When you think of a turtle, you probably think of those hard-shelled, slow-moving, reptilian relics whose ancestry stretches back hundreds of millions of years. What you probably don’t think of are turtles that can live in cold water and dive down to several thousand feet in the ocean.
In the Great Turtle Race, you are watching leatherbacks making half-mile deep dives and swimming in water so cold that a human in a life jacket would be dead in 15 minutes. So how do they do it?
In 1965 Sherman Bleakney found out that leatherback turtles were often seen by fishermen along the coast of New England and Canada in late summer. A few years later, Wayne Frair and colleagues measured the body temperature of a big leatherback turtle (417 kg- 920 pounds) captured in the Atlantic off Nova Scotia as being significantly warmer than the cold water that the turtle was in. These researchers figured that leatherbacks were doing something special to stay warm, but weren’t sure what it was.
In the late 1980s Frank Paladino and I were sitting around discussing the on-going debate about whether dinosaurs were warm-blooded ‘endotherms’ (like mammals and birds) or cold–blooded ectotherms (like other reptiles). So we wondered about leatherbacks and how they stay warm in cold water? Were they warm-blooded? Fired up to find out, we set off to for Costa Rica to measure the metabolic rate of a leatherback and try to solve the riddle of leatherback physiology. What we didn’t realize at the time was that this trip would lead to a 20-year project to study and protect leatherback turtles. For more on that, check out www.leatherback.org.
To measure leatherback metabolic rates, we used every tool at our disposal in the late 1980s in a remote tropical locale. We collected the breath of a female leatherback on the beach and took the air back to the lab and analyzed the oxygen and carbon dioxide levels in the air, which would tell us her metabolic rates. (Don’t worry, we were very careful and the turtles all went happily back to the sea when we were done.)
After arduous laboratory work and some calculations, we discovered that the turtle did not have a mammal-like metabolic rate. It was a little higher than expected for a big turtle, but definitely was not comparable to metabolic rates of leatherback-sized mammals. We did the experiment on several more turtles and got the same results: leatherbacks were really big reptiles, but not exactly like other ectotherms.
Then, Mike O’Connor performed some mathematical modeling wizardry to show that leatherbacks could stay warm in a cold ocean with a reptilian metabolic rate. The conclusion was that leatherback turtles used the combination of low metabolic rate, large body size (mass), thick insulation and changes in blood flow to stay cool in warm water in the tropics and warm in cold water off Alaska, Chile and Nova Scotia.
IN DEPTH: Get the details on leatherbacks.
What was really exciting about this was the realization that leatherbacks weren’t the only huge reptiles to use this suite of adaptations; dinosaurs probably employed the same mechanisms to range from the tropics to temperate latitudes during their heyday.
With our data and conclusions solid, how could we explain this discovery to people? The math was pretty complicated, and the physiology was complex and unique to large-bodied reptiles like leatherbacks. How could we make the idea stick?
I said we should call it “dinosaurthermy,” but Frank and Mike shot that down. Mike wanted to use accurate physiological jargon, but Frank and I said that was too complicated and not catchy enough. So I said “Godzillathermy!” before realizing that copyright infringement might be a problem…
Then it hit me: “gigantothermy!” We thought that it was catchy and captured the idea, and would make a big splash (so to speak) for our major scientific idea. (Actually, Frank will say that he thought of the term, but he isn’t writing this blog…) We all agreed on “gigantothermy,” our paper was published in Nature, the world’s premier scientific journal, and a new scientific term was born.
So now you know how the leatherbacks in the Great Turtle Race stay warm even while at high latitudes: by being “gigantotherms.” But kids, please don’t try it at home. Unless you’re a half-ton turtle with a love for chilly water…
Dr. James R. Spotila is the Betz Chair Professor of Environmental Science at Drexel University, and is the President of The Leatherback Trust, a U.S.A.- and Costa Rica-based non-profit dedicated to the protection of leatherback turtles and their nesting habitats in Las Baulas National Marine Park in Costa Rica. Jim has studied sea turtles and their terrestrial and freshwater relatives for nearly four decades and is a world-renowned researcher and conservationist.