Science

Sea urchins made to order: Scripps scientists make transgenic breakthrough

Published

2 years ago

May 29, 2024

Sea urchins made to order: Scripps scientists make transgenic breakthrough

Consider the sea urchin. Specifically, the painted urchin: Lytechinus pictus, a prickly Ping-Pong ball from the eastern Pacific Ocean.

The species is a smaller and shorter-spined cousin of the purple urchins devouring kelp forests. They produce massive numbers of sperm and eggs that fertilize outside of their bodies, allowing scientists to watch the process of urchin creation up close and at scale. One generation gives rise to the next in four to six months. They share more genetic material with humans than fruit flies do and can’t fly away — in short, an ideal lab animal for the developmental biologist.

Scientists have been using sea urchins to study cell development for roughly 150 years. Despite urchins’ status as super reproducers, practical concerns often compel scientists to focus their work on more easily accessible animals: mice, fruit flies, worms.

Scientists working with mice, for example, can order animals online with the specific genetic properties they are hoping to study — transgenic animals, whose genes have been artificially tinkered with to express or repress certain traits.

Researchers working with urchins typically have to spend part of their year collecting them from the ocean.

“Can you imagine if mouse researchers were setting a mousetrap every night, and whatever it is they caught is what they studied?” said Amro Hamdoun, a professor at UC San Diego’s Scripps Institution of Oceanography.

UC San Diego professor Amro Hamdoun holds a painted urchin. His breakthrough creating the creatures could lead to developments in science and medicine.

(Sandy Huffaker / For The Times)

Marine invertebrates represent about 40% of the animal world’s biological diversity yet appear in a scant fraction of a percentage of animal-based studies. What if researchers could access sea urchins as easily as mice? What if it were possible to make and raise lines of transgenic urchins?

How much more could we learn about how life works?

“You know how during the pandemic, everyone was making sourdough? I’m not good at making sourdough,” Hamdoun said recently at his office in Scripps’ Hubbs Hall. He set his sights instead on a project of a different sort: a new transgenic lab animal, “a fruit fly from the sea.”

In March, Hamdoun’s lab published a paper on the bioRxiv preprint server demonstrating the successful insertion of a piece of foreign DNA — specifically, a fluorescent protein from a jellyfish — into the genome of a painted urchin that passed the change down to its offspring.

The result is the first transgenic sea urchin, one that happens to glow like a Christmas bulb under a fluorescent light. (The paper has been submitted for peer review.)

The animals are the first transgenic echinoderms, the phylum that includes starfish, sea cucumbers and other marine animals. Hamdoun’s mission is to make genetically modified urchins available to researchers anywhere, not just those who happen to work in research facilities at the edge of the Pacific Ocean.

Elliot Jackson, a postdoctoral researcher, works with sea urchin eggs in a lab at Scripps

“If you look at some of the other model organisms, like Drosophila [fruit flies], zebrafish and mouse, there are well-established resource centers,” said Elliot Jackson, a postdoctoral researcher at Scripps and lead author of the paper. “If you want a transgenic line that labels the nervous system, you could probably get that. You could order it. And that’s what we hope we can be for sea urchins.”

Being able to genetically modify an animal supercharges what scientists can learn from it, with implications far beyond any individual species.

“It will transform sea urchins as a model for understanding neurobiology, for understanding developmental biology, for understanding toxicology,” said Christopher Lowe, a Stanford professor of biology who was not involved in the research.

The lab’s breakthrough, and its focus on making the animals freely available to fellow scientists, will “allow us to explore how evolution has solved a lot of really complicated life problems,” he said.

Researchers tend to study mice, flies and the like not because the animals’ biology is best suited to answer their questions but because “all the tools that were necessary to get at your questions were built up in just a few species,” said Deirdre Lyons, an associate professor of biology at Scripps who worked with Hamdoun on early research related to the project.

Expanding the range of animals available for sophisticated lab work is like adding colors to an artist’s palette, Lyons said: “Now you can go get the color that you really want, that best fits your vision, rather than being stuck with a few models.”

Hamdoun holds two painted urchins in an outstretched hand

On the ground floor of Hamdoun’s office building is the Hubbs Hall experimental aquarium, a garage-like space crammed with tanks full of recirculating seawater and a motley assortment of marine life.

On a recent visit, Hamdoun reached into a tank and gently dislodged a painted urchin. It scooched with surprising speed across an outstretched palm, as if exploring alien terrain.

The last common ancestor of L. pictus and Homo sapiens lived at least 550 million years ago. Despite the different evolutionary paths we’ve since traveled, our genomes reveal a shared biological heritage.

The genetic instructions that drive the transformation of a single zygote into a living body are strikingly similar in our two species. Specialized systems differentiating from a single fertilized egg and the translation of a jumble of proteins into a singular living thing — on the cellular level, all of that proceeds in much the same way for urchins and people.

These animals are “really fundamental to our understanding of all of life,” Hamdoun said, placing the urchin back in its tank. “And historically, very inaccessible genetically.”

The experimental aquarium was built in the 1970s, when scooping life from the sea was the only way to acquire research specimens. A few floors up in Hubbs Hall, Hamdoun led the way into the urchin nursery — the first large-scale effort to raise successive generations of the animals in a laboratory. At any given moment, the team has 1,000 to 2,000 sea urchins in various stages of development.

Hamdoun points at rows of greenish tanks holding sea urchins

Row upon row of tiny plastic tanks stood against a wall, each containing a lentil-size juvenile urchin. A strip of tape on each tank noted the animal’s genetic modification and date of fertilization. On some, a second bit of tape indicated animals that had the modification in their sex cells’ DNA, meaning it could be passed down to offspring. (For this reason, the lab keeps its urchins scrupulously separate from the wild population.)

“One of the big questions in all of biology is to understand how the series of instructions in the genome gives you whatever phenotype you want to study,” Hamdoun said — essentially, how the string of amino acids that is an animal’s genetic code gives rise to the characteristics of the living, respiring creature. “One of the fundamental things you have to do is be able to modify that genome, and then study what the outcome is.”

He pointed to a tank containing a tiny urchin from whose genetic code the protein ABCD1 has been snipped.

ABCD1 acts like a bouncer, Hamdoun explained, parking along the cell membrane and ejecting foreign molecules. The protein’s action can preserve the cell from harmful substances but can sometimes work against an organism’s best interest, as when it prevents the cell from absorbing a necessary medication.

Researchers using urchins in which that protein no longer works can study the movement of a molecule through an organism — DDT, for example — and measure how much of the substance ends up in the cell without the confounding interference of ABCD1. They can reverse-engineer how big a role ABCD1 plays in preventing a cell from absorbing a drug.

A transgenic fluorescent sea urchin glows green through a microscope

And then there are the fluorescent urchins.

“The magic happens in this room,” Jackson said, walking into a narrow office with $1 million worth of microscopes at one end and a decades-old hand-cranked centrifuge bolted to a table at another.

He placed a petri dish containing three pencil-eraser-size transgenic urchins under a microscope. At 120 times its size, each looked like the Times Square New Year’s Eve ball come to life — a glowing, wiggling creature of pentamerous radial symmetry.

Fluorescence is not just an echinoderm party trick. Lighting up the cells makes it easier for researchers to track their movement in a developing organism. Researchers can watch as the early cells of a blastula divide and reorganize into neural or cardiac tissue. Eventually, scientists will be able to turn off individual genes and see how that affects development. It will help us understand how our own species develops, and why that development doesn’t always proceed according to plan.

The lab has “done a great job. It’s really been welcomed by the community,” said Marko Horb, senior scientist and director of the National Xenopus Resource at the University of Chicago’s Marine Biological Laboratory.

Horb runs the national clearinghouse for genetically modified species of Xenopus, a clawed frog used in lab research. Funded in part by the National Institutes of Health, the center develops lines of transgenic frogs for scientific use and distributes them to researchers.

Hamdoun envisions a similar resource center for his lab’s urchins. They’ve already started sending tiny vials of transgenic urchin sperm to interested scientists, who can grow bespoke urchins with eggs acquired from Hamdoun’s lab or another source.

Hamdoun vividly recalls the time he spent earlier in his career trying to track down random snippets of DNA necessary for his research, the disappointment and frustration of writing to professors and former postdocs only to find that the material had long been lost. He’d rather future generations of scientists spend their time on discovery.

“Biology is really interesting,” he said. “The more people can get access to it, the more we’re going to learn.”

Science

A retired teacher found some seahorses off Long Beach. Then he built a secret world for them

Published

2 days ago

December 14, 2025

Press Room

A retired teacher found some seahorses off Long Beach. Then he built a secret world for them

Rog Hanson emerges from the coastal waters, pulls a diving regulator out of his mouth and pushes a scuba mask down around his neck.

“Did you see her?” he says. “Did you see Bathsheba?”

On this quiet Wednesday morning, a paddle boarder glides silently through the surf off Long Beach. Two stick-legged whimbrels plunge their long curved beaks into the sand, hunting for crabs.

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But Hanson, 68, is enchanted by what lies hidden beneath the water. Today he took a visitor on a tour of the secret world he built from palm fronds and pine branches at the bottom of the bay: his very own seahorse city.

The visitor confirms that she did see Bathsheba, an 11-inch-long orange Pacific seahorse, and a grin spreads across Hanson’s broad face.

“Isn’t she beautiful?” he says. “She’s our supermodel.”

If you get Hanson talking about his seahorses, he’ll tell you exactly how many times he’s seen them (997), who is dating whom, and describe their personalities with intimate familiarity. Bathsheba is stoic, Daphne a runner. Deep Blue is chill.

He will also tell you that getting to know these strange, almost mythical beings has profoundly affected his life.

“I swear, it has made me a better human being,” he says. “On land I’m very C-minus, but underwater, I’m Mensa.”

Hanson is a retired schoolteacher, not a scientist, but experts say he probably has spent more time with Pacific seahorses, also known as Hippocampus ingens, than anyone on Earth.

“To my knowledge, he is the only person tracking ingens directly,” says Amanda Vincent, a professor at the University of British Columbia and director of the marine conservation group Project Seahorse. “Many people love seahorses, but Roger’s absorption with them is definitely distinctive. There’s a degree of warm obsession there, perhaps.”

Rog Hanson posing in his gear on the beach.

Over the last three years, Hanson has made the two-hour trek from his home in Moreno Valley to the industrial shoreline of Long Beach to visit his “kids” about every five days. To avoid traffic, he often leaves at 2 a.m. and then sleeps in his car when he arrives.

He keeps three tanks of air and his scuba gear in the trunk of his 2009 Kia Rio. A toothbrush and a pair of pink leopard print reading glasses rest on the dash.

Hanson makes careful notes after all his dives in a colorful handmade log book he stores in a three-ring binder. On this Wednesday he dutifully records the water temperature (62 degrees), the length of the dive (58 minutes), the greatest depth (15 feet) and visibility (3 feet), as well as the precise location of each seahorse. His notes also include phase of the moon, the tidal currents and the strength of the UV rays.

“Scientists will tell you that sunlight is an important statistic to keep down,” he says.

He has given each of his four seahorses a unique logo that he draws with markers in his log book. Bathsheba’s is a purple star outlined in red, Daphne’s is a brown striped star in a yellow circle.

A detailed log of seahorse sightings written in a notebook with colorful inks.

He’s learned that the seahorses don’t like it when he hovers nearby for too long. Now he limits his interactions with them to 15 to 30 seconds at a time.

“At first I bugged them too much,” he says. “I was the paparazzi swimming around.”

Hanson traces the origins of his seahorse story back nearly two decades to the early morning of Dec. 30, 2000.

He was diving solo off Shaw’s Cove in Laguna Beach when a slow-moving giant emerged from the abyss. It was a gray whale whose 40-foot frame cast Hanson in shadow.

The whale could have killed him with a flick of its tail, Hanson says, but he felt no fear. The two made eye contact and, as Hanson tells it, he felt the whale’s gaze peering directly into his soul.

It was all over in 10 seconds, but Hanson was altered. He had always wanted to live at the beach, but after this encounter, he vowed to make it happen. It took years —15, in fact — but he finally got a job as a special education teacher in the Long Beach public school system. He bought a van and parked it on Ocean Boulevard. He lived at the beach and dived every day for 3½ months before moving to Moreno Valley.

To amuse himself while he lived at the beach, he built an underwater city he called Littleville out of discarded toys he found at the bottom of the bay.

Hanson saw his first seahorse in January 2016 while checking on Littleville. It was bright orange, just 4.5 inches long, and Hanson, who had logged over a thousand dives in the area, knew it didn’t belong there.

A red seahorse surrounded by sealife under water.

The range of the Pacific seahorse is generally thought to extend from Peru to as far north as San Diego. This seahorse ended up about 100 miles north of that.

Scientists said the seahorse and others that joined her had probably ridden an unusual pulse of warm water up the coast, along with other animals generally found in southern waters.

“We were getting a lot of weird sightings in the fall of 2015,” says Sandy Trautwein, vice president of husbandry at the Aquarium of the Pacific. “There was a yellow-bellied sea snake, bluefin tuna, marlin, whale sharks — a lot of animals associated with warm water.”

Most of these animals eventually left after ocean temperatures returned to normal, but Hanson’s seahorses stayed.

That may be because Hanson had built them a home.

It happened like this: In June 2016 he watched in horror as more than 100 high school football players splashed in the shallow waters, right where his seahorses usually hung out.

“I thought, I gotta do something, I gotta do something,” he says.

“On land I’m very C-minus, but underwater, I’m Mensa.”

— Rog Hanson

Then he remembered that, back in the Midwest where he grew up, he used to help the city park service make “fish cribs.” In early spring they would use brush and twigs to build what looked like a miniature log cabin with no roof on an ice-covered lake. When the ice melted, the cribs would fall to the bottom, creating a habitat for fish and other animals.

“So I said to myself, build them a city that’s deeper, where feet can’t get to it even at low tide,” Hanson says.

And he did.

By July 2016 two pairs of seahorses had moved into the new habitat. Daphne, the runner, was named after the nymph from Greek mythology who flees Apollo, Kenny’s name came from the proprietor of a local kayaking company. “Bathsheba” was inspired by a Bible story, and her mate, Deep Blue, named after a dive shop that has helped sponsor Hanson’s work since he launched his seahorse study.

He’s seen Kenny’s and Deep Blue’s bellies swell with pregnancy and noted how their partners check in on them daily, frequently standing sentinel nearby. He’s visited the fish at odd hours to see how their behavior changes from morning to night. And he mourned when Kenny disappeared in January. He still hasn’t come back. (A new member, CD Street, arrived June 29.)

“It feels like I’m reading a book, the book of their life, and I can’t put it down,” he says.

He’s also reached out to seahorse scientists across the globe to compare notes. “I won’t say I know the most about seahorses in the world, but I know the people who do,” he says.

Amanda Vincent, the director of Project Seahorse, says that seahorses spark an emotional reaction in almost everyone.

Daphne is one of the seahorses that Rog Hanson is studying in Alamitos Bay.

“Remember those books with three flaps where you can mix the head of a giraffe with the body of a snake and the tail of a monkey? That’s what we’ve got here,” she says. “They appeal to the sense of fancy and wonder in us.”

When Mark Showalter, a planetary astronomer at the SETI Institute, recently discovered a moon orbiting Neptune, he named it Hippocamp in part because of his love of seahorses.

“I’ve seen them in the wild and they are marvelously strange and interesting,” he says. “It’s a fish, but it doesn’t look anything like a fish.”

Pacific seahorses are among the largest members of the seahorse family. Males can grow up to 14 inches long, while females generally top out at about 11. They come in a variety of colors, including orange, maroon, brown and yellow. They are talented camouflagers that can alter the color of their exoskeleton to blend into their environment.

“I won’t say I know the most about seahorses in the world, but I know the people who do.”

But perhaps their most distinguishing characteristic is that they are the only known species in the animal kingdom to exhibit a true male pregnancy. Females deposit up to 1,500 eggs in the male’s pouch. The males incubate the eggs, providing nutrition and oxygen for the growing embryos. When the larval seahorses are ready to be released, he goes into labor — scientists call it “jackknifing” — pushing his trunk toward his tail.

After three years of observation, Hanson has collected new evidence about seahorse mating practices. His research suggests that although most seahorses are monogamous, a female will mate with two males if there are no other female seahorses around.

He also found that males, who are in an almost constant state of pregnancy, tend to stick to an area about the size of a king-size mattress, while the females roam up to 150 feet from their home during a typical day.

Eventually, he may be able to help scientists answer another long-standing question: What is the lifespan of Pacific seahorses in the wild? Some researchers say about five years; others think it could be up to 12.

“It will be interesting to see what Roger finds out,” Vincent says.

In June 2017, about one year after Hanson began formally tracking the seahorses, he took on a partner: a young scuba instructor named Ashley Arnold.

Arnold, who has short red hair and a jocular vibe, is a former Army staff sergeant who served in Iraq and Afghanistan. She learned to dive as part of a program the Salt Lake City Veterans Affairs hospital offered to female veterans suffering from post-traumatic stress disorder and military sexual trauma. Arnold suffered from both. Diving became her salvation.

Dive instructor Ashley Arnold sitting at the bed of a truck.

“All the irritation on the surface disappears when you go under the water,” she says. “It’s like, ‘What was I concerned about?’ You forget about everything else. Nothing else matters.”

She used her GI Bill to pay for a scuba instructor course and to set up her own business. Now, she finds that if she dives at least twice a week and has a dog, she does not need to take medication.

“All the irritation on the surface disappears when you go under the water.”

— Ashley Arnold

“That’s a pretty big statement in my opinion,” she says.

Arnold and Hanson met in June 2016 on a dive trip to Catalina. Hanson mentioned his seahorses. Arnold was intrigued, but still lived in Salt Lake City.

One year later, Arnold moved to Huntington Beach and gave Hanson a call.

“I said, ‘Hey Roger, let’s chat. Any chance I could join you at the seahorses you talked about?’” she says. “And he decided I was acceptable.”

Now, Arnold and her boyfriend, Jake Fitzgerald, check in on the seahorses about once a week and help Roger rebuild the city he created for them.

Rog Hanson and Ashley Arnold posing in their gear on the beach.

“We call them our kids because we love them so much,” Arnold says.

Hanson and Arnold are very protective of their seahorse family. They tell visitors to remove GPS tags from their photos. They swear them to secrecy.

There is little chance anyone would find Hanson’s seahorses without a guide. Also, diving in these waters off Long Beach can be a challenge.

The water is shallow. It’s hard to get your buoyancy right. A misplaced flipper kick can stir up blinding sand and silt.

But if Hanson wants to show you his underwater world, nothing will stop him. He will hold you firmly by the hand and guide you down to the forest he built at the bottom of the bay.

Rog Hanson rinses off Ashley Arnold in her gear on the beach.

He will use a plastic tent stake, jabbing it into the bottom to propel himself — and you holding on — across the ocean floor. When he spots a seahorse he will use the stake as a pointer. Through the murky water you strain to see. Then it appears.

Orange and rigid. Thin snout. Bony plates. Stripes down the torso. Totally still.

And if you’ve never seen a seahorse in the wild before, you will feel honored and awed, as if you’ve just seen a unicorn beneath the sea.

Science

California’s summer COVID wave shows signs of waning. What are the numbers in your community?

Published

2 days ago

December 14, 2025

Press Room

California’s summer COVID wave shows signs of waning. What are the numbers in your community?

There are some encouraging signs that California’s summer COVID wave might be leveling off.

That’s not to say the seasonal spike is in the rearview mirror just yet, however. Coronavirus levels in California’s wastewater remain “very high,” according to the U.S. Centers for Disease Control and Prevention, as they are in much of the country.

But while some COVID indicators are rising in the Golden State, others are starting to fall — a hint that the summer wave may soon start to decline.

Statewide, the rate at which coronavirus lab tests are coming back positive was 11.72% for the week that ended Sept. 6, the highest so far this season, and up from 10.8% the prior week. Still, viral levels in wastewater are significantly lower than during last summer’s peak.

The latest COVID hospital admission rate was 3.9 hospitalizations for every 100,000 residents. That’s a slight decline from 4.14 the prior week. Overall, COVID hospitalizations remain low statewide, particularly compared with earlier surges.

The number of newly admitted COVID hospital patients has declined slightly in Los Angeles County and Santa Clara County, but ticked up slightly up in Orange County. In San Francisco, some doctors believe the summer COVID wave is cresting.

“There are a few more people in the hospitals, but I think it’s less than last summer,” said Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert. “I feel like we are at a plateau.”

Those who are being hospitalized tend to be older people who didn’t get immunized against COVID within the last year, Chin-Hong said, and some have a secondary infection known as superimposed bacterial pneumonia.

Los Angeles County

In L.A. County, there are hints that COVID activity is either peaking or starting to decline. Viral levels in local wastewater are still rising, but the test positivity rate is declining.

For the week that ended Sept. 6, 12.2% of wastewater samples tested for COVID in the county were positive, down from 15.9% the prior week.

“Many indicators of COVID-19 activity in L.A. County declined in this week’s data,” the L.A. County Department of Public Health told The Times on Friday. “While it’s too early to know if we have passed the summer peak of COVID-19 activity this season, this suggests community transmission is slowing.”

Orange County

In Orange County, “we appear to be in the middle of a wave right now,” said Dr. Christopher Zimmerman, deputy medical director of the county’s Communicable Disease Control Division.

The test positivity rate has plateaued in recent weeks — it was 15.3% for the week that ended Sept. 6, up from 12.9% the prior week, but down from 17.9% the week before that.

COVID is still prompting people to seek urgent medical care, however. Countywide, 2.9% of emergency room visits were for COVID-like illness for the week that ended Sept. 6, the highest level this year, and up from 2.6% for the week that ended Aug. 30.

San Diego County

For the week that ended Sept. 6, 14.1% of coronavirus lab tests in San Diego County were positive for infection. That’s down from 15.5% the prior week, and 16.1% for the week that ended Aug. 23.

Ventura County

COVID is also still sending people to the emergency room in Ventura County. Countywide, 1.73% of ER patients for the week that ended Sept. 12 were there to seek treatment for COVID, up from 1.46% the prior week.

San Francisco

In San Francisco, the test positivity rate was 7.5% for the week that ended Sept. 7, down from 8.4% for the week that ended Aug. 31.

“COVID-19 activity in San Francisco remains elevated, but not as high as the previous summer’s peaks,” the local Department of Public Health said.

Silicon Valley

In Santa Clara County, the coronavirus remains at a “high” level in the sewershed of San José and Palo Alto.

Roughly 1.3% of ER visits for the week that ended Sunday were attributed to COVID in Santa Clara County, down from the prior week’s figure of 2%.

Science

Early adopters of ‘zone zero’ fared better in L.A. County fires, insurance-backed investigation finds

Published

3 days ago

December 13, 2025

Press Room

Early adopters of ‘zone zero’ fared better in L.A. County fires, insurance-backed investigation finds

As the Eaton and Palisades fires rapidly jumped between tightly packed houses, the proactive steps some residents took to retrofit their homes with fire-resistant building materials and to clear flammable brush became a significant indicator of a home’s fate.

Early adopters who cleared vegetation and flammable materials within the first five feet of their houses’ walls — in line with draft rules for the state’s hotly debated “zone zero” regulations — fared better than those who didn’t, an on-the-ground investigation from the Insurance Institute for Business and Home Safety published Wednesday found.

Over a week in January, while the fires were still burning, the insurance team inspected more than 250 damaged, destroyed and unscathed homes in Altadena and Pacific Palisades.

On properties where the majority of zone zero land was covered in vegetation and flammable materials, the fires destroyed 27% of homes; On properties with less than a quarter of zone zero covered, only 9% were destroyed.

The Insurance Institute for Business and Home Safety, an independent research nonprofit funded by the insurance industry, performed similar investigations for Colorado’s 2012 Waldo Canyon fire, Hawaii’s 2023 Lahaina fire and California’s Tubbs, Camp and Woolsey fires of 2017 and 2018.

While a handful of recent studies have found homes with sparse vegetation in zone zero were more likely to survive fires, skeptics say it does not yet amount to a scientific consensus.

Travis Longcore, senior associate director and an adjunct professor at the UCLA Institute of the Environment and Sustainability, cautioned that the insurance nonprofit’s results are only exploratory: The team did not analyze whether other factors, such as the age of the homes, were influencing their zone zero analysis, and how the nonprofit characterizes zone zero for its report, he noted, does not exactly mirror California’s draft regulations.

Meanwhile, Michael Gollner, an associate professor of mechanical engineering at UC Berkeley who studies how wildfires destroy and damage homes, noted that the nonprofit’s sample does not perfectly represent the entire burn areas, since the group focused specifically on damaged properties and were constrained by the active firefight.

Nonetheless, the nonprofit’s findings help tie together growing evidence of zone zero’s effectiveness from tests in the lab — aimed at identifying the pathways fire can use to enter a home — with the real-world analyses of which measures protected homes in wildfires, Gollner said.

A recent study from Gollner looking at more than 47,000 structures in five major California fires (which did not include the Eaton and Palisades fires) found that of the properties that removed vegetation from zone zero, 37% survived, compared with 20% that did not.

Once a fire spills from the wildlands into an urban area, homes become the primary fuel. When a home catches fire, it increases the chance nearby homes burn, too. That is especially true when homes are tightly packed.

When looking at California Department of Forestry and Fire Protection data for the entirety of the two fires, the insurance team found that “hardened” homes in Altadena and the Palisades that had noncombustable roofs, fire-resistant siding, double-pane windows and closed eaves survived undamaged at least 66% of the time, if they were at least 20 feet away from other structures.

But when the distance was less than 10 feet, only 45% of the hardened homes escaped with no damage.

“The spacing between structures, it’s the most definitive way to differentiate what survives and what doesn’t,” said Roy Wright, president and chief executive of the Insurance Institute for Business and Home Safety. At the same time, said Wright, “it’s not feasible to change that.”

Looking at steps that residents are more likely to be able to take, the insurance nonprofit found that the best approach is for homeowners to apply however many home hardening and defensible space measures that they can. Each one can shave a few percentage points off the risk of a home burning, and combined, the effect can be significant.

As for zone zero, the insurance team found a number of examples of how vegetation and flammable materials near a home could aid the destruction of a property.

At one home, embers appeared to have ignited some hedges a few feet away from the structure. That heat was enough to shatter a single pane window, creating the perfect opportunity for embers to enter and burn the house from the inside out. It miraculously survived.

At others, embers from the blazes landed on trash and recycling bins close to the houses, sometimes burning holes through the plastic lids and igniting the material inside. In one instance, the fire in the bin spread to a nearby garage door, but the house was spared.

Wooden decks and fences were also common accomplices that helped embers ignite a structure.

California’s current zone zero draft regulations take some of those risks into account. They prohibit wooden fences within the first five feet of a home; the state’s zone zero committee is also considering whether to prohibit virtually all vegetation in the zone or to just limit it (regardless, well-maintained trees are allowed).

On the other hand, the draft regulations do not prohibit keeping trash bins in the zone, which the committee determined would be difficult to enforce. They also do not mandate homeowners replace wooden decks.

The controversy around the draft regulations center around the proposal to remove virtually all healthy vegetation, including shrubs and grasses, from the zone.

Critics argue that, given the financial burden zone zero would place on homeowners, the state should instead focus on measures with lower costs and a significant proven benefit.

“A focus on vegetation is misguided,” said David Lefkowith, president of the Mandeville Canyon Assn.

At its most recent zone zero meeting, the Board of Forestry and Fire Protection directed staff to further research the draft regulations’ affordability.

“As the Board and subcommittee consider which set of options best balance safety, urgency, and public feasibility, we are also shifting our focus to implementation and looking to state leaders to identify resources for delivering on this first-in-the-nation regulation,” Tony Andersen, executive officer of the board, said in a statement. “The need is urgent, but we also want to invest the time necessary to get this right.”

Home hardening and defensible space are just two of many strategies used to protect lives and property. The insurance team suspects that many of the close calls they studied in the field — homes that almost burned but didn’t — ultimately survived thanks to firefighters who stepped in. Wildfire experts also recommend programs to prevent ignitions in the first place and to manage wildlands to prevent intense spread of a fire that does ignite.

For Wright, the report is a reminder of the importance of community. The fate of any individual home is tied to that of those nearby — it takes a whole neighborhood hardening their homes and maintaining their lawns to reach herd immunity protection against fire’s contagious spread.

“When there is collective action, it changes the outcomes,” Wright said. “Wildfire is insidious. It doesn’t stop at the fence line.”