Marine Iguanas

by Todd Metcalfe

Marine Iguanas

While Darwin did not describe Marine Iguanas (Amblyrhynchus cristatus) very favorably (he called them "stupid" and "sluggish"), they are really very fascinating animals. Marine Iguanas are widespread on most of the islands. In general they live in large colonies. Marine iguanas are the only living marine lizards in the world. They have a very muscular and "flat" tail which allows them to be very proficient swimmers.

Aside from being powerful swimmers, marine iguanas are excellent climbers. They are able to scale sheer cliffs, and are often seen even at the tops of cliffs.

Marine Iguanas are very docile. It is possible to walk right up next to them, without their reacting. Like many reptiles they spend most of the day inactive, sunning themselves in order to raise their body temperature. It is necessary for them to raise their body temperature before feeding and other activities. Often one can find marine iguanas "dog piling" on each other, to conserve heat. They especially do this overnight in order to maintain body heat.

Marine iguanas feed on algae that grow on the rocks near the shore, both in the intertidal zones and further out to sea. Adult marine iguanas are capable of making dives for algae that can last for up to one hour. During these dives the marine iguanas lower their heart rate and metabolism, and it is possible for their body temperature to lower by 10 degrees Celsius. Since marine iguanas' body temperature can fall so much, they cannot dive until they have basked in the sun long enough to raise their body temperature. In addition to algae, marine iguanas will feed on their own species feces, and that of sea lions and red crabs.

Salt ducts allow marine iguanas to remove salt from their bodies. They expel the salt by "blowing" it out of their noses. Because of this means of removing salt, their heads often become encrusted with salt.

In general marine iguanas live peacefully with each other. However, during mating season, males will fight with each other to protect their territory, and females will sometimes fight over areas for laying their eggs. During mating season males become more colorful; however they lose that coloration during the rest of the year. On Española, marine iguanas will remain red throughout the year. It is believed that their diet is the main reason for their color. Exactly what factor is different in their diet, compared to other marine iguanas, is not well understood at present, but there is currently research being done aimed at answering this mystery. Click here to see picture of red marine iguana.

One of the few native predators of adult marine iguanas is the Galápagos hawk.

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