Fourth of July weekend brought thousands of welcome guests to the Cape Region, but it also brought less welcome visitors: jellyfish.
Lifeguards in Rehoboth Beach said jellyfish appeared on the beach July 4. In Dewey Beach, lifeguards treated a few people for stings, and on Lewes beach swimmers reported large, red jellyfish.
Rehoboth Beach Patrol Capt. Kent Buckson said, “We hadn’t seen this kind of presence in a couple years. It kind of caught us off-guard.”
The Rehoboth lifeguards set up a stinging station at the patrol’s Baltimore Avenue headquarters to deal with the high number of stings. Buckson said swimmers who had been stung were sprayed with a mix of water and vinegar to neutralize the sting. Even the captain was not immune: Buckson said while checking out the water July 4 weekend he was badly stung and had to stand in the shower for 20 minutes to ease the pain.
The good news is that while last week the ocean was saturated with jellyfish, they seem to have drifted out of the area, Buckson said.
Chuck Epifanio, professor of marine science at University of Delaware’s School of Marine Science and Policy, said jellyfish come close to the beach in large numbers some years and smaller numbers other years. Rain, a lot of which has fallen this summer, often results in a large number of stinging jellyfish. He said when cool rainwater falls on warmer ocean waters, it leads to the formation of fronts – boundaries between two water masses colliding with each other.
Although they are capable of swimming, jellyfish are not good swimmers, Epifanio said. They prefer to ride the current and tides. He said it is not unusual to see jellyfish in and out of an area in a short amount of time.
"Movement of jellyfish is strongly affected by currents. So changes in current patterns along the beach can cause quick changes in occurrence," Epifanio said.
Epifanio said jellyfish tend to occur in swarms, to assure sufficient congregation for reproduction.
Dewey Beach Patrol Captain Todd Fritchman said the jellyfish are in their peak reproductive stage. Male jellyfish release sperm into the water that are swept by the tide into the mouth of the females. The egg fertilizes and eventually becomes a polyp, which attaches to the sea floor. The polyp develops into a freefloating larvae before growing into an adult jellyfish.
Mid-summer is typically the middle of the reproductive season for the lion’s mane jellyfish, among the largest species in the world and one of two species of jellyfish that pack a serious sting for humans, Epifanio said. Lion’s mane jellyfish are distinctive for their red-tinted bell.
In Rehoboth, Buckson said the jellyfish that caused the most trouble is the mushroom cap jellyfish, which looks similar to the lion’s mane with its large, bright-colored bell, although mushroom cap jellies have shorter tentacles.
Epifanio said the jellyfish that show up in the Cape Region are usually smaller than the maximum size the species can get. Some lion’s mane jellies can grow to two meters, or six feet wide at the bell, he said. In addition to mid-July being the peak of their reproductive season, lion’s mane jellyfish prefer cooler waters.
The other major jellyfish in the Cape Region is the Chesapeake sea nettle. Epifanio said sea nettles are smaller than lion’s head jellyfish, but have longer tentacles and produce a more severe sting, although some people have a stronger reaction to the lion’s head’s sting. Sea nettles tend to like warmer water, and can usually be found in large numbers near the shore during the late summer and early fall, when the water is warmer and the sea nettle is its reproductive season.
When a jellyfish comes in contact with human skin, the jellyfish instinctively thinks its prey, Fritchan said, and releases little harpoon-like features in their tentacles that cause a hypersensitive reaction in humans. Different jellyfish cause different degrees of damage to human skin, he said.
To treat a jellyfish sting, Epifanio said the best solution is vinegar, which is acidic and breaks down the toxin from the sting. He said the worst thing to do is rub the sting. If vinegar is not available, Epifanio said a warm compress would also do the trick.