Mystery grows over why thousands of jellyfish are gathering along Rhode Island coast

A mysterious gathering of jellyfish continues to grow along the Rhode Island coast, prompting state officials to warn about the increasing threat of painful stings.

Atlantic Sea Nettles are congregating in the coastal Ninigret and Green Hill Ponds, according to a statement issued Tuesday by the Rhode Island Division of Fish and Wildlife Outdoor Education.

State biologists are monitoring the little understood phenomenon — and reporting it is getting worse.

“In the past month, their population has increased to the thousands as water temperatures have risen,” the department said in a Facebook post.

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“While their high abundance in the ponds this summer is not fully understood, their numbers are expected to decline as the summer goes on.”

Rhode Island Department of Environmental Management officials are warning the public to “use common sense and caution” when entering coastal ponds in the region. The popular ponds are separated from the ocean by thin strips of beach, but remain accessible to sea creatures via narrow inlets.

“Folks who plan on recreating in the coastal ponds this summer are encouraged to carry a first-aid kit with vinegar in case of a jellyfish encounter,” the state said.

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“Although their sting is not fatal (unless there is a severe allergic reaction), it can cause moderate discomfort and itchy welts. ... If symptoms worsen, seek medical attention.”

The nonprofit Chesapeake Bay Foundation notes jellyfish easily tolerate the impact of pollution and have few natural enemies in the ocean.

They prefer “warmer, saltier water” and are prone to spawn in late summer and early fall, the foundation reports: “Although mature nettles can achieve a weak swimming motion by contracting and relaxing their bell, their location is mostly controlled by winds and currents.”

Nettles are typically just inches across, with a size that varies by location, according to the Aquarium of the Pacific. The ones found along the upper East Coast have a “bell” that is typically four inches in diameter, while those in open ocean may be double that size.