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Marine Iguana

Updated: Nov 10, 2020


A marine iguana about to munch on some algae. Find original here.



Population: No official count but estimated between 200,000-300,000; studies on the islands suggest between 20,300 and 42,300 known individuals


Brief Description

Far off in the Galápagos exists a lizard capable of swimming within the cold currents. The famed marine iguana, Amblyrhynchus cristatus, relies on its unique adaptations to swim and prey on green algae. These lizards may look scary with their dark grey and black scales, not to mention their sharp dorsal scales, but in fact they are herbivores that crave marine algae. They weigh between 0.5 and 1.5 kilogram (1.1-3.3 lbs), depending on which island they inhabit. Males only measure on average 1.3 meters (4.2 feet) while females only measure at 0.6 meters (2.0 feet) on average. Some scientists believe these iguanas' common ancestor came from South America millions of years ago. Others postulate that they diverged from a common ancestor on the former islands in the archipelago at least 10 million years ago.

Similar to the crocodile, the marine iguanas use their long, flattened tail to swim and navigate until they can latch onto a rock with algae. Hooking into the rocks with their sharp and long claws, the iguanas take advantage of their short snouts and extremely sharp teeth to eat the algae. After an hour, they return to shore to rest and to heat up their bodies from the sun's rays as ectotherms. Their black scales provide extra help in absorbing more sunlight and heat to warm themselves to 36°C (98.6°F). To adapt to swimming in salt water, the marine iguanas pertain one of the most efficient salt glands of any reptile, located near their nasal cavities, to excrete (or rather sneeze out) the salt they gained from salt water.

Human intervention through the introduction of foreign species to the islands and, to a lesser extent, oil spills have threatened the fragile ecosystems. Due to invasive species brought by human excursions, the marine iguanas among other animals in the Galápagos face a constant threat from feral species of cats, rats, goats, and even pigs. They coexist with few natural predators like hawks, short-eared owls, and snakes, thus introduced and invasive species can tip the ecosystems to their demise. In addition, rats pose a threat to the eggs as they can dig up the nests of marine iguanas buried 30 to 80 cm deep in sand or volcanic ash. Feral cats can also prey on females searching for nesting grounds as they become more exposed and more vulnerable.

For many animals in the Galápagos, El Niños, a recurring climatic phenomenon of large currents of warm, poor nutrient water to the equator, can spell out disaster as they can kill off marine life including the algae the marine iguanas feed on. Although El Niños can kill as much as 85% of the marine iguanas like the one in 1982-83, they have evolved the ability to reduce its body size by 20% to cope with food shortage according to recent studies. They do so by disposing of calcium from their bones when food is scarce and then, once the algae grow back, add back the calcium to their diet. The marine iguanas are the only animals on Earth to not only reduce its size willingly but regain all the body mass back

Written by — Edward Keenan


Fun Facts

  1. When swimming in the water, the marine iguanas maintain 10 bpm

  2. They are capable of diving down 30 meters (98 feet), but typically restrict themselves to 20 meters (65 feet)

  3. White stuff on their heads is actually salt sneezed onto them by other iguanas

  4. Marine iguanas on Fernandina and Isabela derive the red pigment on their scales from the seaweed they eat in the summer

  5. Like many lizards, they have a light-sensitive gland called the parietal eye or a “third eye” that helps them determine their position relative to the sun and avoid predators that may block the sun


How You Can Help

The Charles Darwin Foundation relies on tourism, support from the Ecuadorian government, and merchandise to fund hard-working scientists trying to preserve the vulnerable animals and delicate environment of the Galapagos. Donate, sign up for a subscription and newsletter, and buy their high-quality merchandise to support their work.

In support of local programs within the Galapagos to maintain its survival, the Galapagos Conservancy directs all funds to them with the hope to preserve all these creatures, including the only lizard capable of swimming. Buy some apparel and adopt a marine iguana to aid the local scientific and preservationist programs on the Galapagos.

By investing in education programs within Ecuador, the Galapagos Conservation Trust spreads news of the beauty and necessity of the Galapagos for the scientific community. Donate to the trust to help young and old minds alike learn about the wonderful animals like the marine iguanas.

Oceana protects marine life like the marine iguanas by ensuring the preservation of our oceans as they have protected over 4.5 million square miles of the oceans. Donate and sign the petition to protect the endangered species like the marine iguanas.

The Terramer Project accumulates international support by endorsing the protection of endangered species at little inconvenience. Friend the marine iguanas to let them know that you're there for them.

Through their efforts, the World Wildlife Fund allocates donations to aid endangered species across the world. Donate to the fund and adopt a marine iguana.


Photos of Marine Iguanas

We had the special privilege of receiving up-close and personal photos of the animals Darwin once described as "hideous-looking" and "most disgusting, clumsy lizards." Thanks to Bishop O'Dowd High School students Layla Kubukeli, class of 2019, for the first 3 photos and Malcolm McClymont, class of 2020, for the last photo!

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