Marine Iguana subspecies of Santiago (Amblyrhynchus cristatus mertensi).  Photo: Alan Abonyi

Originally described by Darwin as "disgusting clumsy lizards" as well as "imps of darkness", the marine iguana is fascinating creature, unique to the Galápagos and the only lizard adapted to foraging in the sea. On any INCA Galapagos cruise, you'll see a number of marine iguana subspecies on both eastern and western itineraries. 

Fernandina subspecies A. c. cristatus blends easily into the volcanic rock.
Photo: Alan Abonyi

It is believed that the marine iguana diverged from its terrestrial ancestors some 8 million years ago and made its way to the remote island chain by rafting, a biological dispersal mechanism by which organisms move from one land mass to another by the sea. Most commonly, animals are trapped on vegetation washed down rivers and out to sea, where ocean currents can carry animals enormous distances. 

In the case of the marine iguana, 8 million years pre-dates the current existing island chain, which means the marine iguana's original ancestor arrived on islands now long eroded and submerged under the sea.

Brightly colored Española subspecies A. c. venustissimus shares a tidal rock with a Sally Lightfoot crab at Gardner Bay.  Photo: Alan Abonyi

The marine iguana's Latin name, Amblyrhynchus christatus, refers to its physical characteristics of a blunt snout and prominent low crest of spines. Marine iguanas have spread to almost all islands, and over time have evolved into seven distinct subspecies, six of whom may be witnessed on visitor site excursions.

• A. c. albemarlensis - Isabela
• A. c. cristatus - Fernandina
• A. c. hassi - Santa Cruz
• A. c. mertensi - San Cristobal and Santiago
• A. c. nanus - Genovesa 
• A. c. venustissimus - Española

The various subspecies vary both in size and coloration. Largest adult males found on Isabela can tip the scales at 12-13kg, whereas those found on Genovesa barely reach 1-2kg.  Marine iguanas on Fernandina tend to be shades of black and gray and blend into the volcanic rock earning them the affectionate nickname "squishy lava" by our chief naturalist, Richard Polatty.  A far more colorful subspecies is found on Española, where males competing to attract a mate display bright shades of red and green.

Marine iguana swimming back to shore to warm up after feeding at Punta Espinoza, Fernandina.  Photo: Alan Abonyi

Common to all subspecies are a flattened tail for efficient swimming, long powerful claws to cling securely to rocks while grazing algae in surging seas, and special nasal salt glands that enable marine iguanas to expel the excess salt ingested while feeding.  

All marine iguanas are ectothermic. They lack an internal physiological mechanism to regulate their body temperature. Instead, they are solely reliant on their environment. After foraging in the cold waters of the Galápagos, their body cools rapidly and they become sluggish. They must bask in the sun afterwards to bring their body temperature back up. Their predominantly dark coloration aids in heat re-absorption.

The marine iguana's conservation status has been classified as vulnerable.  The Galápagos Islands are the marine iguana's sole habitat. Human encroachment and invasive species are its primary threat.  Conservation efforts include complete protection under Ecuador's laws and listing under CITES Appendix II.  The Ecuadorian Ministry of the Environment, through the Galápagos National Park monitors the health of marine iguana populations throughout the archipelago, especially for the effects of El Niño when elevated sea temperatures affect the availability of their natural food source.

See them on a Galapagos cruise

Enjoy observing marine iguanas first hand on any of the following trips:
Origins of Species - 11 Days aboard the luxury yacht INTEGRITY
Galapagos Safari - 12 Days including 2 nights on Santa Cruz and a 7 night cruise
Ultimate Galapagos - 18 Days encompassing both eastern and western itineraries
Darwin's Isles - 10 Days aboard the deluxe yacht REINA SILVIA
All Galapagos cruises and combinations