The main characteristic of sea turtles is that they are survivors. They have been around for about 100 million years and survived the catastrophe that brought about the extinction of the dinosaurs and numerous other species. Today there are seven species of sea turtles: greens, leatherbacks, loggerheads, hawksbills, flatbacks, Kemp’s ridley and the olive ridley. Six of the seven are members of the family Cheloniidae, while the leatherback is different enough to have its own family, the Dermochelyidae. The chelonid sea turtles all have hard shells while the leatherback has a set of bony plates underneath its leathery skin.
Sea turtles are found world-wide in tropical and subtropical oceans. They may stray into colder waters but breeding occurs only in the tropics. Eggs are laid on land and buried by their mothers. When they hatch, the babies must dig their way out and then race for the sea. Many predators wait for them, including birds, crabs, fish and sharks, so very few babies actually make it to the open ocean. They must then feed and grow for many years before returning to the beach where they were born to begin the cycle again. It is estimated that only one or two hatchlings out of every hundred will survive to breeding age.
Chelonids have strong and heavy, paddle-shaped flippers without ankle joints. The nostrils are level with the surface of the snout. and the head can be withdrawn under the shell. All sea turtles are air breathers and so must surface regularly. They have large lungs and because they are cold-blooded, they can go long periods between breaths if they are not too active. They also have developed a system of anaerobic respiration that allows them to stay submerged for up to three hours. When sea turtles want to float on the surface, they fill their lungs with air and this acts like a buoyancy vest.
Green sea turtles are the only herbivorous sea turtles. The young are carnivorous but the adults feed almost exclusively on sea grasses and algae. They have serrated jaws to help them rip and chew these plants. Hawksbills have narrow heads suitable for getting food out of crevices on coral reefs. They have been observed to eat sponges, crustaceans and squid. Loggerheads and ridley’s turtles have jaws adapted for crushing and grinding and they eat a lot of crustaceans and molluscs as well as jellyfish and some vegetation. Leatherbacks have delicate jaws suitable for eating jellyfish and tunicates.
Adult sea turtles are large, heavy and clumsy on land. In the water though, they are exceedingly graceful and seem to fly through the water with great slow strokes of their paddle-like front flippers. To see one while snorkelling on a reef is such a privilege as is watching them lumber ashore to dig great holes in the sand and lay their eggs and carry on the great cycle of life. For in spite of the fact that they are long term survivors, all seven species of sea turtles are endangered because of human activities. Years of over-hunting, taking of eggs, pollution and habitat destruction have taken their toll on these beautiful animals. The world would be a poorer place without sea turtles. We have a duty to protect them and reverse this terrible destruction.
For more information: http://www.seaturtlefoundation.org/
For a series of photos of mating green turtles go to http://www.helium.com/zone/1614-animal-zone (bottom of the page)