Marine Iguanas are found only on the islands of Galapagos, off the coast off Ecuador. Although not the world's only seagoing lizards - some monitors, such as the Water Monitor Varanus salvator or the Komodo Dragon Varanus komodoensis, will travel fair distances off shore if necessary - they are the only marine lizards to live off the sea, namely by feeding on the algae that grows on the seabed off the islands.
Interestingly, although herbivorous, the sight of these iguanas has been known to invoke fear and dislike in humans. A US captain who stepped ashore the Galapagos in the nineteenth century expected he and his men would be attacked by the reptiles, while Darwin (an innately conservative man) disliked the iguanas and called them "imps of darkness". In fact the marine iguana, like many Galápagos animals, is simply unfazed by humans. The artist Karl Angermeyer, who lived on the islands, lived close to lava reefs that were home to the animals, and the marine iguanas became so used to the presence of the humans that they would wander around and even into his house. Nor were they troubled by the presence of his dog. (It should be noted that Angermeyer's habit of offering them goat meat was probably not a good one, but shows the similarity of the marine iguanas to the green iguana, which is also very adaptable and prone to eat food that really is unsuitable if given an opportunity to do so).
The iguanas spend much of the first part of the day basking to get their body temperature to an optimum level before diving into the rather rough seas for the daily feeding foray. They descend to the seabed for a few minutes of feeding before returning to shore and clambering back onto the rocks to reestablish their body temperature, which will have dropped considerably in the cold waters. Unlike many lizards, Marine Iguanas spend the day in large colonies, resembling in this respect more a large flock of seabirds. In 1964 Carpenter estimated that an area of 20 x 60ft contained on various days from 300 to 500 of these large lizards. However, in some places only a few individuals seem to be present.
The descent for food is interesting and shows the marine iguana's unique adaptations. Although some of the animals will feed from the reefs or tidal pools, many go out into deeper water, swimming up to several hundred metres from shore. Carpenter noted records of marine iguanas descending up to 35ft and staying submerged for over 30 minutes. They swim, like most water-capable lizards, by folding back their limbs and using the tail as a propulsion organ. The water around the Galápagos is cold.
At least one hybrid offspring of a Marine Iguana and a Land Iguana (Conolophus subcristatus) has been reported from the Galapagos. If the two species are descended from a common mainland ancestor this should not be too surprising.
The captive possibilities for Marine Iguanas, certainly outside of large scale zoological facilities, are probably poor to say the least, given their communal nature and highly specialised diet. I believe Brookfield Zoo in Chicago have maintained a colony of marine iguanas until recently, but their website gives no information on this.
Further details on the different subspecies will be added as available.
|Scientific Name||Common Name||Distribution||Size||Notes|
|A. cristatus||Marine Iguana
|Galápagos Islands||Max TL approx 5'
|A. c. cristatus||Narborough|
|A. c. albemarlensis||Albemarle|
|A. c. hassi||Indefatigable|
|A. c. mertensi||James and Chatham|
|A. c. nanus||Tower|
|A. c. sielmanni||Abingdon|
|A. c. venustissimus||Hood/Gardener Island|
"The Marine Iguana of the Galápagos Islands, Its Behavior and Ecology", Charles C Carpenter, Proceedings of the California Academy of Science, Fourth Series, Vol XXXIV, No. 6, pp 329-376, October 21 1966. Useful monograph based on observations of the large populations at Punta Espinosa (Narborough), Punta Suarez (Hood) and in the vicinity of Academy Bay.
"Hybridization between the Galápagos land and marine iguana (Conolophus subcristatus and Amblyrhynchus cristatus) on Plaza Sur", K Rassman, F Trillich and D Tautz, Journal of Zoology, London 1997.
Dr Robert Rothman's page on the Marine Iguana.
Marinebio.org's page on the species.
San Francisco State University's Biogeography page on Amblyrhynchus.
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