The Green Sea Turtle, Chelonia mydas, is one of the largest hard-shelled sea turtle species, distributed across the world’s temperate, tropical, and subtropical waters. These turtles can reach up to 1.3 meters in length and weigh over 200 kilograms. The name refers not to the shell but to the greenish color of their body fat, which is derived from their diet. While the species’ global conservation status has recently been reclassified as “Least Concern,” many distinct regional subpopulations remain classified as either “Endangered” or “Vulnerable,” reflecting a complex recovery trend.
Life Stages and Habitat Segregation
The Green Sea Turtle life cycle involves a shift in habitat use correlating with four developmental stages. Hatchlings swim to the open ocean, entering the pelagic zone where they spend their “lost years” drifting in oceanic currents. This initial phase lasts several years, during which the small turtles are primarily carnivorous, feeding on small crustaceans and animal matter.
As they mature into juveniles, turtles transition to an omnivorous diet while remaining in the open sea. The sub-adult phase marks an ecological shift, as they leave the pelagic environment and settle in the neritic zone, including shallow coastal waters and protected bays. This move introduces them to their primary adult habitat of dense seagrass meadows and algal beds.
The adult stage is defined by permanent residence in these nearshore benthic habitats, where they complete the dietary shift to herbivory. Sexual maturity is reached late, often between 25 and 35 years of age. This long habitat progression minimizes predation risk during their most vulnerable years.
Specialized Foraging and Diet
The adult Green Sea Turtle is unique among sea turtle species because it is almost exclusively herbivorous, relying on seagrasses and algae for nutrition. Mature adults exhibit a specialized feeding ecology focused entirely on vegetation.
Their feeding behavior is facilitated by a specialized jaw structure featuring a finely serrated lower mandible. This structure acts like a clipping tool, allowing them to efficiently shear through tough seagrass blades and scrape algae from hard substrates. They actively select the newest, most nutrient-rich growth, often feeding at the base of the seagrass blades.
This grazing activity creates a localized “gardening” effect within seagrass beds. Constant trimming stimulates the growth of younger, more protein-rich shoots, helping the turtles maintain a high-quality food source. If seagrass is unavailable, they will forage on a variety of red and green algae species.
Navigational Migration
Adult Green Sea Turtles undertake long-distance migrations, routinely traveling hundreds to thousands of kilometers between coastal foraging grounds and natal nesting beaches. These trans-oceanic journeys require maintaining a straight course across open water. The migration is cyclical, typically occurring every two to five years for reproductive females.
The accuracy of these movements is attributed to the turtle’s ability to sense and interpret the Earth’s magnetic field, a process known as magnetoreception. They possess a magnetic compass to maintain direction and a bicoordinate magnetic map to determine geographic position relative to their destination. Each location has a unique magnetic signature defined by the intensity and inclination of the field lines, which turtles imprint upon as hatchlings.
Experiments suggest magnetic cues are important for large-scale navigation, becoming more pronounced as turtles approach their destination. While they do not strictly require magnetic cues for vast distances, they rely on them significantly when within 50 kilometers of the target beach. The magnetic sense acts as a crucial bridge between oceanic travel and final, close-range pinpointing using local cues.
Reproductive Behavior and Nesting Rituals
Reproduction begins with mating aggregations in the shallow waters offshore of the nesting beaches. Males, who may visit annually, use enlarged claws on their front flippers to grasp the female’s shell during copulation. Females mate every two to five years, while males breed more frequently.
Once fertilized, the female crawls onto the sandy beach, exhibiting high site fidelity by returning to her natal area. She first uses her powerful front flippers to excavate a large body pit above the high-tide line. She then uses her rear flippers to meticulously dig a deep, narrow, flask-shaped egg chamber.
The female deposits multiple clutches of eggs within a single nesting season, averaging three to five clutches with a two-week interval between events. Each clutch contains 75 to 200 soft, spherical eggs. After laying, she uses her hind flippers to cover the egg chamber. Finally, she uses her front flippers to scatter sand widely, camouflaging the nest location before returning to the sea.