Sickly Starfish: A Q&A with Dr. Chris Mah
Since summer 2013, starfish along both coasts of the United States have been dying in large numbers—and not gracefully. As their tissues collapse, the starfish (also called sea stars) start to look stretched and weirdly distorted. The observed symptoms are from "starfish wasting syndrome", which has caused mass die-offs of different starfish species over the past few decades. No one is quite sure what causes it, how it is transferred between starfish, or why it showed up this summer.
To learn more about this mysterious disease and how it may affect the ocean ecosystem, we talked to Dr. Chris Mah, a research collaborator and echinoderm expert at the Smithsonian’s National Museum of Natural History. Dr. Mah broke the story on his blog in September, and we're delighted to have him here to take a closer look at this phenomenon.
What does the syndrome look like?
Starfish wasting syndrome causes tissue damage, first showing up as white spots of decaying tissue, which ultimately spread to kill tissue throughout the starfish's body. In many cases, the white tissue decay is seen on the central body of the starfish, but in advanced cases, it spreads to the arms, which may break off. Over a few days, the starfish’s body breaks down and appears to have melted on the seafloor before it is washed away.
What causes starfish wasting syndrome?
Scientists in the field are just now starting to document its spread and what might be causing it. The actual agent of starfish wasting “disease” is unknown (and its unknown nature is why it is often referred to as a syndrome rather than a disease). It is unclear if the cause is a bacterium, a virus, a parasite, or some other kind of specific infectious agent.
In the past, many starfish diseases have been linked to warm water or pollution. Warm water doesn't cause the disease itself, but can make disease more likely to occur or produce worse symptoms. This pattern of disease striking after stress occurs is seen in other ocean animals. For example, coral diseases sometimes become much more common after a mass bleaching event caused by unusually warm water. Earlier studies on starfish wasting syndrome suggested that it might also be associated with warmer temperatures, and thus could be associated with warming seas due to climate change.
Also unclear at this time is whether the disease is the result of a single widespread outbreak or multiple, smaller outbreaks simultaneously occurring up and down the coast.
(Editor's Note 11/18/2014: A new study has confirmed that starfish wasting disease is caused by a virus. Learn more at Smithsonian.com)
Where is starfish wasting syndrome occurring?
Starfish wasting syndrome has been recently observed in several populations of starfish on the West coast, from Alaska down through California. The first observations of this outbreak were made in British Columbia in a large population of sunflower seastars (Pycnopodia helianthoides) in August and September of this year. Reports of wasting disease in California and Washington began showing up a few months later, affecting the Ochre seastar (Pisaster ochraceus) and at least seven other species. There have also been reports of starfish die-offs on the East coast since 2011, which also appear to be the result of starfish wasting syndrome.
What are the impacts of starfish wasting syndrome?
Several of the starfish species being affected are native to the Pacific coast of North America and are not found anywhere else in the world, so the disease could cause them to become endangered or possibly extinct. Also, sea stars often play important roles in marine ecosystems as predators. Some species, such as the ochre seastar and the sunflower seastar, are known as “keystone species,” whose presence affects the structure and dynamic of the animals around it in a profound manner. When these starfish are removed, the intertidal or oceanic community often changes dramatically because the animals that they normally eat become unusually abundant.
For instance, predatory starfish might eat juvenile sea urchins in high numbers. If the starfish are removed from the ecosystem, the urchins could grow unchecked. Too many adult urchins can mow down everything in their path, causing a loss of diversity in the system. This is such a serious problem that it even has its own name: urchin barrens.
So while definitive impacts of starfish wasting disease are unknown so far, scientists are very concerned about how the syndrome will affect these ecologically important species.
What can be done about starfish wasting syndrome?
At the moment, scientists are doing what they can to understand what is happening and how far the condition has spread. A number of monitoring websites have been established in order to aid scientists in understanding the spread of the syndrome, especially on the West coast.
One website shows how to recognize starfish wasting syndrome and two others permit anyone with images or observations to add their data and track the spread of the syndrome online. You can also see a map that shows where the disease has been reported so far.