Sunflower sea stars are the largest sea stars in the world: They have up to 24 arms and grow to the size of a bicycle tire.

Starting in 2013, these creatures and other sea star species along the west coast of North America died in epidemic proportions. The stars had harrowing symptoms: Their arms contorted before falling off completely. Over the past decade, sea star wasting disease has killed billions of sea stars in up to 20 species by effectively “melting” their tissues.

The disease has wiped out more than 90% of the once-common sunflower sea stars, most critically in the continental U.S., landing them on the International Union for Conservation of Nature鈥檚 . The loss of sunflower sea stars, which support kelp forests by feeding on kelp-eating sea urchins, has had widespread and lasting effects on coastal ecosystems.

Until now, no one knew what caused sea star wasting disease. But on Aug. 4, an international research effort including scientists from the 天美影视传媒 has finally revealed the cause: a strain of the bacterium Vibrio pectenicida. Vibrio is a genus of bacteria that has devastated coral and shellfish as well as humans (for example, Vibrio cholerae is the pathogen that causes cholera).

The researchers in Nature Ecology & Evolution.

“This is the discovery of the decade for me,” said co-author , a UW affiliate professor in the School of Aquatic and Fishery Sciences and Friday Harbor Laboratories. “We have studied both the cause and the impacts of this disease for the entire epidemic. What’s crazy is that the answer was just sitting right there in front of us. This Vibrio is a sneaky critter because it doesn’t show up on histology like other bacteria do.”

“From initial studies, we thought the culprit was a virus,” Harvell continued. “So it was a surprise to find the pathogen in a more common group of bacteria.”

The long-awaited result showing V. pectenicida strain FHCF-3 as the causative agent comes after a four-year research process. Scientists explored many possible pathogens, including viruses. At first, the researchers looked in sunflower sea star tissues before they homed in on the high levels of V. pectenicida in sick sea star 鈥渂lood,鈥� or coelomic fluid.

“When we looked at the coelomic fluid between exposed and healthy sea stars, there was basically one thing different: Vibrio,” said senior author , a marine disease ecologist at the Hakai Institute and the University of British Columbia. “We all had chills. We thought, ‘That鈥檚 it. We have it. That鈥檚 what causes wasting.'”

Harvell attributes the team’s success to:

• Having the right facilities at the U.S. Geological Service with proper quarantine and high-quality water flow
• A talented research team that had pathology, virology and bacteriology experience
• Having access to a source of the right test animals, including sunflower sea stars raised in captivity by co-author , UW senior research scientist at Friday Harbor Laboratories.

“I observed and collected health data on nearly every single sea star twice a day for the majority of experiments for all four summers,” said co-author , a UW doctoral student in the School of Aquatic and Fishery Sciences. “I have loved sea stars and have been fascinated by diseases since childhood. To get to participate so actively in research that combines both of these interests has been a dream come true. I’m excited about getting to work on a project with such consequential findings for the conservation of these important sea stars: to find both the cause of sea star wasting disease, and to better understand their immune response.”

To confirm that V. pectenicida was the culprit, co-author , a research scientist at UBC, created pure cultures of V. pectenicida from the coelomic fluid of sick sea stars. The team then injected the cultured pathogen into healthy sea stars, which developed symptoms of sea star wasting disease 鈥� the final proof.

“When we lose billions of sea stars, that really shifts the ecological dynamics,” said lead author , an evolutionary ecologist at the Hakai Institute and UBC. “In the absence of sunflower stars, sea urchin populations increase, which means the loss of kelp forests, and that has broad implications for all the other marine species and humans that rely on them. So losing a sea star goes far beyond the loss of that single species.”

Now that scientists have identified the pathogen behind sea star wasting disease, they can look into the drivers of disease and potential hallmarks of resilience. Researchers are particularly interested in studying the link between sea star wasting disease and rising ocean temperatures. The effects of the disease seem to be stronger in warmer water, and other species of Vibrio are also known to proliferate in warm water, Gehman said.

Researchers and project partners hope the discovery will help guide management and and the ecosystems affected by their decline.

“It’s just heartbreaking to watch them die,” Harvell said. “Sunflower sea stars are enchanting creatures and they’re quite interactive. At feeding time, they will come toward you. If you throw clams to the stars, they can catch them. It’s so gratifying to finally have an answer.”

Additional co-authors on this paper are Katherine M. Davis and Jan F. Finke at UBC and the Hakai Institute; Paul K. Hershberger at the U.S. Geological Survey; Andrew McCracken at the University of Vermont; Colleen T. E. Kellogg, Rute B. G. Clemente-Carvalho and Carolyn Prentice at the Hakai Institute; and Kevin X. Zhong and Curtis A. Suttle at UBC. The research was supported by The Nature Conservancy of California, the Tula Foundation, the Natural Sciences and Engineering Research Council of Canada Discovery Grant, the Canadian Foundation for Innovation and British Columbia Knowledge Development Fund Infrastructure award, the University of British Columbia, the U.S. Geological Survey, Biological Threats Research Program, Ecosystems Mission Area and the Quantitative and Evolutionary STEM Traineeship.

For more information, contact Harvell at cdh5@cornell.edu.

Adapted from a release from The Hakai Institute.

At the , recovery is afoot. Scientists at this 天美影视传媒 facility in the San Juan Islands are working to help sunflower stars 鈥� a type of sea star 鈥� grow and thrive once again after their populations along the West Coast were devastated by a mysterious disease.

鈥淭hey鈥檙e gone in a lot of places, and a lot of what we鈥檙e doing here is testing out ideas for reintroduction,鈥� said , a researcher at the lab.听

In summer 2013, sea star wasting syndrome more than a dozen sea star species up and down the West Coast of North America. Since sea stars 鈥� a group of invertebrates that are also called starfish 鈥� are essential predators, their decimation upended marine ecosystems from Mexico to Alaska.听

鈥淚n regions where these important predators are gone, we鈥檝e seen explosions of species they would normally prey upon, like sea urchins,鈥� said Hodin. 鈥淭hat disrupts kelp forests, turning them into what we call 鈥榰rchin barrens.鈥� It adversely affected food webs all along the West Coast.鈥�听

The outbreak of this syndrome, the cause of which is still unknown, has led scientists like Hodin to study how to help sea stars get a leg up 鈥� or more accurately, an arm up. In partnership with The Nature Conservancy, Hodin and his team have pioneered methods to rear sunflower stars in the laboratory. Sunflower stars were particularly hard hit by sea star wasting syndrome, and they play an especially critical role as predators in marine ecosystems. Hodin鈥檚 team wanted to learn whether lab-raised stars could be introduced successfully into the wild to boost their numbers.听听

“The laboratory studies are also giving us insight into the ecology and behavior of sunflower stars across their whole life history, including the young stages when they are too small to easily find in the wild 鈥� even when populations were strong,鈥� said Hodin. 鈥淭his approach is helping us learn what we need to know to be able to help bring the species back from the brink.鈥�听

Last year, the research team 鈥� led by Scientific Diver Joey Ullmann 鈥� 鈥減lanted鈥� laboratory-grown sunflower stars in cages at three sites in the San Juan Islands to ascertain how well they would grow and thrive during more than two months in the wild. The team discovered that lab-reared stars did well, and Hodin hopes that these efforts will pave a way toward the restoration of healthy kelp forests.听

鈥淚t鈥檚 all pointing in pretty positive signs that this was successful,鈥� said Hodin.听

It鈥檚 a promising start, with more to come.听

For more information, contact Hodin at hodin@uw.edu.听听

Just a few days shy of the first day of spring, scientists at Friday Harbor Laboratories on San Juan Island had reason to celebrate.

Dozens of juvenile sea stars, no bigger than a poppy seed, had successfully metamorphosed from floating larvae to mini stars 鈥� the important first step toward becoming adults. Between now and then, these sunflower sea stars, the largest sea star species in the world, will grow up to 24 arms and a colorful body the size of a serving platter.

These young animals represent the first attempt to raise sunflower sea stars in captivity. The species, once abundant from Alaska to Southern California, was nearly destroyed by a mysterious wasting disease that has affected many sea stars in the ocean, but none so catastrophic as the sunflower star. In December, the species was by the International Union for Conservation of Nature, prompting a new focus on recovery efforts 鈥� including captive breeding.

The project, a partnership between the 天美影视传媒 and The Nature Conservancy, aims to learn more about sunflower sea stars and explore eventual reintroduction to the wild, if determined to be advisable. The research team currently is raising sea stars in several phases of development, including newly born larvae, mini juveniles and fully grown adults.

鈥淲hat we鈥檙e attempting to do here is to raise a new generation of sea stars in the lab,鈥� said , research scientist at Friday Harbor Labs who is leading the captive rearing efforts for the UW. 鈥淲e鈥檙e hoping that our efforts can help in the process of recovery of the sunflower sea star and, ultimately, recovery of the health of ecosystems like the kelp forests that are under threat right now.鈥�

Left to right: Sunflower sea star larvae, about a month old, seen under a microscope; one-year-old juvenile sea stars; adult sea stars (click on each image to enlarge).听Dennis Wise and Kiyomi Taguchi/天美影视传媒.

Kelp forests are already facing increased pressure from marine heat wave events and, combined with exploding sea urchin populations, these threats contribute to an uncertain future for the kelp forest ecosystems that provide important habitat for thousands of marine animals while supporting coastal economies.

Before the wasting disease took hold in 2013, sunflower sea stars were common from Baja California, Mexico, to Alaska and were important predators, especially for purple sea urchins. Now, with 90% of the sunflower sea star population gone and other factors, sea urchins have multiplied and are feeding on, and decimating, kelp forests.

鈥淭he loss of this important predator has left an explosion of purple urchins unchecked and has contributed to devastated kelp forests along the West Coast, making this ecosystem more vulnerable and less resilient to the stressors it鈥檚 already facing,鈥� said , associate director of The Nature Conservancy鈥檚 California Oceans Program.听Eddy and senior scientist are working with the UW team to advance the sea star captive breeding program.

The UW research team first collected about 30 healthy adult sea stars from among the last-known wild colonies in the Salish Sea. Each adult star has a unique color pattern and was named, affectionately, by researchers based on its physical characteristics. For example, 鈥淐looney鈥� is named for his silver hairlike features, 鈥淔anta鈥� is bright orange, and 鈥淧rince鈥� boasts purple tips on each arm.

Every two days the adult stars devour wild mussels and clams collected near San Juan Island, and the researchers are confident the animals know when feeding time is based on their behavior and activity levels.

About a year ago, Hodin and collaborators successfully bred several adult stars, and they soon discovered the challenge of raising the early juvenile stages 鈥� a feat never previously accomplished for this species, and for very few types of sea stars at all. After a challenging year of trial and error, they saw 14 juveniles cross the one-year mark, proving the likelihood they will make it to adulthood. The stars are expected to be fully grown adults after two or three years, but even that isn鈥檛 certain for a species that has never before been grown in captivity and is hard observe over time in the wild.

鈥淯nless an organism lays down signs of yearly growth, like tree rings, it鈥檚 hard to know how old it is,鈥� Hodin said. 鈥淔or sunflower stars, we鈥檒l only know that through raising them in the lab or going out year after year to a population and trying to measure the same stars.鈥�

This past January, the researchers applied what they had learned from the first round and successfully produced tens of thousands of new larvae. The tiny critters, living in mason jars and seen clearly only under a microscope, are being raised in varying water temperatures, in part to test whether the species can survive warmer ocean temperatures expected under climate change.

The first few larvae to undergo the dramatic metamorphosis process into juvenile form 鈥� essentially the mini version of an adult 鈥� were raised at warmer temperatures, which is a positive sign for the sunflower sea star to recover in the midst of a warming world, Hodin said.

鈥淭hese are not typical ocean temperatures around here, and yet their apparent success indicates that the larvae at least are robust to temperature increases expected with climate change,鈥� Hodin explained.

The first step of this project is to learn as much as possible about the life cycle and biology of the sunflower sea star, which is only a step away from extinction in the wild. There are no specific plans for reintroduction yet, and any future effort would involve more discussion among scientists and permission from wildlife agencies, Hodin said.

鈥淚f we can raise them in the lab, it might be possible to reintroduce them to the wild in areas where they鈥檝e disappeared,鈥� he said. 鈥淚n the meantime, we鈥檙e learning more every day from these first-ever lab-raised sunflower stars.鈥�

This research is funded by The Nature Conservancy.

For more information, contact听Hodin at larvador@uw.edu and Heady at wheady@tnc.org. If you’re interested in supporting the UW’s sunflower sea star captive rearing efforts, visit the “” giving page.