Galapagos Marine Iguanas

Just about every rocky shoreline in the Galapagos Islands is home to the marine iguana (Amblyrhynchus cristatus), the only sea-going lizard in the world. The marine iguana is an extraordinary animal which lives on land but grazes on a variety of seaweed, either on exposed rocks or by diving into the cold seawater. This habit, totally unique in iguanas, provides them with an abundant food source but can make them vulnerable to predation by sharks and other large fish. They are found nearly throughout the whole archipelago, in coastal concentrations of up to 4,500 individuals per mile. The total population has been estimated at between 200,000 and 300,000.

Behaviour

The marine iguana eats mainly algae, found underwater and in the tidal pools. They have also been known to consume crustaceans and grasshoppers. Its short, blunt nose is adapted for eating algae growing on rocks. Its flattened tail is perfect for swimming. They get rid of the excess salt taken in from the water by a special gland connected to the nostrils. The marine iguana is an excellent example of having adapted to its environment.

When marine iguanas go hungry, they don't just become thinner, they get shorter too. A scientist recently found that in times of El Nino-induced famine, the marine iguanas will shrink in length and then will regrow as food becomes plentiful again. This finding, reported in the scientific journal Nature, is the first of a shrinking adult vertebrae. The adult iguanas can switch between growth and shrinkage repeatedly throughout their lifetime. The researchers postulate that bone absorption accounts for much of the reduction. The iguanas literally digest part of their bones.

In the breeding season, males defend territories on land where they mate with the females, who then lay their eggs in burrows. The iguanas show their colour as they mature - the young are black, while adults range from red and black to black, green, red and grey depending on the island.

Research carried out in 2002 found high mortality of Galapagos marine iguanas on Isla Santa Fe as a result of subtle long-term effects of the 2001 oil spill from the grounded tanker Jessica.