Swarms of mysterious blue jellyfish are washing ashore on beaches and lakes across the West Coast in the U.S.
The Velella velella jellyfish, also known as "By-the-wind sailor," are known to suddenly increase in population during what scientists call "blooms," according to National Geographic.
But scientists are spooked because the tiny round creatures are washing ashore by the billions, dying on beaches in California, Oregon, Washington and even the U.K.
"The numbers, if you extrapolate, are awe inspiring," biology professor Kevin Raskoff, of California's Monterey Peninsula College, told Southern California Public Radio. "With some of my students we counted more than a thousand per meter. The numbers get astronomical pretty fast," he told the station.
Pictures from beaches in San Pedro, California, and La Push, Washington, show scores of jellyfish carcasses splayed out on the sand. There is not an immediate concern for safety because their stingers are too weak to pierce human skin, Raskoff said.
"They're beautiful blue, these circles with these clear fins that come up," Andy Sway told the radio station from a Santa Monica beach. "I've never seen anything like it."
One possible explanation for the Velella velella swarms could be related to an increase in their food supply. Plankton and algae, the prey of choice, have become more common due to agricultural runoff containing fertilizer and other chemicals, according to National Geographic.
Another explanation is that powerful wind currents on the ocean blow the jellyfish out of the water and onto the shore.
Jellyfish mostly swim on their own using their bell-shaped top as a propeller. But if the ocean current and winds are strong enough it can push the jellyfish together, causing an apparent bloom, the magazine reported. Scientists, however, have no way of predicting the blooms.
"We can't yet look at the ocean and say, 'Gee, this is going to be a jellyfish year,' " Jim Watanabe, an invertebrate biologist from Stanford University, told the magazine.
