20120518-jellyfish -Tiny_Jelly.jpg Most jellyfish are coelenterates and members of the 9,000-species phylum Cnidaria (meaning "stringing thread"). Others are ctenophores (comb jellies). There are also some worms, snails and squid that look like jellyfish. The main difference between Cnidaria and ctenophores is that the former has a sting and the latter doesn't. [Source: Richard Conniff, National Geographic, June 2000; Jack and Anne Rudlow, Smithsonian]

All coelenterates, which also include sea anemones and coral, are simply a hollow sac of cells with a mouth at one end surrounded by tentacles. Armed with stinging cells, the tentacles help them to paralyze small swimming animals which are then pushed into its mouth.

Jellyfish are among the world's oldest creatures. Because they have soft bodies, jellyfish fossils are rare. They oldest, found in Australia, are 650 million years old. Jellyfish "invented" neurons, the cells that build brains and nervous systems, and were among the first to develop stinging poison.

Websites and Resources: National Oceanic and Atmospheric Administration ; Smithsonian Oceans Portal ; Ocean World ; Woods Hole Oceanographic Institute ; Cousteau Society ; Montery Bay Aquarium

Websites and Resources on Fish and Marine Life: MarineBio ; Census of Marine Life ; Marine Life Images ; Marine Species Gallery

Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Wikipedia article Wikipedia ; Coral Reef Alliance ; Global Coral reef Alliance ; Coral Reef Pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.


Sea anemones, jellyfish and corals belong to the family of colonizing organisms called coelenterates (Greek for cavity) and the 9,000-species phylum Cnidarians (meaning "stringing thread"), a group of tentacled creatures which also includes anemones, jellyfish and corals and hydriods. Most reproduce asexually without mating by producing buds from their own bodies.

All coelenterates are simply a hollow sac or shallow cup of cells with a mouth at one end surrounded by tentacles. Armed with stinging cells, the tentacles help them to paralyze small swimming animals which are then pushed into its mouth. Coelenterates have a primitive gut for digestion and their mouth also serves as an anus.

Coelenterates take in food through their mouthes and ingest it in the stomach, with the indigestible parts being expelled back out the mouth. They are almost exclusively carnivores but have no teeth. Instead they have tentacles lined with whiplike structures called nematocysts that release poison barbs that are strong enough to paralyze prey and allow it to be pulled into the coelenterate’s mouth and gut. Jellyfish have their tentacles pointed downward while anemones and corals have theirs pointed upwards.

Cnidarians are essentially the same: cup-like animals but looked at in a slightly different way. The tube can either be a medusa, flattened into a bell shape, or a polyp, with the closed end attached to a hard surface. Corals and sea anemones are polyps. Medusas are mostly jellyfish. Some hydriods and jellyfish exist in both medusa and polyp forms in their lifetimes.

Coral, see Reefs

Jellyfish Characteristics

Jellyfish have no skeleton and less than five percent of their bodies are organic material. Around 95 percent of their bodies are made of a jellylike material that is more like mucous with rubbery fibers than jelly and is composed mostly of water. Because jellyfish are mostly saltwater the can easily manipulate their buoyancy to move up and own in the water column. It doesn't need skeletons to hold itself up as it would if it lived on land and had to deal with gravity.

Television naturalist David Attenborough wrote: "Jellyfish are constructed from two layers of cells. The jelly which separates them gives the organism a degree of rigidity needed to withstand the buffeting of the sea...Their cells, unlike those of sponges, are incapable of independent survival.”

A typical Cnidaria jellyfish is umbrella-shaped with a number of tentacles dangling below and a mouth and digestive cavity at the center of the base of the tentacles. Spoke-like canals deliver nutrient from the digestive cavity to the rest of the body. All of these things are made from mucous.

Jellyfish Movement, Senses and Stingers

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Most jellyfish have groups of cells able to contract in length and are considered simple muscles. Ones on the underside of the bodies can contract but not expand, allowing it to swim. Some have comb-like paddles comprised of cilia.

Regardless of their means of propulsion, most jellyfish just drift with the current. Most large jellyfish spend their time swimming about freely. Some smaller ones spend much of their lives living as attached polyps.

Jellyfish don't have ears or brains. Only a few species have eyes. Some cells are modified to transmit electrical impulses and are linked into a primitive nervous system. Many that seem to pitch and roll in the water can orient themselves with light sensors along their bell margins.

Most jellyfish don’t really need senses as they filter -feed whatever comes their way. They can catch prey and eat in areas of total darkness because they don’t need to see what they catch or eat.

All true jellyfish sting. The venom, which humans only feel if it penetrates their skin, is injected with millions of microscopic barbs, coiled like springs and fired by touch or chemicals. The toxin immobilizes prey by disrupting the transmission of information between the synapses of the prey's nerve cells. The prey is digested by cells in a primitive stomach.

The toxin can also be used as protection from predators. It is automatically discharged when they bump into something warm — like another sea creature — from poison-containing stingers in mantles, arms or long threadlike tendrils which can gro to one meters long.

Jellyfish as a Model of Efficiency

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stages of development
John Dabiri, an assistant professor of aeronautics and bioengineering at Caltech and MacArthur Award winner, is fascinated by jellyfish. He believes jellyfish propulsion can inform engineering, which in turn can inform efficiency in wave and wind technology. On how jellyfish move Dabiri told the Los Angeles Times, “For a long time, people thought of jellyfish swimming as like jet propulsion — like a rocket that shoots out exhaust and goes the other way. But it's a bit more subtle than that. They create vortex rings, like the smoke rings you might create with a cigar. And those doughnut-shaped swirls of water are an efficient way of propulsion because [the animals] can basically push off of those doughnuts of water...What we wanted to understand was how do they form these swirling currents, and whether then we could build underwater vehicles that could also create these same type of water currents while they propelled themselves. [Source: Lori Kozlowski, Los Angeles Times, November 6, 2010]

These vortex rings show up in other animals. So you could have picked a trout, let's say, or a shark. They have more complicated wake flow patterns: The shape of their fins and the way they move is just more complicated. With a trout or a shark, as it's flapping its tail, it's creating these vortex rings, but they are sort of linked up into more complicated chains. So if you were to do that dye experiment — if you could do it with a shark — it would be messier, and harder to interpret what you were seeing.

When asked what species he studied, Dabiri said, “The moon jelly — that's the most common one. You see them in the aquarium; they are sort of white-colored. They don't sting humans very much, and they're very plentiful, so it's pretty easy to find them. Then there's one called the lion's mane — which has a reddish color with really long tentacles. Those are the two main species we looked at because they are easy to access and the sting isn't horrible.

On the applications of what has been learned about jellyfish motions Dabiri said,”There is another technology out there for wind energy generation — instead of using these large wind turbine structures, they rotate around a vertical axis. They are smaller structures, so they are maybe 30 feet tall instead of 300 feet. We've been interested in how many of these smaller structures could be situated very close together in order to generate as much power as you get from the very large ones. We were able to learn something about this from how fish school.

Jellyfish Feeding and Reproduction

giant jellyfish
Most jellyfish are predators that feed on zooplankton, small crustaceans and small fish. Some rely on stealth and the fact they produce no bow wave to sneak up on prey. Most filter food passively and just wait and eat whatever floats their way within their grasp. Many jellyfish have mucous lures that look like larvae. They attract small fish or crustaceans that are zapped with toxins from tentacles and moved to the digestive cavity.

Jellyfish can quickly convert food into mass. When food supplies are plentiful they can regenerate damaged parts and grow in size and number. When food is scarce they can shrink in size and not reproduce.

In many places, jellyfish are their chief predator, consuming more krill and crustaceans than whales and large fish. A single saucer-size sea nettle can consume as many as 18,700 copepods a day. Copepods are flealike seas creatures and one of the most abundant animals on earth.

Jellyfish reproduce by budding, and by releasing eggs and sperm in the sea. Fertilized eggs do not develop into miniature jellyfish but rather free-swimming creatures, quite different from their parents, that settle on a surface and develop onto a flower-like organism called a polyp (coral is also a polyp). The polyps filter feed using cilia. The polyps eventually bud and produce miniature medusas that break away from a surface and begin swimming freely in the sea. Jellyfish budding can result in the blooming of thousands of new individuals.

A typical jellyfish releases sperm and eggs into the water during a specific time or when stressed. The fertilized eggs multiply into "balls of cells" called planulae that settle onto a hard surface like a rock and then grow into a polyp. The polyp reproduces asexually into several creeping polyps which later metamorphose into adult jellyfish (called medusas) in a 12-day period.

Jellyfish as Prey

Jellyfish are preyed on by sea anemones, some birds and some sea turtles. Fish generally don't mess with them because of their toxic and watery tissue.

Since jellyfish are mostly water a predators has to consume a lot of them to get enough nourishment to make it worthwhile. Moreover, they need to get rid of a lot of water. Sunfish, leatherback turtles and some other fish species have pharyngeal "teeth" at the back their throats. After swallowing a jellyfish they regurgitate it against these teeth, which strains out the water and leaves behind the edible material which is swallowed and digested.

To protect themselves from predators some jellyfish shed their tentacles as a diversion. Some even light up their attackers with bioluminescence so predators that feed on the attackers will feed on them before they get to the jellyfish. Their best protection is that they are nearly transparent sea water predators can’t pick them out.

Jellyfish Blooms

Large masses of jellyfish are called blooms, swarms or smacks. Jellyfish blooms make waters off of popular beaches unswimmable, clog seawater intake valves for nuclear power plants, foul fishing nets and catches. Jellyfish blooms sometimes wipe out all the larvae during mass spawns. They can all eat up large amount anchovies and similar fish and can deprive larger fish of food.

No one knows what causes jellyfish blooms. Pollution and fertilizer run-off may be causes. They create increase of plankton which suck oxygen from the water, creating an environment in which jellyfish thrive. Global warming may play a role by heating up the water to above-normal temperatures, creating conditions in which jellyfish are more likely to bloom. Jellyfish do well in conditions created by global warming. Nearly all jellyfish breed better and faster in warmer waters Dr. Jennifer Purcell, a jellyfish expert at Shannon Point Marine Center of Western Washington University told the New York Times.

Jellyfish blooms may also be partly the result of overfishing of species like sharks, swordfish, tuna, oysters and cod that eat the same sea creatures that jellyfish feed on. Overfishing also seems to have benefitted jellyfish by removing fish as competitors for plankton, their food, and allowing them to bloom out of control.

Jellyfish do well in oxygen-poor “dead zones” because their bodies are 95 percent water and hold enough oxygen to support them when they drift into oxygen-poor waters. They thrive in such zones because they also often have plentiful in food and low in fish competitors in part

Jellyfish Swarms

giant jellyfish off Japan
In recent years huge swarms of jellyfish with numbers unseen before have been showing in places around the globe — from Spain to New York to Hawaii to Australia to Japan — where they hadn’t been seen before with a frequency and timing that are so alarming that some scientists suggest they may be a sign that the oceans are in decline. [Source: New York Times]

One swarm that hit beaches in Barcelona left 300 people needing treatment for stings and sent 11 to the hospital. Dr. Joseph-Maria Gili, a leading Spanish jellyfish expert, told the New York Times, “These jellyfish near the shore are a message the sea is sending is, saying, “Look how badly you are treating me.” An offshore swarm of “Pelagia noctiluca” “an iridescent purplish jellyfish that issues a nasty sting — more than 1.6 kilometers long was spotted off Murcia, Spain.

Jellyfish swarm often appear in seas that have been overfished. They can make matters worse by feeding on larvae and eggs and competing for food such as zooplankton. According to a report by the National Science Foundation: “Human-caused stresses including global warming and overfishing, are encouraging jellyfish surpluses in many tourist destinations and productive fisheries.”

Fishermen are also feeling the strain. Many of them complain when they pull up their nets they are often filled more with jellyfish than with fish.

Echizen jellyfish — nasty creatures that can weigh up to 200 kilograms and reach a size of two meters in diameter — have caused havok in the Japanese fishing industry, particularly in the Sea of Japan off of Fukui, Shimane and Ishikawa Prefecture in western Honshu. The jellyfish have brown poisonous tentacles that kill fish and cause them to lose their color. Their huge numbers spoils fish catch and fouls fishing nets with a nasty smell. Their massive weight tears the nets when they are pulled out of the water.

The damage to the fishing industry has been in the tens of billions of yen. On fisherman told the Yomiuri Shimbun, “The nets were fouled by hundreds of jellyfish as soon as they were put out. There was little room for other fish, The fish that touched the tentacles of the jellyfish turned white, and the retail value of the fish is reduced to zero.”

The jellyfish population explosions have been blamed on global warming, increased nutrients in the water, and overfishing of jellyfish competitors. In the old days Echizen jellyfish disappeared by the time the autumn fishing season peaked. But warmer waters, perhaps caused by global warming, have caused the jellyfish to stick around longer than in the past. Some blame China for the problem, saying the jellyfish originate in waters off the coast China and their growth has been triggered by pollutants dumped in the sea.

Jellyfish and Turtles

Leatherback turtle
Sea turtles are among the few creatures that feed on jellyfish. Leatherback turtles feed almost exclusively on jellyfish. They play an important ecological role by eating jellyfish that feed on the fry of tuna and swordfish and other fish. They usually feed at the surface but are capable of making deep dives.

Autopsies of dead leatherbacks have revealed they have huge stomachs, often filled with masses of relatively low-calorie and mostly-water jellyfish, stingers and all. Massive salt glands collect excess salt from the jellyfish and excrete it as viscous tears. A favored prey is the lion’s mane. Among the largest jellyfish, it can weigh more than five kilograms. Leatherback turtles, sunfish and some other species have backward-pointing pharyngeal "teeth" at the back their throats that prevent slippery prey from sliding back out their mouths. After swallowing a jellyfish they regurgitate it against these teeth, which strains out the water and leaves behind the edible material which is swallowed and digested.

Jellyfish offer little nutrition and sustenance. Like pandas eating bamboo, leatherbacks have to eat a lot of jellyfish and spend a lot of time eating it to get enough calories to power their large bodies. By some estimates leatherbacks need to eat their weight in jellyfish every day to get the nutrition they need. One turtle video taped devoured 60 lion’s mane jellyfish in three hours.

Jellyfish Attack Salmon

In August, 2002, dense shoals of tiny jellyfish killed almost one million salmon at fish farms in the Western Isles in Scotland. It is thought that the jellyfish - known as Solmaris - may have found their way to Scottish waters from the Pacific Ocean. They killed the salmon by stinging them and clogging up their gills. Fish with an estimated value of more than $ 3 million were destroyed at two farms off the Isle of Lewis. Vast blankets of jellyfish moved up the sea lochs where the salmon cages are moored. [Source: BBC]

The larger fish were suffocated while smaller ones were stung to death. Western Isles Sea Foods said almost all the fish at the two farms had been destroyed. Managing director Alan Anderson said 750,000 fish were lost at one site and 150,000 at the other. The dead fish are being taken away by boat to a fish meal factory in Shetland. It is thought the jellyfish made their way into the Atlantic from the Pacific by attaching themselves to vessels passing through the Panama Canal in Central America. [Ibid]

Jellyfish and Humans

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Korean jellyfish dish
Jellyfish are the scourge of many swimmers, who find large numbers of floating in the water at some beaches, and fishermen, who find them fowling their nets. Jellyfish have done well in places that have been overfished. With fish they competed with for food gone and turtles that fed on them also gone they consume plankton and their population explodes.

Spicy jellyfish salad and soup are popular in China, South Korea and Japan. Of the 200 or so species of jellyfish, only about 10 are commercially harvested, The largest fisheries are off China and other Asian nations, new ones are being developed in Australia, the United States, Britain, Namibia, Turkey and Canada. Some fishermen have given up fishing and chosen to devote their energy to catching jellyfish for Asian seafood market.

Jellyfish are being studied for various medical applications. A rhesus monkey has been genetically engineered to have jellyfish DNA in every one of its cells. The manipulation was done as step towards genetically manipulating human cells to fight disease. Powerful toxins from the irukandji jellyfish are being studied as a possible cure for impotence

At Okayama University in Japan a team of researchers led by Prof. Toshiyoshi Fujiwara is using genes from fluorescent jellyfish to make cancer cells glow green to understand where the cells will spread and to what extent thereby reducing the amount of tissue needed to be removed in surgery.

Bioluminescent Jellyfish and the Nobel Prize

Florescent protein extracted from a North Pacific jellyfish have been used to make the human brain glow so its cells can be studied by scientists. The same protein has been used to make green-glowing engineered mice and provide color for the film version of the Hulk.

In 2008, Japanese biologist Osamu Shimonmura won the Noble Prize in Chemistry for discovering and developing a glowing jellyfish protein that has helped shed light on such key processes as the spread of cancer, the development of brain cells, the growth of bacteria, damage to cells by Alzheimer’s disease, and the development of insulin-producing cells in the pancreas.

Osamu Shimomura works at the Marine Biological Laboratory in Wood Hole, Massachusetts and the Boston University Medical School. He discovered the jellyfish protein, green fluorescent protein, or GFP, after extracting it from 100,000 jellyfish caught off the coast of Washington state, and figured out how to isolate it. American Martin Chalfie and Roger Tsien explored how it worked and applied it to medicine and other fields.

Shimomura needed a large number of jellyfish to extract and refine GFP. He collected them with the help of students, assistant researchers and his wife and kids. At certain times of the years the jellyfish that bore GFP — “Aequora victoreai” “were so thick local people said you could walk on water. For his research Shimomura needed about 3,000 jellyfish a day which were collected from a pier with long-handled nets and buckets. Many locals thought he intended to eat the jellyfish as sashimi. Over the past decade the number of jellyfish off the Washington coast have declined drastically and it is no longer easy to collect huge masses of them.

Cutting up the jellyfish was another problem. At first Simomura used scissors but later refashioned a meat slicer that he bought at a hardware store. He then dedicated himself to extracting and purifying GFP. In 1979 Shimomura unraveled the structure of GFP and discovered how it became luminous. At this juncture in his career he showed one scientist a fluid solution of GFP, saying “This has been purified from 100,000 jellyfish.”

GFP turns green when exposed to ultraviolet light and easily attaches to other protein whose movements can be tracked. . The Swedish Academy compared the discovery GFP to the development of the microscope and said the protein has been “a guiding star for biochemist, biologist, medical scientists and other researchers.” Shimomura told the Daily Yomiuri, “I was able to extract aequorin because I thought other researchers ideas were wrong...I became successful because I tried to extract only the illuminating substance.”

Relieving Jellyfish Stings

sea nettles
If you get stung by a jellyfish some people recommend applying meat tenderizer, vinegar or even urine to relieve the sting. According to the Medicine Man on, “The theory of urinating on a sting is that the urine contains some ammonia which helps with the stinging. Ideally vinegar is what you'd want to use, though unseasoned meat tenderizer, baking soda, or one-quarter-strength household ammonia can be used. Never wash the sting with fresh water. Use salt water if nothing else as fresh water may release more venom. Taking Benadryl, along with using an ice pack and treating the sting with bacitracin afterwards for about 3 days is what you'd ultimately want to wind up doing.”

According to “Susan Scott, “Oceanwatch” columnist for the Honolulu Star-Bulletin, has investigated jellyfish stings in the field (as well as in the lab) probably as much as anyone, having spent years visiting injured tourists and the like on Hawaii’s beaches. A registered nurse, she and husband Dr. Craig Thomas authored “All Stings Considered: First Aid and Medical Treatment of Hawaii’s Marine Injuries.” In her column in 2001, Scott summed up years of study on a variety of sting “cures”: “Nothing worked.” In an e-mail to me, she summed it up another way: “Anything works.” This paradox goes to the heart of the urine myth. “Nothing worked” means that none of the main folk remedies — including urine, meat tenderizer and commercial sprays — did anything to stop the pain of a sting. On the other hand, “Anything works,” because the vast majority of jellyfish stings are not severe and their effects disappear within a few hours at most, no matter whether you urinate on yourself or simply do nothing.

Image Sources: Wikimedia Commons; 1) NOAA 2) 3) Hector Garcia blog

Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

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