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An undersea plague is obliterating a key ocean species

An “underwater zombie apocalypse.” That’s how wildlife veterinarian Joe Gaydos of the University of California UC, Davis, describes “sea star wasting disease” (SSWD), a blight that has decimated more than 20 species of sea stars from Mexico to Alaska since 2013.

SSWD is a hideous disease, there is no other way to describe it. In 2013, beachgoers and divers along the West Coast began seeing the seafloor littered with severed sea star arms, and sea stars of every species clinging to coastal rocks – covered in sores and disintegrating into white mush, reports Drew Harvell at The Atlantic.

“There were arms separating from sea stars, arms walking off by themselves,” says Harvell, an ecologist at Cornell University who studies marine diseases. “That was my first experience of the magnitude of it.”

Starfish showing signs of SSWD

Starfish showing signs of SSWD
Screen grab

One species that has been hit especially hard is the large sunflower sea star, Pycnopodia helianthoides, a key predator of the kelp forests. This sea star has virtually vanished from the majority of its normal range, leading to large ecosystem-level consequences, according to a new study published in the journal, Science Advances on January 30, 2019.

Previous studies had ascertained that a virus was responsible for SSWD. The new study explains how this pathogen got so lethal, but what turned out to be especially interesting – and troubling – was that not all species were susceptible to the disease, meaning there are likely other broader, overlapping causes.

The culprit that does cause SSWD is called sea-star-associated densovirus, or SSaDV. This virus was discovered in 2014. But researchers found out then that this virus does not cause SSWD in every species of sea star. Not only that, but the research team was puzzled as to why the virus, known since way back in 1942 was so out of control now. So what in the world was going on to cause such a huge outbreak?

A starfish with Sea star wasting disease.

A starfish with Sea star wasting disease.
Screen grab

What is going on in the ocean?
In this new study, researchers tried to quantitate the impact of the disease and understand the cause of the die-off in Pycnopodia helianthoides. These sea stars can grow to have a diameter of three-feet and as many as 24 arms, and are an important ocean predator that protects the kelp forests.

These predators munch on sea urchins and mussels, and without the sea stars keeping them under control, the kelp beds would be decimated. Since SSWD was first identified in 2013, the sunflower sea star has now disappeared from the Pacific coastline, covering over 2,000 miles. And they have also disappeared from depths going down 3,000 feet.

“This thing was as common as a robin,” study author Drew Harvell of Cornell University says. “You would go on a dive and always see sunflower stars.” Harrell also adds that the fact the stars are not sitting in deeper water, waiting out the epidemic is a “bad omen for scientists.”

“This is shocking,” Mark Carr, a University of California, Santa Cruz marine ecologist who was not involved in the study, tells Alex Fox at Science. “This is not just a population reduction, this is virtually the loss of a key species over thousands of miles. We’ve never seen anything like this before.”

Advanced decomposition of sea stars  mostly P. helianthoides but showing one Solaster dawsoni in a l...

Advanced decomposition of sea stars, mostly P. helianthoides but showing one Solaster dawsoni in a less advanced state of decomposition. Image dated September 2, 2013.
Jonathan Martin from Coquitlam, BC, Canada

Researchers note that the SSWD that started in 2013 coincided with warmer Pacific Ocean temperatures, and the sunflower sea star, being more susceptible to SSWD were hit harder because the warmer water made them more likely to be affected by disease.

“The heat wave in the oceans—a product of increasing atmospheric temperatures—is exacerbating the sea star wasting disease,” Harvell says in a press release. “It’s a lethal disease, and when you add a higher temperature to that, it kills faster, causing a bigger impact.”

The Atlantic points out, these types of disease outbreaks compounded by high temperatures are becoming more common and have impacted other marine species as well.

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We are deeply saddened to announce the passing of our dear friend Karen Graham, who served as Editor-at-Large at Digital Journal. She was 78 years old. Karen's view of what is happening in our world was colored by her love of history and how the past influences events taking place today. Her belief in humankind's part in the care of the planet and our environment has led her to focus on the need for action in dealing with climate change. It was said by Geoffrey C. Ward, "Journalism is merely history's first draft." Everyone who writes about what is happening today is indeed, writing a small part of our history.

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