Scientists Breed Sunflower Sea Stars Key to Reviving California’s Imperiled Kelp Forests

One thing that surprised Andrew Kim about raising baby sunflower sea stars is just how hard it is to satisfy their ravenous appetites. Kim, the laboratory manager for the Sunflower Star Laboratory , once tested how many pea-sized purple sea urchins a juvenile star could eat in a day. The star, which was about the size of a hamburger bun, devoured all 44 he offered-and still wasn't satisfied.

"The stars hoover up the urchins and totally balloon up," said Kim. "And then, 3 hours later, like clockwork, they spit out all these perfectly clean urchin skeletons. It shows how important these little guys are to maintain healthy kelp forests."

These laboratory-raised juveniles don't know it, but they're at the center of an ambitious effort to help their species-and California's struggling kelp forests-recover.

With $18 million from NOAA Fisheries Office of Habitat Conservation , The Nature Conservancy and its partners are advancing the science needed to bring California's kelp forests back to life. Once among the most productive and biodiverse ecosystems on earth, these underwater forests virtually disappeared from much of the California coast a decade ago.

When a mysterious wasting disease killed off almost all of California's sunflower sea stars in 2013, the native purple sea urchin population exploded. The urchins ate up most of California's kelp, causing the ecosystem to collapse. Kelp-dependent fisheries crashed, costing hundreds of millions of dollars in lost economic activity.

The Pacific Coast Ocean Restoration Initiative

To reverse this damage, the Pacific Coast Ocean Restoration Initiative (PCOR) aims to restore keystone species-especially the sunflower sea star, one of the system's top predators .They are aided by dozens of other partners working on sunflower star recovery throughout the star's historic range from California to Alaska.

"NOAA's investment builds on the tremendous groundwork laid by researchers across the U.S. and Canada," said NOAA Fishery Biologist Dave Witting, who helped create the initiative. "We're grateful for the many institutions that have contributed knowledge essential to moving this species toward recovery."

PCOR partners-The Nature Conservancy, Sunflower Star Laboratory, Aquarium of the Pacific , and the California Academy of Sciences -are rearing juvenile sea stars and conducting research into their behaviors and genetics. The ultimate goal: reestablishing wild populations to bring balance to California's underwater forests.

With NOAA funding, the aquariums have expanded their laboratory space, purchased new equipment, and hired additional staff. Now they can significantly scale up their work.

Learning to Raise a Species

Rearing sunflower stars in laboratories gives biologists a chance to fill major knowledge gaps about sunflower stars: how they grow, feed, reproduce, and handle stress.

Although some remnant populations of wild stars persist from Washington to Alaska, no one had successfully spawned stars under human care until 2021. With support from The Nature Conservancy, Friday Harbor Laboratories in Washington state spawned the first generation of stars in their lab from wild-caught adults.

On Valentine's Day 2024, San Diego's Birch Aquarium spawned the "cupid cohort" of sunflower star larvae from adult stars in their collection, the first successful spawning in California. The PCOR partners assisted with the spawning and brought larvae back to their labs to rear. Funding for the initiative kicked off in October 2024.

The next thing scientists needed to learn: how to grow the cannibalistic stars and prevent them from killing each other.

"It was a lot of throwing spaghetti at the wall and seeing what sticks," said Johanna Hultberg, Conservation Manager of Fish and Invertebrates for the Aquarium of the Pacific.

Biologists from the Steinhart Aquarium at the California Academy of Sciences discovered that the best way to keep larvae from eating each other was swirling them around in a container using a cheap electric pot stirrer. They found this method allowed hundreds of free-floating larvae to survive and settle into surface-dwelling stars.

After they settle, the stars go through what scientists call "the gauntlet," a growth period where many juveniles die. The biologists grew and then fed the star's baby sand dollars, juvenile red and purple urchins, crushed mussels, and other species. Hundreds of stars across the three labs survived.

Cracking the Genetic Code

Scientists are mapping the DNA of every individual sunflower sea star under human care as well as a select group of wild stars. This work will help scientists spawn a genetically varied group of stars that can survive threats like disease and ocean warming. If they find key genetic traits missing, the team may need to bring additional wild stars into the program.

While waiting for full genetic results, the recovery team is preparing for cross-breeding. They are building a database of all genetically sequenced stars in human care. Eventually, it will function as a matchmaking tool to pair spawning partners strategically.

Researchers from the San Diego Zoo Wildlife Alliance and Omaha Henry Doorly Zoo learned how to deep freeze sunflower star sperm and larvae and thaw them unharmed. Hundreds of thousands of larvae and millions of sperm now rest in cold storage, preserving genetic lines for future aquaculture and eventual reintroduction.

Cryopreservation opens important possibilities. Scientists can use sperm from multiple males with a single spawning female to create many different crosses.

"This will really increase our genetic diversity within the program," said Hultberg.

Recent Discoveries Bring Fresh Hope

Two recent discoveries are reshaping sunflower star recovery: the identification of the cause of wasting disease , and the detection of remnant wild stars in California.

Researchers found the bacterium Vibrio pectenicida caused the wasting disease that killed millions of stars. They also developed a test to detect infected stars. This breakthrough made it possible to safely transfer sea stars between facilities. The California Department of Fish and Wildlife uses the test to confirm sea stars from out of state are safe to import.

"Earlier this year, we successfully secured a permit to bring in five adults and around 100,000 larvae from the Alaska Sea Life Center," said Kylie Lev, senior curator at the California Academy of Sciences' Steinhart Aquarium. "For now, we are keeping them isolated from the California stars while we wait to see if they are good candidates for future spawning."

Rediscovering Wild Stars in California

In 2024, a commercial urchin diver working for a NOAA-funded kelp restoration project in the Greater Farallones National Marine Sanctuary found a lone sunflower sea star. This year, scientific divers from Sonoma State University found a small population of stars at the same site.

The Greater Farallones Association hopes to launch a broader search for wild stars in 2026. Finding surviving wild stars raises hope for natural recovery and the possibility of adding new genetic lines to aquaculture programs. The organization has one caution for curious divers: Don't touch the stars-just report their locations to the biodiversity recording tool iNaturalist .

Can eDNA Help Find More Stars?

The Sunflower Star Laboratory is testing whether environmental DNA, or eDNA, can help find wild stars. All living organisms leave traces of DNA behind. For example, humans shed dead skin cells. If someone detects sunflower star DNA in seawater, that could mean stars are nearby.

"We put 12 of our baby sea stars in the ocean in cages to run this eDNA experiment, which is the first of its kind for a marine invertebrate like this," said Kim. "We had a coordinated ballet of free divers going out at discrete time points and collecting samples to look at the detection limits."

This work could allow researchers and local divers to find sea stars without relying solely on scuba surveys.

Next Steps Toward Reintroduction

Research supported by NOAA laid the base for today's understanding of how to reintroduce an endangered marine invertebrate. This includes work co-led by Witting to recover white abalone, another species important to kelp forests.

However, much work remains before human-reared sunflower stars can go into the wild. Scientists plan to conduct experiments to determine whether there are disease-resistant family lines or other methods to make stars better able to survive.

Previous coral reef research has shown corals can become more resistant to ocean warming and disease when they are paired with beneficial bacteria and algae. This could also work for sunflower stars.

The next challenge will be identifying the best sites along the California coast for reintroduction. Experts think it may take 5 or more years before outplanting can begin. But the pace of discovery is accelerating through collaboration by partners and members of other recovery networks.

"Literally every month there's new information," said Ashley Kidd, conservation program manager at the Sunflower Star Laboratory. "We have the tools, the resources, and the knowledge to solve these problems now."