THE NATURAL HISTORY OF GREEN SEA TURTLE (Chelonia mydas)
1. Introduction
The green sea turtle (Chelonia mydas) is a large sea turtle of the family Cheloniidae (Swash & Still,
2005, p. 116). According to the Integrated Taxonomic Information System (2007) identifies the green
sea turtle is the only species in the genus Chelonia. It inhabits throughout the tropical and subtropical
seas around the world in the Atlantic and Pacific Oceans as mentioned in the National Geographic
Society’s website (http://www3.nationalgeographic.com/animals/reptiles/green-turtle.html).
Green sea turtle's dorsoventrally flattened body is covered by a large, teardrop-shaped shell which has
a pair of large paddle-like flippers. The adults usually inhabit shallow lagoons, feeding mostly on
various species of seaweeds. The green sea turtles migrate long distances between feeding grounds and
hatching beaches. Females crawl out on beaches, dig nests and lay eggs during the night. Later,
hatchlings emerge and scramble into the water.
The green sea turtle (C. mydas) is listed as endangered species on 3 May 2007 by the Convention on
International Trade in Endangered Species (CITES) as a member of the family Cheloniidae and is
protected from exploitation in most countries (Convention on International Trade in Endangered
Species of Wild Flora and Fauna, 2007). It is illegal to collect, harm or kill them in most developed
nations. In addition, many countries have laws and ordinances to protect nesting areas. However,
turtles are still in danger due to human activity. In some countries, turtles and their eggs are hunted for
food. The industrial chemical pollution indirectly harms turtles at both population and individual
scales. Many turtles die when fishermen caught in the fishing nets. In real estate development often
causes habitat loss by eliminating nesting beaches.
2. Body
2.1 Description and Systematic
2.1.1 Description
The species was originally described by Linnaeus in 1758 as Testudo mydas and Johann Schweigger
was first applied the binomial name as Chelonia mydas in 1812 (Integrated Taxonomic Information
System, 2007). The species' common name was derived from the greenish colour of the turtles' fat,
which is only found in a layer between their inner organs and their shell.
The green turtle is among the largest of the sea turtles. The adults normally can reach 1 m in carapace
length and 150 kg in mass (Witherington & Ehrhart, 1989). Hatchling green turtles weigh
approximately 25 g, and the carapace is about 50 mm long. The dorsal surface is black, and the ventral
surface is white. The plastron of Atlantic green turtles remains a yellowish white throughout life, but
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the carapace changes in colour from solid black to a variety of shades of grey, green, brown and black
in starburst or irregular patterns. The carapaces of juveniles turn dark brown to olive, while those of
mature adults are entirely brown, spotted or marbled with variegated rays (Boulenger, 1890). The C.
mydas limbs are dark-coloured and lined with yellow, and usually marked with a large dark brown
spot in the center of each appendage.
2.1.2 Systematic and Palaeontology
In 1758, Carlos Van Linnaeus grouped green sea turtle into Phylum Chordata, Class Reptilia, Order
Chelonia, Suborder Cryptodira, Family Cheloniidae, (Spellerberg, 1982). The status of genus Chelonia
with respect to the other marine turtles was clarified by one of the studies in 1993, (Seminoff, 2004).
The green sea turtle scientifically named as Chelonia mydas. It shared some primitive characteristics
with the out-grouped lancelet. The biologists believed that C.mydas is closely related to the lancelet
group of species that are studying in modern biology today as shown in the phylogenetic tree below.
The lancelet is a small member of phylum chordata that lacks the backbone. However, it was assumed
that green sea turtle and other marine turtles shared primitive characters which were present in the
common ancestor.
The first turtles appeared during the Triassic period, 245 to 209 million years ago (Karl & Brian,
1999). The earliest known sea turtles appear in the fossil record in the Early Cretaceous period, about
110 million years ago. Scientists believe that modern sea turtles are derived from marsh-inhabiting
ancestors that lived during the Late Triassic period. Fossil records show that the now-extinct sea turtle
Archelon ischyros, which lived 75 to 65 million years ago, was one of the largest turtles that ever
lived. It reached a length of 4.6 m (15 ft.) and weighed more than 2,700 kg (6,000 lbs.). Together with
saltwater crocodiles, sea snakes, and marine iguanas, sea turtles are the only surviving seawater
adapted reptiles as shown in the Sea World Park and Entertainment website
(https://seaworld.org/animals/all-about/sea-turtles/classification).
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Controversy rages about splitting Chelonia mydas into subspecies based on the many size differences
between populations in different parts of the world. The Floridian and Mexican population’s website
(http://www.nmfs.noaa.gov/pr/species/turtles/green.html) mention that population found in the eastern
Pacific is often called the black sea turtle, and it sometimes described as a separate species (Chelonia
agassizi). Individuals from the East Pacific are smaller than their counterparts in the Western
Caribbean in a wide range of external measurements, and are particularly dark in colour, a trait that has
shown to be genetically influenced.
2.1.3 Geographical Distribution
The range of C. mydas extends throughout tropical and subtropical oceans worldwide (Roden et.al.
2013). The green sea turtle is a global species in tropical and sub-tropical sea waters. Chelonia mydas
can generally be found throughout the Atlantic Ocean. Individuals have been spotted as far north as
Canada in the western Atlantic, and the British Isles in the east (Seminoff et.al., 2002). In the Pacific,
C.mydas’ range reaches as far north as the southern coast of Alaska and as far south as Chile in the
east and its distribution in the western Pacific reaches north to Japan and southern parts of Russia's
Pacific coast, the northern tip of New Zealand and a few islands in the south of Tasmania and also
throughout the Indian Ocean (Center for Marine Conservation, 1961). The green sea turtle (Chelonia
mydas) found in warm waters of the world.
Conclusion
The green sea turtle (Chelonia mydas) is the largest sea turtle of the family Cheloniidae. The C.mydas’
common name is derived from the greenish colour of the turtles' fat found in a layer between the
internal organs and hard shell. The adults can grow to 1 meter in length and 150kg in weight. Green
sea turtle shared common ancestral characters with the lancelet and other vertebral taxa. The green
turtle inhabits throughout the tropical and subtropical oceans in the worldwide.
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Reference Cited
1. Swash, A. & Still, R. (2005). Birds, Mammals, and Reptiles of the Galápagos Islands. Second
Edition. Hampshire, UK, WildGuides Ltd.
2. Integrated Taxonomic Information System. (2007). Chelonia mydas. Retrieved from
http://www.itis.gov/servlet/SingleRpt.
3. Convention on International Trade in Endangered Species of Wild Flora and Fauna (2007). Green
Sea Turtle. Retrieved from http://www.cites.org/eng/app/appendices.shtml.
4. Boulenger, G. A. (1890). The Fauna of British India, including Ceylon and Burma. Reptilia and
Batrachia. London: Taylor & Francis.
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5. Spellerberg, I.F. (1982). Blackie and Son Limited. Bishopbridge, Glasgow.
6. Seminoff, A., Javier Alvarado; Carlos. D., Jose L. L., & Gabriel H. (2004). Chelonia mydas and
First Direct Evidence of Migration by an East Pacific Green Seaturtle from Michoacan, Retrieved from
www.iucnredlist.org (http://www.iucnredlist.org).
7. Roden, S.E., Philip, A., Army, F & Peter, H., (2013). Green turtle population structure in the
Pacific: Endangered Species Research, Vol. 20: pp. 227–234.
8. Karl, S.H., & Brian W.B., (1999). "Evolutionary Significant Units versus Geopolitical Taxonomy:
Molecular Systematics of an Endangered Sea Turtle (genus Chelonia)". Conservation Biology.
Retrieved from https://dx.doi.org
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2.2 Ecology, Behaviour and Physiology
2.2.1 Ecological Distribution
The green turtle (Chelonia mydas) inhabits high-energy oceanic beaches, convergence zones in the
pelagic habitat, and benthic feeding grounds in relatively shallow, protected waters. Females deposit
egg clutches on high-energy beaches on the islands beaches, where a deep nest cavity can be dug
above the high water line (Carr, 1960). These foraging habitats are commonly pastures of seagrasses
and/or algae, but small green turtles can also be found over coral reefs, worm reefs, and rocky bottoms.
Some feeding grounds only support certain size classes of green turtles. Coral reefs or rocky outcrops
near feeding pastures are often used as resting areas at night and during the day (Collazo, Boulon, &
Tallevast, 1992). The female green turtles nest on the sandy beaches along the coastal areas of many
countries. The green turtles make long-distance migrations from their feeding areas to nesting beaches
in the tropics and sub-tropics. They are more common in all warm seas and sometimes can be seen
during summer in the Atlantic Ocean.
2.2.2 Behaviour
The green turtles have flipper-like forelimbs used for swimming. They always gather together for
mating and travel together to nesting grounds. The female green sea turtles lay about 100 eggs per nest
(Connolly, 2011). They normally nest in every two weeks over several months before leaving the
nesting area and returning to their foraging grounds. The laid eggs take about 2 months to hatch and
the hatchlings make their way to the water (Bjordal et.al., 1999). The newly hatched green sea turtles
are susceptible to night time predators; however, hatchlings emerge at night when fewer predators are
active.
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Green turtles are unique among marine turtles since they are herbivores. They mostly eat seagrasses
and algae. Although green turtles forage on sponges and other small invertebrates, they mainly eat
seagrasses or seaweeds and algae as their daily diets. When the pelagic development phase lasted for
five to seven years, they settled into coastal habitats (United States Fish and Wildlife Service, 1996).
Adults migrate from foraging areas to nesting beaches and may travel hundreds or thousands of
kilometres each way. After emerging from the nest, hatchlings swim to offshore areas, where they live
for several years. When the juveniles reach a certain age/size range, they leave the open ocean habitat
and travel to near-shore foraging grounds. Prior to recruiting to near-shore foraging areas, early-stage
juveniles forage on plant and animal life found in pelagic drift communities.
2.2.3 Sensory Modalities
The green turtles and other sea turtles are typically utilized five senses by hearing, eyesight, tactile,
taste, and smell. The green turtles have ears that contained a single bone in the middle ear that
conducts vibrations to the inner ear. They use eyesight to see well under water; however they are shortsighted in the air or on land. C.mydas is also sensitive to touch on the soft parts of its flippers and on
its shell. The sense of taste is little is known about a green turtle while the sense of smell in the water
is most accurate. This adaptation helps sea turtles to locate food in murky water. The green turtle and
other sea turtles open their mouth slightly and draw in water through the nose. They then immediately
empty the water out again through the mouth. The pulsating movements of the throat are thought to be
associated with smelling.
2.2.4 Physiology
Chelonia mydas is the fastest sea turtle and the body needs enough for the vigorous activity. Hence,
green turtles spend almost all their lives on submerged to breathe air for the oxygen. The single single
explosive exhalation and rapid inhalation of green sea turtles can quickly replace the air in their lungs.
The lungs permit a rapid exchange of oxygen and prevent gases from being trapped during deep dives.
The green turtle and other sea turtles’ blood can deliver oxygen efficiently to body tissues even at the
pressures encountered during diving. During routine activity, green and loggerhead turtles dive for
about four to five minutes, and surface to breathe for one to three seconds.
2.2.5 Other Features
Green turtles have an internal compass which hatchlings use to orient to the Earth’s magnetic field
after they swim through the surf zone. The adults may also use magnetic information to navigate in the
sea. C.mydas usually takes several hours to rest or sleep underwater like other marine turtles.
However, they only take shorter time during the submergence and diving for food or escaping from
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predators. Glick (2005) stated that the C.mydas is drown in shrimp trawlers and fishing gear due to the
breath-holding ability.
Conclusion
The populations of green turtles (Chelonia mydas) are either endangered or threatened by human
activities in the recent decades. The primary threats facing green turtles are direct catch in commercial
and recreational fishing gear, direct killing of turtles and harvest of eggs, vessel strikes, loss and
alteration of nesting habitat, degradation and loss of foraging habitat, and entanglement in or ingestion
of marine debris. In addition, rising sea levels and an increase in the frequency and severity of storm
events are likely to destroy some nesting beaches for green turtles.
Many developed countries have prohibited about the killings of green sea turtles including the United
States and Australia. The other professional organisations and Fisheries are dedicated to protecting and
recovering green turtle populations worldwide. It is more significant to use a variety of innovative
techniques to study, protect, and recover these endangered reptiles for future generations. Papua New
Guinea should develop measures and recovery plans that foster the conservation and recovery of green
sea turtles and their habitats in the southern part of the Pacific Ocean.
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Reference
1. Carr, A.F., and L.H. Ogren. (1960). The ecology and migrations of sea turtles. The green turtle in
the Caribbean Sea. Bulletin of the American Museum of Natural History 121:1-48.
2. Collazo, J.A., R.H. Boulon, and T. Tallevast. (1992). Relative abundance, size class composition
and growth patterns in wild green turtles at Culebra, Puerto Rico. Journal of Herpetology
Vol.26(3):293-300.
3. Connolly, N., 2011). The More turtles nesting in Cayman. Retrieved from
http://www.compasscayman.com/caycompas
4. Bjorndal, K.A., Jerry A.W., Alan B. B., & Jeanne A. M. (1999).Twenty-Six Years of Green Turtle
Nesting at Tortuguero, Costa Rica: An Encouraging Trend. Conservation Biology 13 (1): 126–134.
Retrieved from https://dx.doi.org
5. Glick, D., ( 2005). Back from the Brink. Retrieved from http://www.smithsonianmag.com
6. The United States Fish and Wildlife Service (1996). Hobe Sound National Wildlife Refuge, 1996
Sea turtle nesting report. On file at South Florida Ecosystem Office, U.S. Fish and Wildlife Service;
Vero Beach, Florida
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