Marine Iguanas - Reptiles of the Ocean

Marine iguana
http://en.wikipedia.org/wiki/Marine_iguana

The only marine lizard on Earth lives in the Galapagos Islands and it is called Amblyrhynchus cristatus or the marine iguana. Since there are no marine predators on the islands, they have adapted well to the marine environment around them. They are herbivores and have evolved blunt noses for grazing on seaweed, laterally flattened tails to assist swimming, and powerful limbs and strong claws that help them to cling to rocks. They are grey to black in color but during mating season they sometimes have blotches of green and red on their body. This could possible be a result of eating a particular seaweed that blooms in the summer months. Males are much larger than females but they look similar in appearance.

Color blotches on marine iguana
https://worldwildlife.org/species/marine-iguana

They are active during the day and have to bask in the morning in order to prepare for activity for the rest of the day. Most of the members in the colony feed on the marine algae in the intertidal zones during low tide. Although they can swim only the largest of the individuals in the colony will dive into the water for food and only at midday. This is because the water is very cold and the larger the individual the more they can retain body heat in cold water. They usually graze in shallow water about 2-5 meters down but they can dive up to 25 meters down to rocks where there is an abundance of seaweed and no competition. 

Marine iguana in the water
http://futurepets.files.wordpress.com/2011/12/marine-iguana1

When they feed they consume salt water which can be toxic so they excrete concentrated salt crystals from a nasal gland by sneezing. The excess salt from a crust like layer on their nose.

Marine iguana showing salt crust on nose
http://animals.nationalgeographic.com/animals/reptiles/marine-iguana/

They breed every year but individuals usually breed once every two years. The females lay between 1-6 eggs up to 300 meters inland. they usually guard the burrows for several days and then leave the eggs to incubate. The young hatch and look and act like miniature adults and have no parental care. 

The marine iguana is on most of the islands in the Galapagos and each island shows a little difference on how the iguana looks. The difference could be in size, shape and color. They live in colonies where shallow reefs occur with an extensive intertidal zone and rocky coastline. They are classified as vulnerable and are mostly threatened by non native species such as cats, dogs, and rats which either eat the eggs or kill the adults and juveniles. Interestingly they are very sensitive to environmental fluctuations caused by El Nino. But they are able to recover in years that are not El Nino. The marine iguana is a truly fascinating animal.

Resources: http://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/

http://animals.nationalgeographic.com/animals/reptiles/marine-iguana/

http://www.geo.cornell.edu/geology/GalapagosWWW/MarineIguanas.html