At several visitor sites, you might encounter one of the Galápagos Islands’ most weird and wonderful residents – the marine iguana. Famously, naturalist Charles Darwin called them the “Imps of Darkness.” This was perhaps due to their forbidding appearance and unusual behavior for the lizard family. Yet it is an unfortunate nickname as marine iguanas are harmless to humans unless threatened. Let us find out a bit more about them.
Marine iguanas are usually a black color and on average they are approximately 2.3 feet (0.7 meters long). The largest marine iguanas in the biggest subspecies will reach five feet (1.5 meters) in length. An average marine iguana will weigh between 1 and 3.3 pounds (0.5 and 1.5 kilograms).
While it is possible to easily see that all marine iguanas are part of the same species, the marine iguanas found on each of the islands differs somewhat in color, size and shape. In total there are 11 subspecies. The largest subspecies are found on the western isles, Isabela Island and Fernandina Island. The subspecies that is both the smallest and the darkest in color lives on Genovesa Island.
Marine iguanas have small teeth that are very sharp and mouths that are short and blunt. Their claws are perfectly designed for hanging onto rocks.
One interesting aspect of the marine iguana lifecycle is that those on Espanola Island have been nicknamed the ‘Christmas iguana.’ While black in color most of the year around, during mating season, the males transform into different colors. On Espanola Island, these changes are quite remarkable with males turning a combination of bright red and green. Coincidentally, the breeding season for the marine iguana on Espanola Island runs from December to March, making the name even more perfect for them!
In contrast, mating season on Fernandina Island leads to marine iguanas turning a darker red and green, while on Santa Cruz Island there is no green at all. Here, the males just remain black, with some red coloration emerging.
It is thought that the location of Espanola Island is what has led to the differences in color of the iguanas there. Espanola is a tiny island to the southeast of the Galapagos, making it challenging for others of this species to migrate there, leading to the uniqueness of color of the Espanola Christmas iguana.
Marine iguanas are endemic to the Galapagos Islands so you cannot see them anywhere else in the world. They are found on many islands across the archipelago, including Santa Cruz Island, Floreana Island, Espanola Island, Genovesa Island, Isabela Island and Fernandina Island.
It is believed that both land and marine iguanas originally evolved from the same species of iguanas but that they diverged around 8 million years ago. That original iguana species would very likely have travelled to the Galapagos Islands on logs or other floating items.
A unique feature of marine iguana behavior is that they have developed the capability to forage for food in the sea. They eat the algae they find in the waters, including both red and green algae. This sea-faring activity is believed to be unique among lizards, with no other lizard known to be capable of doing this.
Marine iguanas are perfectly designed to scrape algae from rocks with their sharp teeth. They are also able to grip the rocks with their claws while they are foraging. Their flattened tails provide extra momentum in the water too and they swim gracefully. They can dive to depths of approximately 29 feet (9 meters) in the water. They can stay under the water for up to 10 minutes. As well as algae they may sometimes consume crustaceans, plants and insects such as grasshoppers.
Aside from seeking out food, marine iguanas laze around on the rocks, sunbathing. They do this because the cold water drains their energy, and they need to increase their body temperature after a time in the sea, or to gain the energy to enter the water. The dark color of their bodies helps them to achieve this as efficiently as possible.
Due to the fact that they spend so much time in the ocean, marine iguanas have adapted to deal with the levels of salt that their bodies take on. They have a gland that has evolved such that it can extract the salt from their bodies and then this is ejected through their noses in a sort of sneeze like action. This happens several times a day, so visitors have a good chance of observing them doing it.
Breeding season runs between January and April, but this depends on the specific island. During the mating season, as well as transforming in color, the males will fight to gain control over groups of females. During this time, they can become aggressive with one another and may bite, butt and push each other to retain dominance. Females will lay a few eggs (usually 1-6) in a nest that is usually comprised of sand. The incubation period is 95 days, and the hatchlings are not protected by the parents.
Marine iguanas live on average between five and 12 years, but some have been recorded as living a lot longer than that.
While there may seem to be very healthy sized populations of marine iguanas across the Galapagos archipelago, this species is none the less considered vulnerable. Marine iguanas have faced significant threats as a result of people settling on the islands. This led to an influx of dogs and cats which target the young that are not mature enough to defend themselves effectively. Rats also present a similar threat to marine iguanas. Regular predators include snakes and hawks too.
Another worrisome threat to marine iguanas is the El Nino weather phenomenon. This can have a devastating effect on the species and can, at times, reduce the population by as much as 85%. This is because the food sources for marine iguanas can become very limited during these periods.
When the food source is threatened, marine iguanas shrink in both length and weight. This incredible feat can lead to them being as much as 20% shorter. When they shrink they have a greater chance of survival which is thought to be due to the fact that smaller creatures need less energy to find food. When conditions improve, they can grow again.
In summary, the marine iguana is a fascinating example of a species that has evolved to its environment in extraordinary ways. While not the prettiest creature (except perhaps at Christmas!), they are well worth your time and attention when visiting the islands. Most visitors to the Galapagos Islands will get to see them, whether on a Galapagos Islands cruise or a Galapagos land-based option, so look out for them sunbathing on the rocks.
