Up and down the Pacific Coast, from southern Alaska to the Mexican border, the sea stars are dying — and now, scientists think they know why.
Sea Star Wasting Disease is an epidemic that has killed off thousands of sea stars (also called starfish) since June 2013. It has decimated sea star populations in Washington, central California, Southern California and Oregon. Scientists say it is the largest die-off of sea stars ever recorded. In some areas, the sea star population was wiped out entirely.
Twenty species of sea stars have been affected by the wasting disease, and the deaths all follow the same, grotesque pattern.
First, the sea star’s legs begin to curl up. Then lesions appear on its body. Next, its legs start to crawl away from the central disk and rip off. Finally, the entire starfish disintegrates until all that is left is a pile of mush on the ocean floor.
Scientists say it is almost as if the animal melts.
Researchers have been trying to determine the cause of this sea star plague for the last 18 months.
In a paper published Monday in Proceedings of the National Academy of Sciences, a team of scientists from around the country say the epidemic appears to be caused by a type of virus similar to one that affects cockroaches and is also found in sea urchins. They named it sea star associated densovirus.
Ian Hewson, a professor of microbiology at Cornell University and the lead author of the study, said it wasn’t until October 2013 that he first thought a small infectious agent might be responsible for the massive sea star die-off.
The first clue came when he heard that sea stars living in an aquarium in Vancouver had started to die from the disease. The water in the aquarium came from the ocean but was put through a sand filtration system before filling the sea star’s tank. Whatever was killing the sea stars had to be small enough to make it through the filtration system.
Then he heard from scientists in Seattle that sea stars living in an aquarium where the ocean water was treated with ultraviolet light were doing just fine. This suggested that whatever was hurting the sea stars in the Vancouver aquarium could be killed by ultraviolet light and was not simply an environmental contaminant.
To see if the deadly illness was caused by a bacteria, Hewson and his team compared the bacteria they found in healthy sea stars and in sea stars showing signs of the disease, but they didn’t find any major differences.
Next they turned to viruses. They took tissue samples from sick sea stars and injected them into healthy ones. Within eight to 17 days, the formerly healthy sea stars were showing symptoms of the disease.
A control group of healthy sea stars was injected with a tissue sample from sick sea stars that had been heat treated so the virus was no longer active. These animals did not develop the disease.
This step convinced the researchers that the infection was transmitted by a virus-sized organism.
Next, the researchers found that diseased sea stars had a higher concentration of a densovirus than the healthy sea stars. Healthy sea stars had the virus too, just in smaller quantities.
The paper stops short of saying definitively that the densovirus is the cause of the sea star wasting disease, because in order to do that, scientists would have to isolate the virus, make a culture of it, and inject that into a pure sample of the host.
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SOURCE: LA Times