The Robinson Library
The Robinson Library >> Science >> Zoology >> Reptiles and Amphibians >> Suborder Sauria
Marine Iguana

Amblyrhynchus cristatus; the only marine lizard in the world


Marine iguanas are generally gray to black in color, but males may develop blotches of coppery green and red during the mating season. The extent and vibrancy of those colors varies from island to island. Juveniles usually have a light-colored dorsal stripe. A nasal gland filters its blood for excess salt ingested while eating, which is expelled through the nostrils, often leaving white patches of salt on its face.

Built for marine life, the marine iguana lacks agility on land but is a graceful swimmer. Its laterally flattened tail and spiky dorsal fins aid in propulsion, while its long, sharp claws allow it to hold onto rocks in strong currents.

Marine iguanas vary in body size, which is different depending on the island the individual iguana inhabits. The largest reach a length of about 3 feet and weight of about 3 pounds. Males are up to 70 percent larger than females.

Marine Iguana

Distribution and Habitat

Marine iguanas are only found on the Galapagos Islands. They are most commonly found on rocky shores, but have been seen in marshes and on mangrove beaches. Each individual island has its own subspecies, with size being the most conspicuous difference between each subspecies.

marine iguana swimming


Marine iguanas feed almost exclusively on marine algae. During high low tides, green algae, which is usually avoided, is eaten more often since the usual red algae is not available. Usually, however, the 4-5 red algal species are the food of choice for marine iguanas.

Larger members of the species feed more often by diving at high tide, while smaller animals are restricted to intertidal feeding at low tide. Average dive depth is 5 to 15 feet, but dives of 50 feet have been recorded. Since the waters around the Galapagos Island are usually relatively cold, most dives only last a few minutes, but marine iguanas have been observed staying submerged for more than half an hour when the water is warm.


Breeding season runs from December into March. Males are selected by females on the basis of their body size, with larger males being preferred. Mating territories are established and defended by males.

About a month after mating, the female lays 1-6 eggs in a burrow dug 12-32 inches deep into sand or volcanic ash up to 1,000 feet inland. She guards the burrow for several days before leaving the eggs to finish incubation, which takes about 95 days. Hatchlings are on their own from the beginning, and usually scramble for cover imediately after leaving the burrow.

Females reach sexual maturity at 3-5 years, males at 6-8 years. Average lifespan in the wild has not been recorded.

Other Behaviors and Habits

The marine iguana regulates its body temperature by alternating from cold ocean water to basking on rocks near shore. It is active during the day and spends the first few hours after sunrise basking in the sun in preparation for activity. When their body temperature is low, these animals move more sluggishly and are therefore at greater risk of predators. To counter this vulnerability, the marine iguana displays a highly aggressive behavior to bluff its way to escape.

Conservation Status

The Marine Iguana is currently labeled as vulnerable in its conservation status. Since the Galapagos Islands do not naturally have many predators, the animals that live there never developed the defenses needed to help protect them against new enemies. This lack of development makes them more vulnerable to attack and becoming ill due to new bacteria as these islands attract more and more people and animals from different parts of the world.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Reptilia
order Squamata
suborder Sauria
family Iguanidae
genus & species Amblyrhynchus cristatus

Animal Diversity Web

Questions or comments about this page?

The Robinson Library >> Science >> Zoology >> Reptiles and Amphibians >> Suborder Sauria

This page was last updated on February 01, 2018.