A few miles west of San Diego is a stretch of ocean that’s rather unremarkable from the surface. The water is cold and blue. There’s some green seaweed peeking out.

Sink below the waves, however, and a whole other realm appears. Under the sea here, near Point Loma, is a forest as beautiful as any other. It’s made not of trees but of strands of giant kelp, a species of algae that can grow taller than a 10-story building.

Tethered to the seafloor and buoyed by air-filled chambers, the kelp strands undulate with the current, moving in slow motion. Schools of fish, seals, and other aquatic critters weave through the stalks like birds through a forest canopy.

“Diving into a forest is like descending into a cathedral,” Jarrett Byrnes, a marine ecologist at the University of Massachusetts Boston, said of kelp forests. Light from the surface filters through blades of kelp as if they’re stained glass, said Byrnes, who’s been diving kelp forests for more than 20 years. “It’s just amazing.”

A forest of bull kelp near Carmel-by-the-Sea in California in the fall of 2022.

Our planet has a number of great forests — the Amazon, for example, or the boreal forest of Canada and Russia. These iconic ecosystems not only support an incredible diversity of wildlife but store vast amounts of carbon that might otherwise heat up the planet. It’s not hyperbole to say that our existence depends on them.

But equally important are the forests of the sea. Found in cold waters across roughly a quarter of the world’s coasts, kelp forests are the foundation of many marine ecosystems. They underpin coastal fisheries, helping sustain the seafood industry. They also absorb enormous amounts of pollution and help sequester planet-warming gases. A recent study valued these benefits at roughly $500 billion a year, worldwide.

Yet for all they are worth, scientists know surprisingly little about kelp forests. Globally, data on how they’re responding to climate …


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