Starfish continue to baffle researchers with mysterious disease

Five years after a mysterious disease began killing millions of starfish and turning their tissues to mush, the decimated population has yet to recover. Meanwhile, researchers continue to struggle to identify a cause for the disease, which appears to have uncertain ties to viruses and possibly environmental conditions.

In Puget Sound, it’s not as easy as it once was to find a diseased sea star, which seems to be a promising sign until you consider how many have died. As I learned last week during an outing to Lofall in North Kitsap, the total number of starfish remains low compared to four years ago, and recovery has been minimal, if at all.

Under the Lofall dock, volunteers have observed that the number of sea stars is still low, but sick ones are no longer common.
Photo: Christopher Dunagan

Local volunteers have been observing sea stars at Lofall since the beginning of 2014. I first visited the site the following summer with three retired women who lead the monitoring effort there. (See Water Ways , June 17, 2014.) They are still making regular trips at low tide, counting and measuring the starfish and looking for signs of disease.

“The numbers are way down,” noted volunteer Barb Erickson as we stood beneath the Lofall dock last Friday, “but we haven’t seen many sick ones. We also aren’t seeing the little ones.”

When I first visited the site, I noticed more mottled stars, a species with pointy arms and often orange in color. But nearly all the starfish of late have been ochre stars, also known as purple stars. The mottled stars made a brief comeback in 2015, but they have died back again, as shown by a graph for the Lofall site on the Citizen Science page of the Multi-Agency Rocky Intertidal Network.

In some ways, sea star wasting disease is as mysterious as it ever was. Researchers, including Ian Hewson, associate professor of microbiology at Cornell University, identified a virus that can trigger the disease in one species of sea star, Pycnopodia helianthoides, also known as the sunflower star. But direct exposure to that virus had no effect on Pisaster ochraceus, the ochre star; Evasterias troscheli, the mottled star; or Pisaster brevispinus, the pink sea star.

Ochre, or purple, sea star // Photo: Jerry Kirkhart, Los Osos, Calif./ Wikimedia Commons

“Disease among sea stars is likely caused by multiple factors, not just one factor like SSaDV (sea star associated densovirus) or rising temperature,” Hewson was quoted as saying in Cornell Chronicle magazine. “The ‘disease’ is actually multiple diseases. Understanding this, it’s a lot more complicated to explain…”

What we call a “disease” may actually be multiple diseases with similar symptoms, and there may be a variety of triggers. A factor common to sea stars in all the affected areas on the West Coast has yet to be found. Consequently, in the latest research paper, Hewson and his associates have proposed changing the name to “Asteroid Ideopathic Wasting Syndrome.”

The paper, published in the journal Frontiers in Marine Science, explains the multiple laboratory and field studies that have ruled out many possible connections among the diseased starfish.

“In my mind, we are kind of back to square one,” said Melissa Miner, a researcher with the University of California – Santa Cruz who has helped coordinate a network of volunteer and professional observers from Southern California to Alaska.

Although the cause and progression of the disease has not been identified, there must be a connection to explain the loss of millions of sea stars at the same time, she told me.

“When you have such a large number of sites and the trend is the same across all of those sites, you can be pretty confident that you are capturing something real,” she said.

But even the patterns of infection and recovery are inconsistent, with the first of the outbreak seen off the Washington Coast, an area that overall was less affected than other areas. The outbreak in Oregon Coast came later, was more severe and seems to be recovering faster.

“On the Oregon Coast, we are seeing sub-adult size,” Melissa said. “If those survive, there could be greater numbers than before the disease. It seems like all the subregions are doing their own thing.”

The ability to gather observations from 130 sites along the entire West Coast has helped to increase the understanding of the disease many times over, despite a lack of firm conclusions, Melissa said.

“I have been so impressed by these volunteer groups, and I would say that has been a silver lining,” she said, noting that concerns for the lowly starfish prove that people are committed to understanding and protecting the environment.

Melissa, who I first met at Lofall, said she is particularly impressed with the volunteers at that site and in other areas where people go out in all kinds of weather to collect data that helps to uncover the ecological mysteries of our waterways.

In a paper published in the journal PLOS One, Melissa and 15 other authors review what is known about sea star wasting disease and point out the importance of ongoing monitoring even where problems are not known to exist.

“This SSWD epidemic is a perfect example of an ‘ecological surprise’ that underscores the need for long-term ecological and environmental studies,” the paper states. “Multi-year monitoring programs allow researchers to characterize the range of natural variation in populations and thus to distinguish anomalies from natural fluctuations.

“In addition,” the paper concludes, “the pattern of sustained regular observations puts researchers in a position where they can witness rare events that may otherwise go unnoticed with a snapshot or short-term study.”

By the way, marine ecologist Carter Urnes, a graduate student at Western Washington University, will discuss the recent findings about sea star wasting disease at 6 p.m. on Wednesday at SEA Discovery Center in Poulsbo. His presentation is open to the public.

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