Bloom of Rare, Black Jellyfish Stings Beachgoers in California

What were believed to be dozens of rare, black jellyfish sent swimmers scrambling from the waters of Laguna Beach, Calif. last Friday.

According to the Orange County Register, some swimmers reported severe stings all over their bodies.

Nigela Hillgarth, executive director of Birch Aquarium at Scripps in San Diego, told the Resister that black jellies only recently appeared in Southern California. Hillgarth speculated that increasing ocean temperatures may have contributed to the jellies chasing plankton in the area, and if they get too close to shore, the jellies get caught in currents and cannot break away.

Black jellies can reach nearly 20 feet (6 meters) in length, and while the medusae aren't deadly, their stings will hurt.

The creatures are mysterious and elusive, with large chunks of time where there whereabouts are unknown, as well as a dearth of information about their behavior, distribution and lifecycle.

A bloom of giant black jellies, also known as black sea nettles, once appeared off the San Diego coast in 1989, then disappeared without a trace for a decade, according to Monterey Bay Aquarium.

While sightings are uncommon, they are not unheard of.

In July of 2011 in the waters off the coast of La Jolla, Calif. a kayaker spotted a strange sight: a hula-hoop sized jellyfish with an inky black bell and pink tentacles.

"In 30 years of diving and fishing off San Diego's coast line, I've seen a lot of strange, beautiful, cool things and this ranks up there as one of them," kayaker Joe Richman told local news station CBS 8. Photos Richman took were later confirmed to be of a black jellyfish.