Tuesday, June 7, 2016


Since the Summer of 2013 Sea Star Wasting Disease has devastated the population of many species of sea stars on the Pacific Coast of America.  Among the species affected are Purple Stars and Sunflower Stars.  In surveys I've completed at Constellation Marine Reserve in West Seattle the pupulation of Purple Stars (Pisaster ochraceus) has declined by over 90% and Sunflower Stars by the even more.  While the total cause or causes remain unknown a densovirus is implicated in the decline.  This virus has been around for many decades and why it should now be causing this great wasting disease in stars is a mystery.
I have noticed that certain areas still are home to large Purple Stars that have survived the wasting in relative healthy numbers and while some stars in these areas have become diseased the population of large stars has remained relatively intact.
These areas are on pilings under condos built over water, the pilings of the Fauntleroy Ferry Dock in West Seattle and the floating dock at the West Seattle Water Taxi in West Seattle.  All three of these areas share one habitat property in common.
 Sea Stars living on the pilings and floating docks are shaded from direct sunlight.
This protects the stars from direct sunlight, UV radiation, hot Summer air temperatures.  In addition the stars are not exposed to heavy fresh water runoff during large rain events.  Water temperature during high tides should be equal in all habitats due to current movement of water but in tidepools on the beach Summer exposure can greatly raise the water temperature.
Living in the shaded habitats likely reduces environmental stress on the Purple Stars.  The reduction of stress may make the stars more resistant to SSWD.  As a result there are still healthy populations of large stars on the shaded pilings while on the exposed intertidal areas only very limited numbers of much smaller stars survive.
While I have only limited data it would be interesting to know how populations of Purple Stars are doing on pilings in other areas.
I checked the pilings under the Fauntleroy Ferry Dock on June 6th and found a healthy community of medium to large Purple Stars (50+), two healthy Leather Stars and two small healthy Sunflower Stars and a similar number of Mottled Stars.
In comparison my SSWD survey of Purple Stars on the south side of the breakwater on S. Alki turned up 31 healthy medium size stars and zero with SSWD.  It appears for now that SSWD is in decline.
Only time will tell but at least we have some good news for the first time since SSWD was discovered on the Washington Coast in 2013.

Purple and Sunflower Stars under ferry dock

Purple and Sundlower Stars under ferry dock

Large Purple Stars on piling

Purple Stars under ferry dock

Sea Pen under ferry dock

Moon Snail and Horse Clam under ferry dock

Leather Star on piling under dock

Mottled Star with worm from Lincoln Park Beach

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