Featured Creature: Marine Iguana

Photo by Fine Art America

What creature is the only known lizard to go foraging in the ocean, resides off the coast of South America, and is changing the definition of adaptation?

The Marine Iguana!

Photo by Fine Art America

One of a Kind

Marine iguanas are the only lizards that live partly in the ocean. They are endemic (meaning they only exist in one area of the globe) to the Galapagos Islands off the coast of Ecuador. Each island in this area has a subspecies of marine iguanas. Every subspecies has evolved in response to different conditions on each island, so they vary in traits and gene pools. As a species, though, they have unifying characteristics that set them apart from any other reptile.

Photo by Simon Pierce, Galapagos Conservation UK

How do marine iguanas survive underwater?

Marine iguanas have flat tails which allow them to swim effectively. They can dive 20 meters, or 65 feet, underwater! They can also hold their breath for a maximum of 30 minutes. I certainly would not challenge them to a diving competition! 

Marine iguanas love the ocean for one reason: algae. This is their favorite food, and they tend to munch on it as fast as possible before returning to sweet, sweet oxygen. While on land, marine iguanas will often sneeze to get rid of excess salt that has accumulated inside their body during one of their feasts. Even though they stop breathing when underwater, ocean water tends to go up their nose during their dives (if you have ever had water up your nose, you can imagine the feeling).

Photo by Galapagos Conservation

How are these creatures responding to man-made threats?

Introduced Species

Due to the small areas marine iguanas reside in, any threat that occurs on the island directly impacts them, and these threats tend to be difficult to get rid of. Introduced species such as cats, dogs, pigs, and humans pose a threat to the well-being of iguana populations. The germs introduced by these various species are ones that marine iguanas are not adapted to. Some of these animals also tend to attack marine iguana youngsters or eat marine iguana eggs, decimating population numbers.

Climate Change

Many species are being forced to adapt in response to rapidly changing conditions. Marine iguanas are taking this adaptation to the next level. Rather than migrating or adapting to urban areas as some other species do, they are transforming their bodily structure. For an animal with a backbone, this is rare and mostly unheard of. They are not simply losing weight, they are shortening their lengths in response to severe storms and changing conditions near their home in the Pacific. They may shrink by as much as 20%! Smaller bodies use less energy and require less food to stay healthy, so this adaptation technique is a useful one indeed. 

Marine iguanas can shrink and grow multiple times throughout their lifetime. These changes occur in response to changing temperatures which affect what type of algae is available. In general, red and green algae is their favorite, and brown algae is difficult for them to digest. Unfortunately, when temperatures rise, brown algae becomes the most abundant. In response, Marine iguanas shorten their body lengths.

Looks like we have a shapeshifter on our hands!

For the marine in all of us,


Tania graduated from Tufts University with a Master of Science in Animals and Public Policy. Her academic research projects focused on wildlife conservation efforts, and the impacts that human activities have on wild habitats. As a writer and activist, Tania emphasizes the connections between planet, human, and animal health. She loves hiking, snorkeling, and advocating for social justice.