Green Sea Turtle

## Description

The green sea turtle (Chelonia mydas ), also known as the green turtle, black (sea) turtle or 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, 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 turtles bite off the tips of the blades of seagrass, which keeps the grass healthy.

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* is listed as endangered by the IUCN and CITES 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.

## Appearance

Green sea turtles are amongst the largest turtles. Their heads appear small in comparison with the size of their body, which is covered in brown scales with a light-colored edge. Males are bigger than females and have a longer tail, sticking out well past the shell. The shell of the turtle has smooth, non-overlapping plates colored different shades of brown, with patterns that change as the turtle grows older. The underside of the shell is lighter colored. Green sea turtles are not able to pull their heads into their shells.

## Distribution

Green sea turtles live in the Atlantic Ocean, ranging from the eastern part of the United States along the coast of South America and over to South Africa. They are also found in the Caribbean Sea and parts of the Mediterranean, and throughout the warmer waters of the Pacific and Indian Oceans. 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. In these protected shores and bays, the green sea turtle habitats include coral reefs, salt marshes, and nearshore seagrass beds. The coral reefs provide red, brown, and green algae for their diet and give protection from predators and rough storms within the ocean. The salt marshes and seagrass beds contain seaweed and grass vegetation, allowing ample habitat for the sea turtles. Turtles spend most of their first five years in convergence zones within the bare open ocean that surrounds them. These young turtles are rarely seen as they swim in deep, pelagic waters.

## Behavior

Green sea turtles spend almost all their lives underwater and come out of the water only when nesting. They are not considered social but may congregate offshore or during the breeding season. Some individuals may migrate together. Although they move quickly in the ocean, on land Green sea turtles are slow and also defenseless. Males hardly ever leave the water. Females leave the sea only to lay eggs and nest only at night. Green turtles swim underwater for approximately 4 to 5 minutes during routine activity and come up to breathe at the surface for 1 to 3 seconds. They can sleep underwater for a few hours at a time but stay beneath the surface for a much shorter period when diving for food or escaping from predators. Although green sea turtles can’t pull their heads inside their shells, the adults have protection from predators due to their shells, their large size, and the thick scaly skin covering their heads and necks.

## Diet

The diet of Green sea turtles changes with age. Juveniles are carnivorous, but as they mature they become omnivorous. Young sea turtles eat fish eggs, mollusks, jellyfish, small invertebrates, worms, sponges, algae, and crustaceans. Most adult sea turtles are strictly herbivorous.

## Reproduction

Green sea turtles are polygynandrous, and some populations have a polyandrous mating system, with one female mating with two or more male turtles. As with many species, males compete for a female. Breeding takes place in March-October, with variation between populations. Females mate usually every 2 to 4 years. The males visit the breeding grounds every year, looking for a mate. After copulation, when ready to lay her eggs, the female crawls ashore after dark. She digs a large pit beyond the high tide line and lays 70-200 eggs in it before returning to the ocean. The young turtles hatch after 6-8 weeks, and, with the help of their flippers, come up to the surface. They hatch at night and instinctively head directly into the water. Juveniles spend 3 to 5 years in the open ocean before they settle as still-immature juveniles into their permanent shallow-water lifestyle. It is speculated that they take 20 to 50 years to reach reproductive maturity.

## Population

### Population threats

The main threats to these turtles include the degradation and loss of habitat, consumption of their eggs and meat, capture as bycatch, pollution, and climate change. Beach armoring, building works, and sand extraction degrades the nesting habitat, while light pollution in the nesting areas fatally attracts hatchlings so that they do not head for the sea. Increased effluent, contamination from coastal development, and over-harvesting of algae all threaten the habitat of the green sea turtle.

### Population number

According to the Sea Turtle Conservancy resource the total population size of nesting Green sea turtles is around 85,000-90,000 individuals. Overall, currently, this species is classified as Endangered (EN) on the IUCN Red List and its numbers today are decreasing.

### Ecological niche

Green sea turtles eat seagrasses and algae, thus serving (much like mowing a lawn) to maintain the seagrass beds in a healthy state, making them more productive. Seagrass eaten by the turtles is quickly digested, becoming available as recycled nutrients for the many species of animals and plants that live in the ecosystem of seagrass. Seagrass beds also act as nurseries for a number of species of fish and invertebrates, many being of considerable value for commercial fisheries and thus important for human food security.

## Fun Facts for Kids

The name of this species refers to the usually green fat found beneath its carapace, not to the color of its carapace, which is olive to black.

Male and female Green sea turtles differ by their development and appearance. As adult turtles, males are easily distinguishable from females by having a longer tail (visibly extending past the shell) and longer claws on the front flippers.

Adult Green sea turtles feed mostly on various species of seagrasses. They bite off the tips of the blades of seagrass, which keeps the grass healthy.

Green sea turtles migrate long distances between feeding sites and nesting sites; some swim more than 2,600 kilometers (1,600 mi) to reach their spawning grounds.

Many islands worldwide are known as Turtle Island due to Green sea turtles nesting on their beaches.

Sea turtles return to the beaches on which they were born to lay their own eggs. Their ability to return to their birthplace is known as natal homing. The males also return to their birthplaces in order to mate.

Since green sea turtles migrate long distances during breeding seasons, they have special adaptive systems in order to navigate. In the open ocean, they navigate using wave directions, sun light, and temperatures. The sea turtles also contain an internal magnetic compass. They can detect magnetic information by using magnetic forces acting on the magnetic crystals in their brains. Through these crystals, they can sense the intensity of Earth's magnetic field and are able to make their way back to their nesting grounds or preferred feeding grounds.

Turtles can rest or sleep underwater for several hours at a time, but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles quickly drown in shrimp trawlers and other fishing gear. During the night while sleeping and to protect themselves from potential predators, the adults wedge themselves under rocks below the surface and under ledges in reefs and coastal rocks. Many green sea turtles like to return to the same sleeping location night after night.