The marine iguana is native to the Galapagos Islands off the western coast of South America. This iguana species is the only one that swims in the ocean and feeds off aquatic algae. Slow and clumsy on land, the marine iguana is fast and powerful in the water—adult marine iguanas can dive to depths of almost 50 feet (15 meters), though they generally stay nearer to the surface. The male marine iguana, at 4.27 feet (1.3 meters), is usually larger than the female. Adult iguanas are typically, black but can be several other colors, including green and red.
Like most iguanas, marine iguanas are primarily herbivorous, typically feeding on algae that grows on underwater or tidal pool rocks. Unlike other iguanas, which have pointed snouts, marine iguanas have blunted noses that help them get closer to the rocks where their food supply grows. Marine iguanas have long, curved claws that help them cling to the lava rocks while searching for food. They also have a special salt-expelling gland to remove the huge amounts of salt they ingest while feeding underwater. Before and after marine iguanas dive in the cold ocean waters to feed, they typically bask in the sun to raise their body temperature.
Though some species of iguana, like the blue iguana, are rare or critically endangered, the marine iguana population is reported to be over 200,000-strong. This is generally due to the strict Ecuadorian laws protecting this Galapagos reptile. Marine iguanas are considered to be vulnerable, however, due to increasing numbers of non-native species as predators and the periodic destruction of a reported 85% of the marine iguana population by harmful weather conditions.
Land predators of the eggs and young of marine iguanas include snakes, rats, hawks, and wild dogs and cats. While foraging for food in the waters along the Galapagos shoreline, marine iguanas are often susceptible to shark attack. They are also at risk for damage from oil spills.
The greatest threat to the marine iguana is its own environment. The seasonal El Nino weather conditions warm up the water around the Galapagos Islands and reduce the amount of edible algae. During this food scarcity, the marine iguana population typically drops off dramatically due to starvation. This hardy reptile has adapted to deal with this occasional reduction in food by shrinking its body. Consuming its own bones, the marine iguana can wait out famine, and once the food supply becomes viable again, these iguanas usually rebound to their original adult size.