The Environmental Science Graduate Students at Watlings Castle, San Salvador, Bahamas.(TME 98)
Tropical Marine Ecology
Summer in the Bahamas is Jellyfish season and I think they are fascinating marine creatures. Even though Jellyfish are made up of more that 95% water and can’t swim, they are one of the greatest predators of ocean life. There are up to 200 different species of Jellyfish such as Lion’s Mane, Portuguese Man-of-War, Cannonball Jelly, and Sea Nettle. I have always had a fear of jellyfish, living in Florida, as I often find myself in their presence. My purpose in writing this paper is to better understand this sea creature in the hopes it will calm some of my fears.
OVERVIEW OF JELLYFISH
There are many types of jellyfish. Some are dangerous to humans, while others are harmless. Two types of harmless jellyfish are the Cannonball Jellyfish and the Mushroom Jellyfish. Cannonball Jellyfish are one of the least venomous of all jellyfish. It can be identified by its hemispherical white balls decorated with brown bands. It has no tentacles, but it has a gristly-like feeding apparatus formed by the joining of the oral arms. Cannonball Jellyfish rarely grow larger than eight inches in diameter. The Mushroom Jellyfish is often confused with the Cannonball Jellyfish, but they are much flatter, softer, and they lack the brown bands. Mushroom Jellyfish have no tentacles, but have long finger-like appendages hanging from the feeding apparatus. It can grow up to twenty inches in diameter.
Some of the dangerous Jellyfish include the Moon Jelly, the Lion’s Mane Jellyfish, the Sea Nettle Jellyfish, the Sea Wasp Jellyfish, and the Portuguese Man-of-War Jellyfish. The Moon Jelly is one of the most widely recognized jellyfish. It has a transparent, saucer-shaped bell and reaches 6-8 inches in diameter and some can reach up to twenty inches. The Lion’s Mane Jellyfish is also known as the “Winter Jelly” and is considered a moderate stinger. It usually measures six to eight inches in diameter. It is saucer-shaped with reddish brown oral arms and eight clusters of tentacles hanging underneath. You can find Lion’s Mane Jellyfish in the Atlantic Ocean from above the Arctic Circle to Florida, in the Gulf of Mexico, and in the Pacific Ocean from Alaska to southern California. The Sea Nettle Jellyfish is saucer shaped with brown or red pigments. It is usually six to eight inches in diameter and has four oral arms and long marginal tentacles that hang from the bell. It is considered to give moderate to severe stings. The Sea Nettle can usually be found in the Chesapeake Bay, the Pacific Ocean from Alaska to southern California, the Atlantic Ocean from Massachusetts to Florida, and in the Gulf of Mexico. The Sea Wasp Jellyfish is known as a “Box Jelly” because of its cube-shaped bell. It is the most venomous jellyfish because its sting will probably require hospitalization. It’s usually approximately five to six inches in diameter. The Sea Wasp has several long tentacles hang from the four corners of the cube and it is usually found in the Pacific Ocean near northern Australia or in the Philippines. The Portuguese Man-of-War Jellyfish isn’t a “true” jellyfish. However, it is usually considered one anyway. It has a gas-filled float that is usually bluish purple and can grow up to twelve inches in diameter. It can even inflict shock-like stings when it’s alive in the water, beached, or dead! You can find Portuguese Man-of-War Jellyfish in the Gulf of Mexico, in the Caribbean Sea near the Bahamas, and in the West Indies.
There are about two hundred types of jellyfish and about seventy of them are known to sting. Jellyfish kill more people than great White Sharks. Most Jellyfish use their tentacles to sting their prey. Luckily, their sting is usually too weak to hurt humans. However, if you get stung in the neck, the place where you got stung will swell up and you will suffocate. The Box Jellyfish is one of the most deadly Jellyfish. In Australia, they kill up to 65 people a year. When a Box Jellyfish stings a person, they can die in less than three minutes!
“All cnidaria have stinging cells (cnidocytes), capable of inflicting rashes, stings or even burns. The animals can make these amazing cells at such a rate that they can be used as dispensible tools. They can have different types, for stinging, sticking and gripping. The skin of a jellyfish tentacle is studded with stinging cells. Each has a trigger hair (cnidocil) that activates a nerve circuit to unlatch the lid (operculum) and at the same time compress the cell. Several adjacent cells can be triggered simultaneously. Inside the capsule, the harpoon and its stinging thread (nematocyst) are ejected under pressure. The barbed harpoon is filled with poisons and inverts itself like turning a finger of a rubber glove inside out, punching a hole in one's skin, releasing the poisons and pushing the thread into the punctured skin, to release even more poison. Once used, a stinging cell is discarded and replaced within two days. It is so amazing that such a complicated double-walled structure is made by a single cell!” (Cambell, 1992).
Because jellyfish can be so dangerous, it is important to take some necessary precautions when exposed to them. Some precautions include; applying petroleum jelly to bare skin, wearing a wet suit or other skin covering, being familiar with the likely marine risks in the area where you plan to swim, snorkel, or dive, obtaining information about the local conditions, and being prepared with first aid supplies that might be needed for an injury. You should also watch for warning signs that are posted when there is a jellyfish or Portuguese man-of-war invasion and watch for beached jellyfish and Portuguese man-of-wars. Their tentacles may still sting. Wearing protective shoes when walking on the beach and avoiding swimming or snorkeling in shallow water will help prevent you from getting stung. If you are going to be spending a lot of time in the ocean, you might want to consider using a topical jellyfish sting inhibitor lotion, such as Safe Sea(http://www.discoveringhawaii.com/SF_Medicine/StingingMarineLife/JellyFish.html). Lastly, remember it is never a good idea to touch a jellyfish - which is something I will be keeping in mind for the two weeks I spend in TME!!
Some symptoms of a jellyfish sting include painful raised red lesions or papules (in lines consistent with contact with the tentacle) and muscle spasms (may develop in the affected extremity). With extensive or repeated exposures systemic reactions can take place, such as; nausea, vomiting, headaches, dizziness (vertigo), muscle weakness and irregular heart rate (arrhythmias) may occur. Other symptoms include excessive tearing, runny nose and painful breathing (pleuritic chest pain).
To treat a jellyfish sting, first remove any adherent tentacles that will cause further delivery of venom. The tentacles should be lifted off the skin (don't scrape them off -- this causes further stings). You might want to use a stick or some other object to remove the tentacle(s) so as not to get your fingers stung. Next, rinse the affected area with sea water to wash away any adherent nematocysts. Don’t use fresh water, since this will activate the nematocysts. Don’t scrub as this will only activate the nematocysts and cause further venom delivery. Nematocysts are inactivated by vinegar (or dilute acetic acid 5-10%). If no vinegar is handy, then human urine will do in a pinch. If you have a choice in the matter, use a man's urine rather than a woman's urine. This is because females are more prone to urinary tract infections, thus introducing bacteria. Male urine is considered sterile, since men are much less likely to have a urinary tract infection. Symptoms of pain can be treated with topical anesthetics; these are generally contained in sunburn preparations; look for the active ingredients like lidocaine or benzocaine. Persistent redness, inflammation or itchiness can be treated with topical steroid cream like Hydrocortisone 0.5% cream. If you begin to develop persistent muscle spasms, seek medical attention; your doctor will need to administer intravenous calcium gluconate. Secondary bacterial infection may set in, especially if vesicles form. If this happens you will need to see a doctor for antibiotics (http://www.discoveringhawaii.com/SF_Medicine/StingingMarineLife/JellyFish.html).
Jellyfish are not fish; they are invertebrates related to corals and sea whips. They have no head, heart, eyes, brain, blood, nervous system, or skeleton. Amazingly, jellyfish are made up of 95% water. Their body is comprised of a “bell” which is made up of a jelly-like substance, as well as tentacles and oral arms (sometimes called “flaps”), which are used to eat its prey. The bell is called a medusa, because it resembles the Gorgon Medusa of Greek mythology, with its hair of writhing snakes. A cavity inside the bell (the coelenteron) fulfils a number of purposes. It is a stomach and intestine connected to the outside world with a single opening which is both mouth and anus. A number of oral arms located near the mouth transport food captured by the tentacles. Jellyfish have an outer layer called epidemis which covers the their external body surface and an inner layer called gastrodemis which lines a jellyfish 's gut. In the middle of the epidermis and gastrodermis, jellyfish have a thick elastic jelly-like layer of substance called mesoglea.
Jellyfish come in many colors! Their jelly-like bodies may be nearly clear, or a color such as pale blue, orange, brown, white or pink. Although Jellyfish are often glassy or pale bluish in color, they can also be yellow, deep blue, bright purple, pale lilac, bright orange, deep red. Some Jellyfish, when they are disturbed at night, give off a cold bright light called luminescence (Walsh, 1991).
Some Jelly fish swim using jet propulsion, and some attach themselves by a stalk to other material, such as seaweed. Both are referred to as zooplankton (animal drifters), because their movement is strongly influenced by the ocean’s current. Even jellyfish capable of jet propulsion are not strong enough swimmers to counter the power of the current and waves. Jet propulsion in jellyfish is possible because of special muscles called coronal muscles, embedded on the underside of the bell, which push water out of the hollow bell. As water is pushed in one direction, the jellyfish moves in the opposite direction (Weston, 2003). It is their vertical movement through the water column that really determines their movements. Some species (such as Box jellies and sea wasps) will follow the tide in over shallow water to hunt prey. Without a brain or eyes, jellyfish rely on nerve cells to help them move and react to food or danger. Sensing organs tell them whether they are heading up or down, into the light or away from it (Weston, 2003).
Jellyfish are carnivorous (eat meat). They eat mostly zooplankton, smaller fish and sometimes other jellyfish! Bigger jellies eat large crustaceans (like shrimp) and other sea animals.
Jellyfish are eaten mostly by spadefish, sunfish, and loggerhead turtles. People in China and Japan like to eat the mushroom jellyfish…it’s a delicacy!
The early life cycle of the jellyfish is similar to, though not identical to, coral. Larvae are carried through the water until they find a hard surface onto which to attach, such as a rock or shell. These then develop into polyps, which, at this stage, resemble sea anemones. Horizontal grooves then begin to form and deepen until the polyp is transformed into a stack of individuals, like a stack of pancakes. These flattened polyps break off the stack, one by one, and swim away, now starting to look more like adult jellyfish.
Many jellyfish live in oceans around the world and are capable of withstanding a large flux of temperatures and salinities. Many jellyfish live in shallow coastal water. However, some jellyfish live in deep oceans of 12,000 feet or more. Jellyfish are common in warm oceans.
IMPORTANCE TO HUMANS AND MARINE LIFE
Jellyfish have been exploited commercially by Chinese as an important food for more than a thousand years. Semi-dried jellyfish represent a multi-million dollar seafood business in Asia (Hsieh, 2001). Jellyfish are not an endangered species. For many years, Jelly researchers were more interested in finding ways to get rid of these fascinating animals than they were in understanding them. Today, scientists appreciate the amazing things these simple creatures can do. They are studying the chemicals in Medusa and other Jellies for possible use in treating cancer and other diseases. One of the bioluminescent chemicals found in a Medusa jelly from the Pacific Northwest has already been found to be useful in certain types of Medical research. This substance allows doctors to trace the movement of specific chemicals through the body. Jellyfish are extremely important to marine life as well. They consume large quantities of zooplankton (small floating aquatic animals). Their consumption of zooplankton in the summer helps to control the numbers of these organisms in surface waters which increases water clarity.
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