Sunflower star

Why are sunflower stars important?

Sunflower stars play an especially important role as a top predator in kelp forests—underwater forests that support life on our planet much like forests on land do. Like sea otters, sunflower stars are considered a keystone species in the kelp forest. Sunflower stars eat purple sea urchins, and scare them into changing their behavior. When purple urchins smell a sunflower star nearby, they run away, hide more, and eat less. Purple sea urchins eat kelp. Too many purple sea urchins eating too much kelp can create overgrazed areas called urchin barrens. Over the last 10 years, 97 percent of Northern California’s kelp forests have vanished. This coincides with the outbreak of a deadly disease that killed billions of sunflower stars – almost all the sunflower stars along the west coast of North America. Without the pressure of sunflower stars eating and scaring them, sea urchin populations exploded and consumed all the kelp. 

Today, many people are working together to bring sunflower stars back so that we can also help bring kelp forests back. 

One important difference between sunflower stars and sea otters is that sunflower stars are less picky about the urchins they eat. They eat purple urchins of any size, and they will eat starved, dormant urchins that, after eating all the kelp in an area, can subsist in a low-energy state by consuming biofilms. Sea otters find these zombie urchins less juicy and appetizing, and will choose other prey if they can. Making matters worse, by eating biofilms, the starved urchins also prevent new kelp from establishing in the area. Many scientists think that the presence of hungry sunflower stars could provide an important natural remedy to this urchin imbalance. 

Where do sunflower stars live?

The sunflower star once ranged from Baja California, Mexico, to the Aleutian Islands of Alaska in the U.S. 

Adults were found in a wide range of depths and habitats, including rocky reefs, kelp forests, seagrass beds, and the lower rocky intertidal. 

In 2013, a disease called sea star wasting syndrome killed an estimated 5.75 billion sunflower stars. There have been no confirmed sightings of sunflower stars in the wild south of the San Francisco Bay Area since 2018. 

In California, a number of sunflower stars were under human care at zoos and aquariums at the time of the outbreak. Scientists are working with this population, and their offspring, to try to help restore the species. Monterey Bay Aquarium has collaborated with other sunflower star researchers to release some of these sunflower stars temporarily back into Monterey Bay. 

What do sunflower stars eat?

The sunflower star is a generalist predator and scavenger, meaning it eats a wide variety of small- and medium-sized prey, including snails, abalones, cockles, California sea cucumbers, and sea urchins. Purple sea urchins are an important food source for sunflower stars—and the urchins know it! When urchins detect a sunflower star nearby, they move away and emit a chemical that warns other urchins to escape the area.

Because the sunflower star plays such an important role in its ecosystem, it is considered a keystone predator, much like the sea otter. 

The sunflower star's prey use a variety of escape tactics to avoid being trapped by the Pycnopodia's tube feet. Snails and abalones violently twist their shells to loosen the star's powerful grip; cockles lower their strong foot and pole-vault away; California sea cucumbers, usually sedentary, slither out of the way; and sea urchins use their tube feet to flee. The purple urchin seldom escapes. However, the red sea urchin has another defense—long spines, which can help it get away.

How big do sunflower stars get?

No one really knows how big they can get. The sunflower star is among the largest sea stars in the world. It starts as a tiny swimming larva. Eventually it settles and metamorphoses into a juvenile star with five arms. It continues adding arms over time, and can have as many as 24 arms. It can grow over 39 inches (1 m) from arm tip to arm tip.

How do sunflower stars move?

The sunflower star’s arms are lined with 15,000 tiny tube feet that help it navigate around its underwater habitat. A sunflower star can move as fast as 60 inches (160 cm) per minute. 

How do sunflower stars reproduce?

Sunflower sea stars release their eggs and sperm directly into the water, a reproductive technique called broadcast spawning. We don’t know for certain if they aggregate together to spawn, but they do often congregate in groups, making this a possibility. 

A male and female sunflower star can be cued to release their sperm and eggs by exposing them to a naturally occurring hormone called 1-Methyladenine. This allows them to be cultured, or raised, under human care. Being able to successfully culture sunflower stars has been critical to efforts to conserve this critically endangered species.   

Can sunflower stars regenerate?

Yes, a sunflower star can regrow an arm, and even part of their central disc, so long as the central disc part of its body is mostly intact. 

Conservation

In 2013, a disease began affecting many species of sea stars along the west coast of North America. It caused them to develop lesions, lose their arms, and eventually dissolve their bodies into goo. Some species were more resilient than others. Sunflower stars were particularly vulnerable to this wasting illness.

Scientists called the illness ‘sea star wasting syndrome.’ We knew very little about it, only that it was very deadly and appeared to be exacerbated by a cycle of unusually warm water, a marine heatwave, that followed the outbreak. The outbreak killed over 5.75 billion sunflower stars—99 to 100 percent of the population that once lived along the 1680 miles (2700 km) of coast between Baja California, Mexico, and Cape Flattery, Washington.

Many scientists recognized how important sunflower stars are to healthy ocean ecosystems and began learning as much as they could to help solve this problem. Some focused on what was causing the disease. Others learned as much as possible about the biology and life cycle of these animals. Others mapped sunflower star DNA. Still others studied the different environmental factors present in waters where sunflower stars live. And some took care of the small number of surviving sunflower stars that lived in zoos and aquariums, hoping their offspring could help sunflower stars return to the wild. Many scientists in different research labs, nonprofits, universities, zoos, and aquariums took up different parts of the work, all contributing to a larger plan to save the species. As more and more people learned about what had happened, more and more people came together to help. And bit by bit, they learned more useful information. 

A big breakthrough came in 2021 when Friday Harbor Laboratories in Washington spawned the first generation of stars in their lab from wild-caught adults. A few years later, a project at Birch Aquarium in San Diego resulted in the Valentine’s Day spawning of the “Cupid Cohort” of sunflower star larvae from adult stars in their collection. Many of the larvae from the Cupid Cohort were raised in other labs, including Aquarium of the Pacific, California Academy of Sciences,  Moss Landing Marine Labs and Sunflower Star Laboratory, a nonprofit based in Moss Landing, where scientists had to figure out how to raise them to adulthood. 

Biologists from the Steinhart Aquarium at the California Academy of Sciences developed cutting-edge aquaculture techniques to house, feed, and better understand the developmental needs of sunflower stars. 

Researchers from the San Diego Zoo Wildlife Alliance and Omaha's Henry Doorly Zoo learned how to preserve sunflower star sperm and larvae, allowing scientists to maintain a more robust genetic pool to draw from for future aquaculture efforts. 

More reasons to feel hopeful came in 2025. Researchers identified a strain of bacteria, Vibrio pectenicida, as a cause of wasting disease. Now, biologists can test stars for infection and move them between facilities with less fear of spreading the disease. A handful of surviving sunflower stars have been sighted in the wild across Northern California. And a group of researchers, coordinated by Sunflower Star Laboratory and including biologists from Monterey Bay Aquarium, began conducting field studies that temporarily placed lab-raised stars in Monterey Bay waters. These studies are looking at new methods, like eDNA analysis from water samples, to detect and monitor the presence of sunflower stars in the ocean, as well as monitoring how well juvenile stars raised in human care fare when placed in the ocean. All these learnings will inform future efforts to restore this species in the wild.  

What you can do

Advocate for renewable energy and smart climate policy. Some research showed a connection between high water temperature and the severity of sea star wasting disease. This suggests that an ocean warmed because of human-caused climate change may make it more difficult for the species to fully recover. Taking action to minimize climate change is one way each of us can help. 

Tidepool respectfully. Watch your step. Look closely but don’t touch. You may even want to join a community science campaign or group bioblitz like the ones hosted by Cal Academy. Report the species you see using iNaturalist, a community science app that helps monitor biodiversity. Report sightings of sunflower stars in California, Oregon, and Washington to seasquatch.org to mobilize a rapid conservation response!

Donate. This work takes funding. Members and donors support Monterey Bay Aquarium’s ocean conservation programs. Many of the other institutions working to restore sunflower stars are also nonprofits that rely on donor support. 

Volunteer. Monterey Bay Aquarium and other organizations engaged in this work also need the help of willing volunteers. See volunteer opportunities at Monterey Bay Aquarium or learn about volunteering at Sunflower Star Laboratory. 

Tell the story. Share what you’ve learned about sunflower stars and the people working to help them with others. Help raise awareness about the importance of sunflower stars and kelp forests. Let others know about the power of people coming together to help the ocean, and invite them to join the movement. 

Cool facts

• Juvenile sunflower stars start life with five arms—by maturity they have up to 24 arms.
• Most sea stars have a one-piece, semirigid skeleton. However, the sunflower star's skeleton has a few disconnected pieces. They allow the sunstar's mouth to open wide and its body to enlarge and take in big prey.
• A sunflower star can swallow an entire sea urchin, digest it internally and then expel the urchin's test—its external shell.