How does a marine iguana get rid of extra salt?

It sneezes it out through its nose

It sweats it out through its skin

How does a marine iguana swim?

By swinging its flat tail and body from side to side

By flapping its front legs like flippers

Why does a marine iguana bask on black lava after a swim?

To dry its scales so they don't rot

Who first called marine iguanas 'imps of darkness'?

A visitor whose words were printed in an earlier voyage book

Galápagos Marine Iguana

Amblyrhynchus cristatus

The marine iguana (Amblyrhynchus cristatus) lives only on the Galápagos Islands, on the black lava shores of almost every island. It is the only lizard in the world that finds its food in the sea. Adults graze on red and green seaweed (algae), and the biggest males dive for it. The sea there is cold, so after each trip they warm up again by basking on the rocks. Extra salt from their food comes out through glands in the nose, with a loud sneeze. In El Niño years, when warm water kills off the algae, many starve, and the survivors can actually shrink. Males are much bigger than females, and on islands like Española they turn red and green in the breeding season.

Also known as Sea iguana, Marine Iguana

Marine iguana abilities

≈15 m usual depth for big divers
Big marine iguanas swim out from the shore and dive to the sea floor to graze on algae. No other lizard in the world finds its food in the sea.
- Iguanas heavier than about 1.8 kg dive to around 15 m and stay down for up to 20 minutes. Large adults have been reported diving below 30 m.
- Smaller iguanas mostly stay out of deep water. They graze on rocks that the low tide has uncovered.
- Even so, marine iguanas spend only about 5% of their time at sea. The rest is spent resting and basking on land.
- In a 1965 lab test, iguanas held underwater for 30–50 minutes stayed calm, and their heartbeat slowly got slower.
Sources [1, 2, 5, 11]
red + green algae make up most of its food
A marine iguana presses its blunt face against the rocks and scrapes off the thin red and green algae that grow there. It is a plant-eater that grazes like a cow, but under the sea.
- Its main foods are red and green algae, such as sea lettuce (Ulva).
- Its sharp, pointed teeth scrape the algae off the rock.
- In 1835 Charles Darwin opened the stomachs of several marine iguanas and found nothing but minced seaweed.
- Now and then it eats other things too, such as beach plants, crabs and insects.
Sources [1, 5, 6, 21]
achoo! how the salt comes out of its nose
Seaweed and seawater bring far too much salt into an iguana's body. Glands in the nose pull the salt out of the blood, and the iguana blasts it out with a sneeze.
- After feeding, marine iguanas go back to their resting spots and 'sneeze' out the extra salt.
- The salty spray often lands back on the head, leaving a white crust on the head and snout.
- Darwin noticed that a frightened marine iguana would squirt a drop of fluid from each nostril.
- In 1958, scientists showed that sea-going reptiles, including this iguana, get rid of salt through special glands.
Sources [1, 6, 20, 21]
up to 20% shorter after an El Niño famineStill debated
In El Niño years the sea warms up, the algae die back and marine iguanas go hungry. Instead of only getting thinner, adults can get shorter, and smaller iguanas need less food to stay alive.
- Martin Wikelski and Corinna Thom used 18 years of measurements from two islands. Iguanas shrank by up to 6.8 cm (up to 20% of their length) in two-year spells: 1982–83, 1987–88, 1992–93 and 1997–98, all El Niño years.
- Bigger iguanas shrank the most, and the ones that shrank survived longer. When food came back, the survivors grew longer again.
- Losing soft tissue between the bones could not explain so much shrinking, so the scientists think the bones themselves get shorter. Exactly how is still being studied.
- A 2025 study found that during El Niño, iguanas also used about 20% less energy when resting.
Sources [3, 4, 5]
2× faster at warming up than at cooling down
The Galápagos sea is cold, so an iguana loses heat every time it swims. It warms up again by lying flat on the black lava with its legs spread out, soaking up the sun.
- Marine iguanas bask for the first hours after sunrise and usually go into the sea at about 7:30–8:00 in the morning.
- In a 1965 study, they warmed up about twice as fast as they cooled down, in air and in water. Changes in blood flow and heart rate help them hold on to heat.
- On summer days, their average body temperature ranges from about 27 °C to 35 °C.
- Their dark colour helps them absorb heat faster.
Sources [1, 2, 11, 12]
flat tail shape: a side-to-side paddle
A marine iguana swims like a little crocodile. It presses its legs against its sides and wiggles its body and flat tail from side to side.
- Darwin described it swimming 'with perfect ease and quickness' by a snake-like movement of its body and flattened tail, with its legs held still.
- Near the bottom, it sometimes pulls itself over rough ground with its feet.
- Darwin threw one into a rock pool several times. Each time it swam straight back to the spot where he stood.
- He guessed that the iguana feels safe on land, where it had no enemies, while at sea sharks may catch it.
Sources [1, 6]
up to 45 females that may mate with one top male
In the breeding season, males each defend a small patch of shore. They bob their heads to warn rivals, and if that fails, they push head to head until one gives up.
- A male's display territory measures about 1.2–38.8 m², from about the size of a kitchen table to a large bedroom.
- Fights are head-to-head shoving matches and can sometimes cause serious wounds.
- The largest males win most of the matings, with up to 45 females in a season.
- Choosing is hard work for females too: over 30 days, females ready to mate spent about three-quarters of a whole day's energy just on choosing a mate.
Sources [1, 9]
45% vs 28% went on alert to alarm calls vs normal song
Marine iguanas make no calls of their own, but they listen in on Galápagos mockingbirds. When a mockingbird gives its alarm call, many iguanas raise their heads and watch for danger.
- Galápagos hawks hunt both marine iguanas and mockingbirds, so a mockingbird alarm is useful news for an iguana.
- In 2007, scientists on Santa Fé played recordings to groups of iguanas. About 45% became alert to the alarm call, but only about 28% to a mockingbird's normal song.
- It was the first evidence that an animal without a voice of its own can recognise another species' alarm call.
- Nobody knows yet whether the iguanas learn what the call means or are born knowing it.
Sources [8]

Real marine iguanas

Photos from Wikimedia Commons. Some of them can repaint the 3D model.

An adult on the lava at Las Bachas, Santa Cruz: spiky crest, strong claws and a long flattened tailPhoto: Diego Delso, CC BY-SA 4.0
Feeding underwater off Fernandina, claws hooked into a rock covered in green and red algaePhoto: Sodacan, CC BY-SA 4.0
Swimming near Santa Cruz with only the head and spiky back above the waterPhoto: Adavyd, CC BY-SA 4.0
Two Española iguanas with white crusts of dried salt on their headsPhoto: Gregory "Slobirdr" Smith, CC BY-SA 2.0
Breeding male, EspañolaOn Española and Floreana, top males turn bright red with green or blue legs when breeding. Why is still unknown.Shows off to females and rivalsA red-coloured marine iguana on a beach on Española. Photo: Nicolas Völcker, CC BY-SA 4.0
JuvenileDark grey with a paler stripe down the middle of the back and only a tiny crest.Feeds on rocks uncovered at low tide and hides in cracksA juvenile on Isla Lobos: grey, small and with only a tiny crest. Photo: Diego Delso, CC BY-SA 4.0
Two males shoving head to head at Punta Espinosa, FernandinaPhoto: Andrew Turner from Washington, DC, United States, CC BY 2.0
Close up: knobbly scales on the head and tall spines on the neckPhoto: Andy Morffew from Itchen Abbas, Hampshire, UK, CC BY 2.0
Basking with legs spread on Plaza Sur, while a little lava lizard hunts behindPhoto: Bernard Gagnon, CC BY-SA 4.0
Marine iguanas on the beach at Tortuga Bay, Santa Cruz, beside the mangrovesPhoto: Diego Delso, CC BY-SA 4.0

Marine iguana by the numbers

Measured by scientists in the Galápagos, with comparisons you can picture.

Length: up to 1.33 m; including the tail; males up to 133 cm, females up to 78.5 cm⁠[1]; Biggest males133 cmBiggest females78.5 cm
Weight: 0.9–3.5 kg; heaviest males: 0.9 kg on Genovesa, 3.5 kg on Santa Fé; islands differ up to tenfold; Males are about twice as heavy as females⁠[13]
Dive depth: ≈15 m; usual for big divers; large adults reported below 30 m⁠[1, 5]
Dive time: up to 20 min; for iguanas heavier than about 1.8 kg⁠[1]
El Niño shrinking: up to 20%; of body length (up to 6.8 cm) in two years⁠[3, 4]
Body temperature: 27–35 °C; lowest and highest daily averages in the wild in summer⁠[12]
Eggs per clutch: 1–6; laid in a burrow dug in sand⁠[1, 2]
Time to hatch: 89–120 days; about 3–4 months, with no parent care⁠[1]
Population: 37,000–280,000; estimated total in 2004; up to 8,000 per km of coastline in places⁠[14, 1]
Lifespan: up to ≈30 years; estimated maximum in the wild⁠[1]

Marine iguana myths and facts

Sea dragons, salty heads and shrinking lizards. Here is what the evidence says.

0 of 7 answered

“Charles Darwin invented the name 'imps of darkness'.”
“Marine iguanas go to sea to catch fish.”
“The white stuff on their heads is salt.”
“Marine iguanas spend most of their time in the sea.”
“A grown-up lizard can never get shorter.”
“They shrink because their bones get shorter.”
“Every marine iguana dives to the sea floor.”

The life of a marine iguana

From an egg in a sandy burrow to a big diver on the lava.

Breeding season
Males fight for a patch
The timing varies by island, but it is often around December and January. Males defend small territories with head bobs and head-butting.⁠[1]
About a month after mating
A nest in the sand
The female digs a burrow 30–80 cm deep and lays 1–6 eggs. Some females walk 300 m or more inland to nest.⁠[1, 2]
89–120 days
Eggs on their own
The eggs develop underground with no parent looking after them. Mockingbirds sometimes eat them.⁠[1]
Hatching
Collecting gut helpers
Hatchlings eat the droppings of adults. That gives them the microbes they need to digest algae.⁠[1, 10]
Young iguana
Low-tide grazer
Small iguanas feed on rocks uncovered by the low tide and hide in cracks when danger comes. Galápagos hawks catch many young ones.⁠[1, 8]
Adult
Big enough to dive
Iguanas heavier than about 1.8 kg swim out and dive for algae, often about 15 m down.⁠[1]
El Niño years
Famine and shrinking
Warm water kills off the algae. Up to 90% of some populations may die, and survivors can shrink. In good years that follow, they grow again and females breed younger.⁠[14, 3, 4]
Up to ≈30 years
Old age
The longest a wild marine iguana is thought to live is about 30 years.⁠[1]

Marine iguana vs Galápagos land iguana vs green iguana

Three big iguanas that people mix up. Check the colour, the tail and the food.

Marine iguana vs Galápagos land iguana vs green iguana
	Marine iguana	Galápagos land iguana	Green iguana
Scientific name⁠[1, 24, 25]	Amblyrhynchus cristatus	Conolophus subcristatus	Iguana iguana
Home⁠[1, 24, 25]	Galápagos shores only	Dry inland areas of some Galápagos islands	Mexico to Paraguay and Brazil, and Caribbean islands
Colour⁠[1, 24, 26]	Blackish (some breeding males red and green)	Yellowish	Green, olive, grey or orange
Tail⁠[1, 6, 26]	Flattened like a paddle	Round	Long, with dark bands
Main food⁠[1, 24, 25]	Seaweed (algae)	Cacti, grasses and leaves	Leaves, flowers and fruit
Biggest males⁠[1, 24, 25]	About 1.33 m long	About 1.07 m long	About 2 m long
Eggs per clutch⁠[1, 24, 26]	1–6	8–22	10–70
IUCN status⁠[22, 24, 27]	Vulnerable	Vulnerable	Least Concern

A black iguana sitting on the shore or swimming in the sea is a marine iguana. A yellow one inland is a land iguana. On Plaza Sur the two have occasionally produced hybrids.

Blunt snouts, imps and Godzilla

Where the marine iguana's names come from, and how many kinds there are.

Amblyrhynchus cristatus
Amblyrhynchus comes from Greek words meaning 'blunt snout'. Cristatus is Latin for 'crested', after the spines on its back.⁠[1]
Imps of darkness
An early visitor said they sat on the black lava 'like so many imps of darkness'. Darwin borrowed the phrase in his 1835 diary.⁠[7]
Eleven island forms
A 2017 study kept the marine iguana as one species but split it into 11 subspecies that differ in size, shape, colour and genes.⁠[18, 1]
Godzilla
One of the five new subspecies, from Punta Pitt on San Cristóbal, was named A. c. godzilla.⁠[18]
Cousin of the land iguanas
A 2015 genome study estimated that marine iguanas split from the Galápagos land iguanas about 4.5 million years ago.⁠[30]

Is the marine iguana endangered?

It is listed as Vulnerable. There can be thousands on one stretch of coast, but the species lives nowhere else on Earth.

IUCN Red List

Vulnerable (VU)

Listed as Vulnerable because it lives in such a small area: all its shores add up to less than 500 km². El Niño famines, introduced predators and pollution are its main threats.⁠[22, 1]

IUCN Red List (via GBIF)

Threats

El Niño famines
When warm water kills the algae, 10–90% of a population can die. Stronger or more frequent El Niños could make this worse.⁠[14, 15, 5]
Introduced predators
Cats, dogs, rats and pigs brought by people eat eggs and young iguanas, and dogs also kill adults. Females are at risk when they travel inland to nest.⁠[1, 2]
Oil pollution
After a tanker ran aground in 2001, 62% of the marine iguanas on Santa Fé died within a year, even though only a little oil reached the island. Iguanas on islands the oil did not reach did not decline.⁠[16, 17]
Small, separate populations
Some island populations are tiny and genetically distinct, such as one on north-eastern San Cristóbal. On Marchena, iguanas showed signs of losing genetic variety, possibly because of the 1997–98 El Niño or a 1991 volcanic eruption.⁠[1, 18, 15]

What’s helping

Keep out pets and pests
Cats, dogs and rats are a danger to eggs and young iguanas, so keeping them away from nesting areas helps.⁠[2, 1]
Keep the sea clean
The 2001 spill showed that even small amounts of oil can kill many iguanas, possibly by killing the gut microbes they need to digest algae.⁠[17, 16]

Its closest relative

Galápagos land iguanaVulnerable
The marine iguana's closest relative, with fewer than 10,000 mature adults, threatened by introduced predators.⁠[24]

Marine iguana quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

What do adult marine iguanas mainly eat?

Galápagos Marine Iguana field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

They are vegetarians of the sea, primarily munching on algae scraped from underwater rocks.

Primary Foods

red algae
green algae
seaweed
Foraging Method: Grazing

Ecological connections

Galápagos HawkEaten by
Hunts adults and juveniles.
Lava HeronEaten by
Preys on hatchlings and small juveniles.
Domestic CatEaten by
Introduced predator hunting juveniles.

Safety

Danger 1/5 · Very low

Do not disturb marine iguanas in their natural habitat to keep them safe.

Traits

Collections

Reptiles

Classification

Kingdom: Animalia
Phylum: Chordata
Class: Squamata
Order: Lacertilia
Family: Iguanidae
Genus: Amblyrhynchus

Sources for these marine iguana facts

29 studies and references · checked Oct 29, 2026

Frequently Asked Questions

How to identify Galápagos Marine Iguana?

Compare toes, scales, head shape, crests and tail proportions. Many lizards can drop and regrow their tails, so a short tail isn't always a species trait. Lizard Identifier: upload a photo and compare the visible details.

How long is Galápagos Marine Iguana?

50-130 cm

How much does Galápagos Marine Iguana weigh?

0.5-10 kg

How long does Galápagos Marine Iguana live?

10-20 years

How fast can Galápagos Marine Iguana move?

12 km/h

What does Galápagos Marine Iguana eat?

They are vegetarians of the sea, primarily munching on algae scraped from underwater rocks.

How fast can Galápagos Marine Iguana swim?

15 km/h

Where is Galápagos Marine Iguana usually found?

Coastal areas

Why do marine iguanas sneeze?

To get rid of salt. Eating seaweed brings in lots of salt, so glands in the nose take it out of the blood and the iguana sneezes it out. The spray often dries into a white crust on its head.

Can marine iguanas breathe underwater?

No. They hold their breath. Big iguanas usually stay down for up to about 20 minutes, and their heart slows down while they are underwater.

Do marine iguanas really shrink?

Yes. In El Niño famines, adults shrank by up to 20% of their length, and smaller iguanas were more likely to survive. When food returned, they grew longer again.

What do marine iguanas eat?

Mainly red and green algae (seaweed), grazed from rocks at low tide or on dives. Now and then they also eat other things, such as beach plants, crabs or insects.

Where do marine iguanas live?

Only on the Galápagos Islands of Ecuador, along the rocky coasts, beaches and mangroves of almost every island.

Are marine iguanas dangerous?

No. They eat seaweed, and Darwin noticed that they did not even try to bite when caught. Still, they are wild animals, so watch them from a distance.

Are marine iguanas endangered?

They are listed as Vulnerable. They live nowhere else, and El Niño famines, cats, dogs, rats and oil spills can kill many of them.

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