Marine Iguana

The Marine Iguana (Amblyrhynchus cristatus) is a species of iguana that has the unique ability among modern lizards to live and forage in the sea. It is found only on the Galapagos Islands, but has spread to all the islands in the archipelago, and is sometimes called the "Galapagos marine iguana". 

On his visit to the islands, Charles Darwin was revolted by the animals' appearance, writing: 

"The black Lava rocks on the beach are frequented by large (2-3 ft) most disgusting clumsy Lizards. They are as black as the porous rocks over which they crawl & seek their prey from the Sea. Somebody calls them 'imps of darkness'. They assuredly well become the land they inhabit."

In fact, Amblyrhynchus cristatus is not always black; the young have a lighter colored dorsal stripe, and some adult specimens are gray. The reason for the somber tones is that the species must rapidly absorb heat to minimize the period of lethargy after emerging from the water. They feed almost exclusively on marine algae, expelling the excess salt from nasal glands while basking in the sun, and the coating of salt can make their faces appear white. Also, some Española iguanas have blotches of green and red on their scales from the local seaweed. 

Adult males are approximately 1.3 m long; females 0.6 m, males weigh up to 1.5 kg. 

As an ectothermic animal, the marine iguana can spend only a limited time in the cold sea, where it dives for algae. However, by swimming only in the shallow waters around the island they are able to survive single dives of up to half an hour at depths of more than 15 m1. After these dives, they return to their territory to bask in the sun and warm up again. When cold, the iguana is unable to move effectively, making them vulnerable to predation, so they become highly aggressive before heating up (since they are unable to run away they try to bite attackers in this state). During the breeding season, males become highly territorial, but at other times the species is only aggressive when cold. (Predators include hawks, crabs, and cats - but are rare.) 

Researchers theorize that land and marine iguanas evolved from a common ancestor since arriving on the islands from South America, presumably by raft (for example, Rassman et al. 1997, and marinebio.org). It is thought that the ancestral species inhabited a part of the volcanic archipelago that is now submerged. 

This species is completely protected under the laws of Ecuador, and is listed under CITES Appendix II (nearly threatened with extinction). El Niño effects cause periodic declines in population, with at least 85% mortality, and the marine iguana is threatened by predation by exotic species. The total population size is unknown, but is, according to IUCN, at least 50,000.