“The black Lava rocks on the beach are frequented by large (2–3 ft [60–90 cm]), disgusting clumsy Lizards. They are as black as the porous rocks over which they crawl & seek their prey from the Sea. I call them ‘imps of darkness’. They assuredly well become the land they inhabit”
Charles Darwin – Beagle Diary
Marine iguanas are found on many of the islands in the Galapagos. There are 7 subspecies.
They vary in size from 60 to 150cm and can be distinguished from land iguanas by their flatter, squarer noses, adapted for feeding on algae, and the thinner, laterally flat tail used for swimming. They are the only marine lizard in the world. The adult male body colour varies according to subspecies but all have a row of long spines from the head, along the neck, back and tail. Females, smaller, have shorter spines and are darker in colour. Marine iguanas are most often seen by the shore but are also found in marshes and mangrove beaches. They are less shy than land iguanas.
They have several adaptations to their marine lifestyle. They use their sharp teeth to scrape algae off rocks and their long claws to cling on to rocks both underwater and on shore. They can spend up to an hour beneath the surface of the water, though 5 to 10 minutes is more usual. They use their strong, flat tails to propel them through the water. On shore they often climb trees and cacti to bask in the sun, warming their bodies after spending time in the cold water. They have special nasal glands that clean their blood of extra salt which they take in when they eat.
They are territorial, especially in the mating season, with the male defending not just his territory but also his females. When angry the male shakes his head rapidly up and down and exhales loudly. Females dig burrows and lay between 1 and 6 eggs, which incubate for up to 120 days. Upon hatching the infants run to the nearest cover. Males take about 8 years to reach full maturity while females become sexually mature between 3 and 5 years.