Galápagos marine iguana, Galapagos Marine iguana, Fernandina Marine iguana, Sea iguana, Saltwater iguana
The Marine iguana (Amblyrhynchus cristatus) is a species of iguana found only on the Galápagos Islands (Ecuador). Unique among modern lizards, it is a marine reptile that has the ability to forage in the sea for algae, which makes up almost all of its diet. Marine iguanas are the only extant lizard that spends time in a marine environment. Large males are able to dive to find this food source, while females and smaller males feed during low tide in the intertidal zone.
Marine iguanas are usually black or gray but during the breeding period, adult males gain green and red coloration. The dark skin pigment helps in shielding the animals from ultraviolet rays and also helps to warm their bodies. Young iguanas have a dorsal stripe of a lighter color. Their dorsal scales are triangular in shape and they have a long tail which propels them through the water when swimming. They are often encrusted with a white substance, which mainly consists of excess salt excreted via their nasal glands.
Marine iguanas live in the Galapagos Islands, an archipelago near the South American coast. They inhabit rocky shores in the intertidal zone, but can also be seen in marshes, mangrove swamps, and beaches.
Marine iguanas are diurnal. When not hunting in the sea for food, they bask on rocks, often several thousand individuals together in the same area. They live in colonies. Before it can feed, the marine iguana must increase its body temperature to approximately 36°C. Its temperature can drop as much as 10°C when it is in the ocean. In order to regulate its body temperature, an iguana must spend long periods of time basking in the sun. With a low body temperature it will move more sluggishly, and so is then at greater risk from predators. To combat this vulnerability, the iguana acts in a highly aggressive way to bluff its way out of danger.
Marine iguanas mostly eat marine algae. Larger iguanas will dive into the sea in order to forage, sometimes diving as deep as 12 m (39 ft) and staying submerged for more than an hour. Under normal circumstances, they make shallow dives, usually lasting around 10 minutes. The smaller iguanas keep out of the water, feeding instead on algae on rocks in the tidal area.
Marine iguanas are polygynous. Males fight aggressively to secure a mate, and females select them based on their body size, preferring larger individuals. Large males defend territories for up to three months during the breeding season, and in this period they sometimes fight other males. Medium-sized males roam areas near the territories of large males or walk along beaches looking for females, while small "sneaky" males may enter the territories of large males. The breeding season is from December to March and the nesting season is from January to April. Females go inland to lay 1 to 6 eggs in a burrow of sand, along with thousands of others nesting in the same area, due to suitable sites being scarce. They will defend their burrow for a few days before leaving the eggs to incubate, which takes 89 to 120 days. Upon hatching, the baby iguanas dig themselves out from their nest and move down to the intertidal zone, where they start feeding. Females become reproductively mature at 3 to 5 years of age, and males at 6 to 8 years.
The periodic El Niño events reduce the cold water needed for algae to grow and this can drastically reduce the Marine iguana population, on some islands by as much as 90%. Introduced predators, to which iguanas have little or no protection, include animals such as pigs, dogs, cats, and rats. Dogs may take adult Marine iguanas, while the others may feed on their young or eggs. This inhibits reproduction and the long-term survival of the species. Introduced predators represent a major problem on the islands of Santa Cruz, Santiago, Isabela, Floreana, and San Cristóbal where very few Marine iguana hatchlings survive. Occasional oil spills in the region also present a threat.
According to IUCN Red List, the total population size of the Marine iguana is below 210,000 individuals. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List, and its numbers are decreasing.