Marine Iguana

Cole B.

Jan 23, 20213 min read

Photo by Benjamint444, licensed use GFDL 1.2 http://www.gnu.org/licenses/old-licenses/fdl-1.2.html via Wikimedia Commons

The marine iguana, Amblyrhynchus cristatus, is the world's single species of diving lizard and found solely on the Galapagos Islands. How did they get there? Scientists suggest that land iguanas from South America drifted out to sea millions of years ago on debris and met land on the Galapagos Islands. The marine iguana species that evolved from them then spread to nearly all the islands of the archipelago, just as they are found today. Each island boasts marine iguanas of sizes, shapes, and colors distinct from those present on the other islands.

Marine iguanas have a tail well-suited for swimming, which is useful as they frequently swim out to sea where they dive in order to eat. Their menu? Exclusively underwater algae and seaweed! Their short, blunt snouts and small but sharp teeth are especially well adapted for scraping algae off rocks.

The larger the individual, the more heat a marine iguana can store in its body; thus, the larger individuals (males) go further out to sea and will grip onto algae-covered rocks keep a hold amidst strong currents while they eat. After hunting, a marine iguana has to bask in the sun to warm its body--it loses a lot of heat in the ocean, and as a reptile, it requires an outside heat source to bring its temperature back up. At night, they often group together to conserve heat. At the start of a new day, they bask in the sun until their scales, mostly black to absorb more heat at a faster rate, have taken in enough heat energy to take the next long and cold swim to sea. When they hit the water, their heartbeat slows to half its regular pace so as to conserve energy and consequently give them as much time as possible to feed.

A marine iguana climbing the cement wall of a building in Santa Cruz Island, Ecuador. They have an excellent claw grip!

Adavyd, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Marine iguanas have an average lifespan of 5-12 years. Predators of the marine iguana include cats, rats, dogs, and pigs, all of which were introduced to the Galapagos Islands from foreign regions. Climate change also threatens their existence. Even their nesting habits are sensitive--sea level and air temperature changes their beach nesting habitats and interfere with the development of marine iguana eggs. El Nino, a seasonal storm pattern in the area, wipes out up to 85% of the marine iguana population each year by removing their food source of algae. Tiny plastic particles from human pollution, also called microplastics, may be significantly adding to the many threats they deal with. Currently, they are considered vulnerable to extinction.

Marine iguana swimming on ocean's surface

David Adam Kess, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Interestingly, while marine iguanas are usually black or grey (these colors absorb heat best), the males change colors during their mating season. Subspecies of the marine iguana--which vary depending on which part of the Galapagos islands they inhabit--make the difference in color. Some turn bright green and red, others red and black, or yet others a dull green and brick red. During mating season, males fight for dominance over a group of females, which they will fiercely defend once won.

Marine iguana in its underwater algae-filled feeding grounds (do you see the sea lion in the background?)

Sodacan, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

You may notice that the noses and heads of these iguanas tends to be more white in color. That is actually due to a layer of salt concentrated on the top of their heads! This salt layer is a result of their adaptation to excrete salt--whenever they munch on algae or seaweed in the ocean, marine iguanas ingest a lot of salt water with their herbivorous meals. To take care of the issue, they have special glands in their nose that filter their blood of the excess salt, which they afterwards sneeze out of their systems! Salt residue then sticks and collects over time, forming the distinctive white layer.