Why did a marine virus traced to the 1940s suddenly wipe out starfish? Leslie Willoughby dips into tide pools. Illustrated by Jen Burgess and Lauren Bassing.

Spruce and cedar stand sentinel on a rocky Oregon headland. Gulls call from a distance, invisible in the colorless mist. It’s 5:45 a.m. at Cape Arago, 15 miles southwest of Coos Bay, and it's too cold to slide into rubbery, waterproof overalls still wet from the previous day’s work. We pick up toolboxes, clipboards, and lengths of PVC pipe. Nate Fletcher, a biologist at UC Santa Cruz, leads us down a muddy path. His colleagues have surveyed this shoreline every six months since 2000, and they know something has changed. This morning in the outgoing tide, sea stars—previously plentiful—now barely cling to life.

In June 2013, scientists first watched these flamboyantly colored creatures transmogrify just as Yeats once described in a poem: “Things fall apart; the centre cannot hold. . . .” Within days the animals disintegrated, their arms walked off in different directions, and they melted into goo.

This “sea star wasting syndrome” might be the largest known marine wildlife disease outbreak ever recorded, according to a 2014 scientific paper about the disease. Similar die-offs in the 1970s, 1980s and 1990s also killed sea stars along southern California or in Mexico’s Gulf of California. But the new wave of deaths is so pervasive that marine scientists fear ocean food webs along the coast are changing before their eyes.

The unfolding syndrome claims its victims along the Pacific coast of North America from Mexico to Alaska. It kills sea stars from 19 species, with five nearly disappearing from many sites. The spread has been shockingly rapid. The UCSC researchers observed a high level of wasting at 39 percent of the sites they surveyed in central and northern California. By summer 2014, that figure had soared to 87 percent.

A year of intense detective work at sea and in the lab revealed a startling association: a virus present in marine ecosystems for seven decades suddenly became a killer, and scientists don’t yet understand the trigger. Other species have rushed to fill the void left by the snuffed-out starfish. Meanwhile, some sea urchins—a valuable food source for a fragile population of sea otters and delicacies for humans—have been struck with similar symptoms.

“There is still too much we don't understand about how long this disease event will last, how big of an impact it will have, and how long recovery will take,” says biologist Melissa Miner, a research associate at UCSC. For now, sea stars survive in mere pockets of their former ranges and face an uncertain future.

Falling stars

Ecologist Pete Raimondi of UC Santa Cruz has seen many species ebb and flow during three decades of work in the tidal zones of rocky shorelines. The new syndrome, he says, has stunned and mystified him. “A whole class of species is being removed from the system—essentially the top invertebrate predators in at least two systems, the rocky intertidal and rocky shallow subtidal,” he says.

Video: Leslie Willoughby UC Santa Cruz ecologist Monica Moritsch surveys the intertidal zone near Santa Cruz to gauge the impacts of sea star wasting syndrome on the ecosystem. (Click on image to go to Vimeo page)

The two zones lie along the edge of the sea, forming ribbons of life on the coast. During high tide, crashing waves refresh pools in the intertidal zone. During low tide, the shifting skirts of waves retreat, leaving life exposed to wind and sun. Hardy sea stars, sea urchins and barnacles inhabit this changeable zone—sometimes submerged, other times exposed—and delight seaside visitors. The subtidal zone is more difficult to visit because it almost always remains underwater. Organisms such as kelp and sunflower sea stars that live in this zone avoid the ravages of tides.

Researchers with the National Park Service first reported sea stars wasting away in Olympic National Park in June 2013. Soon thereafter, UCSC scientists working in Washington saw ochre sea stars dying from the syndrome. Ecologist Robert Paine had boosted these orange and purple stars to fame in the 1960s. They average 7 inches across and cling so tightly to rocks that Paine needed a crowbar to dislodge them. In areas he cleared of the stars, Paine saw other species start to flourish. He coined the term “keystone species” to describe organisms such as the ochre star that are central to the mixture of animals and plants in an ecosystem. Yet the syndrome wiped out 75 percent of these tough predators.

Raimondi watched the disease spread from region to region. Within weeks he realized the event fit the pattern of a mass die-off. He immediately set to work to detect the cause.  During previous wasting events, most evidence had pointed to warmer ocean waters as the culprit. But Raimondi’s scan of two decades of sea star data eliminated that as the prime suspect, and screened out the other usual killers: pollution, ocean acidification, and low oxygen.

Other scientists ruled out radiation from the Fukushima nuclear plant disaster following Japan's massive earthquake and tsunami in March 2011. No new radiation had arrived along the Pacific coast of North America when the stars started dying.

By August 2013, sunflower stars were disintegrating on western Canada's rocky shores. A yard in diameter, these 24-armed predators easily engulf entire sea urchins, digest them, and then spit out their spiny shells.

The news worsened in October and November when five species of previously healthy starfish succumbed in and around California's Monterey Bay. Within six weeks, the area's sunflower stars and rainbow stars went from healthy to wasting to absent.

By Christmas, the syndrome had invaded southern California. And by early 2014, it had spread from Alaska to San Diego. By June, the giant pink sea star—one of the world’s heaviest at up to 10 pounds—had vanished from Monterey Bay. And though marine biologists could still find giant stars and bat stars there, they were wasting, too. The reddish-orange bat star, Fletcher’s favorite, sports webbing between its arms. This 8-inch-wide kelp dweller resembles a goose’s foot.

In the face of such geographically extensive die-offs, with no single identifiable trigger, Raimondi surmised that several accomplices—perhaps including viruses or bacteria—might be working in concert. Ironically, the first scientists to describe viruses in animals such as sea stars worked in laboratories 3,000 miles away.

Virus among us

In early 2013, before the first observation of sea star wasting in coastal Washington, microbiologist Ian Hewson of Cornell University was surveying a group of spiny-skinned animals called echinoderms. This group includes sea stars, sea urchins and sand dollars, brittle stars, sea cucumbers, and feather stars. Hewson and his colleagues realized no one had ever looked for viruses in these creatures.

While teaching a course in Hawaii, Hewson collected samples from sea urchins and a sea star. Back in his lab, he ground them up and searched the resulting blend for traces of genetic code. He identified codes from specific viruses, including an unusual type called a densovirus. This kind of virus had been found in insects, but no one had ever associated it with marine organisms. In November 2013, a journal published Hewson’s scientific paper about the virus.

As his projects were coming to a close, he felt ready for a new venture—and the West Coast starfish calamity was well under way. “We had all the tools ready to go," Hewson says. "We knew we could answer this question very quickly.”

Hewson and his team started with five species, but the investigation grew to 20 different kinds of sea stars and 428 specimens. Truck after truck arrived at Hewson’s lab, laden with coolers full of dry ice, pieces of starfish, and living specimens from the Pacific. “It blossomed into this enormous project,” says Hewson.

The samples ranged from a half-dollar-sized star to the arm of a 2-foot-diameter giant pink sea star. Living sea stars smell like fresh fish, but tissue samples have “a very distinctive odor,” says Hewson. He felt sorry for the scientists who dissected soap-like specimens that exuded a sulfurous rotten-egg stench.

In December 2014, a year after they undertook the investigation, Hewson and his colleagues—including Pete Raimondi and Melissa Miner—published their findings. They linked the mass mortalities of sea stars to a densovirus—a virus related to the one Hewson had found previously in Hawaiian sea urchins. The team extracted virus-sized material, smaller than bacteria, from diseased tissue. When they injected the material into healthy sea stars, these stars then developed signs of the syndrome. Genetic analysis revealed the equivalent of fingerprints: the presence of the densovirus. There were more copies of the densovirus in sick sea stars than in healthy ones. The team also found the virus in plankton, sediments, sea urchins, sand dollars and brittle stars. That external presence may explain how the virus moves from one population of starfish to another.

Using the same tests, researchers found no other suspect virus. All clues pointed to a single guilty virus, with one puzzling exception: Hewson found the identical virus in sea star museum specimens collected in 1942. The perpetrator apparently has infested sea stars for at least seven decades, and the animals had made their peace with it—until the coexistence became fatal.

And that is the burning question for Raimondi: Why is sea star wasting so devastating this time? Tissue scientists think ocean warming, or increasing acidity, or some other outside assault has weakened sea stars and made them more vulnerable to the virus. Evolutionary biologists propose that the virus may have evolved and become an extra potent starfish slayer.

Raimondi continues to hunt for these possible partners in crime, a malignant combination of factors that causes sea stars to melt away. His team now works to identify the scenes of the crime—where the syndrome took root and spread. Then they will examine conditions that were in effect at those places and times. “We have this huge network of sites, and we also engage citizen science through our website,” says Raimondi. “That allowed us to really get ahead of the detection efforts.”

As volunteers and scientists puzzle over why the old virus is now thriving, it may be felling a new victim.

Illustrations: Lauren Bassing

Sea stars ordinarily keep sea urchins in check (top). As sea stars disappear, more urchins crop up from cracks and crevices in some nearshore ecosystems (bottom).

Urchin troubles

During previous sea star wasting events in 1983-84 and 1997-98, the disease progressed from sea stars to sea urchins. Today, Raimondi and his volunteers are watching for any spikes in urchin wasting, or any spreading from where it strikes. Reports from June 2014 to January 2015 showed that sea urchins off the coast of southern California were losing spines and showing lesions. White, purple and red sea urchins inhabit the waters off the California coast; observers have reported wasting-like symptoms in all three. “We're almost in the same situation where we were two years ago with sea stars,” says Raimondi.

These observations may be connected to the ongoing sea star wasting event. However, they also may be tied to a different virus or bacteria and unusually warm water. Raimondi says he does not want to cause undue alarm, but it’s becoming more likely that sea urchin wasting is related to the sea star calamity.

Sea urchins teeter at a tipping point between two environmental pressures, Raimondi notes. Although some sea urchins are dying, many of their natural predators—sea stars—are vanishing.

In patches along the Pacific coast, and within the crescent of Monterey Bay, an unusual seascape unfolds, divers say. Where predatory sea stars used to cluster, sea urchins scrabble around in broad daylight. The urchins are adults, not new arrivals. In the past they would have sought safety in the abundant cracks and crevices among the rocks. But now they move about with apparent impunity. “I did not expect to see that, because I thought otters would have eaten them,” Raimondi says. “Urchins can have a profound effect on the community.”

A sparse population of fewer than 3,000 sea otters survives along California’s Central Coast. They compete for the spiky purple urchins, a favored snack for some. So far, though, most otters have not changed their feeding habits to focus on these ready-made meals.

Podcast produced by Leslie Willoughby. Click on image to play.

Humans prize red sea urchins, which can grow to 7 inches across. The total catch of 6,500 tons in 2013 was valued at $9.9 million. They rank in the top five fisheries in California by weight and value, according to a 2014 report from the University of Southern California. Edible sea urchin gonads, called “uni,” grace many Japanese gourmet menus. Time will tell whether wasting will claim more of these delicacies, savored by humans and otters alike, or whether freedom from predatory starfish will allow them to prosper.

Changing tides

Raimondi’s coastal observers have kept an eye on ochre sea stars at Scott Creek beach, a half-hour drive north of UCSC, since 1999. In January 2015, Nate Fletcher returns to the site, one of the places where he first saw sea star wasting syndrome in late 2013. He’s looking for survivors.

He checks a few familiar spots before he finds the first ochre star. It grasps the vertical wall of a wave-splashed channel. Then he discovers another one, just a yard down the channel’s side.

I lie across a mussel bed for a better view. This maroon-colored creature looks as squishy as a slug, yet its entire body is laced with tiny white protrusions. I close my eyes and lightly run my fingers over the star. Its chalky-textured points remind me of braille. Hunting with my fingertips, I find a smooth area where the skin barely yields like the leathery shell of an unripe avocado. It’s difficult to imagine how such a tough and prickly animal could melt away.

Later, Fletcher kneels beside a tide pool chock-full of purple sea urchins. Like amethyst pincushions, they stud the bottom of the pool, apparently bristling with health. Each digs a hemispherical home in the stone with its teeth and spines. In one such scoop we find a third ochre star, surrounded by the pool’s spiny residents. Fletcher sorts through mussels on a rocky ledge and exposes a bit of life the size of a thumbnail. A distinguishing pyramid-shaped pattern glistens on its back. The baby is the last ochre sea star we will see.

Before 2013, adult ochre stars had clustered here, their deep purple or rusty orange arms overlapping in mats of clashing color. When ready to reproduce, they expelled their eggs and sperm to the sea. Their larvae ate plankton and swam free.

Fletcher recalls those previous years. “We would find a lot of ochre stars along the edge [of the mussel beds]. In those two channels, there were a lot—hundreds,” he says. "Looking around today, I’ve seen only four. We’re not looking as hard as if we were sampling, but there aren’t a lot left.”

Baby ochre stars are settling in crevices along the Pacific coast, research teams have found. Some of them have succumbed to wasting syndrome. Every six months, Fletcher and his crew will measure their progress. For sea stars to return to their tidal homes, these babies somehow must hang on.

© 2015 Leslie Willoughby / UC Santa Cruz Science Communication Program

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Biographies

Leslie Willoughby
B.S. and M.S. (natural resources) The Ohio State University
Internships: Stanford Woods Institute for the Environment; U.S. National Park Service, Point Reyes National Seashore

My first love was a horned toad that lived in my backyard in Albuquerque. It disappeared over winter, emerged in spring, and showed me that nature changes over time. Throughout childhood, I yearned to share that lizard's world with others.

In college I studied environmental interpretation. Afterward, at the newly created Ohio EPA, I funded programs that regulated scrubbers in coal-fired power plants and improved sewage treatment facilities. Later, as a science teacher, I set the lab tables with a new narrative each morning. Monday’s tale might compare skeletons; Tuesday’s could mimic a lunar eclipse.

When climate change became the biggest nature story, I signed on as a reporter in the Eastern Sierra. Now, forest fires rage and drought starves our snowpack and water supply. I need epic writing muscle. I work out every day.

Leslie Willoughby's website

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Jen Burgess
B.S. (geography) University of Victoria, Victoria, Canada
Internship: Beaty Biodiversity Museum, Vancouver, Canada

Jen Burgess is a natural science illustrator originally from British Columbia, Canada. Her early years were spent exploring the rainforests and gardens of the Pacific Northwest, and this prompted her interest in the natural world and concern for the environment. Drawing almost non-stop from the time she could hold a crayon, she paused her artistic pursuits when she reached university, hoping that a degree in science would lead to a more sustainable career option. After graduation she set off to travel, teach, volunteer, and through everything she eventually she found her way back to study art and illustration. All of this culminates in her completion of the science illustration program at California State University Monterey Bay, after which she plans to return to Vancouver and begin her career as a freelance illustrator. Jen is also a trained naturalist and interpretive guide, bringing her love for nature and communications skills into her artwork. In her free time she can be found hiking with her dog, reading, gardening, or sitting down to a cup of tea.

Jen Burgess's website

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Lauren Bassing
M.Ed. (education) Antioch University New England
B.F.A. (graphic design) Rhode Island School of Design
Internship: Smithsonian Institution, National Museum of Natural History (Botanical Illustration)

Lauren is a natural science illustrator and artist based in New England. After nearly twenty years as a reading specialist, she decided to follow a long-time dream and attend the Science Illustration program at California State University, Monterey Bay. After her internship at the Smithsonian, she looks forward to a career drawing plants and painting birds.

Lauren Bassing's website

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