The boat bobbed gently off Malibu’s Big Rock Beach as a trio of scientific divers wriggled into wetsuits and double-checked tanks and regulators.

Behind them unfurled a panorama of devastation from the Palisades fire a month earlier. Blackened vegetation dotted the hillsides rising above Pacific Coast Highway. Rubble and lonely chimneys littered the shore where beachfront homes once stood.

One by one, the three divers slipped beneath the surface, nets and knives at the ready. They were seeking evidence of the fire’s underwater toll, particularly its effect on a vital anchor of the coastal ecosystem: kelp.

The divers were with Kelp Ark, a San Pedro-based nonprofit seed bank that preserves and stores genetic material from West Coast kelp species. The Feb. 10 dive was their second since fire and subsequent rains injected tons of ash and debris into the ocean ecosystem.

“When we think about wildfires, we think a lot about how that impacts the terrestrial realm, how destructive it can be to the land,” said Lori Berberian, a second-year PhD student in geography at UCLA who studies the effects of wildfire on kelp abundance and habitat distribution. “But there are huge implications for the coast.”

Forests of kelp, a fast-growing brown algae, provide food and habitat for hundreds of marine species and absorb greenhouse gases that might otherwise hasten climate change.

Yet kelp is also highly sensitive to environmental changes. Fluctuations in temperature, light availability, nutrients and pollutants can have surprisingly swift consequences on kelp populations, which have waxed and waned along the California coast in recent decades.

And few things have shocked L.A.’s ecology like January’s Palisades and Eaton fires, which burned more than 40,000 acres, destroyed at least 12,000 buildings and drained tons of ash, debris and toxic residue into the ocean.

No one yet knows how sea life will respond to an urban fire of this magnitude. Kelp may be one of the first species to tell us.

“They’re a big sentinel species that are indicators of how our coastal ecosystems are thriving,” said Erin Hestir, a remote sensing specialist and associate professor at UC Merced.

Hestir is the principal investigator of KelpFire, a NASA-funded research project that uses remote sensing and on-the-ground observations to track the effects of wildfire runoff on kelp populations.

Sedona Silva enters the water during a kelp collection dive by Kelp Ark off the coast of Malibu.

(William Liang / For The Times)

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While every rainfall washes dirt and urban gunk into the ocean, that process is turbocharged after a wildfire. Fire consumes vegetation that would otherwise hold soil in place and alters soil chemistry so that it absorbs less water.

This massive infusion of sediment disrupts kelp’s access to two things it needs to survive: rocks and sunlight.

A glut of dirt and pollutants can interfere with kelp spores’ ability to securely attach to rocks and reefs, either by binding to the spores themselves or by littering rock surfaces.

And when ash and debris fall upon the ocean’s surface, it reduces the amount of sunlight that filters through the water and provides the light kelp needs to photosynthesize.

Kelp isn’t the only marine species that suffers when deprived of light or pumped with pollution. But the prominent role it plays makes it an important bellwether for broader problems spurred by a changing climate.

Berberian, the UCLA doctoral student, is also a member of the research team. She developed a Post-Fire Kelp Recovery Index to compare kelp canopy extent after a fire to its historical average.

The team found that mature giant kelp beds shrank after the 2016 Soberanes fire in Monterey County, the 2017 Thomas fire in Ventura and Santa Barbara counties, and the 2018 Woolsey fire in the Santa Monica Mountains. They still haven’t returned to pre-fire levels, Hestir said.

Sedona Silva, left, hands off her kelp during a collection dive by Kelp Ark off Malibu. The seed bank is concerned about the health of Southern California’s kelp populations after debris from the recent wildfires was found in the area.

(William Liang / For The Times)

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Recovery rates varied widely by location. Using satellite data, Berberian found that the median recovery rate of kelp beds near Malibu was a mere 7% in the two years after the Woolsey fire. In the same time period, beds off of Palos Verdes rebounded 61%, with some areas recovering almost completely.

All of those fires dumped sediment into the ocean. But January’s infernos introduced a new variable, said Kyle Cavanaugh, a coastal geographer and UCLA professor who is also on the KelpFire team.

Previous wildfires burned mostly brush, trees and other organic material. The Palisades and Eaton fires incinerated homes, cars and everything in them: plastics, electronics, batteries, asbestos, lead pipes and household chemicals. No one knows yet what effect this will have on sea life.

“There’s certainly evidence that certain types of hydrocarbons and metals are toxic to early life stages of giant kelp, and you might expect that would be a bigger issue with all of the urban structures that burnt,” Cavanaugh said. “That’s something somewhat unique about this.”

Declan Bulwa carries kelp he collected during the collection dive. Forests of kelp, a fast-growing brown algae, provide food and habitat for hundreds of marine species and absorb greenhouse gases that might otherwise hasten climate change.

(William Liang / For The Times)

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California’s giant kelp faces a number of different threats, and Hestir cautioned between drawing a direct line between any single disturbance — fire included — and decline of visible canopy.

Yet as the environmental disruptions pile up — prolonged marine heat waves, changing ocean chemistry, stronger and more frequent storms — so does the worry that the next disturbance could be a tipping point.

“What we’re concerned about is that these kelp are already under these stressors . . . and then you end up with a wildfire event, and maybe that’s what really tips it over the edge and doesn’t allow it to recover,” Hestir said.

Kelp Ark’s divers observed these challenging conditions firsthand during an initial post-fire collection trip on Jan. 27.

Days earlier, the first significant rains since May sent contaminants surging into the ocean.

Kelp is shown at Kelp Ark’s laboratory where they store kelp seeds.

(William Liang / For The Times)

The ship’s wake was the color of chocolate milk. The ocean seemed to reek of burnt trash, said crew member Taylor Collins. The anchor chain, which on a typical day is visible for about 10 feet into the water, disappeared into opaque murk mere inches below the surface.

Before the divers rolled in, captain Joey Broyles let down a waterproof camera to assess conditions below.

The first 3 feet of seawater were choked with soot, dirt and pollution, said Bernadeth Tolentino, lead scientific diver and a graduate student in the USC lab of Kelp Ark founder Sergey Nuzhdin.

Visibility beneath the layer of soot was close to zero, she said. Divers held hands to keep track of one another underwater before calling it quits.

“It was almost like someone put a blanket over the ocean,” Tolentino said.

Hayden Schneider examines kelp at the San Pedro-based nonprofit Kelp Ark, which preserves and stores genetic material from West Coast kelp species.

(William Liang / For The Times)

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Two weeks after that murky dive near Malibu Creek, the Kelp Ark team set out again to collect kelp samples to take back to their facility at AltaSea in the Port of Los Angeles for analysis and spore harvesting.

For this outing they chose a spot popular with recreational divers, where kelp was frequently recorded prior to the fires.

Two hours after plunging into the ocean, Tolentino and colleagues Declan Bulwa and Sedona Silva climbed wet and winded back into the boat.

They’d seen all the animals a diver would expect to see in a kelp forest, such as garibaldi fish and kelp bass.

But the only signs of the big brown algae were a few loose floating pieces and some decaying holdfasts on rocks near the shore — a sign that kelp had been there in the recent past, but no longer.