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Marine Animal Encyclopedia

Marine Iguana Amblyrhynchus cristatus

Restricted to the Galápagos Islands, this primeval-looking reptile is the only lizard that feeds exclusively at sea once it is an adult. The size and weight of this species varies between islands. It has a blunt head with powerful jaws and a distinctive spiky crest that runs down its head, neck, and back. This lizard’s powerful claws help it clamber over rocks, while its tail propels its through water. It feeds on seaweeds and other algae. The young feed above the water, but adults dive to 33 ft (10 m), and can hold their breath for over an hour. During the day, they spend their time feeding and sunbathing to raise their body temperature.

During the breeding season, male marine iguanas engage in lengthy headbutting contests as they compete for mates. Females lay up to six eggs in the sand, and the young emerge after an incubation period of up to three months. Marine iguanas have many natural predators, including sharks and birds of prey, and have been severely affected by introduced animals, such as rats and dogs.

Surviving the cold

Although the Galápagos Islands are on the Equator, they are bathed by the chilly Humboldt Current, which flows northward along the west coast of South America. Being a reptile, the marine iguana cannot generate its own body heat and needs special adaptations for feeding in these conditions. When it dives, its heart rate drops by about half, helping it conserve energy to keep its core temperature higher than the water around it. At night, the iguanas often huddle together to keep themselves warm.

Marine Iguanazoom image
  • Order Squamata
  • Length Up to 5 ft (1.5 m), but often smaller
  • Weight Females 1 lb (500 g); males 3 lb (1.5 kg), sometimes larger
  • Habitat Rocky coasts
  • Distribution Galapagos Islands
Marine Iguana habitat mapzoom image