The Marine Iguana, Amblyrhynchus cristatus, is a unique lizard that is capable of living and foraging in the sea. They are found only on the Galapagos Islands, but have spread to all the islands in the archipelago, and they are sometimes referred to as the “Galapagos marine iguana”. It mainly lives on the rocky Galapagos shore, but can also be spotted in marshes and mangrove beaches.
The marine iguana can only spend a limited amount of time in the cold sea, where it dives for algae. However, it swims mostly in shallow areas near the island shore and can dive for up to half an hour at depths up to 50 feet. After these dives they return to the shore and bask in the sun to warm up again. They are vulnerable to predators after diving as they are unable to move quickly when cold. When in this state, instead of running, they become highly aggressive and will bite their attacker.
Marine Iguanas are also known to change their size to adapt to varying food conditions. During El NiÃ±o conditions when the algae that the iguanas feed on suffered a decreased for a period of two years, some were found to decrease their length by as much as 20 percent. When food conditions returned to normal, the iguanas returned to their pre-famine size. It is speculated that the bones of the iguanas actually shorten as a shrinkage of connective tissue could only account for a 10 percent length change.
Breeding-season adult males on the southern islands are the most colorful and will acquire reddish and teal-green colors, while on Santa Cruz they are brick red and black, and on Fernandina they are brick red and dull greenish. Adult males are approximately 50 inches long, females 26 inches long, males weigh up to 53 ounces and females about 25 ounces.