Quick Answer
- Scientific name: Amblyrhynchus cristatus.
- Where: found only in the Galápagos Islands of Ecuador, on rocky shores.
- Unique trait: the only lizard in the world that forages in the sea, eating algae from rocks along the shore and underwater.
- Superpowers: sneezes out excess salt, dives for many minutes at a time and can shrink in body size when food is scarce.
- Status: listed as Vulnerable by the IUCN; El Niño events and introduced predators are major threats.
What Is a Marine Iguana?
The marine iguana is a dark, stocky iguana that lives along the coasts of the Galápagos Islands. When Charles Darwin visited in 1835, he famously described them as "imps of darkness." Today they are one of the most iconic animals of the islands. Thousands can pile together on black lava rocks to warm up after time in the cold sea.
Marine iguanas are related to the Galápagos land iguanas. Their ancestors likely reached the islands from South America by rafting on floating vegetation, and over millions of years they adapted to a life that depends on the ocean.
Marine Iguana at a Glance
| Trait | Details |
|---|---|
| Scientific name | Amblyrhynchus cristatus |
| Range | Galápagos Islands only |
| Size | Varies greatly by island; large males can reach roughly 4–4.5 ft including the tail, while some island forms are much smaller |
| Diet | Red and green marine algae |
| Eggs | Usually 1–6 eggs, laid in sandy burrows |
| Population | Commonly estimated at roughly 200,000–300,000 |
| IUCN status | Vulnerable |
How Marine Iguanas Feed in the Sea
Marine iguanas eat almost nothing but algae. Smaller iguanas usually graze on rocks exposed at low tide, while larger adults swim out and dive to feed on algae growing underwater. They swim by sweeping their flattened tails from side to side and grip rocks with long, sharp claws so the waves do not wash them away. Their short, blunt snouts help them scrape algae off rocks.
Most dives are short and shallow, but sources report that marine iguanas can stay underwater for up to around 30 minutes or more and occasionally dive to depths of around 100 feet (30 meters). The cold Galápagos waters chill them quickly, so they return to shore to bask.
Why Marine Iguanas Sneeze Salt
Feeding in the ocean means swallowing a lot of salt. Marine iguanas have special salt glands above the nose that filter salt from the blood. They then forcefully "sneeze" it out. That is why many marine iguanas have white, crusty salt on their heads.
Why Are Marine Iguanas Black?
Their dark coloring helps them absorb heat from the sun after cold dives. In the breeding season, adult males of some island populations develop striking red and green colors. Those on Española Island are sometimes nicknamed "Christmas iguanas." Learn more about color variation in our iguana colors guide.
The Shrinking Iguana
During El Niño years, warm water causes the algae marine iguanas eat to die back, and many iguanas starve. Sources report that severe events can kill a large share of a population in a single year. Researchers have also found that marine iguanas can shrink in body length during these food shortages, partly by reabsorbing bone, then grow again when food returns. This ability is rare among vertebrates.
Breeding and Life Cycle
In the breeding season, males defend small territories and display by head bobbing. Females dig nests in sand or volcanic ash and usually lay one to six eggs. Hatchlings must avoid predators such as hawks, herons, snakes and introduced cats and rats. Reported lifespans in the wild are often in the range of about 5 to 12 years, though some individuals live longer.
Threats and Conservation
- El Niño and climate change: warming seas reduce the algae marine iguanas depend on.
- Introduced predators: cats, dogs and rats eat eggs and young iguanas.
- Pollution: oil spills and plastics threaten coastal habitat.
The Galápagos Marine Reserve and Galápagos National Park protect much of their habitat. Visitors can see them easily on many islands, but should keep their distance and follow park rules.
Marine Iguana vs. Green Iguana
| Feature | Marine iguana | Green iguana |
|---|---|---|
| Habitat | Rocky coasts, Galápagos only | Tropical forests and waterways, mainland Americas and Caribbean |
| Diet | Marine algae | Leaves, flowers and fruit |
| Color | Mostly black or gray; red and green in breeding males | Green, gray, brown; orange in breeding males |
| Snout | Short and blunt | Longer and more pointed |
| Kept as pets? | No; protected and found only in the Galápagos | Yes, widely |
Marine iguanas are not kept as pets. They are protected, and their specialized diet and habitat cannot be recreated in a home. Read about their neighbors in our Galápagos land iguana guide.
Frequently Asked Questions
Where Do Marine Iguanas Live?
Only in the Galápagos Islands of Ecuador, along rocky shorelines.
What Do Marine Iguanas Eat?
Almost entirely marine algae, which they graze from rocks at low tide or dive underwater to reach.
How Long Can a Marine Iguana Stay Underwater?
Most dives are short, but sources report they can stay underwater for up to around 30 minutes or more.
Are Marine Iguanas Dangerous?
No. They are herbivores and generally tolerate visitors at a distance. Like all wildlife in the Galápagos, they should not be touched.
Are Marine Iguanas Endangered?
They are listed as Vulnerable by the IUCN, threatened mainly by El Niño events, climate change and introduced predators.
Sources: San Francisco Zoo, Galápagos Marine Iguana; BBC Wildlife (Discover Wildlife), Facts About Marine Iguanas; Cousteau Society, Marine Iguana; Wikelski and Thom, "Marine Iguanas Shrink to Survive El Niño," Nature (2000).
