Many Miami environmental science graduate students take the Ecology Field Courses each year.
Jellyfish became the subject of my research topic partly because I wanted to research a type of animal. I figured researching an animal might help me with material in future classes, since my major is zoology. My initial interest in jellyfish stemmed from the fear people have towards them. I wanted to find out exactly how dangerous they were and see if they were feared with good reason. After skimming articles on jellyfish I was also intrigued by their simplicity. Although jellyfish can be feared creatures, when looking at the basic information about them, these relatively simple animals seem to do more good than harm to the ecosystem.
There are various ways of classifying jellyfish. Jellyfish fall under the category of animals called invertebrates (Jones, 1991). Instead of a backbone, they are supported by mesogloea, which is a jelly-like substance that is found between their two layers of skin. Despite their name, jellyfish, also called medusa, are not classified as fish (Muscatine, 1989). They belong to the phylum Coelenterates, and are separated into two classes: Scyphozoa, large jellyfish, and Hydrozoa, small jellyfish (Muscatine, 1989). The difference between these two classes is that the Hydrozoa are not fully matured jellyfish. They are stationary and their mouth points upward instead of downward like free-swimming jellyfish (Nichols, 1971). Some scientists classify jellyfish as plankton because they live near the surface of the water (Jones, 1991). They are the largest form of animal plankton, also known as Zooplankton (Jones, 1991). Common names are given to different types of jellyfish based on their physical features.
Most jellyfish have similar anatomies. The combination of mesogloea, and two skins make up the body of the jellyfish, also known as the bell (Jones, 1991). Mesogloea is not only helpful in support and buoyancy, but is also the reason for the common name of the animal (Muscatine, 1989). Jellyfish have a mouth that consists of a short tube, with four oral arms, that World Book encyclopedia describes as “frilly projections,” around its edges, that hang down from the center of the bowl-shaped body (1989). Tentacles are attached to the edges of the body, and their length and number differ depending on the jellyfish (Muscatine, 1989). Jellyfish can range from pea sized to ten feet in diameter (Stidworthy, 1990). Despite the fact that 95% of their composition is water, they can be brightly colored in a variety of shades (Stidworthy, 1990). Although predominately water with few major organs, jellyfish do possess sensory skills. Each of the eight notches around the radially semetric bell is actually a pigment spot which is sensitive to light (Stidworthy, 1990). These spots are called rhopalia and they contain organs, called statocyts, which help the jellyfish keep its balance (Vancouver, 2000). Simple sense organs such as these will make sure the jellyfish has its bell pointed toward the water’s surface and help to keep its path of movement from straying too far to either side.
Jellyfish, like all animals, must find a way to produce. A jellyfish, only four inches in diameter, can produce 40,000 eggs daily (Earney, 2000). Small jellyfish, called buds, are grown on polyps, hollow cylinders that attach themselves to a stationary surface (Jones, 1991). These polyps are grown from the eggs produced by the mother jellyfish (Muscatine, 1989). The buds are arranged like a stack of saucers on the polyp, often looking like other sea plants rather than jellyfish, until they are released (Nichols, 1971). Jellyfish that are released after reaching an acceptable size are known as medusae, and these medusae then mature into full-grown jellyfish (Nichols, 1971).
Unfriendly features of jellyfish include their ability to sting. Thorny threads that come out of the sides of the tentacles, like little whips, sting animals that come into contact with the jellies (Jones, 1991). It may be a general tendency to assume that only the tentacles of the jellyfish are poisonous, however all surfaces of the jellyfish include cells with stinging capabilities, even those in the digestive cavity (Vancouver, 2000). Even dead jellyfish can sting with the poison left in their tentacles (Jones, 1991). While the common jellyfish cannot kill a human, a type of jellyfish called a sea wasp, found off the coasts of Australia and the Philippines, can kill a human in less than three minutes with its sting (Muscatine, 1989). Young Science encyclopedia states that the tentacles help the jellyfish to feed by giving off a poison that paralyses small sea animals, and these tentacles then pull the animals into the mouth of the jellyfish (1991). The jellyfish gathers its prey while it moves. The jellyfish expands and contracts its body, so that it can move upward as it shoots water out beneath it (Gabb, 1966). When the jellyfish stops this movement, it sinks toward the ocean floor, collecting small animals that touch its tentacles or oral arms on the way (Muscatine, 1989). These animals are passed to the mouth and swallowed after they have been stung (Stidworthy, 1990). Luckily, humans have ways of protecting themselves from jellyfish’s stings.
Because of the pain associated with the jellyfish sting, people have developed ways to avoid and treat these painful stingers. Some people can be seen slowly walking into the ocean, dragging their feet along the sand; a step that is known to some as the “jellyfish shuffle.” This moves the sand and warns jellyfish of ones presence in the water, apparently causing them to avoid the area. Tourists may be warned not to dive head first, or run in the water in order to avoid jellyfish stings (Earney, 2000). If a person is stung by a jellyfish, there are several steps to the treatment process. After one brings the victim to shore and calms the victim, one should check circulation and breathing (Earney, 2000). Large fragments of jellyfish should be removed with tweezers or a gloved hand, and the wound should be washed with seawater or vinegar (Earney, 2000). Vinegar prevents the sting from getting worse by inactivating any stinging cells left on the skin (Scott, 1997). Fragments of jellyfish that are still stuck to the skin can be removed by applying shaving cream to the area and then scraping it off with a flat edge and rinsing it with more seawater (Earney, 2000). A variety of agents have been used as attempts at healing the sting of a jellyfish. These include heat, ice, placebo sugar pills, meat tenderizer, manure, mustard, figs, and urine (Scott, 1997). Contrary to the beliefs of some, laboratory tests did not show urine as being a helpful healing agent, rather, they instead gave evidence that both urine and alcohol can cause stinging cells that were previously inactivated to fire, causing the patient more pain instead of relief (Scott, 1997). Stings should be treated with care and the victim should be monitored in case of side effects other than itching and burning, such as nausea, headaches, weakness, muscle spasms, chest pains, confusion, agitation, unconsciousness or respiratory failure (Earney, 2000). Having the capability to sting creates a safety barrier for the jellyfish.
The sting of the jellyfish, however, does not scare away all predators. Other animals that can be found feeding on jellyfish include the ocean sunfish, banner fish, arrow crab, and the leatherback sea turtle, as well as other jellyfish and humans (Earney, 2000). Jellyfish can also be harmed from factors outside of the food chain. Environmental pollution, such as the pesticide DDT, and pollution from publicly owned treatment works (POTWs) also affect the lives of many water inhabiting creatures, jellyfish included (Unknown, 2001). Tourism can also prove harmful to these ocean dwellers. According to Cornell student Andrea Earney, tourism can lead to erosion of soil, over fishing, and increased environmental waste, all of which can harm the habitats and populations of jellyfish (2000). Some solutions to these man-made problems include upgrading treatment plants, pre-treating industrial wastes and controlling the sources of the pollution (Unknown, 2001). Programs assigned to these tasks, such as the Clean Water Act (CWA) and the Coastal Zone Management Act (CZMA) both controlled by the Environmental Protection Agency, could also make their participation mandatory instead of voluntary (Unknown, 2001). Companies may also be more willing to increase their efforts to protect the beaches if they are more aware of the damage that is taking place.
It is becoming necessary to preserve the lives of jellyfish because they are helping to preserve the lives of humans. These animals are being used for medical research. Some jellyfish are providing the simple pleasure of relaxation to patients just by swimming in an observing tank (Vancouver, 2000). Other jellyfish are used by researchers for a bioluminescent chemical, which is used to help track the movement of chemicals throughout a human body (Earney, 2000). Undoubtedly even more medical research involving jellyfish will evolve in the next few years.
Throughout my research it has become apparent to me that jellyfish play an important role in the ocean and on the land. By just searching Yahoo.com for “jellyfish sushi,” I found such delicacies as “spicy jellyfish with cucumber,” and “jellyfish salad” on the menus of restaurants in Japan and China. I was surprised to learn that jellyfish extend to the food chain above land as well as that of the sea. Along with the important role jellyfish play in the ecosystem, and that which they are beginning to play in medical research, it is clear that it is important to preserve these creatures and their habitat as long as possible.
Earney, A. “The Existance of a Jellyfish.” 24 Jan 2000:
Gabb, M. H. The Life of Animals Without Backbones. London: Sampson, 1966.
Jones, C. M., Ed. Young Scientist. Chicago: World Book, 1991. 8+.
Muscatine, L. “Jellyfish.” World Book Encyclopedia. 1989 ed. 87-88.
Nichols, D., and J. A. L. Cooke. The Oxford Book of Invertebrates. London:
Oxford, 1971. 12-14.
Scott, S. “Ocean Watch: Victims of Jellyfish Stings Invited to Join Pain Study.”
6 Jan 1997. Star Bulletin. Online. 5-6-02.
Stidworthy, J. Simple Animals. New York: Oxford, 1990. 6+.
Unknown. “Marine Pollution.” 2001.
Vancouver Aquarium. “Marine Science Center.” 2000.
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