NATURALIST'S 



NOTEBOOK 



The East Coast sea nettle is commonly found in 80-degree coastal waters. 



Although an encounter with a stinging 

 jellyfish is one that most swimmers are not 

 likely to forget, many jellyfish are actually 

 harmless. Still, sightings in North Carolina 

 waters send swimmers scampering. 



Jellyfish come in many shapes and sizes, 

 from tiny, thimble-shaped Caribbean species 

 to the Arctic lion's mane, whose bell can 

 reach eight feet in diameter, and tentacles can 

 stretch to 200 feet. 



"Jellyfish have been on the Earth for 

 over 650 million years," says Ken Bradley, 

 education instructor at the N.C. Aquarium at 

 Pine Knoll Shores. "So even though they're 

 simple creatures in a lot of ways, they have 

 been around longer than sharks — and even 

 before dinosaurs." 



Though they float mostly with the 

 current, jellyfish are able to swim. Using a 

 primitive kind of a jet propulsion, they push 

 water in and out of their umbrella, or bell- 

 shaped body. Usually they stay within saline 

 waters up to 40 feet deep, but some are found 

 in freshwater lakes. There are also deep-sea 

 jellyfish in oceans all over the world. 



Although jellyfish are composed mostly 

 of water, a complex system of nerves allows 

 them to smell and taste. Through touch 

 receptors and light-sensing organs, they are 

 able to react to the world around them. 



Jellyfish are held together simply by 

 muscle fibers laced through their bodies and 

 connected to their mouths. Special sacks 

 located around the rim of their bodies help 

 them to maintain balance. 



Long tentacles, trailing from beneath 

 their bodies, have the same effect on prey as 

 they do on innocent passers-by. 



"They catch their food pretty much by 

 luck," says Bradley. Whatever brushes against 

 their tentacles is a candidate for their next 

 meal. 



When the tentacles touch a prey, the 

 jellyfish first stuns it with stinging cells called 

 cnidocytes. Each cnidocyte contains a tiny 

 harpoon called a nematocyte. When touch or 

 chemicals trigger the cnidocyte, the 

 nematocyte not only shoots into the prey, but 

 another toxin also is released to stun or kill the 

 food. Then the oral arms, which cover the long 



tube where the mouth is located on its central 

 surface, help the jellyfish to engulf its prey. 



"Since a lot of jellyfish eat tiny 

 zooplankton and other baby sea creatures, 

 their stings are not strong enough to break our 

 skin," says Bradley. 



For the same reason, jellyfish prove to 

 be tasty meals for turtles. "Any sea turtle — 

 especially a loggerhead — loves jellyfish. 

 They are able to eat them without worrying 

 about the sting associated with it." 



THE ODD ONES AMONG US 



Joe Pawlik, professor of marine 

 invertebrate zoology at the University of 

 North Carolina at Wilmington, says that this 

 year large numbers of the Portuguese man-of- 

 war (Physalia physalis) were spotted along 

 Wilmington area beaches. 



"It's unusual to find so many making it 

 to shore here because we usually have 

 offshore breezes," says Pawlik. "But if part of 

 the Gulf Stream breaks off and spins toward 

 the coast, the wind carries their float as a sail. 



"Although the Portuguese man-of-war 

 and the jellyfish are both jelly-like and they 

 both sting, they are in completely different 



classes at the taxonomic level. It's basically 

 the difference between a colonial and a 

 noncolonial organism," Pawlik says. 



The man-of-war is composed of a 

 colony of animals with various organisms 

 working together as one unit, whereas the 

 jellyfish is only one organism. Though the 

 man-of-war is more toxic, it is easier to spot 

 — and avoid — since it floats above the 

 surface. It is also visible by a vivid pinkish-blue 

 body and tentacles that trail as far as 65 feet 

 behind the umbrella. 



Beachgoers here can relax knowing that 

 they won't encounter the Australian box 

 jellyfish (Chironex flecked), or the sea wasp. 

 The most venomous animal on earth, its sting 

 is more toxic than a cobra's, and it can kill a 

 human in minutes, says Pawlik. These jellyfish 

 can see, move toward prey and feed on fish. 



However, a species of box jellyfish lives 

 approximately 300 to 400 yards off the coast 

 of Wrightsville Beach, according to Pawlik. 

 He and colleagues brought up several of the 

 jellyfish while trawling. 



"Despite the fact that they were in our 

 trawls, and we had every opportunity to get 

 very badly stung, no one did. These do not 



24 AUTUMN 2002 



