Galapagos marine iguanas are active during the day and spend the first few hours after sunrise basking in the sun in preparation for activity. The vast majority of individuals in each colony feed almost exclusively on marine algae in the intertidal zones during low tide. Only the largest five percent of individuals dive into the water for food, mostly during the hot midday hours (9). The waters are extremely cold, and cause the iguana to lose heat rapidly when feeding. This forces them to return to the rocks and warm up in the sun again. In fact, an iguana’s size and the way it retains or loses heat determines its method of feeding. Small individuals, which lose heat quickly, forage on rocks at low tide, scraping algae off the surface, and rarely dive into the sea. Larger individuals, however, do not lose as much heat and so they can be active for longer. They graze seaweeds in the shallow water around two to five metres in depth but can dive up to 25 metres down to rocks where there is an abundance of algae, and no competition from other iguanas (5). While feeding they also consume a great deal of salt solution which, in excess, can be toxic. They therefore excrete concentrated salt crystals from a nasal gland by sneezing (4). Activity slows between noon and late evening, and before sunset the iguana retreats into crevices or beneath boulders for the night (2).
This species breeds every year over a three month period, during which the males defend mating territories (4). Individuals breed normally just once every two years (9). Careful not to waste energy, they rely on less energetically expensive bluffs or bites to protect their territory. The nesting months are January through to April depending on the island (5). Females lay between one and six eggs up to 300 meters inland, in sand or volcanic ash burrows that are 30 to 80 centimetres deep. Females often guard the burrows for several days then leave the eggs to finish incubation, which takes approximately 95 days. When the young hatch they look like and act like miniature adults, and have no parental care (7)