Among land and water-based reptiles, marine iguanas are quite unique. They spend much of their time on land, and they have evolved into becoming excellent climbers, climbing rocks and cliffs in order to find the areas with the best available sunlight. Like many reptiles, this species of iguana, exclusive to the Galapagos islands in Ecuador, regulates its body temperature by being in the sun. However, the species has also evolved unique behavioral traits that allow it to maximize its body temperature both on land and while foraging for algae underwater.
On land, the marine iguana is able to regulate its temperature by staying in the sun, just like most ectothermic reptiles. This is a necessary activity before diving for food, since their temperature can drop significantly while in the water, and they have to maintain a high enough body temperature to successfully locate food, and be capable of returning to the surface after a dive. Their preferred body temperature is between 35 and 39 °C, and in order to maintain that temperature, their heat conservation activities have evolved accordingly. In order to maintain their body temperatures at a high enough value, they may also “dog pile” on top of each other, especially during the night.
When diving underwater to find the 4-5 species of red algae that their unique metabolism requires, Galapagos marine iguanas have to lower their metabolic rate to a significant extent. The water temperatures they have to cope with during their 1-hour long dives are normally between 11 and 23 °C, so their body temperature can be diminished by more than 10 degrees as a result of underwater heat loss. For that to work, the iguanas have adapted to lower their heart rate and metabolism during dives. After diving, they proceed to restoring their normal vital functions, once they climb back onto the volcanic rocks near the shore.
As a result of their unique heat conservation abilities, marine iguanas can become quite frail and subject to changing water and air temperatures. When the water gets colder, the iguanas are unable to spend as much time diving for algae, which can prevent them from gaining access to their exclusive food source, unless they try foraging during low tide periods. They are also greatly at risk when basking under the sun, as they are unable to move too much at this time. The result of that is they are often left vulnerable to attacks from predators. However, their nature can change from fragile and docile to aggressive when threatened. Marine iguanas can bite and attack predators in self-defense, using sun exposure and their dark shade to their advantage in gaining strength quickly to fight back.