Sea Star Disease: The Past, the Present, and the Future

Warmer water means it's easier for disease to spread, and so that is definitely something to be concerned about in terms of sea star wasting and warmer seas with El Niños.”

For most low-tide beach-goers, sea stars are a familiar species on local beaches. Basking in the sun in shades of purples, oranges, and pinks, sea stars are not only fun to look at but also play an important role in the marine ecosystem. These marine anomalies — that is, animals with no brains, five or more eyeballs, and coelomic fluid instead of blood — are an essential part of the ecosystem.

Not only do they prey on shellfish and similar species, but some, such as the sunflower star, are also responsible for keeping sea urchin populations in check. If not managed, urchins can destroy kelp forests by using their five-jawed beak, called Aristotle’s Lantern, to chew through the stipes of kelp, decimating habitat and a source of food for other animals.

Since 2013, local populations of sea stars have drastically declined due to sea star wasting disease, also called sea star wasting syndrome. This disease has wiped out native populations of mottled stars, ochre stars, giant pink stars, and sunflower stars, among others. What used to be a common sight during low tides, the sunflower star is now rare, so much so that it gained a spot as a listed species on the International Union for Conservation of Nature as critically endangered. It has also been recommended for threatened status under the U.S. Endangered Species Act.

The Oregon Department of Fish and Wildlife estimated that the sunflower star population has dropped by 88%, meaning 5.75 billion stars have succumbed to the wasting disease. Another 20 species of sea stars have also been affected.

In August of 2025, a collaboration of scientists, including some from the U.S. Geological Survey Marrowstone Marine Field Station, University of Washington, and the University of British Columbia, among others, published a paper outlining the “causative agent of sea star wasting disease.” It is a bacterium named FHCF-3, a strain of Vibrio pectenicida, which kills sea stars on contact.

Sea stars containing this bacterium cannot recover, leading to the high numbers of deaths.

Dr. Mike Behrens, professor of biology at Pacific Lutheran University, described the signs of disease as “a deflated body, followed by erosion of tissues that occurs relatively rapidly even though the star is in an otherwise appropriate habitat.” This causes lesions on the body and dismemberment. Although a star can regrow lost limbs, the rate at which the wasting disease hits is so hard that the star invariably dies.

Seven large experiments between 2021 and 2024 conducted at the Marrowstone Field Station explained these trends.

Sunflower stars were collected during low tides or captive-bred at Friday Harbor Laboratories. After being quarantined for a minimum of two weeks to rule out any prior exposure to the disease, stars were held in isolation. When the experiment began, tissues of diseased stars were taken along with a sample of the diseased star’s coelomic fluid, which was injected into a healthy star. To find other methods of transfer, diseased effluent seawater was used, as well as direct contact between a wasted and non-wasted star.

In the three weeks that each monitoring session occurred, diseased stars developed symptoms as early as three days after being infected in a controlled environment. Shortly after exhibiting the telltale arm twisting, limb loss followed at day five, followed by death as soon as six days after being infected. While a control population was simultaneously being monitored to ensure the animals were not diseased prior, even after a two-week quarantine, all infected stars were dead by day 13.

After DNA and RNA analysis, a whopping 95.7% of the samples from unhealthy stars contained Vibrio pectenicida, while samples from healthy stars had none. To further support the hypothesized cause agent, gene sequencing was done using the same samples, which led to similar results. Coelomic fluid was taken from diseased stars and incubated, leading to pure cultures of the suspected culprit. It was then placed in healthy stars, showing that a specific strain of FHCF-3 was the killer.

Vibrio is common in many different marine species and is the reason shellfish cannot be consumed raw, but it had not yet been found to be the cause of the wasting disease, according to Behrens.

The study showed “that low levels of Vibrio pectenicida can be tolerated under favorable conditions, which could turn into outbreaks with a change in environmental conditions,” such as an increase in water temperature.

“Initially, there was a period of time where we saw no sea stars on any of those surveys because they had been so dramatically impacted by sea star wasting disease,” said Stena Troyer, science director with Harbor WildWatch, a local marine science and education nonprofit that has been monitoring wasting disease since 2014.

Troyer and Behrens lead a group of scientists and local volunteers that collect data on sea star populations twice a year on Key Peninsula beaches. The data is not only used to identify local trends, but is also sent to UC Santa Cruz as part of a wider effort to manage data regarding wasting.

“In the last couple years … there was definitely some recovery, so we’ve been happy to see lots of baby sea stars on our beach walks as well as those surveys,” Troyer said.

While the sunflower star remains on the IUCN red list, it’s thanks to data collected by Harbor WildWatch that helped make that listing possible. The number of suspected wasted stars was higher in the most recent monitoring in June, and both Behrens and Troyer said there is a correlation between water temperature and disease.

Troyer also said that during monitoring last December, the team came across two dinner plate-sized sunflower stars that appeared very healthy. Behrens said some data indicates the possibility of genetic adaptations within stars to combat wasting disease, and emphasized the success of breeding programs to “reintroduce juveniles back into the wild to repopulate and restore the ecological function of the species.”