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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.”

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.

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 farther 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.

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.

Historically, the Hopkins Rose........

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