Mysterious Killer of Pacific Coast Sea Stars Identified Deanna Conners - EarthSky
go to original December 4, 2014

Scientists say a virus is responsible for the wasting disease that has been decimating the starfish population on the Pacific Coast. (Kevin Lafferty)

Scientists think that they have finally figured out what has been causing the deaths of millions of sea stars along the west coast of North America. The disease outbreak, which is known as sea-star wasting disease, started during the summer of 2013, and it has now decimated sea star populations all the way from Baja California in Mexico up to the southern coast of Alaska. The disease is most likely caused by a virus, the scientists say after they painstakingly gathered multiple lines of evidence from both laboratory and field studies. Their new findings were published in Proceedings of the National Academy of Sciences on November 17, 2014.

The first hint that a virus may be responsible for sea-star wasting disease came from observations made at aquariums along the Pacific Coast. At facilities where sea stars were held in sand-filtered seawater, the sea stars succumbed to the disease. However, at facilities where sea stars were held in seawater that was disinfected with ultraviolet light, the sea stars remained disease free. Hence, some type of water-borne pathogen was likely infecting the sea stars.
A sunflower sea star (Pycnopodium helianthoides). Image Credit: Kevin Lafferty, U.S. Geological Survey.

To test their hypothesis that sea-star wasting disease is caused by a virus, scientists took tissue samples from sick sea stars, ground them up, and passed them through a filter that would trap bacteria but allow viruses to pass through. Next, they used heat to kill off any viruses in some samples while allowing other samples to retain their viral loads. These samples were then injected into health sea stars. After about 10 to 17 days, sea stars that had received the non-heat treated samples started showing signs of the disease. In contrast, those that had received the heat treated samples remained disease free.

Samples of viruses collected from the sea stars during the course of the experiment showed that a particular type of virus, known as a densovirus, had increased in number as the disease progressed. Field studies also confirmed that high densovirus loads were more likely to be found in sick sea stars than in healthy sea stars. All of these findings strongly suggest that the sea-star wasting disease is caused by the densovirus.

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