Nov 052009
photo provided courtesy of maveric2003 on Flickr Creative CommonsHomeGalapagos Islands
Habitatrocky seashore, coastal waters
Nichelarge herbivores
Favorite Foodalgae
Lengthup to 40 inches
Weightup to 30 pounds
StatusVulnerable to Extinction
Threatsclimate change, pollution

Darwin called them “imps of darkness” when his ship arrived on the shores of the Galapagos in 1832. These were animals that seemed as hardy as they were hideous, not deterred by the worst of what their surroundings had to offer. And mother nature hurls a lot at these only surviving marine lizards of our times.

The marine iguana is one of the most striking animals inhabiting the Galapagos Islands off the coast of Ecuador. It’s a survivor, literally scraping its existence off rocks. To be exact, the jagged rocks that rim the dangerous coast of the Pacific island chain. Yet for thousands of years, these animals have thrived.

One of the biggest problems for marine iguanas comes from the temperature of their surroundings. On the shores of the Galapagos, it’s brutally hot during the day and borderline freezing at night. Not to mention the murderous surf that conceals their food as it churns ice-cold off the rocks they call home. As a reptile whose body temperature depends on the heat or cold of its surroundings, the marine iguana has a lot to contend with just to stay alive.

To brave the extremes in temperature, Marine Iquanas have a number of tactics at their disposal. The first trick helps them in the early morning when they’re sluggish from the night air. They need energy to hunt, and in order to get that energy, they need to get warm. Fast. So, in order to suck up the most sunlight, the near black-skinned iguanas perch themselves on the equally dark rocks with their flanks to the sun. This allows them to soak up the most sunlight possible and enable their hunt for food.

Since their food lives in the frigid waters of the Pacific, the newly warm and energetic iguanas seem ready to undo all their morning hard work by taking the plunge. But the iguanas have a secret weapon against the cold water. Evolution has allowed them to stay warm underwater by shutting off bloodflow to the limbs and extremities, the regions of the body that lose heat the fastest. As they peel green algae off the underwater rocks with their powerful jaws, they do it with a numbness in their limbs and a heartbeat half the rate it pumps on land.

photo provided courtesy of olliethebastard on Flickr Creative CommonsBy the time he’s had his fill, the marine iguana now has to warm himself again on the rocks to stay alive. But by now, the sun has made the black rocks as murderous as asphalt in the dead of July. To avoid burning themselves on the rocks or raising their core temperature too high, marine iguanas now face the sun head-on. This reduces the amount of skin exposed to the harmful rays. And to reduce the overheating underneath on the hot rocks, they raise their bellies off of it, allowing cool ocean breezes to circulate under their bodies.

Finally, as the sun ebbs into the west, the marine iguana now must find shelter from both predators and the shivering cold that is to follow. The horde of marine iguanas makes it way into the shadow of the rocky crevices, where the animals pile close to one another to retain their body heat. Like penguins in the Antarctic, it’s a community formed by necessity.

As a guardian of the Galapagos Islands, the marine iguana is the ultimate story of survival of the fittest. Its very existence reminds us of just how tenacious nature can be.

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