Marine iguanas are the only lizards on Earth that spend time in the ocean. They live only on the Galapagos Islands, and like many Galapagos species, they have adapted to an island lifestyle. Populations across the archipelago have been isolated from each other for so long that each island has its own subspecies.
Marine iguanas are most noted for their ability to feed in shallow, marine waters. They are herbivores and eat marine algae growing along rocky shores and underwater. In the water, they swim with a snake-like motion and hold themselves against the bottom with their long claws in order to graze. Though they feed in the water, marine iguanas are predominately terrestrial. They are often observed warming themselves in the sun, and they nest along the shore.
Marine iguanas are also known for their very efficient salt glands, where they “sneeze” out salt. Because they feed underwater, they ingest a large amount of saltwater. In order to prevent dehydration, they must expel salt without expelling water, so they have specialized glands that remove salt from their blood. They also have the incredible ability to shrink (in length and in overall size). In times of reduced food availability – particularly during El Niño climate events – they may shrink by as much as 20%. The now smaller individuals require less food. Once their preferred algae return to high levels, they quickly regain the lost size.
As a result of their very small geographic area, marine iguanas are thought to be vulnerable to extinction. They have complete legal protection in the Galapagos Islands, but invasive species continue to threaten subspecies on some islands. Cats, dogs, pigs, germs, and other species brought to the islands by humans attack marine iguana eggs and juveniles. It is very difficult to eradicate invasive species from islands, so this problem is likely to continue to threaten marine iguana populations.
Check out KELP (Kids Environmental Lesson Plans) for free marine science activities for children.