They feed almost exclusively on marine algae. Nine species of algae have been identified as food sources. Tylotus ecuadorianus, Bryopsis indica triseriata, Plocamium pacificum, Priontis abbreviata, Glossophore galapagensis, Loposiponia villum, Ptersosiphonia paucicorticata, Blossevillea galapagensis and Gelidium. They are adapted physiologically to living in the coastal areas of the Galapagos Islands. Male iguanas prefer to feed on submerged algae or at greater distance from the shore, whereas females generally forage intertidally.
Most iguanas feed only once a day.
By flattening their bodies again the lava rocks, the lizards expose as much skin surface as possible to the sun. The flow of heat is regulated by vessels in the chest which close and open to regulate body temperature. Martin Wikelski Females reach sexual maturity when 3 to 5 years old. Breeding season begins in December and extends through March. During mating season the male iguana will turn very vibrant colors.