Jellyfish Or Medusa
Jellyfish are not fish. They are actually invertebrates which means they don’t have a backbone. The jellyfish is made up of ninety-five per cent water. Jellyfish are most recognized because of their jelly-like appearance and this is where they get their name. They are also recognized for their bell-like shape and tentacles. Jellyfish species vary in size, some reaching two meters across the bell and trailing tentacles 30 meters behind them. Some have bodies that are so clear you can see thought them. Jellyfish can be found in every ocean in the world. Jellyfish inhabit all levels of water, right from the surface of the ocean to the very depths. You may find it hard to believe, but there are more than 1500 known species of jellyfish in the waters of the world. Although jellyfish are mainly found in marine waters, some species of jellyfish also exist in freshwater lakes. While some species of jellyfish can be found in the warm, temperate waters of tropical oceans, some other species of jellyfish can be found in the cold, frigid waters of the North Pacific Ocean. While some species of jellyfish are smaller than your thumbnail in size, some other species can grow to over hundreds of feet in diameter and length of tentacles. While most jellyfish are harmless to human beings and may cause a minor sting at most, some species of jellyfish are capable of killing human beings in less than 3 minutes. There are many different species of jellyfish in our oceans, embodying a variety of different characteristics.
Some of the most popular jellyfish from around the world include: Moon Jelly (Aurelia Aurita): This is perhaps the most common and recognizable jellyfish in the world. If you have seen a jellyfish in a public aquarium, there is a very high likelihood that you have seen the moon jellyfish, as they are very commonly bred in aquariums. Moon jellyfish are semi-transparent and have a shallow saucer-like bell shape. Their gonads are visible through their body and they look like four pink horseshoe markings. The moon jellyfish varies in size usually between 6 to 8 inches and 20 inches in diameter. Moon Jellyfish stings are mild and non-fatal.
Lion’s Mane/Winter Jelly (Cyanea capillat): Commonly seen in popular fiction and film, this jellyfish derives its name from it appearance as well as its preference for the cold, frigid waters of winter months. Its bell shaped is the most common representation we see of jellyfish in popular media. This bell is usually about 6 to 8 inches in size. The Lion’s mane jellyfish has reddish-brown oral arms and eight clusters of tentacles hanging underneath the oral arms. The sting of the Lion’s Mane Jellyfish is relatively mild and may cause a rash which is stinging, rather than painful.
Portuguese Man of War (Physalia physalis): The Portuguese Man of War is not even a jellyfish, although it is widely considered to be one. Four individual polyps that perform separate individual functions form a Portuguese Man of War. Together the four polyps act as different parts of the organism and they also appear exactly like a jellyfish. The bell of the Portuguese Man of war is usually purple-blue in color and can reach the size of 10 inches in diameter. Their tentacles can be as long as 30 to 60 feet in length. While the sting of the Portuguese Man of War is rarely fatal, it can be extremely painful and induce symptoms like shock, chills, fever, etc. apart with an extremely painful rash. Jellyfish come in a wide variety of sizes, shapes and colors.
Regardless of their size or shape, most jellyfish are very fragile, often containing less than 5% solid organic matter. Jellyfish inhabit every major oceanic area of the world and are capable of withstanding a wide range of temperatures and salinities. Most live in shallow coastal waters, but a few inhabit depths of 12,000 feet! The life cycle of a typical jellyfish is complex and involves an alteration of generations in which the animal passes through two different body forms. The dominant and conspicuous medusa is the familiar form, while the smaller polyp form is restricted to the larval stage. Jellyfish reproduce sexually, and individuals are either male or female. The reproductive organs (gonads) develop in the lining of the gut. During reproduction, the male releases sperm through its mouth into the water column. Some of the swimming sperm are swept into the mouth of the female, where fertilization occurs. Early embryonic development begins either inside the female or in brood pouches along the oral arms. Small swimming larvae (planulae) leave the mouth or brood pouches and enter the water column. After several days the larvae attach themselves to something firm on the sea floor (rocks, shells, etc.) and gradually transform into flower-like polyps (scyphistoma). These polyps use tentacles to feed on microscopic organisms in the water column. Polyps can multiply by producing buds or cysts that separate from the first polyp and develop into new polyps. When conditions are right, fully developed polyps develop constrictions in their bodies that eventually produce a larval stage (the strobila), which resembles a stack of saucers. Each individual saucer develops into a tiny jellyfish (ephyra stage), which separates itself from the stack and becomes free swimming. In a few weeks, the ephyra will grow into an adult jellyfish (medusa), thus completing the complex life cycle. Jellyfish normally live for a few months; however, the polyp stage may be perennial. Climate change and resulting warmer sea temperatures favor most jellyfish species, and water temperatures of the seas around Japan have definitely increased in recent decades. Higher water temperatures both speed jellyfish reproduction and extend the reproductive season. Warming temperatures result in more polyps.
The most dramatic of all jellyfish blooms are Nomura’s jellyfish that have regularly swarmed into the Sea of Japan over the last decade. These giant creatures, with thousands of stinging tentacles, can be as large as seven feet in diameter and weigh over 600 pounds under normal conditions. When there are blooms, they wreak havoc on the Japanese fishing industry by breaking fishermen’s nets, and crushing the fish or poisoning them with their stingers. The box jellyfish is the most dangerous marine animal to humans. Often called the sea wasp or marine stinger, the box jellyfish is the most dangerous of marine animals. It inhabits the shallow coastal waters around northern Australia during the summer months between October and April. The further north you travel, the longer the jellyfish season can be and in Darwin, the box jellyfish is present almost all year round. If you are stung by a jellyfish flood the sting area with vinegar, which will stop the firing of the stinging cells.
