Green sea turtle

The green sea turtle, also known as the green turtle, black sea turtle, and Pacific green turtle, is a species of large sea turtle of the family Cheloniidae. It is the only species in the genus Chelonia. Its range extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans, but it is also found in the Indian Ocean. The common name refers to the usually green fat found beneath its carapace, due to its diet strictly being seagrass, not to the color of its carapace, which is olive to black.
The dorsoventrally flattened body of C. mydas is covered by a large, teardrop-shaped carapace; it has a pair of large, paddle-like flippers. It is usually lightly colored, although in the eastern Pacific populations, parts of the carapace can be almost black. Unlike other members of its family, such as the hawksbill sea turtle, C. mydas is mostly herbivorous. The adults usually inhabit shallow lagoons, feeding mostly on various species of seagrasses. The green sea turtle is the only aquatic turtle species which is herbivorous when fully grown.
Like other sea turtles, green sea turtles migrate long distances between feeding grounds and hatching beaches. Many islands worldwide are known as Turtle Island due to green sea turtles nesting on their beaches. Females crawl out on beaches, dig nests, and lay eggs during the night. Later, hatchlings emerge, and scramble into the water. Those that reach maturity may live to 90 years in the wild.
C. mydas was listed as endangered by the IUCN and CITES until 2025 and is protected from exploitation in most countries. It is illegal to collect, harm, or kill them. 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 still hunted for food. Pollution indirectly harms turtles at both population and individual scales. Many turtles die after being caught in fishing nets. In addition, real estate development often causes habitat loss by eliminating nesting beaches.

Taxonomy

The green sea turtle is a member of the tribe Cheloniini. A 1993 study clarified the status of genus Chelonia with respect to the other marine turtles. The carnivorous Eretmochelys, Caretta and Lepidochelys were assigned to the tribe Carettini. Herbivorous Chelonia warranted their status as a genus, while Natator was further removed from the other genera than previously believed.
The species was originally described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Testudo mydas. In 1868, Marie Firmin Bocourt named a particular species of sea turtle Chelonia agassizii, in honor of Swiss-American zoologist Louis Agassiz. This "species" was referred to as the "black sea turtle". Later research determined Bocourt's "black sea turtle" was not genetically distinct from C. mydas, and thus taxonomically not a separate species. These two "species" were then united as Chelonia mydas and populations were given subspecies status: C. mydas mydas referred to the originally described population, while C. mydas agassizi referred only to the Pacific population known as the Galápagos green turtle. This subdivision was later determined to be invalid and all species members were then designated Chelonia mydas. The oft-mentioned name C. agassizi remains an invalid junior synonym of C. mydas.
The species' common name does not derive from any particular green external coloration of the turtle. Its name comes from the greenish color of the turtles' fat, which is only found in a layer between their inner organs and their shell. As a species found worldwide, the green turtle has many local names. In the Hawaiian language it is called honu, and it is locally known as a symbol of good luck and longevity.

Description

Its appearance is that of a typical sea turtle. C. mydas has a dorsoventrally flattened body, a beaked head at the end of a short neck, and paddle-like arms well-adapted for swimming. Adult green turtles grow to long. The average weight of mature individuals is and the average carapace length is. They are considered the second largest sea turtle in the United States, after the leatherback sea turtle.
Exceptional specimens can weigh or even more, with the largest known C. mydas having weighed and measured in carapace length.
Anatomically, a few characteristics distinguish the green turtle from the other members of its family. Unlike its close relative the hawksbill turtle, the green turtle's snout is very short and its beak is unhooked. The neck cannot be pulled into the shell. The sheath of the turtle's upper jaw possesses a denticulated edge, while its lower jaw has stronger, serrated, more defined denticulation. The dorsal surface of the turtle's head has a single pair of prefrontal scales. Its carapace is composed of five central scutes flanked by four pairs of lateral scutes. Underneath, the green turtle has four pairs of inframarginal scutes covering the area between the turtle's plastron and its shell. Mature C. mydas front appendages have only a single claw, although a second claw is sometimes prominent in young specimens.
The carapace of the turtle has various color patterns that change over time. Hatchlings of Chelonia mydas, like those of other marine turtles, have mostly black carapaces and light-colored plastrons. Carapaces of juveniles turn dark brown to olive, while those of mature adults are either entirely brown, spotted or marbled with variegated rays. Underneath, the turtle's plastron is hued yellow. C. mydas limbs are dark-colored and lined with yellow, and are usually marked with a large dark brown spot in the center of each appendage.

Distribution

The range of the green sea turtle extends throughout tropical and subtropical oceans worldwide. The two major subpopulations are the Atlantic and the eastern Pacific subpopulations. Each population is genetically distinct, with its own set of nesting and feeding grounds within the population's known range. One of the genetic differences between the two subpopulations is the type of mitochondrial DNA found in individual's cells. Individuals from rookeries in the Atlantic Ocean and Mediterranean Sea have a similar type of mitochondrial DNA, and individuals from the Pacific and Indian Oceans have another type of mitochondrial DNA. Their native range includes tropical to subtropical waters along continental coasts and islands between 30°N and 30°S. Since green sea turtles are a migrating species, their global distribution spans into the open ocean. The differences in mitochondrial DNA more than likely stems from the populations being isolated from each other by the southern tips of both South America and Africa with no warm waters for the green sea turtles to migrate through. The green sea turtle is estimated to inhabit coastal areas of more than 140 countries, with nesting sites in over 80 countries worldwide throughout the year. In the United States Atlantic coast, green sea turtles can be found from Texas to Massachusetts. In the United States Pacific coast, they have been found from southern California north to the southernmost tip of Alaska. The largest populations of green sea turtles within the United States coastline are in the Hawaiian Islands and Florida. Globally, the largest populations of sea turtles are in the Great Barrier Reef in Australia, and the Caribbean Sea.
Recently these Turtles were discovered within Rangaunu Harbour in New Zealand.

Atlantic subpopulation

The green sea turtle can generally be found throughout the Atlantic Ocean. Although the species is most abundant in tropical climates, green sea turtles can also be found in temperate climates, and individuals have been spotted as far north as Canada in the western Atlantic, and the Cimbrian peninsula in the east. The subpopulation's southern range is known until past the southern tip of Africa in the east and Argentina in the western Atlantic. The major nesting sites can be found on various islands in the Caribbean, along the Atlantic coast of Florida in the United States, the eastern coast of the South American continent and most notably, on isolated North Atlantic islands.
In the Caribbean, major nesting sites have been identified on Aves Island, the U.S. Virgin Islands, Puerto Rico, the Dominican Republic, and Costa Rica. In recent years, there are signs of increased nesting in the Cayman Islands. One of the region's most important nesting grounds is in Tortuguero in Costa Rica. In fact, the majority of the Caribbean region's C. mydas population hails from a few beaches in Tortuguero. Within United States waters, minor nesting sites have been noted in the states of Georgia, North Carolina, and South Carolina. Florida's east coast is the largest nesting site in the United States. Hutchinson Island in particular is a major nesting area in Florida waters. Florida has several annual nesting periods when local beaches are closed or cordoned off to protect nesting sites. According to Green Sea Turtle Watch, in 2015 more than 37,000 green sea turtle nests were documented in Florida, a record number. In addition to sporadic distribution of nesting sites, feeding grounds are much more widely distributed throughout Florida. Important feeding grounds in Florida include Indian River Lagoon, the Florida Keys, Florida Bay, Homosassa, Crystal River, and Cedar Key.
Notable locations in South America include secluded beaches in Suriname and French Guiana. In the Southern Atlantic Ocean, the most notable nesting grounds for Chelonia mydas are found on the island of Ascension, hosts 6,000–13,000 turtle nests.