Millions of sea stars along North America's Pacific coast have been suffering from a disease resulting in disintegration and loss of limbs, prompting scientists to investigate its cause. A study published in 2014 suggests that a type of densovirus is responsible for this sea star wasting syndrome. Research indicates that the virus is present in higher amounts in sick sea stars and spreads to healthy ones when exposed. Although the trigger for the outbreak is still unknown, factors such as environmental changes or a surge in infected species may be at play. The current outbreak, which began in Southern California, has spread across several states and affects various sea star species, primarily impacting the common ochre and sunflower sea stars. While extinction of sea stars is unlikely, the disease alters species composition in intertidal regions, potentially leading to increased mussel populations. Ocean acidification, linked to climate change, may heighten sea stars' vulnerability to viruses, affecting their ability to maintain healthy shells and skeletons. Long-term monitoring is crucial to understanding the virus's impact on marine ecosystems.
What's Happening to Sea Stars?
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VANCOUVER, Canada (Achieve3000, February 26, 2015). Millions of sea stars on North America's Pacific coast have been dying, and it's not a pretty picture. Since the summer of 2013, the creatures have been falling apart quite literally—they are losing their limbs and disintegrating into slime and piles of tiny bones. Now, scientists believe they have isolated a virus they think is causing the mysterious disease that is wreaking havoc on the region's starfish population.
A study published in November 2014 in the journal Proceedings of the National Academy of Sciences names a variety of densovirus as the likely cause of wasting syndrome among the sea stars. There are different varieties of densovirus—one infects dogs and can be fatal; another is used to control the cockroach population.
Now, the virus may well be what is causing the sea star wasting. Cornell University marine microbiologist Ian Hewson said that scientists based this conclusion on a number of factors. For one, Hewson said that the scientists found larger amounts of the virus in sick stars than in healthy ones. He also said that the amount of the virus increased as the disease progressed in the animals. In addition, when healthy sea stars were injected with material from sick sea stars, the healthy sea stars got the disease.
Researchers are still unsure about what triggered the outbreak of the virus, which is usually found in plankton and sea urchins. Hewson said that it could be related to a population boom in one of the species heavily infected by the disease, or it could be caused by a change in the virus or changes in the environment.
Past outbreaks of sea star wasting have been smaller and more confined to a certain geographic area. The current outbreak started in the U.S. in Southern California and has since pervaded the waters of the U.S. states of Oregon and Washington, Canada's British Columbia, and all the way to southern Alaska. The outbreak has infected 20 different species of sea stars, but primarily the 5-legged ochre sea stars that are commonly seen in tide pools and the sunflower sea stars that have up to 16 legs.
Hewson said that while it is improbable that the disease will cause any sea stars to go extinct, it is affecting the mix of species in the intertidal regions of the ocean. Mussels, a favorite food of sea stars, are likely to become more abundant, for example.
Chris Suttle, a marine virus expert at the University of British Columbia, and Bruce Menge, a professor of interactive biology at Oregon State University—both not part of the study—agreed that while the study did not definitively identify the virus as the cause of the disease, the report was sufficiently cogent.
The two scientists also concurred that the increasing acidity of ocean waters associated with climate change could be a factor in triggering the outbreak, by making the sea stars to be more vulnerable to attack—after all, acidic water can be damaging to marine animals by weakening their ability to form shells or skeletons. Sea stars are covered by a hard, calcified skin.
"If [viruses] get in through damaged areas [of the sea star], what causes the damaged area?" Menge reasoned, adding, "If they don't get in through damaged areas, how do they get in?"
Suttle said that ocean acidification is affecting other marine invertebrates as well, such as commercial populations of scallops and oysters.
One researcher says that long-term monitoring is critical to determining the overall impact of the virus on ocean ecosystems.
The Associated Press contributed to this story.
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