North Carolina Beach Turns Into Jellyfish Swamp as Thousands Wash Up

A massive swarm of jellyfish has washed up on a beach in North Carolina.

Pictures of the cannonball jellyfish on the shores of Ocracoke Island were shared on Facebook by Cape Hatteras National Seashore.

Cannonball jellyfish, named because of their resemblance to the large spherical object, can grow to up to 10 inches in diameter. They are commonly seen off the U.S. East Coast, but can also be found between New England and Brazil, as well as in the Pacific Ocean.

"Jellyfish rely on winds and currents to help them swim. Colder water temperatures, winds, and currents can all play a role in them washing ashore," Cape Hatteras National Seashore wrote in the caption of the Facebook post.

Mass wash-ups of jellyfish like this one can occur after jellyfish blooms, in which the local population explodes in size after a boom in reproduction.

"Cannonball jellyfish (and others) "bloom" at certain times of year when temperatures are right for their tiny inconspicuous polyp stage (sessile form attached to a substrate) to metamorphose into a swimming jellyfish. So they all seem to appear at once, and then reproduce, and make more polyps for the next year," Cheryl Lewis Ames, an associate professor of Applied Marine Biology at the Graduate School of Agricultural Science, Tohoku University, told Newsweek.

"Why blooms occur in some years and not in others, or why sometimes blooms are larger in some years compared to others is all tied to environmental factors, but not well understood. Some researchers think of it a bit like how certain cicadas are programmed to appear every seven years. Other blooms researchers say bloom frequency and size are connected to sun spots. In my several decades of jellyfish research I have found that few jellyfish species will reliably show up just when you expect them."

According to the post by Cape Hatteras National Seashore, this species doesn't generally sting, but people should avoid touching them anyway.

Cannonball jellyfish can secrete a toxin-filled mucus if disturbed, which harms small fish in the immediate area, and drives away most of their predators. These toxins are also capable of causing cardiac problems in humans, though that is unusual, and they can also harm the eyes and irritate the skin.

According to Ames, the cannonball jellyfish is more harmful than the Cape Hatteras National Seashore post lets on.

"In talking with people on the beaches in the past, I learned that these jellyfish pack a punch, and their stings can be very painful to humans. Keep in mind they are being compared to the mushroom jellyfish (Rhopilema verrilli), and to sea wasps (Tamoya haplonema and Chiropsalmus quadrumanus), the latter which can cause serious stings, although they are less abundant and less likely to be stranded on beaches where swimmers will encounter them."

Swimmers should also be warned of the effects of the jellyfish mucus.

"People [get] stung by water due to stinging mucus in the water that contains stinging structures (we called cassiosomes) released by the jellyfish for predation and protection," Ames said. "Cannonball jellyfish also cause stinging water syndrome. Therefore, bathers should take care not to get close to the jellyfish while they are in the water, or touch the stranded jellyfish due to their stinging mucus."

According to Cape Hatteras National Seashore, the North Carolina swarm will eventually wash back out with the tide, or be eaten by shore animals like seabirds and crabs.