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A Devastating Mortality Event

On a June trip to the Pacific Northwest in 2011, I took advantage of several low and minus tides to photograph the sea anemone, chiton, mussels, barnacles, and sea stars (or starfish) I found at beaches at numerous locations along the coast, especially the Purple Star (P. ochraceus), which seemed to be everywhere. But just a few years later, visiting the same beaches at the same time of year, low tides revealed no more than a half dozen Purple Stars.

At the time, I blamed it on bad timing, not getting to the beaches early enough or simply choosing the wrong location, even though the same beaches had been productive in the past.

When I returned home, however, I found out why I had seen so few starfish. A presumed pathogen had afflicted sea stars—particularly the Purple Star, the most abundant sea star species along the Pacific coast—and record numbers had died, practically dissolving from a wasting disease of unknown origin.

Shortly thereafter, thanks to the research undertaken by Ian Hewson, a scientist at Cornell University, we learned that a virus (Sea Star Associated Densovirus) had been responsible for killing as many as 98% of the sea star population on the west coast. Millions of sea stars had died. From Alaska to British Columbia to Baja California in coastal Mexico. Sea stars all along the Pacific coast, in the ocean, in quiet bays, in aquariums, in laboratories—any environment that used sea water—died, their arms liquifying into an amorphous goo one after another.

What triggered such a devastating mortality event? After identifying the densovirus—“the first virus described in a sea star”—Hewson’s groundbreaking research revealed that the virus had already been present in “museum samples of sea stars collected in 1942, 1980, 1987 and 1991, and may have risen to epidemic levels in the last few years due to sea star overpopulation, environmental changes, or mutation of the virus.”

The presence of the virus in museum samples helps explain isolated incidents of the wasting disease—one or two individuals in a tidepool—that had been reported in the past. The virus existed in the environment, but affected only a tiny percentage of the sea star population, mostly likely injured, sick, or older individuals whose immune system had been compromised and could not defend itself against the densovirus. But it doesn’t explain why millions of otherwise healthy sea stars should suddenly fall victim to the disease and die over an incredibly short period of time.

Research continues and will hopefully provide an answer. And reports from last year at this time present some good news: “in scattered sites along the Pacific Coast, researchers and others have reported seeing hundreds of juvenile starfish.” In fact, “at one site in Santa Cruz, California, more babies were counted in the past year or so than in the previous 15 years combined, said Pete Raimondi, professor of ecology and evolutionary biology at the University of California, Santa Cruz.”

Will these young starfish fall victim to the wasting disease when they mature into adults? No one knows. But sea stars provide numerous, essential environmental functions and need to survive for the good of the ecosystems in which they live.

A keystone species (and apex predator), sea stars help to assure biodiversity in their marine environments by preying on California Mussels, a species that would otherwise dominate its ecosystem and ultimately eliminate less competitive species.

Sea stars can also prevent invasive species from establishing a beach head in new territory. This has become a significant problem worldwide as international shipping—and the accidental or intentional release of ballast in foreign ports—has resulted in the introduction of foreign species that, unchecked, can overwhelm and devastate marine ecosystems and their indigenous plant and animal species.

Their sensitivity to marine pollution—starfish constantly filter sea water through the suckers on their feet—also makes them excellent bioindicators of the environment, allowing biologists to gauge the health of the entire ecosystem by monitoring the health of the sea stars.

For more information about the struggles of the sea star—beloved by beach goers and an important part of popular culture—you might find the following articles of interest:

New Virus Causes Devastating Sea Star Wasting Disease
Falling Stars: Starfish Dying from “Disintegrating” Disease
Starfish Babies Offer Glimmer of Hope Amid Mass Die-off
Mystery Virus that Turned Starfish into Goo Identified
Densovirus Associated with Sea-star Wasting Disease and Mass Mortality
The Planet’s Starfish Are Turning to Goo—and Scientists Finally Think They Know Why
Scientists Find Out What Killed Millions of Starfish
Starfish Are Literally Goo and Scientists Don’t Know Why
A Disease Turning Sea Stars to Goo Will Ruin Your Tide Pool Visit—and the Ecosystem
Starfish Are Turning Into Goo, But Scientists Don’t Know Why
Starfish (wikipedia article)
Pisaster ochraceus (wikipedia article)