start to come back. You can find sea stars like ochre stars, leather stars, and bat stars in California tidepools, for example. But while sunflower sea stars can still be found in the wild further north, in places like Washington state, they have not bounced back along the coast of California. And that, scientists suggest, may have contributed to the issues they're now seeing in kelp forests.
Satellite surveys from a few years ago showed that the kelp forests off of Northern California have shrunk by 95%. Once again, this is probably due to a combination of factors. High water temperatures may have weakened the kelp, for example. But another factor was the explosion of urchin populations.
'This lack of the sunflower star in the kelp forest, especially in Northern California,' Johnson says, 'led to the increase of urchins. And the urchins then ate all the kelp.'
What does this mean for the future of these tidepools?
The tidepools haven't been hit as hard as the kelp forests. Clearly, as our visit last August showed, a place like Pillar Point has not turned into the equivalent of an urchin barren and is instead still home to a diversity of creatures.
Still, Johnson says, they have been affected. She has, anecdotally, noticed grazing species like abalone that normally spend more of their time in the kelp forests moving over to tidepools, probably in search of kelp to eat. And as temperatures continue warming over time, tidepool ecosystems are changing in other ways. A recent paper showed that a species of nudibranch range has moved northward. Another study showed that a whole bunch of different marine species, including nudibranchs, but also species of snail, lobster, and crab were spotted further north than their usual range during a heat wave. Some of these species are predators that might shake up the dynamics and the ecosystems they're coming into.
'We don't actually know what happens when they move north,' Johnson says, ' We don't really know the impact.'
And then, as Lauren Schiebelhut, the geneticist who studies sea stars, told me, there are other stressors like pollution and runoff from wildfires. This January, more than 57,000 acres burned from a series of wildfires in the greater Los Angeles area — a disaster whose scope of damage on intertidal ecosystems is not yet clear, researchers told me.
'The disturbances are becoming more frequent, more intense,' says Schiebelhut, 'It is a challenge to the system.'
Johnson admits that it's hard to know exactly how to interpret all these changes and stressors and use them to predict the future of the tidepools. After all, the California coastal ecosystems have survived the loss of important species before, and survived big natural disasters too.
A brittle star dances across the algae. Byrd Pinkerton
Byrd Pinkerton
My favorite sea slug: an opalescent nudibranch. Byrd Pinkerton/Vox
So I turned to Peter Roopnarine, the paleontologist. He studies how ancient ecosystems weathered — or didn't weather — things like climate change, and what we might learn from them to apply to ecosystems facing challenges today. I hoped he would have a sense of how the current moment fits into the bigger patterns of history.
'If you look in the fossil record,' he told me, 'one of the things that's really remarkable is that ecosystems can last a very long time. Millions of years. Species will come and go in those ecosystems, but what they do, who they do it to, and so on? That doesn't change.'
Ecosystems are a little like, say, a baseball team. You'll always need certain players in certain roles — pitchers and catchers and shortstops and outfielders. Different players can retire and be replaced by other players — if one predator disappears, another predator might be able to take over some of the role that it plays, for example.
But Roopnarine's research into the fossil record also shows that no ecosystem baseball team is endlessly flexible.
'They do eventually come to an end,' he says. Usually, that's when really extreme changes occur. And when he looks at the moments in the past when the climate changed dramatically, and he looks at forecasts for our future, he's very worried.
'We have to be realistic that if we do nothing, the future is extremely grim,' he tells me, 'There is no sugarcoating it.'
What can we do?
When it comes to safeguarding the future health of California's coastal ecosystems, there are lots of people doing lots of things.
Johnson is working with colleagues on a system that uses the community science app iNaturalist to better monitor the health of coastal tidepools.
The Steinhart Aquarium is one of several institutions where researchers are raising and studying baby sunflower stars. This tiny star has two new arms growing. Byrd Pinkerton
Anyone who goes to the tide pools can upload photos of all the species that they see. Those photos, geotagged with locations and timestamps, will hopefully help researchers figure out how populations are changing, to model the future of this ecosystem. They could also potentially serve as a warning system if there are big die-offs again, so scientists can try and intervene earlier.
Lauren Schiebelhut has studied the genomes of sea stars that did recover, to see what can be learned about what made them so resilient to wasting.
The California state government has partnered with nonprofits and commercial fishermen to clear urchins and restore kelp.
And then there's the consortium of institutions up and down the coast, all working on an initiative to try to breed sunflower sea stars in captivity so that they might, eventually, be released back into the wild and resume their role as key predators.
' There is no one person that can do all the things,' says Ashley Kidd, a project manager at the Sunflower Star Lab, one of the many groups working together to bring sunflower sea stars back. What gives her hope is that so many different people, from so many institutions, are working together toward solutions.
' You can't have all the knowledge of disease ecology, behavioral ecology, aquaculture by yourself,' Kidd says, 'It is a much bigger, wonderful group of people that you get to work with and then be connected with. … You're not alone.'
When I first heard that these tidepools might be in trouble, I felt an overwhelming sense of loss.
This ecosystem made me believe that the real world had its own magic — because sure, fairies might not be real, but opalescent nudibranchs come pretty close. It hurts to think that that magic might dim, or even disappear. But walking through these pools with Johnson and watching her walk over to a mother and her daughter to show them nudibranchs, eagerly sharing this world with strangers, I felt delight, and a wonderful sense of present-ness. I felt part of that community. A sense that, whatever the future of these tidepools might look like, they were here, now, and as magical as ever.
'In the midst of climate change and a future that is going to be hotter and harder and more difficult for people, you have to have joy,' Johnson told me, 'I struggle with it. I feel like marine systems especially are pretty complicated to think about restoring. What do you actually do out here? How do you protect things? … But you can't stop doing it, because then you've kind of lost everything.'