The Marine Iguana (Amblyrhynchus cristatus) evolved from a mainland ancestor who arrived on the islands millions of years ago. On first glance of a Marine Iguana, your first thoughts would probably be of a primitive dinosaur, with its dorsal crest and primitive features.
The Marine Iguana appears slow and clumsy on land, but this particular species of lizard is the only sea-going lizard in the world. However, like all reptiles (except some sea snakes), it has to return the the land to breed. The Marine Iguana is well adapted to life in the ocean – it swims gracefully with sinuous movements of its long tail which is powerful enough to act as a propeller, propelling the lizard through pounding waves. It is in most cases, only the males that wade through strong waves to get to places where there is enough food to feed them. Females and young Iguanas tend to feed on the shore and rarely venture into the ocean.
Marine Iguanas are found throughout the Galapagos Islands, but nowhere else in the world, which makes them yet another endemic creature of the Galapagos Isles.
The largest populations and the largest individuals, are found in the western islands of the archipelago. Here the water is coldest and optimal for the species of seaweed the iguanas feed upon.
The general appearance of the Marine Iguana, as afore-mentioned, is very primitive looking. They grow to be 2 – 3 feet long, with long whippy tails which they use for swimming. Marine Iguanas are black or dark grey in colour which matches the colour of the lava rock on which they like to bask in the sun. Like all reptiles, they are cold-bloodied (proper name ‘ectothermic’), so they lay in the sun to warm themselves up and when they get too hot, they move into the shade to cool down. Marine Iguanas warm themselves up on the rocks after a long swim in the ocean, feeding on seaweed. They tend to need a few hours basking in the sun to warm up.
Unfortunately, the reference to the word ‘cold-bloodied’ is quite incorrect. Their blood is not actually cold. Like all reptiles, they are ‘ectothermic’ which means that Iguanas cannot internally regulate their body temperature like birds and mammals. Marine Iguanas have to rely on the external environment, thereby, warming up in the sun and cooling down in the shade.
When they get cold, Marine Iguanas move around slowly until the sun warms them up enough to swim for feeding. When they get too hot, they will cover each other for shade. At night, they gather in large numbers to conserve body heat.
Marine Iguanas feed exclusively on a few species of green or red algae (seaweed). The algae grows less that half an inch from the surface of rocks. The Iguanas mouth is a rounded shape so that they can crop the plant more easily. The males will venture into the ocean to found other food while the females and young eat the algae on the rocks ashore.
Males can stay down in the ocean for a very long time. Their daily feeding times depend greatly on the tide and water temperatures – females and the young will feed at low-tide regardless of what time of day it is. Males will wait until midday when they have warmed up enough in the sun to enter the ocean.
Despite their tropical location, the sea waters around the Galapagos Islands are very cold and the male Marine Iguana can lose 10 degrees centigrade of body heat during a dive into the waters. The same amount of body heat loss in a human could be fatal. For the Marine Iguana – it just returns to the shore and basks in the hot sun to regain its warmth.
There is no known record of underwater predators to the Marine Iguana apart from maybe the odd shark. Young sea-lions love to hassle the swimming Iguanas and pull their tails, only to be studiousy ignored.
During the Marine Iguana breeding season, the males develop reddish patches which vary from island to island. On one particular island – Hood Island – the male will turn almost completely red. The male Marine Iguanas fiercely butt heads to determine superiority – sometimes getting rather violent. Breeding season varies from island to island.
The female Marine Iguana will dig burrows on the shore in the soft sand, and lay between 1 and 4 eggs. The eggs are incubated for up to 4 months. When the eggs hatch, the infant Marine Iguanas are about 3 – 4 inches long and being so small, become vulnerable to predators such as Hawks, Owls, Herons and Mockingbirds. When they are fully grown, the only predator on land is the Galapagos Hawk.