Throughout Saanich Inlet and all down the west coast of North America, millions of sea stars (asteroids) are wasting away into slime and piles of oceanic waste, because of a deadly disease known as sea star wasting disease (SSWD).
First seen in the Northern Pacific Ocean in 1971, SSWD has resulted in numerous collective sea star die-offs. Since June 2013, sea star wasting disease has returned with a vengeance, responsible for mass mortalities of sea stars from Mexico to southern Alaska. Because of the geographic range and volume of species affected, SSWD may be the largest marine epizootic to date. Much has yet to be discovered about SSWD, including how human activity affects the consequences of the disease.
Sea star wasting disease is most likely an infectious agent, or a virus. Many viral investigations and studies revealed the sea star-associated densovirus (SSaDV) as the most likely candidate associated with the infected tissues of sea stars. SSaDV was detected in the tissues of sea stars from 1942, which suggests that it’s been in the waters of the North American Pacific Coast for at least 72 years. It is not known why sea star wasting disease only affects sea stars on the West Coast, and there is no definite explanation for the recent outbreak or how it spreads.
Sea Star wasting disease varies between different species of asteroids, though behavioral changes in all species mimic one another. Typically, lesions appear on the sea star, followed by decay of tissues, ray autonomy, and deflation. Then the animal will appear slime-like, followed by the sea star’s death.
The progression of SSWD is rapid, leading to death in a number of days. When observed in a laboratory, recovery among individual sea stars was rare, but was more frequent in the Saanich Inlet. However, its effects have been devastating on sea star populations.
SSWD was first seen by divers who reported mass die-offs of the sunflower stars (Pycnopodia helianthoides) in the subtidal habitats of North Vancouver and Vancouver Island.
Other subtidal sea star species were quick to follow and began dying off in mass numbers. However, two species of sea stars, the leather star (Dermasterias imbricate) and the bat star (Asterina miniara), remain unaffected by the disease, and the reason is unknown.
Similar deaths were seen in October and November 2013 in Monterey, California and around Seattle, where the disease spread throughout the Puget Sound. During the summer of 2014, the disease was found in Mexico and parts of Oregon, which had never previously been affected, while also intensifying in places where the disease had been observed before.
Though the disease is not likely to result in the extinction of sea stars, over 20 different species of sea stars are affected by SSWD. Primarily, SSWD has affected five-legged ochre sea stars—mostly seen in tide pools—and sunflower stars, which has resulted in the deaths of thousands.
These mass mortality events have serious consequences for biodiversity in the intertidal ecosystems of the Pacific Ocean. In some places, the sea stars have been replaced with mussels and sea urchins, which are usually preyed on by sea stars. In turn, this has affected the giant kelp, a common food for sea urchins, whose population is now suddenly decreasing. Taking a broader look at what is affected by SSWD, it is clear that there will be far-reaching ripples felt throughout the West Coast.