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Chelonia mydasGreen Turtle

By Kendalyn Hersh

Geographic Range

Green sea turtles (Chelonia mydas) are a cosmopolitan species found in tropical and subtropical waters. During the months that this species breeds (June through August), green sea turtles are most frequently found nesting on the coastlines of Cyprus and Turkey. They are also observed nesting on the beaches of Israel, Syria, Egypt and Libya. Overall, green turtles are known to settle on the beaches of over 140 countries. Radio tagging nesting females shows that green turtles are migratory, and their non-breeding range includes locations from as far north as 40 degrees north to as far south as 40 degrees south. These areas include parts of the Pacific Ocean, Atlantic Ocean, Mediterranean Sea, and northern Indian Ocean. ("Status and distribution of the green turtle, Chelonia mydas, in the wider Caribbean region", 2001; Hirth, 1997; Seminoff, 2004; Stokes, et al., 2015)

Habitat

Green sea turtles are common in shallow tropical and subtropical waters as well as coastline beaches. They forage in coastal areas with plentiful of algae and sea grass. Male and female green turtles use major current systems when migrating to nesting beaches. Once females find a suitable beach with accessible sloping platforms, the green turtles will lay their eggs in the sand and then return to the ocean. After the eggs hatch, juvenile green sea turtles will then return to the ocean. Juveniles are known to spend several years drifting in the open ocean as they grow and mature. Once the juveniles have matured, they will return to their natal beach for mating. ("Green sea turtle (Chelonia mydas)", 2015; Seminoff, 2004; Stokes, et al., 2015)

Physical Description

Green sea turtles are so named because of the greenish color of their subdermal fat. They have only one pair of prefrontal scales, although other species of sea turtles that have multiple pairs. The scales are originally black at hatching, but then change color over the course of 27-50 years as the turtle matures. Their skull shape is described as round and smooth. Green turtles have short snouts and strong beaks that cover the bones of the jaw. Their jaws are short and serrated to properly rip and tear plants apart. The carapace is round and consists of four lateral overlapping scutes. The plastron also consists of four scutes.

Sexual dimorphism isn't completely recognized in green sea turtles until early adulthood. Males and females differ morphologically by the length of their tail and cloacal openings. Female green turtles have smaller tails and a cloacal opening between the anus and tip of the tail. Witzel (1982) reports that that male green turtles are slightly smaller in carapace length, have longer claws, and longer tails where their reproductive organs are located. Their cloacal opening is located more posterior on the tail and past the end of their carapace.

Green turtles are the second largest overall species of sea turtles. As hatchlings, green turtles have an average weight of 25g and are 5 cm long. Their plastrons are white and carapaces are blue-black. Juveniles measure to about 40 cm in carapace length and subadults will measure between 70 to 100 cm. Adult green turtles, male or female, tend to be about 100 to 120 cm long in carapace length and weigh around 150 to 200 kg when reaching adulthood. They also have a basal metabolic rate of 47.9 to 73.8 cm^3 oxygen/hour. ("Status and distribution of the green turtle, Chelonia mydas, in the wider Caribbean region", 2001; "The anatomy of sea turtles", 2001; Witzel, 1982)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range mass
    150 to 200 kg
    330.40 to 440.53 lb
  • Range length
    100 to 120 cm
    39.37 to 47.24 in
  • Range basal metabolic rate
    47.9 to 73.8 cm3.O2/g/hr

Development

Female green sea turtles lay eggs 35-58 mm in diameter. Like many turtles, green sea turtles' development is affected by temperature. Eggs that are laid in cooler environments less than 28.5°C tend to produce more males than females, and warm nests greater than 30.3°C are known to hatch more females than males. Both sexes incubate in white, soft shells for 30-90 days depending whether or not it is the wet or dry season. Incubation typically takes longer in the wet season. Once hatchlings leave the nest, their carapace is dark blue-black and about 5 cm in length. Hatchlings average a weight of 25 g. Their plastron is yellow or white, and the skin is black. As the hatchlings mature into juveniles, the will measure about 40 cm in carapace length. Subadults measure between 70 to 100 cm in length. As the hatchlings grow into juveniles, it takes 27-50 years before green turtles reach full maturity. (Ernst and Barbour, 1989; Hirth, 1997)

  • Development - Life Cycle
  • temperature sex determination

Reproduction

Green turtles are polygynandrous, meaning that females and males will have multiple mates. Copulation occurs in the shallow waters off the shore of nesting beaches. When females accept a mate, the male will mount her and grab onto her "mating notches" around her shoulders to assist in copulation (Hirth, 1971). Male green turtles also are known to join other mating pairs during copulation by latching onto other males for hours on end in attempts to dislodge the mating male. The reproduction process usually follows a system such as: male searches for a female mate, the male will visually examine and then approach the female, the female will either submit or reject the male,then possible copulation. Copulation can last several hours, with the longest mounting episode lasting 119 hours. Female green turtles average a total of 15 days between initial mounting by a male to the time they attempt to nest on their respective natal beaches. ("Green sea turtle (Chelonia mydas)", 2015; "South Pacific Islands-marine turtle resources", 1971; "Status and distribution of the green turtle, Chelonia mydas, in the wider Caribbean region", 2001; Ernst and Barbour, 1989; Hirth, 1997)

Females are known to revisit their natal beaches in 2-4 year intervals to breed from June to September. If they don't return to their natal beach, they will select a beach with similar sand texture and color. Hirth (1971, as cited in Carr and Ogren 1960) describes predictable actions by females when they approach a nesting beach. Although they may not complete every action, the process usually begins with the turtles approaching the beach and selecting a suitable nest site. The females begin clearing the area of debris and digging a hole with their front legs. After laying eggs, the females fill the nest with sand as a way to camouflage and conceal the eggs. Then, the female turtles return to the sea.

Female green turtles can lay 1- 9 clutches in a single nesting season, but tend to average around 3. Each of these clutches can include 75-200 eggs. After nesting, it usually takes 45-75 days for the eggs to hatch. The hatchings weigh approximately 26g on average. Once the eggs hatch, the hatchlings will begin their journey towards the ocean. From here the hatchlings will begin the juvenile portion of their life which can last 27-50 years before reaching full maturity. ("Green sea turtle (Chelonia mydas)", 2015; "South Pacific Islands-marine turtle resources", 1971; "Status and distribution of the green turtle, Chelonia mydas, in the wider Caribbean region", 2001; Carr and Ogren, 1960; Hirth, 1997)

  • Breeding interval
    Green sea turtles breed in 2-4 year intervals.
  • Breeding season
    The nesting season for green sea turtles usually lasts from June through September.
  • Range number of offspring
    75 to 200
  • Average number of offspring
    136
  • Average number of offspring
    150
    AnAge
  • Range gestation period
    45 to 75 days
  • Range age at sexual or reproductive maturity (female)
    27 to 50 years
  • Range age at sexual or reproductive maturity (male)
    27 to 50 years

There is no parental investment by green turtles beyond the mother's egg-laying and camouflaging of the nest. (Hirth, 1997)

  • Parental Investment
  • pre-hatching/birth
    • protecting
      • female

Lifespan/Longevity

There is very little research regarding the lifespan of green turtles, due to lack of tagging. However, AnAge reported a maximum green turtle lifespan of 75 years. Green turtles are not often held for long in captivity, so longevity records do not exist. ("AnAge entry for Chelonia mydas", 2014)

  • Range lifespan
    Status: wild
    75 (high) years
  • Average lifespan
    Status: captivity
    75 years
    AnAge

Behavior

Green turtles travel in large groups that usually originate from the same natal beach. They spend a lot of their time swimming, traveling about 20-90 km/day. They also can be found eating, diving, reproducing, and migrating. Juvenile green turtles are said to be faster swimmers than other sea turtles such as loggerheads (Caretta caretta) and olive ridleys (Lepidochelys olivacea) due to the way green turtle hatchlings stroke their foreflippers.

During the breeding season, actively mating pairs are often approached by several "escort" males that will latch on to the pair during copulation. Sometimes these escort males will attempt to remove the male connected to the female. If the copulating male feels threatened by the escort(s), then he might remove himself from the female briefly to drive off the other males. Even though humans are a predator of green sea turtles, most turtles are not affected by human contact while swimming or during copulation. (Hirth, 1997; Seminoff, et al., 2002)

Home Range

Green sea turtles will maintain home ranges throughout the year. These habitats include coastal feeding areas during the non-breeding season and natal beaches that the females visit during the nesting season. Adult green turtles have a home range that can expand from 3.8 ha to 642.2 ha. They are not known to actively defend a territory. (Hirth, 1997; Seminoff, 2004)

Communication and Perception

Green turtles primarily use vision to detect plants and other prey and use visual displays when communicating. Green sea turtles also use a sense of wave propagation direction to help them navigate under water. Magnetic channels are also used to assist the orientation of the turtle in deep waters. In one study, researchers found that the turtles' inner ear can detect the acceleration and direction of the wave which assists their sense of direction (Lohmann and Lohmann, 1992). Females use two displays to communicate with males whether or not they wish to mate. Female green sea turtles will show approval of a mate by being completely submissive when being mounted by the male. Females will clearly reject a male by either swimming away with their hind legs closed or biting a male if he gets too close. Female green turtles also have a "refusal" position, which consists of floating upward having their plastron facing the male and an extending all limbs. (Hirth, 1997; Lohmann and Lohmann, 1996)

  • Communication Channels
  • visual

Food Habits

Green sea turtles begin their lives as omnivores and gradually shift to a more herbivorous diet. As juveniles, green sea turtles will feast on small marine invertebrates and neustonic material like sea serpents (Hydrozoa), moss animals (Bryozoa), and sea hare eggs (Aplysia). They also consume large quantities of wetland plants such as api api (Avicennia schaueriana) and salt-water cord grass (Spartina alterniflora), which are commonly found in salt marshes. Their diet also consists of a variety of red and green algae such as: filamentous red alga (Bostrychia), red moss (Caloglossa), freshwater red algae (Compsopogon), lobster horns (Polysiphonia), sea lettuce (Ulva lactuca), green seaweed (Gayralia), and crinkle grass (Rhizoclonium). Because green sea turtles are highly mobile throughout their lives, their food choices are often opportunistic. (Arthur, et al., 2008; Russell, et al., 2011; Seminoff, 2004; Spotila, 2004)

Predation

Green turtle hatchlings are at a higher risk of predation than adult green sea turtles. Eggs are preyed upon by multiple land mammals, reptiles, and crustaceans. Some of these mammals include: jaguars (Panthera onca), red foxes (Vulpes vulpes), feral dogs (Canis lupus familiaris), golden jackals (Canis aureus) and humans (Homo sapiens). Young green sea turtles also are consumed by crabs (Brachyura) and saltwater crocodiles (Crocodylus porous) which can attack on land or in the water. The only defense mechanism of hatchlings is swarming in large groups toward the ocean. Once the hatchlings reach the water, they face a new group of predators such as tiger sharks (Galeocerdo cuvier) and whitetip sharks (Carcharhinus longimanus). Juvenile and mature sea turtles also are preyed on by sharks. Mature green sea turtles' best form of protection from their predators is their large hard shell. When females come on land to nest, their head and limbs become vulnerable and easily accessible by predators. Green turtles are also hunted by humans for meat. (Alfaro, et al., 2016; Hirth, 1997; Spotila, 2004)

Ecosystem Roles

Juvenile green turtles are predators of sea serpents (Hydrozoa), moss animals (Bryozoa), sea hare eggs (Aplysia) and small jellyfish (Medusoza). Mature green turtles are mostly herbivorous and consume large quantities of sea grass and algae. Green turtles play a role in their ecosystem by facilitating nutrient turnover and sea grass regrowth. As the turtles graze on sea grass, they provide nitrogen-rich fertilizer in the form of fecal matter. Green sea turtles suffer from parasitic trematode eggs known as flukes. These trematodes cause inflamed cardiovascular tissue that infect turtles and commonly result in death. Species of flukes that are found in green turtles include: Learedius leardei, Carettacola hawaiiensis, Hapalotrema dorsopora, and Hapalotrema postorchis. (Aguirre, et al., 1998; Aragones, et al., 2006; Spotila, 2004)

Commensal/Parasitic Species
  • flukes (Learedius leardei)
  • flukes (Carettacola hawaiiensis)
  • flukes (Hapalotrema dorsopora)
  • flukes (Hapalotrema postorchis)

Economic Importance for Humans: Positive

Although many countries have established laws protecting sea turtles, green sea turtles are still poached for their eggs and meat in certain areas around the world, such as South East Asia. The shells are also displayed as decoration or used to make jewelry. ("Green sea turtle (Chelonia mydas)", 2015; Marcovaldi and Marcovaldi, 1999; Spotila, 2004)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of Chelonia mydas on humans.

Conservation Status

Green turtles are considered an endangered species according to the IUCN Red List. The Convention on International Trade in Endangered Species classifies green sea turtles under Appendix I which include species that are most endangered and most at risk of extinction. This specific appendix explains that trade of this species is prohibited unless the species is being used for research. Exceptions to this prohibition are only valid under approval of import and export permits.

The United States Federal List classifies some green sea turtles as endangered, but a majority of populations are classified as threatened. Those considered endangered were found to live in the Mediterranean populations, Central West Pacific populations, and Central South Pacific populations. This dangerous decline in population is mostly due to marine fisheries catching mature and juvenile green turtles in foraging areas and on nesting grounds. Fishing techniques include harpooning, catching by hand, netting, noosing, turning the turtle over on their dorsal side and various other techniques. Green turtles are also threatened by the presence of artificial light. This is seen as a serious threat, because sea turtles sometimes mistake artifical light for sunlight. It has been suggested that artifical light disorientates green turtles, and affects both their general and nesting behavior. Specific effects of artificial light on these turtles include altered adult return crawl and incomplete nest construction.

In efforts to conserve this turtle species, laws have been made and have successfully lessened the threats by fisheries. For instance, both the U.S. Fish and Wildlife Service and National Marine Fisheries Service enforce the laws prohibiting the capture of sea turtles on land and in water. Other contracts that have benefit the conservation of green turtles include the Memorandum of Understanding on ASEAN Sea Turtle Conservation and Protection, the Memorandum of Understanding Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa, and the Inter-American Convention for the Protection and Conservation of Sea Turtles. Even though these agreements have made a positive impact on the lifespan and population of green turtles, this species is still in danger of near-shore fisheries. (Ernst and Barbour, 1989; Hirth, 1997; Seminoff, 2004; Witherington, 1992)

Contributors

Kendalyn Hersh (author), Radford University, Alex Atwood (editor), Radford University, Marisa Dameron (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

food

A substance that provides both nutrients and energy to a living thing.

macroalgae

seaweed. Algae that are large and photosynthetic.

magnetic

(as perception channel keyword). This animal has a special ability to detect the Earth's magnetic fields.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

terrestrial

Living on the ground.

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

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United States Fish and Wild Life Service. Green sea turtle (Chelonia mydas). None. Jacksonville, Florida and Arlington, Virginia: United States Fish and Wildlife Service. 2015. Accessed September 20, 2016 at https://www.fws.gov/northflorida/SeaTurtles/Turtle%20Factsheets/green-sea-turtle.htm.

Food and Agriculture Organization, United Nations. South Pacific Islands-marine turtle resources. None. Rome, Italy: None. 1971.

Wildlife Conservation Society. Status and distribution of the green turtle, Chelonia mydas, in the wider Caribbean region. None. Santo Domingo, Dominican Republic: International Union for Conservation of Nature. 2001.

National Marine Fisheries Service. The anatomy of sea turtles. NMFS-SEFSC-470. Miami, Florida: U.S. Department of Commerce NOAA Technical Memorandum. 2001. Accessed September 15, 2016 at http://s3.amazonaws.com/academia.edu.documents/41147367/Wyneken2002AnatOfSeaTurtles.pdf?AWSAccessKeyId=AKIAJ56TQJRTWSMTNPEA&Expires=1473950906&Signature=MBXAG6x7%2F3%2B8A1KWdacU1Hu%2BZX8%3D&response-content-disposition=inline%3B%20filename%3DAnatomy_of_Sea_Turtles.pdf.

Aguirre, A., T. Spraker, G. Balazs, B. Zimmerman. 1998. Spirorchidiasis and fibropapillomatosis in green turtles from the Hawaiian islands. Journal of Wildlife Diseases, 34/1: 91-98.

Alfaro, L., V. Montal, F. Guimaraes, C. Saenz, J. Cruz, F. Morazan, E. Carrillo. 2016. Characterization of attack events on sea turtles (Chelonia mydas and Lepidochelys olivacea) by jaguar (Panthera onca) in Naranjo Sector, Santa Rosa National Park, Costa Rica. International Journal of Conservation Science, 7/1: 101-108.

Aragones, L., I. Lawler, W. Foley, H. Marsh. 2006. Dugong grazing and turtle cropping: grazing optimization in tropical seagrass systems. Oecologia, 149/4: 635-647.

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Ehrenfeld, D., A. Carr. 1967. The role of vision in the sea-finding orientation of the green turtle (Chelonia mydas). Animal Behaviour, 15/1: 25-26.

Ernst, C., R. Barbour. 1989. Turtles of the World. Washington, District of Columbia: Smithsonian Institution Press.

Hirth, H. 1997. Synopsis of biological data on the green turtle. Biological Report, 97/1: 1-120.

Lohmann, K., C. Lohmann. 1996. Orientation and open-sea navigation in sea turtles. Journal of Experimental Biology, 199/1: 73-81.

Lohmann, K., A. Swartz, C. Lohmann. 1995. Perception of ocean wave direction by sea turtles. The Journal of Experimental Biology, 198/5: 1079-1085.

Marcovaldi, M., G. Marcovaldi. 1999. Marine turtles of Brazil: The history and structure of Projeto TAMAR-IBAMA. Biological Conservation, 91/1: 35-41.

Mortimer, J., R. Brandis. 2013. Mortality of adult green turtles (Chelonia mydas) at the nesting beaches of Aldabra Atoll, Seychelles. Chelonian Conservation and Biology, 12/1: 151-157.

Nagaoka, S., A. Martins, R. Santos, M. Tognella, E. Filho, J. Seminoff. 2012. Diet of juvenile green turtles (Chelonia mydas) associating with artisanal fishing traps in a subtropical estuary in Brazil. Marine Biology, 159/3: 573-581.

Olgun, K., E. Bozkurt, S. Ceylan, M. Tural, S. Özcan, K. Karasüleymanoğlu, Y. Geroğlu. 2015. Nesting activity of sea turtles, Caretta caretta (Linnaeus, 1758) and Chelonia mydas (Linnaeus, 1758) (Reptilia, Cheloniidae), at Patara Beach (Antalya, Turkey) over four nesting seasons. Turkish Journal of Zoology, 40/2: 215-222.

Russell, D., S. Hargrove, G. Balazs. 2011. Marine sponges, other animal food, and nonfood items found in digestive tracts of the herbivorous marine turtle Chelonia mydas in Hawai'i. Pacific Science, 65/3: 375-381.

Salleh, S., S. Sah. 2012. The distribution and conservation status of green turtles (Chelonia mydas) and olive ridley turtles (Lepidochelys olivacea) on Pulau Pinang beaches (Malaysia), 1995–2009. Tropical Life Sciences Research, 23: 63-76. Accessed September 08, 2016 at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3799394/.

Seminoff, J. 2004. "Chelonia mydas" (On-line). The IUCN Red List of Threatened Species 2004: e.T4615A11037468.. Accessed September 08, 2016 at http://www.iucnredlist.org/details/4615/0.

Seminoff, J., A. Resendiz, W. Nichols. 2002. Home range of green turtles Chelonia mydas at a coastal foraging area in the Gulf of California, Mexico. Marine Ecology Progress Series, 242: 253-265.

Spotila, J. 2004. Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation. Baltimore, Maryland: Johns Hopkins University Press.

Stokes, K., A. Broderick, A. Canbolat, O. Candan, W. Fuller, F. Glen, Y. Levy, A. Rees, G. Rilov, R. Snape, I. Stott, D. Tchernov, B. Godley. 2015. Migratory corridors and foraging hotspots: Critical habitats identified for Mediterranean green turtles. Diversity and Distributions, 21/6: 1-10.

Sönmez, B., C. Turan, Ş. Özdilek, F. Turan. 2016. Sex determination of green sea turtle (Chelonia mydas) hatchlings on the bases of morphological characters. Journal of Black Sea/Mediterranean Environment, 22/1: 93-102.

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Witzel, W. 1982. Observations on the green sea turtle (Chelonia mydas) in Western Samoa. Copeia, 1982: 183-185.

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