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Why Are These Weird Blue Jellyfish Washing Up on Oregon's Beaches?

Thousands of Velella velella jellyfish, aka "by the wind sailors," have met a stinky end.

​In recent days, the Oregon and Washington coastlines have seen an onslaught of strange, beautiful blue jellyfish. Properly known as Velella velella, the creatures are blanketing beaches by the thousands, ​according to the Oregonian, with the result being an entrancing sight accompanied by the unholy reek of rotting sea creatures.

Velella carry toxins in their nematocyst-bearing tentacles, but only enough to stun their plankton prey. Humans shouldn't be concerned, but it's probably not a great idea to walk barefoot through a whole pile of them or touch your eyes or mouth after handling one of the creatures (for whatever reason). The problem is mostly the smell.

Image: notafly/Wiki

Velella are alternatively known as "by the wind sailors." Each one is essentially a biological sailboat and sports a translucent vertical fin protruding above the water surface. "Winds blowing gently against its triangular, clear sail move the jellyfish. The sail is set diagonally to the long axis of the animal," an Oregon State University fact-sheet ​explains. "On our side of the north Pacific Ocean, their sails are set in a northwest to southeast direction. On the other side of the north Pacific, the sails are set in a northeast to southwest direction. In the southern hemisphere, sails are reversed."

"As long as the winds blow gently, Velella tacks at about 45˚ away from a following wind," the OSU page continues. "This keeps the animal offshore."

(Disclosure: the author is a student at OSU.)

When the wind is strong enough, the Velella can no longer stay on course and instead start spinning around while being pushed more or less directly by the wind (rather than ​tacking, which is how sailboats are able to travel forward into the wind). So, a strong enough wind out of the west is likely to blow a whole mess of helpless jellyfish ashore.

The result is photogenic, but basically still amounts to a jellyfish massacre.