Marine Iguana Fact File


The marine iguana was described by Charles Darwin as as "hideous-looking" and "most disgusting, clumsy lizards,” on his trips to the Galapagos.

Their long body is colored grey and patterned with green or red. The patterning and the colors which make it up is highly variable depending on the island which they call home. Their color comes from pigments in the seaweed they eat. Often their skin has salt encrusted on to it.

They have a blunt snout. Running down the back is a crest of spikes. They have long, hooked claws which help them to grab on to rocks. Their feet are partially webbed to help them when swimming.

The body ends with a long, oar-like tail which is flattened laterally and helps to push them through the water.

An adult marine iguana will measure between 50 and 100cm (20 and 40in) long. Their weight varies between 1 and 11kg (2.25-24lbs). Males can be up to twice as large as the females. The weight of individuals is also variable between islands.

If food is scarce their body weight including the skeleton can reduce by up to 10 percent.

Marine iguana

Scientific Name

Amblyrhynchus cristatus

Conservation Status



1-11kg (2.25-24lbs)


50-100cm (20-40in)


60 years



-- AD --


Marine iguanas are herbivores which feed in the sea. Here they will dive for algae and seaweed. They have hard, horny lips which are used to scrape the algae off rocks. Some populations supplement their diet with plants which have a high salt content.

Due to the toughness of seaweed they have a bulbous fermentation chamber where gut bacteria breaks it down. This is the reason they have such a round body.

They are highly dependent on algae. During extreme El Niño events the algae will deplete and this can cause their populations to reduce.


Marine iguanas are found only on the Galapagos Islands which are located off the coast of South America. They form part of Ecuador.


Marine iguanas are found only on the Galapagos Islands which are located off the coast of South America. They form part of Ecuador.

Marine iguana


Breeding season is highly variable between islands but typically falls between January and April.

Males exhibit a lek system where they form a territory which they defend against other male marine iguanas and display to females. Mating success depends on body size and their performance of the head-bobbing behavior.

Some males may choose not to form a territory and instead they will roam and attempt to force a mating with a female.

After a successful mating the female will dig a burrow in a sandy area in to which she can place 1-6 eggs. She will defend the nest for the first few days but then leaves the nest alone to finish the incubation process. This lasts 3 months.

Marine iguana hatchlings will make their way to the surface and then run to find cover.

A female will normally breed once every second year. In some parts of their range they have hybridized with land iguanas but this is rare.


Marine iguanas are seen sneezing regularly which expels salt from the glands near their nose.

They start their day by basking in the sun where they warm up their body. As an ectotherm their body temperature is affected by the outside environment. While in the water their body temperature can drop as much as 10°C.

Their dark coloration is an adaptation which allows them to warm up faster.

Once they warm up they dive in to the water to feed. Their claws help them to hold on to rocks in strong currents while they feed. They can remain underwater for up to an hour but most marine iguanas only dive for 10 minutes.

Marine iguana

Predators and Threats

Natural predators of the marine iguana include snakes and birds of prey such as owls, herons and hawks. To avoid predators they hide in rock crevices.

Introduced predators such as cats, rats, dogs and pigs will hunt for iguanas.

Humans impact their populations through climate change. This is affecting their ability to regulate their body temperature and impacting egg development. Sea level rises also affect their nesting sites.

In parts of their range the nesting sites are located on popular tourist beaches where the tourists interfere with breeding behaviors. They are also affected by marine debris and pollution.

Increased ship traffic near their habitat has affected them by introducing invasive species and oil spills.

During El Niño events there is an average mortality of 30-50% though this can spike as high as 90% in some regions.

This occurs mainly due to the environmental conditions encouraging the growth of brown algae which can be toxic for the iguanas and suppresses the growth of green algae.

Larger individuals are at a disadvantage during these periods as they need larger amounts of food to sustain them.

Quick facts

Marine iguanas are the only lizards which forage at sea.

Photo Credits


Diego Delso / CC BY-SA (

Middle and Bottom

Under License


Burnie, D., 2011. Animal. 3rd ed. London: DK

Ambrose, J., 2015. Wildlife Of The World. 1st ed. London: Dorling Kindersley.

World Wildlife Fund. 2020. Marine Iguana | Species | WWF. [online] Available at: <> [Accessed 30 August 2020].

Oceana. 2020. Marine Iguana. [online] Available at: <> [Accessed 30 August 2020].

National Geographic. 2020. Marine Iguana. [online] Available at: <> [Accessed 30 August 2020].

MarineBio Conservation Society. 2020. Marine Iguanas ~ Marinebio Conservation Society. [online] Available at: <> [Accessed 30 August 2020].

Santa Cruz Galapagos Cruise. 2020. The Salt-Spitting Galapagos Marine Iguana, Learn More About This Species!. [online] Available at: <> [Accessed 30 August 2020]. 2020. Marine Iguana Facts | Reptiles | Galapagos Wildlife Guide. [online] Available at: <> [Accessed 30 August 2020].

Most Popular Animal this Week

Credit: Under License

Redbubble Store.

Similar Species

Green Iguana
Fijian banded iguana


Copyright The Animal Facts 2023

Share via
Copy link
Powered by Social Snap