The Disappearing Stars of the Kelp Forest

by Steven Harper

I swim often in the open ocean, sometimes slipping beneath the surface into the kelp forests near my Big Sur home. There is a moment I cherish in every swim: the stillness after the splash, when the rhythm of waves, surge, and my own breathing fall away into a vast silence. The sea holds me—buoyant, alert, and alive.

On one such swim years ago, I descended only a short distance beneath the surface, scanning the color and movement of the seafloor. At first, I mistook the knobby, radiating arms of a creature below me for nothing more than rough stones scattered across the bottom. Then, with a ripple of motion, one of those shapes glided across the ocean floor. Not a stone at all, but a sunflower sea star, its many arms propelling it with surprising grace over barnacles and algae.

The sunflower sea star (Pycnopodia helianthoides) is unlike the sea stars we imagine from tidepools. With 20 to 24 arms, each lined with hundreds of tiny tube feet, these giants can stretch more than three feet across and move several feet in a minute. They are voracious predators, consuming clams, snails, and sea cucumbers—but most importantly, sea urchins.

For millennia, sunflower stars patrolled the seafloor of kelp forests from Baja California to Alaska. Their role was quiet but vital: keeping sea urchins in check. Left unchecked, urchins mow down young kelp and gnaw through the holdfasts that anchor towering kelp to the rocks. What had been lush underwater forests become “urchin barrens”—bare, lifeless rock fields. Sunflower stars, though often unseen, along with the more familiar sea otters, are keystone species of the kelp forests I love to swim through.

That balance was shattered beginning in 2013. A mysterious disease, now known as Sea Star Wasting Disease, swept down the Pacific coast with devastating speed. It began with small white lesions, then twisted arms, then sudden disintegration until the animal literally melted into the seafloor. Entire populations disappeared in a matter of months. Sunflower stars were hit hardest, losing more than 90 percent of their numbers across their range.

The suspected culprit was first thought to be a virus; more recently, scientists have identified a bacterial infection that takes hold under a constellation of factors—warmer waters, stressful conditions, or crowded populations. Whatever the trigger, the effect was catastrophic: more than five billion sea stars, across multiple species, vanished—one of the largest marine die-offs ever recorded.

The collapse of sunflower stars has reshaped the coastal ecosystem. In northern California, purple sea urchin populations exploded by hundreds of times, devouring over 95 percent of the once-thriving kelp canopy. These kelp forests are not only beautiful habitats for swimmers and divers like me; they are nurseries for fish, food for abalone, shelter for crabs, and hunting grounds for seabirds and marine mammals. They also serve as powerful carbon sinks, absorbing carbon dioxide and buffering climate change. Their disappearance ripples into climate, fisheries, and coastal communities.

Even sea otters, themselves a story of recovery, are caught in the loss. While they also eat urchins, they target large, nutrient-rich ones in healthy kelp beds. In the barren stretches now carpeted with starving, shrunken urchins, there is little nourishment. So, despite their presence, otters cannot fill the gap left by the stars. The absence of the sunflower star undermines the very prey otters depend on, and with it, the health of the kelp forest web of life.

It is humbling—and is a wake-up call—to recognize how one species, rarely noticed by swimmers and divers, could quietly anchor the fate of an entire ecosystem. Remove it, and everything shifts.
Still, I find hope in the resilience of the ocean and the passion of dedicated scientists. They are now breeding sunflower stars in aquaria, seeking individuals resistant to disease and planning for reintroductions. Divers and community groups are removing urchins by hand to allow kelp a foothold once again. In areas where sea otters thrive, their feeding still maintains patches of kelp forest. Again and again, I see how, given time and reprieve, the ocean can heal.

For me, swimming through these forests is an act of awe as much as exploration. The kelp holds me in its cathedral-like canopy, fish darting between columns of light, otters cracking shells on their chests. And beneath it all, invisible to most eyes, is the memory of the sunflower star—its absence palpable in the sway and scarcity of the kelp.

The story of the sea star’s disappearance is also a story of interdependence. The fate of a single many-armed creature touches the fate of urchins, which shape the kelp, which feed the otters, which signal the health of the nearshore world. Science is only beginning to map these threads—the visible and the invisible—that bind the ocean and ultimately us humans together.

When we lose a sea star, we lose more than an animal. We lose balance, function, and connection. When we restore one, perhaps we regain not only a species, but the hidden harmony of the forest beneath the sea—and a deeper harmony within our own human being-ness.

 

Authors Note: In 2007, I wrote an article about the California Sea Otter as a keystone species of the kelp forest. At the time, I had little sense of just how complex the kelp forest ecosystem truly is—or, for that matter, any ecosystem. This piece is an attempt to share what we have since learned about the kelp forest, while holding the humbling awareness of how much we still do not know.

copyright 2025, Steven Harper all rights reserved