Puget Sound Sea StarsSea Star Wasting Disease

by Jordan Macke

Take a few seconds and think about the characteristics of a beach:  the salty air, the ocean, a fantastic amount of sand.  For most people, starfish would make it somewhere in their first ten thoughts. They come in all shapes, sizes and colors, possess the super-hero ability to regrow their limbs,  and the ochre and sunflower sea stars have even earned the title of  nearshore keystone species [1]. Starfish are a group of animals that are so important to the intertidal community that they can almost be considered the mascot. While starfish are relatively resilient creatures, a virus has recently destroyed large communities of them along the Pacific Coast of North America [1,2].

 

What Causes SSWD?

Those afflicted with the virus have been aptly described as having Sea Star Wasting Disease (SSWD), which causes sea stars to develop lesions, then decay of tissue, followed by loss of limbs, and ultimately results in death [1].   It can take up to two weeks for infected animals to show signs of disease and once they do they rarely recover [2].  Other starfish death events have occurred in the 1970’s through the 1990’s but none that have affected the same range or the same extent of species [1].

The current outbreak of SSWD was originally discovered along the Washington state coast in June 2013 [1] and continued moving southward. As the summer progressed the same lesions and wasting were seen in sea stars in Vancouver, B.C., and by fall it was seen along the coasts of California. By the start of 2014, starfish were seen sickened in sites along the Oregon coast and Mexico, which had not been affected before[1].

At this time, millions of individuals have succumbed to the disease across twenty different species [2,3]. Because this wasting event was so extensive and was affecting sea stars in aquaria that did not treat in-coming water with UV light, it was found most likely to have been caused by a virus or bacterium with the ability to spread through the water column [2].

In 2014, a team of scientists (Hewson et al., 2014) from across the country set out to discover the cause of the mysterious disease. They collected sea stars from Puget Sound that were not exhibiting symptoms and placed each in their own aquarium with separate flow lines and water filtered with sand and UV light [2]. Tissue was removed from diseased sea stars and homogenized in seawater from the sick animal’s tank [2].  Half of the sample was boiled to kill the virus, in order to be as a control, the other half was filtered through a small syringe to obtain the virus [2]. Each asymptomatic sea star in the experiment got either an injection of the virus or control, and as expected the virus injected animals grew ill within about two weeks’ time [2],   After repeat experimentation and analysis of the different viruses present within the sea star’s tissue, it was found that the sea stars exhibiting symptoms of SSWD had a greater amount of what is being referred to as Sea Star-Associated Densovirus (SSaDV) [2].

 

Puget Sound sea starCan Sea Star Populations Rebound?

Unfortunately, it has yet to be seen. In some areas, the virus is affecting more animals by the day.  Along the Washington Coast, the numbers of sea stars affected by SSWD during summer 2014 was at an all-time low since it was discovered in the area, but that number grew to affect up to 60% of the population by this past winter[3]. As of April 2015, 30% of the population of sea stars were affected by SSWD along the Olympic Coast[3].

There is hope though. Biologists have seen dramatic increases in juvenile sea stars in some locations affected by SSWD [3].  It has been hypothesized that when the adult starfish were stressed by the disease, they released millions of reproductive cells into the water and with the necessary weather and water conditions, they were able to fertilize and grow [3].

Now, we wait and see. Without knowing how the virus is killing the starfish and what is causing it to spread at such an accelerated rate, there isn’t much that can be done to stop it at this point. And while it is promising to see so many juveniles, there is no way of knowing how susceptible to SSaDV they will be as they mature[3].

In the meantime, biologists will be studying how the loss of such an important animal affects the ecosystem [2,3]. Starfish are considered keystone species in many locations, meaning that they have control over the abundance of many other species in their habitat through predation [4]. There have already been reports of urchins taking hold in areas where sea stars once inhabited [3], and changes like this could reshape many coastal ecosystems.

Citations

1. Sea Star Wasting Syndrome, University of California Santa Cruz and the Bureau of Ocean Energy Management.  April 16, 2015. http://www.eeb.ucsc.edu/pacificrockyintertidal/data-products/sea-star-wasting/

2. Hewson, I., et al. 2014.  “Densovirus associated with sea-star wasting disease and mass mortality.” Proceedings of the National Acadmeny of Sciences.  http://www.pnas.org/content/111/48/17278.full.pdf

3. ‘Sea Star Wasting Disease death toll rises, but babies bring hope.’ Kelly House. The Oregonian. May 4, 2015. http://www.oregonlive.com/environment/index.ssf/2015/05/sea_star_wasting_disease_death.html

4. ‘Sea Stars’  San Francisco Bay Area National Parks Science and Learning. http://www.sfnps.org/sea_stars