Iguanas are reptiles belonging to the Iguanidae family. There are at least 8 genera and 35 different species of iguana, and the marine iguana goes by the genus and species Amblyrhynchus cristatus. Marine iguanas are believed to have evolved from land iguanas nearly 4.5 million years ago. There are at least six similar subspecies of marine iguana, and the marine iguana is the only lizard in the world that lives and forages at sea. They are endemic only to the Galapagos Archipelago. While less agile on land, these herbivores are excellent swimmers who consume algae for their diet. They can dive as deep as 20 meters underwater. They are large lizards that grow up to 4 to 5 feet long and can weigh up to 3.3 lbs. They have a wide-set of eyes and smashed-in faces. Their dorsal scales are spiky, and their heads are knotty and salt-encrusted. The adults are black most of the year, but the males will change color during the mating season. Brightness and color variation differs between subspecies. These iguanas live anywhere between 5-12 years.
They are awake during the day and spend a lot of times on the rocks. Younger lizards will feed on the algae off of rocks during low-tide. In the morning, marine iguanas bask in the sun so they have enough energy to swim and forage at sea later if strong enough. They are also social enough that these lizards will group together to keep themselves warm. When swimming, their heartbeat slows to half their normal pace to conserve more energy and feed longer. They only feed for a few minutes, but more energy allows them to stay submerged up to 30 minutes underwater. Consuming marine algae also means there’s a high concentration of salt in the marine iguana’s diet. To compensate, these lizards will filter blood at their nose and sneeze out the excess salt. This is how visible salt crystals form on their snout.
The marine iguana is listed as a vulnerable species. Their eggs and young are devoured by non-native species such as rats, feral cats and dogs. These species were introduced by humans, and the iguanas are not adapted to defending themselves against them. Usually protected by the archipelago, El Niño periodically wipes out the food supply of the iguanas. The iguanas can actually shrink their size by 20% during this time so they require less food, returning to normal size once algae levels are restored. Oil spills and marine plastic pollution also cause problems for this swimming species. Throughout the entire Archipelago, marine iguanas are protected under Ecuadorian law and are listed under CITES Appendix II. Plastic cleanup efforts and research on population dynamics are ongoing.