Green sea turtle does not just rely on one kind of diet because the food varies as the turtle grows bigger. The juvenile individuals of the green turtles are essentially carnivores. With time, however, the grown-ups green turtles start eating plants as well. Since the food of the green turtles is not wholesome enough, the rate of growth of these turtles is very slow. Majority of the adult green turtles are herbivores and do not eat meat at all. In fact, they are the only herbivorous sea turtles in the world. The name of this turtle is derived from the greenish-color of its fat. This green color is due in part to the diet of the green turtle which primarily consists of algae and sea grasses.
Generally, the young individuals of the green turtles tend to feed on jellyfish, fish eggs, crabs, sponges, crustaceans, mollusks, algae and small invertebrates. The jaws of these turtles are serrated and so they can easily graze vegetation like algae and sea grasses. They can digest sea grasses fairly quickly that are in turn, available for other living plants and animals as reused nutrients.
References:
Henry, Leigh. “Green Turtle”. World Wildlife Fund
“Green Turtle”. NOAA Fisheries