Green sea turtles - Chelonia mydas
The Green sea turtle (Chelonia mydas) is a 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. Their common name derives from the usually green fat found beneath their carapace (upper shell).
The Chelonia 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 1.5 metres long. While individuals have been caught that reached weights of up to 315 kilograms (the largest known Chelonia mydas weighed 395 kilograms), the average weight of mature individuals is around 200 kilograms.
Anatomically, a few characteristics distinguish the green turtle from the other members of its family. The green turtle's snout is very short and its beak is unhooked. The sheath of the turtle's upper jaw possesses a denticulated edge while its lower jaw has stronger with 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 infra-marginal scutes covering the area between the turtle's plastron and its shell. Mature C. mydas front appendages have only a single claw (as opposed to the hawksbill's two), 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 C. 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.
Where this turtle lives
The Green sea turtle (Chelonia mydas) is a large sea turtle of the family Cheloniidae. It is the only species in the genus Chelonia.[1] Its range extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans. Is present also in the Eastern Mediterranean area.
Ecology and biology
Only human beings and the larger sharks feed on C. mydas adults, specifically, tiger sharks. Juveniles and new hatchlings have significantly more predators, including crabs, small marine mammals and shorebirds. In Turkey, their eggs are vulnerable to predation by red foxes, golden jackals and dogs.
The ecology of Chelonia mydas changes drastically with each stage of its life history. Newly emerged hatchlings are carnivorous, pelagic organisms part of the open ocean mini-nekton. In contrast, immature juveniles and adults are commonly found in seagrass meadows closer inshore as herbivorous grazers.
Green sea turtles move across three habitat types depending on their life stage. They lay eggs on beaches. Mature turtles spend most of their time in shallow, coastal waters with lush seagrass beds. Adults frequent inshore bays, lagoons and shoals with lush seagrass meadows. Entire generations often migrate between one pair of feeding and nesting areas.
Turtles spend most of their first five years in convergence zones within the open ocean. These young turtles are rarely seen as they swim in deep, pelagic waters.
Green sea turtles migrate long distances between feeding sites and nesting sites. Some C. mydas swim more than 2,600 kilometers to reach their spawning grounds.
Mature turtles often return to the exact beach from which they hatched. Females usually mate every two to four years. Males on the other hand, visit the breeding areas every year, attempting to mate. Mating seasons vary between populations. In the Mediteranean sea Chelonia mydas , mating season is from May to August, but in the tropics, green turtles nest throughout the year.
After mating in the water, the female moves above the beach's high tide line where she digs a hole with her hind flippers and deposits her eggs. Litter size depends on the age of the female and species, but C. mydas clutches range between 100 to 200. She then covers the nest with sand and returns to the sea.
At around 45 to 75 days, the eggs hatch during the night and the hatchlings instinctively head directly into the water. This is the most dangerous time in a turtle's life. As they walk, predators such as gulls and crabs grab them. A significant percentage never make it to the ocean. Little is known of the initial life history of newly hatched sea turtles.
Juveniles spend three to five years in the open ocean before they settle as still-immature juveniles into their permanent shallow-water lifestyle. It is speculated that they take twenty to fifty years to reach sexual maturity. Individuals live up to eighty years in the wild.
Sea turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. During routine activity green and loggerhead turtles dive for about 4 to 5 minutes and surface to breathe for 1 to 3 seconds.
