ANIMALS
Over 200 different species, or types of jellyfish are found throughout the world's oceans and seas. These invertebrates, animals lacking backbones, belong to the phylum Cinder. They come in many shapes and sizes, ranging from the tiny, spherical thimble jellyfish of the Caribbean to the largest jellyfish of them all, the Arctic lion's mane, whose tentacles may stretch over 100 feet in length. But what exactly are these creatures that are neither jelly nor fish? Is there anything else to them beyond their stinging reputation? The word "jellyfish" often brings to mind a white, gelatinous blob encountered on the beach, and many people react to jellyfish with instant fear. Although they do not resemble any other animals on earth, and appear quite bizarre, they are relatives of sea anemones and coral. Let's take a closer look at these beautiful and mysterious creatures so well suited to life in the ocean.
Jellyfish can be found in all the world's oceans, and a few evens inhabit freshwater. Over 95% water themselves; they have no heart, blood, brain, or gills.
The bell, or body of a jellyfish has one or more mouths on its central oral surface. Some jellyfish have frilly oral arms around the mouth. Jellyfish feed on small, drifting animals called zooplankton - which includes other jellyfish, juvenile fish and larval crustaceans. Tentacles, long string-like structures that surround the bell rim, trap food. These tentacles can be longer or shorter than the diameter of the jellyfish's bell.
Despite limited sense organs, jellyfish can smell, taste and remain balanced in the water. Special sacs, located on the bell rim, help jellyfish maintain balance. When a jellyfish shifts too far to one side or the other, the sacs stimulate nerve endings to contract muscles that re-orient the jellyfish in the correct direction (similar balance maintaining sacs are also found in the inner ear of humans). Jellyfish also have light sensing organs around the bell rim, and although jellyfish cannot detect objects, they can distinguish light from dark. Jellyfish can sense smells and tastes using chemoreceptors. Touch receptors on the tentacles, oral arms, and around the mouth sense movement and help jellyfish find food.
In addition to swimming, jellyfish are carried by wind, waves, and currents. They swim using jet propulsion. Special muscles, called coronal muscles, embedded on the underside of the bell push water out of the hollow bell. As water is pushed in one direction, the jellyfish moves in the opposite direction. While this may not seem to be very effective, one species of Mediterranean jellyfish that is only an inch and a half in diameter can move up and down the water column 3600 feet in one day; the equivalence of a 33 mile swim for a six foot tall person!
Some jellyfish, like the moon jellyfish develop in four distinct stages: the larval stage, the polyp stage, the ephyrae stage, and the medusa stage. An adult female jellyfish produces eggs and holds them around her mouth. The male jellyfish then releases sperm into the water, and the female uses her oral arms and tentacles to bring in the sperm and fertilise her eggs. The eggs stay on the jellyfish's oral arms and grow into round, flat at larvae that are released into the water. The larvae are carried through the water until they find a hard surface which they attach to, such as a rock or a shell. After the larvae settle they develop into polyps, which resemble sea anemones. Polyps usually develop over a period lasting a few months, but may live for several years producing clones, or exact copies of themselves during that time. At the end of this period polyps begin to form horizontal grooves that deepen through the body until the single polyp is transformed into a stack of individuals, much like a stack of pancakes. Flattened polyps enter the third stage of development as they break off the stack one by one and swim away. These young jellyfish now begin to resemble the familiar adult form called a medusa, as they develop tentacles and oral arms. A jellyfish in the medusa stage lives 2-6 months, usually perishing in rough waters.
Jellyfish are most known and avoided for stinging cells, located on the tentacles and other body parts. The stinging cell consists of a capsule with a sensory hair, a lid and an interior nematocyst, which actually stings, captures and subdues prey. When the sensory hair is triggered by another animal's movements, the nematocyst fires from the capsule, much like a harpoon. A nematocyst fires in only a few milliseconds, making this cellular process one of the fastest in nature.
Even a jellyfish that has washed ashore should not be handled, since moist nematocysts may still fire. The stings of some jellyfish may be quite painful, causing reactions ranging from mild rashes to death. The most dangerous jellyfish is the Australian box jelly which has toxin more potent than cobra venom (which can kill a person in less than five minutes). Despite its stinging cells, some animals do eat jellyfish. The ocean sunfish, and leatherback sea turtles are two kinds of animals that feed primarily on jellyfish. Certain species of jellyfish prey upon other types of jellyfish, and some people even consider jellyfish quite a delicacy.
Although feared by swimmers, most jellyfish are harmless to human beings. In fact, these graceful creatures can benefit people and should be appreciated. Several different kinds of jellyfish are being used to treat certain cancers and heart diseases. Continuing research may discover other medical areas in which jellyfish will be useful. Some jellyfish are even beneficial to other animals, offering shelter in open water for tiny fish and crabs that travel carefully under their jellyfish host. The East Coast sea nettle, found most often in the Chesapeake Bay, may actually help the oyster population by eating an oyster predator, another gelatinous animal called the comb jelly. Comb jellies eat oyster larvae in large numbers, thus potentially reducing the amount of mature oysters available for harvest. The fewer comb jellies there are in the Bay, the more oysters there can be in the Bay. So although we do not like it when there are many sea nettles in the Bay, if they are eating comb jellies, the oysters appreciate them -- and so do the people!
Free-swimming Scyphozoan medusa jellyfish
occur in all oceans and include the commonly familiar disk shaped
animals that are often found floating along the shoreline. The
bodies of most range in diameter from about 1 to 16 inches (2 to
40 centimetres); however, some species are considerably larger
with diameters of up to 6 1/2 feet (2 meters). The bulk of the
Scyphozoan medusa jellyfish consists of almost 99 percent water
as a result of the composition of the jelly that forms the bulk
in nearly all species.
Most feed on small animals that they catch in their tentacles' stinging cells (nematocysts). Others simply filter feed, extracting minute animals and plants (i. e., plankton and nekton, loosened benthos) from the ocean water as they drift. Like all cnidarians, their bodies are made up of two cellular layers, the ectoderm and the endoderm. Between these dermal layers lies the mesoglea, a layer of connective tissue composed of a gelatinous substance, the jelly. In jellyfish the mesoglea is much enlarged to form the buoyant, transparent jelly. Most live for only a few weeks, although some are known to survive a year or longer.
Sea Wasps - box jellies that are lethal - the class Cubozoa, order Cubomedusae, genera Chironex and Chiropsalmus, occur widely from Queensland northward to about Malaya. These forms are dangerously venomous; a moderate sting can cause death within a few minutes. These types of jellies are NOT prevalent or indigenous to Hawaiian waters.
Jellyfish are very common in all water bodies. Do not go into areas where they are sighted, or if dead ones are seen on the beach. Their primary injury mechanism is their tentacles' stinging cells (nematocysts). Symptoms include stinging, burning sensation, vivid redness in the affected areas, swelling of lymph nodes. There may be severe reaction: difficulty with breathing and cardiac arrest. Visible manifestations include long welt lines.
The Portuguese man-of-war jellyfish is any of various invertebrate, elly-like
marine animals of the genus Physalia, class Hydrozoa (phylum
Cnidaria). They are infamous for their very painful, powerful
sting and very common in Hawaiian waters.
The man-of-war occurs most commonly in the tropical and subtropical regions of the Pacific and Indian oceans, and in the Gulf Stream of the northern Atlantic Ocean, although found in warm seas throughout the world. It is sometimes found floating in groups of thousands. Physalia physalis is the only widely distributed species. P. Utriculus, commonly known as the bluebottle, occurs in the Pacific and Indian oceans.
The body consists of a gas-filled, bladderlike float, - a translucent structure tinted pink, blue, or violet - which may be 3 to 12 inches (9 to 30 centimetres) long and may extend as much as 6 inches (15 centimetres) above the water. Beneath the float are clusters of polyps, from which hang tentacles of up to 165 feet (about 50 meters) in length. The polyps are of three types: dactylozooid, gonozooid, and gastrozooid, concerned, respectively, with capturing prey, with reproducing, and with feeding. The animal moves by means of its crest, which functions as a sail.
Tentacles of the dactylozooids bear stinging nematocystic (coiled thread-like) structures that paralyse small fish and other prey. The gastrozooids then attach to the immobilized victim, spread over it, digesting it. The Portuguese man-of-war is eaten by other animals, including the loggerhead turtle (Caretta caretta). The small fish Nomeus gronovii lives among the tentacles of Physalia and is nearly immune to the poison from the stinging cells. Nomeus feeds on the tentacles, which are constantly regenerated; sometimes the fish is eaten by Physalia. Another interesting food chain manifestation occurs occasionally. When sea turtles feed on men-of-war, sharks are attracted to and feed on the sea turtles, and, may be attracted to and try to feed on things that look like sea turtles, e.g., humans swimming in murky waters, on surfboards, etc.
This is a shark that is very, very dangerous. Some experts consider this shark to be the most dangerous in the world, even surpassing the Great White Shark. Surprisingly few people have even heard of it. It has a number of different names both in Australia and around the world and people think they are a different species of shark. In Africa it is called the Zambezi Shark.
It is
a heavy bodied shark with a short nose and a medium sized second
dorsal fin. It has broad, serrated triangular upper teeth. It has
very powerful jaws. Grows to about 350cm. Studies of this shark
believe it lives for about 14 years and prefers to breed in the
mouth of rivers. It has a broad diet and will eat almost anything.
It has been noted by researchers that it does seem to have a
preference for eating baby Sandbar Sharks.
This shark has been found 4000 km from the sea in the Amazon River. It has penetrated right down the Mississippi River in the USA. It can live in almost any water including water with a high salt content as in St. Lucia Lake in South Africa. It seems to prefer rivers and inlets with shallow water and is not often reported far out at sea. However I have heard of a few sittings of these sharks out in the deep ocean in the same areas as Tiger Sharks.
It is also quite happy being in murky or muddy water. In Australia it is often confused with other species especially the Bronze Whaler. It has been found in most of our water systems including Brisbane River, Herbert River, Swan River, Clarence River, Daly River, and even Lake Macquarie.
In Australia, it is responsible for a large number of attacks and deaths. Many of the experts think this shark is to blame for most of the deaths around the Sydney Harbour inlets in the past. Most of these attacks were previously thought to be Great Whites. The poor Grey Nurse was also blamed in the sixties and seventies. The Bronze Whaler has also been mistakenly identified when it was really a Bull Shark.
Until very recently, researchers thought the sharks in Lake Nicaragua. Was a separate species because there was no way for the sharks to move in or out. It was discovered that they were jumping along the rapids just like Salmon. Sharks tagged inside the lake were later caught in the open ocean.
In India the Bull Shark cruises up the Ganges River where it has killed and attacked a large number of people. It also eats the corpses that the Indians float on the river. Many of these attacks have been wrongly blamed on the Ganges Shark, a fairly rare species that is probably the only other shark that can live comfortably in saltwater or freshwater. Due to the large number of attacks that have occurred along the Ganges River, the Ganges Shark has a dreaded reputation in India.
In 1975 a ferry sunk in the Ganges-Brahmaputa delta and 190 crew and passengers were tipped into the water. Up to 50 of these were killed by sharks.
In Africa where it is often called the Zambesi shark it is known to have caused a lot of deaths among swimmers in shallow water. In a six month period during 1961 it is thought to be responible for 3 attacks in the mouth of the Limpopo River. In 1970, a fisherman was working in about 5 foot of water on his prawn net up a river, about 12 miles from the sea in Mozambique when he was attacked by a Bull shark. His arm was taken and later as he floundered under the water the shark returned and and took off his head.
Amanzimtoti, a popular swimming beach in Africa has been given the nickname of 'the worst shark attack beach on earth'. This beach has more than 12 shark attacks. All have occurred in murky water.
The Bull Shark can be very aggressive towards divers but I have not yet been able to find any attacks on a diver. If anyone knows of one could you please send me an email. From reports I've heard from other divers the behaviour always seems to be the same. The shark starts to circle wide and soon circles again much closer and then finally makes a rush at the diver only turning away at the last moment. I've heard of divers being on safety stops with Bull Sharks swimming around aggressively but no one has been attacked. I've heard a story about one arriving at a controlled shark feed way out in the Coral Sea off Queensland. Once again no one was attacked. There is an interesting account of a Bull Shark in Steve Hogans reviews (See Link) where he encountered a 3 metre Bull shark at the'Eel Gardens' in the Coral Sea when he was on Spoilsport. This shark came very close to him but did not attack. I also received an email from South Africa from a diver who has had up to 100 dives with them and never been attacked.
Tiger Sharks grow very big and can be very dangerous. They are responsible for a large number of human deaths. They are most common in warmer water. Although some adults will stay in one area they are also known to be able to move hundreds of kilometres. Young sharks have the very distinctive tiger stripes but in very large specimens they may not be present. They have strong, serrated upper teeth but instead of being triangular they are hooked or cockscomb shaped. That means the point is not straight down but turned to the side. This shark has been known to come into very shallow water, sometimes with most of their body exposed and they have also been found as deep as 150 metres. The Tiger can get extremely large up to 6 metres, maybe more. Seems to prefer the deep water out to sea during the day and will come in close to reefs and the shoreline at night. It will sometimes also come in close to shore during daytime.
Some of the stories of what this shark will eat are probably exaggerated but it has eaten some rather unusual things. Stomach contents have included clothing, wood, tin cans, wire, bolts, birds, even the head of a crocodile. The famous Shark-Arm criminal case of Australia is one of the more bizarre stories. In 1944 a fisherman near Florida USA caught a large Tiger shark. Inside he found most of a mans body from the ribs to the knees. The man was never identified.
It feeds mostly at night and this is when it is more likely to come in closer to shore and reefs. This shark is often noted for its habit of eating anything it finds and reports of household objects and metal are common. It likes to eat turtles and will often wait around shallow water during the breeding season. Divers will often see turtles with large bite marks out of their shell, a lasting mark of a lucky escape! It is also known to have a liking for sea snakes.
Divers often dive with these sharks with no problems but others unfortunately have been killed. I have been told there are resident Tiger Sharks around the Yongala Shipwreck near Townsville in Queensland as well as Wolf Rock near Noosa in Queensland. Many divers go to these areas especially to see them. As far as I know no divers have had any problems.
There was a really interesting article by Frank West on page 89 of the December issue of Australian Dive Log. In his story a large 4 metres Tiger Shark came up to divers doing a decompression stop near Newcastle in visibility of 2-3 metres. One of the divers didn't know the shark was behind him and accidentally leaned back and bumped him. When he turned and saw what it was he flew to the surface and on the boat. What's interesting here is that the shark was probably quite capable of killing these divers but didn't. That is not to say it wouldn't have taken a bite a bit later but it does show that every encounter with large sharks is not a death situation. Frank goes on to say in his story that the shark may have been following a fishing trawler that passed very close to the divers. I have to admit it does sound like a nightmare situation though.
TIGER SHARKS |
|
| 4 metres | 3 metres |
| Blue & grey | Blue & white |
The noble African
elephant has not been treated well in Africa. They were not
domesticated and trained and worshipped as in Asia. The Africans
did not have much to supplement their diet with protein. So, they
used the elephant for meat. The African Elephant, therefore, was
seem as meat to be hunted and killed. Elephants lived among a
human population that was often sparse. The elephants existence
was unrestricted and not regulated by humans. Humans did not try
to make many changes to the environment. Elephants stayed away
from the human population, rarely moved about the humans'
croplands and were not considered competition with livestock.
The African people, who had seen the elephant, did respect their strength, wisdom, and benevolence and power. The people did not attempt to have a close bond with an elephant. In the terrain in which elephants lived in Africa, elephants could not be used very often in epic battles or as working animals as they were used in Asia. The African Elephants are more difficult to train than the Asian Elephant. They are trainable, however, and have been used in zoos and in battles.
The major cause of the lost of more than half of the elephant population in Africa is the massacre of elephants for the ivory trade. Between 1979 and 1989, the elephant population in Africa fell from 1.34 million to 625,000. In this ten year span, East Africa lost more than 52% of its elephant population. Kenya went from having about 130,000 to less than 17,000. Mature males were targeted more often due to the length of their tusks. Ivory trade has been suspended in most countries (legally), but is still carried on illegally. The residents in the villages in the African countries with elephant population, often see the elephant as a pest--ravaging their crops and and taking up valuable land that could be used for crops or habitation. Government officials, the military and the police are often corrupt and enable the export of ivory by means of false documents and looking the other way. Even if ivory loses its value, will the African people let the elephants proliferate is another question to be considered.
The two surviving species
of the order Proboscidea: the Asian elephant, Elephas maximus and
the African, Loxodonta africana elephant. Elephants can grow to
13 ft/4m and weigh up to 8 tons; they have a thick, grey wrinkled
skin, a large head, and long trunk used to obtain food and water,
and upper incisors or tusks, which grow to a considerable length.
The African elephant has very large ears and a flattened forehead,
and the Asian species has smaller ears and a convex forehead. In
India, Myanmar (Burma), and Thailand, Asiatic elephants are
widely used for transport and logging.
Elephants are herbivorous, highly intelligent, and extremely social, living in matriarchal herds. The period of gestation is about 19 - 22 months (the longest amount mammals), and the life span is about 60 - 70 years. Elephants have one of the lowest metabolic rates amount placental mammals.
In Africa there were 1.3 million elephants in 1981; fewer than 700,000 in 1988 and about 600,000 in 1990. They were placed on the list of endangered species in 1989, and a world ban on trade in ivory was imposed.
Asian elephants are different from the African elephant in appearance, size and habitat. The Asian elephant has smaller ears, smaller tusks. The Asian male elephant has large visible tusks. The females have small tusks called tushes which are generally not visible. Asian elephants have two humps on the forehead and an arched back. Asian elephants have smoother skin than their African relatives. The Asian elephant has only one "finger" on the end of its trunk as compared with two "fingers" that the African elephant has on the end of its trunk.
As for size, the Asian elephant is smaller. Males stand 9 to 10 1/2 feet tall and weigh about 8000 pounds while females are shorter and weigh about 6,000 pounds.
The home of the Asian elephant is in the forests and jungles of India, Sri Lanka, China, Indonesia, and Southeast Asia. Estimates vary, but, there are approximately 29,000 to 50,000 Asian elephants still in the wild. Asian elephants are threatened more by destruction and fragmentation of their habitat rather than poaching (killing elephants for tusks) as is the African elephant. Almost 20% of the world's population lives in or near the range of Asian elephants. Elephant migratory routes have been disrupted by highways and urban development.
Asian elephants often cannot find enough food in small forests for survival. Because of the overpopulation problems in places like India, elephants' feeding grounds have been converted to crop land to feed the ever-growing human population. Conflicts occur when the elephants look for the nearest source of food which is likely to be in the fields of the local farmers.
Humans use elephants as work animals in Asia. Elephants log forests, transport heavy loads and carry tourists. Elephants can walk in areas where machinery can't navigate. Approximately 15,000 Asian elephants are held in captivity as work animals. Elephants seem be be held in a bit more of esteem in Asia than in Africa. They are important in Asian folklore and religion. They are believed to be cousins of the clouds and able to cause lightening.