Green Sea Turtle (Chelonia mydas)

ReptileSea turtleMarine

Overview

The green sea turtle (Chelonia mydas) is one of the largest hard-shelled marine turtles and a familiar inhabitant of tropical and subtropical seas. Despite its name, the "green" does not describe the colour of its shell, which is usually brown, olive, or grey with darker markings. Instead, the name refers to the greenish tint of the body fat beneath the shell, a feature historically noted when the animals were harvested. It belongs to the family Cheloniidae, the hard-shelled sea turtles, and is the only living member of the genus Chelonia.

Green sea turtles are best known for an unusual dietary habit among sea turtles: while hatchlings and juveniles tend to be more omnivorous, adults shift to a largely plant-based diet of seagrasses and algae. This makes them one of the few sea turtles that are predominantly herbivorous as adults. Like all sea turtles, they are air-breathing animals that spend almost their entire lives in the water, returning to land only when females come ashore to nest on sandy beaches.

This profile is an educational overview of the species and not a complete range map, identification key, or care guide. Green sea turtles are wild marine animals, and many populations are protected under national and international law. Their conservation status is assessed and monitored over time, so current listings should always be checked against authoritative sources such as the IUCN Red List.

Taxonomy and animal group

The green sea turtle is a reptile in the order Testudines, which contains all turtles and tortoises. It is classified in the family Cheloniidae, the hard-shelled sea turtles, and is the sole living species of the genus Chelonia, with the scientific name Chelonia mydas. Green sea turtles are marine turtles, not freshwater or land turtles; they are specialised for ocean life and are not the same as the leathery-shelled leatherback (Dermochelys coriacea), which belongs to a separate family. All sea turtles are turtles, but not all turtles are tortoises, and tortoises are land-dwelling turtles rather than marine ones. Some populations in the eastern Pacific have at times been treated as a distinct form sometimes called the black sea turtle, though its taxonomic standing is debated and should be checked against current scientific sources rather than assumed.

Appearance and recognition

Adult green sea turtles are large, with a smooth, broadly oval, hard shell (carapace) that may be brown, olive, grey, or marked with darker streaks and blotches; the underside (plastron) is typically paler. The name "green" comes from the colour of the fat beneath the shell rather than the shell itself. The head is relatively small and rounded, and a distinguishing feature is a single pair of scales (prefrontal scales) between the eyes, which helps separate it from some other sea turtles. Like other sea turtles, it has paddle-shaped flippers rather than clawed feet, and it cannot pull its head and limbs into its shell the way many freshwater turtles can. Hatchlings are much darker, often near-black above and pale below, and grow substantially over many years as they mature.

Habitat & Range

Green sea turtles are found in parts of tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans, and the description here is a general overview rather than a complete range map. Different life stages use different habitats: after hatching, young turtles spend time in the open ocean, while older juveniles and adults typically move into shallower coastal waters. Adults are strongly associated with seagrass meadows, algae-covered reefs, lagoons, and bays where their plant food is abundant. They are highly migratory and can travel long distances between feeding grounds and nesting beaches. Nesting takes place on sandy tropical and subtropical beaches, and females often return to nest in the general region where they themselves hatched.

Diet

The green sea turtle is unusual among sea turtles in that adults are largely herbivorous. Hatchlings and small juveniles tend to be more omnivorous, taking a mix of small animals and plant material while living in the open ocean. As they grow and settle into coastal habitats, their diet shifts toward seagrasses and various algae, which become the main part of the adult diet. Their feeding can influence the structure of seagrass meadows, and they are sometimes described as grazers of these underwater pastures. Because the bulk of the adult diet is plant matter, green sea turtles occupy a different ecological role from sea turtles such as the jellyfish-eating leatherback or the sponge-eating hawksbill.

Behavior

Green sea turtles are graceful, powerful swimmers that spend almost their entire lives at sea, surfacing to breathe air and able to rest underwater for extended periods. They are known for long-distance migrations and accurate navigation between feeding areas and nesting beaches, which can be separated by hundreds or thousands of kilometres. They are generally calm and not aggressive toward people, though like all wild animals they are best observed from a respectful distance without disturbance. During the nesting season, females come ashore, usually at night, to dig nests in the sand and lay clutches of eggs before returning to the sea. Adults are mostly solitary at sea but may gather in numbers at productive feeding grounds.

As grazers of seagrass and algae, green sea turtles play a notable role in coastal marine ecosystems. Their feeding can help maintain the health and productivity of seagrass meadows, which in turn provide habitat and nursery grounds for many other marine species. Eggs and hatchlings are an important food source for a range of predators on beaches and in the sea, so the turtles also form part of broader food webs. Their long-distance movements connect distant habitats, linking feeding grounds, migratory corridors, and nesting beaches across ocean basins. Like other sea turtles, hatchling sex in this species can be influenced by the temperature of the sand during incubation, which links their reproduction to environmental conditions on nesting beaches.

Human Interaction & Conservation

Green sea turtles are wild marine animals, and in many places they and their nesting beaches are legally protected. People most often encounter them while swimming, diving, snorkelling, or visiting nesting beaches, where the recommended approach is calm, quiet observation from a distance without touching, feeding, chasing, or crowding the animals, and without disturbing nests or hatchlings. Bright lights and beach activity can disorient nesting females and hatchlings, so following local guidance helps reduce disturbance. If you find an injured, stranded, or entangled turtle, or a disturbed nest, the appropriate step is to contact local wildlife authorities, a marine rescue organisation, or qualified professionals rather than handling the animal yourself. This profile does not provide handling, rescue, or care instructions.

More photos of the green sea turtle