Working from a dock on St. Helena Island, S.C., on a sweltering day this summer, Ed Atkins pulled in a five-foot cast net from the water and dumped out a few glossy white shrimp from the salt marsh.

Mr. Atkins, a Gullah Geechee fisherman, sells live bait to anglers in a shop his parents opened in 1957. “When they passed, they made sure I tapped into it and keep it going,” he said. “I’ve been doing it myself now for 40 years.”

These marshes, which underpin Mr. Atkins’s way of life, are where the line between land and sea blurs. They provide a crucial nursery habitat for many marine species, including commercial and recreational fisheries.

But these vast, seemingly timeless seascapes have become some of the world’s most vulnerable marine habitats, according to a new study published on Thursday in the journal Science that adds up and maps the ways human activity is profoundly reshaping oceans and coastlines around the world.

Soon, many of Earth’s marine ecosystems could be fundamentally and forever altered if pressures like climate change, overfishing, ocean acidification and coastal development continue unabated, according to the authors.

It’s “death by a thousand cuts,” said Ben Halpern, a marine biologist and ecologist at the University of California, Santa Barbara, and one of the authors of the new study. “It’s going to be a less rich community of species. And it may not be something we recognize.”

Among the other ecosystems at high risk are sea grass meadows, rocky intertidal zones and mangrove forests. These parts of the ocean, near shore, are the ones people most depend on. They provide natural defenses against storm damage. And the vast majority of commercial and recreational fishing, which together support more than two million jobs in the United States alone, takes place in shallower coastal waters.

There’s also an intangible cultural richness at stake. The culture of Gullah Geechee people like Mr. Atkins, a community descended from enslaved West Africans forced to work the rice and cotton plantations of the Southeastern coast, for example, is inextricably linked to fishing and the seashore.

“We have our own language, we have our own food ways, we have our own ecological system here,” said Marquetta Goodwine, the elected head of the Gullah Geechee people and a leader in efforts to protect and restore the coastline. That distinctive culture, she said, depends on things like the oyster beds, the native grasses and the maritime forests that characterize the seashore and the scores of tidal and barrier islands here, collectively known as the Sea Islands.

“You don’t have that, you don’t have a Sea Island,” said Ms. Goodwine, who also goes by Queen Quet. “You don’t have a Sea Island, you don’t have Gullah Geechee culture.”

A Poorer Ocean

The new study tries to measure just how much various human-caused pressures are squeezing, shifting and transforming coastal and marine habitats.

The research began in the early 2000s, when widespread coral bleaching was raising alarm among marine scientists. In response, Dr. Halpern and his colleagues set out to map the parts of the ocean that were healthiest and least affected by humans and, conversely, which parts were the most affected.

The inherent challenge was comparing marine habitats, from coral reefs to the deep ocean floor, and their responses to different human activities and pressures, like fishing and rising temperatures, all on a common scale. They came up with what researchers call an impact score that’s based on a formula incorporating the location of each habitat, the intensities of the various pressures on that habitat, and the vulnerabilities of each habitat to each form of pressure.

Under the world’s current trajectory, the study found, by the middle of the century about 3 percent of the total global ocean is at risk of changing beyond recognition. In the nearshore ocean, which most people are more familiar with, the number rises to more than 12 percent.

That future will look different in different regions. Tropical and polar seas are expected to face more pronounced effects than temperate, mid-latitude ones. Human pressures are expected to increase faster in offshore zones, but coastal waters will continue to experience the most serious effects, the researchers forecast.

There are also countries that are considered more vulnerable because they depend more heavily on resources from the ocean: Togo, Ghana and Sri Lanka top the list in the study.

Across the whole ocean, scientists generally agree that many places will look ecologically poorer, with less biodiversity, Dr. Halpern said. That’s mainly because the number of species that are resilient against climate change and other human pressures is simply far fewer than the number of more vulnerable species.

The study found that the biggest pressures, both now and in the future, are ocean warming and overfishing. But the researchers most likely underestimated the effects of fishing, they wrote, because their model assumes that fishing activity will hold steady rather than increase. They also focused only on the species actually targeted by fishing fleets and did not include by-catch, the unwanted species swept up in gear like gill nets and discarded, or habitat destruction from bottom trawling.

The effects of some other human activities aren’t well represented either, including seabed drilling and mining, which are expanding quickly offshore.

Another limitation of the Science study is the fact that the researchers simply added together the pressures from human activities in a linear way to arrive at their estimate of cumulative effects. In reality, those effects might add up to more than the sum of their parts.

“Some of these activities, they might be synergistic, they might be doubling,” said Mike Elliott, a marine biologist and emeritus professor at the University of Hull in England who was not involved in the study. “And some might be antagonistic, might be canceling.”

Even so, Dr. Elliott said he agreed with the broad conclusions of the new study. Scientists could argue about whether the cumulative effects of human activities will double or triple, he said, “but it will be more, because we’re doing more in the sea.”

“If we wait until we’ve got perfect data,” he added, “we’ll never do anything.”

‘Time to Scale It Up’

One of the benefits of such studies is that they can help inform better ocean planning and management, including initiatives like 30×30, the global effort to place 30 percent of the world’s land and seas under protection by 2030.

In South Carolina, one place that has already been set aside is the ACE Basin, a largely undeveloped 350,000-acre wetland on the state’s southern coast that is named for the Ashepoo, Combahee and Edisto rivers, which thread through it.

Riding a boat across the enormous basin can be disorienting. The world flattens as the sun beats down and salt marsh stretches in every direction. Almost everything is a vivid blue or green, like an abstract painting or a map come to life.

White wading birds dot the green marsh grasses, and occasional groups of gray bottlenose dolphins break the blue surface of the water.

Sometimes the dolphins corral their fish prey onto the mud and temporarily beach themselves for a meal, using the salt marsh islands like giant dinner plates. This behavior, called strand feeding, is rarely seen outside the Southeast.

On a recent visit, in one tucked-away corner of the marsh, something emerged from the mud at low tide: a wall, built with concrete blocks now nearly hidden by thousands of shells. They’re called oyster castles, and they look like something out of a storybook about mermaids.

The blocks were placed by volunteers from the Boeing assembly plant in nearby North Charleston. The effort was organized by the Nature Conservancy and the South Carolina Department of Natural Resources as part of a growing string of living shorelines projects, which aim to stabilize the coast using natural materials like shellfish and native vegetation, in South Carolina and beyond.

The oyster castles are meant to protect the landscapes behind them from erosion, sea level rise and storm surges. Scientists from the Nature Conservancy have been experimenting with a variety of methods for years, and are beginning to see results. Behind the oyster castles, which allow water to pass through and deposit sediment, mud had piled up significantly higher than elsewhere. And in the mud, marsh grass has taken root and grown tall.

“We’ve been testing and piloting things for so long, and now is the time to scale it up,” said Elizabeth Fly, director of resilience and ocean conservation at the Nature Conservancy’s South Carolina chapter.

In fact, the state’s oyster shell recycling program has now built small living shorelines at more than 200 sites, all with the help of volunteers, and often working with other groups, like the Gullah Geechee Nation. There’s a living shoreline taking shape at the Charleston wastewater treatment plant. Another at the entrance to the exclusive Kiawah Island Golf Resort. They’re at Marine Corps bases, at boat launches and at docks.

Many of these efforts are part of a sprawling network called the South Atlantic Salt Marsh Initiative, which includes the Pew Charitable Trusts, the Department of Defense, other federal agencies and state governments. The network spans one million acres of salt marsh across four Southeastern states.

Amid those efforts to reinforce and protect marine ecosystems, and as scientists work to better understand the pressures that are altering the oceans, people in coastal communities everywhere are already living changes large and small.

The day after Mr. Atkins demonstrated his fishing methods, the town of Mount Pleasant, S.C., 80 miles up the coast, held its annual Sweetgrass Festival to celebrate the region’s traditional Gullah Geechee baskets. Dozens of artists braved the heat in booths at a waterfront park, showing off and selling baskets woven from sweetgrass, bulrush, palmetto leaves and pine needles.

One artist and teacher, Henrietta Snype, displayed baskets made by five generations of her family, from her grandmother down to her own grandchildren.

Ms. Snype started making baskets at age 7. Now, at 73, she takes pride in upholding the tradition and teaching others the craft and its history. But she feels the world around her changing.

She said she had noticed the climate shifting for many years now. Big hurricanes seem to have become more frequent and seem to do more damage. And making baskets is harder, too.

Traditionally, the men in basket-making families went out into the dunes, marshes and woods to gather the materials they needed. But lately, Ms. Snype said, the plants have been harder to find. Sweetgrass is diminishing, and harvesters have trouble getting access to built-up and privately owned parts of the coastline.

“The times bring on a lot of change,” she said.

In 2003, the Nobel Prize winner David Baltimore, then president of Caltech, paused to reflect on his role as one of the world’s most decorated scientists.

“People keep e-mailing me to ask, ‘What is the meaning of life?’” Baltimore told an interviewer, with amusement. “And they want me to e-mail them back quickly with an answer!”

Baltimore was then 65, an age when many people are retired from public life, yet he was still actively leading one of the world’s top research universities. Others, he said, found their meaning “in friends, in dogs, in religion, in the self-reflectiveness of writing, etc. But Caltech people largely find it in the continual contest with nature.”

It was a contest that Baltimore waged right to the end of his life as a scientist, businessman and internationally respected conscience of the new world of biological engineering. He died Saturday at his home in Woods Hole, Mass., according to his wife, as reported by the New York Times. Baltimore was 87.

His death concludes one of the most illustrious careers in 20th century science. The bearded scientist with the penetrating blue eyes played a role, usually a leading one, in virtually every important national debate over the use and potential misuse of the science of genetic engineering, whether it was gene-splicing and the search for an AIDS vaccine, or the dangers of tinkering with the human genome.

But it was as a working scientist that he made his most enduring contributions, the role he was most proud of.

“When you are a scientist, and you are trying to prove or disprove a notion, you work at the bench doing the dullest, most routine things over and over and over again,” Baltimore once explained.

“I can’t tell you how many ways things go wrong. All the time you are doing this because there is an idea behind it.”

In a statement, Caltech President Thomas Rosenbaum said Baltimore’s “contributions as a virologist, discerning fundamental mechanisms and applying those insights to immunology, to cancer, to AIDS, have transformed biology and medicine.”

“David’s profound influence as a mentor to generations of students and postdocs, his generosity as a colleague, his leadership of great scientific institutions, and his deep involvement in international efforts to define ethical boundaries for biological advances, fill out an extraordinary intellectual life,” he added.

David Baltimore was born March 7, 1938, in New York City, the son of a garment industry merchant, Richard Baltimore, and Gertrude Lipschitz-Baltimore.

Richard’s family was Orthodox Jewish, from Lithuania, and though the Baltimores in America were not overtly religious, the family communicated a moral code that influenced their son’s concern for the underprivileged.

This led him to take public stands on social issues, such as the AIDS epidemic and nuclear proliferation, that other scientists shunned. In 1970, while performing experiments that would win him the Nobel Prize, he shut down his lab for a week and joined demonstrators in Boston against the Vietnam War-era invasion of Cambodia.

In high school, Baltimore enrolled in a summer program at the prestigious Jackson Laboratory at Bar Harbor, Maine, where he made a discovery that altered his life and set him on the path to science.

“It was the process of research. I discovered that I could investigate the unknown as a high school student, that the frontier of knowledge was actually very close and very accessible,” he said, many years later.

After graduating from Swarthmore College, Baltimore earned his doctorate from the Rockefeller Institute (now University), before doing three years of research at the Salk Institute in La Jolla, where he met his future wife, Alice Shih Huang. His postdoctoral student, Huang collaborated in his research on animal viruses, later becoming a full professor at Harvard Medical School. At this time, Baltimore was particularly interested in the poliovirus, which attacks the RNA (ribonucleic acid) in cells.

“He was on the cutting edge of molecular biology,” said science historian Daniel Kevles, his friend and colleague. “There was no molecular biology to speak of and very little virology. … It was a brave field of work.”

At the time, it was an ironclad rule in molecular biology that genetic information was a one-way street, flowing from the double-helix structure of DNA to the single-stranded RNA, which the cell’s machinery uses to make proteins. But some biologists were beginning to question that assumption, and Baltimore joined the hunt for evidence that genetic information might flow in both directions, which, if true, held enormous potential for understanding the spread of viruses.

After leaving the Salk, Baltimore returned to Boston and became an associate professor of microbiology at MIT. As it became apparent that not all viruses behaved alike, Baltimore launched a new classification system, one that is still in use, grouping them by families according to their genomes and replication systems.

It was during this work that he discovered an enzyme that enabled a virus made of RNA to be copied into DNA, a process known as reverse transcription. The discovery of reverse transcriptase was greeted with overheated predictions that science had at last found a cure for cancer. The thinking went, if one could use RNA to code DNA, scientists could seize control of the body’s defenses.

Baltimore knew his work did not augur a cure for cancer, but the discovery of reverse transcriptase was nonetheless important because it led to an understanding of how genes can modify cells, turning normal cells into cancer cells. Reverse transcriptase is also used by a unique family of viruses, known as retroviruses, to replicate themselves. This finding would be critical to understanding the AIDS virus, HIV, which is a retrovirus, and devising anti-HIV treatments.

Baltimore’s discovery was attended by great fanfare and led to his promotion to full professor at MIT. In 1973, he was awarded a lifetime research professorship by the American Cancer Society, and a year later was elected to the National Academy of Sciences and the American Academy of Arts and Sciences. Finally, in 1975, with Howard Temin, a friend and colleague who had discovered reverse transcriptase around the same time, Baltimore was awarded the Nobel Prize for physiology or medicine.

With the prize came fame; people began referring to Baltimore as the most influential biologist of his generation. To the general public, who did not necessarily understand what he had done, only that it was important, he became, at the age of 37, a full-fledged savant.

The award had a profound effect on colleagues.

“I don’t see it as a burden, but you can’t get away from it,” Baltimore said. “I know that when I talk to young scientists, they are looking at me and saying, ‘God, I am talking to a Nobel Prize winner.’ I try to break that down. It gets harder every year.”

His new celebrity status gave him a platform to address issues of broad cultural and scientific importance, a role Baltimore embraced.

In the 1970s, when people became concerned that gene-splicing techniques could lead to the production of super viruses, Baltimore organized a conference at Asilomar near Monterey to design a self-regulating system to monitor those experiments. In the early 1980s, he led the fight against a crash program to map all human genes, fearing, once again, unknown consequences. In each case, when it was shown the dangers had been overestimated, he then led the effort to relax federal restrictions. He became an early champion of federal AIDS research and chaired a national commission that concluded the federal government’s response to the epidemic was dangerously inadequate.

As his reputation grew, he took leadership roles on political issues. When Pope John Paul II wanted to warn President Reagan of the danger of nuclear weapons, Baltimore was one of four scientists the pontiff appointed to carry his message.

In 1984, Baltimore was chosen founding director of the new Whitehead Institute for Biomedical Research, molding it into one of the world’s leading institutions of its kind. Following that success, he was appointed president of the Rockefeller University.

Along the way, he became not only a respected link between the government and scientists but also a key player in the burgeoning biotechnology industry. His early involvement in the industry made him a “relatively wealthy man,” according to a 1997 Times magazine profile.

The profile described a man in the fullness of middle age, harvesting the benefits he had earned, drinking the best wines and single-malt scotch, driving appropriately luxurious but not ostentatious vehicles. “With his wife, Dr. Alice Huang, he shares a luxury duplex condominium on Union Wharf, which has a commanding view of Boston Harbor,” it said.

In person, “Baltimore’s practiced elegance frames a fierce pride and a sometimes brutal intellect, softened only by his insistence that professional criticism be leavened by personal respect.”

And then, the entire edifice crumbled as Baltimore became the focus and fall guy for one of the more infamous investigations of scientific misconduct in the last half of the 20th century. A colleague wrote a paper claiming sensational results. When others could not reproduce those results, allegations of fraud were aired, causing Congress to get involved. With the decline of the space program, biology had emerged as the preeminent science, and Congress was becoming skeptical about how millions of dollars in federal research grants were being spent.

The whiff of scandal was attached to Baltimore himself, even though his work was never questioned. Still, his refusal to admit error, or to abandon his problematic colleague, came to symbolize for many the arrogance of the new mandarins of the biological sciences.

“The Baltimore case is reminiscent of the Watergate scandal,” the New York Times wrote.

Four federal investigations and a grand jury probe later, Baltimore’s colleague, and Baltimore himself, were exonerated. The ordeal had consumed a decade of his life. Then, within months, everything changed. He was chosen to coordinate the federal effort to develop an AIDS vaccine and then appointed president of Caltech. It was a breathtaking reversal of fortune.

“It is even more breathtaking,” Baltimore said in 1997, shortly after taking the Caltech job, “to live through it.”

Kevles, a professor at Caltech at the time, recalled that when Baltimore’s name was announced to the assembled faculty, “the room erupted in cheers. I had never seen the biologists look so ecstatic. It legitimized their field.”

In his eight years as president, Baltimore raised the university’s profile, both as a place where cutting-edge biology is done and as a respected voice on pressing national scientific debates. Under his leadership, Caltech raised more than $1.1 billion. He cited the gift of $600 million to the school by Intel Corp. co-founder Gordon Moore and his wife, Betty, as the “decisive moment” of his presidency.

“Caltech is a wonderful place, the best place to do science I have ever seen,” Baltimore said in 2005, when he announced his resignation. “I will have done what I can do [as president], and it is time for somebody else to be thinking about it.”

As for what would come next, Baltimore said, “I have a fairly extensive life in science and in business that I will pursue.”

If he thought his return to the laboratory would be a placid coda to his career, he was soon proved wrong, by yet another advance in genetic engineering, this one called CRISPR. “I’ve seen revolution after revolution in biology,” Baltimore said in 2016. “This one is a big deal.”

As one writer noted, if the gene-splicing technology of the 1970s spurred images of laboratory-hatched plagues from the “Andromeda Strain” novel and movie, CRISPR inspired comparisons to “Brave New World.” MIT’s Technology Review wrote of labs in which “man rebuilds creation to suit himself” and warned of “a path toward a dystopia of superpeople.”

Just as he did decades earlier, Baltimore took a leadership role in starting a public discussion about how to manage the powerful new tool. “At Asilomar, we had identified the genetic modification of humans as the biggest coming issue,” Baltimore said. “We just didn’t know when it would come.”

A statement drafted by participants at a meeting in Napa in early 2015 spoke of the promise of “curing genetic disease” but also warned of “unknown risks to human health and well-being.”

The statement listed 18 authors, with Baltimore at the top. Though he wrote an op-ed for the Wall Street Journal entitled, “Let’s Hit ‘Pause’ Before Altering Humankind,” Baltimore admitted later that genome-editing would in all probability take place sooner rather than later.

After retiring as president of Caltech, he remained on staff in an emeritus capacity, and was appointed the Robert Andrews Millikan professor of biology. He finally shuttered his lab in 2019 but remained active in business. He helped found a number of companies, including Calimmune and Immune Design, which carried on the work he began in immunology and virology. Though he was most visible for his public advocacy of cancer and AIDS research, it was his work as a “lab-based, working biologist” that gave him the most pleasure, and for which he hoped to be remembered.

Besides the Nobel Prize, he received the National Medal of Science in 1999, and the Warren Alpert Foundation Prize in 2000. He was the 1999 recipient of the National Medal of Science and published more than 700 peer-reviewed articles.

He was also a member of numerous scientific advisory boards, including Amgen, the Broad Institute, Ragon Institute, and Regulus. Baltimore was past-president and chair of the American Assn. of the Advancement of Science.

He is survived by his wife, Alice, and daughter, T.K. Baltimore.

Johnson is a former Times staff writer. City News Service contributed to this report.

The body of a woman was found by Pasadena firefighters responding to a house fire Saturday morning, officials said.

Firefighters responded at 6:25 a.m. to a house engulfed in flames in the 1500 block of Lancashire Place, said Lisa Derderian, a spokeswoman for the city of Pasadena. They found the body inside as they battled the flames, she said.

Officials are waiting for the coroner to identify the woman, Derderian said. “It appears she lived alone.”

The home, on a dead end street west of the Rose Bowl, was significantly damaged, Derderian said, but neighboring properties were not harmed.

Investigators are looking into the cause of the fire, she said.