Stinging Jellyfish Return To Sedge Lot Pond In Mashpee

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By: Brian Kehrl
Published: 06/29/12

The nasty little jellyfish in Sedge Lot Pond at South Cape Beach are back again this summer, earlier than usual and in large numbers.

Staff at Waquoit Bay National Estuarine Research Reserve are warning swimmers and beachgoers about the small, translucent, bell-shaped creatures in the small tidal pond next to the town parking lot at the popular saltwater beach. The jellyfish have been identified as a species called Gonionemus vertens, also known as GV, clinging jellyfish, orange-striped jellyfish, or angled hydromedusa.

“Remember those aggressive little jellies (Gonionemus vertens) that caused the two researchers to end up in the hospital a couple of years ago? They are back in full force. While sampling with a group we were catching lots of them in each dip net. We watched them swim after and kill silversides and shrimp larger than themselves in the container. Awesome!,” Nancy Church, school and interpretive programs coordinator at WBNERR, wrote in an e-mail.

The incident involving two researchers occurred at the end of July 2010. The two were stung on the face, in the narrow gap between their protective hoods and snorkeling masks. They were taken to the hospital after experiencing muscle cramps, chest tightness, and throat swelling, in addition to a stinging and tingling sensation all over their bodies. Both were treated with antihistamines at the hospital. One of the researchers experienced flu-like symptoms for 24 hours.

“A sting would be overpowering for a little kid,” said MaryKay Fox, assistant research director at WBNERR.
Sedge Lot Pond, a broad, shallow salt pond, is most often accessed at its connection to Waquoit Bay, near Callie’s Beach and the end of Wills Work Road.

There are no reports of any stings this year, Ms. Fox said, but WBNERR is planning to put out signs describing the critters and warning against entering the water at Sedge Lot Pond.

Heidi L. McLaughlin, program director for the Mashpee Recreation Department, said she was not aware of the jellyfish or any incidents involving bathers being stung and requiring assistance from lifeguards. The town lifeguards are scheduled to be on duty seven days a week beginning tomorrow, she said.

The jellyfish are likely to be present in other, similar parts of the Waquoit Bay system, like the upper reaches of Hamblin and Jehu ponds and Tim’s Pond on Washburn Island, according to a prior interview with a field worker for the Marine Biological Laboratory in Woods Hole.

GV are about the size of golf balls, and with nearly clear tissue, they can be difficult to see until they are moving, Ms. Fox said. They typically cling to vegetation in the water, waiting for vibrations to indicate the presence of prey. Then, they swarm in a fashion that has been compared to wasps.

“They are very directional. They just kind of, boom, boom, boom, shoot around. They can go about a foot in two seconds,” she said.

Ms. Fox said she was stung on the foot by a GV last summer and felt a tingling sensation in her toes all day. She attributed the discrepancy between her reaction and that of the researchers two years ago to the location of the sting. Contact on the hands and feet is likely less dangerous than on the face or chest, she said.

This year the jellyfish seem to have arrived about a month earlier than usual, Ms. Fox said, a phenomenon she attributed to the unseasonably warm water. The water in Waquoit is up to about 70 degrees, she said. “Sedge Lot, of course being a small, enclosed shallow pond, tends to warm up very quickly,” she said.

According to biology research, the jellyfish are thought to be native to the Pacific Ocean, transported to the Atlantic along with ship ballast water. They are now located around the Northern Hemisphere, but they are not known in the scientific literature to be toxic anywhere but certain parts of the Russian Pacific coast.

They are thought to be dangerous only from mid-July to August, according to a 1993 article published in the Russian Journal of Marine Biology and provided by Ms. Fox.

Why the GV here in Mashpee are so toxic remains unknown, Ms. Fox said.

Likewise, how the toxin works has not been established, according to the journal article.

The journal article summary included advice on how to respond to a sting: “Prophylaxis, first aid and treatment of stings: a) wash the sting site with fresh water, wet with the alcohol solution, then get to the hospital b) Another folk remedy is the application of raw potato to the sting site although there is no reliable evidence of the effectiveness of this method c) a mixture of sodium bicarbonate and water (1:1) d) don’t go into water that contains these jellyfish!” 

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