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A Blue View: Galapagos Marine Iguanas

It takes a special kind of creature to earn the nickname “imp of darkness.”

Published May 05, 2015

That’s exactly how Charles Darwin referred to the marine iguana while studying the species for its impressive ability to adapt to its aquatic habitat. 

Found only on the Galapagos Islands, the marine iguana is unlike any other lizard in that it forages in the sea. Eight million years of evolution have left this species with a body built for marine life. A flattened tail propels it through the water as it dives for algae and seaweed; extra-strong limbs and claws allow it to cling to rocks despite crashing waves; and a nose shorter than that of land-dwelling lizards enables it to scrape algae off rocks. 

Marine iguanas are strong swimmers, and the largest 5% can dive as deep as 80 feet in search of snacks. They can remain underwater for nearly an hour, withstanding the sea’s cold temperatures until they’re forced to return to land to warm up in the sun. Smaller individuals lose heat more quickly and therefore stick to foraging on rocks at low tide rather than braving the cold water. 

As Darwin noted, the marine iguana isn’t the prettiest of animals, and some of its behaviors do little to remedy its reputation as a “repulsive” species. Take its sneezing habit, for instance. In order to rid itself of the excess salt in its algae diet—which can be toxic at certain levels—this unusual lizard uses a special gland connected to its nostrils to “sneeze” out concentrated salt crystals. Check out the video below to see this behavior in action!

Episode Transcript

You’ve probably heard of the Galapagos Islands, an archipelago of 19 islands deep in the Pacific Ocean. A UNESCO World Heritage site, the Galapagos are 600 miles off the coast of Ecuador, and a world apart from the rest of the planet.

The volcanic, weathered landscape of these islands provides a rich habitat for some famous animals, including Darwin's finches, marine iguanas and giant saddleback tortoises.

The tortoises made headlines in January 2015 when it was discovered that at least 10 saddleback babies had hatched on Pinzon Island. That hadn't happened in 150 years.

It was a major win for a species whose numbers had been decimated in the 17th and 18th centuries by whalers who hunted tortoise for food, and by the introduction of invasive species—rats, dogs and even fire ants—that ate the tortoise eggs and the defenseless hatchlings by the thousands.

Galapagos giant tortoises are called "charismatic megafauna," animals that people relate to easily for their fetching looks and adorable behaviors.

There’s another notable native of the Galapagos archipelago that doesn’t quiet make that grade. In fact, Darwin himself called it "hideous" and "disgustingly clumsy."

It's the marine iguana, a reptile with a fierce, pug-like face covered with nobs of salt expressed from its nasal glands. With sharp, dorsal spikes that might seem more at home on a dragon, the marine iguana is not particularly soulful-looking; but it is a fascinating species, especially to island biogeographers, those scientists who study how and when species arrive and thrive on islands, and also how such isolation from the mainland mothership changes them over time.

Scientists theorize that millions of years ago, land-dwelling iguanas drifted out to sea on flotsam to populate the Galapagos, making them the first and only reptilian swashbuckler.

Each island hosts a population of iguanas unique in size, color and shape. As juveniles, marine iguanas are uniformly black; but as adults, they range in color from red to brown to gray. The island of Espanola hosts a bright red and green variety; the red pigment comes from the particular algae the iguanas eat.

The iguanas grow to 4 feet or more. Half their length is their flattened tail, which is both their rudder and propeller in the water. As swimmers, they are fast, adaptable and strong in the rough waters around the islands. They dive as deep as 50 feet to forage for algae, scraping it off the jagged volcanic rocks with their sharp claws and even sharper teeth. These resilient reptiles are capable of making dives that last over an hour.

Not content with just their aquatic biome, the iguanas are also excellent climbers. Just like land lizards, they are ectotherms, meaning they get their heat from outside their bodies. Since they graze in cold water, losing up to 50 degrees of body heat, they have to recover their body temperature by spending hours in the sun. So they climb the steep, rocky shores to bask in large, docile groups called colonies.

This thermo-regulatory behavior makes them especially vulnerable to introduced species. Dogs and feral cats threaten even adult iguanas whose only natural predator on the islands is the Galapagos hawk.

One of the iguanas' prime nesting sites is near a popular tourist beach on Isabela Island. In 2012, the Galapagos National Park System protected the entire area. Luckily, in contrast to Charles Darwin, many people today find the marine iguana awesome and want to take a peek at this living dinosaur that was rescued from the brink of extinction.

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