Marine Iguana

The marine iguana is one of the several unique residents indigenous to the Galápagos Islands. Despite their fearsome appearance, these lizards are pretty gentle and can be seen hanging out with other iguanas or different species. They feed on algae found only in their habitat, spend time both in water and on land, and vary drastically in color depending on the island where a specific specimen was observed. There are seven to eight recognized sub-species of this iguana.

Description

Size: Length: 4.7–22.0 in (12 to 56 cm)

Weight: 2.2-26 lb (1-12 kg)

Body and Coloration: Males are significantly larger and brighter than females.  These iguanas are thick, have a row of spines running down their backs all the way to their tails, and also have large bony plates on their heads.

While these lizards primarily appear black, there are color variations. Some species have a grey body, whereas the younger lizards have a light-shaded dorsal stripe running across their body. Certain sub-species, particularly the male iguanas, display a drastically diverse coloration, such as the bright pink iguanas of Española, Floreana, and Santa Fé.

Other color morphs include a blackish body with greenish, pale yellowish, ochre, or grey markings. The iguanas native to the Espanola islands are the most colorful of the lot, even referred to as Christmas iguanas.

The varying algae diet of each species plays a significant role in shaping their color.

Range and Distribution

This iguana is only found on the Galápagos Islands in Ecuador.

Habitat

Many islands in the Galapagos have steep rock cliffs, low rock ledges, and intertidal flats, needing to be close to the ocean as well as a sandy area to lay eggs.

Diet

Red and green algae form most of the marine iguana’s diet.

Lifespan

They are long-lived lizards, with some living up to 60 years. However, the average is much smaller being around 12 years or less.

Behavior

• They warm themselves by basking in the sun and, at the same time, navigate through the cold waters to search for food. 
• This temperature fluctuation affects their behavior, as a prolonged stay in the sea lowers their body temperature, making them sluggish. They eventually develop a laid-back attitude that makes them lose their ability to escape from predators. So, they display aggressive behaviors to scare and ward off their enemies as a survival strategy. When they are sufficiently warm, however, these lizards are highly gentle.

• Marine iguanas live in large colonies ranging from 20-500 members per colony.
• They have a mutual relationship with species, such as Darwin’s finches and Sally lightfoot crabs who feed off of mites on the iguana’s bodies and lava lizards, who run all over their bodies while searching for flies.
• While there are no benefits, sea lions and marine iguanas are known to share territories, with the latter sometimes crawling over the former’s bodies.
• Males will fight over territory during the breeding season, though these are relatively harmless.
• They are strong swimmers, the best among all of the iguanas, and can dive underwater for long periods.

Predators

While they have native predators like Galápagos hawks, herons, lava gulls, short-eared owls, and Galápagos racer snakes, introduced species like cats and dogs are a more significant threat.

Adaptations

• They scrape off the algae they eat with the help of their blunt snouts and sharp teeth. Their sharp claws also help in this and give them a firm grip.

• Marine iguanas have a nasal gland to “sneeze” out excess salt they accumulate while swimming.
• Their flat tails allow these lizards to propagate themselves forward underwater, similar to a crocodile.
• The dark color of these lizards’ bodies allows them to absorb heat from the sun more efficiently.
• They have also evolved a special red blood pigment, enabling them to hold more oxygen while staying underwater.
• The presence of certain bacteria in their gut helps them digest algae more efficiently.

Mating and Reproduction

The start of the reproductive period of the marine iguana begins in the colder months, starting from December and ending in April. The first three months are focused on breeding, while the period of January-April is used for nesting. Females select a mate primarily based on their size, but other factors like frequency of displays and the properties of the territory under a male also come into play.

Mating lasts for 3-4 minutes. Males try to mate with many female partners, but once a female iguana has bred, she will not do so again.

Life Cycle

After 1 month, the female lays 2-3 eggs in a hole that they dig in the ground, though 6 have been recorded.  These eggs are large, weighing up to a quarter of the female, and hatch after 3-4 months. The baby marine iguanas immediately begin to run for cover, determining the optimum conditions required for their survival.

Males reach sexual maturity at 6-8 years, while females become sexually mature a bit earlier at 5-7 years.

Conservation Status

As per the IUCN, the marine iguana is listed as “Vulnerable” or “VU”. Though the population is consistent, with around 200,000–300,000 iguanas in all the islands combined, they are isolated to small areas. As a result, all the sub-species have a lack of immunity to pathogens and an inability to ward off invasive threats. This has led to the marine iguana being protected in Ecuador, with the species being considered endangered on Genovesa, San Cristóbal, and Santiago islands.

Global warming and oil spills have also caused issues for marine iguanas.

Interesting Facts

• Marine iguanas can hold their breath underwater for up to 10 minutes or even a little more, varying as per the species. In fact, in some cases, they could hold their breath for about four hours also. However, the iguanas are unable to breathe underwater as they do not have gills.
• It has several different names, such as the saltwater iguana, the sea iguana, or the Galápagos marine iguana.