Green sea turtle - Chelonia mydas

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Chelonia mydas (green sea turtle) is the largest of all the hard shelled marine turtles, averaging 136 kg (up to 180 kg) in weight and measuring about 1 m in carapace (upper shell) length. The shell varies in color from green, grey, brown or black, often with splotches or bold streaks. The plastron (lower shell) is yellowish white. Green sea turtles have 4 pairs of costal scutes (scales that run down each side of the carapace). Hatchlings have a black carapace and white plastron, and measure about 50 mm long and 25 g in weight.

Subspecies Chelonia mydas agassizii is often called the black turtle because of its very dark colored shell.

Green sea turtles can be distinguished from other hard shelled turtles by their smooth carapace and small, rounded heads.

Green turtles are found circumglobally in tropical and subtropical waters. They may be found in three different habitat types: high energy beaches (nesting), pelagic convergence zones (juveniles), and shallow coastal areas (adults). Major nesting colonies for Chelonia mydas exist on Ascension Island, Aves Island, Costa Rica, New Caledonia, Queensland Australia, and Suriname. In the United States, green turtles nest on the east coast of Florida, in the United States Virgin Islands, and in Puerto Rico.

C. m. agassizii is found only in the eastern Pacific Ocean. Important nesting grounds can be found in Maruata Bay, Mexico and the Galapagos Islands.

Hatchling green turtles leave the beach on which their mother nested and swim directly offshore, associating with convergence zones in the open ocean for several years (until they are 20 to 25 cm straight carapace length [SCL] in the Atlantic, 35 cm SCL around Hawaii and Australia). Then the juvenile greens will leave the pelagic habitat and move into benthic feeding grounds.

The age at which Chelonia mydas become sexually mature varies among individuals of the same population and among different populations, with estimates ranging from 16 years (in captivity) to 50 years (in Hawaii). After reaching reproductive maturity, male and female turtles will congregate in waters off of nesting beaches, where courtship and mating take place in early summer months. Females will crawl up the beach at night, dig a nest, and then lay her clutch (group) of eggs, and re-cover the nest with sand. A female green turtle may lay multiple clutches of eggs (approximately 100 to 115 eggs per clutch) through the nesting season (summer and early fall). A female may have between 1 and 9 clutches per season (mean = 3.3 clutches/season). Green turtles do not typically mate every year, usually 2 or more years pass between breeding seasons. Hatchlings incubate for a period of approximately 2 months before emerging; both incubation period length and the sex ratio of hatchlings are determined by the temperature of the nest.

Green turtles exhibit a dramatic dietary shift between their pelagic stage and adult benthic stage. As post-hatchlings occupying pelagic convergence zones, they eat worms, young crustaceans, aquatic insects, grasses and algae. As adults however, they are the only strictly herbivorous (eating only plant material) sea turtle species, though they may consume limited quantities of animal matter incidentally. Adult green turtles have finely serrated jaws that allow them to tear vegetation like sea grasses and algae. Chelonia mydas agassizii may have more carnivorous diets than Chelonia mydas mydas, consuming mollusks, algae, and other invertebrates.

Adults: Algae & Seagrass > Gelatinous zooplankton > Other invertebrates

Prey species for adults include: Halophila ovalis, Thalassia sp., Gelidiella acerosa, Posidonia oceanica, Halodule uninervis, Syringodium isoetifolium, Cymodocea serrulata, Halophila ovata, Chaetomorpha aerea, Sargassum illicifolium, Thalassodendron ciliatum, Zostera capricorni, Halophila spinulosa, Hypnea cervicornis, Catostylus mosaicus, Halodule pinifolia, Physalia sp., Thalassia testudinum, Syringodium filiforme, Halodule whrightii, Chondrilla nucula, Halophila engelmanni

Pelagic juveniles: Coelenterates > Mollusks > Macroplankton

Prey species for pelagic juveniles include: Janthina janthina

Eastern Pacific subspecies (Chelonia mydas agassizii) prey species include: Mytilus sp., Nassarius sp., Semele sp., Gigartina sp., Rhodymenia sp., Hyperia medusarum, Distichlis sp.

Threats to green sea turtles include:

• Harvest of eggs/adults

• Ship strikes

• Fisheries bycatch

• Predators at colonies

• Entanglement in debris/fishing gear

• Oil and plastic pollution

All seven species of sea turtles are protected under the United States Endangered Species Act.

• iOBIS
• World Register of Marine Species (WoRMS)
• Encyclopedia of Life
• Catalog of Life
• Integrated Taxonomic Information System (ITIS)
• Barcode of Life

Caribbean Conservation Corporation/Sea Turtle Survival League. 2011. Species fact sheet: Green sea turtle. Available online here.

Hirth, H.F. 1997. Synopsis of the biological data on the green turtle Chelonia mydas (Linnaeus 1758). U.S. Fish and Wildlife Service, Washington, DC.

Lutz, P.L and J.A. Musick, eds. 1997. The biology of sea turtles. CRC Press LLC, New York, NY.

National Marine Fisheries Service and U.S. Fish and Wildlife Service. 1991. Recovery plan for U.S. population of Atlantic green turtle. National Marine Fisheries Service, Washington, DC.

National Research Council. 1990. Decline of the sea turtles: Causes and prevention. National Academy Press, Washington, DC.