A gruesome disease has decimated sea star populations between Alaska and Mexico in recent years, and a new study has confirmed suspicions: Increased water temperatures are partially to blame.

Many islanders have seen sea stars with the disease’s tell-tale signs — contorted bodies, oozing sores and missing arms — while the iconic creatures seem to just melt away. The illness, called sea star wasting disease, is believed to be the largest marine disease outbreak ever recorded and has been attributed to a virus. But researchers say the virus is commonly found in salt water and can be traced to sea stars as far back as the 1940s.

In search of a better understanding of what is causing the disease, scientists are exploring additional factors, such as the effects of increased ocean acidification and warmer waters, while the future of sea stars hangs in the balance.

“We would like to say it looks like a one-time thing and the populations will rebuild,” said Joel Elliott, Ph.D, who co-authored the study. “But it is still occurring, and we will likely see more sea star wasting syndrome this summer.”

Elliott is a marine ecologist at the University of Puget Sound, and in an interview last week, he discussed the plight of the sea star and major findings of the study: The prevalence of disease is correlated with warmer water, and larger sea stars are the most vulnerable to illness.

Researchers collected data in the San Juan Islands, southern Puget Sound and the coast from 2014 to mid-2015, a time when water temperatures were warmer than normal. The sea stars in the San Juans experienced the “fastest and most devastating” effects, Elliott said, and that area also had the highest water temperatures.

Noting that larger sea stars were the most likely to get sick, he said that while the reasons for their increased mortality rate are not clear yet, he likened the situation to humans, where those who are older and younger are more susceptible to disease.

“We do not see the huge sea stars that we used to see,” he added.

Unlocking the mystery of what is happening may be helpful not just for sea stars, but for other species as well, he said, by providing insight into how marine diseases spread.

As researchers have grappled with the disease, countless people have joined them and are serving as citizen scientists at many beaches, where they count and evaluate sea stars and report their findings.

It’s important work, Elliot said, noting that citizens are providing valuable information to researchers.

“We’re hoping that things are going to get back to normal, but (the disease) is still there, and there is still a lot of data to collect,” he said.

On Vashon, more volunteers are welcome, and Vashon Nature Center’s Bianca Perla said that if enough residents express interest, she will hold a training soon to deploy islanders to local beaches and collect information on Vashon’s sea stars as they do — or do not — make a comeback. Ideally, she said, volunteers would commit to counting sea stars in a specific area multiple times a year and commit to doing so for more than a year.

This spring, the center will work with high school students for the third year on the sea star mystery. The effort with students began in 2014, when students counted sea stars at five beaches. Last year, she said, they only went to one beach — Raab’s Lagoon — and noticed significant differences from the students’ trip there the year before. One species was not found at all in 2015, and the other had declined drammatically. Both years, students counted sea stars in two different areas at the lagoon, but in 2015, they found only two sick sea stars on the beach, far less than 140 sea stars the year before. But a streamlike-area proved better. Though it held nearly 60 fewer sea stars than the year before, there were 73 present.

“It makes me wonder if there is something different about that moving water that is helping them survive,” Perla added.

This year, the high school students will go back to all five beaches first visited and will compare their data to the findings from that visit, when both healthy and sick sea stars were found.

While comparing information from spring to spring offers insight into what might be going on long term, Perla noted more frequent counts provide information on ebbs and flows throughout the year. Rayna Holtz has gathered that kind of information. For 10 years she has been walking the same two-mile stretch of beach, from Robinwood Beach to the Cove Motel, each month with Yvonne Kuperberg. Holtz, a Vashon beach naturalist and a former reference librarian at the Vashon Library, has also kept meticulous records.

Before the outbreak set in, Holtz said they would routinely see at least four sea star species, but in recent years, they have rarely seen more than two, typically the purple and mottled sea stars.

In August of 2012, when the sea stars were healthy, she and Kuperberg counted 113 sea stars from three species. By July of 2014, however, the numbers had plummeted. They found just 16 sea stars in all, including two sick and one dead. Last July, the picture looked more hopeful, as she and Kuperburg found 40 healthy sea stars and none that were sick or dying. But just one month later they returned to find 15 sick sea stars, three dead and only 33 that were healthy.

Her surveys at Dockton Park were even more striking to her, she said. In February of 2014, on eight pilings, she found 23 healthy sea stars, three sick and one dead. When she went back that July, she found only one juvenile sea star and no others.

“That was really mind blowing. There had been just giant, fat sea stars grazing on barnacles and mussels,” she said. “We went from all these different sizes and species to one juvenile.”

The signs of recovery she has seen have been mixed, she added, with some signs of improvement, followed by signs of disease.

Fellow beach naturalist Kelly Keenan, who counted sea stars under the north-end ferry dock until it closed for construction, noted similar findings after the initial spread of disease.

“At the beginning it was almost like there was a bomb that went off,” she said last week, recalling twisted sea stars, legs separated from bodies and sea stars with oozing lesions.

As time went on, she said, the situation looked more hopeful, with many juvenile sea stars present — an indication that adults were surviving and reproducing. But then — disappointment.

“The last time we did not see any,” she said.

Now many are questioning what the future holds, including what will happen this summer, when warm temperatures return. Perla said someone likened the fate of the sea stars — recently so common on the beaches — to what it would be like if all the robins disappeared, or all the crows.

“It is a very obvious change, and it is an uncomfortable thing to watch,” she said. “It is quite drastic to see something so common and so beautiful going away.”

Sea stars are a top predator, and with their numbers greatly reduced, it is unclear how other species will be affected. Elliott noted that anecdotally, he has not heard of large increases in mussels and barnacles, which sea stars eat, but in the coming months it will be clear if population shifts are occurring.

On the beach, Holtz will be looking for answers, too.

“Sea stars weed out the sick to make room for the healthy and strong,” she said. “Now who is going to take their place, or will anything take their place?”

To volunteer to count sea stars, email info@vashonnaturecenter.org.To become a Vashon beach naturalist, see vashonnaturecenter.org under the “What We Do” tab.