Green Sea Turtle Essay, Research Paper
Green Turtle
Introduction
The Green Turtle (Chelonia mydas) is one of the many species of turtles that inhabits the vast oceans. The green turtle is named for the greenish color of it?s fat found under its shell. It is a large, heavy reptile, usually about 0.7-1.0 m in shell length and about 90-140 kg in weight. The maximum length and weight are about 1.2 m and 375 kg respectively. (1) The green turtles upper shell is smooth and wide, the animal is brown, but when the light from the sun hits it, the green color from the fat is visible. The green turtle is found in warm, coastal waters around the world. (2) Sea turtles, in adaptation to an aquatic life, have limbs modified into flippers for efficient swimming. It feeds mainly on marine grasses. Most female sea turtles leave the water only when it is breeding season because the female needs to dig a nest on the land and deposit her eggs. But an unusual characteristic of the green turtle is that it will often emerge onto land to enjoy the sun. (2)
The green turtle is classified as follows:
Kingdom Animalia
Phylum Chrodata
Subphylum Vertebrata
Class Reptilia
Order Testudines
Family Chelydra
Genes Chelonia
Species mydas
(3) And (4)
In this paper the classification and origin of the green turtle will be discussed further. Their diet, mating habits, offspring, senses, and their economic value will also be discussed.
Classification and Origin
There are four characteristics that have played a role in discussion of the relationship and classification of turtles. The characteristics include the dermal armor, the acromion process on the scapula, the astragalus-calcaneum complex, and the hooked fifth metatarsal. (1) The dermal armor (shell) is the interlocking osteoderms that are found lying above the vertebral column and the ribs. The acromion process in the turtle is an extension medioventrally on the scapula. (1) This unique characteristic allows for different muscle attachments in the turtle and accounts for the awkward positioning of the frontal limbs for walking or swimming. The astragalus-calcaneum complex has to do with the fusion of these two junctions to from a mesotarsal joint. (1) The hooked fifth metatarsal is evidence of a delay in ossification compared to the other metatarsals.
It is predicted that the origin of the turtle had to have been around the around the Germanic Basin of southern China and the western United States in about the Lower Permian time, about 280 millions of years ago. (4)
Evolution
Throughout time the turtle has been whimsically portrayed as a slow moving creature. A unique feature to the turtle is that it exists as both a creature of the sea and a creature of the earth. The reputation that it holds as being a slow moving creature on the earth is true, but gliding in the water is another story. The marine green turtle (Chelonia mydas) has been known to swim three hundred miles in ten days. (3)
The green turtles are found distributed throughout the world?s oceans. There are found in the eastern and western hemispheres and on beaches throughout the Atlantic, Pacific and Indian Oceans. (5) The Pacific Green turtle and the Atlantic Green sea turtle are of the same species, they have basically the same length and weight. Since these two are over 3,000 miles away from each other combined with the centuries of separation, evolution has left the two of them with slightly different internal structures. Not only is their coloring a little bit different but also the Pacific green turtle’s limbs are much longer. (5)
Diet
When food is available, the turtle will eat, but characteristic to all reptiles, the turtle can survive long fasts, they can live on weekly or monthly feedings. Their water is stored in cloacal bladders, which allow them to survive long droughts. (3)
The Green Turtle like most turtles, prefers a varied diet. They usually enjoy small invertebrates such as worms, snails, slugs, insects, thin-shelled bivalves and crayfishes and other crustaceans. (3) Many sea turtles love to eat jellyfish. Plastic bags are therefore very hazardous because they look similar to jellyfish, especially since the bags tend to float near the surface. (6) The larger aquatic turtles occasionally catch fish and sometimes birds or small mammals. Marine grasses and plants are also eaten but the fibrous parts are avoided, the green sea turtle does not have a well-developed jaw that is sharp enough to cut and grind. Turtles have been left to fend with out teeth for more than 150,000,000 years. The more modern types have semi-sharp and jagged edges of their jaws to function as teeth. (3) Their food is chewed and with the use of the forelimbs for manipulation of the often cumbersome meal. The floor of the throat is lowered; the head thrusted forward and the mouth opened as wide as possible, water rushed in to assist in the prey moving down. (3)
Mating
A courtship that is highly characteristic for each species or related group of species precedes copulation. The male’s contribution in the mating display includes various types of head-waving, lunging at the female while roaring, and gracefully swimming backward in front of her while stroking her lores (cheeks) with his extremely long nails located on his forelimbs. The turtle has a single penis unlike other reptiles like snakes and lizards. (3). One of the unique characteristics of turtle reproduction is the ability of the female turtle to lay fertilized eggs years after a single mating.
The female green sea turtle will lay her eggs on land. Many studies have been done to determine what characteristics of a beach the female will choose to lay her eggs. Some hypotheses claim that the spot for nesting is random, based on topography on the beach, the vegetation, the amount of pollution, thermal cues, interspecies competition or the amount of human disturbance. The studies have been conducted in order to suggest to the governments of various nations what beaches should be blocked off from human contact for the turtles. It was found that in the Wang and Cheng study (7), the female would select a spot, which she perceives has a high level of vegetation. (7) The placement of the nest is very important, it will determine the survival and sex ratio of the hatchlings, having a direct correlation with the reproductive fitness of the population of green sea turtles.
The female crawls up the beach to a point above high tide, using all four flippers begins to settle her self comfortably into the sand. She will then dig an egg pit removing the sand using her hind flippers alternatively to create a depression. The flipper is used as a scoop, it is curled and lowered carefully retrieve a “handful” of sand. The scoop of sand is sent directly backward to clear the hole. The whole that is dug is about 70-90 centimeters for the green turtle. (2) She then deposits the eggs, usually two at a time that are about 5 centimeters in diameter. The groups of eggs laid are referred to as a clutch. (7) Several clutches could be laid in one season. A clutch may have more than 200 eggs or as few as one. (3) The female will then carefully cover the eggs using her front flippers. This whole process can take a few hours. The mother will leave her young behind; her part is done.
Offspring
The incubation period for the green turtle is between 54-63 days. (2) Many experiments have shown that the temperature at which the nest is incubated at determines the sex of the turtle. Temperatures minutely above the constant temperature for any given moment of time will produce female and then the temperature below the constant temperature threshold will produce males. (2) When the turtle hatches, because it is so high on the beach, and the hatchling is so small it is unable to see the ocean. Yet the turtle is able to detect the direction of the beach and moves toward the ocean in either day or night.
Senses
Turtles appear to depend on their sense of smell the most. They have good sight and can distinguish differences in the intensity of light and can recognize up to four colors- blue, green, yellow and red. (3) Only the eyes of the sea turtles are fully adapted for vision under water they are able to make alterations in the curvature of their lens.
Turtles respond readily to vibrations in the water and in the air. Turtles seem to have a sensitivity and response to aerial sounds. In American in the year1915 experiments reported that turtles do hear but the Japanese contradicted this statement ten years later. Three years later a Soviet investigator concluded that turtles do hear, but his paper was published only in the U.S.S.R. and largely ignored elsewhere. In 1966 two Americans demonstrated that at least some turtles hear low-frequency airborne waves, ranging from about 20 to about 1,000 cycles per second. Whereas the corresponding figures for humans is 20 to 20,000 cycles per second. The fact that the number of cycles heard by turtles is much lower than that of man may explain the difficulty in arriving at a conclusion for the turtle. (3)
With the exception of courting or mating, turtles seldom emit sounds. Unless provoked, the sound is usually minute grunt or roar. When provoked, a loud cry can be heard.
Experiments have shown that turtles are intelligent animals. Then learn quickly; some say they are comparable to a laboratory rat.
Economic value
The tortoise as well as the green turtle have been victims of man?s appetite. The green turtle, with its distribution extending around the world, has supplemented the diet of peoples of more different cultures than has any other wild vertebrate. (3) Tortoise populations of many oceanic islands has dwindled; it has been estimated that 10,000,000 land giants were taken from the Galapagos Islands as food supply for the early whaling ships. Turtle eggs are also prized as food. These are deposited in such abundance on certain beaches that harvesting them has become a national industry in Malaysia.
Unfortunately not just the meat has been sought after by man but the beauty of the shell as an ornament has been coveted as well. Fortunately plastic replications can be made and sold to those that just can?t live without them.
Conclusion
The green sea turtle is a large, remarkable creature of the sea. They are found all over the world. Their diet is varied, enabling them to travel anywhere in the sea. The egg laying process of the female is meticulous and time consuming; the hatchlings are born on land and run to the crest of the sea to begin their lives. The turtle has many predators from the bird that will attack the eggs to the larger squid that will eat the small turtle in the sea. And then there is the man, the green turtles largest preditor, which will hunt the turtle, eat the turtle and kill it with the pollution thrown into the sea.
Bibliography
(6) Blakeslee, April. (1999).?Sea Turtle.? www.cyhaus.com/marine/turtles.htm (November 5, 2000)
(3) Encyclopedia Britannica. (2000). ?Green Turtle?.. www.britannica.com/bcom/eb/article/1/0,5716,68181+1+66460,00.html?query=green%20turtle October 10, 2000
(4) Gould, James L. and Keeton, William T. (1996) Biological Science 6th edition New York W.W. Norton & Company p A1-A5
(5) Hawaii Preparatory Academy (2000). “Green Sea Turtle” http:www.hpa.edu/TurtleTagging/GreenTurtle.html (November 5, 2000)
(2) Kaska, Y. (1998). Natural Temperature regimes for loggerhead and green turtle nests in the eastern Mediterranean. Canadian Journal of Zoology, 76, 723-729
(1) Reisz, R, and Rieppel, O. (1999). The Origin and Early Evolution of Turtles. Annual Reviews of Ecology & Systematics 30, 1-22
(7) Wang, H. and Cheng, I.(1999). Breeding biology of the green turtle. Marine Biology 133, 603-609