The marine iguana is the only lizard species in the world that relies entirely upon the sea for its food. The marine iguana is indeed a very unique lizard. They are, to the casual observer, somewhat similar to other iguanids but other than appearance, everything else about the lizard is entirely unique to the species.
Marine iguanas may be observed in many locations during International Expeditions’ Galapagos cruise , and the males vary a little from one island colony to the next. The colorful red marine iguanas are common on Española Island while those on Fernandina are very black. Marine iguanas took to the sea many millions of years ago and they use the sea as a place for foraging for their favorite food — algae. The marine algae typically adhere to rocks on the ocean floor, and iguanas will dive to the bottom, where they hold onto rocks with their very sharp claws and they graze. Of course in the process, the iguanas also consume large amounts of salt.
Once the iguana returns to shore they take time to bask, elevating body temperature so digestion of food can occur. The lizards also discharge salt which is expelled via sneezing through the nostrils. A note of advice for any photographers getting images of marine iguanas: Exercise caution when approaching a colony! The nasal discharge of salt can be sprayed quite a distance, and it is very unpleasant and difficult to remove from your lens…something I know from experience.
Marine iguanas, when not feeding, spend much of their time in large colonies at prime basking sites. During the breeding season, a male will protect a prime basking site, allowing him to breed with any females at this site. He actually protects the site itself, not a harem of females.
In more recent years, I have observed marine iguanas foraging on terrestrial plants like Salicornia. I don’t know how many lizards are beginning to make a shift in diet or if these are just animals exploring a possible new food source. Nature has a way of evolving quite rapidly in the Galapagos. One of the many reasons that multiple trips are a must for any natural history enthusiast!
Naturalist Greg Greer  is a favorite among IE travelers, and has gained a reputation for his friendliness and good humor, along with his incomparable knowledge of natural history, photos and articles have been widely published in books and magazines, including Georgia Outdoor News, Bird Watcher’s Digest, Alabama Outdoor News, Riversedge and Southern Wildlife.