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“The two species affected most are Pisaster ochraceus (purple sea star or ochre starfish) and Pycnopodia helianthoides (sunflower sea star),” he wrote in a statement in December.

The sunflower sea star is considered among the largest starfish and can span more than a meter in diameter.

The most commonly observed symptoms are white lesions on the arms of the sea star. The lesions spread rapidly, resulting in the loss of the arm. Within days, the infection consumes the creature’s entire body, and it dies.

Scientists who have spent decades studying the local ecosystem have yet to identify the cause.

Then, the creatures become more susceptible to bacteria which is “causing a secondary infection that causes most of the damages that you see.”

A barometer of sea health

Previous cases were believed to be associated with warmer waters — sea stars have sensitive skin and prefer cooler water — but this was not the case in 2013.

And when the die-offs happened previously, the geographic span of the infections was much smaller, and far fewer sea stars were affected.

In 1983, an epidemic nearly wiped out the Pisaster ochraceus from tidal pools along the southern coast of California.

Sea stars eat mussels, barnacles, snails, mollusks and other smaller sea life, so their health is considered a measure of marine life on the whole in a given area.

When sea stars decline in number, “the mussel population has the potential to dramatically increase, which could significantly alter the rocky intertidal zone,” according to Sleeman.

In an effort to find out what is causing the mass deaths, scientists are collecting reports from the public, taking specimens to the lab for analysis and doing genetic sequencing to find out whether a toxin or an infection may be to blame.