The Unique Galapagos
Marine Iguana

The Galapagos marine iguana is thought to have drifted to the islands on something like a log or mat of vegetation. Both it and the Galapagos land iguana and both are thought to have evolved from the mainland spiny-tailed iguana of Central America which is also dark skinned. Over time the original arrivals have changed a great deal. Now they are very well adapted to feeding in the sea, a feat that no other lizard manages.

These curious looking creatures have been considered very ugly and there is no doubt that from some angles they are less than pleasant to look at. Though from front on I think they look magnificent, especially the blacker specimens.

These strange looking creatures have several adaptions that make them successful in the water. The have flattened tails like a crocodile that they use to push themselves through the water. Like crocs, the iguanas keep their legs pressed against their sides while swimming to make themselves more streamlined.

They also have longer, sharper claws than other iguanas that help them cling to the rocks when climbing out of the water. These claws also help them hold onto the slippery algae covered rocks when diving for food. Even their razor like teeth seem to be well adapted to scraping algae off rocks.

They have grey to black skin to soak up heat as quickly as possible between dives. That also helps them digest their food, as their gut is more effective when it's operating at a warm temperature. Between the islands there is some difference in size and colour of the iguanas, but not enough to consider them as separate species or subspecies. It is thought that the difference in colour of the males between the islands is due to differences in their diet more so than any genetic variations.

Though their main diet is sea algae, they have also been recorded eating the cactus that is the staple of the land iguana and also some other succulent plants found away from the beach. These changes in diet tend to happen more when their regular food is hard to find.

Since they eat mostly in the sea, the marine iguanas take in a lot of extra salt. They get rid of this through their noses; they have a gland connected to their nasal passage that removes the excess. The salt is snorted out upwards in a spray. This lands mostly on their heads, giving their faces a whitish colour.

Social Creatures

These iguanas are quite social and live in large groups. This only breaks up during the breeding season when the males compete for females, but these confrontations do not result in injury. When the females are laying their eggs they can also be aggressive toward each other as they seek out the best laying sites. Mother iguanas will protect the newly laid eggs for a short period of time, but do not carry this over to looking after their young.

Predation

These creatures have evolved for millennia without any significant predators and so are quite docile. This is not working in their favour at the moment. While this makes them a good tourist attraction, their trusting nature also makes them easy prey for introduced predators such as cats and dogs. Cats eat young iguanas and dogs prey on both the young and the adults. Rats also eat the eggs and in some places very few young reach adulthood. While marine iguana numbers are healthy at the moment, the problem of egg and juvenile predation may endanger these animals in the future.