Six of the seven species of sea turtles in the world are found on the Great Barrier Reef: Green, Leatherback, Hawksbill, Loggerhead, Flatback and Olive Ridley. Sea turtles lay their eggs in sand. The temperature of the sand determines the sex of the young turtles. Cooler sand produces male turtles, while warmer sand produces females. Sea turtles can lay up to 100 eggs at a time. They become sexually mature at 30-50 years and can live for up to 100 years.