Marine iguanas grow up to 1.2m in length. They have a dull snout, heavy body, awkward-looking legs with long toes and a crest running from neck to tail. The laterally flattened tail is used for swimming. Most marine iguanas are black or very dark gray in color, but on Hood Island, in the southern part of the Galapagos archipelago, their bodies are variegated in black, orange and red, and their front legs and crest They are green.
The tales of the oldest visitors to the Galapagos testify to its repellent appearance. One story describes it as having the most horrifying appearance imaginable, and the same author, a captain of the British Royal Navy, reports that: "Because of this disgusting appearance, no one on board was able to use it as food." While marine iguanas enjoy the sun, large red crabs pass and pass over them, pausing from time to time, pinching and pulling on their skin.
Iguanas do not take it for this, and with good reason, as crabs do nothing but remove ticks from their skin. Darwin's finches also do their utmost in the same service. Occasionally, fights take place, but disputes are usually resolved with exhibitions.
A male iguana threatens an intruder by lifting up on sturdy legs and swinging his head with his mouth open to show a red mucous membrane. If this does not cause the intruder to desist, the owner of the territory steps forward and a fight takes place.
The two oppose pushing each other with their bony heads, until one of them gives in and retreats. Outside the breeding season, when they are not busy feeding in the sea, marine iguanas gather in tight groups, sometimes even one above the other.
They lie on the lava expanses, which are a predominant, but not pleasant, feature of the Galapagos. During his stay in the Galapagos, Darwin realized that marine iguanas did not allow themselves to be pushed into the sea.
In fact, they preferred to let themselves be captured rather than enter the sea. And, if thrown into the water, they rushed to the shore clinging to wherever they could. Such behavior is at least surprising for an aquatic animal, since most of the animals that habitually swim, such as seals and turtles, if threatened, seek safety at sea.
When the tide goes out, the marine iguanas take to the water and eat the algae left in the open on the beach and on the reef. They cling to the rocks with their sharp claws, so as not to be swept away by the undertow. They then eat on the rocks by tearing the strands of algae, holding them firmly to the sides of their mouths and wriggling to pull them away.
Every so often, they stop to swallow and rest. When Darwin, with the ship Beagle, visited the Galapagos, he noticed that a sailor was trying to drown an iguana by immersing it with a heavy weight. But, pulled back to the surface an hour later, he realized she was still alive.
Marine iguanas usually eat nothing but seaweed. Unusual exceptions are the marine iguanas residing in Carl Angermeyer's home. He had trained them to rush to his whistle and be fed raw goat meat, rice and oatmeal. Sometimes they even eat the algae that are at the bottom of the sea.