How Sea Turtles Have Adapted to Ocean Living
Learn About Their Streamlined Bodies and Survival Skills
Jul 31, 2009
Because turtles that live in the sea face challenges that are very different from terrestrial turtles, they have adaptations that allow them to swim, breathe, and find their way during long dives or lengthy swims across the ocean.
Types of Sea Turtles
It is commonly accepted that there are seven species of sea turtles: the leatherback (Dermochelys coriacea); the green turtle (Chelonia mydas); the loggerhead (Caretta caretta); the hawksbill (Eretmochelys imbricata); the flatback (Natator depressus); the Atlantic ridley (Lepidochelys kempii), also known as Kemp’s ridley; and the Pacific ridley (Lepidochelys olivacea), also known as the Olive Ridley.
An eighth type of sea turtle—the Pacific green turtle (Chelonia agassizii) —has been debated to be a distinct type with its own traits, possibly a developing species. This small turtle actually looks black or dark gray due to a variation in pigmentation so it is often called the black turtle. While its genetics have not shown obvious variance from other green turtles, some argue these turtles are an isolated, unique population.
The Unique Physical Characteristics of Sea Turtles
There are five main physical traits common to all these sea turtles that enable them to swim and navigate efficiently in the deep and vast ocean areas:
- A flattened, tapered shell. A sea turtle’s shell—or in the case of the leatherback, the shape of the skeleton beneath thick, rubbery skin—varies from teardrop- or heart-shaped, to circular or barrel-like. But all share the attribute of relative flatness and a tapered back end, compared to terrestrial turtles. A hydrodynamic body that moves smoothly through the water enables a sea turtle to swim more efficiently.
- Wing-like front flippers. Like whales and other vertebrates, a sea turtle’s front flippers have hand- and finger-like bones that support muscles that enable the turtle to swim with powerful strokes. The front flippers are wing-like and broad, with tapered, sharp tips that trace a figure-eight stroke in the water. While the size of the flippers vary among species, in shape or proportion to the body, their function is the same. The leatherback is the only sea turtle whose flippers do not have claws.
- Broad rear flippers. Similarly, the rear flippers on a sea turtle aid swimming by acting as a rudder. They are shorter than the front flippers, but their flatness enables the turtle to use them for steering, the bones in the flipper allowing for precision movements. The dexterity of the rear flippers is also an attribute that allows the female turtle to dig a perfect hole in the sand to lay her eggs.
- Efficient use of oxygen. The sea turtle relies on surface breaths for oxygen and holds this air while submerged. After diving, the turtle’s metabolism slows way down to conserve the stored oxygen, and its activity diminishes. The turtle purposely allows its lungs to collapse from the pressure of the water around it, and any additional oxygen needed is drawn from the turtle’s blood and tissues. At the same time, the sea turtle can tolerate elevated levels of carbon dioxide and lactic acid that accumulate during submersion. With this efficient use of oxygen, the turtle can find all the food it needs and spend time hiding from predators without having to surface repeatedly for air.
- Highly developed hearing, and olfactory and magnetic senses. A sea turtle’s ability to hear low-frequency sounds, some below the human range of hearing, together with its ability to take in water or air through its beak to detect subtle odors, helps the turtle orient itself while out to sea. Additionally, the sea turtle’s highly developed geomagnetic skill enables it to precisely orient itself relative to Earth’s magnetic field. Learn more about this in the article “Geomagnetic Navigation in Sea Turtles: How These Reptiles Use Earth’s Magnetic Field to Find Their Way.”
Unique Adaptations of Sea Turtles Don’t Guarantee Their Survival
While all the aforementioned sea turtle species have the physical characteristics and specialized senses that protect them in their habitat and from predators, their future survival is not guaranteed. Because of man's activities, all of these types of sea turtles are currently considered endangered or critically endangered, with the Flatback turtle solely dependent on the nation of Australia for its protection. Learn more about sea turtle conservation at the website of the NOAA Fisheries Office of Protective Resources.
Sources:
- “Sea Turtle.” The New Encyclopedia Britannica, 15th ed., Vol. 10. Chicago: Encyclopedia Britannica, Inc., 2007.
- Witherington, Blair. Sea Turtles: An Extraordinary Natural History of Some Uncommon Turtles. Saint Paul: Voyageur Press, 2006.
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